JPH11208114A - Thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording material having high sensitivity and being free of occurrence of void or the like and excellent in image uniformity. SOLUTION: In a thermal recording material prepared by laminating sequentially on a substrate an intermediate layer and a thermal recording layer constituted mainly of a leuco dye and a developer developing the color of the leuco dye in heating, the intermediate layer is constituted of thermoplastic resin and contains hollowness percentage resin particles of which the ratio (Dv/Dn) between a volume-average particle size (Dv) and a number-average particle size (Dn) is 1-1.3 and the percentage of hollowness is 6O% or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having an undercoat layer between a support and a heat-sensitive recording layer.

[0002]

2. Description of the Related Art In recent years, with the diversification of information and the expanding needs, various recording materials have been researched, developed and put into practical use in the information recording field. Capable of recording various images,
It has the advantages that the necessary mechanism of the device is simple and easy to make compact, and that the recording material is easy to handle and inexpensive. Therefore, it has advantages such as information processing field (output of desktop computer and computer, etc.), medical measurement recorder field, It is used in a wide variety of fields, such as high-speed facsimile machines, automatic ticket vending machines (passenger tickets, admission tickets, etc.), thermal copying machines, and POS system labels. In recent years, there has been a demand for smaller and faster devices. Accordingly, there is a demand for a heat-sensitive recording material having higher sensitivity in response to a reduction in printing energy accompanying a reduction in size and speed.

A thermosensitive recording material is usually produced by applying and drying a thermosensitive coloring liquid containing a coloring component capable of causing a coloring reaction upon heating on a support such as paper or a synthetic resin film. The resulting heat-sensitive recording material is heated with a hot pen or thermal head to record a color image. As a conventional example of such a heat-sensitive recording material, there is, for example, a heat-sensitive recording material disclosed in JP-A-43-4160 or JP-B-45-14039. And the color density was not sufficient at the time of high-speed recording. As a method for remedying such a defect, for example, Japanese Patent Application Laid-Open No. 49-38424 discloses the use of nitrogen-containing compounds such as acetamide, stearylamide, m-nitroaniline, and dinitrile phthalate. Acetoacetic acid anilide was used in JP-A-53-39139.
Japanese Patent Application Laid-Open No. 53-391 discloses an N, N-diphenylamine derivative benzamide derivative and a carbazole derivative.
No. 39 discloses alkylated biphenyl and biphenyl alkane, and JP-A-56-144193 discloses p-
Methods for increasing the speed and increasing the sensitivity by adding a hydroxybenzoic acid derivative are disclosed, but no satisfactory results have been obtained by any of the methods. Further, as described in JP-A-55-164192, the thermal conductivity of the support is set to 0.04 Kcal / m. h. C. or lower, or various fine hollow particles (resin, glass, aluminosilicate type, etc.) are used as an undercoat layer on a support (JP-A-59-5093 and JP-A-59-225987).
However, in these cases, it is difficult to form a uniform underlayer, and the surface tends to be non-uniform, so that the formed image lacks uniformity.

Japanese Patent Application Laid-Open No. Hei 4-241987 discloses an under layer in which thermoplastic resin particles having an average particle size of 2 to 10 μm and a hollow ratio of 90% or more are used.
Japanese Patent Application Laid-Open No. 939/939 discloses an under layer in which hollow particles having a particle size range of 2 to 20 μm and a specific gravity of 0.21 or less are used. Although a method of containing the above hollow particles and a block copolymer of ethylene oxide and propylene oxide has been proposed, the hollow particles used therein have a wide particle size distribution, and large particles of 10 to 30 μm are also present. When a heat-sensitive recording layer is provided on an undercoat layer using these materials, large particles of the underlayer have portions where the heat-sensitive recording layer is not formed, and white spots tend to occur when a solid image is printed.

