JPH0453791A - Thermal recording material - Google Patents

Abstract

PURPOSE:To prevent the lowering of the saturation and density of a recording image by providing a thermal recording layer containing a diazonium salt and a coupler reacting therewith to form a color on a support and providing a protective layer wherein an org. compound having a specific m.p. is present in a water-soluble polymer in a minute particle state to the uppermost layer. CONSTITUTION:At least one thermal recording layer containing a diazonium salt and a coupler reacting therewith to form a color is provided on a support and a protective layer wherein a 20-100wt.% of an org. compound having an m.p. of 150 deg.C or lower is present in a water-soluble polymer in a minute particle state having a mean particle size of 1mum or less is provided as the uppermost layer. When the org. compound is zinc stearate, the adhesion of refuse to a thermal head is reduced and the adhesion of the protective layer and the thermal head is hard to generate which is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to heat-sensitive recording materials, and in particular to multicolor heat-sensitive recording materials.

(Prior Art) Thermal recording has continued to develop in recent years because it is a simple recording device, highly reliable, and requires no maintenance. Taking advantage of this advantage, several attempts have been made to obtain multicolor images, even full-color images, by thermal recording.

The present inventors have developed a thermosensitive recording layer that can reproduce full-color images by laminating multiple thermosensitive recording layers consisting of a basic dye precursor and an electron-accepting substance and a thermosensitive recording layer consisting of a diazonium salt and a coupler on a support. We have already proposed recording materials. (Japanese Patent Application No. 289384) That is, by sequentially laminating and coating on a support a heat-sensitive recording layer made of an electron-donating dye precursor and an electron-accepting substance, and a heat-sensitive recording layer made of a diazonium salt and a coupler, Recording is carried out using a weak thermal energy that allows only the heat-sensitive recording material made of a diazonium salt and a coupler to develop color, and then the entire surface is irradiated with ultraviolet rays to remove any unreacted material remaining in the heat-sensitive recording layer made of a noazonium salt and coupler. A recording material that can be thermally recorded in two different colors or completely independently by photolyzing the diazonium salt of It is. By using this method and providing multiple heat-sensitive recording layers made of noazonium salts that develop different hues and decompose with light of different wavelengths, it becomes possible to develop three or four colors independently, making it possible to create full-color images. Image records can be obtained.

The present inventors continued intensive research on multicolor thermosensitive recording materials using a thermosensitive recording layer composed of a diazonium salt and a coupler as described above, and as a result, by selecting a diazonium salt, it is possible to obtain an image of any color hue. Although it has excellent features such as being able to fix the recording layer by decomposing the diazonium salt with light of any wavelength, the recording layer becomes cloudy after photofixing due to the nitrogen gas generated during photofixing. I found out that there are also some drawbacks.

That is, in heat-sensitive recording materials, a protective layer is generally provided on the uppermost layer that comes into contact with the thermal head in order to prevent problems such as adhesion with the recording element, ie, the thermal groove, and adhesion of residue to the head. If the protective layer is mainly composed of a water-soluble polymer with a high glass transition point, or if there is a heat-sensitive recording layer made of diazonium salt and a coupler in the heat-sensitive recording layer, it will also prevent the passage of nitrogen gas generated during photofixing. It was confirmed that the particles formed as bubbles and precipitated on the recording layer or the recording layer/protective layer interface. This trend is caused by a recording method in which, after photofixing a heat-sensitive recording layer made of a diazonium salt and a coupler, the heat-sensitive recording layer made of an electron-donating dye precursor and an electron-accepting substance is heated again to develop color. Significant when

If bubbles are generated due to nitrogen gas, the coloring layer will be hidden by the bubbles, which is undesirable as it will significantly reduce the saturation and density of the recorded image.

(Object of the present invention) The object of the present invention is to provide a heat-sensitive recording material having at least one heat-sensitive recording layer containing a diazonium salt and a coupler which reacts with the diazonium salt as a main component on a support. Our objective is to propose a protective layer that suppresses the generation of bubbles caused by nitrogen gas generated by the photolysis of carbon dioxide, and does not cause a decrease in the saturation or density of recorded images.Furthermore, it is possible to record images smoothly using a thermal head. The purpose is to propose a protective layer.

