JPH051149B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a coating composition for pressure-sensitive recording paper having a coating layer of microcapsules, and more specifically to a coating composition for pressure-sensitive recording paper that has improved color development and staining properties. It is about things. (Prior art) Pressure-sensitive recording paper usually consists of an upper paper coated with microcapsules containing an electron-donating colorless leuco dye and an organic solvent on the back side, and an electron-accepting color developer that reacts with the colorless leuco dye to develop color. The microcapsules are destroyed by printing under pressure with a ballpoint pen, typewriter, etc. from the top paper with each coated side facing each other.
The colorless leuco dye in the microcapsules moves to the lower paper together with the organic solvent and reacts with the color developer to form a colored recorded image on the coated surface of the lower paper. It is also possible to make multiple copies by inserting an inner paper having a color developer layer on the surface and a microcapsule layer on the surface between the upper paper and the lower paper. Furthermore, as another form, there is also a sheet called a single coloring paper in which both the above-mentioned microcapsules and color developer are coated on the same side of the sheet. In addition, as a special example, the color developer may be contained in microcapsules. The pressure-sensitive recording paper having a coating layer of microcapsules as referred to in the present invention refers to
The pressure-sensitive recording paper includes all sheet-like materials containing microcapsules. Pressure-sensitive recording paper has shown remarkable growth in demand in recent years, and demands for its quality have also become more sophisticated. The core technology of pressure-sensitive recording paper is the microencapsulation method, and its characteristics greatly influence the performance of pressure-sensitive recording paper. If the microcapsule wall membrane is incomplete or lacks strength, the microcapsules will be destroyed during the manufacturing process, processing steps such as printing and form-making, or during transportation and storage, resulting in contamination. An important characteristic of pressure-sensitive recording sheets is that they form clear colored images when pressurized with a ballpoint pen, typewriter, etc., and that they do not cause color contamination due to unintended pressure during manufacturing, processing, transportation, or storage. It is. Furthermore, it is necessary that the surface strength is such that it does not cause staining when exposed to water or heat, and that it does not cause blanket staining or picking during printing on the surface coated with microcapsules. Conventionally, the core cell pacification method using gelatin has been used to microencapsulate pressure-sensitive recording paper, but in recent years, interfacial polymerization microcapsules with a film of polyurethane, polyurea, etc., or melamine-formalin resin or urea-formalin resin have been used. Synthetic polymer microcapsules such as in-situ microcapsules with resin membranes have also been put into practical use. Conventionally, polyvinyl alcohol,
Water-soluble polymers such as (modified) starch, dextrin, carboxymethylcellulose, and casein have been used. The binder has the role of binding the microcapsules to the support, and also has the function of protecting the microcapsules themselves from external pressure and preventing color staining. but,
Since the water-soluble polymer itself has poor elasticity, its microcapsule protection function was insufficient. Increasing the thickness of the microcapsule film or increasing the amount of binder for the purpose of preventing color staining is undesirable because the color development deteriorates. JP-A-57-72891 and JP-A-57-77589 also disclose a method of protecting the microcapsule membrane by adding an acrylic ester polymer or an ethylene-vinyl acetate copolymer to the microcapsule coating liquid. Although these additives have been proposed, their adhesive strength is insufficient and it is not possible to sufficiently achieve both color development and prevention of color development stains. (Problems to be Solved by the Invention) An object of the present invention is to provide a coating composition for pressure-sensitive recording paper that prevents color staining and has a coating layer of microcapsules with excellent color development. (Means for Solving the Problems) An object of the present invention is to provide a coating composition for pressure-sensitive recording paper having a coating layer of microcapsules, comprising 20% by weight or more of an aliphatic conjugated diolefin monomer. 70
% by weight or less, ethylenically unsaturated acid monomers from 0.5% to less than 5% by weight, and other olefinic monomers copolymerizable with these from more than 25% to 79.5% by weight, and This is achieved by using a coating composition containing a copolymer latex having a gel content of 40% to 90% by weight as a binder for the microcapsules. (Effects of the Invention) Thus, by using the coating composition of the present invention, it is possible to obtain a pressure-sensitive recording paper having a coating layer of microcapsules with extremely little color staining and excellent color development. Further, by using the coating composition of the present invention, a microcapsule coating liquid with high concentration and low viscosity can be obtained, and there is also the advantage that the surface strength required during printing is improved. The copolymer latex used as a binder for microcapsules used in the present invention will be explained below. Examples of aliphatic conjugated diolefin monomers include 1,3-butadiene, 2-methyl-1,3-
Examples include butadiene, 2,3-dimethyl-1,3-butadiene, and halogen-substituted butadiene. The content of the aliphatic conjugated diolefin monomer in the copolymer is 20% by weight or more and 70% by weight or less. If it is less than 20% by weight, the color staining property will be poor, and if it exceeds 70% by weight, the coloring property will decrease. do. The content is preferably 30% by weight or more and 65% by weight or less, and more preferably 40% by weight or more and 60% by weight or less. Ethylenically unsaturated acid monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, butenetricarboxylic acid; itaconic acid monoethyl ester, fumaric acid, etc. acid monobutyl ester,
Examples include monoalkyl esters of unsaturated dicarboxylic acids such as monobutyl maleate; unsaturated sulfonic acids or alkali salts thereof such as sulfoethyl acrylate Na salt, sulfobrovir methacrylate Na salt, and acrylamide propane sulfonic acid. The content of ethylenically unsaturated acid monomer in the copolymer is 0.5% by weight or more to 5% by weight
If the amount is less than 0.5% by weight, the coloring property and surface strength will decrease, and if it is 5% by weight or more, the coloring staining property will be reduced. Preferably 1% by weight or more
It is 4.5% by weight or less. Furthermore, other olefinic monomers copolymerizable with the aliphatic conjugated diolefinic monomer and ethylenically unsaturated acid monomer include, for example, styrene, α-methylstyrene, monochlorostyrene, and vinyltoluene. Aromatic vinyl compounds such as;
Alkyl esters of acrylic acid and methacrylic acid such as methyl acrylate, methyl methacrylate, ethyl acrylate, and butyl acrylate; ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; and also β-acrylic acid.
-Hydroxyethyl, acrylamide, methacrylamide, N-methylol acrylamide, diacetone acrylamide, glycidyl acrylate,
Examples include glycidyl methacrylate, acrolein, allyl alcohol, divinylbenzene, diallyl phthalate, diallyl maleate, triallyl cyanurate, ethylene glycol dimethacrylate, and allyl acrylate. The copolymer latex used in the present invention not only has the above monomer composition but also has a gel content.
The object of the present invention cannot be achieved unless the content is 40% by weight or more and 90% by weight or less. If the amount of gel is less than 40% by weight, the coloring property will be lowered and the coloring staining property will also be lowered.
Moreover, if it exceeds 90% by weight, the color staining property decreases.
Preferably it is 60% by weight or more and 90% by weight or less. The amount of gel in the copolymer latex used in the present invention can be controlled by using a molecular weight regulator that is commonly used in emulsion polymerization. Examples of molecular weight regulators include octylmercabutane, n
-Mercabutanes such as dodecylmercabutane, t-dodecylmercabutane, and n-tetradecylmercabutane; halogenated hydrocarbons such as carbon tetrachloride, carbon tetrabromide, methylene chloride, and methylene bromide; dimethylxanthogen disulfide , xanthogenic acids such as diisopropylxanthogen disulfide, and the like. Furthermore, as a method for regulating the amount of gel, methods such as regulating the reaction temperature and the conversion rate at the end of the polymerization reaction can be used. In addition, in the present invention, the average particle size of the copolymer latex is preferably 0.08μ or more in order to enhance the effect.
More preferably, it is 0.1μ or more. The method for producing the above-mentioned copolymer latex itself is not particularly limited in the present invention, and for example, known emulsion polymerization methods such as batch emulsion polymerization and continuous emulsion polymerization can be employed, and in this case, various known emulsifiers, Various additives used in general emulsion polymerization, such as polymerization initiators, chelating agents, and electrolytes, can be used, and the polymerization temperature can be selected from either high or low temperatures. Furthermore, known PH regulators, dispersants, preservatives, etc. may be added to the copolymer latex after completion of polymerization. A method for producing microcapsules for pressure-sensitive recording paper is well known, and microcapsules prepared using a known method for producing microcapsules can also be used in the present invention. It is known that a coating composition for pressure-sensitive recording paper contains a buffer material together with microcapsules. As the buffering material, generally used are microcapsules, large starch granules, cellulose powder, inorganic powder, and the like. In the present invention, the copolymer latex has the function of binding the microcapsules as well as the cushioning material onto the support sheet. The copolymer latex of the present invention is preferably blended in a proportion of 5 parts by weight or more and 50 parts by weight or less (solid content) per 100 parts by weight (solid content) of the microcapsules. It is effective to use other binders as mentioned above together with the copolymer latex as long as it does not impede the effects of the present invention. Furthermore, various additives such as antifoaming agents, preservatives, and thickeners can be added as necessary. Typically, the microcapsule coating solution is coated onto a support sheet at 2 to 7 gr/m ² (solids content). The coating method is not particularly limited. The present invention will be explained in more detail with reference to Examples below. Note that parts and percentages in Examples and Comparative Examples are based on weight unless otherwise specified. Example 1 Water, emulsifier,
The first along with an inorganic salt, a chelating agent and a polymerization initiator.
The monomers and molecular weight regulator shown in the table were charged, and polymerization was carried out at 60° C. for 15 hours with rotational mixing. The conversion rates reached 95% or higher in all cases. The obtained copolymer latex was cooled with water to remove unreacted monomers, and then the pH of the latex was adjusted to 7 with NaOH. The gel amounts of these latexes are also listed in Table 1. Here, the gel content was measured as follows. Pour the sample latex onto a glass plate with a frame so that the dry thickness is 0.2 mm, and heat it at 20℃ and 65%.
Leave it under constant temperature and humidity at RH for 48 hours to create a dry film. Next, this film is divided into 2 mm squares, 0.5 gr of them are precisely weighed, placed in a cylinder made of 100 mesh stainless wire gauze, and immersed in 100 ml of tetrahydrofuran at room temperature for 24 hours. Thereafter, the wire mesh was taken out, dried in a vacuum dryer for 24 hours, and then accurately weighed to determine the weight of the undissolved matter.The weight percentage of the original copolymer film was calculated as the gel amount. The results are also listed in Table 1.

