JPH06227131A - Thermal recording body - Google Patents

Abstract

PURPOSE:To decrease texture blushing and to enhance shelf stability of a recording image by incorporating caprolactam shown in the specified general formula into a recording layer containing basic dye and a colorant in a thermal recording body wherein the recording layer is provided on a supporting body. CONSTITUTION:A thermal recording body is constituted by providing a recording layer containing colorless or light-colored basic dye and a colorant on a supporting body. In the case, caprolactam compound shown in the general formula mentioned elsewhere is incorporated into the recording layer. By the way, usage of caprolactam compound is not especially limited but set e.g. in a range within 1-500wt.% preferably 10-200wt.% for the colorant. On the other hand, e.g. activated clay, attapulgite, colloidal silica and others are used for the colorant. Thereby the thermal recording body is obtained which is little in texture blushing caused by effect of temperature and humidity or the like and excellent in shelf stability of a recording image for chemicals such as fats and oils and a plasticizer.

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 storage stability of recorded images.

[0002]

2. Description of the Related Art A thermosensitive recording medium is well known in which a reaction between a colorless or light-colored basic dye and a coloring agent is utilized to bring both coloring substances into contact with each other by heat to obtain a recorded image. Since such a thermal recording medium is relatively inexpensive and the recording device is compact and its maintenance is relatively easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

[0003] For example, as one of the fields of use thereof, the use as a label is increasing with the expansion of POS (Point of sales) system in retail stores and the like. However, when a POS system is introduced in supermarkets, labels often come in contact with plastic-added wraps, oils, etc., and as a result, the recorded image (printing) of the heat-sensitive recording label fades. Defects are recognized. Therefore, it is required that the thermosensitive recording medium has storage stability of a recorded image against chemicals such as a plasticizer and oil.

Conventionally, in order to improve the storage stability of a recorded image, a method of providing a protective layer having a film forming ability on the recording layer of a thermosensitive recording medium is disclosed in JP-A-54-128347.
It is described in Japanese Utility Model Publication No. 56-125354. Further, a method of adding an aziridine compound or an epoxy compound in the heat-sensitive recording layer to improve the storage stability is disclosed in JP-A-4-3.
No. 20881 and Japanese Patent Application Laid-Open No. 4-28589, both cases are satisfied with new defects such as a decrease in recording density due to improvement and occurrence of background fog in the recording layer. The current situation is that the expected results have not been obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium which has less background fog due to the influence of temperature and humidity and which is excellent in the storage stability of recorded images against chemicals such as oils and fats and plasticizers. Especially.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have found that in a thermosensitive recording medium having a recording layer containing a colorless or pale basic dye and a color former on a support, It was found that the above object can be achieved by containing the caprolactam compound represented by the general formula [Chemical Formula 1],
The present invention has been completed.

[0007]

[Chemical 1]

[0008]

In the present invention, the amount of the specific caprolactam compound added to the recording layer is not particularly limited, but it is 1 to 500% by weight, preferably 10% by weight based on the coloring agent.
Used in the range of up to 200% by weight.

As the color former used in the present invention, various known colorants can be used, and examples thereof include the following. Activated clay, attapulgite, colloidal silica, inorganic acid substances such as aluminum silicate, 4-cumylphenol, hydroquinone monobenzyl ether, 4,
4'-isopropylidene diphenol, 4,4'-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl-2,2-butane, 4,4'- Dihydroxydiphenylmethane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,2-bis (4-
Hydroxyphenyl) heptane, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, 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, 4,4'-dihydroxydiphenyl sulfide,
Bis (4-hydroxy-3-methylphenyl) sulfine, benzyl 4-hydroxybenzoate, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, (4-hydroxyphenylthio)
Acetic acid-2- (4-hydroxyphenylthio) ethyl ester, di (p-hydroxyphenylthioethyl) ether, N, N'-di-m-chlorophenylthiourea, N-
Phenolic compounds such as (phenoxyethyl) -4-hydroxyphenylsulfonamide, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 4-
Aromatic carboxylic acids such as [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, p-chlorobenzoic acid, and the like. Examples thereof include salts with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel, and organic acid substances such as antipyrine complex of zinc thiocyanate. In particular, one using a compound represented by the following general formula [Chemical Formula 2] as a color developing agent is excellent in color development and has an effect of extremely reducing background fog, and therefore, one of the preferred embodiments of the present invention. Is.

