JPH0453190B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a coating composition for pressure-sensitive copying paper that is improved particularly in terms of color development and color fog. [Prior Art] As pressure-sensitive copying paper called carbonless copying paper, for example, microcapsules containing a coloring agent (hereinafter referred to as "coloring agent microcapsules") are used.
A type in which a color forming agent layer containing a color developer and a color developer layer containing a color developer are formed on the back and front surfaces of two stacked supports (usually paper), or on the surface of a lower support. A type is known in which a recording layer is formed by mixing or laminating a color former microcapsule and a color developer thereon. In such pressure-sensitive copying paper, when mechanical or impact pressure is applied to the surface of the upper support by a writing instrument, a typewriter, or any other type of mechanical printer, the color forming agent is encapsulated. The microcapsules inside the capsules are destroyed, and the color forming agent inside the capsules is exposed and comes into contact with the color developer, thereby developing color and achieving copy recording. Generally, the coating composition for forming the above-mentioned color former layer is composed of color former microcapsules, a protective agent (stilt), a binder, and other additives. The protective agent has the function of preventing the microcapsules from being destroyed by direct exposure to unexpected external forces applied when the purpose is not to copy and record, by being mixed with the color former microcapsules, Usually, they are composed of fine particles of organic or inorganic substances that have a slightly larger particle size than the color former microcapsules. In addition, the binder has the function of binding color former microcapsules, protective agents, and other additives and fixing them to the support. Conventionally, such binders include polyvinyl alcohol, starch, modified starch, carboxymethyl cellulose, Water-soluble polymer compounds such as casein are often used. However, coating compositions using water-soluble polymer compounds as described above as binders have the following problems. Pressure-sensitive copying paper tends to cause so-called color fog. Color-forming fog is caused by the color-forming agent microcapsules being removed by mechanical pressure, frictional force, or heat applied during handling of pressure-sensitive copying paper other than when used for copying and recording purposes, such as during manufacture or storage. This is a phenomenon that is destroyed and produces unnecessary color. One of the reasons why such color fogging tends to occur in coating compositions that use water-soluble polymeric compounds as binders is that, in general, the dried coating film formed by water-soluble polymeric substances is strong, but It is thought that this is because the paint film lacks elasticity, and therefore the external force applied to the paint film is not absorbed but is directly transmitted to and acts on the color former microcapsules. Poor shelf life. Water-soluble polymer compounds are easily perishable, and therefore it is difficult to store coating compositions for long periods without deterioration. Poor coatability. Binders using water-soluble polymer compounds have high viscosity, making it difficult to perform coating operations efficiently and smoothly.Additionally, in order to obtain excellent coating properties, the solids content in the coating composition must be reduced. This results in the inconvenience of having to be made smaller. From the point of view of solving the problem of coloring fog mentioned above, it is effective to increase the content ratio of the protective agent. The color former capsule becomes difficult to be destroyed even by external forces such as, and as a result, a problem arises in that the color density of the pressure-sensitive copying paper decreases. In order to solve these problems, a coating composition for pressure-sensitive copying paper using an acrylic ester polymer latex instead of a water-soluble polymer compound (Japanese Patent Application Laid-open No. 72891/1989) Publications) and those using latex (Japanese Patent Application Laid-open No. 57-77589
No. 2) has been proposed. In these coating compositions, since latex is used as a binder, sufficient improvements were seen in the above-mentioned storage stability and coating properties, but the results are still quite satisfactory in terms of the above-mentioned color fogging. has not been obtained. [Problems to be Solved by the Invention] The present invention comprehensively solves the problems of the prior art in terms of color fogging, storage stability, and coating properties, and in particular, provides color former microcapsules while maintaining excellent color performance. It is an object of the present invention to provide a coating composition for pressure-sensitive copying paper that can form pressure-sensitive copying paper in which the occurrence of colored fog due to unnecessary destruction of color is sufficiently suppressed. [Means for solving the problem] The above problem is solved by: In a coating composition for pressure-sensitive copying paper containing microcapsules encapsulating a coloring agent and a binder, the following monomer components are used as the binder component. (a) Aliphatic conjugated diene 2-30% by weight (b) Ethylenically unsaturated carboxylic acid ester
5-70% by weight (c) Ethylenically unsaturated compounds other than (b)
The copolymer latex contains a copolymer latex obtained by emulsion copolymerization of 10 to 93% by weight, and the content of the emulsifier in the copolymer latex is 1% by weight or less based on the copolymer components. The problem is solved by a coating composition for pressure-sensitive copying paper. That is, the coating composition for pressure-sensitive copying paper of the present invention is produced by emulsion polymerization of a monomer composition containing an aliphatic conjugated diene and an ethylenically unsaturated carboxylic acid ester in a specific proportion. The resulting emulsifier content is 1% to the copolymer component.