Further, JP-A-3-147888 discloses that the hollow volume ratio is 35 to 60% and the average particle size is 0.4 to 1.5.
An undercoat layer containing synthetic resin hollow particles having a thickness of μm has been proposed. Japanese Patent Application Laid-Open No. 224688/1990 discloses an undercoat layer containing non-foamable fine hollow particles having a hollow ratio of 30% or more as a main component. It has been proposed to provide a layer, but these have insufficient hollow insulation due to a low hollow ratio and are insufficient in terms of high sensitivity.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material which is improved in the above-mentioned disadvantages of the prior art and which has high sensitivity and excellent image uniformity without occurrence of white spots or the like. .

[0007]

The inventors of the present invention have conducted intensive studies and as a result, have found that the above problems have been solved by the present invention in (1) the intermediate layer, the leuco dye on the support, and the color development that causes the leuco dye to develop color upon heating. In a heat-sensitive recording material obtained by sequentially laminating a heat-sensitive recording layer mainly containing an agent, a volume average particle diameter (Dv) and a number average particle diameter (Dv) in which the intermediate layer is made of a thermoplastic resin.
a thermosensitive recording material comprising hollow resin particles having a ratio (Dv / Dn) to n) of 1 to 1.3 and a hollow ratio of 60% or more. (2) "The heat-sensitive recording material according to item (1), wherein the hollow resin particles have a volume average particle diameter (Dv) of 0.3 to 10.0 [mu] m.", (3) "The heat-sensitive recording material according to the above item (1) or (2), wherein the hollow resin particles are produced by a film emulsification method", (4) "the hollow resin particles have a hollow ratio of 8;
The above item (1), wherein the content is 0 to 95%.
(3) The heat-sensitive recording material according to any one of the above (1) to (3). To solve the problem.

In the present invention, the volume average particle diameter (Dv) and the number average particle diameter (Dv) of the hollow resin contained in the intermediate layer are determined.
n) and the ratio (Dv / Dn) is 1 to 1.3, and has a sharp particle size. When hollow particles having a sharp particle size distribution are used for the intermediate layer, an intermediate layer having a uniform surface is formed. Therefore, when an image is printed by uniformly applying the heat-sensitive recording layer formed thereon. There are no coating defects such as white spots, and the uniformity of the surface of the thermal recording material is maintained, so the adhesion to the thermal head is good, and the print image is excellent in definition and the thermal head heat is efficiently used for thermal recording. Higher sensitivity is achieved because it is transmitted to the material surface. More preferably, Dv / Dn = 1 to 1.2.

The hollow ratio of the hollow particles is the ratio of the inner diameter to the outer diameter, and is represented by the ratio of the inner diameter of the hollow particles / the outer diameter of the hollow particles × 100 (%). , The thermal energy from the thermal head is efficiently utilized to improve the color sensitivity. The hollow ratio is 60% or more, and preferably hollow particles in the range of 80 to 95% are used. When the hollow ratio is 60% or less, the above effect is small, and when the hollow ratio is high, the heat insulating effect is exhibited. However, when the hollow ratio is 95% or more, the film thickness becomes thin, so that the strength is low and the particle diameter is uniform and small particles. It is difficult to obtain hollow particles of a diameter.

The diameter of the hollow particles is preferably from 0.3 to 10 μm in order to maintain the uniformity of the surface of the heat-sensitive recording material. 0.3
When the hollow ratio is 60% or more, the film thickness is reduced to a thickness of 60 μm or less, and the strength is inferior. The fineness of the printed image is also poor.

Although various methods for producing hollow particles have been proposed, a typical one is a method in which an alkali swellable substance is permeated into polymer particles to polymerize the polymer particles, and after polymerization, alkali is added to swell to hollow the polymer particles. A method of encapsulating a foaming agent or a volatile substance in polymer particles and volatilizing and foaming at the time of drying; a method of forming a W / O / W type monomer emulsion and polymerizing a monomer in an oil layer; There is a method of using a phase separation method by polymerization shrinkage method in a synthetic method, a swelling seed polymerization method, a method of encapsulating a volatile substance as a core substance of a polymer, and a method of volatilizing and foaming the outer layer composed of a thermoplastic polymer. In order to obtain a material having a high rate, a method is preferred in which a volatile substance is included as the core substance of the polymer, and the outer layer is made of a thermoplastic polymer. It is preferable to further employ a membrane emulsification method in the step of dispersing a volatile substance and monomers a particle size distribution in order to obtain a sharp ones in the process.

