JPH091938A - Thermal recording medium - Google Patents

Abstract

PURPOSE: To obtain a thermal recording medium having excellent reading suitability in a near infrared region and excellent preservability by using fluoran compound represented by a specific formula as leuco dye, and forming pigment in an intermediate layer as a hollow particle in the medium utilizing the color developing reaction of the leuco dye with coloring agent. CONSTITUTION: In the thermal recording medium comprising an intermediate layer containing pigment and adhesive, a thermal recording layer containing leuco dye and coloring agent and a protective layer sequentially provided on a support, as the leuco dye, fluoran compound represented by a formula is used, and the intermediate layer contains hollow particles as the pigment. In the formula, R1 , R2 are 1-6C alkyl group, and R3 , R4 are hydrogen atom or 1-6C alkyl group. As the leuco dye, preferably 3-p-dimethylaminophenylamido-5,7- dimethylfluoran is used. As the hollow particle contained as the pigment in the intermediate layer, spherical hollow particle or foamable filler is used.

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 material utilizing a color-forming reaction between a leuco dye and a color-developing agent, and more particularly to a heat-sensitive recording material having near-infrared readability.

[0002]

2. Description of the Related Art A thermosensitive recording medium is known in which a colored or light-colored leuco dye and an organic or inorganic coloring agent are used to obtain a recorded image by contacting both coloring substances with heat. Has been. Since such a thermal recording medium is relatively inexpensive, the recording device is compact, and its maintenance is easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

One of the fields of use thereof is, for example, POS.
(point of sales) Thermal recording labels or thermal recording tags for systems can be mentioned. In conventional food label applications and clothing tag applications, it is relatively rare to be used under severe conditions. However, in recent years, it has come to be used for industrial applications as well, and it is demanded not only the storage characteristics of recorded images but also high-speed recording and high-speed readability.

In order to perform high-speed reading, a semiconductor laser having an oscillation wavelength in the near infrared region has come to be used as a light source of a reader. Since conventional black-colored leuco dyes do not provide sufficient readability for these light sources, use of dyes having absorption in various near-infrared regions has been investigated, but many of them have not been studied yet. The coloring in the colored state was large, and when the recording body was finished, it had a stain on the background. Further, these dyes have poor storage properties such as light resistance, and have insufficient color development sensitivity, so that a satisfactory heat-sensitive recording material for industrial labels has not yet been obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium which is excellent in color development sensitivity, readability in the near infrared region, whiteness and storage characteristics.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a semiconductor device comprising the steps of:
In a thermal recording medium in which an intermediate layer containing a pigment and an adhesive, a thermal recording layer containing a leuco dye and a color former, and a protective layer are sequentially provided, a fluoran compound represented by the following general formula (1) is used as a leuco dye. By using and by incorporating hollow particles as a pigment in the intermediate layer, the above problems were solved and the present invention was completed.

Embedded image [In the formula, R ₁ and R ₂ each represent a C _{1 to} C ₆ alkyl group. R ₃ and R ₄ each represent a hydrogen atom or a C _{1 to} C ₆ alkyl group. ]

[0007]

The specific fluoran compound represented by the above general formula (1) is superior in light resistance to the recorded area and the background area as compared with the conventional near-infrared reading leuco dye, but has a slightly lower recording sensitivity. However, by containing hollow particles in the intermediate layer provided between the support and the thermosensitive recording layer,
The recording sensitivity and the decrease in whiteness due to slight coloring (yellowish green) of the specific fluoran compound itself were remarkably improved.

The hollow particles contained as a pigment in the intermediate layer of the present invention are spherical hollow particles or expandable fillers. The spherical hollow particles are hollow particles having a hollow interior. When the hollowness is obtained by dividing the outer diameter by the inner diameter, the hollowness is preferably 0.5 to 0.95. When the hollowness is less than 0.5, the effect of improving the recorded image cannot be sufficiently obtained. On the other hand, if it exceeds 0.95, the coating liquid becomes unstable, and there is a problem that it is difficult to obtain a uniform coated surface.

