JPS61149391A - Monolayer auto-color-forming pressure-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To improve performance, operability and cost, by a method wherein microcapsules containing a coloring matter precursor and having a synthetic resin wall, an organic color developer, a pigment and a film-forming composition obtained by polymerizing a water-soluble vinyl monomer in the presence of a high molecular weight latex having a glass transition point not higher than a specified temperature are provided as essential constituents on a base. CONSTITUTION:The microcapsules containing a coloring matter precursor provided by microencapsulating a solution of 1-10pts.wt. of a phthalide dericative, a fluoran derivative, an azaphthalide derivative or the like in a high boiling point hydrophobic solvent, by using a synthetic resin film. The amounts of the color developer and the pigment are ordinarily respectively 10-200pts. and 20-100pts. per 100pts. of microcapsule solid components. The film-forming composition is obtained by polymerizing (B) at least one water-soluble vinyl monomer in the presence of (A) a high molecular weight latex having a glass transition point of not higher than 60 deg.C, with a solid weight ratio of (A):(B) being in the range of 100:5-100:20.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a self-coloring pressure-sensitive recording sheet.

More particularly, the present invention relates to an improved single-layer self-coloring pressure-sensitive recording sheet.

(Prior art and their problems) Self-coloring pressure-sensitive recording sheets are made by combining microcapsules containing a colorless dye precursor and a color developer (generally an oil-soluble organic acidic substance) on the same support. A recorded image is obtained by applying pressure to a surface and destroying the microcapsules to cause a coloring reaction between the dye precursor and the color developer.

Self-coloring pressure-sensitive recording sheets currently in practical use are two-layer self-coloring sheets that are obtained by coating one side of a support with a dye precursor microcapsule layer and a color developer layer. Although sexual pressure-sensitive recording sheets are the main type, in recent years, due to advances in microencapsulation technology, single-layer coating type self-coloring pressure-sensitive recording sheets have been proposed, and some of them have come into practical use.

The above-mentioned single-layer self-coloring pressure-sensitive recording sheet microencapsulates a dye precursor (e.g., phthalide compound, fluoran compound, etc.) and a color developer (e.g., oil-soluble phenol resin, salicylic acid derivative, etc.). These are mixed to form a uniform coating solution and coated in the same layer.

The two-layer coating type self-coloring recording sheet is manufactured by laminating the dye precursor microcapsule layer and the color developer layer into two layers as described above. The complex coacervation method, which uses gelatin as the wall material, is used as the coating method, which means that only a low-concentration coating solution can be obtained, and two layers of coating are required, resulting in extremely low production efficiency. However, due to the fact that the developer layer and the microcapsule layer of the dye precursor are separated from each other, it was not possible to obtain a product with excellent color development speed and density. Problems remain from a performance standpoint as well.

On the other hand, the known single-layer self-coloring pressure-sensitive recording sheet has the advantage of significantly improving productivity, such as being able to replace the conventional two-layer coating with just one coating and improving product yield. However, it is necessary to microencapsulate not only the dye precursor but also the developer. Problems include the cost involved in microencapsulating the color developer, and undesired coloring (staining) caused by friction and paper folding due to the coated surface structure, which is more likely to occur than with a two-layer structure. Several points were raised, and a complete solution was not necessarily reached.

□ Several proposals have been made to improve the staining of single-layer self-coloring pressure-sensitive recording sheets using such color developer microcapsules and dye precursor microcapsules, but satisfactory results have not necessarily been obtained.

In addition, the colored images of such self-coloring pressure-sensitive recording sheets are unstable to solvents, and are easily decolored by contact with polar solvents, such as plasticizers such as phthalate esters, making it difficult to read the recorded images. It has the following basic problems.

(Objectives of the Invention and Means for Solving the Problems) The present inventors have made extensive studies on a single-layer self-coloring pressure-sensitive recording sheet that is improved in terms of performance, workability, and cost.