[Table] Microcapsule dispersion for pressure-sensitive recording paper whose wall is a melamine-formalin resin film containing a high-boiling hydrocarbon oil in which crystal violet lactone, which is a colorless leuco dye, is dissolved, the above-mentioned copolymer latex, and A microcapsule coating liquid was prepared using starch granules as a buffer material in the proportions shown below so that the total solids concentration was 20%. Microcapsules 100 parts by weight (solid content) Starch granules 35 parts by weight (solid content) Copolymer latex 20 parts by weight (solid content) The resulting microcapsule coating liquid was applied to a 40gr/ ^m2 base paper in an amount of 4gr/m2. ² and dried to obtain pressure-sensitive recording paper. The resulting upper paper was tested for color development and color stain resistance using the following methods. Color development Layer the obtained top paper and commercially available bottom paper,
The reflectance of the printed material using an electric typewriter was measured, and the degree of color development (%) was determined using the following formula. Coloring degree (%) = Reflectance before printing (%) - Reflectance after printing (%) / Reflectance before printing (%) Color staining property Place the top paper on top of the bottom paper so that the color develops.
Place a 3Kg weight on top of the bottom paper and place it on top of the top paper.
The paper was slid for 50 cm, the reflectance of the lower paper was measured, and the color staining property (%) was calculated using the following formula. Color staining property (%) = Reflectance before staining (%) - Reflectance after staining (%) / Reflectance before staining (%) Coating composition of the present invention using copolymer latexes a to e as a binder Table 3 shows the results of the above tests performed on the upper sheets A to E using the above-mentioned materials. Comparative Example 1 A copolymer latex was prepared in the same manner as in Example 1 using the monomers and molecular weight modifiers shown in Table 2. A top paper was prepared in the same manner as in Example 1 using these copolymer latexes as a binder. The test results are shown in Table 3.