(Structure of the present invention) An object of the present invention is to provide a heat-sensitive recording material in which at least one heat-sensitive recording layer containing a diazonium salt and a coupler that reacts with the diazonium salt as a main component is provided on a support. At least 20% by weight of an organic compound with a melting point of 150°C or less is added to the water-soluble polymer.
This is achieved by a heat-sensitive recording material characterized in that it is provided with a protective layer containing the organic compound in the form of fine particles with an average particle diameter of 1 μm or more.

Furthermore, if the organic compound is zinc stearate,
This is preferable because there is less residue attached to the thermal head and less adhesion between the protective layer and the thermal head.

The reason for this is not clear, but it is presumed that the organic compound contained in the protective layer also melts during thermal recording, making it easier for nitrogen gas produced by photolysis to pass through the protective layer. This means that the melting point of the added organic compound is 15
It is also estimated from the fact that this effect gradually decreases when the temperature exceeds 0° C., and that the bubble suppressing effect gradually decreases when the amount of organic compound added to the water-soluble polymer becomes less than 20% by weight. If the amount of the water-soluble organic compound added exceeds 100% by weight, the organic compound itself will adhere to the thermal head, which is undesirable.

Furthermore, the dispersed particle size of the organic compound is important;
If it is larger than m, the protective layer itself becomes cloudy, which hides the underlying recording layer and reduces the saturation and density of the colored image, which is undesirable. The dispersed particle size of the organic compound is more preferably 0.5 μm or less.

Water-soluble polymers that can be used in the present invention include polyvinyl alcohol, polyvinyl alcohol derivatives, styrene-maleic anhydride copolymers and esters thereof,
Butanene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyacrylamide, polystyrene sulfonic acid, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, oxidized starch,
Examples include phosphorylated starch, gelatin, carboxyl methyl cellulose, methyl cellulose, sodium alginate, sulfated cellulose, and hydroxyethyl cellulose, but polyvinyl alcohol and its derivatives are particularly preferred. Examples of polyvinyl alcohol derivatives include solanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, alkyl-modified polyvinyl alcohol,
Examples include acrylamide/heel alcohol copolymers, and particularly preferred are solanol-modified polyhinyl alcohol and carboxy-modified polyvinyl alcohol, which can be easily crosslinked at room temperature by adding a crosslinking agent.

As the organic compound with a melting point of 150° C. or less that can be used in the present invention, in addition to waxes and metal soaps, any organic compound with low chromaticity can be used, and it does not matter whether it is solid or liquid at room temperature.

Examples of waxes include paraffin wax, polyethylene wax, carnauba wax, microcrystalline wax, rice wax, higher fatty acid amide, and ethylene his higher fatty acid amide.

Metallic soaps include calcium, zinc, and higher fatty acids such as stearic acid, valmitic acid, oleic acid, and behenic acid.
Aluminum, lead, nickel salts, etc. are used, and zinc salts are most preferred from the viewpoint of preventing adhesion of thermal heads.

Furthermore, as an organic compound with a melting point of 150° C. or less and a low sublimation property, materials used for boat fishing thermal recording materials can be used as they are, and specifically, 2.2-bis, which is known as an electron-accepting compound. (p-hydroxyphenyl)pentane, 2,2bis(p-hydroxyphenyl)ethane, 2゜2-bis(p-hydroxyphenyl)butane, 22-bis(4'-hydroxy-3゛-
dichlorophenyl)propane, 1.1-(p-hydroxyphenyl)propane, 1.1-(p-hydroxyphenyl)pentane, 1. I-(p-hydroxyphenyl)
-2-ethylhexane, 3,5-di(α-methylbenzyl)salicylic acid and its polyvalent metal salts, 3,5-di(t
ert-butyl) salicylic acid and its polyvalent metal salts, 3
-α,α-dimethylbenzylsalicylic acid and its polyvalent metal salts, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, 2-ethylhexyl p-hydroxybenzoate, p-phenylphenol p-cumylphenol, sensitization Known as p-hennoloxybenzoic acid, α-naphthyl pencyl ether, β-
Naphthylbenzyl ether, β-naphthoic acid phenyl ester α-hydroxo-β-naphthoic acid phenyl ester, β-su71·-(p-chlorobenzyl) ether, I,4-butanediol phenyl ether, 1,4
-butarenool-p-methylphenyl ether, I,
4-butanediol-p-ethyl phenyl ether, 1
．． 4-butanediol m-methylphenyl ether, 1
-phenoxy-2-(p-tolyloxo)ethane, 1-phenoxy-2-(p-ethylphenoxy)ethane, 1-phenoxy-2-(p-chlorophenoxy)ethane, p-
Examples include benzylbiphenyl.

