JP2020126162A - Light guide plate for image display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an influence on a displayed image due to yellowing of a transparent material in a light guide plate for image display. An image display light guide plate 5 includes a resin base material 1, a hologram layer 2, and an absorption layer 4. The absorption layer 4 has an absorption peak in a wavelength range of 500 nm or more and 600 nm or less. [Selection diagram] Fig. 1

Description

The present invention relates to a light guide plate for image display.

An image display light guide plate may be used in a display device. For example, in a display device using VR (Virtual Reality) technology, AR (Augmented Reality) technology, MR (Mixed Reality) technology, and the like, an image display light guide plate having a hologram layer supported by a transparent substrate is used. Holograms having various optical functions such as waveguiding, reflection, and diffraction are formed on the hologram layer.
For example, Patent Document 1 discloses a hologram laminate having a hologram sandwiched between resin bases via an optical adhesive, the hologram laminate having the entire outer peripheral portion covered with a protective coating layer. Further, Patent Document 1 describes that a so-called short wavelength cut filter that transmits light having a wavelength used in a hologram and absorbs light having a shorter wavelength may be provided.
On the other hand, although it is not a technique relating to a light guide plate for image display having a hologram layer, Patent Document 2 discloses that the surface of a pigment is used for the purpose of improving the yellowness of a lens due to yellowing of a plastic material for a lens during thermosetting. It has been proposed to disperse a bluing agent for plastic optical materials in which a hydrophobic silica coating is applied to the lens forming material.

JP, 11-184363, A JP, 2003-105227, A

However, the related art as described above has the following problems.
Since yellow has a high relative luminous efficiency, if the transparent material such as the hologram layer is yellowed in the image display light guide plate, the contrast (brightness) becomes low when the image is viewed. As a result, the image looks unclear.
In the technique described in Patent Document 1, short-wavelength light, such as ultraviolet light, which is not used for image display of the image display light guide plate is cut, so that the change over time in the resin material used for the image display light guide plate due to ultraviolet light, For example, it is possible to suppress a decrease in transparency and coloring.
However, the photopolymer material forming the hologram layer, the optional barrier layer, and the like are particularly liable to yellow, so that they are yellowish even immediately after production. For this reason, there is a problem in that even if a short-wavelength cut filter is provided as in Patent Document 1, the yellowish color generated immediately after manufacturing cannot be removed.
On the other hand, it may be possible to apply the technique described in Patent Document 2 to the hologram layer. However, since the bluing agent of Patent Document 1 has an average particle size of about 0.4 μm to 0.6 μm, mixing the bluing agent in the hologram layer causes a problem in recording interference fringes in the hologram layer. There's a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image display light guide plate that can reduce the influence of yellowing of a transparent material on a displayed image.

In order to solve the above problems, for example, the present invention has the following aspects.
[1] A light guide plate for image display having a resin base material and a hologram layer, which includes an absorption layer having an absorption peak in a wavelength range of 500 nm or more and 600 nm or less.
[2] The light guide plate for image display of [1], wherein the absorption layer, the resin base material, and the hologram layer are arranged in this order in the thickness direction.
[3] The light guide plate for image display according to [1], wherein the absorption layer is arranged in a range overlapping with a display image emission part in the hologram layer in the thickness direction.
[4] The light guide plate for image display according to [1], wherein the absorption layer is formed by dispersing a coloring material in at least a part of the inside of the resin base material.
[5] The light guide plate for image display according to [1], further including a barrier layer.
[6] The light guide plate for image display of [5], wherein the barrier layer is arranged between the resin base material and the hologram layer.

ADVANTAGE OF THE INVENTION According to this invention, the light guide plate for image displays which can reduce the influence on the display image by yellowing of a transparent material can be provided.

It is a typical sectional view showing an example of a light guide plate for image display of an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing an example of a display device including the image display light guide plate according to the embodiment of the present invention. It is a typical sectional view showing an example of an image display light guide plate of the 1st modification of an embodiment of the present invention. It is a typical sectional view showing an example of a light guide plate for image displays of the 2nd modification of an embodiment of the present invention. It is a typical sectional view showing an example of an image display light guide plate of the 3rd modification of an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. In all the drawings, the same or corresponding members are denoted by the same reference numerals even if the embodiments are different, and common description is omitted.

An image display light guide plate according to an embodiment of the present invention will be described.
The image display light guide plate of the present embodiment has a resin base material, a hologram layer, and an absorption layer.
The image display light guide plate of the present embodiment may further include an appropriate transparent layer. Examples of transparent layers may include barrier layers, adhesive layers, hard coat layers, anchor coat layers, and the like.
The image display light guide plate of the present embodiment may further include a glass base material.

The image display light guide plate includes an incident portion that makes image light incident, and a display image emitting portion that displays an image by the image light. The hologram layer is arranged between the incident portion and the display image emitting portion. The hologram layer is formed with a diffraction grating pattern for guiding at least the image light incident from the incident portion to the display image emitting portion and causing the image light to be emitted from the display image emitting portion. The diffraction grating pattern in the display image emitting portion transmits at least a part of external light incident from the outside of the image display light guide plate.
The image light incident from the incident portion is guided inside the hologram layer and emitted to the outside from the display image emitting portion. On the other hand, as a result of external light also passing through the resin base material and the display image emitting part, an observer of the display image emitting part can observe both the image light and the external light in the visual field.
The image display light guide plate of the present embodiment is preferably used for a display device using VR technology, AR technology, MR technology, and the like. For example, the image display light guide plate of the present embodiment is used for a display, as well as a hologram optical element (HOE) represented by a combiner of a head-up display (HUD) mounted on an automobile and a reflector of a reflective liquid crystal display device. ) Or the like.

The material of the resin base material is not particularly limited as long as it is a transparent material.
The material used for the resin substrate more preferably contains one or more resins selected from the group consisting of acrylic resins, cyclic polyolefin resins, and polycarbonate resins.

In the image display light guide plate of the present embodiment, two resin base materials may be provided with the hologram layer interposed therebetween. When the image display light guide plate includes a glass base material, a hologram layer may be disposed between the resin base material and the glass base material.
The resin base material and the hologram layer, or the glass base material and the hologram layer may be in contact with each other, or an appropriate transparent layer may be arranged between them.

The hologram layer is sandwiched between two resin base materials or between a resin base material and a glass base material.
A well-known hologram forming resin material is used for the hologram layer. For example, as an example of the hologram material, specifically, a hologram recording material composed of a thermosetting resin having at least one cationically polymerizable ethylene oxide ring in a structural unit and a radically polymerizable ethylenic monomer ( JP-A-8-1676, JP-A-8-1677, JP-A-8-1678, JP-A-8-1679) and the like can be mentioned.

