JP2002052842A - Heat sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat sensitive recording material excellent in coloring and heat resistance. SOLUTION: In the heat sensitive recording material, which is produced by providing a heat sensitive color developing layer mainly made of a leuco dye and a developer on a support, the heat sensitive color developing layer includes either one developer among ones represented by constitutional formulae (1), (2) and (3) and a sensitizer represented by constitutional formula (4).

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, and more particularly, to a heat-sensitive recording material having excellent color developability and excellent heat and storage stability in an image area and a background area.

[0002]

2. Description of the Related Art A thermosensitive recording material is a recording material having a structure in which a thermosensitive coloring layer (thermosensitive recording layer) which develops a color upon heating is formed on a support such as paper, synthetic paper, resin film or the like. For this purpose, a thermal printer with a built-in thermal head is used.

[0003] Compared to other methods, this recording method does not require processing such as development and fixing, enables recording using a relatively simple device in a short time, and has the advantages of low cost. There is P for fresh foods, bento and prepared food
It is used in various fields such as the OS field, copying fields such as books and documents, communication fields such as facsimile, and ticketing fields such as ticket vending machines, receipts, and receipts. Among the fields in which these heat-sensitive recording materials are used, at present, they are rapidly being used in POS fields, particularly in products that sell warmth, such as lunch boxes and prepared dishes.

Here, since the heat-sensitive recording material is a recording method that develops color by heat, the color-forming sensitivity and the heat resistance are contradictory to each other, but efforts have been made to make the color-forming sensitivity and the heat resistance as compatible as possible. . For example, (1) a method in which a layer containing hollow particles is provided as an under layer, and the heat energy from the thermal head is effectively used by its heat insulating effect, and (2) the dispersion of leuco dye is submicron using a method such as emulsion dispersion. It is a method of processing. However, both methods (1) and (2) have insufficient sensitivity,
At present, it has not been possible to achieve both due to background fog.

As a conventional technique, a heat-sensitive recording material using a 4-hydroxyphenyl-4'-alkoxyphenylsulfone derivative is disclosed in JP-A-62-225391 and JP-B-63-61198. Specific examples include 4-hydroxyphenyl-4'-octyloxyphenylsulfone, 4-hydroxyphenyl-4'-
Dodecyloxyphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 4-hydroxyphenyl-4'-isopropoxyphenyl sulfone, and the like.

However, the mere use of these 4-hydroxyphenyl-4'-alkoxyphenylsulfone derivatives in combination with a leuco dye causes disadvantages such as insufficient color development and heat-resistant storage stability of an image area and a background area. Have.

[0007] It is a widely used technique to improve the heat resistance without lowering the color sensitivity by combining these developers with a high melting point leuco dye and further adding a sensitizer. It is one of. However, when these 4-hydroxyphenyl-4'-alkoxyphenylsulfone derivatives are combined with a high-melting leuco dye and a sensitizer is further added, other disadvantages often appear, and an effective sensitizer has been found. It was not at present. For example, the drawbacks include fogging of the background portion and fading of the image portion over time, and its use has been limited.

As a conventional technique, a heat-sensitive recording material using 4-acetylbiphenyl is disclosed in Japanese Patent Application Laid-Open No. 61-2460.
No. 88, JP-A-10-138645 and the like. However, even when 4-acetylbiphenyl was used as the sensitizer, the mere combination with a color developer did not provide sufficient heat-resistant storage stability at 80 ° C. for the image portion and the background portion.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a heat-sensitive recording material having excellent heat resistance and high sensitivity which can be used especially as a side dish or a lunch box POS.

[0010]

According to the present invention, there is provided a thermosensitive recording material comprising a support having thereon a thermosensitive coloring layer containing a leuco dye and a color developer as main components. There is provided a thermosensitive recording material characterized by containing any of the compounds represented by the following structural formulas (1), (2) and (3) and a compound represented by the structural formula (4). Further, by using the above compound as the same dispersion, a highly sensitive thermosensitive recording material can be provided without lowering the heat resistance.

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According to the present invention, there is further provided a thermosensitive recording material comprising an under layer provided on a support, and a thermosensitive coloring layer as described above provided on the intermediate layer, wherein the under layer has a hollow ratio of 50%. There is provided a heat-sensitive recording material characterized by containing the above-mentioned plastic hollow particles and further improved in color-forming sensitivity.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The heat-sensitive recording material of the present invention comprises the heat-sensitive coloring layer containing a compound represented by any one of the structural formulas (1), (2), and (3) and a compound represented by the structural formula (4).
It is excellent in color developability and heat-resistant storage stability of an image portion and a background portion without impairing the heat resistance of the heat-sensitive coloring layer itself. In addition, by providing an under layer containing fine hollow particles between the thermosensitive coloring layer and the support, the coloring sensitivity can be further improved.

