JPS61280985A - Coating composition for pressure-sensitive recording paper - Google Patents

Abstract

PURPOSE:To prevent contamination due to a developed color and to provide a microcapsule coating layer excellent in color developability, by using a coating composition containing a microcapsule comprising specific copolymer latex as a binder. CONSTITUTION:The titled coating composition is constituted of a dispersion of a microcapsule for pressure-sensitive recording paper including high b.p. hydrocarbon oil having Crystal Violet lactone being a leuco dye dissolved therein and having a melamine formaldehyde resin film as a wall film, 20-70wt% of an aliphatic conjugated diolefin, 0.5-5wt% of an ethylenic unsaturated acid monomer and 25-79.5wt% of other olefinic monomer copolymerizable with the above-mentioned components and prepared so as to adjust the total solid component of the latex of the copolymer of which the gel amount is 40-90wt% and starch particles as a buffer material to 20%. Thus obtained microcapsule coating solution is applied to base paper and dried to obtain pressure-sensitive recording paper.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coating composition for pressure-sensitive recording paper having a coating layer of microcapsules. The present invention relates to a coating composition for pressure recording paper.

(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, and the colorless leuco dye in the microcapsules is destroyed by printing under pressure with a ballpoint pen or tie writer from above the upper paper with each coated surface facing each other. 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 sheet with a color developer layer on the front side and a microcapsule layer on the back side between the upper sheet and the lower sheet. 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 used in the present invention includes all sheet-like materials containing microcapsules, regardless of their form or inclusions.

Pressure-sensitive recording paper has shown remarkable growth in demand in recent years, and demands for its quality have also become more sophisticated.

In pressure-sensitive recording paper, the core of the seven technologies is the microencapsulation method, and its characteristics greatly improve the performance of pressure-sensitive recording paper. If the microcapsules are thick or lack 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.

Pressure-sensitive recording sheets should not only form a clear colored image when pressurized with a ballpoint pen or typewriter, but also should not cause color contamination due to unintended pressure during the manufacturing process, processing process, transportation, or storage. is an important property 0
Furthermore, it is necessary to have a surface strength that does not cause staining when exposed to water or heat, and does not cause blanket stains or piping when printing on the surface coated with microcapsules. The core-cell-pecking method using gelatin has been used for microencapsulation, but in recent years, interfacial microcapsules with a film of polyurethane or polyurea, or microcapsules with a film of melamine-formalin resin or urea-formalin resin have been used. Synthetic polymer microcapsules such as 1n-situ method microcapsules have also been put into practical use.

Conventionally, water-soluble polymers such as polyvinyl alcohol, (modified) dengue, dextrin, carboxymethyA, cellulose, and casein have been used as binders that bind the microcapsules prepared by the above method to the support sheet. It has been used. The binder has the role of binding the microcapsules to the support, as well as protecting the microcapsules themselves from external pressure and preventing color staining. However, the above water-soluble polymers themselves have elasticity. Due to the lack of properties, the microcapsule protection function was insufficient. In order to prevent color development contamination, the thickness of the microcapsule film is increased, and if the amount of binder is increased, the color development property decreases, which is undesirable.
Publication No. 589 also proposes a method of protecting the microcapsule membrane by adding an acrylic ester polymer or an ethylene vinegar-based copolymer to the microcapsule coating liquid, but these additives have poor adhesive strength. This is insufficient, and it is not possible to achieve both color development and prevention of color development stains.

[Problem that the invention seeks to solve]

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 that exhibits excellent color development.

(Means for Solving the Problems) It is an object of the present invention to provide a pressure-sensitive recording paper having a coating layer of microcapsules containing 20 to 70 aliphatic conjugated diolefin monomers, an ethylenically unsaturated Acid monomer α5~
A copolymer latex composed of 25 to 79.5% by weight of 5-fold violet and other olefinic monomers copolymerizable with these and having a gel amount of 40 to 90% by weight is used as a binder for microcapsules. This is achieved by using a coating composition comprising:

(Effects of the Invention) Thus, by using the coating composition of the present invention, it is possible to obtain pressure-sensitive recording paper having a coating layer of microcapsules with extremely little coloring staining (and excellent coloring properties). can.

