JP2010201833A - Heat reversible recording medium and image processing method employing the same - Google Patents

Abstract

A thermoreversible recording medium having sufficient recording density and erasability, high sensitivity, and excellent light resistance of a photothermal conversion material, and an image processing method using the thermoreversible recording medium.
In a thermoreversible recording medium having at least a support and a layer containing a photothermal conversion material that absorbs light of a specific wavelength and converts it into heat on the support, the photothermal conversion material includes plasmon absorption. A thermoreversible recording medium that is metal fine particles having A mode in which the layer containing the photothermal conversion material is a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature, the layer containing the photothermal conversion material is a photothermal conversion layer, An embodiment having a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature is preferable.
[Selection figure] None

Description

  The present invention relates to a thermoreversible recording medium having good light resistance and repeated durability, and an image processing method using the thermoreversible recording medium.

To date, image recording and image erasing on a thermoreversible recording medium (hereinafter sometimes simply referred to as “recording medium” or “medium”) is performed by contacting a heating source with the recording medium to heat the medium. Has been done in the formula. As the heat source, a thermal head is usually used for image recording, and a heat roller, a ceramic heater, or the like is used for image erasing.
In such a contact-type recording method, when the thermoreversible recording medium is a flexible material such as a film or paper, uniform image recording and recording can be performed by pressing the recording medium uniformly against a heating source with a platen or the like. There is an advantage that image erasing can be performed, and an image recording apparatus and an image erasing apparatus can be manufactured at low cost by diverting components of a conventional thermal paper printer.

However, when the thermoreversible recording medium incorporates an RF-ID tag or the like as described in Patent Document 1 and Patent Document 2, the thickness of the thermoreversible recording medium increases and flexibility decreases. Therefore, a high pressure is required to uniformly press the heating source. Further, when irregularities occur on the surface of the thermoreversible recording medium, it becomes difficult to record and erase images using a thermal head or the like. Furthermore, while reading and rewriting of stored information is performed from where the RF-ID tag is separated without contact, there is a demand for rewriting the image from a distant position on the thermoreversible recording medium.
Therefore, a recording method using a non-contact type laser has been proposed as a method for recording and erasing an image on a recording medium when the surface of the thermoreversible recording medium has irregularities or from a distance. (See Patent Document 3).

Conventionally, as a method of performing image formation and erasure by a laser, a method of recording with a near infrared laser beam by combining a leuco dye, a reversible developer, and various photothermal conversion materials has been proposed (Patent Documents 4 and 4). 5).
However, when the metal vapor deposition film of titanium, chromium, nickel or the like described in Patent Document 4 is used as a photothermal conversion layer, high absorbance can be selectively given according to the wavelength of near infrared laser light. The recording sensitivity is insufficient. Moreover, when the organic pigment | dye which has absorption in the near-infrared absorption area | region of the said patent document 4 and the patent document 5 is used as a photothermal conversion material, it becomes possible to select suitably according to the wavelength of a near-infrared laser beam. Although good recording sensitivity can be obtained, the organic dye generally has low durability against light, and particularly when mixed with a leuco dye, the organic dye decomposes over time due to the interaction between the two, and thus the near infrared There is a problem that the absorption of the area is lowered and the recording sensitivity and the erasing sensitivity are remarkably lowered.

In contrast, the thermoreversible recording layer and the photothermal conversion layer are laminated so that the leuco dye and the photothermal conversion material in the thermoreversible recording layer are not mixed, so that the resins constituting each layer are not compatible with each other. A method of selecting a material and separating both layers (Patent Document 6), a thermoreversible recording layer and a photothermal conversion layer laminated via an intermediate layer, and the resins constituting each layer are not compatible with each other Thus, a method of selecting a material and separating each layer (Patent Document 7) has been proposed.
However, in the method described in Patent Document 6, when repeated recording and erasing are performed, the photothermal conversion material in the photothermal conversion layer is gradually moved into the thermoreversible recording layer by heat and mixed with the leuco dye, There exists a problem that light resistance will fall. Moreover, in the method described in Patent Document 7, mixing of the leuco dye and the photothermal conversion material can be suppressed by providing an intermediate layer between the thermoreversible recording layer and the photothermal conversion layer. The generated heat is difficult to be transmitted to the thermoreversible recording layer, and there is a problem that recording sensitivity and erasing sensitivity are lowered. From this point of view, it is currently desired to improve the light resistance of the photothermal conversion material.

  An object of the present invention is to solve various problems in the prior art and achieve the following objects. That is, the present invention provides a thermoreversible recording medium having sufficient recording density and erasability, high sensitivity, and excellent light resistance of a photothermal conversion material, and an image processing method using the thermoreversible recording medium. For the purpose.

Means for solving the problems are as follows. That is,
<1> In a thermoreversible recording medium having at least a support and a layer containing a photothermal conversion material that absorbs light of a specific wavelength and converts it into heat on the support,
The thermoreversible recording medium, wherein the photothermal conversion material is metal fine particles having plasmon absorption.
<2> The thermoreversible recording medium according to <1>, wherein the layer containing the photothermal conversion material is a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature.
<3> The thermoreversible recording medium according to <1>, wherein the layer containing the photothermal conversion material is a photothermal conversion layer, and has a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature. It is.
<4> The thermoreversible recording medium according to any one of <1> to <3>, wherein the metal fine particles having plasmon absorption are gold nanorods.
<5> The thermoreversible recording medium according to any one of <2> to <4>, wherein the thermoreversible recording layer contains a leuco dye and a reversible developer.
<6> The thermoreversible recording medium according to any one of <2> to <4>, wherein the thermoreversible recording layer contains a resin and an organic low molecular weight substance.
<7> An image recording step of recording an image on the thermoreversible recording medium by irradiating and heating the thermoreversible recording medium according to any one of <1> to <6>, and the above An image processing method comprising: at least one of image erasing steps for erasing an image recorded on the thermoreversible recording medium by irradiating the thermoreversible recording medium with laser light and heating it.
<8> The image processing method according to <7>, wherein the wavelength of the laser beam to be irradiated is 600 nm to 1,200 nm.
<9> The image processing method according to any one of <7> to <8>, wherein the laser beam to be irradiated is at least one of a YAG laser beam, a fiber laser beam, and a semiconductor laser beam.

  According to the present invention, a thermoreversible recording medium that can solve conventional problems, has sufficient recording density and erasability, is highly sensitive, and has excellent light resistance of a photothermal conversion material, and the thermoreversible recording medium. An image processing method using can be provided.

FIG. 1 is a schematic diagram illustrating an example of a layer configuration of a thermoreversible recording medium. FIG. 2A is a schematic diagram illustrating another example of the layer configuration of the thermoreversible recording medium. FIG. 2B is a schematic diagram illustrating still another example of the layer configuration of the thermoreversible recording medium. FIG. 2C is a schematic diagram illustrating still another example of the layer configuration of the thermoreversible recording medium. FIG. 3A is a graph showing the transparent-white turbidity characteristics of a thermoreversible recording medium. FIG. 3B is a schematic explanatory diagram showing a mechanism of a change in transparency-white turbidity of a thermoreversible recording medium. FIG. 4A is a graph showing the color-decoloring characteristics of the thermoreversible recording medium. FIG. 4B is a schematic explanatory diagram showing the mechanism of color development-decoloration change of the thermoreversible recording medium. FIG. 5 is a diagram for explaining an example of an image processing apparatus used in the image processing method of the present invention.

(Thermal reversible recording medium)
The thermoreversible recording medium of the present invention has at least a support and a layer containing a photothermal conversion material that absorbs light of a specific wavelength and converts it into heat on one surface of the support, and thermoreversible recording. Layer, photothermal conversion layer, oxygen blocking layer, ultraviolet absorbing layer, intermediate layer, protective layer, and undercoat layer, back layer, adhesive layer, adhesive layer, colored layer, air layer, light reflecting layer, etc. as necessary It has the layer of. Each of these layers may have a single layer structure or a laminated structure.

  Here, the layer containing the photothermal conversion material means a thermoreversible recording layer when the photothermal conversion material is contained in the thermoreversible recording layer, and the photothermal conversion material contains the photothermal conversion material. When it is, it means a photothermal conversion layer, and when both the thermoreversible recording layer and the photothermal conversion layer contain a photothermal conversion material, it means a thermoreversible recording layer and a photothermal conversion layer. Among these, it is particularly preferable that a photothermal conversion material is contained in the thermoreversible recording layer in order to obtain good recording sensitivity.

-Layer structure-
Here, as a layer structure of the thermoreversible recording medium 100 of the present invention, as shown in FIG. 1, there is an embodiment in which a support 101 and a thermoreversible recording layer 102 are provided on the support.
Further, as shown in FIG. 2A, a support 101 and an embodiment having a thermoreversible recording layer 102 and a photothermal conversion layer 103 in this order on the support, or as shown in FIG. 2B, There is an embodiment in which the photothermal conversion layer 103 and the thermoreversible recording layer 102 are provided in this order on the support.
Further, as shown in FIG. 2C, a support 101, and a first thermoreversible recording layer 102, a photothermal conversion layer 103, and a second thermoreversible recording layer 102 ′ are provided in this order on the support. There are aspects.
Although not shown, an under layer and / or an oxygen blocking layer may be provided between the support and the thermoreversible recording layer, and the ultraviolet absorbing layer and / or the thermoreversible recording layer or the photothermal conversion layer may be provided. Alternatively, an oxygen blocking layer may be provided, and a back layer and / or an oxygen blocking layer may be provided on the surface of the support that does not have the thermoreversible recording layer.

-Photothermal conversion material-
As the photothermal conversion material, fine metal particles having plasmon absorption are used.
The metal fine particles have high durability against light unlike organic pigments, and even when mixed with a leuco dye, there is no interaction between them, and even when irradiated with light, absorption in the near infrared region does not decrease. A highly light-resistant thermoreversible recording medium can be obtained.

The metal fine particles have a property of absorbing light of a specific wavelength called so-called plasmon absorption depending on the particle size. Therefore, good recording sensitivity can be obtained by making the plasmon absorption wavelength substantially coincide with the wavelength of the laser beam used for image recording and erasing.
The particle size of the metal fine particles is preferably 1 nm to 50 nm, more preferably 1 nm to 30 nm, and still more preferably 1 nm to 20 nm.
Examples of the metal fine particles include gold, silver, copper, platinum, and alloys thereof. These may be used individually by 1 type and may use 2 or more types together.
Among these, gold nanorods that are rod-shaped gold fine particles are particularly preferable. The gold nanorods can absorb any specific wavelength from the visible region to the near infrared region by controlling the aspect ratio (long axis / short axis value). As the aspect ratio of the gold nanorod is larger, the absorption wavelength is shifted to the longer wavelength side, preferably 2.5 to 8.0, and more preferably 3.5 to 6.0.

