JPH05568A - Multi-color thermal recording material - Google Patents

Abstract

PURPOSE:To improve thermal fractionation properties and shelf life by adding at least, one type or more of alkylester parahydroxy benzoate to one of thermal color development layers containing a diazo compound and a coupler which developes colors through a chemical reaction with the diazo compound. CONSTITUTION:A multi-color thermal recording material consists of at least, two tiers or more of thermal color development layer 2, 3 formed on a support 1. Further, at least, one 3 of the thermal color development layers 2, 3 contains a diazo compound 31 and a coupler which develops a color through a chemical reaction with the diazo compound as main ingredients. Under the mentioned constitution, at least, one type or more of alkylester parahydroxybenzoate 33 with a 8 to 18C alkyl group is added to one of the thermal color development layers. On the other hand, an electron-donative dye precursor 21 and an electron- receptive compound 22 as color development ingredients are added to the other thermal color development layer 2. In addition, at least, one of the color development ingredients is enveloped in a microcapsule.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor thermosensitive recording material, and more particularly to a multicolor thermosensitive recording material having high sensitivity and excellent storage stability.

[0002]

2. Description of the Related Art A thermal recording method has achieved remarkable progress in recent years and has been applied to various purposes because it is highly reliable and requires no maintenance despite the simple recording apparatus used. It has been said that reproduction of multicolor images is difficult as compared with electrophotographic recording methods and inkjet methods. In this regard, a thermosensitive coloring layer containing an electron-donating dye precursor and an electron-accepting compound as main components on a support and / or a diazo compound and a coupler capable of coloring when reacted with the diazo compound at the time of heating are contained. It has been found that a multicolor thermosensitive recording material can be obtained by laminating two or more thermosensitive color developing layers as a whole. However, in this method, since it is necessary to separately develop a plurality of color developing layers within the allowable heat energy range, it is necessary to make a difference in the thermal sensitivity of each color developing layer (heat fractionation) and From the viewpoint of not losing value, it has been required that these thermal sensitivities are stable even under high temperature and high humidity.

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors from such a viewpoint, a thermosensitive color forming layer containing a diazo compound and a coupler which reacts with the diazo compound to develop a color,
By containing at least one kind of parahydroxybenzoic acid alkyl ester having an alkyl group having 8 to 18 carbon atoms, it is possible to realize a multicolor heat-sensitive recording material excellent in heat fraction and excellent in storage stability. Find out,
The present invention has been reached. Therefore, an object of the present invention is to provide a multicolor thermosensitive recording material which is excellent in heat fractionation property and storage stability.

[0004]

The above objects of the present invention are as follows.
Multicolor thermosensitive recording having at least two thermosensitive coloring layers on a support, and at least one of the thermosensitive coloring layers containing a diazo compound and a coupler that develops a color by reacting with the diazo compound as a main component. In the material, in the thermosensitive coloring layer containing the diazo compound and a coupler that reacts with the diazo compound to develop a color, the carbon number of the alkyl group is 8 to
It has been achieved by a multicolor heat-sensitive recording material characterized by containing at least one kind of 18 parahydroxybenzoic acid alkyl ester.

FIG. 1 is a conceptual diagram showing a constitutional example of the heat-sensitive recording material of the present invention. In the figure, reference numeral 1 is a support, 2 is a second thermosensitive coloring layer containing an electron-donating dye precursor and an electron-accepting compound as main components, and 3 is a diazo compound and a color is developed by reacting the diazo compound with heat. It is a first thermosensitive coloring layer containing a coupler. Reference numeral 21 is an electron-donating dye precursor, 22 is an electron-accepting compound, 31 is a diazo compound, 3
2 is a coupler that reacts with the diazo compound when heated to develop a color,
Reference numeral 33 represents parahydroxybenzoic acid ester.

In the case of recording on this multicolor recording material, first, heat is applied so that the first thermosensitive recording layer indicated by reference numeral 3 is colored, and after the color is developed, the entire surface of the recording material is irradiated with light. The diazonium salt contained in the first recording layer is decomposed. Then, sufficient heat is applied to the second thermosensitive recording layer indicated by reference numeral 2 to develop a color and record. In this case, strong thermal energy is applied to the first recording layer, but no color develops because the diazo compound has already been decomposed by light. First
Also, by selecting different hues for the hues of the respective second heat-sensitive recording layers, multicolor image recording can be obtained. Further, as shown in FIG. 2, if the first to third thermosensitive recording layers that develop different hues are provided, it is possible to record more hues.

Raw materials used in the present invention will be described below. As a known raw material used in a heat-sensitive recording layer containing an electron-donating dye precursor and an electron-accepting compound as main components, an electron-donating dye precursor and an electron-accepting compound react with each other when heated. There are low melting point organic compounds and the like that help. Examples of the electron-donating dye precursor include triarylmethane-based compounds, diphenylmethane-based compounds, thiazine-based compounds, xanthene-based compounds, spiropyran-based compounds, and the like. It is useful because it is expensive.