[Table] Comparative Example 2 A top paper was prepared in the same manner as in Example 1 using a commercially available acrylic ester copolymer latex (Nipol Lx852 manufactured by Nippon Zeon) as a binder. The test results are shown in Table 3. Comparative Example 3 A top paper was prepared in the same manner as in Example 1 using a commercially available ethylene vinyl acetate latex (Kuraray OM-4000 manufactured by Kuraray Co., Ltd.) as a binder. The test results are shown in Table 3.

【table】

[Table] As shown in Table 3, the examples of the present invention had excellent color development and little color staining. Comparative example 1-2, 1
-3, 1-4, and Comparative Example 3 had poor color development, and Comparative Examples 1-1, 1-3, 1-4, 1-5, and 1
-6 and Comparative Examples 2 and 3 had poor color staining properties.

Claims (1)

[Claims] 1. A coating composition for pressure-sensitive recording paper having a coating layer of microcapsules, comprising 20% by weight or more and 70% by weight or less of an aliphatic conjugated diolefin monomer, and 0.5% by weight of an ethylenically unsaturated acid monomer. % to less than 5% by weight, and other olefinic monomers copolymerizable with these from more than 25% to 79.5% by weight, and the gel amount is from 40% to 90% by weight. A coating composition for pressure-sensitive recording paper, comprising a copolymer latex as a binder.