JPH0252637B2 - - Google Patents

Description

[Detailed description of the invention]

A thermosensitive recording material is a recording material in which a so-called thermosensitive coloring layer that develops color when heated is formed on the surface of a support such as paper, and is heated and printed using a thermal printer with a built-in thermal head. be. Conventionally, the above-mentioned heat-sensitive color forming layer has been composed of a composition consisting of a combination of a color forming substance, a color developer that causes the color forming substance to develop color when heated, and a binder. Does not develop color as it twists,
Various performances are required, such as not having a negative effect on the thermal head. In preparing the above composition, ultrafine powder (1 to
It is not an exaggeration to say that the quality of this technology directly affects the practicality of thermal recording paper. Even if dispersion is possible if a surfactant is used easily, the storage stability of thermal recording paper becomes a problem, and for example, the print becomes unclear after several tens of days after printing. In this case, there are problems such as the need for extremely strong stirring operations. Therefore, in the invention of the present inventors, since it is essential to use a binder in the composition, if the binder also functions as a dispersant, the above problems can be solved at once. However, there have been no reports on such a binder so far. However, as a result of intensive research, the present inventors found that
The present inventors have discovered that a vinyl acetate resin containing a sulfonic acid group satisfies this objective, and have completed the present invention. That is, the present invention provides a heat-sensitive recording material comprising a color-forming substance, a color developer that causes the color-forming substance to develop color when heated, and a vinyl acetate resin containing a sulfonic acid group. The vinyl acetate resin has the ability to uniformly disperse color-forming substances and functions as a binder, so it does not cause any problems with the storage stability of thermal recording paper and is easily compatible with thermal heads, etc. Its usefulness is extremely great. Such a sulfonic acid group-containing vinyl acetate resin can be produced by any method. The content of sulfonic acid groups in the resin is 0.1 to 20 mol%, preferably 1 to 20 mol%.
10 mol% is suitable for the purpose of the present invention, and below 0.1 mol% it is difficult to obtain the effects of the present invention, and 20 mol%
If this is the case, the adhesion ability will be lowered and the adhesive will be impractical. The sulfonic acid group may be in the form of a free acid or in the form of a sodium salt, potassium salt, ammonium salt, or the like. Furthermore, the vinyl acetate resin may be a saponified product in which the vinyl acetate moiety is substituted with a hydroxyl group. It is also possible to introduce components other than sulfonic acid groups, vinyl acetate groups, and hydroxyl groups, such as carboxylic acids (salts), carboxylic acid esters, olefins, amides, nitriles, and vinyl ethers. When using a saponified product, it is usually advantageous to have a degree of saponification in the range of 20 to 100 mol%, particularly 60 to 100 mol%, in terms of adhesive strength and prevention of staking.
The preferred range of polymerization degree is 150-2000. The following is an example of a method for producing such a sulfonic acid group-containing vinyl acetate resin. ○B A method of polymerizing olefin sulfonic acid or a salt thereof such as ethylene sulfonic acid, allyl sulfonic acid, meta-allylsulfonic acid, etc. and vinyl acetate in alcohol or an alcohol/water mixed solvent.
Or a method of further saponifying the polymer. ○B General formula

[Formula] or

A method of copolymerizing a sulfoalkyl maleate represented by the formula [R is an alkyl group, R' is an alkylene group, M is hydrogen or an alkali metal ammonium ion] and vinyl acetate, or a method of further saponifying the same. Examples of the above-mentioned sulfoalkyl malates include sodium sulfopropyl 2-ethylhexyl maleate, sodium sulfopropyl tridecyl maleate, and sodium sulfopropyleicosyl maleate. ○C General formula

