JPH02117881A - Monolayer-type self-color-forming pressure sensitive recording sheet - Google Patents

Abstract

PURPOSE:To prevent coloration of a sheet or color development contamination due to contact, rubbing or the like from occurring and contrive a higher color forming speed and a higher density by incorporating (leuco) dye-containing microcapsules, an organic color developer, polyvinyl alcohol and sodium polyacrylate in specified ratios. CONSTITUTION:The mixing ratio (wt.%) of (leuco) dye-containing microcapsules : an inorganic color developer : polyvinyl alcohol used is 100:(40 60):(50-80), and sodium polyacrylate is used in an amount of 5-10wt.% based on polyvinyl alcohol. A capsule protective agent and a pigment, together with the microcapsules, the color developer, polyvinyl alcohol and sodium polyacrylate, are applied to a support such as a paper by an air knife, curtain coater or other similar system. By this, a monolayer-type self-color-forming pressure sensitive recording sheet can be obtained which is excellent in migration and leveling properties, has an enhanced smoothness of a coated surface, is free of color development contamination, has excellent color forming speed and density, and has a high commercial value.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a single-layer type self-coloring pressure-sensitive recording sheet, and more particularly relates to color density when obtaining a colored image.

(B) Prior Art Self-coloring pressure-sensitive recording sheets are developed from so-called carbonless copying paper and are also called self-contained paper. A method in which a layer coated with microcapsules containing a dye dissolved in a high-boiling point solvent and an electron-accepting inorganic and/or organic color developer is coated and laminated, and a single layer coating in which both layers are mixed together. By using this method, a self-coloring pressure-sensitive recording sheet that allows pressure-sensitive coloring images to be obtained even on one sheet of paper can be directly printed without using a type ribbon.

In addition, it has unique effectiveness, such as the ability to obtain a copy record by writing on top of high-quality paper with a ballpoint pen, etc., and the demand for it has continued to increase in recent years.

Electron-donating colorless (leuco) dyes include crystal violet lactone, 3-3-bis(P-dimethylaminophenyl)natutalide, 3-(P-dimethylaminophenyl)-3-(2-methylindol-3-yl) )−
Triallylmethane phthalide such as 6-dimethylaminophthalide and acyl derivatives such as benzoyl, anisoyl and pivaloyl of methylene blue; 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7- Dibenzylaminofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3
-Methyl-cyclohexylamino-6-methyl-7-anilinofurane, 3-ethyl-P-)lylamino-6
- Colorless (leuco) dyes such as xanthine phthalide series such as methyl-7-anilinofluorane, alkylnaphthalenes represented by diisopropylnaphthalene, 1-
Aromatic hydrocarbons such as diallyl alkanes represented by phenyl-1-xylylethane, alkyl biphenyls represented by isopropylbiphenyl, other triallyl dimethanes, alkylbenzenes, benzylnaphthalenes, diallylalkylenes, and allyl indanes. ; Carboxylic acid ester compounds represented by dibutyl phthalate, dioctyl maleate, diethyl azelate, etc.; Phosphoric acid ester compounds represented by tricresyl phosphate; Naturally occurring plants and animals such as castor oil, soybean oil, cottonseed oil, and whale oil It is used after being dissolved in fats and oils or their modified oils; natural high-boiling fractions (consisting of aliphatic hydrocarbons) such as mineral oils.

Conventional microencapsulation methods include coacervation methods, in-situ polymerization methods, interfacial polymerization methods, and the like.

Electron-accepting color developer is an inorganic color developer that is made by acid clay, natural clay minerals such as attapulgide, and clay; acid clay, which is a montmorillonite clay mineral, is lightly or moderately softened with mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid. Treated activated clay and clay minerals with a layered structure consisting of regular tetrahedrons of silica have a 5in2 content of 82 to 82% on a dry basis (drying at 105°C for 3 hours).
96.5% by weight, and the resulting clay mineral is contacted in an aqueous medium with compounds of magnesium and/or aluminum that are at least partially soluble in said medium, such that the soluble compounds form hydroxides. In other cases, a semi-synthetic solid acid etc. obtained by neutralizing with an alkali or acid to form a hydroxide, introducing magnesium and/or aluminum components into the acid-treated clay mineral, and drying. Various phenolic compounds, novolak type phenolic resins, aromatic carboxylic acids or polyvalent metal salts thereof, etc. have already been proposed and used as organic color developers.