[0010]

[Chemical 2] [In the formula, R ₁ , R ₂ and R ₃ each represent a hydrogen atom, an alkyl group or an alkenyl group. In the general formula [Formula 2], the alkyl group and the alkenyl group preferably have about 1 to 10 carbon atoms. Further, specific examples of the compound represented by the general formula [Chemical Formula 2] include, for example, bis (4
-Hydroxyphenyl) sulfone, bis (3-allyl-
4-hydroxyphenyl) sulfone, 2,4'-dihydroxydiphenylsulfone, 2-hydroxy-5-tert
-Butylphenyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-amylphenyl-4 '
-Hydroxyphenyl sulfone, 2-hydroxy-5-
tert-isopropylphenyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-butylphenyl-3'-methyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-butylphenyl-3 '
-Isopropyl-4'-hydroxyphenyl sulfone,
2-hydroxy-5-tert-butylphenyl-2'-methyl-4'-hydroxyphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-
Hydroxy-4'-methoxydiphenyl sulfone, 4-
Hydroxy-4'-methyldiphenyl sulfone and the like can be mentioned. Among these, 4-hydroxy-4'-isopropoxydiphenyl sulfone and 2,4'-dihydroxydiphenyl sulfone are preferable because they are particularly excellent in terms of color developability and the effect of fogging on the background.

In the thermosensitive recording medium of the present invention, various known compounds can be used as the colorless or light-colored basic dye used in the recording layer, and examples thereof include the following. 3,3
-Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl)-
6-dimethylaminophthalide, 3-diethylamino-7
-Dibenzylamino-benzo [a] fluorane, 3-
(N-Ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3,6- Bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-
6-methyl-7-chlorofluorane, 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-anilinofluorane, 3-di (N-pentyl) amino-6-methyl-
7-anilinofluorane, 3-diethylamino-7-
(O-chlorophenylamino) fluorane, 3-di (n
-Butyl) amino-7- (o-chlorophenylamino)
Fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane, 3- (N-ethyl-p-toluidino)- 6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3- (N-ethyl-N-furfurylamino)-
6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3- (N
-Methyl-N-n-propylamino) -6-methyl-7
-Anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl)
Ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-
Il] -4,5,6,7-tetrachlorophthalide, 3,
3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3-p- (p-anilinoanilino) anilino-
6-methyl-7-chlorofluorane, 2,2-bis {4
-[6 '-(N-cyclohexyl-N-methylamino)
-3'-methylspiro [phthalide-3,9'-xanthen-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, and two or more kinds may be used in combination as required.

In the heat-sensitive recording material of the present invention, the ratio of the basic dye and the coloring agent contained in the recording layer is not particularly limited, but the basic dye 1 is generally used.
10 to 500 parts by weight, preferably 5 to 100 parts by weight
It is desirable to use about 0 to 300 parts by weight of a coloring agent.

In the heat-sensitive recording material of the present invention, a sensitizer can be added to the recording layer according to the purpose. Specific examples of the sensitizer include stearic acid amide and methoxycarbonyl-
N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebistearic 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, dibenzyl oxalate, oxalate-di-p-methylbenzyl,
Oxalic acid-di-p-chlorobenzyl, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, 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- (2-methylphenoxy) ethane, p-
Methylthiophenyl benzyl ether, 1,4-di (phenylthio) butane, p-acetotoluidide, p-acetophenetide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxy) Examples include ethoxy) benzene and 1-isopropylphenyl-2-phenylethane. The amount of these sensitizers used is not particularly limited, but it is generally desirable to adjust the amount within the range of about 4 parts by weight or less relative to 1 part by weight of the color developing agent.

Further, a preservative improving agent may be used in combination so as to further enhance the preservability of the recorded image depending on the purpose as long as the effect is not impaired. Specific examples of such a storability improver include, for example, 1,4-diglycidyloxybenzene,
Epoxy compounds such as 4,4'-diglycidyloxydiphenyl sulfone, diglycidyl terephthalate, and bisphenol A type epoxy resin, 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 (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4,
4'-butylidene bis (6-tert-butyl-m-cresol), 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-3,5-dibromophenyl) propane, 2,2-
Hindered phenol compounds such as bis (4-hydroxy-3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 1- [α-methyl-α- (4 '-Hydroxyphenyl) ethyl] -4- [α', α'-bis (4 "-hydroxyphenyl) ethyl] benzene, N, N'-di-2-
Examples thereof include naphthyl-p-phenylenediamine and 2,2'-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate.