Next, the heat-sensitive recording material used in the present invention will be described.

The present invention has a heat-sensitive recording layer containing at least one diazonium salt and a coupler as main components, or the diazonium salt that can be used as the heat-sensitive recording layer is a compound that is stable to heat and easily decomposed by appropriate light. selected.

A diazonium salt compound is a compound represented by the general formula % (in the formula, Ar represents an aromatic moiety, N, ゛ represents a diazonium salt, and They have various maximum absorption wavelengths depending on the position and type of the group.

Specific examples of the diazonium salt compound used in the present invention include 4-(N-(2-(2,4-noter)
t-Amylphenogino)butyryl)piperazino)pensendiazonium, 4-dioctylaminohensenazonium, 4-(N-(2-ethylhexanoyl)piperazino)hensendiazonium, 4-dihexolamino-2-hexol Oxybenzenoazonium, 4-N-ethyl-N-hexadecylamino-2-ethoquinohensinazonium, 3-chloro-4-dioctylamino-2-
Octyloquinopenzene diazonium, 2,5-nbutquine-4-morpholinobenzenoazonium, 2,5
-octoquino-4-morpholinopenzene diazonium,
2.5-sibutquin-4-(N-(2-ethylhexanoyl)piperazino)pensensoazonium, 2.5-dieI·ki'/-4-(N-(2-(2,4-: /-t
er tamylphenoxy)butyryl)piperazino)hensendiazonium, 2,5-dibutoxy-4tolylthiobenzendiazonium, 3-(2-octyloxyethogyso)-4-morpholinohensendiazonium, etc. can give.

Couplers that react with the above-mentioned diazonium salts under heat to develop a color include resorcinol, flurgulunone, 23-dihydroxynaphthalene-6-sulfonate, l-lium, l-hydroxy-2-naphthoic acid morpholinopropylamide, 1
, 5-dihydroxonaphthalene, 2,3-dihydroquinonaphthalene, 2,3-nohytoquino-6-sulfanylnaphthalene, 2-hy-1-quino-3-naphthoic acid anilide 2-hydroquino-3-naph]/engineering acid ethanolamide, 2-hyroquine-3-naphthoic acid octylamide,
2-Hydroxy-3-naf]・Engineering acid-N todenoquinobrobilamide, 2-hydroquine 3-naf]・Engineering acid detradesolamide, ace]・anilide, acetoacetanilide toanilide, 2-chloro-5 -Octylacetoacetanilide, l-phenyl-3-methyl-5-pyrazolone, l
-(2°-octylphenyl)3-methyl-5-pyrazolone, l-(2',4'6°-trichlorophenyl)-3-benzamido-5-pyrazolone, l-(2
°． 4″,61-lichlorophenyl)-3-anilino-
Examples include 5-viralone, l-phenyl-3-phenylacetamido 5-pyrazolone, and the like. Two or more of these couplers can be used in combination to obtain the desired color hue.

For the purpose of promoting the reaction between the diazonium salt and the coupler,
Additionally, basic substances are often added. In addition to inorganic or organic basic compounds, the basic substances include compounds that decompose upon heating and release alkaline substances. Representative examples include organic ammonium salts, organic amines, amides, urea and thiourea, and their derivatives, thiazoles, pyrroles, pyrimidines, piperidines, guanidines, indoles, imidazoles, imidacillins, l - Nitrogen-containing compounds such as lyazoles, morpholines, piperidines, amidines, phor I, anones, and pyridines can be mentioned. Specific examples of these include trinochlorohequinylamine, tribenzylamine, octadesol pencylamine, stearylamine, allyl urea, thiourea, methylthiourea, allylthiourea, ethylenethiourea, 2-hencylimidazole,
4-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undenolimidacillin, 2,4.
5-) Rifuryl-2-imidacillin 1,2-diphenyl-4,4-dimethyl-2-imidacillin, 2-phenyl-
2-Imidacillin 1,2,3-triphenylguanine, 1. 2 synchhexylguanidine, 1,2. ll
-Link clohexylguanidine, guanidine trichloroacetate, N,N'-nobenzylpiverazine, 4.4
Examples include dichizai morpholine, morpholinium trichloroacetate, 2-aminobenzothiazole, and 2-penzoylhydranohenzothiazole. Two or more of these can be used in combination.