Specific examples thereof include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (that is, crystal violet lactone),
3,3-bis (p-dimethylamino) phthalide, 3-
(P-Dimethylaminophenyl) -3- (1,3-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole-
3-yl) phthalide, 3- (o-methyl-p-dimethylaminophenyl) -3- (2-methylindole-3-)
Yl) phthalide, 4,4′-bis (dimethylamino) benzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, rhodamine-B-anilinolactam,
Rhodamine (p-nitroanilino) lactam, Rhodamine-B- (p-chloroanilino) lactam, 2-benzylamino-6-diethylaminofluorane, 2-anilino-6-diethylaminofluorane, 2-anilino-3
-Methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-anilino-3-methyl-6-isoamylethylaminofluorane, 2- (o-chloroanilino)-
6-diethylaminofluorane, 2-octylamino-
6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-2-diethylaminofluorane, 2
-Anilino-3-chloro-6-diethylaminofluorane, benzoylleuco methylene blue, p-nitrobenzyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran,
3,3′-dichloro-spiro-dinaphthopyran, 3-benzylspirodinaphthopyran, 3-propyl-spiro-
There are dibenzopyran and the like.

Examples of the electron accepting compound include phenol derivatives, salicylic acid derivatives, hydroxybenzoic acid esters and the like. Among these, bisphenols and hydroxybenzoic acid esters are particularly preferable. Examples of some of these include 2,2-bis (p-hydroxyphenyl) propane (ie, bisphenol A), 2,2
-Bis (p-hydroxyphenyl) pentane, 2,2-
Bis (p-hydroxyphenyl) ethane, 2,2-bis (p-hydroxyphenyl) butane, 2,2-bis (4'-hydroxy-3 ', 5'-dichlorophenyl)
Propane, 1,1- (p-hydroxyphenyl) cyclohexane, 1,1- (p-hydroxyphenyl) propane, 1,1- (p-hydroxyphenyl) pentane,
1,1- (p-hydroxyphenyl) -2-ethylhexane, 3,5-di (α-methylbenzyl) salicylic acid and its polyvalent metal salt, 3,5-di (tert-butyl) salicylic acid and its polyvalent Metal salts, 3-α, α-dimethylbenzyl salicylic acid and polyvalent metal salts thereof, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p
Examples include 2-ethylhexyl hydroxybenzoate, p-phenylphenol, p-cumylphenol and the like.

A sensitizer for promoting the reaction is preferably added to the heat-sensitive recording layer composed of the electron-donating dye precursor and the electron-accepting compound. As the sensitizer, a low melting point organic compound having an aromatic group and a polar group in the molecule is preferable, and specific examples thereof include benzyl p-benzyloxybenzoate, α-naphthylbenzyl ether, β-naphthylbenzyl ether, β-naphthoic acid phenyl ester, α-hydroxy-β-naphthoic acid phenyl ester, β-naphthol- (p-chlorobenzyl) ether, 1,4-butanediol phenyl ether, 1,4-butane Diol-p-methylphenyl ether, 1,4-butanediol-p-ethylphenyl ether, 1,4-butanediol-m-methylphenyl ether, 1-phenoxy-2- (p-tolyloxy)
Examples thereof include ethane, 1-phenoxy-2- (p-ethylphenoxy) ethane, 1-phenoxy-2- (p-chlorophenoxy) ethane and p-benzylbiphenyl.

On the other hand, the compound used in the heat-sensitive color forming layer containing a diazo compound and a coupler which reacts with the diazo compound to form a color when heated is a known photodegradable diazo compound, and a dye is reacted with the diazo compound to form a dye. Examples include couplers that can be formed and basic substances that accelerate the reaction between the diazo compound and the coupler. The photodecomposable diazo compound in the present invention mainly refers to an aromatic diazo compound, and more specifically, an aromatic diazonium salt, a diazosulfonate compound, a diazoamino compound and the like. Among these, it is particularly preferable to use a diazonium salt from the viewpoint of thermal sensitivity.

[0012] The diazonium salt of the general formula Ar-N2 ⁺ X ^- (wherein Ar represents an aromatic moiety, N2 + diazonium salt, X - represents an acid anion) is a compound represented by the. These have various maximum absorption and absorption wavelengths depending on the position and type of the substituent of the Ar portion.

Specific examples of the diazo compound used in the present invention include 4- (N- (2- (2,4-di-tert-
Amylphenoxy) butyryl) piperazino) benzenediazonium, 4-dioctylaminobenzenediazonium, 4- (N- (2-ethylhexanoyl) piperazino) benzenediazonium, 4-dihexylamino-2
-Hexyloxybenzenediazonium, 4-N-ethyl-N-hexadecylamino-2-ethoxybenzodiazonium, 3-chloro-4-dioctylamino-2-octyloxybenzenediazonium, 2,5-dibutoxy-4-morpholinobenzene Diazonium, 2,5-octoxy-4-morpholinobenzenediazonium, 2,
5-dibutoxy-4- (N- (2-ethylhexanoyl) piperazino) benzenediazonium, 2,5-diethoxy-4- (N- (2- (2,4-di-tert-amylphenoxy) butyryl) piperazino ) Benzenediazonium, 2,5-dibutoxy-4-tolylthiobenzenediazonium, 3- (2-octyloxyethoxy)
-4-morpholinobenzenediazonium and the like. In the present invention, in particular, these hexafluorophosphate salts, tetrafluoroborate salts, 1,5
-Naphthalene sulfonate salts are useful because they have low water solubility and are soluble in organic solvents.