In order to prepare a coating liquid for a recording layer containing these substances, water is generally used as a dispersion medium, and a basic dye, a colorant, and further a basic dye, a coloring agent and further are required by a stirrer / pulverizer such as a ball mill, attritor or sand mill. A sensitizer or the like added according to the above is dispersed together or separately to prepare a coating liquid.
In the coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, arabic gum as an adhesive,
Carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, fully saponified and partially saponified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid Copolymer salts, styrene / acrylic acid copolymer salts, styrene / butadiene copolymer emulsions, etc. are used in an amount of 10 to 40% by weight, preferably about 15 to 30% by weight, based on the total solid content.

It is also possible to use various pigments in combination in the coating liquid, for example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, titanium oxide, diatomaceous earth,
Inorganic pigments such as fine particulate anhydrous silica and activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and organic pigments such as raw starch particles can be used.

Further, various auxiliary agents can be added to the coating solution, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt and the like. Dispersant, benzophenone type,
Examples thereof include UV absorbers such as triazole type, defoaming agents, fluorescent dyes, and coloring dyes.

In the present invention, the method of forming the recording layer, etc. is not particularly limited, and the recording layer can be formed according to a conventionally well-known and common technique, for example, air knife coating, varibar blade coating, pure blade coating, It can be formed by a method of coating and drying a coating liquid on a support by short dwell coating, curtain coating or the like. The coating amount of the coating liquid is also not particularly limited, and is usually ² to 12 g / m ² , preferably 3 to 10 g / m ² in dry weight.
It is in the range of m ² . As the support, paper, synthetic paper, plastic film or the like is appropriately selected and used.

In the thermosensitive recording medium of the present invention, by providing a protective layer on the recording layer, the storability of the recorded image can be further improved. The protective layer is generally formed by using a water-soluble or water-dispersible polymer and a pigment as main components, and specific examples of such a polymer include the adhesives described above. Among them, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol and silicon-modified polyvinyl alcohol are particularly preferably used because they are excellent in action and effect as a protective layer. Specific examples of pigments added to improve printability and sticking include, for example, calcium carbonate, zinc oxide, titanium dioxide, aluminum hydroxide, barium sulfate, silicon dioxide, kaolin, clay, urea / formalin resin filler. etc. In addition, it is desirable that the amount of such a pigment is adjusted within a range of 10 to 500 parts by weight with respect to 100 parts by weight of the adhesive.

In order to further improve the water resistance of the protective layer,
Glyoxal, formalin, glycine, glycidyl ester, glycidyl ether, dimethylol urea, ketene dimer, dialdehyde starch, melamine resin, polyamide resin, polyamide-epochrohydrin, borax, boric acid, ammonium zirconium carbonate, epoxy compounds and other curing agents It can also be used together. Furthermore, in the coating liquid for forming 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 sodium dioctylsulfosuccinate, an antifoaming agent. It is also possible to appropriately add various auxiliaries such as fluorescent dyes and colored dyes. The coating liquid for protective layer thus prepared was applied onto the recording layer by the above coating device so that the dry coating amount was 0.5.
It is applied in the range of 10 to 10 g / m ² .

In the present invention, it is possible to further improve the storability of a recorded image by providing a resin layer on the back side of the recording body, if necessary. Further, in the field of heat-sensitive recording material manufacturing, such as providing an undercoat layer on the support to improve image quality and sensitivity, processing the back surface of the recording material into an adhesive label by processing with an adhesive, and providing a magnetic layer on the back surface of the recording material. Various known techniques can be added. Further, the image quality and the image density can be improved by performing a super calendering process after forming the recording layer. In the present invention, it is possible to add the specific caprolactum compound contained in the recording layer to the protective layer or the undercoat layer.

[0022]

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, "part" and "%" in an example show "weight part" and "weight%", respectively, unless there is particular notice.

Example 1 Preparation of Solution A 10 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 5% aqueous solution of methylcellulose 5
Parts and 40 parts of water were pulverized with a sand mill until the average particle size became 1.5 μm. Preparation of Solution B A composition consisting of 30 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 80 parts of water was pulverized with a sand mill until the average particle diameter became 1.5 μm. Preparation of liquid C 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 diameter became 1.5 μm. Liquid D Preparation A composition consisting of 20 parts of 1,1 ′-(1,4-phenylenedicarbonyl) bis (hexahydro-2-azepinone), 5 parts of a 5% aqueous solution of methylcellulose, and 40 parts of water was sand milled to give an average particle diameter. Was pulverized to 2 μm. Formation of recording layer 55 parts of solution A, 115 parts of solution B, 80 parts of solution C, 30 parts of solution D,
A recording layer coating liquid obtained by mixing and stirring 160 parts of a 10% polyvinyl alcohol aqueous solution and 25 parts of calcium carbonate,
45 g / m ² of high-quality paper coated on one side with a coating amount of 4 g /
A recording layer was formed by coating and drying so as to obtain m ^2, and further subjected to a super calender treatment to obtain a heat-sensitive recording material.

Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 2,4'-dihydroxydiphenylsulfone was used in place of 4-hydroxy-4'-isopropoxydiphenylsulfone in the preparation of solution B. Obtained.

Example 3 In the preparation of solution B, bis (3-allyl-butanol was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4-hydroxyphenyl) sulfone was used.

Example 4 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 4,4'-isopropylidenediphenol was used in place of 4-hydroxy-4'-isopropoxydiphenyl sulfone in the preparation of solution B. Got

Example 5 Preparation of Solution E A composition comprising 100 parts of calcined clay [trade name: Ansilex, manufactured by EMC, oil absorption; 110 ml / 100 g], 100 parts of a 10% aqueous solution of polyvinyl alcohol, and 200 parts of water was prepared. The mixture was stirred to obtain a coating liquid for undercoat layer. Preparation of solution F Aluminum hydroxide [Product name: Hydilite H42, Showa Denko KK] 60 parts, Silicon modified polyvinyl alcohol [Product name: R1105, Kuraray KK] 10% aqueous solution 3
A composition comprising 00 parts and 35 parts of a 30% aqueous zinc stearate dispersion was mixed and stirred to obtain a protective layer coating liquid. Formation of Undercoat Layer, Recording Layer and Protective Layer On one surface of a high quality paper of 45 g / m ² , the coating amount after drying the liquid E, the recording layer coating liquid of Example 1 and the liquid F was 7 g / m ² ,
A thermal recording material was obtained by applying and drying in order to obtain 3 g / m ² and 2 g / m ² and then performing super calendering.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the D liquid was removed in the formation of the recording layer of Example 1.

Comparative Example 2 In the preparation of solution D, 4,4'-diglycidyloxydiphenyl sulfone was used in place of 1,1 '-(1,4-phenylenedicarbonyl) bis (hexahydro-2-azepinone). A thermal recording material was obtained in the same manner as in Example 1 except for the above. The seven types of thermal recording materials thus obtained were subjected to the following evaluation tests, and the results are shown in [Table 1].

1. [Whiteness] In order to evaluate the degree of background fog, a thermosensitive recording medium was used with 40
After standing for 48 hours under the condition of ° C-90% RH, the whiteness of the recording layer side was measured by a Hunter whiteness meter. 2. [Coloring Density] Each thermal recording material was colored with an applied voltage of 24 V and a pulse time of 2 ms using a thermal recording material evaluation device [trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.] The color density was measured in a visual mode with a Macbeth densitometer [RD-914 type, manufactured by Macbeth Co.]. 3. [Oil resistance] The edible oil is dropped on the heat-sensitive recording body on which the color has been printed, and 24
The state of printing after being left for a time was visually evaluated. 4. [Plasticizer resistance] A vinyl chloride wrap film (manufactured by Mitsui Toatsu Kagaku Co., Ltd.) is wound three times on a polypropylene pipe (40 mmφ pipe),
A thermosensitive recording material with printed color was sandwiched on it so that the printed color surface was on the outside, and a vinyl chloride wrap film was wrapped around it in three layers. The drug properties were evaluated.

[Evaluation Criteria] Evaluation criteria for oil resistance and plasticizer resistance were as follows. ◎ ・ ・ ・ ・ ・ ○ ・ ・ ・ ・ ・ △ ・ ・ ・ ・ ・ × Excellent Excellent

[0032]

[Table 1]

[0033]

As is clear from the results of [Table 1], each of the thermosensitive recording materials of the present invention is excellent in storage stability of recorded images, particularly in oil resistance and plasticizer resistance, and has less background fog. It was a record.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Yoshihiro Shimizu Inventor Yoshihiro Shimizu 4-3-1, Jokoji, Amagasaki City, Hyogo Kanzaki Paper Mill Kanzaki Mill

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a coloring agent, wherein the recording layer is represented by the following general formula [Chemical formula 1]. A heat-sensitive recording material containing a caprolactam compound. [Chemical 1] 2. The heat-sensitive recording material according to claim 1, wherein the recording layer contains a compound represented by the following general formula [Chemical Formula 2] as a color former. [Chemical 2] [In the formula, R ₁ , R ₂ and R ₃ each represent a hydrogen atom, an alkyl group or an alkenyl group. ]