Further, by using the copolymer latex of the present invention, a microcapsule coating liquid with high concentration and low viscosity can be obtained, which also has the advantage of improving the surface strength required during printing.

The copolymer latex used as a binder for microcapsules used in the present invention is explained below:
Examples include 2-methyl-1,3-7'tadiene, 2,5-dimethyl-1,3-butadiene, and halogen-substituted butadiene. The content of the aliphatic conjugated diolefin monomer in the copolymer is 20 to 70% by weight, and 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. Preferably it is 30 to 65% by weight, more preferably 40 to 60% by weight.

Ethylenically unsaturated acid monomers include acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, unsaturated carboxylic acids such as fumaric acid, maleic acid, and butenetricarboxylic acid; monoethyl itaconate. Monoalkyl esters of unsaturated dicarboxylic powders such as esters, motsubutyl fumarate, and monobutyl maleates; unsaturated sulfonic acids or their alkali salts such as sulfonityl acrylate Na salt, sulfoglopyru methacrylate NIL salt, acrylamide propane sulfonic acid, etc. The content of ethylenically unsaturated acid monomer in the zero copolymer is 15 to 5''xi, and if it is less than α5 weight, the coloring property will be decreased and the surface strength will be decreased. When the weight exceeds the weight, the color staining property decreases.Preferably 1 to 4.5
Heavy ◎Furthermore, the remaining olefin monomers that can be copolymerized with the above aliphatic conjugated diolefin monomers and ethylenically unsaturated acid monomers include styrene, α-methylstyrene, etc. , aromatic vinyl compounds such as monochlorostyrene and vinyltoluene; methyl acrylate,
Alkyl esters of acrylic acid and methacrylic acid such as methyl methacrylate, ethyl acrylate, and butyl acrylate; ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile, as well as β-hydroxy 7-ethyl acrylate, acrylamide, and methacryl Amide, N-methylol acrylamide, diacetone acrylamide, glycidyl acrylate, glycidyl methacrylate, acrolein, allyl alcohol, divinylbenzene, diallyl phthalate, diallyl maleate, triallyl cyanurate, ethylene glycol dimethacrylate, allyl acrylate, etc. - The copolymer latex of the present invention must have the above monomer composition and have a gel amount of 40 to 90% by weight to achieve the goal of the present invention. If the gel amount is less than 40% by weight, color will not develop. As the properties decrease, the color staining properties also decrease. Moreover, when the weight exceeds 90%, the coloring staining property decreases.◇The weight is preferably 60 to 90%.

The amount of gel of the copolymer latex having a monomer composition in the present invention can be controlled by using a molecular weight regulator used in ordinary emulsion polymerization. Examples of molecular weight modifiers include mercaptans such as octyl mercaptan, rhododecyl mercaptan, t-dodecyl mercaptan, and lutetradecyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, carbon tetrabromide, methylene chloride, and methylene bromide. xanthogenic acids such as dimeterxanthogen disulfide and diisoglobilxanthogen disulfide;

Further, as a method for regulating the amount of gel, a method such as regulating the conversion rate at one reaction temperature and the completion of the polymerization reaction can also be used.

Further, in the present invention, in order to enhance the effect, the average particle diameter of the copolymer latex is preferably Q, 08μ or more, more preferably α1μ or more.

The method for producing the copolymer latex as described above 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, Polymerization initiator, chelating agent,
As for the electrolyte, various additives used in general emulsion polymerization can be used, and the polymerization temperature can be selected from either high or low temperatures. Furthermore, it is possible to add a known pH adjuster, dispersant, preservative, etc. 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 the coated bile composition d for pressure-sensitive recording paper of the present invention contains a buffer material together with the microcapsules.

As the buffering material, microcapsules, large dengue grains, cellulose powder, inorganic powder, etc. are generally used.

