JP3358276B2 - Thermal recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording medium, and more particularly to a heat-sensitive recording medium which has little deterioration of fluorescent whitening and has a high recording density.

[0002]

2. Description of the Related Art Conventionally, a heat-sensitive recording method in which a color-forming image is obtained by contacting both color-forming substances by heat utilizing a color-forming reaction between a color-forming agent and a color-forming agent that forms a color in contact with the color-forming agent. The body is well known. Such a thermosensitive recording medium is relatively inexpensive, and since the recording equipment is compact and its maintenance is relatively easy, recording of a facsimile, various computers, medical equipment, a computer, a thermal copying machine, a printer of various other equipment, and the like is performed. It is used not only as a medium but also in a wide range of fields such as thermal labels. However, there are drawbacks such as poor fingerprint resistance and solvent resistance. For example, when human sebum or a solvent comes into contact with the recording layer, the recording density is reduced, and unnecessary color formation called background fog is caused. As a method for improving such a defect, Japanese Patent Publication No. 1-48353 discloses a thermosensitive recording method in which an intermediate layer mainly composed of an aqueous resin and an overcoat layer containing an electron beam curable resin are sequentially provided on a thermosensitive recording layer. Although a recording medium is described, there is a problem in whiteness.

[0003]

In recent years, there has been a demand for such a thermosensitive recording medium having a higher apparent whiteness. If the whiteness of the surface of the heat-sensitive recording material is 70 to 85% as measured by a Hunter whiteness meter (using a blue filter), the apparent whiteness differs depending on the presence or absence of the fluorescent dye, rather than the difference in the numerical value. For this reason, it is conceivable to add a fluorescent dye.However, the fluorescent dye is generally vulnerable to ionizing radiation and sunlight, and in a thermosensitive recording medium provided with an overcoat layer containing an ionizing radiation-curable resin, the fluorescent dye is irradiated with ionizing radiation, particularly electron beams. The problem is that the fluorescence decay decreases.
SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium which has little deterioration of fluorescent whitening and has a high recording density.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a semiconductor device comprising the steps of:
Heat-sensitive recording layer containing a color former and a color former that forms a color upon contact with the color former, an intermediate layer mainly containing an aqueous binder and a pigment, and an overcoat containing a resin cured by irradiation with ionizing radiation after coating In the heat-sensitive recording medium in which the layers are sequentially provided, the optical density of the background portion is less than 0.2, and a diaminostilbene disulfonic acid-based fluorescent brightener and a naphthol-based azo pigment or disazo are provided in the heat-sensitive recording layer and / or the intermediate layer. This is an invention in which the above object has been achieved by incorporating a pigment.

[0005]

The present invention relates to a heat-sensitive recording material comprising a heat-sensitive recording layer or an intermediate layer provided on the heat-sensitive recording layer, containing a diaminostilbene disulfonic acid-based fluorescent whitening agent and a naphthol-based azo pigment or disazo pigment. The naphthol-based azo pigment or disazo pigment is not particularly limited. Particularly, the naphthol-based azo pigment is preferably represented by the following formula (1) or (2), and the disazo pigment is represented by the following formula ( What is expressed in 3) is preferred.

[0006]

Embedded image

[0007]

Embedded image [In the formula (2), R ₁ represents a hydrogen atom or a phenyl group. R ₂ represents a hydrogen atom, a phenyl group, or a p-ethoxyphenyl group. ]

[0008]

Embedded image [In the formula (3), R ₁ represents a toluyl group, a xylyl group,
Or a methoxy group and a phenyl group substituted with a chlorine atom. ]

[0009]

[0010] is added to the optical density of the background portion of the heat-sensitive recording material is an appropriate amount of the specific azo pigment is less than 0.2
The specific azo pigment is desirably adjusted within a range of 1 to 30% by weight based on the diaminostilbene disulfonic acid-based fluorescent whitening agent. Specific examples of the diaminostilbene disulfonic acid-based fluorescent whitening agent include, for example, sodium 4,4′-diaminostilbene-2,2′-disulfonate, sodium bistriazinylaminostilbene sulfonate, and the like. The amount added is not particularly limited, but is preferably in the range of 0.01 to 5% by weight, more preferably 0.2 to 3% by weight, based on the total solids of the heat-sensitive recording layer or the intermediate layer.