It is constructed by dispersing color former microcapsules, a protective agent, and other additives as necessary in a binder containing a copolymer latex in an amount of % by weight or less. The present invention will be explained in detail below. Examples of aliphatic conjugated dienes that can be used in the production of the copolymer latex of the present invention include butadiene, isoprene, 2-chloro-1,
Examples include 3-butadiene, and butadiene is particularly preferred. The amount of aliphatic conjugated diene used is 2 to 30% by weight, preferably 5 to 20% by weight, based on the total monomer components. If the amount used is less than 2% by weight, the color development in pressure-sensitive copying paper will be insufficient, while if the amount used exceeds 30% by weight,
Color fogging due to friction or heating on the pressure-sensitive copying paper is likely to occur, both of which are undesirable. Examples of ethylenically unsaturated carboxylic acid esters that can be used in the production of the copolymer latex of the present invention include methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and acrylic acid. Mention may be made of hydroxyethyl, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, in particular butyl acrylate, 2-ethylhexyl acrylate, methacrylate. Butyl methacrylate and 2-ethylhexyl methacrylate are preferred. The amount of the ethylenically unsaturated carboxylic acid ester used is 5 to 70% by weight, preferably 10 to 60% by weight based on the total monomer components. This usage amount is 5% by weight.
When the amount is less than 70% by weight, color fogging is likely to occur due to heating, while when the amount used exceeds 70% by weight, color fogging due to pressure or friction is likely to occur, both of which are unfavorable. Examples of ethylenically unsaturated compounds other than ethylenically unsaturated carboxylic acid esters that can be used in the synthesis of the copolymer latex of the present invention include monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and methacrotonic acid; acids, dicarboxylic acids such as maleic acid and fumaric acid, and unsaturated carboxylic acids such as anhydrides of these dicarboxylic acids, aromatic vinyls such as styrene, α-methylstyrene, and vinyltoluene, acrylamide,
Examples include alkylamides of unsaturated carboxylic acids such as methacrylamide and N-methylolacrylamide, vinyl cyanides such as acrylonitrile, and vinyl acetate, which may be used singly or in combination.
More than one species can be used in combination. The copolymer latex in the present invention is produced by emulsion polymerization, and is used to emulsify and disperse monomers during emulsion polymerization or to stably disperse copolymer particles generated after emulsion polymerization. Contains emulsifiers used in As such emulsifiers, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, and the like may be used alone or in combination of two or more. Preferred emulsifiers are anionic surfactants, such as sodium lauryl sulfate,
Sodium dodecylbenzenesulfonate, sodium laurylnaphthalenesulfonate, sodium dialkylsulfosuccinate, etc. alone or in combination
More than one species can be used in combination. In the present invention, the emulsifier content in the copolymer latex is 1% by weight based on the copolymer components.
It is preferably 0.5% by weight or less. If the content of the emulsifier exceeds 1% by weight, the coloring properties of the pressure-sensitive copying paper will be low. In particular, when using gelatin microcapsules synthesized by the coacervation method as color former microcapsules, the color former inside the capsules may be extracted by the surfactant because the gelatin membrane has low resistance to surfactants. The content of the emulsifier is preferably 0.4% by weight or less, since this tends to cause color fog. The glass transition temperature of the copolymer constituting the copolymer latex in the present invention is preferably -50°C.