The material of the spherical hollow particles is not particularly limited, but for example, acrylic resin such as acrylic acid ester or acrylonitrile, styrene resin,
Alternatively, copolymer resins thereof may be used.

The average particle size of the spherical hollow particles is preferably 0.1 to 3 μm, more preferably 0.3 to 1.5 μm.
m. If the average particle size is less than 0.1 μm, sufficient hollowness cannot be obtained. On the other hand, when it exceeds 3 μm, not only the smoothness of the surface of the intermediate layer is deteriorated and the quality of the color image is deteriorated, but also the strength of the hollow particles themselves is deteriorated, which is not preferable.

The expandable filler is a resin having a shell made of a thermoplastic resin and propane, butane or the like contained in the shell as a foaming agent. The expandable filler is prepared as a coating material for an intermediate layer together with an adhesive, After being coated and dried on a support, it is heated and foamed. The foaming temperature added at the time of heat foaming is the softening temperature of the thermoplastic resin used for the foamable filler. The average particle diameter of the expandable filler is preferably adjusted in the range of about 2 to 20 μm in the unfoamed state, and in the range of about 10 to 50 μm in the foamed state. As the thermoplastic resin forming the shell of the expandable filler, for example, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic ester,
Examples thereof include polyacrylonitrile, polybutadiene, and copolymers thereof.

In the intermediate layer, various adhesives are used in addition to the spherical hollow particles or the expandable filler. Specific examples thereof include polyvinyl alcohol, modified polyvinyl alcohol, starch and its derivatives, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose,
Carboxymethylcellulose, methoxycellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid terpolymer, styrene-maleic anhydride copolymer salt, isobutylene-anhydrous Water-soluble polymers such as maleic acid copolymer salts, polyacrylamide, sodium alginate, gelatin, and casein,
In addition, styrene-butadiene copolymer, styrene-butadiene-acrylic copolymer, vinyl acetate resin, vinyl acetate-acrylic copolymer, styrene-acrylic acid ester copolymer, acrylic acid ester resin, polyurethane resin, etc. Examples thereof include emulsions, but are not limited to these.

In the intermediate layer, other inorganic or organic pigments may be used in combination, and various auxiliaries such as dispersants and defoamers may be added. The coating amount of the intermediate layer is ^{2 to 20} g / m ²
The thickness may be adjusted within a range of about 2 or more, and two or more layers may be formed if necessary. Since the surface state of the intermediate layer is rough after application or after application and foaming, it is desirable to apply a smoothing treatment such as a super calender.

Specific examples of the fluorane compound represented by the general formula (1) contained as a leuco dye in the heat-sensitive recording layer include, for example, 3-p-dimethylaminophenylamino-
6-methylfluorane, 3-p-dimethylaminophenylamino-7-methylfluorane, 3-p-dimethylaminophenylamino-6-ethylfluorane, 3-p-
Dimethylaminophenylamino-7-butylfluorane, 3-p-dimethylaminophenylamino-5,7-
Dimethylfluorane, 3-p-diethylaminophenylamino-6-methylfluorane, 3-p-diethylaminophenylamino-7-methylfluorane, 3-p-diethylaminophenylamino-7-propylfluorane, 3-p- Diethylaminophenylamino-7-butylfluorane, 3-p-diethylaminophenylamino-5,7-dimethylfluorane, 3-p-dibutylaminophenylamino-5,7-methylfluorane, 3-p
-Dibutylaminophenylamino-7-propylfluorane, 3-p-dibutylaminophenylamino-6,7
-Dimethylfluorane, 3-p- (N-propyl-N-
Methylamino) phenylamino-5,7-dimethylfluorane, 3-p- (N-butyl-N-ethylamino) phenylamino-7-methylfluorane, 3-p- (N-
Butyl-N-ethylamino) phenylamino-6-ethylfluorane, 3-p- (N-butyl-N-ethylamino) phenylamino-7-ethylfluorane, 3-p-
(N-Butyl-N-ethylamino) phenylamino-7
-Propylfluorane, 3-p- (N-butyl-N-ethylamino) phenylamino-7-butylfluorane,
3-p- (N-butyl-N-ethylamino) phenylamino-5,7-dimethylfluorane, 3-p- (N-butyl-N-ethylamino) phenylamino-6,7-dimethylfluorane, etc. Is mentioned. Of course, it is not limited to these, and if necessary, two or more kinds may be used together. Among these, 3-p-
Dimethylaminophenylamino-5,7-dimethylfluorane is particularly excellent in light resistance and background fog,
preferable.