As a result, (1) microcapsules having a synthetic resin film containing a dye precursor, (2) an organic color developer (43) pigment, and (4) a polymer latex (with a glass transition point of 60°C or less) were formed on the support. At least one water-soluble vinyl monomer (B) is polymerized in the presence of A), and the solid weight ratio of (A):(B) is 100:5 to 100:200. It has been discovered that a single-layer self-coloring pressure-sensitive recording sheet having a coating layer containing as an essential component a film-forming composition characterized by the following can solve all of the problems of the self-coloring pressure-sensitive recording sheet described above, and the present invention has been made based on the present invention. Reached.

The microcapsules containing the dye precursor used in the present invention are phthalide derivatives such as crystal violet lactone, fluoran derivatives such as 3-diethylamino-6-methyl-7-anilinofluorane, azaphthalide derivatives, etc. Various types of synthesis can be carried out by dissolving 1 to 10 parts by weight of a solution in a high-boiling hydrophobic solvent such as phenylxylylethane, alkylnaphthalene, alkylterphenyl, or hydrogenated terphenyl, which are usually known as carbonless solvents. A general term for anything microencapsulated using a resin film.

Microcapsules for hydrophobic high-boiling solvents using various synthetic resins as membrane materials include (A) interfacial polycondensation method, such as polyamide membrane (acid chloride and amine), polyester membrane, polyurea membrane, polyurethane membrane, etc. Microcapsules, (B) Amino-aldehyde resin membrane microcapsules produced by in-situ polymerization, specifically urea/formaldehyde resin membranes, melamine/
Examples include microcapsules having a formaldehyde resin film.

Preferably, amines obtained by in-situ polymerization are preferred for reasons such as workability during microcapsule production, safety, denseness of microcapsule membranes, or ability to obtain microcapsule slurry with a high solid content concentration. It is preferable to use an aldehyde resin membrane microcapsule slurry.

More preferably, microcapsules with a substantially melamine-formaldehyde resin membrane obtained by an in-3 in-tu polymerization method are used, and among these, the present applicant has disclosed Japanese Patent Application Nos. 59-130867 and 58-136871. The melamine-formaldehyde resin membrane microcapsules proposed in (1) have a low viscosity despite an ultra-high solids concentration, and (2) have excellent dispersion stability with little viscosity change in a wide pH range from acidic to alkaline. (3) It is most preferable because it has an extremely dense wall film and has the best solvent resistance, water resistance, and heat resistance.

Such microcapsules are usually used in the preparation of an aqueous coating solution for producing the pressure-sensitive recording sheet of the present invention by adding the produced microcapsule slurry.

Examples of the color developer used in the present invention include organic or inorganic solid acid substances that develop color by reacting with the colorless to light-colored dye precursors described above.

Examples of the organic color developer include p-substituted phenol formaldehyde resin, metal-modified phenol formaldehyde resin,
Examples include oil-soluble organic solid acids such as salicylic acid derivatives and their polyvalent metal salts. Preferred examples include p-phenylphenol formaldehyde resin, zinc-modified p-
Examples include octylphenol-phenol formaldehyde cocondensation resin, 3,5-di(α-methylbenzyl)salicylic acid or its zinc salt, and these can be used as a wet-milled aqueous suspension in the presence of a dispersant. preferable.

As the inorganic color developer, natural or semi-synthetic inorganic solid acids such as montmorillonite clay minerals, acpardisate clay, activated clay, and acid clay are used. These inorganic solid acids are generally in the form of fine powder.

When producing the sheet of the present invention, it is generally used by suspending and dispersing it in water in the presence of some dispersant.

The amount of these color developers used is generally 10 to 200 parts, preferably 20 to 1 part per 100 parts of microcapsule solid content.
There are 50 copies.

Pigments typically include clays, kaolin, calcined resin, calcium carbonate, titanium oxide, zinc oxide, plastic picment, and the like. The amount of pigment used is generally 20 to 100 parts per 100 parts of the solid content of the microcapsules.