Among these color developers, inorganic color developers have fast ink drying properties, which are important for printing suitability, and have excellent plasticizer resistance for colored images. Difficult to apply.

This is because the color developer itself has a large specific surface area and requires a large amount of water when preparing the solution. Furthermore, the light fastness of the colored image is poor.

On the other hand, organic color developers such as novolac-type phenolic resin and substituted salicylic acid (salt) enable high-concentration coating and have excellent light resistance of colored images, but they tend to yellow due to Nox gas, etc. Plasticizer resistance is also insufficient.

However, organic color developers are generally widely used due to their liquid preparation properties and light resistance of colored images.

As a method for producing a self-coloring pressure-sensitive recording sheet using an organic color developer, first, as described above, an electron-donating colorless (
The leuco) dye is dissolved in a high boiling point solvent and microencapsulated, mixed with starch and latex as a binder, and coated on a support such as paper with an air knife, curtain coater, etc., usually at 3 to 10 g/rrf ( After coating and drying, an electron-accepting organic color developer is added to the upper layer using a dispersant such as sodium pyrophosphate, sodium hexametaphosphate, sodium ligninsulfonate, or sodium naphthalenesulfonate, and then the mixture is coated and dried. Grind to a suitable particle size using a grinder such as a sand mill or attritor, mix with starch or latex as a binder, and process with an air knife, curtain coater, etc., usually from 5 to Log/ A so-called laminated type self-coloring pressure-sensitive recording sheet is manufactured by laminating and coating the sheet and drying it so as to achieve rrf (dry weight solid content). Furthermore, microcapsules containing the above-mentioned (leuco) dye and an organic color developer pulverized to a suitable particle size are mixed together with a binder, and usually 5 to 15 g is mixed with a single coater.
There is a method of forming a single-layer type self-coloring pressure-sensitive recording sheet by coating and drying the composition to obtain /r+f (dry weight solid content).

The laminated type requires two coats, which requires a large amount of heat energy and electricity.In terms of quality, the color development speed is slow due to the two layers of microcapsules containing (leuco) dye and color developer. It is slow and the concentration is low.

On the other hand, the single-layer type has the great advantage of improving operability because it only needs to be coated once.Also, since the microcapsules and color developer coexist in close proximity, the single-layer type has excellent color development speed and density even under low pressure. is obtained.

However, in the single-layer self-coloring pressure-sensitive recording sheets that are actually commercialized, the coating liquid itself is colored because the (leuco) dye-containing capsules and the color developer coexist closely together. When applied to a support such as paper, the color appears to have already developed, so it has little value as a commercial product. Furthermore, there was a problem that the obtained recording sheet easily became colored and smeared due to contact, abrasion, etc.

(C) Problems to be Solved by the Invention As mentioned above, the single-layer type self-coloring pressure-sensitive recording sheet is more effective overall than the laminated type, but it is still one step away from coloring and staining of the sheet.

As a method to improve these problems, there is a method of reducing the coloring of the coating liquid by increasing the thickness of the capsule membrane of microcapsules containing a (leuco) dye, and further preventing colored staining of the obtained sheet. However, this method has the drawback that the color density is low even if the writing pressure and printing pressure are increased because the capsule membrane is thick.

In addition, coloring of the coating solution can be prevented by adding a small amount of low-molecular-weight polyethylene glycol to the coating solution, but since polyethylene glycol is a desensitizer, the color density of the sheet is low, and the colored image disappears during storage. It gets colored.

Furthermore, there is a method of dissolving an organic color developer in a high boiling point solvent and encapsulating it into microcapsules, but this requires a step of encapsulating the color developer, which reduces operability and reduces the color development of the resulting sheet. It has insufficient characteristics and is not practical.

(D) Object of the Invention Accordingly, the object of the present invention is to provide a single-layer type self-coloring pressure-sensitive recording sheet in which there is no coloring of the sheet, and there is no coloring stain due to contact, rubbing, etc. Furthermore, it is an object of the present invention to provide a practically excellent single-layer type self-coloring pressure-sensitive recording sheet with improved coloring speed and density.

(E) Means for Solving the Problems As a result of extensive research, the inventors of the present invention have found that the sheet does not become colored, images with excellent color development speed and density are obtained, and smoothness is improved. As a result, we succeeded in developing a single-layer self-coloring pressure-sensitive recording sheet that is free from colored stains.