The couplers which react with the diazo compound used in the present invention to produce a color when heated are resorcin, phloroglucin, sodium 2,3-dihydroxynaphthalene-6-sulfonate, 1-hydroxy-2-naphthoic acid morpholinopropylamide, 1,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,3-dihydroxy-6-sulfanylnaphthalene, 2-hydroxy-3-naphthoic acid anilide, 2-hydroxy-3-naphthoic acid ethanolamide, 2-hydroxy- 3-naphthoic acid octylamide, 2-hydroxy-3-naphthoic acid-N-dodecyloxypurupyramide, 2-hydroxy-3-naphthoic acid tetradecylamide, acetanilide, acetoacetanilide, benzoylacetanilide, 2-chloro-5- Cu Chi Le acetoacetanilide,
1- (2-Tetradecanoxyphenyl) -2-carboxymethylcyclohexane-3,5-dione, 1-phenyl-3-methyl-5-pyrazolone, 1- (2'-octylphenyl) -3-methyl- 5-pyrazolone, 1-
(2 ', 4', 6'-Trichlorophenyl) -3-benzamido-5-pyrazolone, 1- (2 ', 4', 6'-
Trichlorophenyl) -3-anilino-5-pyrazolone, 1-phenyl-3-phenylacetamido-5-pyrazolone and the like can be mentioned. Two or more of these couplers may be used in combination.

A basic compound is added to the heat-sensitive recording layer composed of a diazonium salt and a coupler in order to accelerate the reaction thereof. The basic substance includes an inorganic or organic basic compound as well as a compound that decomposes when heated to release an alkaline substance.

Typical examples include organic ammonium salts,
Organic amines, amides, urea and thiourea, their derivatives, thiazoles, pyrroles, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines,
Examples thereof include nitrogen-containing compounds such as piperidines, amidines, formazines and pyridines. Specific examples of these include tricyclohexylamine, tribenzylamine, octadecylbenzylamine, stearylamine,
Allylurea, thiourea, methylthiourea, allylthiourea, ethylenethiourea, 2-benzylimidazole, 4
-Phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazoline, 2,4,5
-Trifuryl-2-imidazoline, 1,2-diphenyl-4,4-dimethyl-2-imidazoline, 2-phenyl-2-imidazoline, 1,2,3-triphenylguanidine, 1,2-dicyclohexylguanidine, 1, Two
3-tricyclohexylguanidine, guanidine trichloroacetate, N, N'-dibenzylpiperazine, 4,
There are 4′-dithiomorpholine, morpholinium trichloroacetate, 2-aminobenzothiazole, 2-benzoylhydrazinobenzothiazole and the like. These may be used in combination of two or more.

The parahydroxybenzoic acid alkyl ester used in the heat-sensitive color developing layer containing the diazo compound of the present invention and a coupler which reacts with the diazo compound to develop a color is a substance having an action of increasing the color density of a printed image by heating. It is preferable that the alkyl group has 8 to 18 carbon atoms.

A carbon number of 7 or less has the effect of increasing the coloring density during heating printing, but when it is used, it tends to cause coloration under high temperature and high humidity, resulting in poor storage stability. Not preferable. Also, those having a substituent having 19 or more carbon atoms have good storage stability under high temperature and high humidity,
It is not preferable because the effect of increasing the color density is low.

Specific examples of the parahydroxybenzoic acid ester having 8 to 18 carbon atoms include octyl parahydroxybenzoate, nonyl parahydroxybenzoate, decyl parahydroxybenzoate, undecyl parahydroxybenzoate, and dodecyl parahydroxybenzoate. And so on. These alkyl groups may be linear or branched. The addition amount is 0.5 to 10 parts by weight, preferably 1 to 3 parts by weight, based on 1 part by weight of the coupler used. Furthermore, they are preferably used as solid dispersions or as emulsions with suitable protective colloids.

In the present invention, an intermediate layer may be provided between the color forming layers in order to improve the heat fraction of each layer. The material of the intermediate layer used is preferably an emulsion or latex of a water-soluble polymer or hydrophobic polymer.

Examples of the water-soluble polymer include polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, styrene-maleic anhydride copolymer and its ester, butadiene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer. Polymer, isobutylene-maleic anhydride copolymer, polyacrylamide, polystyrenesulfonic acid, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, oxidized starch, phosphorylated starch, gelatin, carboxymethyl cellulose , Methyl cellulose, sodium alginate, sulfated cellulose, hydroxyethyl cellulose and the like. Examples of the hydrophobic polymer emulsion or latex include a styrene-butadiene copolymer, a carboxy-modified styrene-butadiene copolymer, and an acrylonitrile-butadiene copolymer.

Next, a method for producing the multicolor thermosensitive recording material of the present invention will be described. In the heat-sensitive recording material of the present invention, all the heat-sensitive recording layers have their color-forming components, that is, the electron-donating dye precursor and the electron-accepting compound, or the diazo compound and the coupler, respectively, so that they do not come into contact with each other before heating. It must be uniformly dispersed in the binder and held in the recording layer.