The absorption layer has a wavelength characteristic of absorbing the yellow component in the light transmitted through at least a part of the image display light guide plate.
[Absorption peak]
The absorption layer has an absorption peak in a wavelength range of 500 nm to 600 nm (hereinafter, wavelength range A).
Here, the “absorption peak” is the minimum value in the U-shaped spectral distribution in which the transmittance changes from a decrease to a minimum value and then to an increase in the spectral transmittance curve of the absorption layer in the visible light range (400 nm to 800 nm). Refers to the spectral distribution that minimizes. It is more preferable that the U-shaped spectral distribution is formed at one location in the visible light range.
In the present specification, a wavelength having a minimum value (peak top) of such an "absorption peak" in a specific wavelength range is defined as "having an absorption peak in a specific wavelength range".
The absorption peak is more preferably in the wavelength range of 550 nm to 585 nm (hereinafter, wavelength range B).
The full width at half maximum of the absorption peak may be 100 nm or less, more preferably 70 nm or less, and particularly preferably 40 nm or less.
Here, the full width at half maximum of the absorption peak means the wavelength width of the absorption peak at which the transmittance is Th=(100−Tp)/2 or less when the transmittance at the peak top of the absorption peak is Tp(%). To do.
When the full width at half maximum is 100 nm or less, the color balance and brightness of transmitted light can be well secured.
The transmittance at the absorption peak may be 80% or less, more preferably 70% or less, and particularly preferably 60% or less.

[Transmittance characteristics]
The average transmittance of the absorption layer in the wavelength range of 590 nm to 700 nm (hereinafter, wavelength range C) may be 20% or more, more preferably 50% or more, and further preferably 70% or more.
The reason why the average transmittance is 20% or more in the wavelength range C is to maintain the brightness of red light.
The average transmittance of the absorption layer in the wavelength range of 470 nm or more and 550 nm or less (hereinafter, wavelength range D) may be 20% or more, more preferably 50% or more, and further preferably 70% or more.
The reason why the average transmittance is 20% or more in the wavelength range D is to ensure the color balance and brightness of the transmitted light.
Regarding the transmittance characteristics of the absorption layer, the lower the transmittance of ultraviolet light that is prone to photodegradation, the more preferable. For example, the transmittance of the absorption layer in the wavelength range of 380 nm or less may be 5% or less, more preferably 3% or less, and further preferably 1% or less.

[Yellowness]
The YI value (JIS K7373) representing the yellowness of the absorbing layer may be 10 or less, more preferably 5 or less, and particularly preferably 3 or less.

[Absorbance]
The absorbance of the absorption layer at a wavelength of 580 nm may be 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.

^{[L * a} * ^b * ^b in the color system *]
The b ^* of the absorption layer may be 5 or less, more preferably 3 or less, and particularly preferably 1 or less.

The structure of the absorption layer is not particularly limited as long as it has an absorption peak in the wavelength range A.
For example, the absorption layer may have a structure in which a coloring material is dispersed in a transparent base resin.
The material of the base resin is not particularly limited as long as it is transparent. The refractive index of the base resin is also not particularly limited.
For example, the base resin may have a refractive index equal to or higher than that of the resin base material, or may have a refractive index lower than that of the resin base material.
For example, as the base resin, a resin material having a surface hardness higher than that of the resin base material may be used.
For example, a resin material having low hygroscopicity may be used as the base resin.

The color material is not particularly limited as long as the wavelength characteristics described above are obtained. For example, as the coloring material, a dye, a pigment or the like is used. It is particularly preferable to use a bluing agent as the coloring material.
For example, the absorption layer may be formed by a multi-layer thin film in which a plurality of high refractive index materials and low refractive index materials are laminated.

[Bluing agent]
The bluing agent used in the absorbing layer is not particularly limited, but anthraquinone dye is generally easily available and more preferable.
As a specific bluing agent, for example, a common name Solvent Violet 13 [CA. No. (color index No.) 60725], common name Solvent Violet 31 [CA. No. 68210], common name Solvent Violet 33 [CA. No. 60725], common name Solvent Blue 94 [CA. No 61500], common name Solvent Violet 36 [CA. No. 68210], general name Solvent Blue 97 [“Macrolex Violet RR” manufactured by Bayer, Inc.], general name Solvent Blue 45 [CA. No. 61110] is a typical example. These bluing agents may be used alone or in combination of two or more. These bluing agents are added to the base resin in an appropriate amount so as to obtain the optical characteristics required for the absorbing layer. For example, when the base resin is a polycarbonate resin, the polycarbonate resin may be blended in a ratio of 0.1×10 ⁻⁵ parts by mass or more and 2×10 ⁻⁴ parts by weight or less with ^respect to 100 parts by mass.
Examples of other bluing agents include DIARESIN (registered trademark) Blue N (trade name; manufactured by Mitsubishi Chemical Corporation), DIARESIN (registered trademark) Blue G (trade name; manufactured by Mitsubishi Chemical Corporation), and Macrolex (registered trademark). Trademark) Blue RR (trade name; manufactured by Bayer), Macrolex (registered trademark) Blue 3R (trade name, manufactured by Bayer), Polycinthrene (registered trademark) Blue RLS (trade name, manufactured by Clariant), and the like.

The absorption layer is provided at least in a range where image light and external light are transmitted. For example, the absorption layer may be arranged in a range that overlaps the display image emitting portion of the hologram layer in the thickness direction.
However, the absorption layer may be arranged in a range that covers the entire resin base material or the hologram layer when viewed from the thickness direction.

The arrangement of the absorption layer in the thickness direction of the image display light guide plate is not particularly limited.
For example, the absorption layer may be provided at at least one of a position closer to the incident surface of external light than the hologram layer and a position closer to the exit surface of the image light than the hologram layer.
When the absorption layer is arranged outside the resin base material, the absorption layer, the resin base material, and the hologram layer may be arranged in this order in the thickness direction of the light guide plate for image display. That is, the absorption layer may be arranged outside the resin base material in the thickness direction. For example, the absorption layer may be arranged at the outermost part in the thickness direction of the image display light guide plate.
When the color material is dispersed inside the resin substrate to form the absorbing layer, the color material may be dispersed uniformly in the resin substrate, or may be dispersed unevenly in the thickness direction. When the color material is biased in the thickness direction, it is more preferable that the color material is biased outward in the thickness direction of the image display light guide plate.

The barrier layer is made of a transparent inorganic material. The refractive index of the barrier layer is more preferably 1.48 or more.
As a material for the barrier layer, a water vapor barrier material is more preferably used. The barrier layer more preferably contains one or more substances selected from the group consisting of silicon oxide, silicon nitrogen oxide, and diamond-like carbon (DLC).
The barrier layer may be arranged on the resin film. In this case, the resin film is more preferably arranged between the barrier layer and the resin base material.

The barrier layer is more preferably arranged in the order of the resin base material, the barrier layer, and the hologram layer in the thickness direction of the image display light guide plate. The barrier layer is particularly preferably arranged on the surface of the hologram layer.
The barrier layer may be provided in two layers with the hologram layer interposed therebetween. More preferably, the barrier layer is arranged on the front surface and the back surface of the hologram layer.
When the glass substrate is arranged, the glass substrate itself has a barrier property, and thus the glass substrate may be arranged on the surface of the hologram layer opposite to the surface facing the barrier layer.

Hereinafter, based on the example shown in FIG. 1, a detailed configuration of an example of the image display light guide plate of the present embodiment will be described. FIG. 1 is a schematic sectional view showing an example of an image display light guide plate according to an embodiment of the present invention.