In the present invention, the combination of the color former and the color former contained in the heat-sensitive recording layer is not particularly limited, and any combination may be used as long as the two are brought into contact by heat to cause a color reaction. Can be used,
Examples thereof include a combination of a colorless or light-colored basic dye and an inorganic or organic acidic substance, and a combination of a metal salt of a higher fatty acid such as ferric stearate and a phenol such as gallic acid.

[0012] However, when applied to a combination of a basic dye and an acidic substance, the recording characteristics are extremely excellent, so that it is particularly preferable. Various types of colorless or light-colored basic dyes are known, and examples thereof include the following. 3,3-bis (p-dimethylaminophenyl)
-6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl)
Triallylmethane dyes such as -6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydryl benzyl ether, N-halophenyl-leuco auramine, N-2,4,5-trichlorophenyl leuco aura Diphenylmethane dyes such as min, thiazine dyes such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-
Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-pyran
Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran, 3- Diethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran,
Fluorane dyes such as 3-diethylamino-7-chlorofluoran and 3-dibutylamino-7- (o-chlorophenylamino) fluoran; and other colorless or light-colored basic dyes described in JP-A-3-79387. .

Various inorganic or organic acidic substances which are colored upon contact with a basic colorless dye are also known. Examples thereof include activated clay, acidic clay, attapulgite, bentonite, colloidal silica, and aluminum silicate. Acidic substances, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol and the like, and JP-A-3-79387. And the colorants described in (1).

In the present invention, the use ratio of the color former and the color former in the recording layer should be appropriately selected according to the type of the color former and the color former to be used, and is not particularly limited. Alternatively, when a light-colored basic dye and an acidic substance are used, generally 1 part by weight of the basic dye is used.
10 to 10 parts by weight, preferably about 1 to 5 parts by weight of an acidic substance is used. In preparing a coating solution containing these substances,
Generally, water is used as a dispersion medium, and ball mills, attritors,
The color former and the color former are dispersed together or separately by a stirring / pulverizer such as a sand mill to prepare a coating liquid.

In such a coating liquid, starches, hydroxyethyl cellulose, methyl cellulose,
Carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene
Maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, etc. To 40% by weight, preferably about 15 to 30% by weight.

Further, various auxiliaries can be added to the coating liquid, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, sodium alginate, metal salts of fatty acids Dispersants such as benzophenone,
Examples thereof include triazole-based ultraviolet absorbers and other antifoaming agents.

If necessary, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica Inorganic pigments such as activated clay, 1,2-bis (3-methylphenoxy) ethane, di-p-methylbenzyl oxalate, stearamide, methylenebisamide stearate, oleamide, palmitamide,
Sensitizers such as odorized oleic acid amide and coconut fatty acid amide may also be added.

The coating amount of the coating solution is not particularly limited either, but is usually ² to 12 g / m ² in dry weight,
Preferably, it is in the range of about 3 to 10 g / m ² . In the heat-sensitive recording medium of the present invention, on the heat-sensitive recording layer thus obtained,
The intermediate layer is provided. The aqueous binder used for the intermediate layer includes a water-soluble binder and a water-dispersible binder, and examples thereof include the following.

As a water-soluble binder, completely saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol into which an acetoacetyl group has been introduced by reacting polyvinyl alcohol with diketene, etc.
Reaction products of polyvinyl alcohol with polycarboxylic acids such as fumaric acid, phthalic anhydride, trimellitic anhydride, and itaconic anhydride or esterified products of these reaction products, and furthermore, vinyl acetate and maleic acid, fumaric acid, itaconic acid ,
Crotonic acid, acrylic acid, carboxy-modified polyvinyl alcohol obtained as a saponified copolymer of an ethylenically unsaturated carboxylic acid such as methacrylic acid, vinyl acetate and ethylene sulfonic acid, olefin sulfonic acid such as allyl sulfonic acid or the like. Sulfonic acid-modified polyvinyl alcohol obtained as a saponified product of a copolymer with a salt, saponified copolymer of vinyl acetate and an olefin such as ethylene, propylene, isobutylene, α-octene, α-dotecene, α-octadodecene, etc. Olefin-modified polyvinyl alcohol, and nitrile-modified polyvinyl alcohol obtained as a saponified product of a copolymer of vinyl acetate with nitriles such as acrylonitrile and methacrylonitrile, and amides such as vinyl acetate and acrylamide and methacrylamide. Amide-modified polyvinyl alcohol obtained by saponifying a copolymer of classes, vinyl acetate and N
-Pyrrolidone-modified polyvinyl alcohol obtained by saponifying a copolymer with vinylpyrrolidone, methylcellulose, ethylcellulose, hydroxyethylcellulose,
Examples include cellulose derivatives such as carboxymethylcellulose, and starches such as casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch, and esterified starch.