As a specific method, each material is separately dispersed in a water-soluble polymer (for example, polyvinyl alcohol) aqueous solution, and the water-soluble polymer is sufficiently adsorbed on the surface of each material, and then mixed. There are a method of microencapsulating at least one of the components, a method of separating the reaction components layer by layer, and the like, and a method of microencapsulating one of the color-forming components is particularly preferable.

The electron-donating dye precursor and the electron-accepting compound will be described below as examples, but the same applies to the case of the diazo compound and the coupler. In the above method, an electron-donating dye precursor (for example, crystal violet lactone) is put into an aqueous solution of a water-soluble polymer (for example, polyvinyl alcohol) and dispersed by means of a ball mill or the like. In this operation, the crystal of the electron-donating dye precursor is pulverized into fine particles, and at the same time, the water-soluble polymer is adsorbed on the surface of the crystal, and the electron-donating dye precursor is protected by the water-soluble polymer adsorption layer. A fine particle dispersion of is obtained. Similarly, a fine particle dispersion of an electron accepting compound (for example, bisphenol A) can be obtained. Even if both dispersions thus obtained are mixed, no color-forming reaction occurs because each color-forming component is protected by the water-soluble polymer adsorption layer. Therefore, a recording material can be obtained by coating this mixed liquid on a support. However, when heated for recording, at least one of the color components melts, breaks the adsorption layer and diffuses, and as a result, both color components come into contact with each other, so that a color reaction occurs and a color image is obtained.

As the water-soluble polymer used in the above method, the water-soluble polymer used in the above-mentioned intermediate layer can be used. In particular, polyvinyl alcohol and its derivative, polyacrylamide and its copolymer,
Hydroxyethyl cellulose, starch derivatives and the like are preferable.

In the method of microencapsulating at least one of the components, the electron-donating colorless dye and / or the electron-accepting compound may be encapsulated by a conventional method.

The microcapsules used in the present invention are
It is a thermo-responsive microcapsule that has the property of strictly isolating the substance inside the capsule from the substance outside the capsule at room temperature, and at the same time can accelerate the reaction of the coloring component by increasing the permeability of the wall during heating. Need to be

As the wall material of the capsule, gelatin, polyurea, polyurethane, polyimide, polyester, polycarbonate, melamine and the like can be used, but polyurea or polyurethane is preferably used from the viewpoint of obtaining thermoresponsive microcapsules. Further, in order to impart thermal responsiveness to the capsule wall, the glass transition point of the capsule wall may be room temperature to 200 ° C, particularly 70 ° C to
It is preferably in the range of 150 ° C.

The glass transition temperature of the capsule wall can be controlled by selecting the polymer species of the capsule wall or adding an appropriate plasticizer. Such plasticizers include phenol compounds, alcohol compounds, amide compounds, sulfonamide compounds and the like, which may be contained in the core material of the capsules or added outside the microcapsules as a dispersion. ..

Specific examples of the microencapsulation method, materials and compounds used are described in, for example, US Pat. No. 372.
6804 and 3796696. The method for microencapsulating the electron-donating dye precursor will be described below, but the same applies to the case of microencapsulating other materials.

For example, when polyurethane or polyurea is used as the capsule wall material, the polyvalent isocyanate and the second substance (for example, polyol or polyamine) which reacts with the polyisocyanate to form the capsule wall are water phase or oily to be encapsulated. After mixing in a liquid to form a core composition, the core composition is emulsified and dispersed in water, and then the temperature is raised to cause a polymer forming reaction at the oil droplet interface to form a microcapsule wall. In this case, the glass transition point of the capsule wall can be significantly changed by appropriately selecting the polyvalent isocyanate as the first wall film forming substance and the polyol or polyamine as the second wall film forming substance.

A high boiling point oil is used as the organic solvent used in the preparation of the core composition, and specifically, phosphoric acid ester, phthalic acid ester, acrylic acid ester,
Methacrylic acid ester, other carboxylic acid ester,
Fatty acid amide, alkylated biphenyl, alkylated tar
Phenyl, alkylated naphthalene, diarylethane,
Examples include chlorinated paraffin.

Further, a low-boiling auxiliary solvent may be added in order to assist the dissolution of the electron-donating dye precursor. Specific examples of the auxiliary solvent include ethyl acetate, isopropyl acetate, butyl acetate, methylene chloride, cyclohexanone and the like. Further, a protective colloid or a surfactant may be added to the aqueous phase in order to make the emulsified oil droplets stable.

As the protective colloid, water-soluble polymers can be generally used, and specific examples thereof include polyvinyl alcohol, modified polyvinyl alcohol, methyl cellulose, sodium polystyrene sulfonate, ethylene / maleic acid copolymer and the like. Can be mentioned.

The size of the microcapsules is 0.2 μm in volume average, especially from the viewpoint of improving image resolution and handling.
m to 20 μm is preferable, and more preferably 0.4 μm to
It is 4 μm.