-30°C, more preferably -40°C - 25°C. If the glass transition temperature is lower than -50 DEG C., the elasticity of the binder tends to become excessive, resulting in a decrease in the coloring properties of the pressure-sensitive copying paper, which is undesirable. On the other hand, if the glass transition temperature exceeds 30°C, color fogging due to heating tends to occur, which is not preferable. The toluene insoluble content of the copolymer constituting the copolymer latex of the present invention is preferably 30% by weight or more, particularly preferably 40 to 100% by weight.
If the toluene-insoluble content is less than 30% by weight, the color development of the pressure-sensitive copying paper tends to decrease, which is not preferable. The toluene-insoluble content here refers to copolymer latex adjusted to pH 6 to 8 with sodium hydroxide, coagulated with methanol, further washed and dried, and 0.3 of the coagulated product obtained is taken as a sample. This refers to the ratio of insoluble matter to the total sample obtained when a sample is immersed in 100 ml of toluene for 20 hours. The amount of copolymer latex used in the present invention is calculated based on the copolymer component.
It is preferably 3 to 50 parts by weight, more preferably 5 to 40 parts by weight per 100 parts by weight. If the amount of copolymer latex used is less than 3 parts by weight, the adhesive strength of the coating composition will be insufficient;
If the amount exceeds parts by weight, the microcapsules in the coating layer will be thickly covered with the copolymer component.
As a result, the color development in pressure-sensitive copying paper is reduced. The copolymer latex used in the present invention preferably satisfies either one of the above-mentioned conditions regarding glass transition temperature and toluene insoluble content, preferably both. The color former microcapsules used in the present invention can be produced by various methods such as coacervation method, interfacial polymerization method, and in situ polymerization method, which will be specifically described below. Coacelvation method As disclosed in, for example, U.S. Pat. emulsify and disperse the hydrophilic polymer colloid in the form of minute oil droplets in an aqueous solution, phase-separate (coacervate) the colloid of the hydrophilic polymer on the surface of the minute oil droplets, and harden it to form a wall film;
Microcapsules are obtained. Interfacial polymerization method This method is described in, for example, Japanese Patent Publication No. 44-27257,
Publication No. 42-771, Publication No. 46-18127, Publication No. 50-
As disclosed in Publication No. 72507, two types of substances that react with each other to form an insoluble film at the interface of a hydrophilic liquid and a hydrophobic liquid are dissolved in a hydrophilic liquid and a hydrophobic liquid, respectively, and then the interface is formed. By reacting, microcapsules composed of, for example, a polyamide capsule wall membrane are obtained. In situ polymerization method This method, as disclosed in Japanese Patent Publication No. 44-3495, combines a core material (oil droplets containing a coloring agent) with a reactant, i.e., monomers, prepolymers, or catalysts necessary to form a polymer. By performing polymerization in a dispersion system in which reactive components such as Microcapsules are obtained by forming a polymer outer shell. According to this method, the capsule wall membrane is melamine-
Microcapsules made of formalin resin, urea-formalin resin, etc. can be obtained. Microcapsules made with a wall film such as melamine-formalin resin or urea-formalin resin produced by such an in situ method have excellent heat resistance, solvent resistance, water resistance, and chemical resistance, and are easy to process. Therefore, since it can be stably produced, it can be advantageously used as the color former microcapsule in the present invention. The coloring agent constituting the coloring agent microcapsules may be any commonly used coloring agent, such as crystal violet lactone, benzoylleucomethylene blue, fluorans, spiropyrans, and the like. In addition, as a color developer to develop a color by contacting this color former, for example, an inorganic color developer such as acid clay or activated clay, or an organic color developer such as a phenolic resin or a salicylic acid derivative salt is used. can do. The protective agent used in the present invention may be any commonly used protective agent, such as starch,
Powders of organic or inorganic substances such as cellulose are used, and the amount used is generally 20 to 80 parts by weight per 100 parts by weight of color former microcapsules. In the present invention, various additives such as an antifoaming agent and a waterproofing agent can be further included as necessary. In addition to the copolymer latex used in the present invention, as a binder, water-soluble polymers such as water-soluble modified starch, polyvinyl alcohol, hydroxyethyl cellulose, etc. may be used in combination as necessary to supplement adhesive strength. can. The coating composition of the present invention is prepared by mixing the above-mentioned various materials, and the solid content in the coating composition is generally in a concentration of 15 to 50% by weight. This coating composition is coated onto the base paper using an on-machine coater equipped with coating equipment such as a blade coater, air knife coater, bar coater, roll coater, and size press coater, which are commonly used in coated paper manufacturing. It is called pressure-sensitive copy paper. The preferred coating amount of the coating composition of the present invention is 2 to 5 g/m ² per unit area of base paper.
