JPH0430917B2 - - Google Patents

Description

Detailed Description of the Invention (A) Field of Industrial Application The present invention relates to a heat-sensitive recording sheet whose main components are a dye precursor and a color developer that develops color when the dye precursor is heated. The present invention relates to a heat-sensitive recording sheet that prevents deterioration of the white paper area and the colored area due to chemicals by providing an overcoat layer.

(B) Prior art and its problems The thermal recording method has many features such as non-impact, no noise during recording, no need for developing and fixing, and easy equipment maintenance.
It is used in a wide variety of applications, including various printers and facsimile machines, as well as barcode labels and tickets.

The characteristics required for this type of thermal recording paper are as follows:
It goes without saying that it has sensitivity suitable for various uses, as well as white background, long-term stable colored images that do not fade, no residue that forms during recording, and no dust that adheres to the thermal head during recording. (King) There are things you don't do, etc. Excellent products that meet many of these requirements can be manufactured, but in practical handling after recording, if they come into contact with erasers or vinyl chloride bags containing a large amount of plasticizer,
If you touch it with hands covered with hand cream or hair styling oil, if you overlap it with diazo photosensitive paper that has just been processed, or if you write underlines etc. with a highlighter, the image will disappear or the background will become discolored. This has the disadvantage that fog occurs, making it difficult to read the recorded image. This decoloring development is thought to be due to the lactone ring of the color-forming lactone compound ring-opened with an acidic developer being ring-closed in the presence of a plasticizer such as dibutyl phthalate, dioctyl phthalate, or dioctyl adipate. There is. It is also believed that the fogging phenomenon is caused by the developer of the diazo photosensitive paper and the solvent contained in the fluorescent pen dissolving the color developer and bringing it into contact with the dye precursor to cause a coloring reaction.

Therefore, it has been proposed that this phenomenon can be prevented by forming a film on the thermosensitive recording paper to prevent the penetration of the plasticizer. (Japanese Patent Publication No. 54-128347,
JP-A-543-549) The present inventors also developed an overcoat agent having chemical resistance and filed applications in JP-A No. 55-182557 and Japanese Patent Application No. 56-981.

However, in the past, the coating film of the overcoat layer was prone to cissing, pinholes, unevenness, etc., and satisfactory chemical resistance could not be obtained unless it was coated very thickly. This not only causes problems in terms of production, such as requiring a long drying time and making it impossible to increase the smearing speed, but also causes a decrease in sensitivity, which is undesirable. In particular, as there is a recent trend toward high-speed printing, it is necessary to keep the film thickness as thin as possible to reduce heat loss.In this case, improvement of repellency, pinholes, unevenness, etc. is an urgent issue from the viewpoint of film properties. It's summery.

Therefore, attempts have been made to add various surfactants to improve the revising properties of the coating film, but these methods significantly deteriorate the water and oil resistance of the coating film, and at the same time prevent the preservation of blank areas and recorded areas over time. It also deteriorated my sexuality. Leveling properties can be improved to some extent by adding pigments, but this inhibits film formation, reduces color development sensitivity, and wears out the facsimile heat head, so there is a limit to the amount.
Not satisfied.

(C) Purpose of the Invention The present inventor has provided an overcoat layer on the heat-sensitive coloring layer that prevents the occurrence of cissing, pinholes, and unevenness and has excellent film properties, and has water resistance and oil resistance. As a result of extensive research into a heat-sensitive recording sheet that does not inhibit color development or decrease sensitivity and has good print quality, the present invention was arrived at.

(D) Structure of the Invention In other words, the present invention provides a water-soluble coloring layer provided on a heat-sensitive coloring layer, the main components of which are a colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated to develop a color. An overcoat layer mainly composed of a polyhydric polymer compound contains an esterification reaction product of boric acid or a boric acid triester of a lower alcohol and one or more polyhydric alcohols having adjacent hydroxyl groups. The object of the present invention is to provide a heat-sensitive recording sheet "same as claimed in the claims" characterized by the following.

The main components used in the present invention will be explained in detail below, but unless it goes beyond the gist of the present invention,
This is not intended to limit the invention.