Since the separating action of the material by the microcapsule wall is generally more complete than the separating action of the material by the adsorption layer of the water-soluble polymer, microcapsulation of either one of the reaction components allows the reaction components to be sufficiently separated. Can be suppressed. Therefore, for example, when the electron-donating dye precursor is microencapsulated, the electron-accepting compound can be mixed with the capsule liquid as a dispersion liquid in which the electron-accepting compound is simply dispersed in fine particles. However, it is also possible to dissolve the electron-accepting compound in a high boiling point solvent, emulsify it in an aqueous solution of a water-soluble polymer, and then mix with the capsule liquid.

In the latter case, there is an advantage that a transparent heat-sensitive recording layer can be obtained by applying a coating solution on a support and drying it. Therefore, in this case, a transparent thermosensitive recording material can be obtained by using a transparent support such as a plastic base as the support.

As the support used in the multicolor heat-sensitive recording material of the present invention, paper, laminated paper in which polyethylene or the like is laminated on paper, synthetic paper, polyethylene terephthalate, polyimide, plastic film such as triacetyl cellulose, etc. are known materials. Is used. Further, these supports may be undercoated to improve the adhesion with the coating layer.

As a method for coating the support, an air-knife coat method, a carten coat method, a slide coat method,
Roller coating method, dip coating method, wire bar coating method, blade coating method, gravure coating method, spin coating method, extrusion coating method and the like can be mentioned. However, the present invention is not limited to these. By these methods, the multicolor thermosensitive recording material of the present invention can be obtained by sequentially coating each thermosensitive recording layer on the support. or,
If necessary, a protective layer may be provided on the heat-sensitive layer as is well known.

Next, the multicolor thermosensitive recording material of the present invention (FIG. 2)
The recording method of will be described. First, the outermost heat-sensitive layer (first heat-sensitive recording layer) containing the diazo compound is colored by heat recording with low heat energy, and then light in the absorption wavelength range of the diazo compound contained in the heat-sensitive layer is emitted. The entire surface is irradiated with light using a light source to photolyze the diazo compound remaining in the uppermost heat-sensitive layer.

Then, the second heat-sensitive layer (second layer) containing a diazo compound having a higher energy than the previous time and having a light absorption wavelength range different from that of the diazo compound contained in the first layer.
After the color of the thermosensitive recording layer) is developed, the entire surface is irradiated again with a light source that emits light in the absorption wavelength range of the diazo compound, whereby the diazo compound remaining in the second heating layer is photolyzed. To do. Finally, with further higher energy, the innermost layer (third heat-sensitive recording layer) of the layer containing the electron-donating dye precursor is colored to complete the image recording. In the above case,
It is preferable that the outermost layer and the second layer are transparent heat-sensitive layers because each color becomes vivid.

In the present invention, a transparent support is used as the support, and one of the above three layers is coated on the back surface of the transparent support to obtain a multicolor image similar to that shown in FIG. You can also get it. In this case, the uppermost heat-sensitive layer on the side opposite to the image viewing side does not need to be transparent.

An ultraviolet lamp is usually used as the light source used for the photolysis of the diazo compound. The ultraviolet lamp is a fluorescent tube in which mercury vapor is filled in the tube, and fluorescent tubes having various emission wavelengths can be obtained depending on the type of fluorescent material applied to the inner wall of the tube.

[0044]

INDUSTRIAL APPLICABILITY The multicolor heat-sensitive recording material of the present invention uses a heat-sensitive layer containing a photodecomposable diazo compound capable of being photofixed as a color-forming component, and therefore has a good heat fraction.
Further, since the heat-sensitive layer contains para-hydroxybenzoic acid having 8 to 18 carbon atoms, the storability is good even though a high image density can be obtained.

[0045]

EXAMPLES Examples will be shown below, but the present invention is not limited thereto. All "parts" in the examples indicate parts by weight.

Example 1. (1) Preparation of third thermosensitive recording layer liquid [Preparation of capsule liquid of electron-donating dye precursor] Crystal violet lactone which is an electron-donating dye precursor
After dissolving 3.0 parts in 20 parts of ethyl acetate, 20 parts of alkylnaphthalene, which is a high boiling point solvent, was added and heated to be mixed uniformly. Next, as a capsule wall agent in this mixed solution,
20 parts of xylylene diisocyanate / trimethylolpropane adduct was added and stirred uniformly.

Next, a 6 wt% aqueous solution of separately prepared polyvinyl alcohol (polymerization degree 1700, saponification degree 88%) 5
The above electron-donating dye precursor solution was added to 4 parts, and the mixture was emulsified and dispersed using a homogenizer. 68 parts of water was added to the obtained emulsion for homogenization, the temperature was raised to 50 ° C. with stirring, and the encapsulation reaction was carried out for 3 hours to obtain a target capsule solution. The average particle size of the capsule was 1.6 μm.

[Preparation of Dispersion of Electron-Accepting Compound] 30 parts of bisphenol A, which is an electron-accepting compound, was added to 150 parts of an aqueous 4% by weight polyvinyl alcohol solution, and the mixture was dispersed for 24 hours using a ball mill to obtain a dispersion. It was made. The average particle size of the electron-accepting compound in the dispersion was 1.2 μm.