It is. As the base paper, high quality base paper, medium quality base paper, etc. obtained by acidic or alkaline paper making can be used. [Examples] Examples of the present invention will be described below, but the present invention is not limited thereto. In the following description, "parts" and "%" indicate parts by weight and % by weight, respectively. Examples 1 to 7, Comparative Examples 1 to 5 (1) Production of copolymer latexes A to K <Copolymer latex A> 160 parts of water, 0.2 parts of sodium dodecylbenzenesulfonate, 0.6 parts of sodium hydrogen carbonate, and persulfuric acid 0.5 part of potassium was charged into a 100 volume autoclave. Next, 15 parts of butadiene, styrene
A monomer composition consisting of 62 parts of butyl acrylate, 20 parts of acrylic acid, and 2 parts of fumaric acid was added all at once with 2 parts of carbon tetrachloride, and the mixture was heated to 70 parts with stirring.
Warmed to ℃. When polymerization was continued in this state for 20 hours, the polymerization conversion rate reached 100%. The copolymer latex thus obtained had a good polymerization pattern and little coagulation. Adding sodium hydroxide solution to this copolymer latex,
After adjusting the pH to 9, monomer stripping,
The latex was concentrated by vacuum distillation. The obtained copolymer latex is referred to as "latex A". <Copolymer Latexes B to K> Nine types of copolymer latexes were obtained in the same manner as in Copolymer Latex A using the monomer components shown in Table 1. These copolymer latexes are referred to as "latexes B to K." Latexes G to K are comparative latexes, and latex G is aliphatic conjugated diene ((a)).
Latex H contains too much aliphatic conjugated diene ((a)); latex J contains too little ethylenically unsaturated carboxylic acid ester ((b)); If the proportion of unsaturated carboxylic acid ester ((b)) is excessive,
Lattesk K is an example of a case where the proportion of emulsifier is excessive. The glass transition temperature (Tg) and toluene insoluble content of the above latte skus A to K are also listed in Table 1.

【table】

[Table] (2) Synthesis of color former microcapsules A color former solution prepared by dissolving 3.5 parts of crystal violet lactone in 100 parts of organic solvent "SAS296" (manufactured by Nisseki Co., Ltd.) was mixed with styrene-maleic anhydride copolymer. It was added to an aqueous solution containing 4 parts of the combined product and emulsified. Next, 60 parts of an aqueous solution of melamine-formalin initial condensate "SR613" (manufactured by Sumitomo Chemical Co., Ltd.) with a solid content of 15% was added, and the mixture was heated to 70°C and reacted for 3 hours. Next, an aqueous solution of sodium hydroxide was added to this reaction product solution until the pH reached 9.0 to prepare a dispersion of color former microcapsules. The average particle size of the microcapsules was 4.5 μm. (3) Preparation of coating composition Using the copolymer latex and color former microcapsules obtained as above, each material having the composition shown in Table 2 was mixed to prepare a coating composition with a solid content of 35%. Seven types of Examples and five types of Comparative Examples were prepared. (4) Characteristic test Each of the coating compositions obtained in (3) above was applied to base paper using a rod at a coating amount of 3.0 g/m ² to obtain top paper for pressure-sensitive copying paper. Ta. These top paper and commercially available bottom paper “ccp” (manufactured by Jujo Paper Co., Ltd.)
