JPH074985B2 - Thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a colorless or slightly pale color forming dye, and a developer containing an organic acid or a phenolic substance capable of coloring the coloring dye by heating. , A thermosensitive recording material having a thermosensitive coloring layer containing a binder.

More specifically, the storage stability, especially the water resistance of the coating film, the water resistance of the color-developed part, the fading resistance (hereinafter referred to as plasticizer resistance) that occurs when adhered to a plastic film containing a large amount of plasticizer, and meat and edible oil The present invention relates to the heat-sensitive recording material having improved discoloration (hereinafter referred to as oil resistance) that occurs when oil adheres.

[Prior Art] Conventionally, there are various known heat-sensitive recording sheets obtained by coating a support with a coating obtained by dispersing a lactone compound such as crystal violet lactone and a phenol compound such as bisphenol A in a binder such as a polyvinyl alcohol solution. JP-B-45-14039). When a heat-sensitive recording sheet of this type receives heat, the color-forming lactone compound chemically reacts with an organic acid or a phenol compound to develop a color. The basic properties required for a heat-sensitive recording material are that the color development is good, the appearance is as white as possible, it has the appearance of natural paper, and it has long-term storage stability, high sensitivity, and sticking (sticking). Nothing,
Also, it is required that the thermal head has good compatibility with the thermal head because there is no adherence of lees.

However, this type of heat-sensitive recording material is
Since it is unstable with respect to plasticizers and oils, the change over time during storage is always a problem. That is, when the desired printing is performed using such a heat-sensitive recording material, the recorded color develops extremely clearly, but a plastic film containing a large amount of a plasticizer in the color-developed portion, for example, a soft film of polyvinyl chloride. However, there is a drawback in that the adhered part will be discolored if it is adhered or stored with oil or fat attached. Also, when the color-developed part is in contact with water for a long period of time, marked discoloration always occurs.

Such discoloration is particularly remarkable in a color-forming system using a dye mainly composed of a colorless or light-colored lactone compound, that is, a dye-coloring type heat-sensitive recording material. This discoloration does not depend on the chemical structure of the chromophoric lactone compound to be used, and it is presumed that the above-mentioned inconveniences occur particularly because the organic acid or the phenol compound dissolves in the plasticizer or oil, and it has been solved in the past. Is strongly requested.

Therefore, it has been proposed to provide the surface of the heat-sensitive recording material with a protective coating containing, for example, saponified polyvinyl alcohol, a water-soluble polymer compound having a barrier property such as casein, and a crosslinking agent. However, even if such a protective coating is provided, for example, when it is left at 40 ° C.
It cannot be said that the coloring part disappears in 5 to 5 hours, which is not enough.

[Problems to be solved by the invention] For this reason, light, water,
It is required to prevent adverse effects of temperature, plasticizer, oil, etc. as much as possible, and surely avoid discoloration of the color-developed portion.

An object of the present invention is to solve all of these problems and provide a heat-sensitive recording material having improved long-term storage stability with improved water resistance, plasticity resistance and oil resistance.

[Means and Actions for Solving the Problems] As a result of earnest studies, the present inventors have found that a polyvinyl alcohol-based resin and an organic compound represented by the following formula (1) are formed on a thermosensitive coloring layer provided on a support. Polymer of boron compound By providing a protective layer containing, it is possible to prevent the penetration of plasticizers, oils, etc. into the thermosensitive coloring layer, and to prevent discoloration during the adhesion of polyvinyl chloride to a soft film and the adhesion of oil. It has been found that it exhibits an excellent effect and is excellent in its storability, and that the coloring part hardly disappears even after passing 40 ° C. for 24 hours or more. Moreover, the heat-sensitive recording material of the present invention can be adjusted in viscosity and pot life of the coating liquid as appropriate, and has no possibility of trouble such as coloring due to water resistance and has excellent properties in practical use.

As the polyvinyl alcohol-based resin used in the protective layer in the present invention, in addition to polyvinyl alcohol having an arbitrary degree of polymerization and a degree of saponification, an unsaturated carboxylic acid or its partial or complete ester or acetoacetic acid esterification, etc. Polyvinyl alcohol is also used. The degree of polymerization is preferably in the range of 300 to 1700, especially 500.
The range of up to 1000 is particularly preferable from the viewpoint of paint viscosity and coatability.