As the composition of the shell of the hollow particles, for example, acrylate, acrylonitrile, vinyl chloride,
Vinylidene chloride, ethylene, propylene, vinyl acetate,
Polymers or copolymers such as styrene are exemplified. In order to keep the hollow ratio large, it is preferable that the resin has a small oxygen permeability. To provide the intermediate layer on a support,
The hollow particles are obtained by dispersing in water together with a binder such as a known water-soluble polymer or aqueous polymer emulsion of the above-mentioned hollow particles, applying this to the upper surface of the support, and drying.
In this case, the coating amount of the hollow particles is at least 1 g per 1 m ² of the support, and the coating amount of the binder resin may be an amount such that the intermediate layer is strongly bonded to the support. It is 2 to 50 weight based on the total amount.

Known binders for water-soluble polymers and aqueous polymer emulsions include polyvinyl alcohol, starch and its derivatives, methoxycellulose,
Hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer,
Examples include alkali salts of styrene / maleic anhydride, alkali salts of isobutylene / maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, casein and the like.

Examples of the water-soluble emulsion include styrene / butadiene copolymer, styrene / butadiene / acrylic ester copolymer latex, vinyl acetate, vinyl acetate / acrylic acid copolymer, styrene / acrylic ester copolymer, and acrylic ester resin. And emulsions of polyurethane resins and the like. In the undercoat layer, auxiliary additives commonly used in this type of heat-sensitive recording material, such as fillers, heat-fusible components, and surfactants, may be used together with the hollow particles and the binder, if necessary. Can be. Further, in order to smooth the surface of the undercoat layer already formed on the support as described above, the surface may be smoothed by calendering after forming the undercoat layer.

The leuco dye used in the thermosensitive coloring layer of the present invention is used alone or as a mixture of two or more kinds. As such a leuco dye, those applied to this kind of thermosensitive material can be arbitrarily applied. For example, leuco compounds of dyes such as triphenylmethane type, fluoran type, phenothiazine type, auramine type, spiropyran type and indolinophthalide type are preferably used. Specific examples of such leuco dyes include, for example, those shown below.

3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis ( p-dimethylaminophenyl) -6-diethylaminophthalide,
3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino-5,7 -Dimethylfluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7,8-benzfluoran,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
(Np-tolyl-N-ethylamino) -6-methyl-
7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 2- {N- (3'-trifluoromethylphenyl) amino} -6-diethylaminofluoran, 2- {3 6-bis (diethylamino)-
Lactam 9- (o-chloroanilino) xanthylbenzoate, 3-diethylamino-6-methyl-7- (m-trichloromethylanilino) fluoran, 3-diethylamino-7- (o-chloroanilino) fluoran, 3-di- n-butylamino-7- (o-chloroanilino) fluoran, 3-N-methyl-N, n-amylamino-6-
Methyl-7-anilinofluoran, 3-N-methyl-N
-Cyclohexylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3- (N, N-diethylamino) -5
-Methyl-7- (N, N-dibenzylamino) fluoran,

