JPS6161995B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material used in information equipment, such as facsimile machines, printers, data communications, computer terminals, and various measuring instruments.

It is particularly useful to prepare a heat-sensitive recording material by dispersing a color-forming lactone compound (for example, crystal violet lactone) and a phenolic compound (for example, bisphenol A) in a binder (polyvinyl alcohol) solution and coating it on a support. It is already known as described in Publication No. 45-14039.

Generally, a two-component color-forming heat-sensitive material consisting of an electron-donating color-forming dye and an electron-accepting phenolic substance is produced on a single support as follows. The chromogenic dye and the phenolic substance are each separately dispersed in a binder at an appropriate concentration to a size of several microns or less using a ball mill or the like. Next, the two dispersions thus obtained are mixed to form a single liquid, and a filler, wetting agent, non-adhesive substance, etc. are added thereto as appropriate to obtain a heat-sensitive coating liquid. A heat-sensitive recording material is obtained by applying this coating liquid to a suitable support and drying it.

Current thermal recording paper includes recording paper for thermal pens such as nichrome wire for electrocardiograms and industrial records, recording paper for thermal printers used in desktop computers, computer terminals, etc., as well as recording paper for facsimile and high-precision recording. There is recording paper for calculations. In general, such recording sheets are basically required to have good color development as a quality issue, but other characteristics include keeping the appearance as white as possible without losing the appearance of natural paper, and long-term storage stability. Weather resistance against temperature, humidity, and light, as well as pressure resistance and abrasion resistance are required, and thermal recording paper for facsimile use in particular is required to have various even more severe performances in addition to these performances. That is, (1) high sensitivity, (2) staking, (3) lees adhesion, and matching with the thermal head. Staking is a phenomenon in which the recording paper sticks to the head during thermal printing, making it impossible to feed the paper or creating a sagging image. When this phenomenon occurs, not only the paper cannot be fed, but also the head This will cause overheating and shorten the life of the head.
Furthermore, as for the issue of scum, if scum accumulates on the head during printing, the density of the print will be uneven, making the print quality unclear.

As described above, thermal recording paper for facsimile is required to have strict performance as described above. Therefore, generally known water-soluble or water-dispersible polymers are unsuitable as binders for such heat-sensitive recording sheets since they are subject to many restrictions. Properties required of the binder include the following.

When triphenylmethane-based or fluoran-based color-forming dyes and phenolic compounds are dispersed into fine particles, they are required to act as a dispersant without causing aggregation and to not generate bubbles. When the respective dispersions of the components are mixed, it is undesirable that the liquid develops color, agglomerates, or has a high viscosity. Further, the film formed on the heat-sensitive recording sheet is required to be strong, to have no desensitizing effect, to have good thermal conductivity, and to be suitable for the above-mentioned staking.

Heat-sensitive recording sheets coated with water-soluble binders have problems with water resistance, and if water is spilled on them or touched with wet hands during storage or handling, the coating may run off. This is undesirable because it causes stains and stains, and if the humidity is high during storage, the image is likely to fade, so it is necessary to make it waterproof.

Known methods for making such heat-sensitive recording sheets water resistant include formalin, glyoxal, chromium alum, melamine-formalin resin, compounds having two or more epoxy ring structures in one molecule, and dialdehyde starch.

However, these hardeners crosslink during preparation of the coating solution and cause aggregation of the coating solution, making it impossible to apply the coating, or have almost no hardening effect, or may cause poor background coloration or may cause problems with heat-sensitive recording sheets. It has disadvantages such as desensitization to color development, and also requires drying or heat treatment at high temperatures (100℃ or higher) and long curing to obtain water resistance. There is. Drying or heat treatment at high temperatures cannot be carried out in the production of heat-sensitive recording sheets because it causes color development.

The present inventors conducted various studies to design a heat-sensitive recording sheet that does not have all of the above-mentioned drawbacks and has excellent water resistance. As a result, the acrylic emulsion, which is self-crosslinking and hardens even at room temperature, shows good results. I discovered that.