Materials for heat-sensitive recording layers other than heat-sensitive recording layers containing diazonium salts and couplers as main components include so-called leuco-type heat-sensitive recording layers made of electron-donating dye precursors and electron-accepting compounds, and polyvalent metal salts of higher fatty acids. The most common is a so-called chelate type heat-sensitive recording layer made of gallic acid or the like, or a heat-sensitive recording layer containing an electron-donating dye precursor and an electron-accepting compound as heat-sensitive coloring components.

Typical examples of electron-donating dye precursors include triarylmethane compounds, diphenylmethane compounds, thianone compounds, gysanthene compounds, and spiropyran compounds, among others]-realylmethane compounds, gysanthene compounds It is very useful to have one ship with deep color. Some examples of these include 3,3-his(p-dimethylaminophenyl)-6-dimethylaminophthalyl'
(i.e. crystal violet lactone), 3.3-
His(p-dimethylamino)phthalide, 3-(p-dimethylaminophenyl)-3-(1,3-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylin ]・-3-yl)phthalide, 3-(0-methyl-p-dimethylaminophenyl)-1-(2methylindol-3-yl)phthalide, 4゜4゛-bis(dimethylamino)benz Hydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, Rhodamine-B-anilinolactam, Rhodamine (
p-nitroanilino)lactamrhodamine-B-(p-
chloroanilino)lactam, 2-hensylamino-6-
Diethylaminofluorane, 2-anilino-6-diethylaminofluorane, 2-anilino-3-methyl-6-
Diethylaminofluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-anilino-3-methyl-6-ithamylethylaminofluorane, 2-(o-chloroanilino)-6-diethylaminofluorane , 2-year-old cutylamino-6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-2-diethylaminofluorane, 2-anilino-3
-Chloro-6-diethylaminofluorane, benzoylleucomethylene blue p-nitrobenzylleucomethylene blue-3-methyl-spiro-dinaphthopyran, 3-
Examples include ethyl-spiro-dinaphthopyran, 3,3'-cyclolosevirodinaphthopyran, 3-pensol spiro-dinaphthopyran, and 3-propyl-spiro-dibenzopyran.

The electron-accepting compound can be selected from the compounds listed above as examples of organic compounds that can be added to the protective layer.

Furthermore, a thermofusible substance having a relatively low melting point may be added for the purpose of promoting the reaction between the electron-donating dye precursor and the electron-accepting compound during heating. These can also be selected from among the sensitizers listed above as examples of organic compounds that can be added to the protective layer.

The heat-sensitive recording material is used in the form of fine particles dispersed in a water-soluble polymer, and the water-soluble polymer may be selected from water-soluble polymers that can be used in the protective layer of the present invention. can.

Next, the method for producing the heat-sensitive recording material of the present invention will be described.

In the heat-sensitive recording material of the present invention, all the heat-sensitive recording materials are
It is used by being dispersed in the form of fine particles in a water-soluble polymer.

As a means for this, a heat-sensitive recording material such as a diazonium salt, a coupler, an electron-donating dye precursor, an electron-accepting compound, etc. is added to an aqueous solution of a water-soluble polymer,
There are methods such as finely pulverizing the material using methods such as Santomill and Ryotriter, dissolving it in a solvent and emulsifying the solution using water as a dispersion medium, and microcapsulating the heat-sensitive material as a core material.

In particular, the microencapsulation method is an excellent method for obtaining a heat-sensitive recording material with little coloration on the background, since the color-forming reaction component is strictly isolated by the capsule wall. Furthermore, since diazonium salts are very active substances and easily decompose in the air, it is practical to encapsulate them in microcapsules.