Copolymer latex L ordinary microcapsules of the present invention have the function of fixing the cushioning material on the support sheet together with the expanded copolymer latex microcapsules of the present invention 1
It is preferable to blend it at a ratio of 5 to 50 parts by weight (solid content) per 00 parts by weight (solid content). The use of other binders as described above together with the copolymer latex does not impede the effects of the present invention. Furthermore, if necessary, various additives such as antifoaming agents, preservatives, thickeners, etc. can be added.

Usually, the microcapsule coating solution is coated on the support sheet with 2 to 7 microcapsules.
gr/m" (solid content). The coating method is not particularly limited. The present invention will be explained in more detail with reference to Examples below. In addition, in Examples and Comparative Examples, Parts and parts are based on the weight of the whole piece.

Example 1 Water, emulsifier, inorganic salt,
The monomers and molecular weight regulator shown in Table 1 were added together with the chelating agent and polymerization initiator, and the mixture was heated at 60°C while rotating.
Polymerization was carried out for 15 hours. The O conversion rate reached 95% or more in all cases. After cooling the obtained copolymer latex with water and removing unreacted monomers, the pH of the latex was adjusted to 7 with NaOH. ! ! I4 The gel content of these latexes is also listed in Table 1.0 Here, the gel content was measured as follows.The sample latex had a dry thickness of 0.211.
Pour onto a glass plate with a frame so that the temperature is 20°C.

Leave for 48 hours under constant temperature and humidity at 65ToRTl to create a dry film.Next, this film is subdivided into 2n squares, of which n and sgr are precisely weighed, and 100 mesh stainless steel sheets are precisely weighed. It is placed in a wire mesh cylinder and immersed in 1001 Lt of tetrahydrofuran at room temperature for 24 hours. After that, the wire mesh was taken out and dried in a vacuum dryer for 24 hours, and then accurately weighed to measure the weight of the unbathed decomposition. A microcapsule dispersion for pressure-sensitive recording brass paper whose wall is a melamine-formalin resin film containing a high-boiling hydrocarbon oil in which a colorless leuco dye, crystal violent raftone, is dissolved; A microcapsule coating liquid was prepared using copolymer latex and dengue grains as a buffer material in the proportions shown below so that the total solid content concentration was 20%.
Particles: 35 parts by weight (solid content) Copolymer latex: 20 parts by weight (solid content) The obtained microcapsule coating liquid was applied to a base paper of 40 gr/m'' in a coating amount of 'g r
/ m'' and dried to obtain a pressure-sensitive recording paper.

■Coloring degree: Layer the obtained top paper and the commercially available lower paper, measure the reflectance of the printed material using an electric typewriter, and calculate the degree of coloring (%) using the following formula. 90 ■Coloring stainability Place the bottom paper on top of the top paper so that the color develops, place a 5kg weight on top of the bottom paper, slide it over the top paper for 50 minutes, measure the reflectance of the bottom paper, and use the following formula. Color staining (
%l tl-determined.

Table 6 shows the results of the above tests conducted on upper sheets A to E using the co-X latex of the present invention as a binder.

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-C using these copolymer latexes as a binder. The test results are shown in Table 3.

Comparative Example 2 A top paper was prepared in the same manner as in Example 1 using a commercially available acrylic ester copolymer latex (Nippon Zeon Group N1po'i LX 852) as a binder. The test results are shown in Table 3.

Comparative Example 3 Commercially available ethylene vinyl acetate latex (Kuraray 0M)
A top paper was prepared in the same manner as in Example 1 using 4000) as a binder. The test results are shown in IF, Table 5.〇Table 3

Claims (1)

[Claims] In pressure-sensitive recording paper with a coating layer of microcapsules,
20 to 70% by weight of aliphatic conjugated diolefin monomer, 0.5 to 5% by weight of ethylenically unsaturated acid monomer, and 25 to 79.5% of other olefinic monomer copolymerizable with these.
% by weight and contains a copolymer latex having a gel amount of 40 to 90% by weight as a binder.