Water-dispersible binders: styrene-butadiene copolymer emulsion, vinyl acetate-vinyl chloride-ethylene copolymer emulsion, methacrylate-
Butadiene copolymer emulsion and the like. Among these aqueous binders, various modified polyvinyl alcohols,
Cellulose derivatives and casein are preferred, and acetoacetylated polyvinyl alcohol and carboxy-modified polyvinyl alcohol are more preferred.

It is desirable to add a pigment to the intermediate layer in order to enhance smoothness and adhesion to the overcoat layer due to the anchoring effect. Examples of pigments in this case include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, and colloidal silica, and styrene. Examples include microballs, nylon powder, polyethylene powder, urea / formalin resin filler, organic pigments such as raw starch granules, and the like. In addition, the amount of use is generally 5 to 500% by weight, preferably 80 to 35% by weight based on the resin component.
It is blended in the range of about 0% by weight.

Further, if necessary, the coating solution for forming the intermediate layer may be cured with glyoxal, methylol melamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, or the like. If necessary, a lubricant such as zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, Surfactants such as sodium lauryl alcohol sulfate, alginates and fatty acid metal salts, benzophenone-based and triazole-based ultraviolet absorbers, and various assistants such as defoamers can also be added as appropriate.

The coating liquid for forming the intermediate layer is generally prepared as an aqueous coating liquid, and, if necessary, after being sufficiently mixed and dispersed by a mixing / stirring machine such as a mixer, attritor, ball mill, roll mill, etc. It is coated on the heat-sensitive recording layer by a known coating device. After the application, curing and drying may be performed by irradiating ultraviolet rays or electron beams. When a curing agent is used in combination, the curing agent can be applied not only in the coating liquid for forming the intermediate layer but also separately from the coating liquid for forming the intermediate layer. There is an advantage that there is no need to worry about life and a strong curing agent can be selected. The coating amount of the intermediate layer coating solution is not particularly limited. However, if the dry weight is less than 0.1 g / m ² , the desired effects of the present invention cannot be sufficiently obtained, and 20 g / m 2
^If it exceeds ² , the recording sensitivity of the thermosensitive recording medium may be significantly reduced.
² , preferably in the range of about 0.5 to 10 g / m ² .

In the present invention, high-quality paper or
Papers such as art paper and coated paper, laminating films on paper, synthetic paper, plastic films and the like are used. The method for applying the recording layer is not particularly limited, and the recording layer can be formed according to a conventionally known technique. For example, a coating solution is applied by bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating, or the like. Is formed by a method of applying and drying.

Further, if necessary, a similar coating layer may be provided on the back side of the thermosensitive recording medium to further enhance the storability. Further, various known techniques in the field of heat-sensitive recording materials can be added as necessary, such as providing an undercoat layer on the support, applying a pressure-sensitive adhesive treatment to the back surface of the recording material, and processing the pressure-sensitive adhesive label.

By increasing the smoothness of the surface of the intermediate layer, it is possible to obtain a recording medium having a high recording density and gloss. In this case, it is desirable to adjust the time to 100 seconds or more, more preferably to 500 seconds or more, and to adjust the film or synthetic paper base to 500 seconds or more, more preferably 1600 seconds or more.

In the thermal recording medium of the present invention, an overcoat layer containing an ionizing radiation-curable resin is provided on the intermediate layer thus formed. Examples of the ionizing radiation curable resin forming the overcoat layer include the following prepolymers and monomers. As the prepolymer,
(a) aliphatic, alicyclic, aromatic divalent to hexavalent polyhydric alcohols and poly (meth) acrylates of polyalkylene glycols; (b) aliphatic, alicyclic, aromatic, aromatic divalent to hexavalent (C) polyhydric alcohol poly (meth) acrylate obtained by adding an alkylene oxide to the polyhydric alcohol;
Poly (meth) acryloyloxyalkyl phosphate ester; (d) Polyester poly (meth) acrylate; (e)
Epoxy poly (meth) acrylate; (f) polyurethane poly (meth) acrylate; (g) polyamide poly (meth) acrylate; (h) polysiloxane poly (meth) acrylate; (i) ) Vinyl- or diene-based low polymers having an acryloyloxy group; (j) Modified oligoester (meth) acrylates described in the above (a) to (i).