[Preparation of Coating Liquid] The above electron-donating dye precursor capsule liquid and the electron-accepting compound dispersion liquid were mixed so that the ratio of the electron-donating dye precursor / electron-accepting compound was 1/2. To prepare a coating solution.

(2) Preparation of second thermosensitive recording layer liquid [Preparation of capsule liquid of diazo compound] 4- (N- (2-
(2,4-di-tert-amylphenoxy) butyryl) piperazinobenzenediazonium hexafluorophosphate 2.0 parts was dissolved in 20 parts ethyl acetate, and then 20 parts of a high boiling solvent alkylnaphthalene was added and heated. And mixed evenly. Next, xylylene diisocyanate /
15 parts of trimethylolpropane adduct was added and stirred uniformly.

Next, a 6 wt% aqueous solution of separately prepared polyvinyl alcohol (polymerization degree 1700, saponification degree 88%) 5
To 4 parts, add the solution in which the diazo compound is dissolved,
It was emulsified and dispersed using a homogenizer. 68 parts of water was added to the obtained emulsion to homogenize it, and the mixture was stirred at 40 ° C.
The temperature was raised to 3, and the encapsulation reaction was performed for 3 hours to obtain a capsule liquid. The average particle size of the capsule was 1.1 μm.

[Preparation of Coupler Dispersion] 10 parts of 1- (2′-octylphenyl) -3-methyl-5-pyrazolone as a coupler and 20 parts of dodecyl parahydroxybenzoate in a 4% by weight polyvinyl alcohol aqueous solution. 150
It was added to each part and dispersed using a ball mill for 24 hours to prepare a dispersion liquid. The average particle size of the coupler in the dispersion is 1.
It was 2 μm.

[Preparation of Coating Liquid] The above-mentioned diazo compound capsule liquid and coupler dispersion liquid were mixed at a diazo compound / coupler ratio of 2/3 to prepare a coating liquid.

(3) Preparation of first heat-sensitive recording layer liquid [Preparation of capsule liquid of diazo compound] 2,5-dibutoxy-4-tolylthiobenzenediazonium hexafluorophosphate: 3.0 parts of ethyl acetate 20 After dissolving in 1 part, 20 parts of a high boiling point solvent, alkylnaphthalene, was added and heated to uniformly mix. Next, 15 parts of xylylene diisocyanate / trimethylolpropane adduct as a capsule wall agent was added to the obtained mixed liquid,
Stir evenly.

Next, a 6 wt% aqueous solution of separately prepared polyvinyl alcohol (polymerization degree 1700, saponification degree 88%) 5
The above solution of the diazo compound was added to 4 parts and emulsified and dispersed using a homogenizer. 68 parts of water was added to the obtained emulsion to homogenize it, and then the temperature was raised to 40 ° C. with stirring and 3
The encapsulation reaction was performed for a time to obtain a capsule liquid. The average particle size of the capsule was 1.0 μm.

[Preparation of Coupler Dispersion] 2-Chloro-5
-Octylacetoacetanilide as coupler 10
Parts, 5 parts of 1,2,3-triphenylguanidine as an organic base and 20 parts of dodecyl parahydroxybenzoate were added to 200 parts of a 4% by weight polyvinyl alcohol aqueous solution,
A ball mill was used for dispersion for 24 hours to prepare a dispersion liquid. The average particle size of the dispersion was 1.2 μm.

[Preparation of Coating Liquid] The above-mentioned diazo compound capsule liquid and coupler dispersion liquid were mixed at a diazo compound / coupler ratio of 4/5 to prepare a coating liquid.

(4) Coating On a printing paper support prepared by laminating polyethylene on a high-quality paper, a wire bar is used to sequentially coat and dry the third heat-sensitive recording layer, the second heat-sensitive recording layer and the first heat-sensitive recording layer. The intended multicolor thermosensitive recording material was obtained. The coating amount as solid content was 5.2 g / m ² , 6.3 g / m ² and 6.8 g / m ² , respectively.
^{Was 2} .

(5) Thermal recording Using a thermal head (KST type) manufactured by Kyocera Corporation,
The applied power and pulse width to the thermal head were determined so that the recording energy per unit area was 25 mJ / mm ^2, and the first heat-sensitive recording layer was thermally printed to obtain a yellow image, and the emission center wavelength was 420 nm. The whole surface was irradiated with light for 10 seconds using an ultraviolet lamp with an output of 40W.

Then, the applied power to the thermal head and the pulse width were determined so that the recording energy per unit area was 40 mJ / mm ^2, and thermal printing was performed on the second thermosensitive recording layer to obtain a magenta image, and then the light was emitted. Center wavelength is 365
The whole surface was irradiated with light for 15 seconds using a UV lamp having a wavelength of 40 W and an output of 40 W.

Finally, the power applied to the thermal head and the pulse width were determined so that the recording energy per unit area was 60 mJ / mm ^2, and thermal printing was carried out on the third thermosensitive recording layer to obtain a cyan image. This gives magenta,
Image recordings of yellow, cyan, cyan + magenta (blue), magenta + yellow (red), cyan + yellow (green) and cyan + magenta + yellow (black) were obtained. The unrecorded area was grayish white, and it was confirmed that the image clarity was excellent.

