JPS62198492A - Recording sheet - Google Patents

Abstract

PURPOSE:To obtain a recording sheet less susceptible to contamination due to undesired color development under pressure and having excellent printability and handleability, by incorporating an alkali salt of a methacrylic acid copolymer into a coated layer. CONSTITUTION:An alkali salt of a methacrylic acid copolymer is incorporated in a coated layer comprising microcapsules having a synthetic high molecular weight wall film and enclosing a color developer therein. The salt is an alkali salt of a copolymer of methacrylic acid with at least one monomer copolymerizable therewith. The copolymerizable monomer is preferably an alkyl methacrylate having an up to 18C alkyl, acrylamide, acrylonitrile, styrenesulfonic acid or 2-acrylamide-2-methylpropanesulfonic acid. When the content of methacrylic acid is less than 8mol%, sufficient water solubility can not obtained, whereas when the content is more than 90mol%, there is a possibility that property for re-dissolution through absorbing moisture of the copolymer is increased. Therefore, it is preferable to use methacrylic acid in an amount of 8-90mol% based on the copolymer.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a recording sheet in which a support is provided with a coated layer of microcapsules having a synthetic polymer wall film containing a coloring agent, and particularly relates to The present invention relates to capsule-coated recording sheets that have improved stain resistance and handling properties.

``Prior Art'' Recording sheets that utilize a coloring reaction between a coloring agent and a coloring agent are well known.For example, pressure-sensitive copying paper is made of microcapsules containing a hydrophobic core material in which an electron-donating coloring agent is dissolved. and,
It is composed of a combination of electron-accepting coloring agents in various forms.

A capsule sheet made by coating a support with a coating solution containing microcapsules is an embodiment of this, and the performance of the resulting pressure-sensitive copying paper is greatly influenced by the characteristics of the capsules, so the encapsulation method is not suitable. Various studies are being conducted mainly on this topic.

Conventionally, microcapsules for pressure-sensitive copying paper have been manufactured mainly by the coacervation method using gelatin, but only low-concentration capsules can be obtained, and the process is complicated, as well as stability and Various methods of improvement have been proposed because they have poor putrefaction and water resistance, and also have the disadvantage that internal phase substances are easily extracted by surfactants and the like.

For example, methods of producing polyurethane resins, polyurea resins, polyamide resins, etc. at the interface of oil and water by interfacial polymerization (Japanese Patent Publications No. 42-446, 771-1971, 6506-1986, 58 -55036 etc.), urea-formalin resin, melamine-formalin resin, melamine-urea-
Formalin M Method using fat etc. as capsule wall membrane (
JP-A-51-9079, JP-A-54-49984,
JP-A-56-51238, JP-A-56-102934
No.) etc. have been proposed. .

Capsules with these synthetic polymer wall membranes have become the mainstream of capsule coating recording sheets in recent years, but compared to capsules with natural polymer wall membranes such as gelatin, these capsules have a high concentration. Since it can be prepared into paint, high-speed application is possible and productivity can be increased. (2) Since the capsule wall film is dense, there is little natural exudation of the oil droplets contained therein, making it suitable for use in so-called stand-alone pressure-sensitive copying paper, which is composed of a laminated or mixed capsule and coloring agent.

Furthermore, (1) the manufacturing process is simple, inexpensive, and has excellent water resistance. This is because it has various advantages such as.

"Problems to be Solved by the Invention" However, synthetic polymer-based wall capsules with such excellent characteristics also come with new drawbacks due to the inherent characteristics of the wall resin, so they are not practical. However, there is still room for improvement.

That is, polyurethane resins, polyurea resins, polyamide resins, amino aldehyde resins, etc. are very hard and provide capsules with excellent heat resistance, moisture resistance, and solvent resistance, but they are brittle and cannot be used in writing, typewriters, etc. It may be easily destroyed by unwanted friction other than striking pressure, resulting in colored stains. Furthermore, since it has poor retention and absorption properties for hydrophobic substances, the printing pressure during printing may destroy the capsules and cause colored stains. Furthermore, since it does not have appropriate smoothness, there are problems in that when recording sheets are stacked in sheets, they are difficult to slide (and lack suitability for handling), and conversely, they may slip too much and become unsuitable for handling.

The purpose of the present invention is to improve the above-mentioned drawbacks associated with synthetic polymer-based wall capsules, and to provide a recording sheet with less color staining due to undesired pressure (and excellent printability and handleability). be.

"Means for Solving the Problem" The present invention provides a recording sheet in which a support is provided with a coating layer of microcapsules having a synthetic polymer wall film containing a coloring agent, in which the coating layer is a methacrylic acid copolymer. This is a recording sheet characterized by containing a combined alkali salt.

"Function" In the present invention, the alkali salt of the methacrylic acid copolymer contained in the capsule coating layer is obtained by copolymerizing methacrylic acid and at least one monomer copolymerizable with the methacrylic acid. It is an alkali salt of a copolymer.