Examples of the monomer include (a) a carboxyl group-containing monomer represented by an ethylenically unsaturated mono- or polycarboxylic acid and a carboxylate-containing monomer such as an alkali metal salt, an ammonium salt or an amine salt thereof. Monomers; (b) ethylenically unsaturated (meth) acrylamide or amide group-containing monomers represented by vinyllactams such as alkyl-substituted (meth) acrylamide, N-vinylpyrrolidone; (c) aliphatic or Sulfonic acid group-containing monomers represented by aromatic vinyl sulfonic acids and sulfonic acid group-containing monomers such as alkali metal salts, ammonium salts and amine salts thereof; (d) ethylenically unsaturated ethers of polyols, Hydroxyl-containing monomers represented by (meth) acrylate esters of polyhydric alcohols; (e) dimethylaminoethyl (meth) Amino group-containing monomers such as acrylate-2-vinylpyridine; (f) quaternary ammonium base-containing monomers; (g) alkyl esters of ethylenically unsaturated carboxylic acids; (h) nitriles such as (meth) acrylonitrile (I) styrene; (j) esters of ethylenically unsaturated alcohols such as vinyl acetate and (meth) allyl acetate; (k) mono-alkylene oxide addition polymer of a compound containing active hydrogen (Meth) acrylates; (l) ester group-containing bifunctional monomers represented by diesters of polybasic acids and unsaturated alcohols; (m) alkylene oxide addition polymers of compounds containing active hydrogen and (meth) Bifunctional monomers consisting of diesters with acrylic acid;

(N) Bisacrylamide such as N, N-methylenebisacrylamide; (o) Bifunctional monomer such as divinylbenzene, divinylethylene glycol, divinylsulfone, divinylether, divinylketone; (p) polycarboxylic acid (Q) a polyfunctional monomer comprising a polyester of an alkylene oxide addition polymer of a compound containing active hydrogen and (meth) acrylic acid; (R) a polyfunctional unsaturated monomer such as trivinylbenzene; The above-mentioned ionizing radiation-curable resins may be used in combination of two or more.

In the present invention, in addition to the ionizing radiation-curable resin, various inorganic pigments such as calcium carbonate and titanium dioxide, pigments obtained by surface-treating inorganic pigments with an organic acid, and benzoguanamine resin powder in the overcoat layer, if necessary. ,
Additives such as raw starch granules, organic pigments such as polyolefin microballs, non-electron beam curable resins, defoamers, silicone and non-silicone leveling agents, lubricants, surfactants, plasticizers, and ultraviolet absorbers You can also.

By adjusting the types and proportions of the various additives, it is possible to form a heat-sensitive recording material having a wide range of surface properties from matte to high gloss. In addition, examples of the non-electron beam curable resin include an acrylic resin, a silicone resin, an alkyd resin, a fluorine resin, and a butyral resin.

The resin component as described above is sufficiently mixed by a suitable mixing stirrer such as a mixer and then applied on the colored layer by various known methods. If necessary, the resin component may be heated. To adjust the viscosity. The amount of coating is not necessarily limited, but may be 0.1 g / m
^If it is less than ² , the desired effects of the present invention cannot be expected, and 20 g /
If the coating amount exceeds m ² , the recording sensitivity of the obtained recording medium may be reduced, so that 0.1 to 20 g / m ² ,
More preferably, it is desirable to adjust within the range of about 1 to 10 g / m ² .

The overcoat layer formed on the intermediate layer is cured by irradiation with ionizing radiation. Examples of ionizing radiation include electron beam, ultraviolet ray, α-ray, β-ray, γ-ray, and X-ray.
Rays, neutron rays, etc., but α rays, β rays, γ rays, X rays
Since there is a danger to the human body, an electron beam or an ultraviolet ray which is easy to handle is preferably used. When an electron beam is used, the amount of the irradiated electron beam is preferably in the range of about 0.1 to 15 Mrad, more preferably about 0.5 to 10 Mrad. 0.1
If it is less than Mrad, the resin component cannot be sufficiently cured, and excessive electron beam irradiation exceeding 15 Mrad may cause coloration or discoloration of the heat-sensitive recording medium, and further reduce the paper strength of the support. There is fear. As a method of irradiating an electron beam, for example, a scanning method, a curtain beam method, a broad beam method, or the like can be adopted, and an acceleration voltage for irradiation is suitably about 100 to 300 KV.