Example 2. (1) Preparation of third thermosensitive recording layer liquid [Preparation of capsule liquid of electron-donating dye precursor] As an electron-donating dye precursor, 3- (o-methyl-p-dimethylamino) was used instead of crystal violet lactone. A capsule liquid was prepared in the same manner as in Example 1 except that phenyl) -3- (1′-ethyl-2′-methylindol-3-yl) phthalide was used.

[Preparation of Emulsion of Electron-Accepting Compound] 1,
A solution prepared by dissolving 5 parts of 1- (p-hydroxyphenyl) -2-ethylhexane as an electron accepting compound, 0.3 parts of tricresyl phosphate and 0.1 part of diethyl maleate in 10 parts of ethyl acetate, 50 g of a 6% by weight polyvinyl alcohol solution and 2 g of a 2% by weight sodium dodecyl sulfonate solution were put into an aqueous solution and emulsified with a homogenizer for 10 minutes to obtain an electron-accepting compound emulsion.

[Preparation of Coating Liquid] The above electron-donating dye precursor capsule liquid and the electron-accepting compound emulsion are mixed so that the ratio of electron-donating dye precursor / electron-accepting compound is 1/4. Then, a coating solution was prepared.

(2) Preparation of Second Thermosensitive Recording Layer Liquid [Preparation of Capsule Liquid of Diazo Compound] The capsule liquid prepared in Example 1 was used as it was.

[Preparation of Coupler Emulsion] The coupler used in Example 1 was: 2 parts, 1,2,3-triphenylguanidine: 2 parts, parahydroxybenzoic acid dodecyl: 4
Parts, tricresyl phosphate: 0.3 parts and diethyl maleate: 0.1 parts, dissolved in 10 parts ethyl acetate,
The obtained solution is a 6% by weight polyvinyl alcohol solution 5
0 g and 2 wt% sodium dodecyl sulfonate solution 2
g into a mixed aqueous solution, and use a homogenizer to
Emulsified for minutes to obtain a coupler emulsion.

[Preparation of Coating Solution] The capsule solution of the diazo compound and the coupler emulsion described above were mixed at a diazo compound / coupler ratio of 2/3 to prepare a target coating solution.

(3) Preparation of first thermosensitive recording layer liquid [Preparation of capsule liquid of diazo compound] The capsule liquid prepared in Example 1 was used as it was.

[Preparation of coupler emulsion] 2-chloro-5- (3- (2,4-di-tert-pentyl) phenoxypropylamino) acetoacetanilide as a coupler: 2 parts, 1,2,3-triphenyl Guanidine: 1
Parts, dodecyl parahydroxybenzoate: 4 parts, tricresyl phosphate: 0.3 parts and diethyl maleate:
0.1 part was dissolved in 10 parts of ethyl acetate, and the obtained solution was put into an aqueous solution in which 50 g of a 6% by weight polyvinyl alcohol solution and 2 g of a 2% by weight sodium dodecylsulfonate solution were mixed, and a homogenizer was used. It was emulsified for 10 minutes to obtain an emulsion of coupler.

[Preparation of Coating Liquid] The above-mentioned diazo compound capsule liquid and coupler emulsion were mixed so that the ratio of diazo compound / coupler was 2/3 to prepare a coating liquid.

(4) Coating On a polyethylene terephthalate support having a thickness of 75 μ,
Using a wire bar, the third thermosensitive recording layer, the second thermosensitive recording layer, and the first thermosensitive recording layer were sequentially coated and dried to obtain a multicolor thermosensitive recording material. The coating amount of the solid content respectively ^{6.1g / m 2, 7.8g / m} 2 and 7.2 g / m ²
Met. The resulting thermal recording material was almost transparent and light transmissive.

(5) Thermal recording Using a thermal head (KST type) manufactured by Kyocera Corporation,
The applied power to the thermal head and the pulse width were determined so that the recording energy per unit area was 25 mJ / mm ^2, and the yellow image was formed by thermal printing on the first thermosensitive recording layer and then the emission center wavelength was 420 nm. Output 40W
The whole surface was irradiated with the ultraviolet lamp for 10 seconds.

Next, the applied power to the thermal head and the pulse width were determined so that the recording energy per unit area was 40 mJ / mm ^2, and the second thermal recording layer was thermally printed to form a magenta image. Emission center wavelength is 36
The entire surface was irradiated with light for 15 seconds using an ultraviolet lamp of 5 nm and an output of 40 W.

Further, the recording energy per unit area is 6
The applied power and pulse width to the thermal head were determined so as to be 0 mJ / mm ^2, and thermal printing was performed on the third thermosensitive recording layer to obtain a cyan colored image, whereby 7 colors were developed as in the case of Example 1. I got an image.

Example 3. A thermosensitive recording material was obtained in the same manner as in Example 2 except that octyl parahydroxybenzoate was used instead of dodecyl parahydroxybenzoate used in Example 2, and recording was carried out in the same manner as in Example 2, Example 2
The same good image was obtained.

Example 4. A thermosensitive recording material was obtained in the same manner as in Example 2 except that 2-ethylhexyl parahydroxybenzoate was used in place of the dodecyl parahydroxybenzoate used in Example 2, and an image was recorded in the same manner as in Example 2. As a result, the same result as in Example 2 was obtained.