In the image display light guide plate 5 shown in FIG. 1, the absorption layer 4, the resin base material 1, the hologram layer 2, and the resin base material 3 are arranged in this order in the thickness direction. The image display light guide plate 5 is an example in which the barrier layer is not included.
The plan view shape of the image display light guide plate 5 is not particularly limited. For example, the image display light guide plate 5 may be shaped into a shape that can be attached to a display device used.
For example, the image display light guide plate 5 may be a rectangular plate larger than the shape to be attached to the display device. In this case, the image display light guide plate 5 is shaped by being cut into a shape attachable to the display device before being assembled into the display device.
The image display light guide plate 5 may have a flat plate shape or a curved plate shape as necessary.
In the following, an example in which the image display light guide plate 5 is a flat plate having a rectangular shape in plan view will be described.

The absorption layer 4 is arranged on the outermost side in the thickness direction of the image display light guide plate 5. The absorption layer 4 is disposed on the surface of the image display light guide plate 5 on the display image emission side.
The layer thickness of the absorption layer 4 is not particularly limited. For example, the layer thickness of the absorption layer 4 may be 0.1 μm or more and 10 μm or less.
In the example shown in FIG. 1, the absorption layer 4 is formed on the entire surface of the resin base material 1 described later.
The method for forming the absorption layer 4 is not particularly limited. For example, the absorption layer 4 can be formed by applying a coating liquid made of a base resin material mixed with a coloring material to the film formation surface (the surface of the resin substrate 1) and then curing the coating liquid.
As the coating method of the coating liquid, an appropriate coating method can be selected depending on the viscosity of the coating liquid, for example, as the coating method, bar coating, dip coating, reverse gravure coating, direct gravure coating, roll coating, die coating, Conventionally known coating methods such as curtain coating can be used.
As the base resin material, for example, a (meth)acrylate monomer having a radically polymerizable unsaturated group in the molecule, or a (meth)acrylate oligomer having a radically polymerizable unsaturated group in the molecule is irradiated with an active energy ray. A polymerizable monomer or polymerizable oligomer that forms a cured product, or a curable resin material such as urethane, epoxy, or polyester may be used. As the coloring material to be mixed with the base resin material, for example, the above-mentioned bluing agent may be used.

The resin base material 1 has a shape similar to the outer shape of the image display light guide plate 5.
Image light Ld emitted from the hologram layer 2 and external light Lo that passes through the resin substrate 3 and the hologram layer 2 described later are transmitted to the resin substrate 1.
The thickness of the resin base material 1 is not particularly limited. For example, the thickness of the resin substrate 1 may be 0.01 mm or more and 10 mm or less.

The material forming the resin substrate 1 is not particularly limited as long as it is a transparent resin material. For example, polyolefin resins such as homopolymers or copolymer pairs of ethylene, propylene, butene; amorphous polyolefin resins such as cyclic polyolefins; polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); Polyamide resins such as nylon 6, nylon 66, nylon 12, copolymer nylon; ethylene-vinyl acetate copolymer partial hydrolyzate (EVOH), polyimide resin, polyetherimide resin, polysulfone resin, polyether sulfone Phone resin, polyether ether ketone resin, polycarbonate resin, polyvinyl butyral resin, polyarylate resin, fluororesin, poly(meth)acrylic resin, styrene resin such as polystyrene, polyvinyl alcohol, ethylene vinyl alcohol copolymer Coalesce, polyvinyl chloride, cellulose, acetyl cellulose, polyvinylidene chloride, polyphenylene sulfide, polyurethane, phenol resin, epoxy resin, polyarylate resin, polynorbornene, styrene-isobutylene-styrene block copolymer (SIBS), allyl diglycol carbonate , And organic materials such as biodegradable resins. The resin substrate 1 may be formed of two or more kinds of materials, or may have a laminated structure in which two or more kinds of materials are laminated.
From the viewpoint of transparency, it is more preferable to use polycarbonate, poly(meth)acrylic resin, or the like. From the viewpoint of process resistance, it is more preferable to use poly(meth)acrylic resin, epoxy resin, cyclic polyolefin, or the like.

The hologram layer 2 is laminated on the surface opposite to the surface of the resin substrate 1 on which the absorption layer 4 is formed. The structure of the hologram layer 2 is not particularly limited. The hologram layer 2 is formed with an appropriate diffraction grating corresponding to the function required for the image display light guide plate 5.

The resin base material 3 is laminated on the surface of the hologram layer 2 opposite to the surface on which the resin base material 1 is arranged. As the resin base material 3, the same structure as that illustrated in the description of the resin base material 1 is used. However, the thickness, material, etc. of the resin base material 3 may be different from that of the resin base material 1. In particular, since the resin base material 3 is disposed on the surface of the image display light guide plate 5 on the outside light incident side which is located opposite to the display image emission side, a material having a higher surface hardness than the resin base material 1 is used. You may be asked.

Such an image display light guide plate 5 can be manufactured, for example, as follows.
The resin base materials 1 and 3 are prepared, and the coating liquid that forms the absorption layer 4 is prepared.
For example, the coating liquid is applied to the surface of the resin base material 1. Then, the coating liquid is cured to form the absorbing layer 4.
For example, a photopolymer material for hologram formation is applied to the surface of the resin substrate 1 opposite to the surface on which the absorption layer 4 is formed. At this time, a transparent seal layer having the same thickness as the hologram layer 2 may be provided on the outer peripheral portion of the surface of the resin substrate 1. In this case, the photopolymer material is applied to the recess formed surrounded by the sealing layer. The seal layer seals the outer peripheral portion of the hologram layer 2 after the hologram layer 2 is formed. Then, the resin base material 3 is placed on the photopolymer material.
However, the above manufacturing sequence is an example. For example, the photopolymer material may be applied to the surface of the resin base material 3, and the resin base material 1 on which the absorption layer 4 is formed may be placed on the photopolymer material.
After that, the laminated body including the absorption layer 4, the resin base material 1, the photopolymer material, and the resin base material 3 is attached by a vacuum press.
Thereafter, interference fringes corresponding to the diffraction pattern are formed on the photopolymer material of the laminated body, and a diffraction grating is formed in the photopolymer material.
In this way, the image display light guide plate 5 is manufactured.

Next, an example of a display device including the image display light guide plate 5 will be described.
FIG. 2 is a schematic sectional view showing an example of a display device including the image display light guide plate according to the embodiment of the present invention.

As shown in FIG. 2, the display device 10 includes an image light projection unit 12 and an incident optical system 11 in addition to the image display light guide plate 5.
The image light projection unit 12 projects the image light Li to be displayed on the image display light guide plate 5 in accordance with an image signal sent from a controller (not shown).
The incident optical system 11 includes an optical element such as a prism that causes the image light Li to enter the image display light guide plate 5. The incident optical system 11 causes the image light Li to be incident on the incident portion 5a formed on the surface of the image display light guide plate 5. For example, the incident portion 5a is provided on the absorption layer 4.
The image light Li incident on the incident part 5 a is guided to the display diffraction grating part 2 b of the hologram layer 2 via the guided diffraction grating part 3 a formed on the hologram layer 2. In the display diffraction grating portion 2b, the image light Li is diffracted at the position corresponding to each display pixel to form the image light Ld. The image light Ld passes through the hologram layer 2, the resin base material 1, and the absorption layer 4, and is emitted to the outside of the image display light guide plate 5 as the image light Ld′. Therefore, the display diffraction grating portion 2b in the thickness direction, and the region of the resin base material 1 and the absorption layer 4 facing the display diffraction grating portion 2b in the thickness direction have the display image emitting portion 5b for displaying the image light Ld. I am configuring. The display image emitting portion 5b is formed at a position apart from the incident portion 5a in the surface direction that is a direction orthogonal to the thickness direction.