The walls of microcapsules used in heat-sensitive recording materials need to have the property of strictly separating substances inside the capsule from substances outside the capsule at room temperature, but at the same time, when heated, the permeability of the wall increases and promotes the reaction between the two. In other words, it is necessary to use thermoresponsive microcapsules. As the capsule wall material, gelatin, polyurea, polyurethane, polyimide, polyester, polycarbonate, melamine, etc. can be used. In order to obtain thermoresponsive microcapsules, polyurea and polyurethane walls are preferred. In addition, in order to impart thermal responsiveness to the capsule wall, the temperature of the capsule wall should be below the glass transition point or 200°C.
Particularly preferred is a temperature range of 70°C to 150°C.

The glass transition temperature of the capsule wall can be controlled by selecting a type of polymer for the capsule wall or by adding a suitable plasticizer. Such auxiliary agents include phenolic compounds, alcohol compounds, amide compounds, sulfonamide compounds, etc. These may be contained in the core material of the capsule, or may be added outside the microcapsule as a dispersion. good.

For specific examples of microencapsulation techniques, materials and compounds used, see U.S. Pat.
The heat-sensitive recording materials finely dispersed in water-soluble polymers described in No. 796,696 are mixed to form a heat-sensitive recording coating liquid and coated on a support. Since the coated heat-sensitive recording material is protected by the capsule wall or a water-soluble polymer adsorption film, no color reaction occurs at room temperature.

In the present invention, in order to obtain a multicolor image, a plurality of heat-sensitive recording layers that develop different hues are laminated.

In this case, it is preferable to provide an intermediate layer to ensure separation of the heat-sensitive recording layers. As the material for the intermediate layer, the water-soluble polymer mentioned above can be used as is.

Furthermore, a protective layer is provided to provide smooth recording characteristics during thermal head printing.

Is it essential for the protective layer of the present invention to contain an organic compound dispersed in fine particles in a water-soluble polymer aqueous solution? There is a method of adding an organic compound finely dispersed or emulsified by another means into the protective layer, and a method of finely dispersing or emulsifying the organic compound in a water-soluble polymer solution which is the main component of the protective layer.

The coating liquid for each recording layer obtained as described above is sequentially applied onto a support to obtain the desired heat-sensitive recording material.

The coating amount is 05 g/rd to 3.0 g/rd as the coloring layer component (the sum of the electron-donating dye precursor and the electron-accepting compound, or the sum of the diazonium salt and coupler) in each heat-sensitive recording layer.
g/rd, more preferably 0°8g/rr? or 2
．． It is 0g/nf. If it is less than 0.5 [B/rd, sufficient coloring layer density cannot be obtained, and 3.0 g/rr? If it is more than that, it is economically disadvantageous. The solid content of the intermediate layer and protective layer is 0.5g/rr? 30 g/rrf is preferable. If it is less than 0.5 g/nf, sufficient layer separation or resistance to heating of the thermal head cannot be achieved.

Moreover, if the amount exceeds 3.0 g/rrf, heat transfer becomes poor and printing sensitivity decreases.

As the support, known materials such as paper, laminated paper obtained by laminating polyethylene and the like on paper, synthetic paper, and plastic bases such as polyethylene terephthalate, polyimide, and triacetyl cellulose are used.

As a method of coating on the support, air knife coat 1.
Common methods include curtain coat method, slide coat method, roller coat method, dip coat method, wire bar code method, plate coat method, graphia coat method, spin code method, etc. In case of multi-layer structure, multiple layers can be applied at the same time. Bead coating or curtain coating is economically preferred.

Examples will be shown below, but the present invention is not limited thereto. In addition, "1 part" in the examples all indicate parts by weight.

[Example] Examples 1 to 3, Comparative Examples 1 to 2 (11 Preparation of fan coloring leuco-based thermosensitive recording layer liquid [Preparation of electron donating dye precursor capsule liquid] 3- as electron donating dye surface precursor (o-methylp-dimethylaminophenyl') -3-(1ethyl-2'-methylindole-3
-yl) phthalide is dissolved in 20 parts of ethyl acetate, and further 20 parts of alkylnaphthalene, which is a high boiling point solvent, is added.
Heat and mix evenly.