Example 5. A thermosensitive recording material was obtained in the same manner as in Example 2 except that hexadecyl parahydroxybenzoate was used in place of dodecyl parahydroxybenzoate used in Example 2, and the image recording was carried out in the same manner as in Example 2.
The same result as in Example 2 was obtained.

Example 6. A thermosensitive recording material was obtained in the same manner as in Example 2 except that octadecyl parahydroxybenzoate was used instead of dodecyl parahydroxybenzoate used in Example 2, and the result of image recording was performed in the same manner as in Example 2,
The same result as in Example 2 was obtained.

Example 7. A thermosensitive recording material was obtained in the same manner as in Example 2 except that the second thermosensitive coloring layer used in Example 2 did not use dodecyl parahydroxybenzoate.
As a result of recording an image in the same manner as, the same result as in Example 2 was obtained.

Comparative Example 1. A thermosensitive recording material was obtained in the same manner as in Example 1 except that dodecyl parahydroxybenzoate in the thermosensitive coloring layer used in Example 1 was not used, and recording was carried out in the same manner as in Example 1 to obtain yellow and magenta image densities. Were as low as 0.95 and 0.92, respectively.

Comparative Example 2. A thermosensitive recording material was obtained in the same manner as in Example 2 except that dodecyl parahydroxybenzoate in the thermosensitive coloring layer used in Example 2 was not used. Recording was carried out in the same manner as in Example 2, and the image densities of yellow and magenta were obtained. Were as low as 0.91 and 0.89, respectively.

Comparative Example 3. A thermosensitive recording material was obtained in the same manner as in Example 1 except that ethyl parahydroxybenzoate was used instead of dodecyl parahydroxybenzoate in the thermosensitive coloring layer used in Example 2, and printing was performed in the same manner as in Example 1. did. The obtained image density was sufficiently high, but the background density was also high,
It was confirmed that the image lacked sharpness.

Comparative Example 4. A thermosensitive recording material was obtained in the same manner as in Example 1 except that hexyl parahydroxybenzoate was used instead of dodecyl parahydroxybenzoate in the thermosensitive coloring layer used in Example 2, and printing was performed in the same manner as in Example 1. did.
The obtained image density was sufficiently high, but the background density was also high, and it was confirmed that the image lacked sharpness.

Comparative Example 5. A thermosensitive recording material was obtained in the same manner as in Example 1 except that eicosyl parahydroxybenzoate was used instead of dodecyl parahydroxybenzoate in the thermosensitive coloring layer used in Example 2, and printing was performed in the same manner as in Example 1. did. In this case, the background density was high relative to the image density, and the image clarity was poor.

Table 1 shows the coloring density of each color and Table 2 shows the background density in each of the examples and comparative examples. Further, the thermal recording materials obtained in each of the examples and the comparative examples were heated to 40 ° C.
Table 3 shows the coloring density of each color and Table 4 shows the density of the background when the ink is left in a constant temperature and humidity tank of −90% RH for 24 hours, taken out, adjusted to room temperature and normal humidity for 1 hour, and then printed in the same manner. Shown in.

These results show that the alkyl group has 8 carbon atoms.
In the case of the present invention using ~ 18 parahydroxybenzoic acid esters, all of them are excellent in color developability and have good background, while as comparative examples, those not using parahydroxybenzoic acid ester and having 20 carbon atoms. It has been proved that the ones having poor coloring properties and the ones having 2 or 6 carbon atoms of the alkyl group have high coloring of the background and cannot be practically used from the viewpoint of storage stability.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Brief description of drawings]

FIG. 1 is a cross-sectional conceptual diagram of a multicolor thermosensitive recording material of the present invention in which the thermosensitive layer has two layers.

FIG. 2 is a conceptual cross-sectional view of the multicolor thermosensitive recording material of the present invention when the thermosensitive layer has three layers.

[Explanation of symbols]

1: Support 2: Thermosensitive recording layer containing an electron-donating dye precursor and an electron-accepting compound as a coloring component 3: Thermosensitive recording layer containing a diazo compound and a coupler as a coloring component 4: A diazo compound and a coupler as coloring components Heat-sensitive recording layer 21: Electron-donating dye precursor 22: Electron-accepting compound 31: Diazo salt compound 32: Coupler 33: Parahydroxybenzoic acid ester 41: Diazo salt compound 42: Coupler 43: Parahydroxybenzoic acid ester

Claims (1)

Claim: What is claimed is: 1. A support has at least two or more thermosensitive coloring layers, and at least one layer of the thermosensitive coloring layers reacts with a diazo compound and the diazo compound to develop a color. In a multicolor thermosensitive recording material containing a coupler as a main component, a thermosensitive coloring layer containing the diazo compound and a coupler that reacts with the diazo compound to form a color, a parahydroxybenzoic acid having an alkyl group having 8 to 18 carbon atoms. A multicolor heat-sensitive recording material comprising at least one alkyl ester. 2. The multicolor thermosensitive recording material according to claim 1, wherein at least one of the color-forming components in each layer is encapsulated in microcapsules.