JPH05177935A - Thermal recording material and its manufacturing method - Google Patents

Abstract

PURPOSE:To provide a thermal recording material of which a rear surface has a high brightness to look at and its manufacturing method. CONSTITUTION:The title thermal recording material is equipped with a base material 1, a recording layer 3 which contains a colorless or light colored basic dye and a color agent and is formed on the base material 1, and a rear surface treated layer 4 which is formed by applying a coating solution containing a fluorescent dye to a surface side of the base material 1 wherein the recording layer 3 is not formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium and a method for producing the same.

[0002]

2. Description of the Related Art A thermosensitive recording medium provided with a thermosensitive recording layer which utilizes a reaction between a colorless or light-colored basic dye and a coloring agent to bring a recording image by contacting both color forming substances with heat is well known. ing. Conventionally, the whiteness of the surface of the thermosensitive recording layer was inferior to that of the support, so special consideration was given to the whiteness of the backside of the support, that is, the surface on the side on which the thermosensitive recording layer is not formed. There wasn't.

[0003]

However, in recent years, a heat-sensitive recording layer having an excellent whiteness has been obtained. Furthermore,
Nowadays, consumers are demanding high quality for the appearance of thermal recording materials. Under such circumstances, the back surface of the thermosensitive recording medium is required to have the same whiteness as the front surface. Therefore, attention has been paid to the back surface of the recording body, which has not been considered in the past, and it has been a subject to whiten this surface to the same extent as the heat-sensitive recording layer surface side. However, when a white pigment such as titanium oxide is applied to the back surface of the thermosensitive recording medium, that is, the back surface of a support such as paper or film, general whiteness is improved, but so-called whiteness is not so much improved. There was a problem. Here, the whiteness to be viewed means the whiteness measured by taking into consideration the ultraviolet rays generally emitted from a light source such as sunlight and a fluorescent lamp. The whiteness for viewing is measured by the measuring method described in the examples.

An object of the present invention is to provide a thermal recording material having a high whiteness on the back surface and a method for manufacturing the same.

[0005]

A heat-sensitive recording material according to the present invention comprises a support, a recording layer formed on the support, containing a colorless or light-colored basic dye and a coloring agent, A backside treatment layer formed by applying a coating liquid containing a fluorescent dye to the side of the surface of the support on which the recording layer is not formed.

The method for producing a thermosensitive recording medium according to the present invention comprises the steps of forming a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, and forming the recording layer on which the recording layer is not formed. Forming a backside treatment layer by applying a coating liquid containing a fluorescent dye on the side of the surface.

[0007]

The fluorescent dye used in the present invention contains one or more substances selected from the following groups. 4,4'-diaminostilbene disulfonic acid, stilbenzene, 4,4'-bistriazinylaminostilbene-2,2'-disulfonic acid, 4,4'-diaminostilbene, coumarin, bisoxazole, pyrazoline, pyrene, oxazole , Thiazole, imidazole, imidazolone, pyrazole, benzidine, diaminocarbazole, derivatives such as naphthalic acid. A backside treatment layer containing the above fluorescent dye in a dry weight range of preferably 0.005 to 1.0 g / m ² is formed on the side of the surface of the support on which the thermal recording layer is not formed. Since the fluorescent dye absorbs ultraviolet rays and emits blue fluorescent light, the back surface of the thermosensitive recording medium exhibits high whiteness for viewing.

Since the above fluorescent dyes are generally water-soluble, they are appropriately diluted before coating. Further, a water-soluble polymer, for example, binders such as polyvinyl alcohol and starch, an antifoaming agent, and a wetting agent can be added as necessary.