The present invention is characterized in that the fluoran compound represented by the general formula (1) is used in the heat-sensitive recording layer. However, various known colorless and / or colorless compounds are used within a range that does not impair the effects of the present invention. You may use together with a light leuco dye. For example, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide , 3-
(N-Ethyl-N-p-tolyl) amino-7-N-methylanilinofluorane, 3,6-bis (diethylamino) fluorane-γ-anilinolactam, 3-diethylamino-6-methyl-7-chloro Fluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl)
Amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane,
3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 3-di (n-pentyl) amino-6-methyl-7-anilinofluoran, 3-di (n-butyl)
Amino-7- (o-chlorophenylamino) fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-diethylamino-7- (m-
Trifluoromethylanilino) fluorane, 3- (N-
Ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6
-Methyl-7- (p-toluidino) fluorane, 3-diethylamino-6-chloro-7-anilinofluorane,
3,3-bis [1- (4-methoxyphenyl) -1-
(4-Dimethylaminophenyl) ethylene-2-yl]
-4,5,6,7-Tetrachlorophthalide, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthene -2'-ylamino] phenyl} propane,
3,6, -bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide and the like can be mentioned. Of course, it is not limited to these,
If necessary, two or more kinds can be used together.

Various materials are known for the color former used in combination with the leuco dye as described above, and the following are exemplified. 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, hydroquinone monobenzyl ether, 4-hydroxybenzoic acid Benzyl, 4,4 '
-Dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, bis (3-allyl-
4-hydroxyphenyl) sulfone, 4-hydroxy-
4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4
-Dihydroxyphenyl-4'-methylphenyl sulfone, bis (4-hydroxyphenylthioethoxy) methane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α -(4 '
-Hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4'-hydroxyphenyl) ethyl] benzene and other phenolic compounds, N, N'-
Thiourea compounds such as di-m-chlorophenylthiourea, N- (p-toluenesulfonyl) carbamoyl acid p
-Cumylphenyl ester, N- (p-toluenesulfonyl) carbamoyl acid p-benzyloxyphenyl ester, N- (o-toluoyl) -p-toluenesulfoamide, N- (p-toluenesulfonyl) -N '-( p-
Those having a -SO ₂ NH- bond in the molecule, such as tolyl) urea, 4- [2-(p-methoxyphenoxy) ethyloxy] zinc salicylate, 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, zinc , 5- [p-
(2-p-Methoxyphenoxyethoxy) cumyl] zinc salt of salicylic acid derivative such as zinc salicylate. Among them, bis (3-allyl-4-hydroxyphenyl) sulfone is preferably used because it is excellent in storage stability of recorded images. Further, 4,4′-isopropylidenediphenol and 1,1-bis (4-hydroxyphenyl) cyclohexane are preferably used because a high saturated color density can be obtained by combining them with a specific fluorane compound.

The use ratio of the leuco dye and the color-developing agent is appropriately selected according to the type of the leuco dye or the color-developing agent used, and is not particularly limited, but generally 1 part by weight of the leuco dye is used. 1 to 50 parts by weight, preferably 2 to
About 10 parts by weight of a color former is used. A coating material for a heat-sensitive recording layer containing these substances is generally prepared by dispersing a dye and a colorant together or separately with a stirring / pulverizing machine such as a ball mill, an attritor, and a sand mill using water as a dispersion medium. You.