Since the metal fine particles may easily aggregate with each other, the outermost surface is preferably coated with a dispersant or the like.
Suitable examples of the dispersant include nitrogen-containing polymers. Examples of the nitrogen-containing polymer include polyacrylic (PAN), polyamide, polyimide, melamine, and amine-modified polyethylene glycol. When the nitrogen-containing polymer is adsorbed on the outermost surface of the metal fine particles, highly stable metal fine particles can be dispersed. Further, as described in JP-A-2006-330683, a silane coupling agent can be allowed to act on the metal fine particles to form a silica film on the outermost surface. By using the silane coupling agent, the formation of the agglomerates of the metal fine particles can be suppressed, and an effect of reducing the film thickness distribution for each particle can be obtained.

  Since the metal fine particles have some absorption in the visible region, too much addition causes a reduction in contrast. Therefore, it is preferable to set the addition amount of the metal fine particles so that the average transmittance in the visible region of 400 nm to 700 nm can ensure 60% or more.

<Support>
The support is not particularly limited in its shape, structure, size and the like, and can be appropriately selected according to the purpose. Examples of the shape include a flat plate shape, May have a single-layer structure or a laminated structure, and the size may be appropriately selected according to the size of the thermoreversible recording medium.

Examples of the material for the support include inorganic materials and organic materials.
Examples of the inorganic material include glass, quartz, silicon, silicon oxide, aluminum oxide, SiO ₂ and metal.
Examples of the organic material include paper, cellulose derivatives such as cellulose triacetate, synthetic paper, polyethylene terephthalate, polycarbonate, polystyrene, polymethyl methacrylate, and the like.
The said inorganic material and the said organic material may be used individually by 1 type, and may use 2 or more types together. Among these, organic materials are preferable, films of polyethylene terephthalate, polycarbonate, polymethyl methacrylate, and the like are preferable, and polyethylene terephthalate is particularly preferable.

For the purpose of improving the adhesion of the coating layer, the support is subjected to surface modification by performing corona discharge treatment, oxidation reaction treatment (chromic acid, etc.), etching treatment, easy adhesion treatment, antistatic treatment, etc. Is preferred.
Moreover, it is preferable to make it white by adding a white pigment such as titanium oxide to the support.
There is no restriction | limiting in particular as thickness of the said support body, Although it can select suitably according to the objective, 10 micrometers-2,000 micrometers are preferable, and 50 micrometers-1,000 micrometers are more preferable.

<Thermal reversible recording layer>
The thermoreversible recording layer (hereinafter, sometimes simply referred to as “recording layer”) has a material in which either transparency or color tone reversibly changes depending on temperature, and plasmon absorption as a photothermal conversion material. It contains at least metal fine particles, and further contains other components as necessary.

As the metal fine particles having a plasmon absorption as the photothermal conversion material, it is possible to use those mentioned above, the content thereof is ^preferably from ^{1mg / m 2 ~200mg / m 2} , 5mg / m 2 ~100mg / m 2 Is more preferable.

The material whose transparency and color tone reversibly change depending on the temperature is a material capable of exhibiting a phenomenon in which a visible change is reversibly caused by the temperature change. The heating temperature and the cooling after the heating are possible. Depending on the difference in speed, it can be changed between a relatively colored state and a decolored state.
In this case, the visible change is divided into a color state change and a shape change. The change in the color state is caused by, for example, changes in transmittance, reflectance, absorption wavelength, scattering degree, etc., and the thermoreversible recording medium actually changes in color state due to a combination of these changes. To do.

  The material in which either transparency or color tone reversibly changes depending on the temperature is not particularly limited and can be appropriately selected from known materials. Among them, temperature control is easy and high contrast is obtained. In view of the above, it is particularly preferable that either the transparency or the color tone reversibly change between the first specific temperature and the second specific temperature.

For example, it becomes transparent at the first specific temperature and becomes cloudy at the second specific temperature (see Japanese Patent Application Laid-Open No. 55-154198), develops color at the second specific temperature, and at the first specific temperature. Those that are decolored (see JP-A-4-224996, JP-A-4-247985, JP-A-4-267190, etc.), become cloudy at the first specific temperature, and transparent at the second specific temperature. (See Japanese Patent Laid-Open No. 3-169590), which develops black, red, blue, etc. at a first specific temperature and decolorizes at a second specific temperature (Japanese Patent Laid-Open No. 2-188293, Japanese Patent 2-188294), and the like.
Among these, a thermoreversible recording medium comprising a resin base material and an organic low molecular weight substance such as a higher fatty acid dispersed in the resin base material has a relatively low second specific temperature and first specific temperature, This is advantageous in that erasure recording with low energy is possible. Moreover, since the color development / decoloration mechanism is a physical change depending on the solidification of the resin and the crystallization of the organic low molecular weight substance, it has a strong characteristic against environmental resistance.
In addition, a thermoreversible recording medium that uses a leuco dye and a reversible developer, which will be described later, to develop color at a second specific temperature and to erase at the first specific temperature is reversible between a transparent state and a colored state. In the colored state, black, blue, and other colors are shown, so that a high-contrast image can be obtained.

As the organic low molecular weight substance (dispersed in the resin base material, becoming transparent at the first specific temperature and becoming cloudy at the second specific temperature) in the thermoreversible recording medium, As long as it changes from a polycrystal to a single crystal by heat, there is no particular limitation, and it can be selected appropriately according to the purpose. Those having a melting point of 50 ° C to 150 ° C are preferred.
Such an organic low molecular weight substance is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include alkanol; alkanediol; halogen alkanol or halogen alkanediol; alkylamine; alkane; alkene; alkyne; Alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or unsaturated mono- or dicarboxylic acids and their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids and their esters, amides or ammonium salts Aryl carboxylic acids and their esters, amides or ammonium salts; halogen allyl carboxylic acids and their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids and their Ester, amine or ammonium salts; carboxylic acid esters of thioalcohol; and the like. These may be used individually by 1 type and may use 2 or more types together.

As carbon number of these compounds, 10-60 are preferable, 10-38 are more preferable, and 10-30 are especially preferable. The alcohol group part in the ester may be saturated or not saturated, and may be halogen-substituted.
Further, the organic low molecular weight substance contains at least one selected from oxygen, nitrogen, sulfur and halogen, for example, —OH, —COOH, —CONH—, —COOR, —NH—, —NH, in the molecule. ₂ , -S-, -SS-, -O-, a halogen atom and the like are preferable.
More specifically, these compounds include, for example, higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, alginic acid, and oleic acid; stearic acid Examples include esters of higher fatty acids such as methyl, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, and dodecyl behenate. Among these, as the organic low molecular weight substance used in the third aspect of the image processing method, higher fatty acids are preferable, and higher fatty acids having 16 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, and lignoceric acid are more preferable. A higher fatty acid having 16 to 24 carbon atoms is more preferable.

  In order to widen the temperature range in which the thermoreversible recording medium can be made transparent, the above-mentioned various organic low molecular substances may be used in appropriate combination, or the organic low molecular substances may have different melting points. These materials may be used in combination. These are disclosed in, for example, JP-A-63-39378, JP-A-63-130380, and Japanese Patent No. 2615200, but are not limited thereto.

The resin base material forms a layer in which the organic low molecular weight substance is uniformly dispersed and held, and affects the transparency at the time of maximum transparency. For this reason, the resin base material is preferably a resin having high transparency, mechanical stability, and good film forming properties.
There is no restriction | limiting in particular as such resin, According to the objective, it can select suitably, For example, polyvinyl chloride; Vinyl chloride-vinyl acetate copolymer, Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, Vinyl chloride copolymers such as vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer; polyvinylidene chloride; vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, etc. Examples thereof include vinylidene chloride copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylate-methacrylate copolymers; silicone resins. These may be used individually by 1 type and may use 2 or more types together.

The ratio of the organic low-molecular substance and the resin (resin base material) in the recording layer is preferably 2: 1 to 1:16, more preferably 1: 2 to 1: 8 in terms of mass ratio.
When the mass ratio of the resin is smaller than 2: 1, it may be difficult to form a film holding the organic low molecular weight substance in the resin base material. When the mass ratio is larger than 1:16, Since the amount of the organic low molecular weight material is small, it may be difficult to make the recording layer opaque.

  In addition to the organic low molecular weight substance and the resin, other components such as a high boiling point solvent and a surfactant can be added to the recording layer in order to facilitate recording of a transparent image.

The method for producing the recording layer is not particularly limited and may be appropriately selected depending on the purpose. For example, a solution in which two components of the resin base material and the organic low molecular weight substance are dissolved, or the resin base For example, a dispersion liquid in which the organic low molecular weight substance is dispersed in the form of fine particles in a material solution (the solvent is insoluble in at least one selected from the organic low molecular weight substances) is applied onto the support, for example. And drying.
The solvent for preparing the recording layer is not particularly limited and can be appropriately selected according to the kind of the resin base material and the organic low molecular weight substance. For example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, four Examples include carbon chloride, ethanol, toluene, and benzene. In addition, when using the said dispersion liquid, also when using the said solution, in the obtained recording layer, the said organic low molecular weight substance precipitates as a fine particle, and exists in a dispersed state.

Next, a thermoreversible recording layer that uses a leuco dye and a reversible developer and develops color at a second specific temperature and decolorizes at the first specific temperature will be described.
The leuco dye is itself a colorless or light dye precursor. The leuco dye is not particularly limited and may be appropriately selected from known ones. For example, triphenylmethane phthalide, triallyl methane, fluorane, phenothiazine, thioferolane, xanthene Preferable examples include leuco compounds such as phthalocyanine, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilinolactam, rhodamine lactam, quinazoline, diazaxanthene, and bislactone. Among these, a fluoran-based or phthalide-based leuco dye is particularly preferable in terms of excellent color development / decoloring properties, color, storage stability, and the like. These may be used individually by 1 type, may use 2 or more types together, and can also respond | correspond to multi-color and full color by laminating | stacking the layer which color-emits a different color tone.