Self-crosslinking acrylic emulsion technically solves the problems of conventional emulsions such as poor water resistance, low gloss, and poor coating properties. It provides water resistance, and the mechanism of self-crosslinking reaction and reaction between functional groups and crosslinking agent is carboxyl group + epoxy resin in acrylic or methacrylate copolymer, similarly amide self-crosslinking, carboxyl There are various types such as group + melamine resin, hydroxyl group + melamine resin, etc., but these examples are not intended to limit the present invention. As these self-crosslinking acrylic emulsions, so-called soapless emulsions that do not contain emulsifiers (surfactants) or organic solvents are more desirable, and they have excellent post-film formation properties due to the synergistic effect of crosslinking and soapless effects. Shows water resistance.

The self-crosslinking acrylic emulsion used in the present invention can be used not only as a binder, but also as a water-resistant agent when using other water-soluble binders or dispersed binders such as latex of various resins. I can do it. To obtain an effective water-resistant effect, the amount of self-crosslinking acrylic emulsion to be added is 1 to 100% of the water-soluble binder.
50% by weight, but between 3 and 15% is particularly preferred.

The above-mentioned binders include polyvinyl alcohol, gum arabic, hydroxyethyl cellulose, methyl cellulose, gelatin, polyvinylpyrrolidone, polyacrylate, carboxymethyl cellulose, starch derivatives, styrene-anhydride, which are common binders for heat-sensitive recording sheets. Maleic acid copolymers, styrene-butadiene latexes, etc., self-crosslinking properties (soapless)
Acrylic emulsion is effective in making water resistant to any of the above binders.

The phenolic compound used in the present invention is one that liquefies or vaporizes at room temperature or higher, preferably 70°C or higher, and reacts with a color-forming dye to develop color. Representative examples include 4,4'-isopropylidene diphenol [bisphenol A], 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis(2-methyl-phenol), 4,4'-isopropylidene bis(2,1-tert-butylphenol), 4 , 4'-sec-butylidene diphenol, 4,4'-cyclohexylidene diphenol,
4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, naphthol, β-naphthol, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxy-acetophenone, salicylic acid anilide, novolac type phenolic resin,
Examples include halogenated novolac type phenolic resins, but these representative examples are not intended to limit the present invention. Among these, phenol compounds having two or more hydroxyl groups in the molecule are often used.

Examples of color-forming dyes that are usually colorless or light-colored and develop color by reacting with the phenolic compound used in the present invention include 3,3-bis(paradimethylaminophenyl)-6-dimethyl-aminophthalide (crystal violet lactone); , 3-bis(paradibutylaminophenyl) phthalide (malachite green lactone), 3,3-bis(paradimethylaminophenyl) phthalide, 1-amino-3,
6,7-trimethylfluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-(N-methylanilino)fluorane, 3-dimethylamino-6-methoxyfluorane, 3-dibutylamino-6 -Methyl-7-
Examples include, but are not limited to, chlorofluorane, 3-morpholino-5,6-benzofluorane, and the like.

As the support used in the present invention, paper is generally used, but synthetic resin films, laminated paper, woven fabric sheets, etc. can also be used.

Additive materials include fillers such as talc, clays, and granular starch, as well as compatible erasers, to improve coating suitability, adjust color development sensitivity, and prevent sticking or scum from adhering to heating heads. It is also possible to add surfactants such as foaming agents, dispersants and anti-cissing agents, and waxes to the dispersion.

Examples will be shown below, but the invention is of course not limited to these ranges as long as they do not go beyond the gist of the invention.

Example 1 Liquid A crystal violet lactone 1 g 20% hydroxypropylated starch aqueous solution 1 g (trade name Stacodex, manufactured by Matsutani Chemical Co., Ltd.) Water 4 g Liquid B 4,4'-isopropylidene diphenol 5 g Petrolite R-50 2 g (Varico Co., Ltd.) 20% hydroxypropylated starch aqueous solution (Microcrystalline Wax) 5g water 15g The above A and B solutions were each ground in a ball mill for 24 hours, then both solutions were mixed, and 30% self-crosslinking acrylic emulsion (Dyurimer SEK101 , manufactured by Nippon Pure Chemical Industries, Ltd.) to prepare a paint for heat-sensitive recording sheets. This paint was applied to the paper surface to obtain a heat-sensitive recording paper sheet with a coating weight of 7 g/m ² after drying.