On the other hand, external light Lo is incident on the image display light guide plate 5 via the resin base material 3. The external light Lo is transmitted through the resin base material 3, the hologram layer 2, the resin base material 1, and the absorption layer 4, and is emitted to the outside of the image display light guide plate 5 as external light Lo′.
The user of the display device 10 can see an image by the image light Ld′ and the external light Lo′. Therefore, the user who puts the display image emitting unit 5b in the field of view sees an image in which the external scene based on the external light Lo′ and the image based on the image light Ld′ are superimposed.

The transparent material used for the image display light guide plate 5 is photo-degraded over time due to the influence of, for example, ultraviolet light. A typical photodegradation is yellowing of the material. In particular, since the hologram layer 2 is made of a photopolymer material, it has turned yellow to some extent immediately after its production. Therefore, the light transmitted through the resin base materials 1 and 3 and the hologram layer 2 has a yellowish tint.
Since yellow has a high relative luminous sensitivity, human vision is sensitive to yellowing. As a result, the yellowish image has a low contrast (brightness), and the observed image becomes unclear.
However, in the present embodiment, since the absorption layer 4 is provided in the display image emitting unit 5b, the yellow components of the image light Ld and the external light Lo are reduced in the image light Ld′ and the external light Lo′, respectively. As described above, the absorption layer 4 cancels out the yellow component of the yellowish image light Ld and the external light Lo, thereby eliminating the influence of yellowing of the resin base materials 1 and 3 and the hologram layer 2. It
Specifically, the absorption layer 4 absorbs light centering on the light component in the wavelength range of 500 nm to 600 nm, whereby the yellow tint decreases and the blue tint relatively increases. This improves the white balance and contrast of the image.
Further, even if the photodegradation of the transparent material such as the resin base materials 1 and 3 progresses with time due to the ultraviolet light exposed when the display device 10 is used, the degree of image deterioration due to yellowing does not have the absorption layer 4. It is reduced compared to the case.

As described above, according to this embodiment, it is possible to provide the image display light guide plate that can reduce the influence of the yellowing of the transparent material on the display image.

Particularly in the present embodiment, the absorption layer 4 is arranged at the outermost part of the image display light guide plate 5. Therefore, for example, when a material having a hardness higher than that of the resin base material 1 is used for the absorption layer 4, scratches on the surface of the resin base material 1 are prevented. For example, when the transmittance of ultraviolet light is low in the wavelength characteristics of the absorption layer 4, it is possible to suppress the incidence of ultraviolet light from the resin base material 1 side, and thus it is possible to reduce the time-dependent photodegradation of the image display light guide plate 5.

[First Modification]
The image display light guide plate of the first modified example of the present embodiment will be described.
FIG. 3 is a schematic cross-sectional view showing an example of the image display light guide plate of the first modified example of the embodiment of the present invention.

As shown in FIG. 3, the image display light guide plate 7 of the present modification example further includes an absorption layer 6 in the image display light guide plate 5 of the embodiment.
The differences from the above embodiment will be mainly described below.

The absorption layer 6 is laminated on the surface of the resin substrate 3 opposite to the surface on which the hologram layer 2 is arranged. That is, like the absorption layer 4, the absorption layer 6 is arranged at the outermost part of the image display light guide plate 7. In the image display light guide plate 7, a laminated body including the resin base material 1, the hologram layer 2, and the resin base material 3 is sandwiched between the absorption layers 4 and 6.
As the absorption layer 6, the same structure as that illustrated in the description of the absorption layer 4 is used.
However, the thickness, material and the like of the absorption layer 6 may be different from those of the absorption layer 4. For example, since the absorption layer 6 is disposed on the surface of the image display light guide plate 7 opposite to the display image emitting side, even if a material having a higher surface hardness than the resin base material 3 or the absorption layer 4 is used. Good.
In this modification, since the absorption layers 4 and 6 are arranged at the outermost part of the image display light guide plate 7, it is more preferable that the absorption layers 4 and 6 have a low ultraviolet transmittance in the wavelength characteristics.

The image display light guide plate 7 is manufactured in the same manner as the image display light guide plate 5 in the embodiment, except that the absorption layer 6 is formed on the resin base material 3. As the forming method of the absorbing layer 6, the same forming method as that of the absorbing layer 4 is used.

The image display light guide plate 7 according to the present modification is configured similarly to the image display light guide plate 5 except that the image display light guide plate 7 has the absorption layer 6. Therefore, the image light Ld is reduced in yellow component by passing through the absorption layer 4 in the same manner as the image display light guide plate 5 (image light Ld′).
On the other hand, the external light Lo is further transmitted through the absorption layer 6 and then enters the resin base material 3. Therefore, the outside light Lo has a reduced yellow component when passing through the absorption layer 6. When the outside light Lo passes through the resin base material 3, the hologram layer 2, and the resin base material 1, the yellow component is increased according to the degree of yellowing of each, and then the yellow component is reduced by the absorption layer 4. ..
Since the resin base material 3 is disposed on the incident side of the external light Lo when in use, photodegradation due to the external light Lo is likely to proceed. As a result, the yellowing of the resin base material 3 may be more likely to proceed than the yellowing of the resin base material 1 over time. As the yellowing of the resin base material 3 progresses, the external light Lo that has passed through the resin base material 3 may have a stronger yellow component than the image light Ld that does not pass through the resin base material 3.
However, in this modified example, since the absorbent layer 6 is provided, it is possible to offset the increase in yellowness due to the yellowing of the resin base material 3 by the absorbent layer 6. Therefore, the yellowness of the external light Lo″ emitted from the absorption layer 4 is reduced as compared with the external light Lo′ emitted from the image display light guide plate 5. As a result, it is possible to improve the balance of the yellowishness of each of the image light Ld′ and the outside light Lo″.
In particular, when the transmittance of ultraviolet light is low in the wavelength characteristics of the absorption layer 6, the photodegradation itself of the resin base material 3 due to the external light Lo can be reduced.

As described above, according to this modification, it is possible to provide the image display light guide plate that can reduce the influence of the yellowing of the transparent material on the display image.

[Second Modification]
A light guide plate for image display of a second modified example of the present embodiment will be described.
FIG. 4 is a schematic cross-sectional view showing an example of the image display light guide plate of the second modified example of the embodiment of the present invention.

As shown in FIG. 4, the image display light guide plate 20 of the present modification example further includes barrier layers 8 and 9 in the image display light guide plate 7 of the first modification example.
Hereinafter, the points different from the first modified example will be mainly described.