As a capsule wall agent, xylylene diisosoana-1-/
Further 20 parts of trimethylolpropane adduct were added to this solution and stirred uniformly.

Separately, 54 parts of 6% by weight aqueous solution of phthalated gelatin, and 2% by weight aqueous solution of sulfur and lithium dodecol sulfonates.
2 parts of the solution was added, and the electron-donating dye precursor solution was added thereto, followed by emulsification and dispersion using a homogenizer.

After adding 68 parts of water to the obtained emulsion to make it homogeneous, the temperature was raised to 50° C. while stirring, and the encapsulation reaction was carried out for 3 hours to obtain the desired capsule liquid. The average particle size of the capsules is 1.
It was 2 μm.

[Preparation of electron-accepting compound emulsion]

As electron-accepting compounds, 5 parts of 1.1-(p-hydroxyphenyl)-2-ethyl beef sanitation, 0.3 parts of tricresyl phosphate, malein (m') xf-L
Dissolve 1 part of O in 10 parts of ethyl acetate, pour the solution into an aqueous solution containing 50 g of a 6% polynyl alcohol solution and 2 g of a 2% sodium dodecyl sulfonate solution, and emulsify with a homogenizer for 10 minutes to obtain the desired solution. An emulsion was obtained.

[Preparation of coating liquid]

Next, compare the electron-donating dye precursor capsule liquid and electron-accepting compound emulsion with the electron-donating dye precursor/one-child accepting compound ratio. /4 to prepare a desired coating solution.

(2) Preparation of yellow coloring diazo thermosensitive recording layer liquid [Preparation of diazonium salt compound capsule liquid] As a noazonium salt compound, 2,5-butoxo-4-tolylthiobenzene diazonium hexafluorophosphate (420 nm)
(decomposed by light) in 20 parts of ethyl acetate, and further added 20 parts of alkylnaphthalene, a high boiling point solvent.
1 part was added and heated to mix uniformly.

As a capsule wall agent, 15 parts of xylylene shiisophanate/trimethylolpropane adduct was further added to this solution and stirred uniformly.

Separately, add 2 parts to 54 parts of a 6% aqueous solution of phthalated gelatin.
% sodium dodecyl sulfonate solution is prepared, the above diazonium salt compound solution is added,
It was emulsified and dispersed using a homogenizer.

After 68 parts of water was added to the obtained emulsion to make it homogeneous, the temperature was raised to 40° C. without stirring, and the encapsulation reaction was carried out for 3 hours to obtain the desired capsule liquid. The average particle size of capsules is 1.3
It was μ.

[Preparation of coupler dispersion]

As coupler 2-chloro-5-(3-(24-di-tcrt-pentyl)phenoxypropylamino)acetoacetanilide 2 parts, l.

2.3-) 1 part of liphenylguanicine, 3 parts of tricresyl phosphate, 0.1 part of diethyl maleate were dissolved in 10 parts of ethyl acetate, 50 g of 6% aqueous seratin solution, 2% sodium dodecol sulfonate solution Pour the solution into the mixed aqueous solution and mix with a homogenizer for 1
Emulsification was carried out for 0 minutes to obtain the desired emulsion.

(Preparation of coating liquid) Next, mix the above diazonium salt compound capsule liquid and coupler emulsion liquid in a ratio of diazonium salt compound/coupler to 2/2/
3 to prepare a desired coating solution.

(3) Preparation of intermediate layer A 6% aqueous solution of gelatin was used as is.

(4) Preparation of protective layer Noranol modified borihinyl alcohol (Kuraray 2105
) and 5 g of a 30% dispersion of colloidal silica (Snowtex-30, manufactured by Isan Kagaku) as a crosslinking agent were mixed, and polyvinyl alcohol was used as a protective colloid, using a sand mill to reduce the average particle size to 0.5μ.
20% of zinc stearate (melting point 140°C) dispersed in
Five types of coating liquids were prepared, each containing 5g, 7g, 15g, 25g, and 35g of the % dispersion.

(5) On a polyethylene terephthalate support with a coating thickness of 75μ,
A cyan thermosensitive recording layer, an intermediate layer, a yellow thermosensitive recording layer, and a protective layer were laminated in this order on a slide using a slide type hopper type bead coating device to obtain five types of coated sheets for each different protective layer coating solution.