The reversible developer is not particularly limited as long as it can reversibly develop and decolorize by using heat as a factor, and can be appropriately selected according to the purpose. For example, (1) A structure having a color developing ability for developing the leuco dye (for example, phenolic hydroxyl group, carboxylic acid group, phosphoric acid group, etc.), and (2) a structure for controlling cohesion between molecules (for example, long-chain hydrocarbon) Preferred examples include compounds having one or more structures selected from the group wherein the groups are linked to each other in the molecule. The linking moiety may be connected to a divalent or higher valent linking group containing a heteroatom, and the long-chain hydrocarbon group also contains at least one of the same linking group and aromatic group. May be.
Phenol is particularly preferred as the structure having the ability to develop (1) the color of the leuco dye.
The (2) structure for controlling the cohesive force between molecules is preferably a long chain hydrocarbon group having 8 or more carbon atoms, more preferably 11 or more, and the upper limit of the carbon number is 40 or less. Preferably, 30 or less is more preferable.

Among the reversible developers, a phenol compound represented by the following general formula (1) is preferable, and a phenol compound represented by the following general formula (2) is more preferable.
In the general formulas (1) and (2), R ¹ represents a single bond or an aliphatic hydrocarbon group having 1 to 24 carbon atoms. R ² represents an aliphatic hydrocarbon group having 2 or more carbon atoms which may have a substituent, and the number of carbon atoms is preferably 5 or more, and more preferably 10 or more. R ³ represents an aliphatic hydrocarbon group of 1 to 35 carbon atoms, and carbon number, preferably 6 to 35, 8 to 35 is more preferable. These aliphatic hydrocarbon groups may be used alone or in combination of two or more.
The sum of the carbon numbers of R ¹ , R ² , and R ³ is not particularly limited and may be appropriately selected depending on the purpose. However, the lower limit is preferably 8 or more, more preferably 11 or more. Preferably, the upper limit is preferably 40 or less, and more preferably 35 or less.
If the sum of the carbon numbers is less than 8, the color development stability and decoloring property may be lowered.
The aliphatic hydrocarbon group may be linear or branched, and may have an unsaturated bond, but is preferably linear. In addition, examples of the substituent bonded to the hydrocarbon group include a hydroxyl group, a halogen atom, and an alkoxy group.
X and Y may be the same or different and each represents a divalent group containing an N atom or an O atom. Specific examples include an oxygen atom, an amide group, a urea group, and a diacylhydrazine. Group, oxalic acid diamide group, acylurea group and the like. Among these, an amide group and a urea group are preferable.
n shows the integer of 0-1.

The electron-accepting compound (developer) is used in the process of forming a decolored state by using a compound having at least one -NHCO- group or -OCONH- group in the molecule as a decoloring accelerator. It is preferable because an intermolecular interaction is induced between the decolorization accelerator and the developer, and the color development and decoloring characteristics are improved.
There is no restriction | limiting in particular as said decoloring promoter, According to the objective, it can select suitably.

  In the recording layer, a binder resin and, if necessary, various additives for improving or controlling the coating layer's coating properties and coloring / decoloring properties can be used. Examples of these additives include surfactants, conductive agents, fillers, antioxidants, light stabilizers, color stabilizers, and decolorization accelerators.

  The binder resin is not particularly limited as long as the recording layer can be bound on the support, and can be appropriately selected according to the purpose. One or more kinds of conventionally known resins can be selected. Can be mixed and used. Among these, resins that can be cured by heat, ultraviolet rays, electron beams or the like are preferably used in order to improve durability during repetition, and resins using isocyanate compounds as crosslinking agents are particularly preferable. Examples of the binder resin include a resin having a group that reacts with a crosslinking agent such as a hydroxyl group or a carboxyl group, or a resin obtained by copolymerizing a monomer having a hydroxyl group, a carboxyl group, or the like with another monomer. Examples of such resins include phenoxy resin, polyvinyl butyral resin, cellulose acetate propionate resin, cellulose acetate butyrate resin, acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, and the like. Among these, acrylic polyol resin, polyester polyol resin, and polyurethane polyol resin are particularly preferable.

  In the binder resin, the hydroxyl value is preferably 100 to 300 mgKOH / g. If the hydroxyl value is less than 100 mgKOH / g, sufficient coating strength cannot be obtained, and repeated printing and erasure tends to cause deterioration of the recording medium. On the other hand, when the hydroxyl value exceeds 300 mgKOH / g, the film cannot be completely crosslinked, and the uncrosslinked component adversely affects the coloring system, which is not preferable. Moreover, the solubility with respect to an organic solvent falls and it may be unable to melt | dissolve in an organic solvent completely.

  The mixing ratio (mass ratio) of the color former and the binder resin in the recording layer is preferably 0.1 to 10 with respect to the color former 1. If the ratio of the binder resin is too small, the thermal strength of the recording layer may be insufficient, and if it is too large, the color density may be lowered, causing a problem.

  There is no restriction | limiting in particular as said crosslinking agent, According to the objective, it can select suitably, For example, isocyanate, amino resin, a phenol resin, amines, an epoxy compound, etc. are mentioned. Among these, isocyanates are preferable, and polyisocyanate compounds having a plurality of isocyanate groups are particularly preferable.

As for the addition amount with respect to the binder resin of the said crosslinking agent, the ratio of the functional group of a crosslinking agent with respect to the number of the active groups contained in binder resin has 0.01-2. Below this, the heat strength is insufficient, and when added more than this, the coloring and decoloring properties are adversely affected.
Furthermore, you may use the catalyst used for this kind of reaction as a crosslinking accelerator.

  The gel fraction of the resin when thermally crosslinked is preferably 30% or more, more preferably 50% or more, and still more preferably 70% or more. When the gel fraction is less than 30%, the crosslinked state is not sufficient and the durability may be inferior.

  As a method for distinguishing whether the binder resin is in a crosslinked state or in a non-crosslinked state, for example, it can be distinguished by immersing the coating film in a highly soluble solvent. That is, the binder resin in the non-crosslinked state is dissolved in the solvent and does not remain in the solute.

  Other components in the recording layer are not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include surfactants and plasticizers from the viewpoint of facilitating image recording.

Known methods can be used for the solvent used in the recording layer coating liquid, the coating liquid dispersing device, the recording layer coating method, the drying / curing method, and the like.
The recording layer coating liquid may be prepared by dispersing each material in a solvent using the dispersing device, or may be separately dispersed in a solvent and mixed. Further, it may be dissolved by heating and precipitated by rapid cooling or slow cooling.

  The method for forming the recording layer is not particularly limited and may be appropriately selected depending on the purpose. For example, (1) the resin, the electron-donating color-forming compound, and the electron-accepting compound are contained in a solvent. A method in which a recording layer coating solution dissolved or dispersed in is coated on a support, and the solvent is evaporated to form a sheet or the like, or at the same time or thereafter, (2) a solvent in which only the resin is dissolved A method of coating the recording layer coating liquid in which the electron-donating color-forming compound and the electron-accepting compound are dispersed on a support, and evaporating the solvent to form a sheet or the like, or at the same time or thereafter, 3) A method in which the resin, the electron-donating coloring compound and the electron-accepting compound are heated and melted and mixed with each other without using a solvent, and the molten mixture is formed into a sheet or the like and cooled and then crosslinked. Etc. That. In these, a sheet-like thermoreversible recording medium can be formed without using the support.

The solvent used in (1) or (2) varies depending on the type of the resin and the electron-donating color-forming compound and the electron-accepting compound, and cannot be defined unconditionally. For example, tetrahydrofuran, methyl ethyl ketone, Examples include methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, and benzene.
The electron-accepting compound is dispersed in the form of particles in the recording layer.

  Various pigments, antifoaming agents, pigments, dispersants, slip agents, preservatives, crosslinking agents, plasticizers, and the like are added to the recording layer coating solution for the purpose of developing high performance as a coating material. May be.

  The recording layer coating method is not particularly limited and may be appropriately selected depending on the intended purpose. A support that is cut continuously in a roll shape or in a sheet shape is transported on the support. For example, blade coating, wire bar coating, spray coating, air knife coating, bead coating, curtain coating, gravure coating, kiss coating, reverse roll coating, dip coating, die coating, etc. Apply by the method.

  There is no restriction | limiting in particular as drying conditions of the said coating liquid for recording layers, According to the objective, it can select suitably, For example, about 10 second-about 10 minutes at the temperature of room temperature-140 degreeC etc. are mentioned.

  There is no restriction | limiting in particular in the thickness of the said recording layer, According to the objective, it can select suitably, For example, 1 micrometer-20 micrometers are preferable, and 3 micrometers-15 micrometers are more preferable. If the thickness of the recording layer is too thin, the color density may be low and the contrast of the image may be low. On the other hand, if the thickness is too thick, the heat distribution in the layer will be large, and there will be a portion that does not reach the color temperature and does not develop color. In some cases, the desired color density cannot be obtained.

<Photothermal conversion layer>
The light-to-heat conversion layer contains fine metal particles having plasmon absorption as a light-to-heat conversion material, a binder resin, and further contains other components as necessary.
As the metal fine particles having a plasmon absorption as the photothermal conversion material, it is possible to use those mentioned above, the content thereof is ^preferably from ^{1mg / m 2 ~200mg / m 2} , 5mg / m 2 ~100mg / m 2 Is more preferable.

  The binder resin used for the light-to-heat conversion layer is not particularly limited, and can be appropriately selected from known ones as long as the metal fine particles can be held. Thermoplastic resins, thermosetting resins, etc. It is preferable that the same binder resin as that used in the recording layer can be used. Among these, in order to improve durability at the time of repetition, a resin that can be cured by heat, ultraviolet rays, electron beams, or the like is preferably used, and a thermal crosslinking resin using an isocyanate compound or the like as a crosslinking agent is particularly preferable. In the binder resin, the hydroxyl value is preferably 100 mgKOH / g to 300 mgKOH / g.

  The mixing ratio (mass ratio) of the light-to-heat conversion material and the binder resin in the light-to-heat conversion layer is such that the background is not colored by the light-to-heat conversion material, recording sensitivity is good, and sufficient coating strength is obtained. Moreover, 0.1-100 are preferable with respect to the photothermal conversion material 0.1. If the amount of the binder resin is too small, the heat intensity of the light-to-heat conversion layer may be insufficient. On the other hand, if the amount of the binder resin is too large, the recording sensitivity may be deteriorated.