The polyvinyl alcohol-based resin having an acetoacetic acid ester group in the molecule is obtained by converting polyvinyl alcohol into an acetoacetic acid ester. The acetoacetic acid esterification is achieved by a method of adding diketene to a polyvinyl alcohol-based resin or transesterifying the acetoacetic acid ester. The degree of polymerization is preferably in the range of 700 to 2000, and particularly preferably around 1000 in order to achieve the effects of the present invention and in practical use.

The content of the acetoacetic acid ester group may be water-soluble at 0.05 mol% or more with respect to the water-soluble polymer compound. Usually, the range of 0.1 to 20 mol%, particularly 0.5 to 10 mol% is preferable.

Formula (1) which is one of the polymers constituting the protective layer of the present invention
The polymer of the organic boron compound shown in (1) has a very good compatibility with the polyvinyl alcohol-based resin, brings about an appropriate thickening effect, and acts to attract the hydrophilic group of polyvinyl alcohol to the boron portion. Therefore, it is presumed that the OH groups of polyvinyl alcohol are oriented in a certain direction in the protective layer, and an excellent barrier property against plasticizer and oil is exhibited.

The polymer is used in an amount of 1 to 30 parts by weight, preferably 2 to 15% by weight, based on 100 parts by weight of the polyvinyl alcohol resin. If the amount used is less than 1 part by weight, the resistance to plasticizer and oil is insufficient. If the amount used is more than 30 parts by weight, the viscosity of the coating liquid increases, and further gelation causes problems such as short life of the coating liquid. It will be difficult.

The protective layer of the heat-sensitive recording material in the present invention, in addition to a polyvinyl alcohol-based resin and a polymer of an organic boron compound,
A lubricant and / or a pigment can be contained, which can prevent sticking of the thermal head to the film surface and adhesion of lees to the thermal head when recording on the coating surface.

As the filler that can be added in this way,
Examples include kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, silica, synthetic aluminum silicate, synthetic magnesium silicate, aluminum oxide, polystyrene fine particles, and urea-formalin resin fine particles.

In particular, oil absorption of 100 ml / 100 g or more, apparent specific volume of 3 ml / g or more,
The finely divided silicic acid having an average particle size of 3.0 μm or less has good compatibility with the protective layer forming agent of the present invention, has better head compatibility such as sticking and head meal, and can also be provided with printability, and has the above plasticizer resistance. It is an excellent filling material that can record clear images with high density even with minute heat energy without deteriorating oil resistance and water resistance.

As the lubricant, higher fatty acid, higher fatty acid amide, higher fatty acid metal salt, paraffin wax, microcrystalline wax and the like can be blended.

However, in the composition of the protective layer, the total amount of the polyvinyl alcohol resin and the polymer of the organic boron compound must be 50% by weight or more of the entire protective layer. If it is less than this range, the plasticizer resistance and oil resistance are deteriorated, which is not suitable.

The coating amount of the protective layer is appropriately adjusted so as not to hinder the heat conduction from the thermal head to the color forming layer,
It is usually 1 to 10 g / m ^2, preferably ² to 7 g / m ² . As a result, a desired effect can be obtained without lowering the thermal sensitivity.

The support and the heat-sensitive color forming layer of the heat-sensitive recording material of the present invention may be any materials. For example, as the support, high-quality paper, medium-quality paper, art paper, coated paper, cast coated paper,
Papers such as paperboard and thin paper can be generally used, but plastic film, synthetic paper, laminated paper, aluminum foil and the like can also be used.

Any colorless or slightly light-colored coloring dye used in the thermosensitive coloring layer can be used. For example, 3-
Diethylamino-6-methyl-7-anilinofluorane, 3-
Pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinoflu Oran, 3-diethylamino-7-chloroanilinofluorane, 3- [N-ethyl-N- (p-methylphenyl) amino] -6-methyl-7-anilinofluorane, 3-diethylamino-7- ( (Metatrifluoromethyl) anilinofluorane, 3- [N-ethyl-N-tetrahydrofurfuryl] amino-6-methyl-7-anilinofluorane, 3- [N-ethyl-N-
Fluoranes such as isopentyl] amino-6-methyl-7-anilinofluorane, 3- [N, Ndibutyl] amino-6-methyl-7-anilinofluorane, 3,3-bis- (p-dimethyl Aminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis- (p-dibutylaminophenyl) phthalide, 3,3-bis- (p-dimethylaminophenyl) phthalide, 4-hydroxy- Triphenylmethanes such as 4'-dimethylaminotriphenylmethanelactone, 3-methyl-di-β-naphthospirane,
Spirolane dyes such as 1,3,3-trimethyl-6'-chloro-8'-methoxyindolinobenzospirolane, and leuco dyes such as auramine dyes, rhodamine lactam dyes, and phenothiazine dyes are also used. However, it is not limited to these representative examples.