The solid content (dry) coating amount of each coating layer is the same, starting from the bottom layer (cyan layer): 6.1g, 1.0g, 7.2g, 2.
It was 0g.

The five heat-sensitive recording materials obtained were almost transparent and light-transmissive.

Table (6) Thermal Recording Using Kyocera's Maruhead KST type, the applied power and pulse width to the thermal head were determined so that the recording energy per unit area was 34 mJ/mm', and nuclear thermosensitive recording material was printed. did.

The recording material was exposed to an ultraviolet lamp with an emission center wavelength of 420 nm and an output of 40 W for 10 seconds, and the power and pulse width applied to the thermal head were determined so that the recording energy per unit area was 60 mJ/mm8 again. was printed.

(n) In the resulting recorded image, areas where only (I) was recorded are colored yellow, areas where only (II) was recorded are colored cyan, and both (I) and (If) are colored yellow. A green image was obtained where the two overlapped.

Table 1 also shows the degree of contamination of the thermal head after printing and the degree of cloudiness of the recording layer.

In cases where cloudiness was observed, the saturation of the colored image decreased, resulting in a blurred recorded image. Furthermore, when the density of the cyan colored portion was measured using Macbeth's reflection densitometer Model RD-918, reflection densities of 1.8 to 2°0 were obtained for Examples 1 to 3 and Comparative Example 2. On the other hand, the sample of Comparative Example 1 had a value of 1.55.

Comparative Example 3 In Example 2, when a dispersion of zinc stearate having an average particle diameter of 2.1 μm was used, the transparency of the protective layer was insufficient, and even after printing, the colored image appeared to be faded or faded.

It was not possible to make a sufficient judgment as to whether or not bubbles were generated.

Second Person Examples 4 to 5, Comparative Example 4 In Example 1, the amount of zinc stearate used was reduced to 1/3
and the remainder was paraffin wax (melting point 55°C) emulsion (average particle size 0.9 μm), alkylnaphthalene (room temperature liquid) emulsion (average particle size 0.7 μm), ], ]l-bis p-hydroxyphenyl) Cyclohexane (melting point 17
5°C) dispersions (average particle size 1.0 μm) were used to prepare heat-sensitive recording materials. They were evaluated in the same way. Show the results to a second person.

Example 6 When zinc stearate in Example 1 was completely replaced with paraffin wax, adhesion (stick) between the thermal head and the heat-sensitive recording material occurred during recording, and a loud peeling sound was observed during printing.

However, there was no cloudiness in the printed area, and there was only slight head staining.

Example 7 In Example 1, when polyvinyl alcohol was replaced with gelatin as the water-soluble polymer, no clouding of the recording layer was observed, but some head staining occurred.

Comparative Example 5 In Comparative Example 1, only a cyan coloring layer and a protective layer made of an electron-donating dye precursor and an electron-accepting compound were coated on the support without coating a yellow coloring layer containing a diazonium salt and an intermediate layer. Coating. The recording material has an emission center wavelength of 420 nm,
The thermal head was exposed to an ultraviolet lamp with an output of 40 W for 10 seconds, and the power and pulse width applied to the thermal head were determined so that the recording energy per unit area was 60 mJ/mm'.
I printed it. The printed area developed a bright cyan color, and no head stains or clouding of the recording layer were observed at all.

Claims (3)

[Claims] (1) In a heat-sensitive recording material in which at least one heat-sensitive recording layer containing a diazonium salt and a coupler that reacts with the diazonium salt as a main component is provided on a support, the uppermost layer contains a water-soluble polymer with a melting point It is characterized by providing a protective layer containing an organic compound having a temperature of 150° C. or lower from 20% by weight to 100% by weight based on the water-soluble polymer, and in which the organic compound exists in the form of fine particles with an average particle size of 1 μm or less. Heat-sensitive recording material. (2) The heat-sensitive recording material according to claim 1, wherein the organic compound having a melting point of 150° C. or lower is zinc stearate. (3) The heat-sensitive recording material according to claim 2, wherein the water-soluble polymer is polyvinyl alcohol or modified polyvinyl alcohol.