A sample of pressure-sensitive copying paper was formed by overlapping each of the above, and the following four items were tested. Color development Each sample was printed using a typewriter,
After 30 minutes, the color density of the lower paper was measured using a Hunter colorimeter, and the whiteness (%) was determined, thereby evaluating the color development. The smaller the whiteness value, the better the color development. Pressure Resistance (Color Fog Occurrence Due to Pressure) After each sample was pressurized at a pressure of 50 kg/cm ² for 5 minutes, the whiteness of the lower paper was measured using a Hunter colorimeter. The larger the whiteness value, the less color fog occurs and the better the pressure resistance. Friction resistance (state of color fogging caused by friction) Place the bottom paper of each sample on top, place a weight of 3 kg on top of it, and hold it at a certain distance (30 cm).
After sliding across the paper, the whiteness of the bottom paper was measured using a Hunter colorimeter. The larger the whiteness value, the less color fog occurs and the better the abrasion resistance. Heat resistance Each sample was placed in an oven set at 120℃ for 3
After heating for a period of time, the whiteness of the bottom paper was measured by a Hunter colorimeter. The larger the whiteness value, the less color fog occurs and the better the heat resistance. The results of the above characteristic tests are shown in Table 2.

〔Effect of the invention〕

In the coating composition for pressure-sensitive copying paper of the present invention, the content of an emulsifier obtained by emulsion polymerization of a monomer composition containing a specific monomer component in a specific ratio as a binder is higher than that of the copolymer component. The copolymer latex is used in an amount of 1% by weight or less, and has the following effects. (1) Excellent coating properties. The coating composition of the present invention uses a copolymer latex as a binder, and does not require the use of a water-soluble polymer compound with high viscosity, or even if it is used, only a small amount thereof is used. Coating work can be carried out smoothly. Further, for the same reason, it is possible to increase the solid content concentration of the coating composition while maintaining good coating properties, which is advantageous in terms of coating productivity. (2) Excellent storage stability. The coating composition of the present invention uses a copolymer latex as a binder, and does not require the use of perishable water-soluble polymer compounds, or even if it is used, only a small amount is used, so it has good storage stability and long-lasting properties. There is no deterioration in quality over a period of time. (3) Pressure-sensitive copying paper with excellent color development and color fog can be obtained. Since the coating composition of the present invention uses a copolymer latex as a binder, it can impart appropriate elasticity to the coating film (coloring agent layer), and as a result, it has an effect on pressure-sensitive copying paper even when not in use. External forces such as relatively small pressing force, frictional force, which naturally or accidentally act during manufacturing, storage, etc.
It can sufficiently absorb thermal stress and weaken the force acting on the coloring agent capsule, effectively preventing the occurrence of coloring fog without interfering with the coloring function during use. be able to.

Claims (1)

[Scope of Claims] 1. A coating composition for pressure-sensitive copying paper containing microcapsules encapsulating a coloring agent and a binder, wherein the binder comprises the following monomer components (a) an aliphatic conjugated diene 2-30 Weight% (b) Thylenic unsaturated carboxylic acid ester
5-70% by weight (c) Ethylenically unsaturated compounds other than (b)
The copolymer latex contains a copolymer latex obtained by emulsion copolymerization of 10 to 93% by weight, and the content of the emulsifier in the copolymer latex is 1% by weight or less based on the copolymer components. A coating composition for pressure-sensitive copying paper. 2. The coating composition for pressure-sensitive copying paper according to claim 1, wherein the copolymer component in the copolymer latex has a glass transition temperature in the range of -50°C to +30°C. 3. The coating composition for pressure-sensitive copying paper according to claim 1, wherein the toluene-insoluble content of the copolymer component in the copolymer latex is 30% by weight or more.