That is, the present inventors have developed a microcapsule containing a (leuco) dye in a solution state, an organic color developer, a mixture of polyvinyl alcohol and sodium polyacrylate as a binder, and their use. The present invention was based on the knowledge that by limiting the mixing ratio, a single-layer self-coloring pressure-sensitive recording sheet without sheet coloration, high coloring speed and density, and no coloring stains can be obtained.

The (leuco) dye-containing microcapsules used in the present invention are microencapsulated by an in-situ method, and are specifically described in Japanese Patent Application Laid-Open No. 51-9079 and Japanese Patent Application Laid-Open No. 52-668.
No. 78, JP-A-53-84861, JP-A-Sho 5
Urea-formaldehyde resin or melamine-formaldehyde resin, which has a capsule membrane that is highly resistant to heat and solvents, is used, as described in Japanese Patent No. 4-49984.

The organic color developer used in the present invention is a polyvalent metal of substituted salicylic acid and/or a novolac type phenol resin.

Examples of polyvalent metal salts of substituted salicylic acids include 3-phenylsalicylic acid, 3-+erl-butyl-5-
Methyl salicylic acid, 3゜5-di-ten+-butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3-(α,α-dimethylbenzyl)-
These are polyvalent metal salts such as zinc, aluminum, and magnesium, such as 5-methylsalicylic acid.

Novolac type phenolic resins are produced by polycondensing various phenol derivatives and lower aldehydes such as formaldehyde as raw materials in the presence of an acidic catalyst.

The phenolic raw materials used at this time include, for example, unsubstituted phenol, alkyl group-substituted phenol (e.g. cresol, ethylphenol, butylphenol, octylphenol, nonylphenol, etc., mainly para-substituted products), aralkyl group-substituted phenol (e.g. (para-penzylphenol, para-cumylphenol, etc.), aryl group-substituted phenol (eg, para-phenylphenol), or halogen-substituted phenol (eg, para-chlorophenol). These can be used alone or in combination of two or more types as phenolic raw materials.

Among the above, the present invention uses a novolak type phenol resin using an alkyl group-substituted phenol or an aryl group-substituted phenol as a phenolic raw material, which has a high color developing ability.

The water-soluble binder used in the present invention, polyvinyl alcohol, has a degree of polymerization of 500 to 2,400 and a degree of saponification of 80 to 1.
00 mol%, particularly preferably a degree of polymerization of 500 to 15
00, the degree of saponification is 85 to 100 mol%.

The effects of polyvinyl alcohol used in the present invention are that it has better viscosity behavior than other water-soluble binders and hydrophobic binders, has good film-forming properties, and improves the smoothness of the coated sheet surface. This effect is further promoted by mixing and using sodium polyacrylate having an average degree of polymerization of 3,000 or less.

If the average degree of polymerization of sodium polyacrylate is 3.000 or more, the viscosity of the coating solution will become high and no effect will be obtained.

The sodium polyacrylate used in the present invention is a sodium salt of an acrylic ester/acrylic acid copolymer.

The mixing ratio (wt%) of (leuco) dye-containing microcapsules used in the present invention; organic color developer: polyvinyl alcohol is 100:40 to 60:50 to 80, and the ratio of sodium polyacrylate is (% by weight) is 5 to 10% based on polyvinyl alcohol.

If the ratio is other than the above, there will be disadvantages in color development speed, density, color development stain prevention, etc., and the practical value will decrease.

The present invention uses capsule protectants such as cellulose powder, starch particles, and talc; kaolin, calcined kaolin, natural silica, titanium oxide, and calcium carbonate to further prevent color development stains, improve color development speed, density, and printability. One and/or two or more types of organic white pigments such as synthetic silica, urea-formaldehyde resin, styrene methacrylic acid copolymer, and polystyrene resin are used.

These capsule protectants and pigments are used together with the capsule of the present invention, a color developer, polyvinyl alcohol, and sodium polyacrylate to form a coating solution for a single-layer self-coloring pressure-sensitive recording sheet, and coated with an air knife, carn coater, etc. It is applied to a support such as paper. Application amount is 3-15g/
Particularly preferably 5 to 10 g in rrf (dry weight solid content)
/m range.