Further, it is also possible to use an overlayer mainly composed of a binder and a filler, which will be described later.

The amounts of the compounds represented by the structural formulas (1), (2), (3) and (4) are determined based on one part by weight of the compounds (1), (2) and (3) based on 1 part by weight of the leuco dye. 1
To 5 parts by weight (preferably 1.5 to 4.5 parts by weight), and 0.1 to 4 parts by weight of the compound (4) (preferably 0.5 to 3.0 parts by weight).
5 parts by weight) is suitable.

The compounds (1), (2) and (3) are color developers. When the amount is less than 1 part by weight, the color is naturally insufficient. It is not preferable because a developer which does not contribute to color development causes a decrease in density.

Compound (4) is a sensitizer,
When the amount is less than 10 parts by weight, the effect of improving the color sensitivity is insufficient, and when the amount is more than 4 parts by weight, a decrease in density occurs due to an increase in an amount not involved in the improvement in sensitivity.

In the present invention, the leuco dye used in the thermosensitive coloring layer is applied alone or as a mixture of two or more.
As such a leuco dye, those applied to this kind of heat-sensitive material are arbitrarily applied, and examples thereof include triphenylmethane, fluoran, phenothiazine, auramine, spiropyran, and indolinophthalide. A leuco compound of a dye is 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- (N-methyl-N-isobutyl) -6
-Methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) -6-methyl-7-anilinofluoran,

3-diethylamino-7-chlorofluoran, 3-diethylamino-7-methylfluoran,
Diethylamino-7,8-benzfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 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)-
9- (o-chloroanilino) xanthylbenzoic acid lactam｝,

3-Diethylamino-6-methyl-7-
(M-trichloromethylanilino) fluoran, 3-diethylamino-7- (o-chloroanilino) fluoran, 3-dibutylamino-7- (o-chloroanilino)
Fluoran, 3- (N-methyl-N-amylamino)-
6-methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluoran,

3-Diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-
7- (2 ′, 4′-dimethylanilino) fluoran, 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-
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-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- (N-methyl-N-isopropylamino) -6-methyl-7-anilinofluoran, 3-dibutylamino-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- {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.

The developer used in the thermosensitive coloring layer of the present invention is a compound represented by the structural formulas (1), (2) and (3). If necessary, an electron-accepting agent may be used as an auxiliary additive. However, various hindered phenol compounds having relatively low coloring ability can be used in combination. Specific examples thereof include the following.

2,2'-methylenebis (4-ethyl-6
-Tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-2-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,
1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 4,4′-thiobis (6-tert-butyl-2-methylphenol),
Tetrabromobisphenol A, tetrabromobisphenol S, 4,4'-thiobis (2-methylphenol), 4,4'-thiobis (2-chlorophenol) and the like.

In order to produce the heat-sensitive recording material of the present invention,
When the leuco dye and the developer are bound and supported on the support, various conventional binders can be appropriately used, and specific examples thereof include the following.

Polyvinyl alcohol, starch and derivatives thereof, hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, cellulose derivatives such as methyl cellulose and ethyl cellulose, polyacrylic acid -Da, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide /
Water solubility of acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, etc. In addition to molecules, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride /
Emulsions such as vinyl acetate copolymer, polybutyl methacrylate and ethylene / vinyl acetate copolymer, and latex such as styrene / butadiene copolymer and styrene / butadiene / acrylic copolymer.

In the present invention, various heat-fusible substances can be used in combination as a sensitivity enhancer.
When heat resistance is required for applications such as POS for lunch boxes, it is necessary to add as little as possible or to select and use a compound having a melting point of 100 ° C. or higher. Specific examples include, but are not limited to, the following.

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-benzylbiphenyl, terphenyl, triphenylmethane, p -Benzyl benzyloxybenzoate, β-benzyloxynaphthalene, β-phenyl phenyl naphthoate, phenyl 1-hydroxy-2-naphthoate, methyl 1-hydroxy-2-naphthoate, diphenyl carbonate, greyacol carbonate, dibensil 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) bifer, p-aryl Oxybiphenyl, p-propargyloxybiphenyl, dibenzoyloxymethane, dibenzoyloxypropane, dibenzyldisulfide, 1,1-diphenylethanol, 1,1
-Diphenylpropanol, p-benzyloxybenzyl alcohol, 1,3-phenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene, 1,2-bis (4-methoxyphenoxy) propane , 1,5-bis (4-methoxyphenoxy) -3-oxapentane and the like.