Examples of monomers copolymerizable with methacrylic acid include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, octyl methacrylate,
ter L-butyl methacrylate, 2 methacrylate
- Methacrylic acid, alkyl ester, maleic acid having an alkyl group with a carbon number of 18 or less, such as ethylhexyl, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, lauryl-tridecyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, hensyl methacrylate, etc. butyl acid, dibutyl maleate,
Unsaturated acid alkyl esters such as ethyl fumarate, alkyl vinyl ethers having an alkyl group of 18 or less carbon atoms such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, 2-ethylhexyl vinyl ether, octyl vinyl ether, lauryl vinyl ether, stearyl vinyl ether, styrene sulfonic acid ,
2-acrylamido-2-methylpropanesulfonic acid,
Acrylic acid, acrylamide, mectarylamide, N-
Examples include methylol acrylamide, acrylonitrile, acrolein, styrene, α-methylstyrene, divinylhensen, vinyl acetate, vinyl chloride, butadiene, N-vinylpyrrolidone, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-ethoxyethyl methacrylate, etc. It will be done.

Among these, methacrylic acid alkyl esters having an alkyl group having 18 or less carbon atoms, acrylamide, acrylonitrile, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid are more preferably used.

In the methacrylic acid copolymer used in the present invention,
If the content of methacrylic acid is less than 8 mol%, sufficient water solubility will not be obtained, and if it exceeds 90 mol%, the copolymer may become more soluble in moisture. It is desirable to copolymerize so that the amount is 8 to 90 mol%.

Such a copolymer is produced by oxidizing methacrylic acid and a monomer copolymerizable with it in a single or mixed solvent such as water, methanol, ethanol, isopropanol, butanol, ethyl acetate, methyl ethyl ketone, toluene, or xylene. Polymerization initiators such as potassium sulfate, ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, iron (■), chromium ion, sulfite, hydroxylamine, hydrazine, benzoyl peroxide, azobisisobutyronitrile, secondary Polymerization regulators such as alcohol, mercaptosuccinic acid,
It is prepared by copolymerization by a well-known method using various polymerization aids such as emulsifiers such as sodium lauryl sulfate.

The obtained copolymer is further neutralized with amines such as ammonia, ethylamine, propylamine, ethanolamine, and propatoolamine, and alkalis such as sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide. It is not necessarily necessary to neutralize all the carboxyl groups in the copolymer, and free carboxylic acid may remain.

However, in order to obtain sufficient water solubility, it is necessary to neutralize the copolymer so that at least 8 mol % or more of the alkali salt of carboxylic acid is present in the copolymer.

The salt of the copolymer used in the present invention is generally at a concentration of 1
~50% by weight, pH 3-12, viscosity 1-100000c
It is prepared as an aqueous solution or aqueous dispersion of about 20% by weight ps (20°C), but more preferably the polymerization degree is about 500 to 3000 cps (20°C) in a 20% by weight aqueous solution, and ammonia is used as the main neutralizing agent. An aqueous solution or aqueous dispersion with a pH of 8 to 10 using a volatile neutralizing agent such as the like is desirable.

The blending ratio of the copolymer salt in the microcapsule coating layer is adjusted as appropriate depending on the type of copolymer salt used, but 0 parts by weight per 100 parts by weight of the hydrophobic core substance in the capsule. .5-20% by weight, more preferably 1-10
It is desirable to mix it in a proportion of about % by weight.

In addition to the capsule and the alkali salt of the above-mentioned specific methacrylic acid copolymer, the capsule coating solution contains adhesives such as polyvinyl alcohols, starches, carboxymethyl celluloses, and latexes, and valves according to conventional techniques. Various materials such as stilting agents such as powder and raw starch powder are appropriately blended. The method of applying the capsule coating liquid to the support is not particularly limited, and the capsule coating liquid is applied to the surface of a suitable support substrate such as paper, synthetic paper, synthetic film, etc. using an ordinary coating device and dried.

"Example" Examples of the present invention will be described below, but of course the present invention is not limited thereto. In addition, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively.

[Preparation of microcapsules]

■ Add 150 parts of a 6% aqueous solution of ethylene maleic anhydride copolymer (trade name HMA-31, manufactured by Monsanto Chemical Co., Ltd.) into a stirring mixing vessel equipped with a heating device, and adjust the pH to 4.0 with a 20% aqueous caustic soda solution. to prepare an aqueous medium.

Separately, diisopropylnaphthalene (-113 in the product name,
(manufactured by Kureha Chemical Co., Ltd.), 5 parts of crystal violet lactone, and 5 parts of polymethylene polyphenylisocyanate (manufactured by Kureha Chemical Co., Ltd.).
Obtained by dissolving 5 parts of 2-isocyanatoethyl-2,6-diitzyanatohexanoate (trade name T-100, manufactured by Toshi Co., Ltd.) The capsule core material was added to the aqueous medium and emulsified and dispersed so that the average particle size was 5 μm.

