JP2698990B2 - Microcapsules for pressure-sensitive recording sheet - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a microcapsule for a pressure-sensitive recording sheet,
More specifically, the present invention relates to a microcapsule for a pressure-sensitive recording sheet using a colorless reaction between an almost colorless electron donating dye and an electron accepting compound.

(Prior Art) A pressure-sensitive recording sheet is formed by dissolving a substantially colorless electron-donating dye (hereinafter referred to as a color forming agent) in a suitable solvent, and supporting a microcapsule layer including microcapsules in which oil droplets are microencapsulated. Upper paper coated on top, lower paper coated with a color-developing layer containing an electron-accepting compound (hereinafter referred to as a color developer) on another support, and in some cases, one side on the support. A microcapsule layer on one side, a combination of middle paper sheets coated with a color developer layer on the other side, or a support containing the capsule and the color developer on the same side of the support, or in the support One containing the above-mentioned capsule or developer and the other being coated.

These pressure-sensitive recording sheets are described, for example, in U.S. Pat.
470, 2,505,489, 2,550,471, 2,730,457
No. 3,418,250 and the like.

As a method for producing a microcapsule for a pressure-sensitive recording sheet, a coacervation method, an interfacial polymerization method, an in-situ polymerization method and the like are known. Regarding the coacervation method, U.S. Patent Nos. 2,800,457, 2,800,458, and 3,687,865
No. 3,429,827 for the interfacial polymerization method.
Nos. 3,577,515 and 3,886,085, and the in-situ polymerization method is described in U.S. Pat. Nos. 3,726,804 and 3,796,669.

Of these, microcapsules formed by an interfacial polymerization method using a polyurethane urea film obtained by reacting a polyvalent isocyanate with water, a polyvalent amine or a polyhydric alcohol, and an in-situ polymerization method have attracted attention in recent years.

Microcapsules using a polyurethane urea membrane can provide a high-concentration capsule solution, are superior in water resistance of capsules, and can be encapsulated in a shorter time than microcapsules of the coacervation method using gelatin, which has been widely used in the past. It has features such as being able to be done.

However, conventionally known microcapsules using a polyurethane urea film do not always have satisfactory performance.

As the performance of the pressure-sensitive recording sheet, it is important to obtain a high color density in the case of typewriter printing or ballpoint pen printing. In general, when the color developing property is improved, the pressure resistance becomes insufficient, and pressure fog is likely to occur during processing such as printing cutting. It is very difficult to obtain satisfactory performance in both the color development and the pressure resistance.

(Object of the Invention) An object of the present invention is to provide a microcapsule for a pressure-sensitive recording sheet having a polyurethane urea wall, which is excellent in coloring property and pressure resistance.

(Constitution of the Invention) An object of the present invention is to provide a microcapsule for a pressure-sensitive recording sheet comprising, as a core substance, a solution of an electron-donating color former dissolved in a hydrophobic liquid, wherein the microcapsule has a polyurethane urea wall. The present invention has been achieved by a microcapsule for a pressure-sensitive recording sheet, wherein the particle size distribution of the microcapsules in the resin wall is within the following range.

Above D ₅₀ represents an median diameter, D ₅₀ is not obtained 4.0μ smaller than sufficient coloring property, also 12.0μ larger than not obtained sufficient pressure resistance. The preferred range of D ₅₀ is
5.0 to 10.0μ, and a _more preferable range of D50 is 6.5 to 8.5.
μ.

D ₉₀ / D ₁₀ indicates how sharp the particle size distribution is, and a smaller value of D ₉₀ / D ₁₀ means that the particle size distribution is sharper. As for the microcapsules for a pressure-sensitive recording sheet, it is expected that the coloring property and the pressure resistance will be improved as the particle size distribution is reduced. The reason for this is that capsules that are considerably smaller than the median diameter are not broken at the time of color development and do not contribute to color development, and capsules that are too large are likely to be broken at low pressure and cause pressure fog.

The present inventors produced capsules in which the particle size distribution was changed in a wide range of D ₉₀ / D ₁₀ = 1.7 to 5.0 in order to confirm the effect of shaping the particle size distribution, and evaluated the color development and pressure resistance. did.