Benzoylleucomethylene blue, 6'-
Chloro-8'-methoxy-benzoindolino-spiropyran, 6'-bromo-3'-methoxy-benzoindolino-spiropyran, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2 ' -Methoxy-5 '
-Chlorophenyl) phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-nitrophenyl) phthalide, 3- (2'-
(Hydroxy-4'-diethylaminophenyl) -3-
(2′-methoxy-5′-methylphenyl) phthalide,
3- (2'-methoxy-4'-dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-
Methylphenyl) phthalide, 3- (N-ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluoran, 3-N-ethyl-N- (2-ethoxypropyl) amino-6-methyl -7-anilinofluoran, 3-N-methyl-N-isobutyl-6-methyl-7
-Anilinofluoran, 3-diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino) fluoran, 3-pyrrolidino-7- (di-p-chlorophenyl) methylanilinofluoran, 3 -Diethylamino-5-chloro-7- (α-phenylethylamino) fluoran, 3- (N-ethyl-p-toluidino)
-7- (α-phenylethylamino) fluoran, 3-
Diethylamino-7- (o-methoxycarbonylphenylamino) fluoran, 3-diethylamino-5-methyl-7- (α-phenylethylamino) fluoran, 3
-Diethylamino-7-piperidinofluoran,

2-chloro-3- (N-methyltoluidino) -7- (pn-butylanilino) fluoran, 3
-Di-n-butylamino-6-methyl-7-anilinofluoran, 3,6-bis (dimethylamino) fluorenespiro (9,3 ')-6'-dimethylaminophthalide,
3- (N-benzyl-N-cyclohexylamino)-
5,6-benzo-7-α-naphthylamino-4′-bromofluoran, 3-diethylamino-6-chloro-7-
Anilinofluoran, 3-diethylamino-6-methyl-7-mesitidino-4 ′, 5′-benzofluoran, 3
-N-methyl-N-isopropyl-6-methyl-7-anilinofluoran, 3-N-ethyl-N-isoamyl-
6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (2 ', 4'-dimethylanilino) fluoran, 3-morpholino-7- (N-propyl-trifluoromethylanilino ) Fluoran, 3-pyrrolidino-7-trifluoromethylanilinofluoran,
3-diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino) fluoran, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluoran, 3-diethylamino-5-chloro- ( α-
Phenylethylamino) fluoran,

3- (N-ethyl-p-toluidino) -7
-(Α-phenylethylamino) fluoran, 3-diethylamino-7- (o-methoxycarbonylphenylamino) fluoran, 3-diethylamino-5-methyl-
7- (α-phenylethylamino) fluoran, 3-diethylamino-7-piperidinofluoran, 2-chloro-3- (N-methyltoluidino) -7- (p-N-butylanilino) fluoran,

3,6-bis (dimethylamino) fluorenespiro (9,3 ')-6'-dimethylaminophthalide, 3- (N-benzyl-N-cyclohexylamino)
-5,6-benzo-7-α-naphthylamino-4′-bromofluoran, 3-diethylamino-6-chloro-7
-Anilinofluoran, 3-N-ethyl-N- (2-ethoxypropyl) amino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl- 7-anilinofluoran, 3-
Diethylamino-6-methyl-7-mesitidino-4 ′,
5'-benzofluoran,

3- (p-dimethylaminophenyl) -3
-{1,1-bis (p-dimethylaminophenyl) ethylene-2-yl} phthalide, 3- (p-dimethylaminophenyl) -3- {1,1-bis (p-dimethylaminophenyl) ethylene-2 -Yl} -6-dimethylaminophthalide, 3- (p-dimethylaminophenyl) -3-
{1-p-dimethylaminophenyl-1-phenylethylene-2-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (1-p-dimethylaminophenyl-
1-p-chlorophenylethylene-2-yl) -6-dimethylaminophthalide, 3- (4'-dimethylamino-
2'-methoxy) -3- (1 "-p-dimethylaminophenyl-1" -p-chlorophenyl-1 ", 3" -butadiene-4 "-yl) benzophthalide, 3- (4'-dimethylamino-2 '-Benzyloxy) -3- (1 "-
p-dimethylaminophenyl-1 ″ -phenyl-1 ″,
3 "-butadiene-4" -yl) benzophthalide, 3-
Dimethylamino-6-dimethylamino-fluorene-9
-Spiro-3 '-(6'-dimethylamino) phthalide,
3,3-bis {2- (p-dimethylaminophenyl)-
2- (p-methoxyphenyl) ethenyl} -4,5
6,7-tetrachlorophthalide, 3-bis {1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl}-
5,6-dichloro-4,7-dibromophthalide, bis (p-dimethylaminostyryl) -1-naphthalenesulfonylmethane, bis (p-dimethylaminostyryl)-
1-p-tolylsulfonylmethane and the like.