On the other hand, when ultraviolet rays are used, it is necessary to incorporate at least a polymerization initiator or a sensitizer into the coating liquid composition, and 0.2 to 10% by weight based on the above resin component, preferably Is added in the range of about 0.5 to 5% by weight. As a light source for ultraviolet irradiation, 1 to 50 ultraviolet lamps, xenon lamps, tungsten lamps and the like are used, and ultraviolet light having an intensity of about 40 to 200 W / cm is preferably irradiated.

Examples of the polymerization initiator and sensitizer include thioxanthone, benzoin, benzoin alkyl ether xanthone, dimethylxanthone, benzophenone, anthracene, 2,2-diethoxyacetophenone, benzyldimethylketal, benzyldiphenyldisulfide, anthraquinone, Chloroanthraquinone, 2-
Ethyl anthraquinone, 2-tert-butylanthraquinone, N, N'-tetraethyl-4,4'-diaminobenzophenone, 1,1'-dichloroacetophenone and the like.

The above-described electron beam irradiation system has higher productivity than the ultraviolet irradiation system, and has an odor due to the addition of a sensitizer.
It is most preferably used because there is no problem of coloring and it is easy to form a uniform crosslinked structure. The thermosensitive recording medium of the present invention having the overcoat layer thus obtained can be further subjected to a smoothing treatment using a super calender or the like to further improve the recording density and the recording density unevenness.

[0037]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto. Unless otherwise specified, parts and% in examples are parts by weight and% by weight, respectively.

Example 1 Preparation of Solution A 10 parts of 3-di (n-butylamino) -6-methyl-7-alininofluorane, 5% aqueous solution of methylcellulose 5
Part of water and 30 parts of water were pulverized with a sand mill until the average particle diameter became 3 μm to obtain a liquid A.

Liquid B Preparation A composition comprising 20 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone, 5 parts of oxalic acid di-P-methylbenzyl ester, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was subjected to sand milling. And the mixture was pulverized until the average particle diameter became 3 μm to obtain a liquid B.

Formation of heat-sensitive recording layer 45 parts of solution A, 80 parts of solution B, 50% aqueous solution of oxidized starch 50
Parts, 10 parts of water, 2 parts of sodium bistriazinylaminostilbene sulfonate, and 0.2 part of a naphthol azo compound represented by the formula (1) were mixed and stirred to obtain a coating liquid. 80 g / m ² of synthetic paper (trade name; YUPO FPG)
-80, manufactured by Oji Yuka Co., Ltd.) after coating with 5 g / m ²
And dried to form a heat-sensitive recording layer.

Formation of Intermediate Layer Acetoacetylated polyvinyl alcohol (trade name: Z-
200, manufactured by Nippon Synthetic Chemical Co., Ltd.)
A coating solution obtained by mixing and stirring a composition consisting of 100 parts of calcium carbonate (trade name: Softon 1800, manufactured by Bihoku Powder Chemical Co., Ltd.), 20 parts of zinc stearate, and 100 parts of water is coated on the heat-sensitive recording layer. The coating was dried so that the coating amount after drying was 3 g / m ² , dried, and smoothed with a super calender to form an intermediate layer having a Beck smoothness of 8000 seconds.

Formation of Overcoat Layer An acrylate prepolymer (trade name: GRANDI) is formed on the intermediate layer.
100 parts of C EB C20B (Dainippon Ink and Chemicals, Inc.) was applied so that the dry coating amount was 1 g / m ^2, and 4 Mrad was applied with an electron curtain type electron beam irradiation device (CB: 150 type, manufactured by ESI). The resin component was cured by treatment with the irradiation dose to obtain a thermosensitive recording medium having an overcoat layer.

Example 2 The procedure of Example 1 was repeated except that sodium 4,4'-diaminostilbene-2,2'-disulfonate was used instead of sodium bistriazinylaminostilbene sulfonate in forming the heat-sensitive recording layer. A thermosensitive recording medium was obtained in the same manner as in Example 1.

Example 3 In the preparation of solution A, 3-di (n-butylamino) -6
Instead of methyl-7-alininofluoran, 3- (N-
Ethyl-N-isoamylamino) -7- (o-chloroalinino) fluoran was used.
Example 1 except that zinc 4- [3 (p-tolylsulfonyl) propyloxy] salicylate was used in place of -hydroxy-4'-isopropoxydiphenylsulfone.
A thermosensitive recording medium was obtained in the same manner as described above.