The barrier layer 8 is arranged between the resin base material 1 and the hologram layer 2, and is in close contact with the respective surfaces of the resin base material 1 and the hologram layer 2. The barrier layer 8 prevents the gas that permeates from the outside of the image display light guide plate 20 and the resin substrate 1 from permeating the hologram layer 2.
A transparent inorganic material is used as the material of the barrier layer 8. The type of inorganic material used for the barrier layer 8 is not particularly limited as long as it can barrier the gas that causes deterioration of the hologram layer 2.
For example, the barrier layer 8 is more preferable as the oxygen permeability and the water vapor permeability are smaller. In particular, the barrier layer 8 is more preferably made of a material having excellent water vapor barrier properties (small water vapor permeability).
For example, the oxygen permeability of the barrier layer 8 may be 1 cm ³ /m ² ·day or less.
For example, the water vapor transmission rate of the barrier layer 8 may be 1 g/m ² ·day or less. The water vapor permeability of the barrier layer 8 is more preferably 0.5 g/m ² ·day or less.

The inorganic material used for the barrier layer 8 may have a higher refractive index than the resin base material 1. For example, the refractive index of the barrier layer 8 may be 1.48 or more and 3.0 or less. When the barrier layer 8 has a high refractive index, light transmitted through the resin substrate 1 via the barrier layer 8 enters the optically dense resin substrate 1 from the optically dense barrier layer 8. The emission angle of light from the barrier layer 8 toward the resin base material 1 increases in accordance with the difference in refractive index between the barrier layer 8 and the resin base material 1. Thereby, the FOV (field of view) in the image display light guide plate 20 can be expanded.

Examples of the material of the barrier layer 8 include silicon oxide, silicon nitrogen oxide, DLC, and aluminum oxide. For example, the material of the barrier layer 8 is zinc oxide, antimony oxide, indium oxide, cerium oxide, calcium oxide, cadmium oxide, silver oxide, gold oxide, chromium oxide, silicon oxide, cobalt oxide, zirconium oxide, tin oxide, titanium oxide. An oxide such as iron oxide, copper oxide, nickel oxide, platinum oxide, palladium oxide, bismuth oxide, magnesium oxide, manganese oxide, molybdenum oxide, vanadium oxide or barium oxide may be used.

When the barrier layer 8 is made of silicon oxide, the layer thickness may be 10 nm or more and 300 nm or less. If the layer thickness is less than 10 nm, the moisture resistance may be insufficient. When the layer thickness exceeds 300 nm, the silicon oxide thin film is likely to be cracked and may be peeled off from the film formation surface.
A particularly preferable layer thickness is 20 nm or more and 200 nm or less.
The method of forming the barrier layer 8 with silicon oxide is not particularly limited. For example, the barrier layer 8 can be formed by any conventionally known method such as a vacuum vapor deposition method, a sputtering method, an ion plating method, and a plasma CVD method. When forming the barrier layer 8 with silicon oxide, in order to improve the adhesion between the film-forming surface and the silicon oxide, the film-forming surface is subjected to corona discharge treatment, low-temperature plasma treatment, or a silane coupling agent. Alternatively, a surface treatment such as coating a mixture of saturated polyester and isocyanate may be performed.
For example, when a silicon oxide thin film is formed by a vacuum evaporation method, silicon, silicon monoxide, silicon dioxide, or a mixture thereof is used as an evaporation substance, and 1.0×10 ⁻³ Torr to 1.0 is used. It is heated and evaporated by electron beam, resistance heating, or high-frequency heating under a vacuum of ×10 ^-5 Torr.
Further, a reactive vapor deposition method performed while supplying oxygen gas can also be adopted.
If the silicon oxide forming the barrier layer 8 is 10% by mass or less, calcium, magnesium or an oxide thereof may be mixed therein as an impurity.

When barrier layer 8 is made of silicon nitrogen oxide, the same structure as barrier layer 8 containing silicon oxide as a main component is used, except that silicon oxide is replaced by silicon nitrogen oxide.

DLC is an amorphous carbon material having a ternary structure, which is generally a diamond-like structure, a graphite-like structure, and a polyethylene-like polymer structure containing hydrogen atoms in its structure. When a hydrocarbon such as ethylene, acetylene, or benzene is used as a carbon source for DLC formation, a basically ternary structure containing hydrogen is usually formed.
DLC is excellent in hardness, lubricity, wear resistance, chemical stability, heat resistance, surface smoothness and the like. Since DLC forms the dense polymer structure described above, it is also excellent in gas barrier properties and water vapor barrier properties.
The method of forming the barrier layer 8 by DLC is not particularly limited. As the DLC coating method, a well-known appropriate coating method such as a plasma CVD method, an ion plating method, a physical vapor deposition method such as an ion beam sputtering method, or the like can be used.

When the barrier layer 8 is made of aluminum oxide, the barrier layer 8 may be formed of, for example, Al ₂ O ₃ alone, or may be formed by mixing Al, AlO, Al ₂ O _{3, and the} like. The atomic ratio of Al:O in the aluminum oxide layer varies depending on the manufacturing conditions of the aluminum oxide layer. The aluminum oxide layer that can be used as the barrier layer 8 may contain a small amount of other components (up to 3% with respect to all the components) as long as the barrier performance is not impaired.
The layer thickness of the aluminum oxide layer may be set according to the need for barrier performance. For example, the layer thickness of the aluminum oxide layer may be 5 nm or more and 800 nm or less.
The method of forming the barrier layer 8 with aluminum oxide is not particularly limited. For example, the barrier layer 8 may be formed by a PVD method (physical vapor deposition method) such as a vacuum vapor deposition method, a sputtering method, an ion plating method, or a CVD method (chemical vapor deposition method).
For example, in the vacuum vapor deposition method, Al, Al ₂ O ₃ or the like may be used as a vapor deposition source material, and resistance heating, high frequency induction heating, electron beam heating or the like may be used as a heating method of the vapor deposition source. .. In the vacuum vapor deposition method, oxygen, nitrogen, water vapor or the like may be introduced as the reactive gas, or reactive vapor deposition using means such as ozone addition or ion assist may be used. Furthermore, a bias may be applied to the substrate on the film forming surface, the temperature of the film forming surface may be raised, or the substrate may be cooled. The same applies to other film forming methods such as the sputter method and the CVD method.

The barrier layer 9 is laminated on the surface of the hologram layer 2 opposite to the surface of the hologram layer 2 on which the barrier layer 8 is formed.
As the configuration of the barrier layer 9, the same configuration as that exemplified in the description of the barrier layer 8 is used. However, the material and thickness of the barrier layer 9 may be different from that of the barrier layer 8.