In the present invention, if necessary, auxiliary additives commonly used in this type of heat-sensitive recording material, for example, fillers, surfactants, lubricants, pressure-coloring inhibitors and the like can be used in combination.

In this case, examples of the filler include inorganic fillers such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, kaolin, talc, and surface-treated calcium and silica. In addition to fine powder, urea-formalin resin, styrene /
Organic fine powders such as methacrylic acid copolymer, polystyrene resin and vinylidene chloride resin can be mentioned.

As the lubricant, higher fatty acids and metal salts thereof,
Examples include higher fatty acid amides, higher fatty acid esters, various animal, vegetable, mineral or petroleum waxes.

The hollow particles used in the under layer of the present invention are fine hollow particles which have a thermoplastic resin as a shell and contain air or other gas therein and are already in a foamed state. Particles having a particle size of 2 to 10 μm are used. This average particle diameter (particle outer diameter) is 2μ
If the diameter is smaller than m, there is a problem in production such that it is difficult to obtain an arbitrary hollow ratio. Conversely, if the diameter is larger than 10 μm, the smoothness of the surface after coating and drying is reduced. And the effect of improving sensitivity is reduced. Therefore, it is preferable that such a particle distribution is such that the particle diameter is within the above-mentioned range and the distribution peak with a small variation is uniform.

The hollow particles used in the present invention preferably have a hollow ratio of 50% or more, more preferably 70 to 98%. When the hollowness is less than 50%, the heat insulating property is insufficient, so that the thermal energy from the thermal head is released through the support to the outside of the heat-sensitive recording material, and the sensitivity improving effect becomes insufficient.

Here, the hollow ratio is a ratio of the outer diameter to the inner diameter of the hollow particles, and is represented by the following equation. Hollow ratio = (inner diameter of hollow particle) / (outer diameter of hollow particle) × 1
00 (%)

The hollow particles used in the present invention have a shell made of a thermoplastic resin as described above. Examples of the thermoplastic resin include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and polyacryl. Examples include acid esters, polyacrylonitrile, polybutadiene, and copolymer resins thereof. Particularly, a copolymer resin mainly composed of vinylidene chloride and acrylonitrile is preferable.

Usually, the hollow particles are used as an under layer between the heat-sensitive coloring layer and the support to improve the heat insulating property and the adhesion to the head, thereby improving the coloring sensitivity.

In order to provide an under layer on a support, the hollow particles are dispersed in water together with a binder such as a known water-soluble polymer or aqueous polymer emulsion, and the resultant is coated on the support surface and dried. Formed by In this case, the coating amount of the hollow particles is at least 1 g, preferably about ^{2 to} 15 g per 1 m ² of the support, and the coating amount of the binder resin may be an amount that strongly bonds the intermediate layer to the support. Usually, it is 2 to 50% by weight based on the total amount of the hollow particles and the binder resin.

In the present invention, the binder used for forming the under layer is appropriately selected from conventionally known water-soluble polymers and / or water-soluble polymer emulsions. Specific examples thereof partially overlap with the binder for the thermosensitive coloring layer, but as the water-soluble polymer, for example, polyvinyl alcohol, starch and derivatives thereof, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, cellulose derivatives such as ethylcellulose , Sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer Coalesced alkali salts, polyacrylamide, sodium alginate, gelatin, casein and the like. Examples of the aqueous polymer emulsion include latexes such as styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic acid copolymer, and styrene / acrylic ester copolymer. And emulsions of acrylic acid ester resins and polyurethane resins.

With respect to the layer constitution of the heat-sensitive recording material of the present invention, a protective layer and a back layer can be provided, if necessary, in addition to the heat-sensitive coloring layer and the under layer.

The support used in the present invention is not particularly limited. For example, high-quality paper, recycled paper, matte paper, oil-resistant paper,
Coated paper, art paper, cast coated paper, finely coated paper, resin laminated paper, polyolefin-based synthetic paper, synthetic resin film, and the like can be used as appropriate.

The heat-sensitive recording material of the present invention is produced, for example, by applying the above-mentioned coating liquid for forming each layer on a suitable support such as paper or a plastic film and drying.

In particular, in the heat-sensitive recording material of the present invention, the adhesion to the thermal head is significantly improved by the calendering treatment. Therefore, it is very preferable to apply the calendering treatment to the under layer, the heat-sensitive recording layer or the protective layer. That is, by controlling the smoothness of the surface by the magnitude of the pressure of the calender on the under layer, the heat-sensitive recording layer or the protective layer, a heat-sensitive recording material having no background fog and higher definition than before can be obtained.