There is no restriction | limiting in particular as another component in the said photothermal conversion layer, According to the objective, it can select suitably, Conventionally well-known various additives, pigments, etc. may be added.
Known methods can be used as the solvent, the coating liquid dispersing device, the coating method, the drying / crosslinking method and the like used in the photothermal conversion layer coating solution.
There is no restriction | limiting in particular in the thickness of the said photothermal conversion layer, Although it can select suitably according to the objective, 0.1 micrometer-30 micrometers are preferable, and 0.5 micrometer-20 micrometers are more preferable.

<Ultraviolet absorbing layer>
In the present invention, it is preferable to provide an ultraviolet absorbing layer for the purpose of preventing the leuco dye in the recording layer from being colored by ultraviolet rays and disappearing due to photodegradation, whereby the light resistance of the recording medium can be improved.

  The ultraviolet absorbing layer contains at least a binder resin and an ultraviolet absorber, and further contains other components such as a filler, a lubricant, and a coloring pigment as necessary.

  There is no restriction | limiting in particular as said binder resin, According to the objective, it can select suitably, Resin components, such as binder resin of the said recording layer, a thermoplastic resin, and a thermosetting resin, can be used. Examples of the resin component include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide, and the like.

As the ultraviolet absorber, any of organic and inorganic compounds can be used.
Further, it is preferable to use a polymer having an ultraviolet absorbing structure (hereinafter sometimes referred to as “ultraviolet absorbing polymer”).
Here, the polymer having an ultraviolet absorbing structure means a polymer having an ultraviolet absorbing structure (for example, an ultraviolet absorbing group) in the molecule. Examples of the ultraviolet absorbing structure include a salicylate structure, a cyanoacrylate structure, a benzotriazole structure, a benzophenone structure, and the like. Among these, an ultraviolet ray of 340 to 400 nm, which is a cause of photodegradation of a leuco dye, is absorbed. A benzotriazole structure and a benzophenone structure are particularly preferable.
The ultraviolet absorbing polymer is preferably crosslinked. Therefore, as the ultraviolet absorbing polymer, it is preferable to use a polymer having a group that reacts with a curing agent such as a hydroxyl group, an amino group, or a carboxyl group, and a polymer having a hydroxyl group is particularly preferable. In order to improve the strength of the polymer-containing layer having the ultraviolet absorbing structure, a sufficient coating strength can be obtained by using a polymer having a hydroxyl value of 10 mgKOH / g or more, more preferably 30 mgKOH / g or more. More preferably, it is 40 mgKOH / g or more. By providing sufficient coating strength, deterioration of the recording medium can be suppressed even if repeated erasure printing is performed.

  The thickness of the ultraviolet absorbing layer is preferably 0.1 μm to 30 μm, and more preferably 0.5 μm to 20 μm. For the solvent used in the coating solution of the UV absorbing layer, the dispersion device of the coating solution, the coating method of the UV absorbing layer, the drying / curing method of the UV absorbing layer, etc., use the known methods used in the recording layer. Can do.

<Protective layer>
In the thermoreversible recording medium of the present invention, a protective layer can be provided on the recording layer for the purpose of protecting the recording layer. There is no restriction | limiting in particular in this protective layer, According to the objective, it can select suitably, For example, you may form in one or more layers, and it is preferable to provide in the outermost surface exposed.

  The protective layer contains a binder resin and, if necessary, other components such as a filler, a lubricant and a color pigment.

  There is no restriction | limiting in particular as resin of the said protective layer, According to the objective, it can select suitably, For example, a thermosetting resin, an ultraviolet-ray (UV) curable resin, an electron beam curable resin, etc. are preferable, These Among these, ultraviolet (UV) curable resins and thermosetting resins are particularly preferable.

  The UV curable resin can form a very hard film after curing, and can suppress damage due to physical contact with the surface and deformation of the medium due to laser heating, so that thermoreversible recording with excellent repeated durability A medium is obtained.

Moreover, although the said thermosetting resin is a little inferior to the said UV curable resin, it can make the surface hard similarly and is excellent in repeated durability.
There is no restriction | limiting in particular as said UV curable resin, According to the objective, it can select suitably according to the objective, for example, urethane acrylate type, epoxy acrylate type, polyester acrylate type, polyether acrylate type, vinyl type And monomers such as unsaturated polyester oligomers and various monofunctional and polyfunctional acrylates, methacrylates, vinyl esters, ethylene derivatives, and allyl compounds. Among these, tetrafunctional or higher polyfunctional monomers or oligomers are particularly preferable. By mixing two or more of these monomers or oligomers, the hardness, shrinkage, flexibility, coating strength, etc. of the resin film can be appropriately adjusted.

In order to cure the monomer or oligomer using ultraviolet rays, it is necessary to use a photopolymerization initiator and a photopolymerization accelerator.
The addition amount of the photopolymerization initiator or photopolymerization accelerator is preferably 0.1% by mass to 20% by mass, and more preferably 1% by mass to 10% by mass with respect to the total mass of the resin component of the protective layer.

The ultraviolet irradiation for curing the ultraviolet curable resin can be performed using a known ultraviolet irradiation apparatus, and examples of the apparatus include a light source, a lamp, a power source, a cooling device, a conveyance device, and the like. Can be mentioned.
Examples of the light source include a mercury lamp, a metal halide lamp, a potassium lamp, a mercury xenon lamp, and a flash lamp. The wavelength of the light source can be appropriately selected according to the ultraviolet absorption wavelength of the photopolymerization initiator and photopolymerization accelerator added to the thermoreversible recording medium composition.

The conditions for the ultraviolet irradiation are not particularly limited and may be appropriately selected depending on the purpose. For example, the lamp output, the conveyance speed, etc. may be determined according to the irradiation energy necessary for crosslinking the resin. .
In order to improve transportability, a silicone having a polymerizable group, a silicone-grafted polymer, a wax, a release agent such as zinc stearate, and a lubricant such as silicone oil can be added. As these addition amounts, 0.01 mass%-50 mass% are preferable with respect to the resin component total mass of a protective layer, and 0.1 mass%-40 mass% are more preferable. These may be used individually by 1 type and may use 2 or more types together. Moreover, it is preferable to use a conductive filler as a countermeasure against static electricity, and it is more preferable to use a needle-like conductive filler.

  As a particle size of the said conductive filler, 0.01 micrometer-10.0 micrometers are preferable, for example, and 0.05 micrometer-8.0 micrometers are more preferable. As addition amount of the said conductive filler, 0.001 mass part-2 mass parts are preferable with respect to 1 mass part of the said heat resistant resin, and 0.005 mass part-1 mass part are more preferable.

Furthermore, the protective layer may contain conventionally known surfactants, leveling agents, antistatic agents and the like as additives.
Moreover, as a thermosetting resin, the thing similar to binder resin used by the said recording layer can be used suitably, for example.
Further, a polymer having the ultraviolet absorbing structure may be used.
The resin of the protective layer is preferably cross-linked, and for example, a resin having a group that reacts with a curing agent such as a hydroxyl group, an amino group, or a carboxyl group is preferably used. Preferred is a polymer.
As the curing agent, for example, the same curing agent as that used in the recording layer can be suitably used.

As the solvent used in the coating liquid of the protective layer, the dispersion device of the coating liquid, the coating method of the protective layer, the drying method, etc., known methods used in the recording layer can be used. When an ultraviolet curable resin is used, a curing step by ultraviolet irradiation that is applied and dried is required, but the ultraviolet irradiation device, the light source, and the irradiation conditions are as described above.
The thickness of the protective layer is preferably 0.1 μm to 100 μm, and more preferably 0.5 μm to 50 μm.

<Oxygen barrier layer>
In the thermoreversible recording medium, an oxygen blocking layer is provided on the recording layer to prevent oxygen from entering the recording layer, thereby preventing the leuco dye in the recording layer from disappearing due to photodegradation.
Examples of the oxygen blocking layer include a resin or a polymer film having a large visible portion transmittance and a low oxygen permeability. These oxygen barrier layers are selected depending on their use, oxygen permeability, transparency, ease of coating, adhesion, and the like. Specific examples of these oxygen barrier layers include polyacrylic acid alkyl ester, polymethacrylic acid alkyl ester, polymethacrylonitrile, polyalkyl vinyl ester, polyalkyl vinyl ether, polyfluorinated vinyl, polystyrene, vinyl acetate copolymer, Cellulose acetate, polyvinyl alcohol, polyvinylidene chloride, acetonitrile copolymer, vinylidene chloride copolymer, poly (chlorotrifluoroethylene), ethylene-vinyl alcohol copolymer, polyacrylonitrile, acrylonitrile copolymer, polyethylene terephthalate, nylon- No. 6 and polyacetal, etc., or silica vapor deposited films with inorganic oxide deposited on polymer films such as polyethylene terephthalate and nylon, alumina vapor deposited films, silica / alcohol Na deposited film, ethylene - but vinyl alcohol copolymer film and the like, but is not limited thereto.

The oxygen blocking layer may be provided on the lower side of the recording layer or the back surface of the support so that the recording layer is sandwiched between the oxygen blocking layers. As a result, it is possible to more effectively prevent oxygen from entering the recording layer, and it is possible to reduce the disappearance of the leuco dye due to photodegradation.

There is no restriction | limiting in particular in the formation method of the said oxygen interruption | blocking layer, A normal melt extrusion method, a coating method, a lamination method, etc. can be mentioned. The thickness of the oxygen blocking layer varies depending on the oxygen permeability of the resin or polymer film, but is preferably 0.1 to 100 μm. If it is thinner than this, the oxygen barrier is incomplete, and if it is thicker, the transparency is lowered.
An adhesive layer or an adhesive layer may be provided between the oxygen barrier layer and the lower layer. Examples of the method for forming the adhesive layer or the pressure-sensitive adhesive layer include a normal coating method and a laminating method without particular limitation. There is no restriction | limiting in particular in the thickness of the said contact bonding layer or the adhesion layer, Although it can select suitably according to the objective, 0.1-5 micrometers is preferable.

<Under layer>
In the present invention, the recording layer and the recording layer are used for the purpose of improving the sensitivity by effectively using the applied heat, or for the purpose of improving the adhesion between the support and the recording layer and preventing the recording layer material from penetrating into the support. An under layer may be provided between the supports.
The under layer contains at least hollow particles, and contains a binder resin and, if necessary, other components.

  Examples of the hollow particles include single hollow particles in which one hollow portion is present in the particles, and multi-hollow particles in which many hollow portions are present in the particles. These may be used individually by 1 type and may use 2 or more types together.