As a commonly used emulsifier, a simple stirrer,
There are a homogenizer, a homomixer, and a dissolver. The particle size distribution of the microcapsules obtained by emulsification by these emulsifiers was in the range of D ₉₀ / D ₁₀ = 2.4 to 5.0. Double cylindrical emulsifier with uniform gap and uniform shear force (hereinafter referred to as cylindrical mill)
The particle size distribution of the microcapsules obtained by emulsification by the above was D ₉₀ / D ₁₀ ≦ 2.0, which was considerably sharper than the particle size distribution of the microcapsules obtained by emulsification by the above-mentioned general emulsifier.

Coloring of these microcapsules, the results of evaluating the pressure resistance, a clear difference between microcapsules in the range of the microcapsules and D ₉₀ / D ₁₀ ≦ 2.0 in the range of D ₉₀ / D ₁₀ = 2.4~5.0 In addition, the microcapsules in the range of D ₉₀ / D ₁₀ ≦ 2.0 were superior to the microcapsules in the range of D ₉₀ / D ₁₀ = 2.4 to 5.0 in color development and pressure resistance.

The microcapsules of the polyurethane urea resin wall of the present invention are obtained by emulsifying and dispersing a solution in which a polyvalent isocyanate, a polyvalent hydroxy compound and a coloring agent are dissolved in a hydrophobic liquid, in a hydrophilic liquid, and then adding the polyvalent isocyanate in the emulsified dispersion. It is obtained by adding an amine and coating hydrophobic droplets with a polyurethane urea resin. A polyhydroxy compound and a polyamine may both be used, or only one of them may be used.

The polyvalent isocyanate used in the present invention refers to a compound having two or more isocyanate groups, and specific examples thereof include 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, and naphthalene-1, 5-diisocyanate,
4,4'-diphenylmethane diisocyanate, xylylene-1,4-diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, ethylidine diisocyanate, cyclohexylene -1,4-diisocyanate, isophorone diisocyanate, adduct of hexamethylene diisocyanate and trimethylolpropane, adduct of hexamethylene diisocyanate and hexanetriol, biuret of hexamethylene diisocyanate, isocyanurate of hexamethylene diisocyanate, isocyanate of isophorone diisocyanate Nurate, polymethylene polyphenyl isocyanate, tolylene diisocyanate and trimethylolpropane Addendum, adduct of xylylene diisocyanate and trimethylolpropane, an isocyanurate of tolylene diisocyanate, tris - (p
-Isocyanatophenyl) thiophosphite;

These polyvalent isocyanates may be used alone or in combination of two or more.

Examples of polyhydric hydroxy compounds include aliphatic or aromatic polyhydric alcohols, hydroxypolyesters, hydroxypolyalkylene ethers, and alkylene oxide adducts of polyvalent amines. Of these polyhydric hydroxy compounds, alkylene oxide adducts of polyvalent amines are preferred from the viewpoints of color development and pressure resistance. The amine alkylene oxide adduct refers to a compound in which at least one or more of the hydrogens in the amino group of the amine is substituted with an alkylene oxide and which is soluble in a hydrophobic liquid. Examples of the amine for producing an alkylene oxide adduct of an amine include stearylamine, oleylamine, and the like.
Aromas such as ethylenediamine, 1,3-propylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, aliphatic amines such as 1,6-hexamethylenediamine, o-phenylenediamine, p-phenylenediamine, and diaminonaphthalene There are group amines.

As the alkylene oxide to be added to these amines, ethylene oxide, propylene oxide,
Butylene oxide and long-chain α-olefin oxide. Of these, butylene oxide is most preferable in terms of pressure resistance.

The molecular weight of the alkylene oxide adduct of the amine is 250.
It is preferably about 4,000. Two or more of these alkylene oxide adducts of amines may be used in combination.

The amount of the amine alkylene oxide adduct used is 1 to 100% by weight based on the total weight of the polyvalent isocyanate used,
Preferably it is 2 to 50% by weight.

As the polyvalent amine used in the present invention, two or more Alternatively, it refers to a compound having an —NH ₂ group that is soluble in a hydrophilic liquid. Specific examples include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-propylenediamine, hexamethylenediamine, phenylenediamine, diaminonaphthalene, xylylenediamine, and the like. More than one species can be used in combination.

The amount of the polyamine used is 0.2 to 50% by weight, preferably 0.5 to 20% by weight, based on the total weight of the polyvalent isocyanate.