As the color developer, all those which liquefy or vaporize at room temperature or higher, preferably 70 ° C. or higher, and react with the color forming dye to develop color can be used. For example, 4,4'-isopropylidene diphenol [bisphenol A], 4,4'-isopropylidene bis (2-chlorophenol), 4,4'-
Isopropylidene bis (2-methylphenol), 4,4-isopropylidene bis (2,1-tert-butylphenol),
4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene phenol, 4-tert-butylphenol, 4-
Phenylphenol, 4-hydroxydiphenoxide, naphthol, β-naphthol, methyl-4-hydroxybenzoate, 4-hydroxy-acetophenone, anilide salicylate, novolac type phenol resin, halogenated novolac type phenol resin, 4,4′-thio- Bis (3-methyl-6-tert-butylphenol), propyl p-hydroxybenzoate, isopropyl p-hydroxybenzoate, butyl p-hydroxybenzoate, isobutyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,
Fatty acid carboxylic acids such as methylbenzyl p-hydroxybenzoate, oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid, stearic acid, benzoic acid, p-tert-butylbenzoic acid, phthalic acid, gallic acid, salicylic acid, 3-isopropylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, bis (4-hydroxyphenyl) sulfide, 1,
7-di (4-hydroxyphenylthio) -3,5-dioxaheptane, p-nitrobenzoic acid, and organic developers such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel. Salt with valent metal,
4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 3,3'-dihydroxydiphenyl sulfone, 3,3'-diamino-4,4'-dihydroxy-diphenyl sulfone, 3,3'-diamino -4,4'-
Dihydroxydiphenyl sulfone, 3,3'-diallyl-
4,4'-dihydroxydiphenyl sulfone, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-diphenyl sulfone, 4-hydroxy-4'-
Isopropyl diphenyl sulfone, 4-hydroxy-4 '
-Isopropyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 2,4-dihydroxy-diphenyl sulfone, 2,4-dihydroxy-
4'-methyldiphenyl sulfone, 3,4-dihydroxyphenyl-p-trisulfone and the like can be mentioned. Of course, it is not limited to this. The developer is used in an amount of 1 to 5 parts by weight, preferably 1.5 to 3 parts by weight, based on 1 part by weight of the color forming dye.

As the binder for the thermosensitive coloring layer, all known binders can be used. It is preferable that such a binder does not cause the liquid to develop color, aggregate, or have a high viscosity when it is mixed with each dispersion of the color-forming dye and the color-developing substance. In addition, properties such as not impairing color development and strong formation film are required. However, in order to provide a protective layer, compatibility with a thermal head such as sticking, dust adhesion, and abrasion is particularly required. For example, polyvinyl alcohol, starch, hydroxyethyl cellulose, arabic gum, polyvinylpyrrolidone, alkali salt of acrylic acid (or methacrylic acid) ester copolymer, alkali salt of styrene / maleic anhydride copolymer, isobutylene / maleic anhydride copolymer. Examples thereof include a water-soluble polymer compound such as an alkali salt of a polymer and an acrylamide copolymer, a polymer latex such as a styrene / butadiene copolymer, polyvinyl acetate and an acrylate copolymer, or an emulsion.

In addition, if necessary, the thermosensitive coloring layer may further contain auxiliary additives commonly used in thermosensitive recording materials of this type, such as fillers, surfactants, heat-fusible substances (or lubricants), and the like. That doesn't matter. In this case, as the filler, for example, calcium carbonate, magnesium carbonate, kaolin,
Clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, synthetic magnesium silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface-treated calcium carbonate, silica and other inorganic fine powder Other examples include organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin. Examples of the heat-fusible substance include stearic acid amide, stearic acid ethylenebisamide, and olein. Fatty acid amides such as acid amide, palmitic acid amide, coconut fatty acid amide, behenic acid amide,
Waxes such as zinc stearate, calcium stearate, polyethylene wax, carnapa wax, paraffin wax, and ester wax, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, 1-hydroxynaphthoic acid phenyl ester 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane,
Diphenyl carbonate, p-benzylbiphenyl, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4 '
-Butylidene bis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2,2'-methylenebis (4-ethyl) -6-t-butylphenol), 2,4-di-t-butyl-3-methylphenol, hindered phenols such as 4,4'-thiobis (3-methyl-6-t-butylphenol), 2-
Sensitizers such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, and various heat-fusible substances such as lubricants, antioxidants and UV inhibitors To be The amount of the heat-fusible substance added is not particularly limited, and is generally in the range of about 4 parts by weight or less relative to 1 part by weight of the color developer.