There is no restriction | limiting in particular as a material of the said hollow particle, Although it can select suitably according to the objective, For example, a thermoplastic resin etc. are mentioned suitably. The hollow particles may be appropriately manufactured or commercially available. Examples of the commercially available products include Microsphere R-300 (manufactured by Matsumoto Yushi Co., Ltd.); Ropaque HP1055, Ropaque HP433J (both manufactured by Nippon Zeon Co., Ltd.); and SX866 (manufactured by JSR Corporation).
There is no restriction | limiting in particular in the addition amount in the said under layer of the said hollow particle, According to the objective, it can select suitably, For example, 10 mass%-80 mass% are preferable.

As the binder resin, the same resin as the recording layer or the layer containing the polymer having the ultraviolet absorption structure can be used.
The under layer may contain at least one of inorganic fillers such as calcium carbonate, magnesium carbonate, titanium oxide, silicon oxide, aluminum hydroxide, kaolin, and talc, and various organic fillers.
In addition, the under layer may further contain a lubricant, a surfactant, a dispersant, and the like.

  There is no restriction | limiting in particular in the thickness of the said under layer, According to the objective, it can select suitably, 0.1 micrometer-50 micrometers are preferable, 2 micrometers-30 micrometers are more preferable, and 12 micrometers-24 micrometers are still more preferable.

<Back layer>
In the present invention, a back layer may be provided on the side opposite to the surface on which the recording layer of the support is provided in order to prevent curling and charging of the thermoreversible recording medium and to improve transportability.
The back layer contains at least a binder resin, and further contains other components such as a filler, a conductive filler, a lubricant, and a color pigment as necessary.

  There is no restriction | limiting in particular as said binder resin, According to the objective, it can select suitably, For example, a thermosetting resin, an ultraviolet-ray (UV) curable resin, an electron beam curable resin, etc. are mentioned, These Among these, ultraviolet (UV) curable resins and thermosetting resins are particularly preferable.

  For the ultraviolet curable resin, the thermosetting resin, the filler, the conductive filler, and the lubricant, the same ones used in the recording layer, the protective layer, or the ultraviolet absorbing layer are preferably used. Can be used.

<Adhesive layer or adhesive layer>
In the present invention, a thermoreversible recording label can be obtained by providing an adhesive layer or a pressure-sensitive adhesive layer on the surface opposite to the recording layer forming surface of the support. Commonly used materials can be used for the adhesive layer or pressure-sensitive adhesive layer.

  There is no restriction | limiting in particular as a material of the said adhesive bond layer or an adhesive layer, According to the objective, it can select suitably, For example, a urea resin, a melamine resin, a phenol resin, an epoxy resin, a vinyl acetate resin, vinyl acetate- Acrylic copolymer, ethylene-vinyl acetate copolymer, acrylic resin, polyvinyl ether resin, vinyl chloride-vinyl acetate copolymer, polystyrene resin, polyester resin, polyurethane resin, polyamide resin, chlorine Polyolefin resin, polyvinyl butyral resin, acrylic acid ester copolymer, methacrylic acid ester copolymer, natural rubber, cyanoacrylate resin, silicone resin and the like.

  The material of the adhesive layer or the pressure-sensitive adhesive layer may be a hot melt type. Release paper may be used or non-release paper type may be used. By providing the adhesive layer or the pressure-sensitive adhesive layer in this way, it can be applied to the entire surface or a part of a thick substrate such as a magnetic stripe-added vinyl chloride card, which is difficult to apply the recording layer. This improves the convenience of the medium, such as displaying a part of the information stored in the magnetism. The thermoreversible recording label provided with such an adhesive layer or pressure-sensitive adhesive layer can also be applied to thick cards such as IC cards and optical cards.

  The thermoreversible recording medium may be provided with a colored layer for the purpose of improving visibility between the support and the recording layer. The colored layer can be formed by applying a solution or dispersion containing a colorant and a resin binder to a target surface and drying, or simply pasting a colored sheet.

  The thermoreversible recording medium can be provided with a color print layer. Examples of the colorant in the color printing layer include various dyes and pigments contained in color inks used in conventional full color printing. Examples of the resin binder include various thermoplastic, thermosetting, and ultraviolet curing. Or electron beam curable resin. Since the thickness of the color printing layer is appropriately changed with respect to the printing color density, it can be selected according to the desired printing color density.

  The thermoreversible recording medium may be used in combination with an irreversible recording layer. In this case, the color tone of each recording layer may be the same or different. In addition, the recording layer of the thermoreversible recording medium of the present invention may be optionally formed on a part of the entire surface or a part of the opposite surface by printing such as offset printing or gravure printing, or an inkjet printer, thermal transfer printer, sublimation printer, or the like. A colored layer having the above-described pattern or the like may be provided, and an OP varnish layer mainly composed of a curable resin may be provided on a part or the entire surface of the colored layer. Examples of the arbitrary pattern include characters, patterns, patterns, photographs, information detected by infrared rays, and the like. It is also possible to add a dye or pigment to any one of the simply configured layers for coloring.

  Further, the thermoreversible recording medium of the present invention can be provided with a hologram for security. In addition, a design such as a person image, a company emblem, a symbol mark, or the like can be provided by providing irregularities in a relief shape or an intaglio shape for designability.

  The thermoreversible recording medium can be processed into a desired shape according to the application, for example, a card shape, a tag shape, a label shape, a sheet shape, a roll shape, or the like. Moreover, about what was processed into the card form, the application to a prepaid card, a point card, and also a credit card etc. is mentioned. Tag size smaller than card size can be used for price tags. A tag size larger than the card size can be used for process management, shipping instructions, tickets, and the like. Since the label can be affixed, it can be processed into various sizes and affixed to carts, containers, boxes, containers, etc. that are used repeatedly, and can be used for process management, article management, and the like. In addition, since the printing range becomes wider when the sheet size is larger than the card size, it can be used for general documents, process management instructions, and the like.

<Image recording and erasing mechanism>
Next, an image recording and image erasing mechanism will be described.
The image recording and image erasing mechanisms include an aspect in which the transparency changes reversibly depending on the temperature and an aspect in which the color tone changes reversibly depending on the temperature.
In the aspect in which the transparency changes reversibly, the organic low molecule in the thermoreversible recording medium is dispersed in particles in the resin, and the transparency is reversible by heat between a transparent state and a cloudy state. To change.
The visual recognition of the change in transparency results from the following phenomenon. That is, (1) in the transparent state, the organic low-molecular substance particles dispersed in the resin matrix and the resin matrix are in close contact with each other without any gap, and there are voids inside the particles. Therefore, the light incident from one side is transmitted to the opposite side without being scattered and looks transparent. On the other hand, in the case of (2) white turbidity, the particles of the low molecular weight organic substance are formed of fine crystals of the low molecular weight organic substance, and the interface between the crystal or the particle and the resin base material. A gap (gap) is generated, and light incident from one side is refracted and scattered at the interface between the gap and the crystal, or the interface between the gap and the resin, and thus appears white.
First, FIG. 3A shows a temperature-transparency change of a thermoreversible recording medium having a thermoreversible recording layer (hereinafter sometimes referred to as “recording layer”) in which the organic low molecular weight substance is dispersed in the resin. An example of a curve is shown.
For example, the recording layer is in a cloudy opaque state (A) at room temperature of T0 or less. As this is heated, it gradually becomes transparent from the temperature T1, and becomes transparent (B) when heated to the temperature T2 to T3, and remains transparent (D) even if it is returned to room temperature below T0 in this state. is there. This is because the resin begins to soften from around the temperature T1, and as the softening progresses, the resin shrinks, and the interface between the resin and the organic low molecular substance particles or the voids in the particles is gradually reduced. Transparency increases, and at temperatures T2 to T3, the organic low molecular weight material is in a semi-molten state, and the remaining voids become transparent by filling the organic low molecular weight material, and when the seed crystal remains cooled, Crystallization at a high temperature, and the resin is still in a softened state. Therefore, the resin follows the change in the deposition of particles accompanying crystallization, and the void is not formed, and the transparent state is maintained. It is done.
Further heating to a temperature of T4 or higher results in a translucent state (C) intermediate between maximum transparency and maximum opacity. Next, when this temperature is lowered, the first white turbid opaque state (A) is restored without becoming transparent again. This is because after the organic low molecular weight substance is completely melted at a temperature of T4 or higher, it becomes supercooled and crystallizes at a temperature slightly higher than T0. At that time, the resin may follow a volume change accompanying crystallization. This is considered to be because voids cannot be generated.
Here, in FIG. 3A, when the temperature of the recording layer is repeatedly raised to a temperature T5 that greatly exceeds the temperature T4, an erasing defect that cannot be erased even when heated to the erasing temperature may occur. This is presumably because the internal structure of the recording layer changes as the organic low molecular weight substance melted by heating moves in the resin. In order to suppress the deterioration of the thermoreversible recording medium due to repetition, it is necessary to reduce the difference between the temperature T4 and the temperature T5 in FIG. 3A when the thermoreversible recording medium is heated. In the intensity distribution of the laser beam, the ratio (I1 / I2) is preferably 2.00 or less, more preferably 1.80 or less, and particularly preferably 1.67 or less.
However, in the temperature-transparency change curve shown in FIG. 3A, when the type of the resin, the organic low-molecular substance, or the like is changed, the transparency of each state may change depending on the type.

Further, FIG. 3B shows a transparency changing mechanism of the thermoreversible recording medium in which the transparent state and the cloudy state are reversibly changed by heat.
In FIG. 3B, one long-chain low-molecular particle and the surrounding polymer are taken out, and the generation and disappearance change of voids accompanying heating and cooling are illustrated. In the cloudy state (A), voids are generated between the polymer and the low molecular particles (or inside the particles), and the light scattering state is obtained. When this is heated and exceeds the softening point (Ts) of the polymer, voids decrease and transparency increases. When further heated to near the melting point (Tm) of the low molecular particle, a part of the low molecular particle is melted, and due to the volume expansion of the melted low molecular particle, the void is filled with the low molecular particle. Disappears and becomes transparent (B). When cooled from here, the low-molecular particles crystallize immediately below the melting point, no voids are generated, and the transparent state (D) is maintained even at room temperature.
Next, when heated to the melting point of the low molecular particle or higher, the refractive index between the molten low molecular particle and the surrounding polymer is shifted, and a translucent state (C) is obtained. When cooled to room temperature from this point, the low molecular particles undergo a supercooling phenomenon and crystallize below the softening point of the polymer. At this time, the polymer is in a glass state, so the volume accompanying the crystallization of the low molecular particles The surrounding polymer cannot follow the decrease, and voids are generated to return to the original cloudy state (A).