Furthermore, as mentioned above, the film-forming composition, which is an important component of the present invention, contains at least one water-soluble vinyl monomer ( It is obtained by polymerizing B) and is characterized in that the solid weight ratio of (B) to (B) is 100:5 to 100:20. Specifically, such film-forming compositions include SBR, MBRSMSBR, and NBR.

Synthetic rubber latex such as CR, IR and polybutadiene, latex such as vinyl acetate emulsion, vinyl acetate-acrylic emulsion, vinyl acetate-ethylene emulsion and acrylic ester emulsion,
A polymer latex such as vinyl chloride latex or vinylidene chloride latex is used. It is necessary that the glass transition temperature of these polymer latexes is 60°C or lower, and preferably 40°C or lower. In the presence of these polymer latexes, water-soluble vinyl monomers,
For example, nonionic vinyl monomers such as acrylamide, methacrylamide, diacetone acrylamide, vinylpyrrolidone, anionic vinyl monomers such as acrylic acid, methacrylic acid, maleic acid, maleic acid half ester, and crotonic acid. The film-forming composition of the present invention can be obtained by polymerizing one or more cationic vinyl monomers such as dimethylamine ethyl methacrylate and triethylamine ethyl methacrylate.

Regarding the production of the film-forming composition used in the present invention, it is unclear what kind of polymerization behavior the water-soluble monomer component takes in the presence of the latex component; The pressure-resistant and friction-staining properties of pressure-sensitive recording paper are completely different from when a latex polymer is used alone or when a mixture of latex and water-soluble polymer is used.

The amount of film-forming composition used is 10 microcapsule solids.
30 to 100 parts per 0 parts is common.

The film-forming composition used in the present invention has the effect of significantly improving the pressure resistance and friction stain resistance of a single-layer self-coloring pressure-sensitive recording sheet, and also functions as a binder for paints. . The above-mentioned film-forming composition is practically sufficient as a binder for an aqueous coating solution for pressure-sensitive recording sheets, but depending on the composition of the aqueous coating, starch-based binders, polyvinyl alcohol-based binders, and synthetic rubbers may also be used. A water-soluble or water-dispersible binder, which is widely used as an effective binder, such as a latex binder, may be used in combination.

In addition, starch particles or cellulose flocs as a so-called stylte material (buffering agent) can be added in addition to the above essential ingredients, but the amount used is usually based on the microcapsule solid containing the dye precursor. It does not exceed 150 parts per 100 mold parts, and generally 20 to 100 parts.
100 parts are used. Depending on the choice of film-forming material used, it may be possible to eliminate the use of stilt material at all.
A single-layer self-coloring pressure-sensitive recording sheet having sufficient pressure resistance and abrasion resistance can be obtained.

The single-layer self-coloring pressure-sensitive recording sheet of the present invention is prepared by mixing the synthetic resin microcapsules containing the dye precursor described above, an organic color developer, a pigment, and a film-forming composition in the amounts used as described above. If necessary, the above-mentioned stilt material,
Wax components (for example, animal and vegetable waxes, petroleum waxes, synthetic waxes, metal salts of higher fatty acids, amides, esters, etc.), ultraviolet absorbers, antioxidants, dispersants, antifoaming agents, waterproofing agents, etc. Prepare an aqueous coating solution mixed with
It can be obtained by coating and drying to give -209 parts m.

The aqueous coating liquid used for producing the single-layer color-forming pressure-sensitive recording sheet of the present invention can be freely prepared from a low solids content and low viscosity to a high solids content of over 50% by weight. It is possible to use all the methods generally used for producing pressure-sensitive recording sheets, such as air knife coating, bar coating, curtain coating, roll coating, and blade coating.