In the present invention, various known dyes can be used as the colorless or light-colored basic dye which constitutes the recording layer, and specific examples thereof include the following. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2) -Dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl)-
3- (2-methylindol-3-yl) phthalide,
3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -6-dimethylaminophthalide,
3,3-bis (2-phenylindol-3-yl)-
6-Dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6
-Triarylmethane dyes such as dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenylleucoalamin, etc. Diphenylmethane dyes, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and other thiazine dyes, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-
Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-
Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3- Diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
Diethylamino-6,7-dimethylfluorane, 3-
(N-ethyl-p-toluidino) -7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino- 7-dibenzylaminofluorane, 3-diethylamino-7-N
-Methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-toluidino) −
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-p-toluidino) -6-methyl-7- (p-
Toluidino) fluorane, 3-dimethylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3
-Di-n-butylamino-6-methyl-7-phenylaminofluorane, 3-di-n-pentylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7- (2-carbomethoxy -Phenylamino) fluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-phenylaminofluorane, 3
-Pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-
Xylidinofluorane, 3-diethylamino-7- (o
-Chlorophenylamino) fluorane, 3-di-n-butylamino-7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3- (N-methyl-) N-n-
Amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-amyl) amino-
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-N-isoamyl) amino-6-methyl-7-
Phenylaminofluorane, 3- (N-methyl-Nn)
-Hexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-hexyl) amino-6-methyl-7-phenylaminofluorane, 3
-(N-ethyl-N-β-ethylhexyl) amino-6
-Methyl-7-phenylaminofluorane, 3- (N-
Ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-cyclopentyl) amino-6-methyl-7-phenylaminofluorane, 2,2-bis {4- [6'-
(N-Cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthene] -2 '
Fluorane dyes such as -ylamino] phenyl} propane. Of course, it is not limited to these dyes,
It is also possible to use two or more dyes in combination. Among these dyes, 3-di-n-butylamino-6-methyl-7-
Phenylaminofluorane and 3-di-n-butylamino-7- (o-chlorophenylamino) fluorane are
In particular, it is more preferably used because a heat-sensitive recording material can be obtained in which the whiteness of the white paper on the surface of the heat-sensitive recording layer is high.

Various compounds are known as colorants used in combination with the above basic dyes, and examples thereof include the following. 4-tert-butylphenol, α-naphthol, β-naphthol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidene diphenol, 4-phenylphenol, 4,4′-dihydroxy-diphenylmethane, 4,4'-isopropylidene diphenol, hydroquinone, 4,4'-cyclohexylidene diphenol, 4,4 '-(1,3-dimethylbutylidene) bisphenol, 2,2-bis (4-hydroxyphenyl)- 4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol), 4,
4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4 '
-Methyldiphenyl sulfone, 4-hydroxy-4'-
Methoxydiphenyl sulfone, 4-hydroxy-4'-
Isopropoxydiphenyl sulfone, 4-hydroxy-
3 ', 4'-trimethylene diphenyl sulfone, 4-hydroxy-3', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) Sulfone, 1,3-di [2- (4-hydroxyphenyl) -2-propyl] benzene, hydroquinone monobenzyl ether, bis (4-hydroxyphenyl) acetic acid butyl ester, 4-hydroxybenzophenone, 2,
4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate Propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, 4-hydroxybenzoate Acid chlorophenyl, 4-hydroxybenzoic acid phenylpropyl, 4-
Phenethyl hydroxybenzoate, 4-hydroxybenzoic acid-p-chlorobenzyl, 4-hydroxybenzoic acid-p
-Methoxybenzyl, novolac type phenolic resin, phenolic compound such as phenolic polymer, benzoic acid, p
-Tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid,
3-cyclohexyl-4-hydroxybenzoic acid, 3,5
-Dimethyl-4-hydroxybenzoic acid, salicylic acid, 3
-Isopropyl salicylic acid, 3-tert-butyl salicylic acid, 3,5-di-tert-butyl salicylic acid, 3-benzyl salicylic acid, 3- (α-methylbenzyl) salicylic acid, 3-chloro-5- (α-methylbenzyl) salicylic acid , 3-phenyl-5- (α, α-dimethylbenzyl)
Aromatic carboxylic acids such as salicylic acid and 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, magnesium,
Aluminum, calcium, titanium, manganese, tin,
Organic acidic substances such as salts with polyvalent metals such as nickel. As a matter of course, two or more kinds of the above-mentioned color developing agents can be used in combination.

The use ratio of the basic dye and the color developing agent should be appropriately selected according to the types of the basic dye and the color developing agent to be used and is not particularly limited, but in general, the basic dye 1 is used.
About 100 to 700 parts by weight, preferably about 150 to 400 parts by weight, of the coloring agent is used with respect to 00 parts by weight. The coating liquid containing these is generally prepared by using water as a dispersion medium and dispersing a basic dye, a coloring agent and the like together or separately by a stirrer / pulverizer such as a ball mill, attritor or sand mill. To be done.

In such a coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, sulfo group-modified polyvinyl alcohol, acetoacetyl group-modified are usually used as binders. Polyvinyl alcohol, various modified polyvinyl alcohol such as silicone modified polyvinyl alcohol, styrene, maleic anhydride copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, etc. are contained in the total solid content of 2 to 2.
40% by weight, preferably about 5 to 25% by weight. Of course, these binders can be used in combination of two or more kinds.