Next, in an embodiment in which the color tone reversibly changes depending on the temperature, a leuco dye and a reversible developer (hereinafter sometimes referred to as “developer”) are included in the resin, and the color tone is However, it changes reversibly by heat into a transparent state and a colored state.
FIG. 4A shows an example of a temperature-color density change curve of a thermoreversible recording medium having a thermoreversible recording layer containing the leuco dye and the developer in the resin, and FIG. 4B shows a transparent state. And a color development / decoloration mechanism of the thermoreversible recording medium in which the color development state changes reversibly with heat.
First, when the temperature of the recording layer in the decolored state (A) is raised, the leuco dye and the developer are melted and mixed at the melting temperature T1, and color development occurs, resulting in a molten color state (B ) When rapidly cooled from the melt color state (B), the color state can be lowered to room temperature, and the color state is stabilized and becomes a fixed color state (C). Whether or not this color development state has been obtained depends on the rate of temperature decrease from the melted state. In slow cooling, the color disappears in the process of temperature decrease, and the same color disappearance state (A) as the initial state or the color development state by rapid cooling ( The density is relatively lower than in C).
On the other hand, when the temperature is raised again from the color development state (C), the color disappears at a temperature T2 lower than the color development temperature (D to E). Return to.
The colored state (C) obtained by quenching from the molten state is a state in which the leuco dye and the developer are mixed in a state in which molecules can contact each other and form a solid state. There are many cases. In this state, the molten mixture of the leuco dye and the developer (the color mixture) crystallizes and maintains color development, and it is considered that the color development is stabilized by the formation of this structure. On the other hand, the decolored state is a state in which both phases are separated. This state is a state in which molecules of at least one compound aggregate to form a domain or crystallize, and the leuco dye and the developer are separated and stabilized by aggregation or crystallization. It is considered to be a state. In many cases, the color developer is crystallized as a result of the phase separation of the two, thereby causing more complete decoloring.
In addition, as shown in FIG. 4A, the decolorization due to slow cooling from the melted state and the decoloration due to the temperature rise from the colored state both change the aggregation structure at T2, causing phase separation and crystallization of the developer. Yes.
Furthermore, in FIG. 4A, when the recording layer is repeatedly heated to a temperature T3 that is equal to or higher than the melting temperature T1, an erasing defect that cannot be erased even when heated to the erasing temperature may occur. This is presumably because the developer undergoes thermal decomposition and is difficult to aggregate or crystallize and separate from the leuco dye. In order to suppress the deterioration of the thermoreversible recording medium due to repetition, the difference between the melting temperature T1 and the temperature T3 in FIG. 4A is reduced when the thermoreversible recording medium is heated, whereby the thermoreversible recording due to repetition. Deterioration of the medium can be suppressed.

(Image processing method)
The image processing method of the present invention includes at least one of an image recording step and an image erasing step, and further includes other steps appropriately selected as necessary.
The image processing method of the present invention includes both an aspect in which both image recording and erasing are performed, an aspect in which only image recording is performed, and an aspect in which only image erasing is performed.

<Image recording process and image erasing process>
The image recording step in the image processing method of the present invention is a step of recording an image on the thermoreversible recording medium by heating the thermoreversible recording medium. As a method for heating a thermoreversible recording medium, a conventionally known heating method can be mentioned. However, when a distribution line is assumed, a method of irradiating a thermoreversible recording medium with laser light to heat the image in a non-contact state. This is particularly preferred because it can be formed.

The image erasing step in the image processing method of the present invention is a step of erasing an image recorded on the thermoreversible recording medium by heating the thermoreversible recording medium, and a laser beam may be used as a heat source. A heat source other than laser light may be used. Among the heat sources, when heating by irradiating laser light, it takes time to scan and irradiate the entire predetermined area with one laser light. It is preferable to erase by heating using a heat roller, hot stamp, dryer or the like. In addition, when the foamed polystyrene box is equipped with the thermoreversible recording medium as a transport container for use in the distribution line, the foamed polystyrene box itself melts when heated, so that the thermoreversible recording is performed by irradiating a laser beam. It is preferable to erase by locally heating only the medium.
By irradiating the thermoreversible recording medium with the laser light and heating it, an image can be recorded in a non-contact state with the thermoreversible recording medium.
In the image processing method of the present invention, the image is normally updated (the image erasing step) for the first time when the thermoreversible recording medium is reused, and then the image is recorded by the image recording step. The order of erasing is not limited to this, and the image may be erased by the image erasing step after the image is recorded by the image recording step.

  There is no restriction | limiting in particular in the said laser beam, According to the objective, it can select suitably, For example, normally used lasers, such as a YAG laser, a fiber laser, and a semiconductor laser (LD), are mentioned. Among these, a semiconductor laser beam is particularly preferable when assuming a physical distribution line because of the advantage that the apparatus can be reduced in size and further reduced in price.

There is no restriction | limiting in particular as an output of the laser beam irradiated in the said image formation process, Although it can select suitably according to the objective, 1W or more are preferable, 3W or more are more preferable, and 5W or more are still more preferable. If the output of the laser beam is less than 1 W, it takes time to form an image. If an attempt is made to shorten the image formation time, the output is insufficient and a high-density image cannot be obtained. Moreover, there is no restriction | limiting in particular as an upper limit of the output of the said laser beam, Although it can select suitably according to the objective, 200W or less is preferable, 150W or less is more preferable, and 100W or less is still more preferable. If the output of the laser beam exceeds 200 W, the laser device may be increased in size.
There is no restriction | limiting in particular as scanning speed of the laser beam irradiated in the said image formation process, Although it can select suitably according to the objective, 300 mm / s or more is preferable, 500 mm / s or more is more preferable, 700 mm / s More preferably, s or more. If the scanning speed is less than 300 mm / s, it takes time to form an image. The upper limit of the scanning speed of the laser beam is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 15,000 mm / s or less, more preferably 10,000 mm / s or less, and 8 More preferably, it is 1,000 mm / s or less. If the scanning speed exceeds 15,000 mm / s, it is difficult to form a uniform image.
The spot diameter of the laser beam irradiated in the image forming step is not particularly limited and can be appropriately selected according to the purpose, but is preferably 0.02 mm or more, more preferably 0.1 mm or more, and 0.15 mm. The above is more preferable. The upper limit of the laser beam spot diameter is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 3.0 mm or less, more preferably 2.5 mm or less, and 2.0 mm or less. Further preferred. If the spot diameter is small, the line width of the image becomes narrow, the contrast becomes small, and the visibility is lowered. In addition, when the spot diameter is increased, the line width of the image is increased, adjacent lines are overlapped, and it is impossible to form an image of a small character.

Further, the output of the laser beam irradiated in the image erasing step of erasing the image by irradiating the thermoreversible recording medium with laser light is not particularly limited and is appropriately selected according to the purpose. However, 5W or more is preferable, 7W or more is more preferable, and 10W or more is more preferable. If the output of the laser beam is less than 5 W, it takes a long time to erase the image. If an attempt is made to shorten the image erasing time, the output is insufficient and an image erasing failure occurs. Moreover, there is no restriction | limiting in particular as an upper limit of the output of the said laser beam, Although it can select suitably according to the objective, 200W or less is preferable, 150W or less is more preferable, and 100W or less is still more preferable. If the output of the laser beam exceeds 200 W, the laser device may be increased in size.
The scanning speed of the laser light irradiated in the image erasing process for erasing the image by irradiating the thermoreversible recording medium with laser light and heating is not particularly limited and may be appropriately selected according to the purpose. However, 100 mm / s or more is preferable, 200 mm / s or more is more preferable, and 300 mm / s or more is still more preferable. When the scanning speed is less than 100 mm / s, it takes time to erase the image. Moreover, there is no restriction | limiting in particular as an upper limit of the scanning speed of the said laser beam, Although it can select suitably according to the objective, 20,000 mm / s or less is preferable, 15,000 mm / s or less is more preferable, 10 More preferably, it is 1,000 mm / s or less. If the scanning speed exceeds 20,000 mm / s, it may be difficult to erase a uniform image.
The spot diameter of the laser light irradiated in the image erasing process for erasing the image by irradiating the thermoreversible recording medium with laser light and heating is not particularly limited and may be appropriately selected according to the purpose. However, 0.5 mm or more is preferable, 1.0 mm or more is more preferable, and 2.0 mm or more is still more preferable.
Moreover, there is no restriction | limiting in particular as an upper limit of the spot diameter of the said laser beam, Although it can select suitably according to the objective, 14.0 mm or less is preferable, 10.0 mm or less is more preferable, and 7.0 mm or less is preferable. Further preferred.
When the spot diameter is small, it takes time to erase the image. Further, when the spot diameter is increased, the output is insufficient and an image erasing failure occurs.

<Image processing device>
The image processing apparatus used in the present invention includes at least laser beam irradiation means, and further includes other means appropriately selected as necessary.

-Laser light emitting means-
The laser beam emitting means in the image recording step and / or the image erasing step may be a laser beam having a maximum wavelength in the vicinity of the maximum absorption peak of the photothermal conversion material contained in the thermoreversible recording medium. For example, a YAG laser, a fiber laser, a semiconductor laser (LD), and the like can be used, but the invention is not limited to these. Here, the wavelength of the laser beam is particularly preferably a single wavelength.
The wavelengths of the laser beams emitted from the YAG laser, the fiber laser, and the semiconductor laser are in the visible to near infrared region (several hundred μm to 1.2 μm), and because the wavelength is short, high-definition images can be formed. There is an advantage that it is possible. Further, since the YAG laser and the fiber laser have high output, there is an advantage that the image processing speed can be increased. Since the semiconductor laser is small, the semiconductor laser has an advantage that the apparatus can be downsized and the cost can be reduced. When a physical distribution line is assumed from this, a semiconductor laser beam is particularly preferable.
The wavelength of the laser light emitted from the laser light emitting means can be appropriately selected according to the purpose, and is preferably 600 nm to 1,200 nm with little absorption of various resins contained in the thermoreversible recording medium. 700 nm to 1,100 nm is more preferable. When the wavelength is smaller than 600 nm, there is a problem that the thermoreversible recording medium is likely to be deteriorated by laser light irradiation. If the wavelength is greater than 1,200 nm, the laser light is absorbed by various resins contained in the thermoreversible recording medium, so that there is a problem that a high-power semiconductor laser is required and the apparatus is enlarged.