(Function and Effects of the Invention) The single-layer self-coloring pressure-sensitive copying sheet of the present invention (1) does not require the step of microencapsulating the color developer component and can be used as a commonly used aqueous suspension; (2) Since the dye precursor synthetic resin film capsule with high solid content is used, it is easy to create coatings ranging from low solid content, low viscosity, aqueous coating liquids to high solid water dispersion paints exceeding 5Qwt%, depending on the coating conditions. (3) It is possible to sufficiently prevent contamination caused by slight pressure and friction without necessarily using the steel sheet material that was conventionally required for coating the microcapsule-containing layer. 4) It is possible to retain a substantially sufficient amount of dye precursor and color developer with a small coating amount, and it is possible to obtain superior color development speed and density compared to conventional self-coloring pressure-sensitive recording sheets. (5) The colored image of the obtained pressure-sensitive recording sheet has excellent solvent resistance stability and does not easily fade even when it comes into contact with polar solvents such as phthalate esters. (6) The obtained pressure-sensitive recording sheet It is possible to obtain a single-layer self-coloring pressure-sensitive recording sheet which has significantly superior productivity and quality compared to known self-coloring pressure-sensitive recording sheets, which have extremely low water resistance stability.

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. The performance evaluation method of the resulting single-layer self-coloring pressure-sensitive recording sheet is as follows.

(1) Color development performance 5FM on the self-color development pressure-sensitive recording sheet obtained on each side.
electric typewriter (HERMES)
-808) to develop color by embossing. 1 minute and 2 after color development
The color density after 4 hours was measured using a Hunter colorimeter (manufactured by Toyo Seiki, using an amber filter) and expressed as a reflectance value. The smaller the number, the darker the color is.

(2) Pressure staining property Similar to (1), self-coloring pressure-sensitive recording sheet and 551/n
A static pressure of 10 kg/d was applied to the steel plate using a Mullen rupture tester and held for 1 minute.
The degree of coloring of the coloring layer before and after the test was determined as a difference in reflectance values using a Hunter colorimeter (using an amber filter). The smaller the difference in reflectance before and after the test, the less the tendency for contamination due to capsule destruction due to weak static pressure (stacked weight, winding pressure after coating, etc.).

(3) Friction staining property Using a JIS-L-1048 JIS-L-1048 JIS-type dyed fabric abrasion fastness tester, high-quality paper with a load of 200g was placed on the coated surface of the self-coloring pressure-sensitive recording sheet on each side. Reciprocating rubbing was performed five times, and the degree of coloration (contamination) on the coated surface after one hour was measured using a Hunter colorimeter (amber filter) and expressed as a difference in reflectance values. The smaller the difference between the values before and after the test, the less the capsule is destroyed by friction.

This test is used to determine the degree of contamination caused by friction that occurs during cutting, cutting, and other handling of pressure-sensitive recording sheets on coated paper.

(4) Humid and heat resistance The pressure-sensitive recording sheets on each side were kept in a constant temperature and humidity chamber at 50°C and 95% RH (relative humidity) for 10 hours, and the degree of color contamination due to moist heat before and after the test was measured using a Hunter colorimeter. It was measured and expressed as the difference in reflectance values. The smaller the values before and after the test, the greater the contamination caused by moist heat, especially humidity.

(5) Colored image solvent resistance
It was placed in close contact with a commercially available vinyl chloride film containing 3% n-butyl phthalate as a plasticizer, covered with glass plates on the top and bottom, and then stored in a dark place at 60°C for 8 hours.The remaining color image was observed with the naked eye. I determined it.

Example-1 Phenylxylylethane in which 4% by weight of crystal violet lactone was dissolved (Japan Petrochemical Co., Ltd. HiC/L/
5AS-296) was mixed with 200 parts of a styrene maleic anhydride copolymer aqueous solution with a pH of 5.4,
Emulsification was performed using a high-speed stirrer to obtain an O/W type emulsion.

A melamine-formalin initial condensate prepared by adjusting 20 parts of melamine and 45 parts of 37% formalin to pH 8.5 with caustic soda and heating to 80°C is added to the above emulsion, and the temperature of the system is set to 70'C and reacted for 1 hour to form a dye precursor. Microencapsulated LaIJ-(A) containing the body was obtained. The average particle diameter was 3°5μ.