Various auxiliaries can be further added to the coating liquid, for example, dioctylsulfosuccinic acid sodium salt, dodecylbenzenesulfonic acid sodium salt,
Examples thereof include dispersants such as lauryl alcohol sulfate / sodium salt and fatty acid metal salt, defoaming agents, fluorescent dyes, and coloring dyes. Further, in order to improve the adhesion of dust to the recording head, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, styrene microballs, nylon powder, polyethylene. Powder, urea
Organic pigments such as formalin resin filler and raw starch particles can also be added. Furthermore, a dispersion liquid or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax or the like may be added so that sticking does not occur due to contact with a recording device or recording head.

Further, in the heat-sensitive recording material of the present invention, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, and coconut fatty acid amide are used as long as the desired effects of the present invention are not impaired. , 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-3-methylphenol), 1,1,3-tris (2-methyl) -4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-
Hindered phenols such as tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, p
-Benzylbiphenyl, p- (4-tolyloxy) biphenyl, 1,5-bis (4-methoxyphenoxy) -3
-Oxa-pentane, 1,2-bis (phenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane,
1,2-bis (3-methylphenoxy) ethane, 1-
Ethers such as (2-methylphenoxy) -2- (4-methoxyphenoxy) ethane, 2-naphtholbenzyl ether, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid phenyl ester, oxalic acid dibenzyl ester, oxalic acid Esters such as di (4-methylbenzyl) ester, oxalic acid di (4-chlorobenzyl) ester, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2-hydroxy-4-benzyloxybenzophenone It is also possible to use an ultraviolet absorber such as the above and various known heat-fusible substances together as a sensitizer. Among these heat fusible substances, 1,2-bis (3-methylphenoxy) ethane, 1,2-bis (phenoxy) ethane, 1- (2-methylphenoxy) -2-
(4-methoxyphenoxy) ethane, oxalic acid dibenzyl ester, oxalic acid di (4-methylbenzyl) ester, oxalic acid di (4-chlorobenzyl) ester, p-
Benzylbiphenyl, p- (4-tolyloxy) biphenyl, and 1,5-bis (4-methoxyphenoxy)-
3-oxa-pentane is more preferable because it exhibits a particularly excellent sensitizing effect. The amount of the heat-fusible substance used is not particularly limited, but is generally 50 to 1000 parts by weight, preferably 100 to 500 parts by weight, based on 100 parts by weight of the basic dye. Is desirable.

As the support, paper, plastic film, synthetic paper and the like are used, but paper is preferably used in terms of cost and coating suitability. In the present invention, the method for forming the heat-sensitive recording layer and the backside treatment layer is not particularly limited, and the heat-sensitive recording layer and the backside treatment layer can be formed according to a conventionally well-known and commonly used technique. As a coater head on the above, a method such as coating and drying with a suitable coating device using a roll coater, an air knife coater, a blade coater, a bar coater, a gravure coater, a rod blade coater, a curtain coater, a short dwell coater, etc. Be done.
Further, the coating amount of the coating liquid for the heat-sensitive recording layer is not particularly limited, and generally 2 to 12 g / m 2 in dry weight.
² , preferably in the range of ^{2 to} 8 g / m ² . An overcoat layer may be provided on the recording layer for the purpose of protecting the recording layer, a protective layer may be provided between the support and the backside treatment layer, or the support and the thermosensitive recording layer may be separated from each other. It is of course possible to provide an undercoat layer between them, and various known techniques in the field of manufacturing a thermosensitive recording medium such as adhesion processing can be added.

[0016]

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. The parts and% in the examples are parts by weight and% by weight, respectively, unless otherwise specified. FIG. 1 shows a sectional view of the thermal recording paper of the present invention. The undercoat layer 2 is formed on a high-quality paper generally used as the support 1. A thermosensitive recording layer 3 is further formed thereon. The back surface treatment layer 4 is formed on the surface of the support 1 on which the thermosensitive recording layer 2 is not formed, which surface is simply referred to as the back surface.

Example 1 Formation of Undercoat Layer Fired clay (trade name: Ansilex, manufactured by EMC)
100 parts styrene-butadiene copolymer latex (solid content: 5
0%) 15 parts 10% aqueous polyvinyl alcohol solution 30 parts water 20 parts The above composition was mixed and stirred to prepare a coating liquid for the undercoat layer. The obtained coating liquid was applied to a high-quality paper of 50 g / m ² by a rod blade coater so that the coating amount after drying was 10 g / m ^2, and dried to form an undercoat layer.