Such an image display light guide plate 20 can be manufactured, for example, as follows.
Resin base materials 1 and 3 are prepared, and barrier layers 8 and 9 are formed on the surfaces of the resin base materials 1 and 3, respectively. As a method of manufacturing the barrier layers 8 and 9, an appropriate manufacturing method is selected according to the material of the barrier layers 8 and 9.
For example, a hologram-forming photopolymer material is applied to the surface of the barrier layer 8 in the resin substrate 1 on which the barrier layer 8 is formed. At this time, a transparent seal layer having the same thickness as the hologram layer 2 may be provided on the outer peripheral portion of the barrier layer 8. In this case, the photopolymer material is applied to the recess formed surrounded by the sealing layer. The seal layer seals the outer peripheral portion of the hologram layer 2 after the hologram layer 2 is formed.
Thereafter, the resin base material 3 having the barrier layer 9 formed thereon is placed on the photopolymer material with the barrier layer 9 facing the photopolymer material.
However, the above manufacturing sequence is an example. For example, the resin base material 3 on which the barrier layer 8 is formed may be applied to the resin base material 3 on which the barrier layer 9 is formed, and then the resin base material 1 on which the barrier layer 8 is formed may be placed on the photopolymer material.
After that, a laminated body including the absorption layer 4, the resin base material 1, the barrier layer 8, the photopolymer material, the barrier layer 9, the resin base material 3, and the absorption layer 6 is attached by depressurizing press.
Thereafter, interference fringes corresponding to the diffraction pattern are formed on the photopolymer material of the laminated body, and a diffraction grating is formed in the photopolymer material.
In this way, the image display light guide plate 20 is manufactured.

The image display light guide plate 20 is configured similarly to the image display light guide plate 7 of the first modification, except that the barrier layers 8 and 9 are added.
Although the barrier layers 8 and 9 are made of a transparent inorganic material such as DLC or silicon oxide, they easily absorb blue light in the wavelength range of 400 nm to 480 nm, and as a result, the transmittance of the blue component decreases, resulting in the transmitted light. Becomes yellowish.
As described above, the barrier layer 8 easily increases the yellowness of the outside light Lo and the image light Ld, and the barrier layer 9 easily increases the yellowness of the outside light Lo. However, in this modified example, as in the first modified example, since the absorption layers 4 and 6 are provided, the increase in yellowness due to the barrier layers 8 and 9 is offset by appropriately adjusting the wavelength characteristics of the absorption layers 4 and 6. can do. That is, the yellowness of the external light Lo′″ and the image light Ld″ emitted from the absorption layer 4 can be reduced. Further, similarly to the first modification, it is possible to improve the balance of the yellowness of the outside light Lo′″ and the image light Ld″.

As described above, according to this modification, it is possible to provide the image display light guide plate that can reduce the influence of the yellowing of the transparent material on the display image.

Further, according to the image display light guide plate 20, since the barrier layers 8 and 9 are provided, deterioration of the hologram layer 2 with time can be suppressed.

Although the gas barrier properties of the resin base materials 1 and 3 differ to some extent depending on the type of resin material, they are significantly lower than those of glass. Therefore, the resin base materials 1 and 3 have higher hygroscopicity and water vapor permeability than glass.
As a result, the gas outside the image display light guide plate 5 permeates the resin base materials 1 and 3 to some extent or accumulates inside. In particular, water is likely to accumulate on the resin base materials 1 and 3.
However, the gas and water that have permeated the resin substrates 1 and 3 from the outside are shielded by the barrier layers 8 and 9 even if they diffuse in the image display light guide plate 20. This suppresses the permeation of gas and water vapor into the hologram layer 2.
For example, deterioration of the hologram layer 2 is prevented by suppressing the permeation of water into the hologram layer 2.
Furthermore, since the image display light guide plate 20 has the above-mentioned layer structure, the hologram layer 2 is not in contact with the resin base materials 1 and 3. This prevents the hologram layer 2 from eroding the resin base materials 1 and 3 even if the image display light guide plate 20 is placed in a high temperature environment.

In particular, if the refractive index of the barrier layers 8 and 9 is higher than that of the resin base materials 1 and 3, as described above, the emission angle of light from the barrier layer 8 toward the resin base material 1 becomes large. .. Similarly, the light entering the barrier layer 9 from the resin base material 3 has a narrowed emission angle. Therefore, the light that enters from the outside on the resin base material 3 side and that passes through the image display light guide plate 5 has a wider range of light than that in the case where the barrier layer 9 is not provided, and the barrier layer 8 is emitted in a wider angle range as compared with the case where 8 is not provided. As a result, the range of the visual field of the external light is expanded and the FOV on the display side is expanded.
As for the image light from the hologram layer 2, as described above, the emission angle of the light from the barrier layer 8 toward the resin base material 1 becomes large, so that the FOV of the display screen is higher than that in the case where the barrier layer 8 is not provided. spread.
Particularly, in the present embodiment, the barrier layers 8 and 9 are laminated on the hologram layer 2, so that the diffusion position of the external light and the image light and the diffraction position of the hologram layer 2 forming the display screen are close to each other. Therefore, as compared with the case where the barrier layers 8 and 9 are provided at positions apart from the hologram layer 2, a clearer image can be observed from a wide range of angles.

Here, a method of measuring the brightness value and the FOV in the image display light guide plate 20 will be briefly described.
For the brightness value in the image display light guide plate 20, a display device similar to the display device 10 in the above-described embodiment and a luminance meter are used except that the image display light guide plate 5 is replaced with the image display light guide plate 20. Is measured.
In the measurement of the brightness value, the display device is arranged at a position where the center of the display image emitting portion of the image display light guide plate 20 faces the brightness meter on the measurement optical axis of the brightness meter. The distance between the display image emitting unit and the luminance meter is the distance corresponding to the position of the eyes of the user when the display device is worn. For example, when the display device is a head mounted display, the distance is 15 mm.
The brightness value is the brightness measured by a brightness meter when a white image with the maximum brightness is displayed on the display device.

In the measurement of the FOV of the light guide plate 20 for image display, the luminance is measured by tilting the measurement optical axis of the luminance meter with respect to the display image emitting portion in a state where the white image with the maximum luminance is displayed on the display device. For example, the luminance meter is supported by a gonio stage or the like so as to be swingable so as to be inclined at an appropriate angle from a position vertical to the image display light guide plate 20.
The FOV is obtained as an angular range in which the brightness corresponding to the disappearance of the white image is set as a threshold and the brightness equal to or higher than the threshold is obtained. When the brightness equal to or higher than the threshold value is obtained in the range of −θ1 to +θ2, the FOV is θ1+θ2. Here, regarding the angle, the normal angle of the image display light guide plate 20 is 0°.

[Third Modification]
An image display light guide plate of a third modification of the present embodiment will be described.
FIG. 5 is a schematic cross-sectional view showing an example of a light guide plate for image display of a third modified example of the embodiment of the present invention.

As shown in FIG. 5, in the image display light guide plate 24 of the present modification, the absorption layer 4 of the image display light guide plate 5 of the embodiment is deleted, and instead of the resin base materials 1 and 3, the resin base material 21. , 23 (absorption layer).
The differences from the above embodiment will be mainly described below.

The resin base material 21 includes a base resin similar to the resin base material 1 and a color material dispersed in the base resin.
As the coloring material contained in the resin base material 21, the same coloring material as the absorbing layer 4 in the embodiment is used. The blending amount of the color material is set so that the resin base material 21 has the same light absorbing property as the absorbing layer 4 in the embodiment.
The resin base material 23 is configured similarly to the resin base material 21.