The timing of adding the polyvalent amine may be any time after the solution in which the alkylene oxide adduct of the polyvalent isocyanate and the amine and the color former are dissolved in the hydrophobic liquid is emulsified and dispersed in the hydrophilic liquid.

Examples of the color former used in the present invention include a triphenylmethanephthalide-based compound, a fluoran-based compound, a phenothiazine-based compound, an indolylphthalide-based compound, an indolylazaphthalide-based compound, a leuco-aluminamine-based compound, and a rhodamine lactam-based compound. Compounds, triphenylmethane compounds, triazene compounds, spiropyran compounds and the like.

Natural or synthetic oils can be used alone or in combination as the hydrophobic liquid. Examples of the hydrophobic liquid include cottonseed oil, kerosene, paraffin, naphthenic oil, alkylated biphenyl, alkylated terphenyl, chlorinated paraffin, alkylated naphthalene, diarylalkane, dibasic acid esters such as phthalic acid esters, and the like. it can.

As the hydrophilic liquid, an aqueous solution of a protective colloid and / or a surfactant is used. Examples of the protective colloid include hydrophilic polymer substances such as gelatin, gum arabic, casein, carboxymethylcellulose, starch, polyvinyl alcohol styrene sulfonic acid polymer, copolymer of styrene and maleic anhydride, and polyacrylic acid. Examples of the surfactant include ionic agents such as alkylbenzenesulfonic acid, polyoxyethylene sulfate, and funnel oil, and nonionic agents such as polyoxyethylene alkyl ether, polyoxyethylene, and sorbitan fatty acid ester. .

The microcapsules obtained in the present invention are added with a general water-soluble binder, a latex-based binder, and a capsule protective agent such as cellulose powder, starch particles, and talc to obtain a microcapsule coating solution for a pressure-sensitive recording sheet.

Examples of the color developing agent that reacts with the color forming agent used in the recording sheet of the present invention include acid clay, activated clay, atabaldiite, zeolite, bentonite, clay materials such as kaolin, metal salts of aromatic carboxylic acids, and phenol resins. can give.

These developers are applied to a support such as paper together with a binder such as styrene butadiene latex.

The performance of the microcapsule sheet for pressure-sensitive recording of the present invention was tested using the following developer sheet.

(Adjustment of developer sheet)

(Preparation of dispersion) Zinc 3,5-di-α-methylbenzylsalicylate 15 parts,
120 parts of calcium carbonate, 30 parts of activated clay, 20 parts of zinc oxide,
Using 1 part of sodium hensametaphosphate and 200 parts of water, the mixture was uniformly dispersed with a sand grinder so as to have an average particle diameter of 3 μ to obtain a dispersion (A).

(Adjustment of coating liquid)

400 parts of dispersion (A), 10 parts of 10% PVA-203 (Kuraray) aqueous solution, 10 parts of 10% PVA-117 (Kuraray) aqueous solution, and 10 parts of carboxy-modified SBR latex (SN-307 manufactured by Sumitomo Nogatafu) Min) and the solids concentration is 20%
To obtain a coating solution.

[Application of developer sheet]

This coating solution was applied to a 50 g / m ² base paper with an air knife coater so that a solid content of 5.0 g / m ² was applied, and dried to obtain a developer sheet.

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the examples.

(Example) Example 1 As a coloring agent, 100 g of crystal violet lactone, 10 g of benzoylleucomethylene blue and 3- [4-
(Diethylamino) -2-ethoxyphenyl] -3-
40 g of (2-methyl-1-ethyl-3-indolyl) -4-azaphthalide is dissolved in 2000 g of diisopropylnaphthalene. 160 g of polymethylene polyphenyl isocyanate (manufactured by Nippon Polyurethane Co., Ltd., trade name "Millionate MR200") as a polyvalent isocyanate and a piuret of hexamethylene diisocyanate (manufactured by Sumitomo Bayer Urethane Co., Ltd., trade name "Sumijur N3200") 140
g and 64 g of a butylene oxide adduct of ethylenediamine (addition mole number of butylene oxide to ethylenediamine: 16.8 mol, molecular weight: 1267) as an alkylene oxide adduct of an amine were dissolved to prepare a primary solution.

Next, a secondary solution was prepared by dissolving 200 g of polyvinyl alcohol and 100 g of carboxymethyl cellulose in 2800 g of water.