As a dye precursor, triphenylmethane type,
Examples include fluoran-based, diphenylmethane-based, thiazine-based, and spiropyran-based compounds. For example, crystal violet lactone, 3-diethylamino-7-methylfluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7 -anilinofluorane, 3-diethylamino-7-(2-
chloroanilino)fluoran, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3
-diethylamino-7-(3-chloroanilino)
Fluoran, 3-diethylamino-6-methyl-
7-anilinofluorane, 3-(N-ethyl-p
-toluidino)-6-methyl-7-anilinofluorane, 3-(N-methylcyclohexylamino)
-3-methyl-7-anilinofluorane, 3-piperidino-3-methyl-7-anilinofluorane, and the like.

As the color developer, acidic substances generally used for thermal paper can be used, such as phenol, p-t
-butylphenol, p-phenylphenol,
naphthol, p-hydroxyacetophenone,
2,2'-dihydroxydiphenol, 4,4'-isopropylidene (2-t-butylphenol),
4,4'-isopropylidenediphenol, 4,
Examples include 4'-cyclohexylidene diphenol, novolac type phenolic resin, benzoic acid, pt-butylbenzoic acid, p-hydroxybenzoic acid, p-hydroxybenzoic acid pendyl ester, p-hydroxybenzoic acid methyl ester, etc. .

As a binder, starch acid, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol,
Styrene-maleic anhydride copolymer, ethylene-
Examples include water-soluble binders such as maleic anhydride copolymers, and latex-based water-insoluble binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and methyl acrylate-butadiene copolymers.

Examples of pigments include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and the like.

In addition, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide, and castor wax, dispersants such as sodium dioctyl sulfosuccinate, Ultraviolet absorbers such as benzophenone type and benzotriazole type, as well as surfactants, fluorescent dyes, etc. may be used.

Paper is mainly used as the support for the heat-sensitive recording material according to the present invention, but various non-woven fabrics,
Plastic film, synthetic paper, metal foil, etc., or a composite sheet made of a combination of these may be used as desired.

Next, regarding the material forming the overcoat layer in the present invention, water-soluble polymer compounds are generally preferred, and polymer compounds selected from alginate, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol are preferred. It is best to use them alone or in combination of two or more.

In addition, film-forming polymer emulsions such as acrylic latexes, vinyl acrylic resins, vinyl acetate/ethylene copolymers, silicone/acrylate resins, and styrene/butadiene latexes have been introduced with great success. There is.

Furthermore, by using one or more of water resistance agents, ultraviolet absorbers, and mold release agents in combination, water resistance and light resistance can be imparted, and the film can be peeled off by adhesion (blocking).
It is preferable to use one that prevents this.

The esterification reaction product of boric acid or a boric acid triester of a lower alcohol and one or more polyhydric alcohols having an adjacent hydroxyl group, which is a feature of the present invention, is disclosed in, for example, JP-A No. 48-8731.
It is known as an intermediate raw material obtained in the manufacturing process of surface-active organic boron compounds disclosed in No. Examples of polyhydric alcohols having adjacent hydroxyl groups that can be reacted with boric acid or a boric acid triester of a lower alcohol include ethylene glycol, propylene glycol, butylene glycol, glycerin, sorbitan, sorbitol, mannitol, and the like. On the other hand, examples of boric acid triesters of lower alcohols include trimethylborate, triethylborate, tripropylborate, triisopropylborate, and tributylborate.

The esterification reaction product of boric acid or a boric acid triester of a lower alcohol and one or more polyhydric alcohols having adjacent hydroxyl groups is extremely compatible with water-soluble polymer compounds and has a moderate amount of It imparts thickening properties and also makes the surface of the various hydrophobic substances added to the overcoat layer hydrophilic, which has the effect of improving adhesion with the heat-sensitive coloring layer, reducing repellency, pinholes, and unevenness. It is thought that this will prevent the occurrence. Of course, there was no deterioration in water resistance or oil resistance, which occurs when a surfactant is added, or deterioration in color development sensitivity or printability when a pigment is added. Regarding water resistance, a considerable improvement was observed, and the effect of improving adhesion and water resistance was greater than when boric acid was simply added in an amount that would not cause gelation.

(E) Examples The present invention will be explained in more detail with examples.

Example 1 Liquid A 3-(N-methylcyclohexylamino)-6
-Methyl-7-anilinofluorane...12g 10% by weight polyvinyl alcohol aqueous solution...18g Water...30g Solution B Benzyl p-hydroxybenzoate...40g Benzyl terephthalate 10g 10% by weight polyvinyl alcohol aqueous solution...75g Water...42g With Solution A Pulverize liquid B in a separate ball mill for 48 hours.
A coating liquid was prepared using the following formulation.