Example 4 In the same manner as in Example 1 except that the compound represented by the following formula (5) was used instead of the compound represented by the formula (1) in forming the heat-sensitive recording layer of Example 1. To obtain a thermosensitive recording medium.

[0046]

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Example 5 In forming the heat-sensitive recording layer of Example 1, sodium bistriazinylaminostilbene sulfonate and the naphthol azo compound represented by the formula (1) were not used. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that (Coating liquid for forming intermediate layer) 1000 parts of an 8% aqueous solution of acetoacetylated polyvinyl alcohol (trade name: Z-200, manufactured by Nippon Synthetic Chemical Company), calcium carbonate (trade name: Softon 1800, manufactured by Bihoku Powder Chemical Co., Ltd.) A composition comprising 100 parts, 20 parts of zinc stearate, 10 parts of sodium fluorescent dye bistriazinylaminostilbene sulfonate, 1 part of a naphthol azo compound represented by the formula (1), and 100 parts of water is mixed and stirred. liquid.

Comparative Example 1 The procedure of Example 1 was repeated, except that a dioxazine pigment represented by the following formula (6) was used in place of the compound represented by the formula (1) in forming the heat-sensitive recording layer of Example 1. In the same manner as in Example 1, a thermosensitive recording medium was obtained.

[0049]

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Comparative Example 2 A thermosensitive recording medium was obtained in the same manner as in Comparative Example 1, except that phthalocyanine blue B was used instead of the compound represented by the formula (6).

Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the compound represented by the formula (1) was not used in forming the thermosensitive recording layer of Example 1.

Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the overcoat layer was not provided.

Comparative Example 5 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that sodium bistriazinylaminostilbene sulfonate was not used in forming the heat-sensitive recording layer of Example 1.

The following quality tests were performed on each of the thus obtained thermosensitive recording media, and the results are shown in Table 1. (1) Initial print color density Each thermal recording medium was subjected to a thermal gradient tester (Toyo Seiki Co., Ltd .: Condition 120).
2Kg / cm ² , 10 seconds).
The maximum color density of the obtained recorded image was measured with a Macbeth densitometer (model RD-914, manufactured by Macbeth).

(2) Gloss The gloss of the surface of each thermosensitive recording medium was measured using a variable angle photometer (MURAKA).
MI COLOR RAB. Made, gross meter GM
-3D) at an incident angle of 75 degrees. (The higher the value, the higher the gloss.)

(3) Whiteness The whiteness of the surface of each thermosensitive recording medium was measured with a Hunter whiteness meter (using a blue filter).

(4) Fluorescence Whiteness The fluorescence of the surface of each thermosensitive recording medium was measured with a spectrometer (Hitachi Spectrofluorometer MPF-3). Relative% when the sample of Comparative Example 7 is set to 100 at an excitation wavelength of 347 nm and a fluorescence wavelength of 440 nm. (The higher the value, the higher the fluorescent white color.)

[0058]

[Table 1]

[0059]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention was a thermosensitive recording medium with little deterioration of fluorescent whitening and high recording density.

Claims (3)

(57) [Claims] 1. A heat-sensitive recording layer containing a color former and a color former which forms a color upon contact with the color former, an intermediate layer mainly containing an aqueous binder and a pigment, and irradiation with ionizing radiation after coating. Optical density of the background portion in a thermosensitive recording medium sequentially provided with an overcoat layer containing a resin cured by
Is less than 0.2, and wherein the heat-sensitive recording layer and / or the intermediate layer contains a diaminostilbene disulfonic acid-based fluorescent whitening agent and a naphthol-based azo pigment or disazo pigment. 2. The thermosensitive recording medium according to claim 1, wherein the naphthol azo pigment is represented by the formula (1) or (2). Embedded image Embedded image [In the formula (2), R ₁ represents a hydrogen atom or a phenyl group. R ₂ represents a hydrogen atom, a phenyl group, or a p-ethoxyphenyl group. ] 3. The heat-sensitive recording material according to claim 1 , wherein the disazo pigment is represented by the formula (3) . Embedded image [In the formula (3), R ₁ represents a toluyl group, a xylyl group,
Or a methoxy group and a phenyl group substituted with a chlorine atom. ]