Preparation of Solution A 3-di-n-butylamino-6-methyl-7-phenylaminofluorane 10 parts 1,2-di (3-methylphenoxy) ethane 25 parts methylcellulose 5% aqueous solution 5 parts water 50 parts This composition was ground with a sand mill until the average particle size became 1.0 μm.

Preparation of Solution B 4,4′-isopropylidenediphenol 20 parts Methylcellulose 5% aqueous solution 5 parts Water 40 parts This composition was ground with a sand mill until the average particle size became 1.5 μm.

Formation of Thermosensitive Recording Layer 10 parts of light calcium carbonate is sufficiently dispersed in 120 parts of water,
Next, after adding 100 parts of a 15% aqueous solution of polyvinyl alcohol, a silicon oxide pigment (oil absorption 180 ml / 100
g) 15 parts of fluorescent dye, 1 part of fluorescent dye (trade name “WhitexBB” manufactured by Sumitomo Chemical Co., Ltd.), 15 parts of 30% zinc stearate aqueous dispersion, and 65 parts of solution B and 90 parts of solution A are mixed. A coating liquid was obtained by stirring. Using the coating apparatus shown in FIG. 2, the above coating liquid was applied onto the undercoat layer so that the coating amount after drying was 4 g / m ² and dried. Unwinder 2
The heat-sensitive recording layer was coated on the undercoat layer by passing the undercoat layer No. 1 support between the rod blade 22 used as a coater head and the backing roll 23. After the heat-sensitive recording layer is dried at about 60 ° C. in the oven 24, the backside treatment layer described next is continuously formed.

Preparation of Liquid C (Coating liquid for forming back surface treatment layer) Fluorescent dye (trade name “WhitexBB” Sumitomo Chemical Co., Ltd.)
(Manufactured) 1 part (This "Whitex BB" is one of the derivatives of 4,4-diaminostilbenedisulfonic acid.) Water 99 parts This composition is a water-soluble fluorescent dye, so no special operation such as stirring is required. In both cases, a sufficiently uniform coating solution can be obtained.

Formation of Backside Treatment Layer The backside treatment layer was applied and dried using a roll coater 25, an oven 26, etc., which constitute the latter half of the coating apparatus shown in FIG. That is, the liquid C was applied to the back surface of the support by a roll coater 25 so that the dry weight was 0.04 g / m ² , immediately dried in an oven 26 at about 60 ° C., and then wound on a winder 27.

Since the liquid C, which is a water-based paint, is applied in the step of forming the back surface treatment layer, the water application step which has been conventionally performed after the formation of the heat-sensitive recording layer is unnecessary to prevent curling. In other words, this back surface treatment layer forming step fulfills two functions at the same time: the original purpose of applying a fluorescent dye for improving the whiteness for appearance and the application of water for curling prevention. That is, two effects of improving whiteness and preventing curling can be obtained by one simple process. Further, it goes without saying that this coating process of the C liquid is economical because the same device as that of the conventional water coating process can be used since the C liquid is a water-soluble coating liquid.

Finishing Treatment After the formation of the various layers described above and the completion of drying, a super calendering treatment was performed to smooth the surface, and a thermosensitive recording paper was obtained.

Example 2 The dry weight of the liquid C was adjusted to 0.0 of that of Example when forming the back surface treatment layer.
A thermal recording paper was obtained in the same manner as in Example 1 except that the amount was increased from 4 g / m ² to 0.08 g / m ² .

Example 3 3-di-n-butylamino was used instead of 3-di-n-butylamino-6-methyl-7-phenylaminofluorane in the preparation of the liquid A when forming the thermosensitive recording layer. A thermal recording paper was obtained in the same manner as in Example 1 except that -7- (o-chlorophenylamino) fluorane was used. This 3-di-n-butylamino-7- (o-chlorophenylamino) fluorane is one of the more preferable basic dyes for increasing the whiteness of the heat-sensitive recording layer.

Example 4 3- (N-ethyl-N) was used in place of 3-di-n-butylamino-6-methyl-7-phenylaminofluorane in the preparation of solution A when forming the thermosensitive recording layer. -Isoamyl) amino-6-methyl-7-phenylaminofluorane was used. This 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-phenylaminofluorane has a lower basicity than the whiteness of the thermosensitive recording layer as compared with the whiteness of Example 1. It is a dye. Therefore, in Example 4, the dry weight of the liquid C was set to 0.0 of Example 1 during the formation of the back surface treatment layer so that the apparent whiteness of the back surface could be slightly reduced.
It was reduced from 4 g / m ² to 0.01 g / m ² . A thermal recording paper was obtained in the same manner as in Example 1 except for the above points.