In the image display light guide plate 24, the resin base materials 21 and 23 prepared in the base material preparation step are molded using a material in which a coloring material is kneaded into each base resin, and the absorption layer forming step is performed. Except not being omitted, it is manufactured in the same manner as the image display light guide plate 5 in the embodiment.

The image display light guide plate 24 is an example in which the absorption layer is formed of the resin base materials 21 and 23.
According to the image display light guide plate 24, since the resin base materials 21 and 23 are the absorption layers, it is possible to reduce the yellow tint in the external light and the image light as in the first modification.

As described above, according to this modification, it is possible to provide the image display light guide plate that can reduce the influence of the yellowing of the transparent material on the display image.

In addition, in the said embodiment and each modified example, the case where the absorption layer was arrange|positioned at the outermost part of the image display light-guide plate was demonstrated. However, the absorption layer can reduce the yellow tint of the light emitted from the image display light guide plate, wherever it is arranged, on the optical paths of the external light Lo and the image light Ld.

In the above-mentioned embodiment and each modification, the example in which the absorption layer is in contact with the resin base material has been described. However, the absorption layer may be laminated on a transparent resin film. In this case, for example, since the absorbent layer can be formed on the resin film and then fixed to the arrangement surface via an adhesive or the like, the absorbent layer can be easily formed.

In the second modified example, an example in which the barrier layers are arranged on the front and back surfaces of the hologram layer has been described. However, the barrier layer may be disposed between the resin base material and the hologram layer for the purpose of blocking moisture or the like penetrating through the resin base material and for preventing the contact between the hologram layer and the resin base material. ..
However, in this case, if the hygroscopicity of the transparent layer sandwiched between the barrier layer and the hologram layer is high, water may penetrate through the side surface of the transparent layer. Therefore, it is more preferable that the transparent layer between the barrier layer and the hologram layer is made of a material having a low hygroscopic property. When the transparent layer between the barrier layer and the hologram layer has hygroscopicity, the thickness of the transparent layer is more preferably reduced. In this case, the exposed surface area of the side surface serving as a water permeation port is reduced, so that the amount of moisture absorbed can be reduced.

In the second modified example, the example in which the barrier layer is in contact with the hologram layer and the resin base material has been described. However, the barrier layer may be laminated on the transparent resin film. In this case, for example, since the barrier layer can be formed on the resin film and then fixed to the resin base material with an adhesive or the like, the barrier layer can be easily formed.

Hereinafter, Examples 1 and 2 of the embodiment will be described together with Comparative Example 1. The present invention is not limited to these examples.

The following [Table 1] shows the configurations of the resin substrate and the absorption layer used in each of the examples and comparative examples, and the evaluation results.

[Example 1]
Example 1 is an example corresponding to the image display light guide plate 5 of the embodiment.
As shown in [Table 1], an acrylic resin (PMMA) is used as a material for the resin base materials 1 and 3 (“resin base material” in [Table 1]).
The resin substrates 1 and 3 each have a rectangular plate shape of 60 mm×60 mm×1 mm.
The hologram layer 2 is common to each example and each comparative example. As the material of the hologram layer 2, 100 parts by weight of bisphenol epoxy resin jER (registered trademark) 1007 (degree of polymerization n=10.8, epoxy equivalent: 1750-2200, trade name of Mitsubishi Chemical), triethylene glycol diacrylate 50 Parts by weight and 4,4'-bis(tert-butylphenyl)iodonium hexafluorophosphate 5 parts by weight, 3,3'-carbonylbis(7-diethylamino)coumarin 0.5 parts by weight to 2-butanone 100 parts by weight. It is mixed and dissolved and used as a photosensitive material for hologram. The hologram layer 2 has a thickness of 5 μm. The size of the hologram layer 2 in plan view is 50 mm×50 mm.

Next, a manufacturing process of the image display light guide plate 5 according to the first embodiment will be described. The image display light guide plate 5 is manufactured by performing a substrate preparation step, an absorption layer formation step, and a light guide plate production step, which will be described below, in this order.

[Substrate preparation process]
In the substrate preparation step, the resin base materials 1 and 3 are washed and dried. Hereinafter, when it is not necessary to distinguish between the resin base materials 1 and 3, the reference numerals will be omitted and simply referred to as the resin base material.
The resin base material is ultrasonically cleaned for 5 minutes while being immersed in a 5% surfactant aqueous solution of Semi Clean (registered trademark) M-LO (trade name; manufactured by Yokohama Yushi Kogyo Co., Ltd.) which is a neutral cleaning agent. It
Then, the resin base material is ultrasonically cleaned for 5 minutes while being immersed in ultrapure water. Further, the resin base material is rinsed with ultrapure water, and the resin base material is air dried and then dried in an oven at 100° C. under a nitrogen atmosphere. Thereafter, the air-dried evaluation sample B is cleaned with UV ozone in a UV ozone cleaner for 1 minute.
This is the end of the substrate preparation process.

[Absorption layer forming step]
In the absorption layer forming step, the absorption layer 4 (“absorption layer” in [Table 1]) is formed on the surface of the resin substrate 1.
To 100 parts by mass of acrylate (UPIMER (registered trademark) UV-HH2100 (trade name; manufactured by Mitsubishi Chemical Co., Ltd.)), 5 parts by mass of a photopolymerization initiator was added, and as a coloring material, Diarene (registered trademark) blue was added. A curable resin composition (coating liquid) is prepared by adding 0.05 part by mass.
This curable resin composition was applied onto the resin substrate 1 using a metal bar coater, dried at 90° C. for 1 minute, and then exposed to an exposure amount of 500 mJ/cm ² using an ultraviolet light irradiation device, A laminate having an absorption layer with a thickness of 5 μm is obtained.
This is the end of the absorbing layer forming step.
Below, the resin base material in which the absorption layer was formed is called an intermediate laminated body.

[Light guide plate manufacturing process]
In the light guide plate manufacturing step, the image display light guide plate 5 is manufactured using the intermediate laminate and the resin base material 3.
A seal layer having a width of 5 mm and a thickness of 5 μm is applied to the peripheral portion of the surface of the intermediate laminate opposite to the absorption layer.
The sealing layer is made of a transparent material and is not particularly limited as long as it is a material capable of adhering resin base materials to each other, but in Example 1, a photo-adhesive hard lock (registered trademark) OP-1045K (trade name; electrochemical) Industrial Co., Ltd.) is used.
As a result, an intermediate layered product with a seal layer step is prepared in which the opening surrounded by the seal layer has a size of 50 mm×50 mm.
Then, the photosensitive material as a hologram photopolymer material is applied onto the intermediate laminate by spin coating. The above light-sensitive material is applied so as to have a thickness of 5 μm after drying.
After that, the resin base material 3 is laminated on the seal layer and the above-mentioned photosensitive material so as to face the barrier layer of the intermediate laminate with the seal layer, and press-bonded under reduced pressure. The conditions for press bonding are an absolute pressure of 5 kPa, a temperature of 70° C., and a press pressure of 0.04 MPa.
After that, a diffraction grating is recorded on the above-mentioned light-sensitive material of the press-bonded laminate. In this step, the temperature of the laminated body is kept at 20°C. The diffraction grating forms interference fringes so that a necessary diffraction pattern is formed by irradiating the laminated body with two laser beams and adjusting the irradiation angles and intensities of the two laser beams. As a result, a diffraction grating is recorded on the photosensitive material.
As a specific diffraction grating, each light in the wavelength region of red, green, and blue that is incident as image light incident on the incident portion is diffracted and is emitted from the display portion at a position corresponding to a pixel of the image light. A diffraction grating for color display is formed.
Thereafter, with the laminated body kept at 20° C., ultraviolet light (wavelength 365, irradiance 80 W/cm ² ) is entirely irradiated for 30 seconds from the direction of one side of the laminated body. A high pressure mercury lamp is used as a light source of ultraviolet light.
As a result, the seal layer is cured, and the image display light guide plate 5 of Example 1 is formed.