In the coating liquid for the heat-sensitive recording layer, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, or
Casein, gum arabic, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid At least one of a copolymer salt, a styrene / acrylic acid copolymer salt, a styrene / butadiene copolymer emulsion, a urea resin, a melamine resin, an amide resin, a polyurethane resin and the like is 5 to the total solid content of the recording layer. It is mixed in the range of about 30% by weight.

If desired, various auxiliaries can be added, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, dispersant such as fatty acid metal salt, zinc stearate, Waxes such as calcium stearate, polyethylene wax, carnauba wax, paraffin wax and ester wax, defoaming agents, coloring dyes, pigments, sensitizers and storability improvers are appropriately added.

Specific examples of the pigment include kaolin,
Clay, calcium carbonate, calcined clay, calcined kaolin,
Examples thereof include inorganic pigments such as titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, and organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and raw starch particles.

Specific examples of the sensitizer added to increase the recording sensitivity include, for example, stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, and ethylene bis. Stearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate. , 2-naphthylbenzyl ether, m-
Terphenyl, dibenzyl oxalate, oxalic acid-di-p
-Methylbenzyl, oxalic acid-di-p-chlorobenzyl, p-benzylbiphenyl, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,
2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-
Chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p −
Acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane and the like can be mentioned. . The use amount of these sensitizers is not particularly limited, but it is generally desirable to adjust the sensitizer within a range of about 4 parts by weight or less based on 1 part by weight of the color former.

Examples of the storability improver added to enhance the storability of a recorded image include the following. 2,2'-methylenebis (4-methyl-6-tert-
Butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert-butylphenol),
4,4′-thiobis (2-methyl-6-tert-butylphenol), 4,4′-butylidenebis (6-tert-butyl-m-cresol), 1- [α-methyl-α-
(4'-Hydroxyphenyl) ethyl] -4- [α ',
α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3
-Tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4'-thiobis (3-methylphenol), 4,4'-dihydroxy-3,3 ',
5,5'-tetrabromodiphenyl sulfone, 4,4 '
-Dihydroxy-3,3 ', 5,5'-tetramethyldiphenyl sulfone, 2,2-bis (4-hydroxy-
Hindered phenols such as 3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane Compound, 1,4-diglycidyloxybenzene, 4,4'-
Epoxy compounds such as diglycidyloxydiphenyl sulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenyl sulfone, diglycidyl terephthalate, cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, N, N′-di-2-naphthyl-p-phenylenediamine, sodium or polyvalent metal salt of 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, bis (4-ethyleneiminocarbonyl) Aminophenyl) methane, etc. Among them, 1,1,3-
Tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is preferably used because it has an excellent effect on the water resistance of a recorded image and is less likely to cause background fog.

In the present invention, a protective layer containing an adhesive is formed on the heat-sensitive recording layer. Examples of such an adhesive include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and silicon-modified. Polyvinyl alcohol, starch and its derivatives, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin,
Casein, gum arabic, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, silicone-acrylic acid copolymer salt, styrene-acrylic acid copolymer Examples thereof include coalescing salts, styrene-butadiene copolymer emulsions, polyurethane-silicone copolymer emulsions, urea resins, melamine resins, amide resins, polyurethane ionomers and the like. Among them, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol form a strong film, and are therefore preferable as the adhesive for the protective layer.

Various pigments may be used in combination in the protective layer. For example, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, talc, kaolin, clay, and calcination. Examples thereof include inorganic pigments such as kaolin and colloidal silica, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, and raw starch particles. It is generally desirable to adjust the amount used in the range of about 5 to 500 parts by weight with respect to 100 parts by weight of the adhesive component.

Further, in the protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, a surfactant such as dioctyl sulfosuccinate (dispersant, wetting agent). ), Antifoaming agents, various aids such as water-soluble polyvalent metal salts such as antibacterial agents, potassium alum, and aluminum acetate. Further, a curing agent such as glyoxal, boric acid, dialdehyde starch, or an epoxy compound may be added to further improve water resistance.