Next, a solution of 0.5 parts of diethylene triamine and 0.5 parts of polyvinyl alcohol (product name PVA-117, manufactured by Kuraray Co., Ltd.) dissolved in 10 parts of water was added, and after stirring at room temperature for 30 minutes, the temperature of the system was lowered. Raise the temperature to 70℃ and continue stirring 3.
Allowed time to react. A synthetic resin wall capsule (A) was prepared by lowering the temperature to room temperature.

■ 100 parts of diisopropylnaphthalene, 5 parts of crystal violet lactone, 1 part of terephthalic acid chloride
The capsule core material obtained by dissolving 0 part was heated to 50°C. This was added to the same aqueous medium as in (1) above, cooled to 10° C., and emulsified and dispersed so that the average particle size was 5 μm.

Next, a solution prepared by dissolving 6 parts of diethylene triamine and 4 parts of sodium carbonate in 50 parts of water was cooled to 10° C., and stirred for 30 minutes at room temperature to prepare a synthetic resin wall capsule (B).

(2) A capsule core material obtained by dissolving 5 parts of crystal violet lactone in 100 parts of diisopropylnaphthalene was added to the same aqueous medium as in (2) above, and emulsified and dispersed so that the average particle size was 5 μm.

Separately, 30 parts formalin, 10 parts melamine, 1 part glycine
A melamine prepolymer solution was prepared by adding 50% of the melamine prepolymer solution and heating it to 60°C. This prepolymer liquid was added to the emulsified dispersion liquid heated to 60°C, the temperature of the system was raised to 70°C, and the mixture was reacted for 3 hours while stirring. A synthetic resin wall capsule (C) was prepared by lowering the temperature to room temperature.

To the thus obtained capsule dispersion, 70 parts of wheat starch and 20 parts of dissolved oxidized starch (solid content) were added to each 100 parts of the core material in the capsule, and an alkali salt of the copolymer shown in the table was added. 11 types of capsule coating solutions were prepared.

Separately, 65 parts of aluminum hydroxide, 20 parts of zinc oxide, 3
, 5-di(α-methylbenzyl)salicylate zinc and α-
A dispersion obtained by grinding 15 parts of a mixed melt with methylstyrene/styrene copolymer (melt ratio 80/20), 5 parts of polyvinyl alcohol aqueous solution (solid content) and 300 parts of water in a ball mill for 24 hours, A coloring agent coating solution prepared by adding 20 parts (solid content) of carboxy-modified styrene-butadiene copolymer latex was applied to 40 g/rd base paper to a dry weight of 5 g.
A lower sheet for pressure-sensitive copying paper was prepared by coating, drying, and calendering so as to give /rd.

The capsule coating solution was applied to the surface opposite to the coloring agent-coated surface of the lower sheet and dried to give a dry weight of 4 g/rd to prepare a middle sheet for pressure-sensitive copying paper.

A performance comparison test was conducted using the middle paper and bottom paper thus obtained, and the results are listed in Table 1.

[Cosplay dirt test]

The middle paper and the bottom paper are stacked so that the capsule coated side of the middle paper and the coloring agent coated side of the bottom paper face each other, and the weight is 4kg/c.
The degree of colored stain on the surface coated with the coloring agent was determined by scrubbing five times under a load of ffl.

[Print color stain test]

With a business form printing machine (Mei Seisakusho, 17BH),
Printing was performed on the coloring agent-coated surface of the medium paper using a wet offset printing method, and the paper was rolled up to a length of 300 m.

After being left at 50℃ for 3 days, 100m from the winding core.
The degree of staining on the surface coated with the coloring agent was determined.

[Smoothness]

The coefficient of friction between the capsule coated surface of the inner leaf paper and the coloring agent coated surface of the inner leaf paper was measured using MODIiL D manufactured by KAYENESS.
-1055 measuring machine with a thread load of 200 g and a speed of 0.5 feet/min. In terms of handling suitability, the static friction coefficient is preferably 0.65 or less.

In addition, the neutralization ratio of carboxylic acid in the table is Na0HsN II with respect to all carboxyl groups in the copolymer.
, expressed as the proportion of carboxyl groups neutralized with OII, and the amount of the copolymer added is expressed as parts by weight based on 100 parts of the core material in the capsule. In addition, the evaluation criteria were as follows.

○: Hardly dirty.

△: Slightly dirty.

×: Extremely dirty.

"Effects" The recording sheet of the present invention had less colored stains due to contact rubbing, etc., and less printed colored stains caused by capsule destruction due to printing pressure during printing. Furthermore, the volatile solvent in the printing ink component had the effect of improving the phenomenon in which hydrophobic substances in the capsule were extracted, and the suitability for handling was also good due to the moderate smoothness.

Claims (1)

[Claims] In a recording sheet in which a coating layer of microcapsules having a synthetic polymer wall film containing a coloring agent is provided on a support,
A recording sheet characterized in that the coating layer contains an alkali salt of a methacrylic acid copolymer.