[Example 2]
Example 2 is an example corresponding to the image display light guide plate 7 of the first modification.
As shown in [Table 1], in Example 2, the absorption layers were provided on both surfaces. Specifically, the absorption layer 6 is formed on the surface of the resin substrate 3 opposite to the hologram layer 2.
In this embodiment, the absorption layer 6 (“absorption layer” in [Table 1]) is configured in the same manner as the absorption layer 4 of the first embodiment.
Therefore, the substrate preparing process of the second embodiment is the same as that of the first embodiment.
The absorbent layer forming process of Example 2 is different from Example 1 in that, in addition to the intermediate laminate having the absorbent layer 4, an intermediate laminate made of the resin base material 3 having the absorbent layer 6 formed thereon is formed. ..
The light guide plate manufacturing process of Example 2 is different from Example 1 in that two intermediate laminated bodies are used.

[Comparative Example 1]
As shown in [Table 1] and FIG. 5, the image display light guide plate 100 of Comparative Example 1 is configured by laminating the resin base material 1, the hologram layer 2, and the resin base material 3 in this order. That is, the structure is the same as that of the first embodiment except that the absorption layer is not provided.
The image display light guide plate 100 of Comparative Example 1 is manufactured in the same manner as in Example 1 except that the absorption layer forming step is not performed.

Next, the evaluation method of each example and comparative example will be described. As the evaluation, sharpness evaluation is performed.

[Clearness evaluation]
The sharpness of the displayed image is achieved by using each display device using each image display light guide plate. Each display device is configured similarly to the display device 10, except that the image display light guide plate of each of the examples and comparative examples is used.
As the image used for evaluation, a display image by the image light diffracted by the hologram layer and an external light image through which external light is transmitted are used.
A white image and a character image are used as the input image of the display image.
As the outside light image, a landscape of a room, a town, or a forest 0.5 m to 50 m away from the display device is used. In the evaluation of the external light image, a white image or a character image is displayed and evaluated.
The evaluation is performed by visually determining the appearance of the white image and the character image and the appearance of the external light image. As the character image, hiragana, katakana, kanji, Arabic numerals or alphabets having a size of 0.1 to 2.0 converted into visual acuity are displayed as the size.

[Criteria for display image sharpness evaluation]
The sharpness evaluation of the display image is performed in three stages.
When the rainbow color is not visible in the white image and the character is clearly visible in the character image, it is determined to be good (good, described as “◯” in [Table 1]).
When the rainbow color is slightly visible in the white image but the character is clearly visible in the character image, it is determined to be acceptable (fair, described as “Δ” in [Table 1]).
When at least a part of the rainbow color appears in the white image and the outline of the character appears blurred in the character image, it is determined to be impossible (no good, described as “x” in [Table 1]).

[Criteria for evaluation of sharpness of outside light image]
The sharpness evaluation of the external light image is performed in four stages.
When the color tone of the scenery in the outside light image is clear and clearly visible, it is determined to be very good (very good, described as “⊚” in [Table 1]).
When the scene in the outside light image looks slightly dark, it is determined to be good (good, described as “◯” in [Table 1]).
When the scene in the outside light image is dark and the color is slightly uncomfortable, it is determined to be acceptable (fair, described as “Δ” in [Table 1]).
When the scenery by the outside light image looks blurry, it is determined to be impossible (no good, described as “x” in [Table 1]).

[Weather resistance test]
As the light guide plate for image display used for the sharpness evaluation, a sample subjected to a weather resistance test (“after weather resistance test” in [Table 1]) and a sample not subjected to a weather resistance test (“table resistance” in [Table 1]) "Before the test") is prepared.
The weather resistance test is performed using an ultraviolet fade meter U48AU (trade name; manufactured by Suga Test Instruments Co., Ltd.). The test condition is that the BP temperature is 63° C.±3° C. The test time is 500 hours.

[Evaluation results]
As shown in [Table 1], the sharpness of Example 1 is evaluated as “good” in both the displayed image and the external light image before and after the weather resistance test. The sharpness of Example 2 was evaluated as “good” except that the weather resistance test of the external light image was “very good”.
From this evaluation result, it is understood that in Examples 1 and 2, the display image and the external light image have good sharpness by including the absorption layer. In particular, in Example 2, since the absorption layer was provided also on the incident side of external light, the sharpness of the external light image was improved as compared with Example 1 before the weather resistance test.
On the other hand, the sharpness of Comparative Example 1 was “good” in both the display image and the external light image before the weather resistance test, which is inferior to that of Examples 1 and 2. It is “impossible” after the weather resistance test, and is significantly inferior to Examples 1 and 2.

Although the preferred embodiments, modifications and examples of the present invention have been described above, the present invention is not limited to these embodiments, modifications and examples. Additions, omissions, substitutions, and other changes can be made to the configuration without departing from the spirit of the present invention.
Also, the invention is not limited by the above description, but only by the appended claims.

INDUSTRIAL APPLICABILITY The image display light guide plate of the present invention can suppress deterioration of the hologram layer even if a resin base material is used, and is useful, for example, for display device applications in VR and AR applications. For example, the light guide plate for image display of the present invention is useful for display device applications such as a head-up display, a wearable display and a head mounted display.

1 and 3 resin base material 2 hologram layers 4 and 6 absorption layers 5, 7, 20, and 24 image display light guide plate 5b display image emitting portion 8 and 9 barrier layer 10 display device 21 and 23 resin base material (absorption layer)
Li, Ld, Ld', Ld'' image light Lo, Lo', Lo'', Lo''' outside light

Claims (6)

An image display light guide plate having a resin substrate and a hologram layer,
A light guide plate for image display, comprising an absorption layer having an absorption peak in a wavelength range of 500 nm to 600 nm. The light guide plate for image display according to claim 1, wherein the absorption layer, the resin base material, and the hologram layer are arranged in this order in the thickness direction. The absorption layer is
The light guide plate for image display according to claim 1, wherein the light guide plate for image display is arranged in a range overlapping with a display image emitting portion in the hologram layer in a thickness direction. The absorption layer is
The light guide plate for image display according to claim 1, wherein a coloring material is dispersed in at least a part of the inside of the resin base material. The light guide plate for image display according to claim 1, further comprising a barrier layer. The light guide plate for image display according to claim 5, wherein the barrier layer is arranged between the resin base material and the hologram layer.

Images