The method for forming the heat-sensitive recording layer and the protective layer is not particularly limited, and examples thereof include air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating and gravure coating. The coating liquid for heat-sensitive recording layer is applied and dried on the support by a suitable coating method, and then the coating liquid for protective layer is further applied and dried on the recording layer.

As the support, paper (acidic paper, neutral paper),
A plastic film, synthetic paper, non-woven fabric, metal vapor deposition, etc. may be appropriately selected for use, and a second intermediate layer containing an organic or inorganic pigment as a main component may be provided between the intermediate layer and the thermosensitive recording layer. It is also possible to improve the recording image quality. The coating amount of the coating liquid for the heat-sensitive recording layer is 2 to dry weight.
12 g / m ^2, preferably from 3 to 10 g / m ² approximately, 0.1 to 20 g / m ² coating amount of the protective layer coating liquid for a dry weight,
It is preferably adjusted in the range of about 0.5 to 10 g / m ² .

If necessary, a protective layer may be provided on the back surface to further improve the storability, and smoothing treatment such as super calendering may be applied after each layer is applied.
Further, various known techniques in the field of manufacturing a thermal recording medium, such as a pressure-sensitive adhesive treatment applied to the back surface of the recording medium to form an adhesive label or a magnetic recording layer, may be added as necessary.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a weight part and weight%, respectively.

Example 1 Preparation of solution A Hollow pigment (average particle size: 0.4 μm, hollowness 70
%) Of 300%, 50% of a 10% aqueous solution of polyvinyl alcohol, and 30 parts of water were mixed and stirred to obtain a liquid A.

Formation of Intermediate Layer Liquid A is applied to a high-quality paper of 50 g / m ² and the coating amount after drying is 7 g.
After coating and drying so as to be / m ² , super calendering was performed to form an intermediate layer.

Preparation of Solution B A composition comprising 10 parts of 3-p-dimethylaminophenylamino-5,7-dimethylfluorane, 5 parts of a 5% aqueous solution of methylcellulose and 40 parts of water has a mean particle diameter of 2 μm in a sand mill. Was pulverized to obtain a liquid B.

Liquid C Preparation 30 parts of bis (3-allyl-4-hydroxyphenyl) sulfone, 5 parts of a 5% aqueous solution of methylcellulose and 8 parts of water.
0 parts of the composition was sand-milled to have an average particle size of 2 μm
It was crushed until it became C liquid.

Preparation of Solution D A composition consisting of 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was pulverized with a sand mill until the average particle size became 2 μm. Liquid D was obtained.

Formation of Thermosensitive Recording Layer 55 parts of solution B, 115 parts of solution C, 80 parts of solution D, 80 parts of 10% aqueous solution of polyvinyl alcohol, and calcium carbonate 3
The coating solution obtained by mixing and stirring 5 parts was applied and dried on the intermediate layer so that the coating amount after drying was 6 g / m ² , to form a heat-sensitive recording layer.

Formation of protective layer Kaolin [trade name: UW-90, manufactured by EMC] 65 parts,
Acetoacetyl group-modified polyvinyl alcohol [Product name:
Gocefimer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.]
A coating solution for a protective layer obtained by mixing and stirring a composition consisting of 300 parts of a 0% aqueous solution, 6 parts of a 30% dispersion of zinc stearate and 140 parts of water was applied to the obtained thermosensitive recording layer after drying. After coating and drying so that the coating amount was 4 g / m ² , a protective layer was formed, and then super calendar processing was performed to obtain a heat-sensitive recording material.

Example 2 Preparation of solution E Foamable plastic filler (softening temperature: 80-85
℃) 100 parts, 10% aqueous solution of polyvinyl alcohol 1
A composition consisting of 00 parts and 30 parts of water was mixed and stirred to obtain E
A liquid was obtained.

Formation of Intermediate Layer Liquid E is applied on a high-quality paper of 50 g / m ^{2 in} an amount of 4 g after drying.
/ M ² was applied and dried, followed by heat-foaming treatment with a dryer at 150 ° C. for 3 minutes and then super calender treatment to form an intermediate layer.