The primary solution was poured while stirring the secondary solution at 800 rpm with a propeller blade stirrer having a blade diameter of 70 mm to form an oil-in-water emulsion to obtain a preliminary emulsion.

Next, this pre-emulsion was subjected to a cylindrical mill with a flow rate of 0.3 kg / min, a clearance of 300 μm, and a rotation speed of 1300 rp.
An emulsion was obtained by treating under the conditions of m and the number of passes = 1. Then, after adding 2000 g of water at 20 ° C. to the emulsion, the temperature of the system was gradually raised to 65 ° C. and kept at this temperature for 90 minutes to obtain a capsule liquid.

When the particle size distribution of this capsule was measured with a Coulter Counter TA-II, D ₅₀ = 6.6 μ, D ₉₀ / D ₁₀ = 1.7
It was 0.

To the capsule solution thus obtained, 2000 g of a 15% aqueous solution of polyvinyl alcohol, 600 g of carboxy-modified SBR latex in solid content, and 1200 g of starch particles (average particle size 15 μ)
Was added.

Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution.

As will be 4.0 g / m ² The coating liquid by dry weight, 40 g / m
^{(2) The} base paper was coated and dried with an air knife coating machine to obtain a microcapsule sheet.

Example 2 Example 1 was repeated except that the conditions for treating the pre-emulsion liquid with the cylindrical mill were changed to the following conditions: flow rate = 0.4 kg / min, clearance = 500 µ, rotation speed = 1200 rpm, and number of passes = 1. In the same manner as in Example 1, a microcapsule sheet was obtained.

When the particle size distribution of this capsule was measured using a Coulter Counter TA-II, D ₅₀ = 8.0 μ, D ₉₀ / D ₁₀ = 1.7
I got 4.

Comparative Example 1 The secondary solution of Example 1 was applied to a dissolver having a wing diameter of 100 mm for 200 times.
The primary solution of Example 1 was poured while stirring at 0 rpm, and stirring was continued for 1 minute to form an oil-in-water emulsion. Next, after adding 2000 g of water at 20 ° C. to the emulsion, the temperature of the system was gradually raised to 65 ° C. and kept at this temperature for 90 minutes to obtain a capsule liquid.

When the particle size distribution of this capsule was measured using a Coulter Counter TA-II, D ₅₀ = 6.7 μ, D ₉₀ / D ₁₀ = 3.0
It was.

To the capsule solution thus obtained, 2000 g of a 15% aqueous solution of polyvinyl alcohol, 600 g of carboxy-modified SBR latex in solid content, and 1200 g of starch particles (average particle size 15 μ)
Was added.

Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution.

As will be 4.0 g / m ² The coating liquid by dry weight, 40 g / m
^{(2) The} base paper was coated and dried with an air knife coating machine to obtain a microcapsule sheet.

Comparative Example 2 The secondary solution of Example 1 was dispensed with a dissolver having a wing diameter of 100 mm.
The primary solution of Example 1 was poured while stirring at 0 rpm, and stirring was continued for 1 minute to form an oil-in-water emulsion. Next, after adding 2000 g of water at 20 ° C. to the emulsion, the temperature of the system was gradually raised to 65 ° C. and kept at this temperature for 90 minutes to obtain a capsule liquid.

When the particle size distribution of this capsule was measured using a Coulter Counter TA-II, D ₅₀ = 7.9 μ, D ₉₀ / D ₁₀ = 4.3
It was.

To the capsule solution thus obtained, 2000 g of a 15% aqueous solution of polyvinyl alcohol, 600 g of carboxy-modified SBR latex in solid content, and 1200 g of starch particles (average particle size 15 μ)
Was added.

Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution.

As will be 4.0 g / m ² The coating liquid by dry weight, 40 g / m
^{(2) The} base paper was coated and dried with an air knife coating machine to obtain a microcapsule sheet.

Example 3 120 g of 2-anilino-3-methyl-6-N-ethyl-N-isopentylaminofluorane and 20 g of 2-dibenzylamino-6-diethylaminofluoran were used as color formers in 2000 g of 1-phenyl-1-xylylethane. Dissolve in

To this oily liquid, 200 g of ethyl acetate was added, and 320 g of a polyvalent isocyanate adduct of 3 mol of tolylene diisocyanate / 1 mol of trimethylolpropane (trade name "Barnock D750" manufactured by Dainippon Ink Co., Ltd.) was added to an alkylene oxide adduct of amine. 80 g of butylene oxide adduct of ethylenediamine (the number of moles of butylene oxide added to ethylenediamine: 12 mol, molecular weight: 924)
The next solution was prepared.