[Examples] The present invention will be described more specifically below with reference to Examples. Parts in each example indicate parts by weight.

Example 1 (1) Preparation of solution A 3- (N-methyl-N-cyclohexylamino) -6-methyl-
7-anilinofluoran 6 parts 10% polyvinyl alcohol aqueous solution 10 parts (2) Preparation of solution B 4,4'-isopropylidenediphenol 25 parts stearic acid amide 16 parts 10% polyvinyl alcohol aqueous solution 100 parts Solution A and solution B Are separately pulverized and dispersed by a sand mill to have an average particle size of 3 μm or less.

(3) Preparation of solution C 10% polyvinyl alcohol aqueous solution 50 parts Polymer of 10% organic boron compound (manufactured by Boron International Co., Ltd., trade name: Hyboron DDGB90, average molecular weight approximately
10,000, Boron content 6.2%) 10 parts 30% Microsilicic acid 10 parts 30% Polyaldehyde solution 2 parts 30% Zinc stearate 2 parts (4) Formation of coloring layer Calcium carbonate 60% Aqueous dispersion 40 parts, A liquid 30 Part, B liquid 200
Parts and 10% polyvinyl alcohol aqueous solution as binder
Mix 100 parts to make a coating solution. This coating solution was coated on a base paper of 50 g / cm ^{2 so} that the dry weight was 7 g / m ² , and then calendered to form a thermosensitive coloring layer having a Bekk smoothness of 250 seconds.

(5) Formation of Protective Layer Liquid C was coated on the above color-developing layer so that the dry weight was 3 g / m ² , and a protective layer was provided to obtain a thermosensitive recording material having a two-layer structure.

Comparative Example (6) Preparation of D solution 10% Polyvinyl alcohol aqueous solution 60 parts 30% Fine pulverized silicic acid 10 parts 30% Polyaldehyde solution 2 parts 30% Zinc stearate 2 parts Solution D was used instead of solution C to prepare the organic boron compound. A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1 except that the polymer was removed.

Each of the thermal recording materials of the above Examples and Comparative Examples was stored at room temperature for 3 hours.
After standing for one day, color was developed with solid black recording by Copix 7100 (trade name, manufactured by Toshiba Electric Co.), and a clear black color image was obtained at a high density of 1.2 or more with a Macbeth reflection densitometer (RD-514). Then, a predetermined test piece was prepared from this by a conventional method, and the water resistance, the vinyl chloride film resistance and the oil resistance of the colored portion were measured by the following tests. The results are shown in the table. As is clear from this table, in the examples, satisfactory results were obtained, but in the comparative examples, appropriate results were not obtained in some properties.

(1) Water resistance test: Specimens in water for 24 hours (at room temperature)
It is taken out after the immersion, evaluated by the elution state of the protective layer and the residual concentration after drying.

(2) PVC film resistance test: A soft polyvinyl chloride film was overlaid on the test piece, and the load was 20 ° C and a load of 300 g / m ^2.
Measure the concentration when both are contacted for 24 hours.

(3) Oil resistance test: Specimen is coated with cottonseed oil by a conventional method, and evaluated by the residual concentration after standing for 24 hours at each temperature of 20 ° C and 40 ° C.

As is clear from the above table, it is known that the examples are improved in PVC film resistance and oil resistance as compared with the comparative examples.

EFFECTS OF THE INVENTION The present invention can provide a heat-sensitive recording material having excellent water resistance, plasticizer resistance and oil resistance, and is used as, for example, a heat-sensitive recording type ticket for an automatic ticket vending machine. Of course, it is used for coupons and commuter passes that require long-term storage, and on the packaging surface when wrapped with vinyl chloride film such as fresh food and oily meat using the POS bar code pricing system. Not only is it suitable for use as label paper to be attached, but it can also be used as facsimile paper or printer paper for long-term storage.

Claims (1)

[Claims] 1. A protective layer containing a polyvinyl alcohol resin and a polymer of an organic boron compound represented by the following formula (1) is provided on the thermosensitive coloring layer provided on a support. Thermosensitive recording material.