  The image processing apparatus, except for having at least the laser beam emitting means, has the same basic configuration as that usually called a laser marker, and includes at least an oscillator unit, a power supply control unit, and a program unit. Yes.

Here, FIG. 5 shows an example of the image processing apparatus used in the present invention, focusing on the laser irradiation unit. The image processing apparatus shown in FIG. 5 uses a fiber-coupled semiconductor laser manufactured by LIMO (LIMO25F100-DL808-EX362) as a laser light source, and can output up to 25 W with an oscillation wavelength of 808 nm and a fiber diameter of 100 μm. . Laser light is emitted from the fiber and immediately after that, it is collimated by a collimator. A mask or aspherical lens is incorporated in the parallel light path as a means for adjusting the light irradiation intensity distribution, and the light intensity in the cross section orthogonal to the direction of travel of the laser light. The distribution can also be adjusted to change.
The oscillator unit includes a laser oscillator 1, a beam expander 2, a scanning unit 5, and the like.
The scanning unit 5 includes a galvanometer (not shown) and a mirror 4A attached to the galvanometer. Then, the laser beam output from the laser oscillator 1 is scanned at high speed by two mirrors 4A in the X-axis direction and the Y-axis direction attached to the galvanometer (not shown), whereby a thermoreversible recording medium 7, an image is formed or erased.
The power control unit includes a drive power source for a light source that excites a laser medium, a drive power source for a galvanometer, a cooling power source such as a Peltier element, and a control unit that controls the entire image processing apparatus.
The program unit is a unit for inputting conditions such as the intensity of laser light and the speed of laser scanning, and for producing and editing characters to be recorded for recording or erasing images by touch panel input or keyboard input. .
The laser irradiation unit, that is, the image recording / erasing head portion is mounted on an image processing apparatus. In addition to the above, the image processing apparatus includes a transport unit and a control unit for the thermoreversible recording medium. And a monitor unit (touch panel).

  The image processing method of the present invention is capable of repeated recording and erasing at high speed on a thermoreversible recording medium such as a label affixed to a container such as a cardboard or a plastic container at high speed, and is exposed to light for a long time. However, since a thermoreversible recording medium having sufficient erasability without use of image density reduction or background coloration is used, it can be used particularly suitably for a distribution / distribution system. In this case, for example, an image can be formed and erased on the label while moving the cardboard or plastic container placed on a belt conveyor, and it is not necessary to stop the line, thereby reducing the shipping time. it can. Further, the cardboard or the plastic container to which the label is attached can be reused as it is without peeling off the label, and the image can be erased and formed again.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
<Preparation of thermoreversible recording medium>
A thermoreversible recording medium whose color tone is reversibly changed by heat (transparent state-colored state) was produced as follows.

-Support-
As the support, a white polyester film having a thickness of 125 μm (Tetron film U2L98W, manufactured by Teijin DuPont Co., Ltd.) was used.

-Under layer-
30 parts by mass of a styrene-butadiene copolymer (manufactured by Nippon A & L Co., PA-9159), 12 parts by mass of a polyvinyl alcohol resin (manufactured by Kuraray Co., Ltd., Poval PVA103), hollow particles (manufactured by Matsumoto Yushi Co., Ltd., Microsphere R) -300) 20 parts by mass and 40 parts by mass of water were added and stirred for about 1 hour until a uniform state was obtained to prepare an under layer coating solution.
Next, the obtained under layer coating solution was applied onto the support with a wire bar, and heated and dried at 80 ° C. for 2 minutes to form an under layer having a thickness of 20 μm.

-Thermoreversible recording layer-
5 parts by mass of a reversible developer represented by the following structural formula (1), and 0.5 parts by mass of two types of decoloring accelerators represented by the following structural formulas (2) and (3) 10 parts by mass of a polyol 50% by mass solution (hydroxyl value = 200 mg KOH / g) and 80 parts by mass of methyl ethyl ketone were pulverized and dispersed using a ball mill until the average particle size was about 1 μm.
[Reversible developer]
<Structural formula (1)>
[Discoloration accelerator]
<Structural formula (2)>
<Structural formula (3)>
C ₁₇ H ₃₅ CONHC ₁₈ H ₃₇

Next, in the dispersion in which the reversible developer is pulverized and dispersed, 1 part by mass of 2-anilino-3-methyl-6-diethylaminofluorane as a leuco dye, and metal fine particles having plasmon absorption, the average minor axis length 0.4 parts by weight of a 5% by weight dispersion solution of gold nanorods (maximum absorption peak: 810 nm) having a length of 4.8 nm and an average major axis length of 19.2 nm, and isocyanate (Nihon Polyurethane Co., Ltd., Coronate HL) 5 A mass part was added and stirred well to prepare a coating solution for a thermoreversible recording layer.
Next, the obtained coating liquid for thermoreversible recording layer was applied onto the support on which the under layer had been formed using a wire bar, heated and dried at 100 ° C. for 2 minutes, and then at 60 ° C. Curing was performed for 24 hours to form a thermoreversible recording layer having a thickness of 10 μm.

-UV absorbing layer-
Add 10 parts by weight of a 40% by weight UV-absorbing polymer solution (manufactured by Nippon Shokubai Co., Ltd., UV-G302), 1.0 part by weight of an isocyanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate HL), and 12 parts by weight of methyl ethyl ketone. A UV-absorbing layer coating solution was prepared by stirring.
Next, on the support on which the under layer and the thermoreversible recording layer are formed, the ultraviolet absorbing layer coating solution is applied with a wire bar, heated and dried at 90 ° C. for 1 minute, and then 60 Heating was performed at a temperature of 24 ° C. for 24 hours to form a 10 μm-thick ultraviolet absorbing layer.

-Oxygen barrier layer-
Add 5 parts by mass of urethane adhesive (TM-567 manufactured by Toyo Morton Co., Ltd.), 0.5 parts by mass of isocyanate (CAT-RT-37 manufactured by Toyo Morton Co., Ltd.), and 5 parts by mass of ethyl acetate, and stir well. Thus, a coating solution for an adhesive layer was prepared.
Next, an adhesive layer coating solution was applied on a silica-deposited PET film (Dai Nippon Printing Co., Ltd., IB-PET-C, oxygen permeability 15 ml / m ² / day / MPa) with a wire bar. After heating and drying at 0 ° C. for 1 minute, the substrate was laminated on the support on which the under layer, the thermoreversible recording layer, and the ultraviolet absorbing layer were formed, heated at 50 ° C. for 24 hours, and oxygen having a thickness of 12 μm. A barrier layer was formed.

-Back layer-
Pentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd., KAYARAD DPHA) 7.5 parts by mass, urethane acrylate oligomer (manufactured by Negami Kogyo Co., Ltd., Art Resin UN-3320HA) 2.5 parts by mass, acicular conductive titanium oxide ( FT-3000 manufactured by Ishihara Sangyo Co., Ltd., long axis = 5.15 μm, short axis = 0.27 μm, composition: 2.5 parts by mass of titanium oxide coated with antimony-doped tin oxide, photopolymerization initiator (Nippon Ciba-Geigy Corporation) Manufactured, Irgacure 184) and 0.5 parts by mass of isopropyl alcohol and 13 parts by mass of isopropyl alcohol were added, and the mixture was thoroughly stirred with a ball mill to prepare a coating solution for a back layer.
Next, the back layer coating solution is applied with a wire bar on the surface of the support on which the thermoreversible recording layer is not formed, heated and dried at 90 ° C. for 1 minute, and then 80 W A back layer having a thickness of 4 μm was formed by crosslinking with a / cm ultraviolet lamp. Thus, a thermoreversible recording medium of Example 1 was produced.

(Example 2)
-Production of thermoreversible recording media-
Except for changing the metal fine particles having plasmon absorption of Example 1 to gold nanorods having an average minor axis length of 10 nm and an average major axis length of 42 nm (maximum absorption peak: 822 nm), the same as in Example 1. A thermoreversible recording medium was produced.

(Example 3)
-Production of thermoreversible recording media-
The metal fine particles having plasmon absorption of Example 1 were added to gold nanorods (maximum absorption peak: 810 nm) having an average minor axis length of 4.8 nm and an average major axis length of 19.2 nm. A thermoreversible recording medium was produced in the same manner as in Example 1 except that gold nanorods having a silica thin film formed on the surface thereof were changed by the action of ethoxysilane.

Example 4
<Preparation of thermoreversible recording medium>
A thermoreversible recording layer was formed in the same manner as in Example 1 except that the metal fine particles having plasmon absorption were removed from the thermoreversible recording layer of Example 1.
Next, on the support on which the recording layer is formed, the following coating solution for photothermal conversion layer is applied with a wire bar, heated and dried at 90 ° C. for 1 minute, and then heated at 60 ° C. for 2 hours. Then, a photothermal conversion layer having a thickness of 3 μm was formed.
-Preparation of coating solution for photothermal conversion layer-
6 parts by mass of acrylic polyol resin 50% by mass solution (manufactured by Mitsubishi Rayon Co., Ltd., LR327), gold nanorods having an average minor axis length of 4.8 nm and an average major axis length of 19.2 nm (maximum absorption) 1.1 parts by weight of 5% by weight dispersion solution (peak: 810 nm), 2.4 parts by weight of isocyanate (manufactured by Nippon Polyurethane Co., Ltd., Coronate HL), and 14 parts by weight of methyl ethyl ketone are added, and the mixture is stirred well and applied for a photothermal conversion layer. A liquid was prepared.

  Subsequently, the intermediate layer, protective layer, and back layer of Example 1 were formed in the same manner as in Example 1 to produce a thermoreversible recording medium of Example 4.

(Example 5)
-Production of thermoreversible recording media-
The metal fine particles having plasmon absorption of Example 4 were converted into (3-aminopropyl) ethyldioxide on gold nanorods (maximum absorption peak: 810 nm) having an average minor axis length of 4.8 nm and an average major axis length of 19.2 nm. A thermoreversible recording medium was produced in the same manner as in Example 4 except that gold nanorods having a silica thin film formed on the surface thereof were changed by the action of ethoxysilane.

(Example 6)
-Production of thermoreversible recording media-
Example 1 except that the support of Example 1 was changed to one in which the oxygen barrier layer of Example 1 was provided on the support of a 125 μm thick white polyester film (Tetron Film U2L98W, manufactured by Teijin DuPont Co., Ltd.) In the same manner, a thermoreversible recording medium was produced.