Example-2 2-acrylamido-2-methylpropanesulfonic acid 0
．． 08 mol, acrylic acid 0.58 monoacrylonyl
- 20% aqueous solution of a terpolymer having a monomer composition of 0.36 mol (viscosity 150 eps at 25°C)
) 30 parts diluted with water, pH 4.5 aqueous solution 111.7
4.0 parts by weight of crystal violet lactone dissolved in alkylnaphthalene (KMC-1 manufactured by Kureha Chemical Co., Ltd.)
13J) Add 130 parts and emulsify with a homomixer to make 1
After 0 minutes, an O/W type emulsion with an average particle size of 3.5 μm was obtained. Next, 36 parts of a methylated methylolmelamine resin aqueous solution (80% non-volatile content) was added to the system with stirring, and the system was heated to 60 parts.
The mixture was heated to 0.degree. C. and fed for 2 hours, and then cooled to complete microencapsulation. To remove residual formaldehyde, add a small amount of 28% aqueous ammonia to adjust the pH to 8.0.
As a result, the formalin odor completely disappeared. The resulting microcapsule slurry had a solids content of 60% and 9
The viscosity was 0 cps (at 25°C).

Example-3 solid content Se.

Turnip rice ru of Example-1 100 parts p
-Phenylphenol resin (40% dispersion) 3
0 parts Wheat starch granules 60 parts Film-forming composition [1 deconvex 0% emulsion] 50 parts Kaolin clay 50 parts Oxidized starch 20% aqueous solution 30 parts *1) Film-forming composition [1] Styrene 30% by weight, methacrylate 30% by weight of methyl acid,
A milky-white emulsion (solid) obtained by polymerizing 40 parts of acrylamide solids and 10 parts of acrylic acid solids per 100 parts of solids of MSBR latex (glass transition point 16°C) consisting of 40% by weight of butadiene. minute 30%
) A water-based paint with a solid content of 25 wt% was created,
A self-coloring pressure-sensitive recording sheet (&) was obtained by coating on a 50 g/7F11 high-quality paper using a Mayer bar coater so that the dry coating amount was sy/rrl.

Example-4 Solid content Capsules of Example-2 100 parts p
-Phenylphenol resin (40% dispersion)
40 parts wheat starch granules 5
0 parts film-forming composition J-] 80
Part calcined kaolin 50 parts Stearic acid amide 20 parts *2) Film-forming composition [■] SBR latex (glass transition point -1°C) Solid content 100
A water-based paint with a solid content of 30% was prepared and had the composition of a milky white emulsion (solid content 4Qwt%) obtained by polymerizing with 15 parts of acrylamide solids and 5 parts of methacrylamide per part.
A self-coloring pressure-sensitive recording sheet (b) was obtained by applying the mixture to a high-quality paper (section m) using an air knife coater so that the dry coating amount was 9 yim.

Example-5 Solid content Capsule of Example-2 100 parts Acidic clay (Mizusawa Kagaku Jiruton) 100 parts Wheat starch granules 40 parts Film-forming composition (Cm) 70 parts Calcium carbonate Solid content having a composition of 20 parts 25 % of water-based paint (NaOH).

Comparative Example-1 Solid content Capsules of Example-2 100 parts p
-Phenylphenol resin
30 parts wheat starch granules 6
0 parts kaolin clay 5
0 parts Oxidized starch 20% aqueous solution 80
A water-based paint with a solid content of 25% having a composition of 50% was prepared.
A self-coloring pressure-sensitive recording sheet was obtained by coating 11 parts of high-quality paper with a Mayer bar coater at a dry coating weight of 8 g/7 FLt.