In the present invention, additives such as a waterproofing agent, an antifoaming agent, and other anti-dusting agents are used, if desired.

(F) Using polyvinyl alcohol having the properties as described above and sodium polyacrylate, etc. in an appropriate ratio as the capsule of the present invention, a color developer, and a binder thereof on a support such as a working paper. Although the principle is unknown, the so-called migration rate and leveling, in which the coating solution penetrates into a support such as paper during coating, are excellent, the smoothness of the coated surface is improved, there is no color staining, and the color development speed and speed are improved. A single-layer self-coloring pressure-sensitive recording sheet with excellent density and high commercial value can be obtained.

(G) Examples Preferred embodiments and excellent effects of the present invention will be specifically explained below using the most typical examples. In addition, all parts below represent parts by weight.

Example 1 Method for creating microcapsules containing 40% colorless (leuco) dye 7 parts of crystal violet lactone (CVL), which is a colorless (leuco) dye, was mixed with phenylxyleleethane, a high boiling point hydrocarbon oil (boiling point 296°C, Hysol SAS). After heating and dissolving in 93 parts of styrene maleic anhydride copolymer (manufactured by Nippon Petrochemical), 120 parts of a 5% aqueous solution (pH 4,8) of styrene maleic anhydride copolymer
and emulsified at a liquid temperature of 60° C. so that the average particle size was 4.5 μm.

Melamine-formaldehyde initial condensate was obtained by heating and dissolving 12.5 parts of melamine, 16.1 parts of a 37% formaldehyde solution, and 60 parts of water in water at pH 9.5, and adding it to the above emulsion and stirring at 75°C. After reacting for 2 hours, the liquid temperature was lowered to 40° C. or less, and the pH was adjusted to 8.5, thereby creating microcapsules containing 40% (leuco) dye. The microcapsule film thickness of this microcapsule is calculated to be about 1250 angstroms (A).

Method for preparing 25% substituted salicylate salt dispersion 3-1
erf-butyl-5-methylsalicylate zinc 100 parts sodium naphthalenesulfonate 2.5 parts water
300 parts of the above mixture was ground in a ball mill to an average particle size of 3μ,
% substituted salicylate salt drug dispersion.

10 parts of a 5% sodium pyrophosphate aqueous solution was added to 240 parts of water, 20 parts of calcium carbonate (Shiraishi Calcium Co., Ltd., Brilliant-15) and 80 parts of wheat starch were almost completely mixed and dispersed. % (leuco) dye-containing microcapsules 62.5 parts, 25% substituted salicylate acid salt dispersion 52 parts, 10% polyvinyl alcohol aqueous solution (manufactured by Kuraray, PVA-110, molecular weight 10
00, degree of saponification 98-99 mol%) 150 parts, 20% aqueous sodium polyacrylate solution (average degree of polymerization 1000)
3.8 parts were sequentially added and mixed to prepare a coating liquid. This coating liquid was applied to a high-quality paper having a basis weight of 50 g and 10 f using an air knife coater in a coating amount of 8 g/m (dry weight solid content) and dried to prepare a single-layer self-coloring pressure-sensitive recording sheet.

Example 2 Method for preparing a 25% novolac type phenolic resin color developer dispersion Novolac type phenol resin containing phenylphenol as the main phenolic raw material 100 parts Sodium naphthalene sulfonate 2.5 parts Water
300 parts of the above mixture was ground in a ball mill to an average particle size of 3μ,
A 5% novolac type phenolic resin developer dispersion was prepared.

Single-layer self-coloring pressure-sensitive recording was performed in the same manner except that the 25% substituted salicylate salt dispersion of Example 1 was replaced with the same amount of the 25% novolac type phenolic resin developer dispersion to prepare a coating solution. I created a sheet.

Example 3 10 parts of a 5% sodium pyrophosphate aqueous solution was added to 215 parts of water, 20 parts of calcium carbonate (Brilliant-15) and 80 parts of wheat starch were almost completely mixed and dispersed, and then the above 40% was gradually mixed with stirring. (Leuco) 62.5 parts of dye-containing microcapsules, 60 parts of 25% novolac type phenolic resin developer dispersion, 200 parts of 10% polyvinyl alcohol aqueous solution (PVA-110), 20% sodium polyacrylate aqueous solution (average degree of polymerization) A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner as in Example 1, except that 10 parts of 1000) were sequentially added and mixed to prepare a coating solution.