When the coating film of this sheet was wetted with water and rubbed with a fingertip, no stickiness or falling off of the coating film was observed, indicating that the film was sufficiently water resistant. Furthermore, no aggregation was observed in this paint even after storage for several days.

For comparison, a heat-sensitive recording sheet was also prepared using a coating solution in which hydroxypropylated starch was added instead of the self-crosslinking acrylic emulsion, and a water resistance test was conducted in the same manner, but there was almost no water resistance.

Example 2 9 g of 30% hydroxypropylated starch and a self-crosslinking acrylic emulsion were added to the mixture of A and B in Example 1 so that the solid content was 8% by weight of the total binder to prepare a coating liquid. The coating solution was applied to general paper having a basis weight of 50 g/m ² so that the coating amount after drying was approximately 5 g/m ² to obtain heat-sensitive recording paper.

A water resistance test was conducted in the same manner as in Example 1, and the result showed sufficient water resistance.

Example 3 Part A 3-diethylamino-6-methyl-7-p-butylanilinofluorane 1g Kaolinite 3g 5% polyvinyl alcohol aqueous solution 6g Water 5g Part B 4,4'-Secondary-butylidene diphenol
5g 5% polyvinyl alcohol 20g Water 10g After pulverizing and dispersing the above A and B solutions in a ball mill, mix both A and B and add 20% wax emulsion (trade name Cybinol, PC-10,
A heat-sensitive recording paint was prepared by adding 5 g (manufactured by Saiden Chemical) and 10 g of a 30% self-crosslinking acrylic emulsion (Dyurimer SEK101, manufactured by Nippon Pure Chemical Industries, Ltd.).
A heat-sensitive recording paper is obtained by coating general paper having a basis weight of 50 g/m ² so that the coating amount after drying is approximately 6 g/m ² . This recording paper exhibited superior water resistance and good color development compared to a heat-sensitive recording paper prepared by adding polyvinyl alcohol without using self-crosslinking acrylic emulsion.

Example 4 Liquid A crystal violet lactone 1g 20% hydroxyethylcellulose aqueous solution 5g (trade name HEC BL-15 manufactured by Fuji Chemical) Liquid B 4,4'-isopropylidene diphenol 8g 20% hydroxyethylcellulose aqueous solution 30g Water 7g Above A, After pulverizing both liquids B in the same manner as in Example 1,
Mix both liquids B and add 5 g of 20% wax emulsion (trade name: Repole No. 50 manufactured by Daikyo Chemical Co., Ltd.) and 40% self-crosslinking acrylic emulsion (trade name: Jyurimer SEK103, manufactured by Nippon Pure Chemical Industries, Ltd.) as a water resistant agent. Add 1.5g and mix to make a heat-sensitive coating liquid. The coating liquid is 50g/m ²
The coating weight after drying on general paper with a basis weight of about 6
g/m ² to obtain heat-sensitive recording paper.
This heat-sensitive recording sheet also had sufficient water resistance, and the coated surface did not peel off even when wet with water and rubbed with a finger, and there was very little background coloration, giving good results with a clear blue color.

Claims (1)

[Scope of Claims] 1. A normally colorless or light-colored electron-donating color-forming substance, an electron-accepting substance such as a phenolic compound or organic acid or a polymer thereof that causes the color-forming substance to develop color when heated, and a water-soluble binder. 1. A heat-sensitive recording sheet comprising a heat-sensitive recording composition comprising: a self-crosslinking acrylic emulsion as a binder or a coating film waterproofing agent. 2. A heat-sensitive recording sheet according to claim 1, characterized in that a soapless emulsion is used as the acrylic emulsion.