Example 5 A thermal recording paper was obtained in the same manner as in Example 1 except that a medium-quality paper was used instead of the high-quality paper used as the support in Example 1. Here, the reason for using the medium quality paper is to observe what effect the back surface treatment layer of the present invention exerts on the medium quality paper having a poor whiteness like the recycled paper whose range of use has been expanded recently, and actually This is to examine whether or not there is a possibility of being applied to recycled paper.

Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the back surface treatment layer was not provided.

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 5 except that the back surface treatment layer was not provided.

Measurement of Whiteness for Viewing To check the surface (the thermal recording layer side) and the back surface (the back surface processing layer side or the back surface side of the support) of the thermal recording papers of the respective Examples and Comparative Examples obtained above. Was measured for whiteness. The measurement conditions are as follows. Measuring device Erlejo 2000 (manufactured by Swiss Data Color Co., Ltd.) Measurement conditions Light source D ₆₅ Main measurement wavelength 457 nm UVIN (means setting conditions for measurement including ultraviolet rays) The measurement results are shown in Table 1.

[0032]

[Table 1]

If the difference in the whiteness value for visual observation is within 2 to 3%, it is usual that the difference in whiteness cannot be visually perceived. The following conclusions can be drawn from Table 1. As can be seen from Example 1 and Comparative Example 1, by providing the back surface treatment layer, the difference in apparent whiteness between the front surface and the back surface was improved to the extent that it could not be visually recognized. As can be seen from Examples 1 and 2, by appropriately changing the amount of the fluorescent dye contained in the backside treatment layer, a backside treatment layer having a desired whiteness can be obtained. As can be seen from Example 3, even when the basic dye contained in the heat-sensitive recording layer is appropriately changed to increase the whiteness for appearance of the surface, the back surface having the whiteness for appearance corresponding to that is obtained. A treated layer is obtained. As can be seen from Example 4, even when the basic dye contained in the heat-sensitive recording layer is appropriately changed to reduce the whiteness of the visible surface, the fluorescence contained in the backside treatment layer is accordingly changed. By appropriately reducing the amount of dye, a backside treatment layer with a correspondingly reduced whiteness for appearance can be obtained. As can be seen from Comparative Example 2, when a medium quality paper having a low whiteness for viewing is used, there is a large difference in whiteness for viewing between the front surface and the back surface. However, as can be seen from Example 5, this large difference is reduced to the extent that it cannot be visually recognized by providing the back surface treatment layer. Thus, by applying this backside treatment layer to a medium-quality paper or recycled paper which originally has a low whiteness, a greater effect can be obtained as compared with applying this layer to a high-quality paper which originally has a high whiteness.

[0034]

EFFECTS OF THE INVENTION According to the present invention, a back surface having a back surface treatment layer having a visually similar whiteness corresponding to the visible whiteness on the side of the thermal recording layer (front surface side) is provided. A heat-sensitive recording material having the same can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a thermosensitive recording medium of the present invention.

FIG. 2 is a side view of a coating apparatus that coats a heat-sensitive recording layer and a back surface treatment layer of the heat-sensitive recording material of the present invention.

[Explanation of symbols]

 1: Support 2: Undercoat layer 3: Thermal recording layer 4: Backside treatment layer 21: Unwinder 22: Rod blade 23: Backing roll 24: Oven 25: Roll coater 26: Oven 27: Winder

Claims (5)

[Claims] 1. A support, a recording layer containing a colorless or pale basic dye and a colorant and formed on the support.
A heat-sensitive recording medium, comprising: a backside treatment layer formed by applying a coating liquid containing a fluorescent dye on the side of the surface of the support on which the recording layer is not formed. 2. The thermosensitive recording medium according to claim 1, wherein the coating liquid containing the fluorescent dye is an aqueous coating liquid. 3. A step of forming a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, and containing a fluorescent dye on the side of the surface of the support on which the recording layer is not formed. A step of forming a backside treatment layer by applying a coating liquid, and a method for manufacturing a thermosensitive recording medium. 4. The coating liquid containing the fluorescent dye is an aqueous coating liquid, and the step of forming the backside treatment layer is performed to prevent curling of the support. A method for producing the thermosensitive recording medium described. 5. The coating liquid containing the fluorescent dye is an aqueous coating liquid, and the step of forming the recording layer and the step of forming the back surface treatment layer are continuously performed. 4. The method for producing a thermal recording material according to 4.