Sulfoalkyl (meth)acrylamide represented by [Formula] or [R ₁ is hydrogen or a methyl group, R ₂ is hydrogen or an alkyl group, R' and M are the same as ○RO] For example, N
- A method of copolymerizing sulfoisobutylene acrylamide sodium salt and vinyl acetate. How to saponify this further. Furthermore, a method of copolymerizing a sulfoalkyl (meth)acrylate represented by the general formula CH ₂ =R ₁ | C -CO-O-(CH ₂ ) _o SO ₃ M, such as sodium 2-sulfoethyl acrylate and vinyl acetate; How to saponify this. ○D A method in which polyvinyl alcohol is treated with bromine, iodine, etc. and then heated in an acidic sodium sulfite aqueous solution. ○E A method of heating polyvinyl alcohol in a concentrated aqueous sulfuric acid solution. ○F A method of acetalizing polyvinyl alcohol with an aldehyde compound having a sulfonic acid group. etc. Among these, a saponified copolymer of olefin sulfonic acid or its salt and vinyl acetate is preferably used. The chromogenic substances used in the present invention have a lactone ring, a lactam ring, a sultone ring, and a spiropyran ring, and develop a color by reacting with a color developer when heated. Representative examples include the following: However, it is not intended to limit the invention. Crystal violet lactone, malachite green lactone, 3,3-bis(p-dimethylaminophenyl)-
6-Aminophthalide, 3,3-bis(p-dimethylaminophenyl)-
6-(p-toluenesulfamide) phthalide, 3
-diethylamino-7-(N-methylanilino)
Fluoran, 3-diethylamino-7-(N-methyl-p-toluidino)fluoran, 3-dimethylamino-6-methoxyfluoran,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-phenylfluorane, 3-morpholino-5,6-benzofluorane, 3-diethylamino -5-methyl-7-dibenzylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7,8-benzofluorane, 3-cyclohexylamino-6-chlorofluorane, N- Phenylrhodamine B lactam, acidrhodamine B sultone, benzo-β-naphthospiropyran, 2-methyl-spiropinaphthopyran, 1,3,3-trimethyl-6'-chloro-8'-methoxy-indolinobenthospiropyran, etc. Further, the color developer used in the present invention has the property of liquefying and/or vaporizing at room temperature or higher, preferably 70°C or higher, and reacts with a color-forming substance to develop color. For example, 4,4'-isopropylene Lydenediphenol, 4,4'-isopropylidenebis(2-chlorophenol), 4,4'-isopropylidenebis(2-t-butylphenol), 4,4'-secbutylidenediphenol, 4,4' -(1-methyl-n-hexylidene) diphenol, 4,4'-cyclohexylidene diphenol, 4,4'-thiobis(6-t-butyl-3-methylphenol), and the like. Combinations of these are also possible. In preparing the composition, an aqueous dispersion of a color-forming substance and an aqueous dispersion of a color developer are prepared separately and then mixed. The sulfonic acid group-containing vinyl acetate resin may be added to at least one of the dispersions. The sulfonic acid group-containing vinyl acetate resin is suitably used in an amount of 2 to 200% by weight based on the total amount of the color forming substance and color developer. The solid content concentration of the coating liquid is selected from the range of 10 to 40% by weight in consideration of workability and the like. If necessary, known additives such as glyoxal, water-resistant agents such as urea resins, antifoaming agents, dispersants, clay, calcium carbonate, satin white, titanium dioxide, etc. can be added to the coating liquid.
Furthermore, other binders such as polyvinyl alcohol,
Modified polyvinyl alcohol such as carboxyl group-containing polyvinyl alcohol, starch, methyl cellulose, carboxymethyl cellulose, acrylic latex, SBR latex, etc. can also be mixed. There are no particular restrictions on the paper to be coated. For coating, any known method such as a roll coater method, an air doctor method, a blade coater method, etc. may be employed. However, the coating amount of the coating liquid is 0.1 to 20 g/m ² , especially 2 to 10 g/m ²
It is appropriate to keep the amount within a certain range. The composition of the present invention will be explained in more detail below with reference to Examples. In the following, "parts" or "%" are based on weight unless otherwise specified. Example 1 Liquid A Crystal violet lactone 1.5 parts 20% vinyl acetate/sodium allylsulfonate copolymer saponified aqueous solution 5.0 parts (Sodium sulfonate content 5 mol% Saponification degree 88 mol% Polymerization degree 300) Water 43.5 parts B Liquid Bisphenol A 6.0 parts Calcium carbonate 3.0 parts Stearamide 1.0 parts Aqueous solution of the same saponified vinyl acetate/sodium allylsulfonate copolymer as Part A 10 parts Water 30 parts Use a sand grinder to prepare Parts A and B respectively. The particles were ground to a particle size of about 1 to 3 μm, and then the two were mixed to obtain a composition. The composition was coated on paper with a basis weight of 50 g/m ² at a coverage of 6 g/m ² and dried to obtain thermal recording paper. The dispersion stability of the composition and the storage stability of the recording paper were measured. The results are shown in Table 1. In addition, as a control example 1, polyvinyl alcohol with a degree of saponification of 99 mol% and a degree of polymerization of 500 was used instead of the saponified vinyl acetate/sodium allylsulfonate copolymer, and as a control example 2, a surfactant (oleyl methyl laurate) was used. The same experiment as in Example 1 was conducted using each. The results are also shown in Table 1.

[Table] Examples 2 to 12 The same experiment as in Example 1 was conducted using various sulfonic acid group-containing vinyl acetate resins as shown in Table 2. The results are shown in Table 2.

[Table] Good: Indicated by ○〓.

Claims (1)

[Claims] 1. A heat-sensitive recording material comprising a color-forming substance, a color developer that causes the color-forming substance to develop color when heated, and a vinyl acetate resin containing a sulfonic acid group.