[0051]

Next, the present invention will be described more specifically with reference to examples. All parts and percentages shown below are based on weight.

(Example 1) [Solution A] and [B
Liquid] and [Liquid C] were prepared using a sand grinder so that the average particle size would be 1.0 μm or less. [Solution A] 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane 20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Water 60 parts [Solution B] Compound 20 of structural formula (1) Parts 10% aqueous solution of polyvinyl alcohol 20 parts Silica 10 parts Water 50 parts [Solution C] Compound of structural formula (4) 20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Water 60 parts

Next, 10 parts of [solution A], 30 parts of [solution B]
[Solution C] 25 parts of a heat-sensitive recording layer coating solution was mixed, and this was applied to a surface of a commercially available high-quality paper (basis weight: 52 g / m ² ) so that the dye adhesion amount after drying was 0.5 g / m ^2. To form a thermosensitive coloring layer. Furthermore, the surface smoothness is 500-8
The heat-sensitive recording material of the present invention was calendered so as to be 00 seconds.

(Example 2) [Example A]
In the same manner except that 3-dibutylamino-6-methyl-7-anilinofluoran was used in place of 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluoran. A heat-sensitive recording material of the present invention was prepared.

(Example 3) In Example 1, [Solution B]
The heat-sensitive recording material of the present invention was prepared in the same manner except that the compound of the structural formula (2) was used instead of the compound of the structural formula (1).

(Example 4) [Example B]
The thermosensitive recording material of the present invention was prepared in the same manner except that the compound of the structural formula (3) was used instead of the compound of the structural formula (1).

(Example 5) [D solution] for forming an under layer having the following composition was prepared. [D-liquid] Plastic spherical hollow particle dispersion (hollow ratio 90%, solid content concentration 40%) 25 parts Styrene / butadiene copolymer latex (solid content concentration 50%) 20 parts Water 55 parts

This was coated and dried so that the dry adhesion amount on the support of Example 1 was 3.5 g / m ^2, and an under layer was provided. Further, the same thermosensitive coloring layer as in Example 1 was further formed thereon. The recording material was calendered to prepare a heat-sensitive recording material having a surface smoothness of 500 to 800 seconds.

(Comparative Example 1) [Example C]
A heat-sensitive recording material for comparison was prepared in the same manner except that no was added.

(Comparative Example 2) [Example C]
In place of the compound of the structural formula (4), bis (oxalate) (p-
A thermosensitive recording material for comparison was prepared in the same manner except that methylbenzyl) was used.

(Comparative Example 3) [Example B]
Using 4-isopropoxy-4′-hydroxydiphenyl sulfone instead of the compound of the structural formula (1)
Liquid], a comparative heat-sensitive recording material was prepared in the same manner except that bis (p-methylbenzyl) oxalate was used instead of the compound of the structural formula (4).

(Comparative Example 4) [Example B]
A heat-sensitive recording material for comparison was prepared in the same manner except that 4-isopropoxy-4'-hydroxydiphenylsulfone was used in place of the compound of the structural formula (1).

The heat-sensitive recording material prepared as described above was printed by a printing simulator manufactured by Okura Electric Co., Ltd., and its color density was measured by a Macbeth densitometer RD-914. Further, in order to check the storability (heat resistance), the image portion and the background portion printed at 0.9 ms were subjected to 2 deg.
After standing for 4 hours, the density of the image portion and the background portion was measured.
Table 1 shows the above results.

[0064]

[Table 1]

[0065]

As is clear from Table 1, the heat-sensitive recording material of the present invention has high color-forming sensitivity and excellent storage stability, that is, excellent background coloration at high temperatures and stability of a color-formed image.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Kajikawa 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H026 BB02 BB25 DD02 DD45 DD48 DD53 DD57 FF01 FF15

Claims (3)

[Claims] 1. A thermosensitive recording material comprising a support and a thermosensitive coloring layer comprising a leuco dye and a color developing agent as main components. In the thermosensitive coloring layer, the following structural formulas (1), (2) ( 3)
And a sensitizer represented by Structural Formula (4). Embedded image Embedded image Embedded image Embedded image 2. A weight ratio of any one of the developers represented by the structural formulas (1), (2) and (3) and the sensitizer represented by the structural formula (4) to 3: 7 to 9: 1. 2. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material is used as a mixture. 3. A hollow ratio of 50 between the support and the heat-sensitive recording layer.
3. A thermosensitive recording material according to claim 1, further comprising an under layer containing at least 3% by weight of plastic hollow particles.