(Comparative Example 1)
-Production of thermoreversible recording media-
The metal fine particles having plasmon absorption were removed from the thermoreversible recording layer of Example 1, and 0.5 mass of a 5 mass% solution of a phthalocyanine-based photothermal conversion material (Yamamoto Kasei Co., Ltd., YKR-3070, maximum absorption peak: 810 nm) was used. A thermoreversible recording medium was produced in the same manner as in Example 1 except that a part thereof was added.

(Comparative Example 2)
-Production of thermoreversible recording media-
By removing the metal fine particles having plasmon absorption from the photothermal conversion layer of Example 4, 1.5 parts by mass of a 5% by mass solution of a phthalocyanine photothermal conversion material (Yamamoto Kasei Co., Ltd., YKR-3070, maximum absorption peak: 810 nm) A thermoreversible recording medium was produced in the same manner as in Example 4 except for the addition.

(Example 7)
<Preparation of thermoreversible recording medium>
A thermoreversible recording medium whose transparency is reversibly changed by heat (transparent state-white turbid state) was produced as follows.

-Support-
A transparent PET film having a thickness of 188 μm (manufactured by Toray Industries, Inc., Lumirror 188-T60) was used as the support.

-Thermoreversible recording layer-
3 masses of a low molecular weight organic substance represented by the following structural formula (4) in a resin solution obtained by dissolving 26 mass parts of a vinyl chloride copolymer (manufactured by Zeon Corporation, MR110) in 210 mass parts of methyl ethyl ketone. And 7 parts by mass of docosyl behenate were added, ceramic beads having a diameter of 2 mm were put in a glass bottle, and dispersed for 48 hours using a paint shaker (manufactured by Asada Tekko Co., Ltd.) to prepare a uniform dispersion.
<Structural formula (4)>

Next, a 5% by mass dispersion solution of gold nanorods (maximum absorption peak: 810 nm) having an average minor axis length of 4.8 nm and an average major axis length of 19.2 nm as the metal fine particles was added to the obtained dispersion liquid. 1.8 parts by mass and 4 parts by mass of an isocyanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate 2298-90T) were added to prepare a thermoreversible recording layer solution.
Next, the obtained thermoreversible recording layer solution is applied onto the support, heated and dried, and further stored in a 65 ° C. environment for 24 hours to crosslink the resin, thereby thermoreversible recording with a thickness of 10 μm. A layer was provided.

-Protective layer-
A solution consisting of 10 parts by mass of a 75% by weight butyl acetate solution of urethane acrylate-based UV curable resin (Unidic C7-157, manufactured by Dainippon Ink & Chemicals, Inc.) and 10 parts by mass of isopropyl alcohol is heated with the wire bar. After coating on the reversible recording layer, heating and drying, it was cured by irradiating with an ultraviolet ray with an 80 W / cm high-pressure mercury lamp to form a protective layer having a thickness of 3 μm. Thus, the thermoreversible recording medium of Example 7 was produced.

(Comparative Example 3)
The metal fine particles having plasmon absorption were removed from the thermoreversible recording layer of Example 7, and 2.4 mass of a 5 mass% solution of a phthalocyanine-based photothermal conversion material (Yamamoto Kasei Co., Ltd., YKR-3070, maximum absorption peak: 810 nm) was used. A thermoreversible recording medium was produced in the same manner as in Example 7 except that a part thereof was added.

<Laser recording evaluation>
As a semiconductor laser light source as shown in FIG. 3, a semiconductor laser device provided with a semiconductor laser LIMO25-F100-DL808 (center wavelength: 808 nm) manufactured by LIMO is used to irradiate thermoreversible recording media manufactured in Examples and Comparative Examples. An image was recorded by adjusting the distance to 152 mm and the linear speed to 1,000 mm / s. At this time, image recording was performed with a recording energy in the range of 10 to 40 mJ / mm ² , and the recording energy at which the saturation density was reached was defined as the saturation recording energy.
The image is erased by using the semiconductor laser device, adjusting the irradiation distance to 200 mm, the linear velocity of 500 mm / s, and the spot diameter of 3.0 mm, and scanning the laser beam linearly at intervals of 0.5 mm. The image was erased. At this time, the laser output was 14 W in Examples 1 to 3 and Comparative Example 1, and 16 W in Examples 4 to 7 and Comparative Examples 2 to 3.

<Light resistance evaluation 1>
For the thermoreversible recording media of Examples 1 to 7 and Comparative Examples 1 to 3, the absorbance at a wavelength of 808 nm was first measured in the initial state using a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, U-4100). The results are shown in Table 1.
Then, after performing light irradiation for 12 hours under the conditions of 80% RH and 130 klx at 30 ° C. using an artificial sunlight irradiation device manufactured by Celic Co., Ltd., the absorbance at a wavelength of 808 nm was similarly measured with a spectrophotometer, Each was compared with the absorbance in the initial state. The results are shown in Table 1. The evaluation with artificial sunlight here is a compulsory test, and the light resistance required for the thermoreversible recording medium from the market corresponds to the exposure of light for 12 hours with this apparatus.
Next, images were recorded on the thermoreversible recording media of Examples 1 to 7 and Comparative Examples 1 to 3 before and after light irradiation in the artificial sunlight irradiation apparatus under the above laser recording conditions, and saturation recording was performed. Energy was evaluated. The results are shown in Table 1.

<Light resistance evaluation 2>
Using the thermoreversible recording media of Examples 4 to 5 and Comparative Example 2, recording and erasing were repeated 100 times under the above laser recording conditions and laser erasing conditions, and then a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, U -4100), the absorbance at a wavelength of 808 nm was first measured in the erased state. The results are shown in Table 2.
Then, after performing light irradiation for 12 hours on the conditions of 80% RH and 130 klx at 30 degreeC using the artificial sunlight irradiation apparatus by Celic Co., Ltd., the light absorbency of wavelength 808nm was similarly measured with the spectrophotometer. The results are shown in Table 2.
Next, images were recorded under the above laser recording conditions on the thermoreversible recording media of Examples 4 to 5 and Comparative Example 2 before and after light irradiation with the artificial sunlight irradiation device, and saturation recording energy was set. evaluated. The results are shown in Table 2.

From the results of Table 1, in Examples 1 to 6, since gold nanorods are used as the photothermal conversion material, there is no interaction with the leuco dye even if the photothermal conversion material is added to the thermoreversible recording layer, and the light resistance Even after the evaluation, the absorbance of the photothermal conversion material did not change greatly, and good recording sensitivity was obtained. Particularly in Examples 1 to 3 and Example 6, since the photothermal conversion material is present in the thermoreversible recording layer, higher sensitivity is obtained than in Examples 4 and 5 in which the photothermal conversion material is present in the photothermal conversion layer.
On the other hand, in Comparative Example 1, an organic dye is used as the photothermal conversion material and mixed with the leuco dye in the thermoreversible recording layer. Therefore, after the light resistance evaluation, the absorbance of the photothermal conversion material is greatly reduced, and sufficient Recording sensitivity could not be obtained.
In Example 7, since gold nanorods were used as the light-to-heat conversion material, it was found that the light resistance was superior to Comparative Example 3 in which an organic dye was used as the light-to-heat conversion material.
Further, from the results in Table 2, in Examples 4 to 5, there was no significant change in the absorbance of the photothermal conversion material even after the light resistance evaluation after 100 times of recording and erasing, and sufficient recording sensitivity was obtained. .
On the other hand, in Comparative Example 2, before recording and erasing, even if an organic dye is used as the photothermal conversion material, it is not mixed with the leuco dye in the thermoreversible recording layer. Although there is no significant decrease in the absorbance of the material, after 100 times of recording and erasing, the photothermal conversion material and the leuco dye are mixed, and after the light resistance evaluation, the absorbance of the photothermal conversion material is greatly reduced, which is sufficient Recording sensitivity could not be obtained.

  The thermoreversible recording medium of the present invention contains metal fine particles having plasmon absorption as a photothermal conversion material, has sufficient recording density and erasability, is highly sensitive, and has excellent light resistance of the photothermal conversion material. Therefore, the thermoreversible recording medium is affixed to a container such as a corrugated cardboard or a plastic container, and a high-contrast image can be repeatedly recorded and erased at high speed in a non-contact manner, even when exposed to light for a long time. A decrease in recording sensitivity and erasing sensitivity due to photodegradation of the photothermal conversion material can be suppressed, and it can be used particularly suitably in a physical distribution / distribution system.

DESCRIPTION OF SYMBOLS 1 Fiber 2 Beam collimator 3 Mirror 4A Mirror 5 Scanning unit 6 f (theta) lens 7 Thermoreversible recording medium 8 Lens 10 Semiconductor laser 101 Support body 102 Thermoreversible recording layer 103 Photothermal conversion layer

JP 2004-265247 A Japanese Patent No. 3998193 Japanese Patent Application Laid-Open No. 2000-136022 JP-A-5-8537 JP-A-11-151856 JP 2005-238746 A JP 2005-238745 A

Claims (9)

In a thermoreversible recording medium having at least a layer containing a support and a photothermal conversion material that absorbs light of a specific wavelength and converts it into heat on the support,
A thermoreversible recording medium, wherein the photothermal conversion material is metal fine particles having plasmon absorption.   The thermoreversible recording medium according to claim 1, wherein the layer containing the photothermal conversion material is a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature.   The thermoreversible recording medium according to claim 1, wherein the layer containing the photothermal conversion material is a photothermal conversion layer, and has a thermoreversible recording layer in which either transparency or color tone reversibly changes depending on temperature.   The thermoreversible recording medium according to any one of claims 1 to 3, wherein the metal fine particles having plasmon absorption are gold nanorods.   The thermoreversible recording medium according to any one of claims 2 to 4, wherein the thermoreversible recording layer contains a leuco dye and a reversible developer.   The thermoreversible recording medium according to any one of claims 2 to 4, wherein the thermoreversible recording layer contains a resin and an organic low molecular weight substance.   An image recording step of recording an image on the thermoreversible recording medium by irradiating the thermoreversible recording medium according to any one of claims 1 to 6 with laser light and heating, and the thermoreversible recording medium. An image processing method comprising: an image erasing step of erasing an image recorded on the thermoreversible recording medium by irradiating and heating a laser beam.   The image processing method according to claim 7, wherein the wavelength of the laser beam to be irradiated is 600 nm to 1,200 nm.   The image processing method according to claim 7, wherein the laser beam to be irradiated is at least one of a YAG laser beam, a fiber laser beam, and a semiconductor laser beam.