As the color developer used in the heat-sensitive color-forming layer of the present invention, various compounds having an electron-accepting property, or an oxidizing agent, for coloring the leuco dye upon contact are applied. These are conventionally known, and specific examples thereof include the following, but are not limited thereto.

4,4'-isopropylidenebisphenol, 4,4'-isopropylidenebis (o-methylphenol), 4,4'-sec-butylidenebisphenol, 4,4'-isopropylidenebis (2-tert −
Butylphenol), zinc p-nitrobenzoate, 1,
3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 2,
2- (3,4'-dihydroxydiphenyl) propane,
Bis (4-hydroxy-3-methylphenyl) sulfide, 4- (β- (p-methoxyphenoxy) ethoxy)
Salicylic acid, 1,7-bis (4-hydroxyphenylthio) -3,5-dioxaheptane, 1,5-bis (4-
(Hydroxyphenylthio) -5-oxaheptane,

Phthalic acid monobenzyl ester monocalcium salt, 4,4'-cyclohexylidenediphenol,
4,4′-isopropylidenebis (2-chlorophenol), 2,2′-methylenebis (4-methyl-6-te
rt-butylphenol), 4,4′-butylidenebis (6-tert-butyl-2-methylphenol),
1,1,3-tris (2-methyl-4-hydroxy-5
-Tert-butyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 4,4'-thiobis (6-tert-
Butyl-2-methylphenol), 4,4'-diphenolsulfone, 4-isopropoxy-4'-hydroxydiphenylsulfone, 4-benzyloxy-4'-hydroxydiphenylsulfone, 4,4'-diphenolsulfoxide, p -Isopropyl hydroxybenzoate, p-
Benzyl hydroxybenzoate, benzyl protocatechuate,

Stearyl gallate, lauryl gallate,
Octyl gallate, 1,3-bis (4-hydroxyphenylthio) -propane, N, N'-diphenylthiourea, N, N'-di (m-chlorophenyl) thiourea, salicylanilide, bis- (4- (Hydroxyphenyl) acetic acid methyl ester, bis- (4-hydroxyphenyl)
Benzyl acetate, 1,3-bis (4-hydroxycumyl) benzene, 1,4-bis (4-hydroxycumyl) benzene, 2,4′-diphenolsulfone, 2,
2′-diallyl-4,4′-diphenol sulfone,
3,4-dihydroxyphenyl-4′-methyldiphenyl sulfone, zinc 1-acetyloxy-2-naphthoate, zinc 2-acetyloxy-3-naphthoate, zinc 2-acetyloxy-1-naphthoate, α, α -Screw (4
-Hydroxylphenyl) -α-methyltoluene, an antipyrine complex of zinc thiocyanate, tetrabromobisphenol A, tetrabromobisphenol S, 4,4′-
Thiobis (2-methylphenol), 4,4′-thiobis (2-chlorophenol) and the like.

In the heat-sensitive recording material of the present invention, the developer is used in an amount of 1 to 20 parts, preferably 2 to 10 parts, per part of the color former. The color developer can be used alone or in combination of two or more, and the color developer can also be used alone or in combination of two or more. For producing the thermosensitive recording material of the present invention, when a leuco dye and a developer are bonded and supported on a support, various conventional binders can be appropriately used, and specific examples thereof include, for example, And the like.

Polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate Water-soluble polymers such as terpolymer / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, alkali salt of isobutylene / maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, casein, Polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer Emulsion and styrene / butadiene copolymer polymer, styrene / butadiene / latex such as acrylic copolymer.