Comparative Example 1 A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner as in Example 1, except that the 20% aqueous sodium polyacrylate solution was used as a coating solution.

Comparative Example 2 20% aqueous sodium polyacrylate solution of Example 1 3.
A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner except that the coating solution was reduced from 8 parts to 2.2 parts.

Comparative Example 3 20% aqueous sodium polyacrylate solution of Example 1 3.
A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner except that the coating solution was increased from 8 parts to 11.3 parts.

Comparative Example 4 10 parts of a 5% sodium pyrophosphate aqueous solution was added to 270 parts of water, and after almost completely mixing and dispersing 20 parts of calcium carbonate (Brilliant-15) and 80 parts of wheat starch, the above 40% ( leuco) dye-containing microcapsules (62.5 parts), 30 parts of 25% novolac type phenolic color developer dispersion, 100 parts of 10% polyvinyl alcohol aqueous solution (PvA-110), 20% sodium polyacrylate aqueous solution (average degree of polymerization 1000) ) A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner as in Example 1, except that 2.5 parts of the following were sequentially added and mixed to prepare a coating solution.

Comparative Example 5 10 parts of 5% sodium pyrophosphate was added to 90 parts of water,
After almost completely mixing and dispersing 20 parts of calcium carbonate (Brilliant-15) and 80 parts of wheat starch, gradually add the above 40% (leuco) dye-containing microcapsules 6 while stirring.
2.5 parts, 25 parts Color developer dispersion 70 parts, 10% polyvinyl alcohol aqueous solution (PVA-110) 225 parts, 20 parts
% sodium polyacrylate aqueous solution (average degree of polymerization 100
A single-layer self-coloring pressure-sensitive recording sheet was prepared in the same manner as in Example 1, except that 11.3 parts of 0) were sequentially added and mixed to prepare a coating solution.

Comparative Example 6 A simple procedure was carried out in the same manner except that 3.8 parts of the 20% sodium polyacrylate aqueous solution (average degree of polymerization 1000) of Example 1 was replaced with the same amount of 20% sodium polyacrylate aqueous solution (average degree of polymerization 7500). A single-layer self-coloring pressure-sensitive recording sheet was prepared.

Testing/Measurement Methods The produced single-layer self-coloring pressure-sensitive recording sheet was tested and measured in the following manner, and the results are shown in Table 1.

Color Development Speed/Color Development Density The single-layer self-recording sheet was passed through a calendar to develop color, and the color density after 1 minute and 1 hour was measured by reflectance using a color difference meter, and the following values were calculated. The time after 1 minute was taken as the color development rate, and the time after 1 hour was taken as the color development density. The numerical value is small and the culm color density is high.

Reflectance of colored area Color density (%) = X100 (%) Reflectance of white area Colored stain Overlap the coated surface of the high-quality paper and the single-layer self-recording sheet 2
When the sheets were rubbed together six times under a load of 50 kg/ad, colored stains on the sheet surfaces were visually observed and evaluated using ○, @, and Δ marks.

○ mark: hardly stained, ■ mark: slightly stained, △ mark: slightly stained.

Test Results Table 1 (H) Effect of the Invention As is clear from the above, the capsule of the present invention, the color developer, and their binder use a mixture of polyvinyl alcohol and sodium polyacrylate with a low degree of polymerization, and By limiting the mixing ratio, the resulting sheet was a single-layer self-coloring pressure-sensitive recording sheet that had excellent coloring speed and density, was free from coloring stains, and had high practical commercial value.

Claims (1)

[Claims] 1) A support such as paper contains a colorless or light-colored electron-donating (leuco) dye as a coloring agent and an organic color developer as an electron-accepting color developer capable of coloring the (leuco) dye, and In a single-layer self-coloring pressure-sensitive recording sheet made by coating and drying a mixture of polyvinyl alcohol and sodium polyacrylate, microcapsules containing the (leuco) dye: organic color developer: polyvinyl alcohol: sodium polyacrylate The usage ratio (weight%) is 100:40~
60:50 to 80:2.5 to 8. 2) The sodium polyacrylate is average polymerized with a sodium salt of an acrylic ester/acrylic acid copolymer. 2. The single-layer self-coloring pressure-sensitive recording sheet according to claim 1, which has a power of 3000 or less.