Next, a secondary solution was prepared by dissolving 200 g of polyvinyl alcohol and 40 g of gum arabic in 2800 g of water.

The primary solution was poured while stirring the secondary solution at 800 rpm with a propeller blade stirrer having a blade diameter of 70 mm to form an oil-in-water emulsion to obtain a preliminary emulsion.

Next, this pre-emulsion was subjected to a cylindrical mill with a flow rate of 0.3 kg / min, a clearance of 300 μm, and a rotation speed of 1300 rp.
An emulsion was obtained by treating under the conditions of m and the number of passes = 1. Next, 2,000 g of water at 20 ° C and 7.2 g of diethylenetriamine as a polyamine are added to the emulsion, and the mixture is stirred at room temperature for 10 minutes. Then, the temperature of the system is gradually increased to 65 ° C and maintained at this temperature for 60 minutes. Was.

When the particle size distribution of this capsule was measured using a Coulter Counter TA-II type, D ₅₀ = 7.1 μ and D ₉₀ / D ₁₀ = 1.7
I got one.

1600 g of a 15% aqueous solution of polyvinyl alcohol, 400 g of carboxy-modified SBR latex in solid content, and 1000 g of starch particles (average particle size 15 μ) were added to the capsule solution thus obtained.
Was added.

Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution.

As will be 4.0 g / m ² The coating liquid by dry weight, 40 g / m
^{(2) The} base paper was coated and dried with an air knife coating machine to obtain a microcapsule sheet.

Comparative Example 3 The secondary solution of Example 3 was applied to a 200-mm dissolver with a wing diameter of 100 mm for 200 times.
The primary solution of Example 3 was poured while stirring at 0 rpm, and stirring was continued for 1 minute to form an oil-in-water emulsion.

Next, 2,000 g of water at 20 ° C and 7.2 g of diethylenetriamine as a polyamine are added to the emulsion, and the mixture is stirred at room temperature for 10 minutes. Then, the temperature of the system is gradually increased to 65 ° C and maintained at this temperature for 60 minutes. Was.

When the particle size distribution of this capsule was measured using a Coulter Counter TA-II, D ₅₀ = 7.1 μ, D ₉₀ / D ₁₀ = 3.3
It was.

1600 g of a 15% aqueous solution of polyvinyl alcohol, 400 g of carboxy-modified SBR latex in solid content, and 1000 g of starch particles (average particle size 15 μ) were added to the capsule solution thus obtained.
Was added.

Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution.

As will be 4.0 g / m ² The coating liquid by dry weight, 40 g / m
^{(2) The} base paper was coated and dried with an air knife coating machine to obtain a microcapsule sheet.

An evaluation test as a pressure-sensitive recording sheet was performed by combining each of the microcapsule sheets and the developer sheet. The results are shown in Table 1. The evaluation test was performed by the following method.

1) Color development test Each microcapsule sheet is overlaid with a developer sheet and IBM6
Alphabet small letter m with 747 type electronic typewriter
Was continuously pressed and colored. One day after the color development, the print density D (type-writer) in the visible region was measured with a Masbeth RD-918 densitometer.

2) Pressure resistance test Each microcapsule sheet is superimposed on a developer sheet and 10 kg
A load of / cm ² was applied to generate pressure fog on the surface of the color developing sheet. After these samples were overlaid for 3 days, the density D (fog) of fog on the developer sheet surface at 610 nm was measured with a Hitachi Color Analyzer Model 307.

As shown in Table 1, the microcapsule sheet of the present invention is excellent in color development and pressure resistance and has extremely good performance as compared with the microcapsule sheet for comparison.

Claims (1)

(57) [Claims] 1. A microcapsule for a pressure-sensitive recording sheet, comprising a microcapsule containing a solution of an electron-donating color former dissolved in a hydrophobic liquid as a core substance, wherein the wall of the microcapsule is a polyurethane urea resin wall, and the microcapsule is a microcapsule. Having a particle size distribution in the following range.