Calcium carbonate...20g B solution...60g 10% by weight polyvinyl alcohol aqueous solution 70
g Solution A...20g Water...60g Coat the prepared coating solution on a base paper with a basis weight of 49g/ ^m2 so that the coating amount after drying is 5g/ ^m2 , and apply it at 60℃ for 1 hour.
After drying for a minute, heat-sensitive recording paper was prepared by using a super calendar to achieve a Beck smoothness of 100 seconds or more.

Solution C 7% by weight ammonium alginate aqueous solution (manufactured by Fuji Chemical Industry Co., Ltd., trade name: Snow Ammon)
…72g 10% by weight polyvinyl alcohol aqueous solution 50g
30% by weight zinc stearate dispersion...10g Solution D A boric acid triester obtained by the dehydration reaction of boric acid (1 mol) and glycerin (2 mol) (manufactured by Toho Chemical Industry Co., Ltd., trade name: Emalbon)
GB)...16.5g Water...83.5g An overcoat coating liquid prepared by adding 3g of liquid D to liquid C has a dry film thickness of approximately 4μm.
The mixture was coated on the above-mentioned thermosensitive recording paper to give an overcoat heat-sensitive recording paper using a super calender to give a Beck smoothness of about 400 seconds.

Example 2 Instead of the boric acid triester compound obtained by the dehydration reaction of boric acid and glycerin used in Example 1 and Solution D, boric acid obtained by the deethanol reaction of triethylborate (1 mol) and glycerin (2 mol) was used. An overcoated thermosensitive recording paper was produced in the same manner as in Example 1 except that the triester compound was used.

Example 3 Instead of the boric acid triester compound obtained by the dehydration reaction of boric acid and glycerin used in Solution D of Example 1, a debutanol reaction of tributylborate (1 mol) and sorbitan monostearate (2 mol) was used. An overcoated thermosensitive recording paper was produced in the same manner as in Example 1 except that the obtained boric acid triester compound was used.

Comparative Example Same procedure as in Example except that only liquid C was used.
An overcoated thermosensitive recording paper was produced.

Test Example Diazo developer resistance test: The overcoated thermal recording papers obtained in Examples 1, 2, 3 and comparative examples were developed to an optical density of 1.20 using Panafux UF-920 manufactured by Matsushita Electric Transmission Co., Ltd., and then overcoated. After overlaying the coated surface with the diazo photosensitive paper (developer activator PD) surface immediately after development, leave it at room temperature for 3 minutes to remove fog on the background.
The presence or absence of deterioration of the colored area was observed. Through the above test, it is possible to determine whether or not the overcoat layer has chemical resistance, that is, the degree of film completion.

In particular, when observing blank areas, areas that are not protected by the film develop a black color with the diazo developer.
The presence of cissing, pinholes, and unevenness can be identified.

DOP resistance test: The overcoated thermal papers obtained in Examples 1, 2, 3 and Comparative Example were colored in the same manner as above.

Dioctyl phthalate (DOP) is used in this coloring part.
was applied and observed for discoloration of the colored area.

The areas on which the film was not formed disappear instantly after being applied, allowing the presence of repellency, pinholes, and unevenness to be determined.

(F) Effect of the invention As a result, in the comparative example, fogging phenomenon caused by the developer for diazo photosensitive paper occurred partially in the background area, and black spots indicating the presence of cissing, pinholes, and unevenness were observed on the entire surface. . In addition, the colored portion caused by DOP faded, and the color completely disappeared over time, making the printed characters illegible.

On the other hand, the product of the present invention not only has no deterioration in legibility caused by the developer for diazo photosensitive paper, but also has no black spots indicating the presence of repelling, pinholes, or unevenness, and no fading of the coloring area due to DOP. , which was quite satisfactory.

Claims (1)

[Claims] 1. A heat-sensitive coloring layer is provided whose main components are a colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated, and furthermore, a water-soluble polymer is provided on this heat-sensitive coloring layer. In a heat-sensitive recording sheet provided with an overcoat layer mainly composed of a compound, the overcoat layer contains one or more of boric acid or a boric acid triester of a lower alcohol, and a polyhydric alcohol having an adjacent hydroxyl group. A heat-sensitive recording sheet characterized by containing an esterification reaction product with.