In the present invention, various heat-fusible substances can be used as a sensitivity improver. Specific examples thereof include the following, but are not limited thereto. Absent. Fatty acids such as stearic acid and behenic acid, fatty acid amides such as stearic acid amide and palmitic acid amide, fatty acid metal salts such as zinc stearate, aluminum stearate, calcium stearate, zinc palmitate and zinc behenate, p-benzyl Biphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, phenyl β-naphthoate, 1-hydroxy-
Phenyl 2-naphthoate, methyl 1-hydroxy-2-naphthoate, diphenyl carbonate, gliacol carbonate, dibenzyl terephthalate, dimethyl terephthalate, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4 -Dibenzyloxynaphthalene, 1,2-diphenoxyethane, 1,2-bis (3-
Methylphenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane, 1,4-diphenoxy-2-butene, 1,2-bis (4-methoxyphenylthio) ethane, dibenzoylmethane, 1,4- Diphenylthiobutane, 1,4-diphenylthio-2-butene, 1,3-bis (2-vinyloxyethoxy) benzene, 1,4-bis (2-vinyloxyethoxy) benzene, p- (2-
Vinyloxyethoxy) biphenyl, p-aryloxybiphenyl, p-propargyloxybiphenyl, dibenzoyloxymethane, dibenzoyloxypropane,
Dibenzyl disulfide, 1,1-diphenylethanol, 1,1-diphenylpropanol, p-benzyloxybenzyl alcohol, 1,3-phenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoyl Benzene, 1,2-bis (4-methoxyphenoxy)
Propane, 1,5-bis (4-methoxyphenoxy)-
3-oxapentane, dibenzyl oxalate, bis (4-methylbenzyl) oxalate, bis (4-chlorobenzyl) oxalate and the like.

The thermosensitive coloring layer is prepared by uniformly dispersing or dissolving in a solvent together with a coloring agent, a developing agent, a binder and the like, and coating and drying it on a support. Not done. The dispersed particle size of the color forming layer coating solution is preferably 10 μm or less, more preferably 5 μm or less, and still more preferably 1 μm or less. The thickness of the coloring layer depends on the composition of the coloring layer and the use of the heat-sensitive recording material, but is about 1 to 50 μm, preferably about 3 to 20 μm. In addition, various additives used in ordinary thermosensitive recording paper can be added to the color forming layer coating solution, if necessary, for the purpose of improving coatability or recording characteristics.

As the support in the present invention, either acidic paper or neutral paper can be used. As for the release paper comprising the neutral paper support and the neutral paper, those having a small amount of calcium are preferable. Such a neutral paper having a small amount of calcium and a release paper composed of the neutral paper can be obtained by reducing the ratio of used paper used for papermaking. In addition, calcium carbonate is usually used as an internal additive for the production of neutral paper, and alkyl ketene dimer or alkenyl succinic anhydride is used as a sizing agent. Obtained by combining with a rosin size. The recording method of the thermosensitive recording material of the present invention is not particularly limited, such as a hot pen, a thermal head, and laser heating, depending on the purpose of use.

Next, a production example of the hollow particles of the present invention will be described in detail. Production Example 1 Methyl methacrylate; 30 parts, n-hexane; 30 parts,
Azobisisobutyronitrile; a solution of a mixture of 1.35 parts as a dispersion phase, 2% aqueous polyvinyl alcohol solution;
50 parts are set as the aqueous phase in the membrane emulsification system, and the diameter is;
An O / W emulsion was obtained using microporous glass having a diameter of 10 mm, a length of 100 mm, and a pore diameter of 0.1 μm. This emulsion was heated and foamed to obtain a hollow ratio of 72% and D
A hollow particle emulsion having v / Dn = 1.15, a volume average particle diameter of 0.43 μm, and a solid content of 40% was obtained.

Production Example 2 Methyl methacrylate of Production Example 1; 30 parts, n-hexane; 48 parts of vinylidene chloride, 12 parts of isobutane instead of 30 parts, and a microporous glass having a pore diameter of 0.2 μm. Is a hollow ratio of 8 in the same manner as in Production Example 1.
3%, Dv / Dn = 1.18, volume average particle size 7.5 μ
m, a hollow particle emulsion having a solid content of 40%.