Comparative Example-2 Solid content Capsules of Example-2 100 parts p
-Phenylphenol resin
30 parts wheat starch granules 6
0 parts calcium carbonate 50
1 part polyvinyl alcohol (10% aqueous solution)
Comparative Example-3 Capsules of Solid Content Example-2 100 parts p
-Phenylphenol resin
30 parts wheat starch particles 6
0 parts calcium carbonate 50
Part SBR latex 40
A water-based paint with a solid content of 25% having a composition of
Part Zn-modified p-octylphenol-phenol
40 parts co-condensed resin (50% Unaguri) Calcined kaolin 5
0 parts calcium stearate 40
Part *3) Film-forming composition Cm) 40% by weight of styrene, 42% by weight of methyl methacrylate,
Acrylic ester latex consisting of 3% by weight of acrylic acid and 15% by weight of butyl acrylate (glass transition point -
1°C) 50 parts of acrylamide was added and polymerized per 100 parts of solid content to create an aqueous coating liquid with a solid content of 5 Q wt% and a milky white viscous emulsion (solid content of 43 wt%). This high-quality water-based paint for self-coloring pressure-sensitive recording sheets does not use large-particle stilt materials such as starch particles, which were conventionally considered essential components of coating fluids for microcapsule-type pressure-sensitive recording sheets. First, it is possible to obtain a self-coloring pressure-sensitive recording paper having sufficient pressure resistance and abrasion resistance stability.

When a blade coater is used with a paint made from styirt material, most of the large particles of styirt material are scraped off by the blade, making it impractical to coat the paint. The water-based paint of this example allows high-speed blade coating, and a significant improvement in productivity is observed.

Comparative Example-4 Microcapsules of Solid Content Example-2 100
Partly calcined kaolin 50
An aqueous coating liquid with a solid content of 50% having a composition of 1 part calcium stearate 40 parts SBR latex 40 parts oxidized starch 20% aqueous solution was prepared and used in Examples.
Similar to step 5, apply a dry coating amount of 7 using a blade coater on high-quality paper.
A self-coloring pressure-sensitive recording sheet was obtained by applying the mixture in an amount of y/rrt. The pressure-sensitive recording sheet of this example was sensitive to pressure and friction and was susceptible to contamination, making it impractical.

Comparative Example 5 A water-based paint with a solid content of 25% having a solid content of 100 parts of kaolin clay, 6 parts of SBR latex, and 9 parts of an oxidized starch aqueous solution was coated with microcapsules obtained by a commercially available gelatin complex near-acervation method. Pressure paper (CCB) was obtained.The pressure-sensitive recording sheet of this example has a microcapsule layer and a color developer layer separated from each other, so it is relatively resistant to contamination due to friction, etc., but the color density is low and it is difficult to use under moist heat conditions. There is a significant tendency for contamination at the bottom.

Comparative Example 6 40 parts of p-phenylphenol resin (RB resin manufactured by Mitsui Toatsu Chemical Co., Ltd.) was heated and dissolved in 60 parts of phenylxylylethane to form an internal phase, which was encapsulated in the same manner as in Example 1.

Solid content Capsules of Example-1 (dye precursor) 100 parts Capsules obtained in this example (color developer) 100 parts Wheat starch granules 500 parts Kaolin clay 60 parts Oxidized starch 20% aqueous solution 100 parts Aqueous with the composition Since the paint used in Example 3 is a mixture of two types of capsules, an extra step of microencapsulating the color developer is required, and the color development performance and stain resistance are not perfect. I can not say.

Table 1 summarizes the performance and evaluation results of the self-coloring pressure-sensitive recording sheets of Examples and Comparative Examples.

Claims (1)

[Scope of Claims] 1) Synthetic resin membrane microcapsules containing (1) a dye precursor, (2) a color developer, (3) a pigment, and (
4) Polymer latex with a glass transition point of 60°C or less (A
) in the presence of at least one water-soluble vinyl monomer (
A coating layer containing as an essential component a film-forming composition obtained by polymerizing B) and characterized in that the solid weight ratio of (A):(B) is 100:5 to 100:200. A single-layer self-coloring pressure-sensitive recording sheet. 2) The microcapsules containing the dye precursor are In-S
The single-layer self-coloring pressure-sensitive recording sheet according to claim 1, which is an aminoaldehyde resin membrane microcapsule prepared by an in-tu polymerization method. 3) The microcapsules containing the dye precursor are In-S
The single-layer self-coloring pressure-sensitive recording sheet according to claim 1 or 2, which is a melamine formaldehyde resin film microcapsule prepared by an in-tu polymerization method.