Formation of Thermosensitive Recording Body A thermal recording layer was formed on the above intermediate layer in the same manner as in Example 1.
Then, a protective layer was sequentially formed to obtain a thermosensitive recording medium.

Example 3 In the preparation of solution B, 3 parts of 3-p-dimethylaminophenylamino-5,7-dimethylfluorane was used instead of 10 parts.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of -p-diethylaminophenylamino-5,7-dimethylfluorane was used.

Example 4 In the preparation of solution B, 3 parts was used instead of 10 parts of 3-p-dimethylaminophenylamino-5,7-dimethylfluorane.
5 parts of -p-dimethylaminophenylamino-5,7-dimethylfluorane and 3-di (n-butyl) amino-7-
A thermosensitive recording medium was obtained in the same manner as in Example 2 except that 5 parts of (o-chlorophenylamino) fluorane was used.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the thermosensitive recording layer and the protective layer were formed on the support without forming the intermediate layer.

Comparative Example 2 In the preparation of solution A, hollow pigments (average particle size: 0.
Instead of 300 parts of a 30% dispersion having a particle size of 4 μm and a hollowness of 70%, non-hollow styrene microballs (average particle size: 0.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 300 parts of a 30% dispersion having a particle size of 4 μm) was used.

Comparative Example 3 In the preparation of solution B, 3-p-dimethylaminophenylamino-5,7-dimethylfluorane was used in place of 10 parts of 3-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of di (n-butyl) amino-7- (o-chlorophenylamino) fluorane was used.

The heat-sensitive recording material thus obtained was subjected to the following evaluation tests, and the results are shown in [Table 1] and [Table 2].
It described in.

[Coloring property] Thermosensitive evaluation machine [Product name: TH-P
MD, Okura Electric Co., Ltd.] applied energy 0.15, 0.25, O.3
The color density of the recorded image obtained by color development at 5,0.45 (mj / dot) was measured by Macbeth densitometer [Macbeth RD-914 type].
It was measured in (visual mode).

[Whiteness] The optical density of the unrecorded area of the obtained thermosensitive recording medium was measured with a Macbeth densitometer (blue filter).

[Lightfastness] The obtained heat-sensitive recording material was colored with an applied energy of 0.45 (mj / dot) in the same manner as in the above-mentioned evaluation of color-developing property, and then 1 with a weather meter (xenon lamp).
After exposure for 5 hours, the optical density of the recorded area was measured with a Macbeth densitometer (visual mode) and the unrecorded area was measured with a Macbeth densitometer (blue filter) to evaluate the light resistance.

[Near infrared reading suitability] A bar code was recorded on the obtained thermal recording material with a label printer [TEC H-9606, manufactured by Tokyo Electric Co.], and a near infrared reading and evaluating device [Laser Check II, Symbol company 355
0-100 type, light source: 675 nm] with barcode PC
The S value was measured and the suitability for reading in the near infrared region was evaluated.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

As is apparent from [Table 1] and [Table 2], the heat-sensitive recording material of the present invention is excellent in color development and stability of the background portion, and is also excellent in light resistance and readability in the near infrared region. It was an excellent thermosensitive recording medium.

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a support, on which an intermediate layer containing a pigment and an adhesive, a thermal recording layer containing a leuco dye and a color former, and a protective layer are sequentially provided. A fluoran compound represented by the formula (1),
A heat-sensitive recording material characterized in that the pigment in the intermediate layer is hollow particles. Embedded image [In the formula, R ₁ and R ₂ each represent a C _{1 to} C ₆ alkyl group. R ₃ and R ₄ each represent a hydrogen atom or a C _{1 to} C ₆ alkyl group. ] 2. The heat-sensitive recording material according to claim 1, wherein the leuco dye is 3-p-dimethylaminophenylamino-5,7-dimethylfluorane. 3. The hollow particles are a foamable filler.
Alternatively, the heat-sensitive recording material described in 2.