Production Example 3 The same procedure as in Production Example 1 was carried out except that methyl methacrylate; 30 parts, n-hexane; 40 parts of vinylidene chloride, 8 parts of acrylonitrile, and 12 parts of isobutane were used instead of 30 parts. Hollow ratio 87%, Dv / Dn = 1.2
2. A hollow particle emulsion having a volume average particle diameter of 3.5 μm and a solid content of 40% was obtained.

Production Example 4 Methyl methacrylate of Production Example 1; 30 parts, n-hexane; 30 parts of vinylidene chloride instead of 30 parts, acrylonitrile; 8 parts, styrene; 5 parts, isobutane;
Except for using the part, the hollow ratio was 92% and D was the same as in Production Example 1.
A hollow particle emulsion having v / Dn = 1.19, a volume average particle diameter of 1.5 μm, and a solid content of 40% was obtained.

Production Example 5 Methyl methacrylate of Production Example 1; 30 parts, n-hexane; vinylidene chloride; 35 parts, acrylonitrile; 8 parts, methyl methacrylate; 5 parts, izobtan; 12 parts instead of 30 parts In the same manner as in Production Example 1, a hollow particle emulsion having a hollow ratio of 90%, Dv / Dn = 1.08, a volume average particle size of 5.6 μm, and a solid content of 40% was obtained.

Production Examples 6 and 7 An O / W emulsion having the same composition as in Production Example 5 was prepared, and the heating and foaming were stopped in the course of Production Example 5 to obtain hollow particle emulsions shown in Table 1.

[0037]

[Table 1]

Production Example 8 The same composition as in Production Example 1 was dispersed using a homomixer instead of the membrane emulsification system, and the other conditions were the same as in Production Example 1, except that the hollow ratio was 73%, Dv = 0.48 μm, Dv / Dn
= 1.35, a hollow particle emulsion having a solid content of 40% was obtained.

[0039]

Next, the present invention will be described more specifically with reference to examples. The “parts” and “%” shown below are all based on weight. Example 1 Preparation of Coating Solution The following undercoat layer forming solution, thermosensitive coloring layer forming solution, overcoat layer forming solution, and backcoat layer forming solution are prepared.

Preparation of Undercoat Layer Forming Solution Liquid A Fine hollow particles (hollow particles of Production Example 1) 36 parts Styrene / butadiene copolymer latex (solid content concentration 47.5%) 10 parts Water 54 parts The above mixture is stirred and dispersed. Thus, an undercoat layer forming liquid was prepared.

Preparation of thermosensitive coloring layer forming solution Liquid B 3-dibutylamino-6-methyl-N-7-anilinofluorane 20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Water 60 parts Liquid C 4-isopropoxy-4 '-Hydroxydiphenyl sulfone 20 parts 10% aqueous solution of polyvinyl alcohol 25 parts Water 50 parts Liquid D 20 parts 5% aqueous solution of methylcellulose 20 parts Water 50 parts Each of the above mixtures was ground in a magnetic ball mill for 2 days, and liquid B was obtained. Liquid C and liquid D were prepared.

Preparation of thermosensitive color-forming layer forming solution 15 parts of solution B 45 parts of solution C 45 parts of solution D 20% aqueous alkali solution of isobutylene / maleic anhydride copolymer 5 parts The above mixture was stirred to prepare a thermosensitive coloring layer forming solution. Prepared.

Preparation of Overcoat Layer Forming Solution Liquid E 20 parts Aluminum hydroxide 10% aqueous solution of polyvinyl alcohol 20 parts Water 60 parts The above mixture was ground in a magnetic ball mill for 2 days to prepare Liquid E.

The undercoat layer (intermediate layer) was coated with the coating solution of each layer prepared as described above so that the coating amount was 3.0 g / m ² , and the dye coating amount was 0% on the undercoat layer (intermediate layer). .35g / m ² to become as the thermosensitive coloring layer coating and drying, further thereon an overcoat layer so that the amount of the resin attached is 1.6 g / m ^2, also the amount of resin attached to the support backside 0 The backcoat layer was coated and dried so as to have a coating weight of 0.7 g / m ² (the amount of adhesion is a dry adhesion amount), and then subjected to surface treatment with a super calender to obtain the heat-sensitive recording material of the present invention.

Example 2 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used in place of the hollow particles of Production Example 1 in Liquid A of Example 1. . Example 3 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used instead of the hollow particles of Production Example 1 in Liquid A of Example 1. Example 4 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used in place of the hollow particles of Production Example 1 in Liquid A of Example 1. Example 5 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used in place of the hollow particles of Production Example 1 in Liquid A of Example 1. Example 6 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used instead of the hollow particles of Production Example 1 in Liquid A of Example 1.

Comparative Example 1 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the solution A of Example 1 was not used. Comparative Example 2 An under liquid (liquid a) was prepared using the liquid A of Example 1 without using the hollow particles of Production Example 1, and this liquid (a) was used in place of the liquid A of Example 1. A heat-sensitive recording material was obtained in the same manner as in Example 1. Comparative Example 3 In Example A, except that the hollow particles having a hollow ratio of 89%, Mv / Mn = 1.38, and a volume average particle diameter of 3.5 μm were used instead of the hollow particles of Production Example 1, in the liquid A of Example 1. In the same manner as in Example 1, a heat-sensitive recording material of the present invention was obtained. Comparative Example 4 In Example A, except that the hollow particles having a hollow ratio of 40%, Mv / Mn = 1.09, and a volume average particle diameter of 0.7 μm were used instead of the hollow particles of Production Example 1, in the liquid A of Example 1. In the same manner as in Example 1, a heat-sensitive recording material of the present invention was obtained. Comparative Example 5 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used instead of the hollow particles of Production Example 1 in Liquid A of Example 1. Comparative Example 6 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the hollow particles of Production Example 1 were used instead of the hollow particles of Production Example 1 in Liquid A of Example 1.

Evaluation method The heat-sensitive recording material obtained as described above was tested under the following conditions. Table 2 shows the evaluation results. The calendered product with a sensitivity magnification of 0.45 W / head power was applied to a thermal printing tester with a thin film head manufactured by Matsushita Electric Parts Co., Ltd.
Printing is performed with a pulse width of 0.0 to 0.7 mmsec every 1 msec under the condition of one dot per line, recording time of 20 msec / L, and scanning density of 8 × 385 dots / mm, and the print density is measured by Macbeth densitometer RD-914. Then, the pulse width at which the concentration became 1.0 was calculated. (Pulse width of Comparative example 1) / (Pulse width of measured sample) based on Comparative example 1
Calculate as = sensitivity magnification. The larger the value, the better the sensitivity (thermal response). The white calendered product was heated closely at 200 ° C. for 3 seconds using a stunn print to develop color, and white voids were visually determined. ：: no white spots Δ: slight white spots ×: white spots present

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[Table 2]

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As described above, the present invention can provide an excellent heat-sensitive recording material having high sensitivity and no white spots.

Claims (4)

[Claims] 1. A heat-sensitive recording material comprising a support and a heat-sensitive recording layer mainly composed of an intermediate layer and a leuco dye and a color developing agent capable of developing the leuco dye upon heating. The ratio (Dv / D) of the volume average particle diameter (Dv) made of a thermoplastic resin to the number average particle diameter (Dn)
n) is 1 to 1.3, and contains a hollow resin particle having a hollow ratio of 60% or more. 2. The hollow resin particles have a volume average particle diameter (D
2. The heat-sensitive recording material according to claim 1, wherein v) is 0.3 to 10.0 [mu] m. 3. The heat-sensitive recording material according to claim 1, wherein the hollow resin particles are produced by a film emulsification method. 4. The hollow resin particles have a hollow ratio of 80 to 95%.
The heat-sensitive recording material according to any one of claims 1 to 3, wherein