JPH05309939A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material good in the adhesion with a thermal head by successively laminating an undercoat layer containing fine hollow particles having a specific particle size and a thermal recording layer containing a leuco dye and a developer on a support. CONSTITUTION:Fine hollow particles with a particle size of 2-20mum composed of a thermoplastic resin such as a styrenic resin, an acrylic resin or a polyvinyl chloride resin are dispersed in water along with a binder such as a water-soluble polymer to prepare a coating solution for an undercoat layer. Separately, a leuco dye and a developer allowing the dye to develop a color at the time of heating are dispersed in water along with a binder such as a water-soluble polymer to prepare a coating solution for a thermal recording layer. The coating solution for the undercoat layer is applied to a support such as paper or a plastic film and dried to form the undercoat layer. Next, the coating solution for the thermal recording layer is applied on the undercoat layer and dried to form the thermal recording layer to produce a thermal recording material.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, various recording materials have been researched, developed and put into practical use in the information recording field with the diversification of information and the expansion of needs. It is possible to record images easily only by the process. (2) The information processing field (desktop computer) has the advantages that the required device mechanism is simple and compact, and the recording material is easy to handle and inexpensive. , Output of computers, etc., medical measurement recorder field, low / high speed facsimile field, automatic ticket vending machine field (tickets, entrance tickets, etc.), thermal copying machine field, POS system label field, etc. ..

In recent years, the demands in these fields are expanding, and there is a demand for downsizing and speeding up of devices. Therefore, the thermal recording material is also required to have high sensitivity in response to the reduction in printing energy due to miniaturization and speeding up.

The heat-sensitive recording material is usually produced by coating and drying a heat-sensitive color-forming layer liquid containing a color-forming component capable of causing a color-forming reaction by heating on a support such as paper or a synthetic resin film. The heat-sensitive recording material thus obtained is heated with a hot pen or thermal head to record a color image. As a conventional example of such a heat-sensitive recording material, for example, a heat-sensitive recording material disclosed in JP-A-43-4160 or JP-B-45-14039 can be cited. The thermal response was low, and sufficient color density was not obtained during high speed recording. As a method of improving such a defect, for example, JP-A-49-38424 discloses a nitrogen-containing oxide such as acetamide, stearamide, m-nitroaniline, and dinitrile phthalate, and JP-A-52-10674.
No. 6, acetoacetic acid anilide is disclosed in JP-A-53-11.
No. 036 discloses N, N-diphenylamine derivatives, benzamide derivatives and carbazole derivatives.
JP-A-39139 discloses alkylated biphenyls and biphenylalkanes, and JP-A-56-144193 discloses a method for increasing the speed and sensitivity by incorporating a p-hydroxybenzoic acid ester derivative. However, no satisfactory result was obtained by any of the methods. In addition, in addition, Japanese Patent Laid-Open No. 5
As disclosed in Japanese Patent Laid-Open No. 5-164192, the thermal conductivity of the support is set to 0.04 kcal / m · h · ° C. or less, and various fine hollow particles (resin, glass, aluminosilicate, etc.) are provided on the support. Although methods for using the undercoat layer have been proposed (JP-A-59-5093 and JP-A-59-225987), in these cases, it is difficult to form a uniform underlayer, and the surface is likely to be uneven. For,
There is a problem that the formed image lacks uniformity. Furthermore,
Styrene-acrylic resin and polystyrene resin may be used as a material for the partition walls of the fine hollow particles (JP-A-63-2).
No. 81886), a method of providing an undercoat layer containing non-expandable fine hollow particles having a hollow ratio of 30% or more as a main component (JP-A-2-214688) is also proposed. Since it is low, a sufficient heat insulating effect cannot be obtained, and the high-sensitivity heat-sensitive recording material currently demanded has not yet been obtained.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a high-sensitivity heat-sensitive recording material having excellent adhesion to a thermal head.

[0006]

According to the present invention, an undercoat layer is provided on a support, and a leuco dye and a thermosensitive recording layer containing a developer which develops a color upon heating the leuco dye as a main component. In the heat-sensitive recording material provided with, the particle size of the fine hollow particles contained in the undercoat layer is 2 to 20 μm.
There is provided a heat-sensitive recording material characterized by having a specific gravity of 0.21 or less in the range of m.

In the present invention, the particle diameter of the resin hollow fine particles contained in the undercoat layer must be regulated to 2 to 20 μm, preferably 3 to 10 μm. When the particle diameter of the hollow resin particles is regulated to 2 to 7 μm in this way, the uniformity of the surface of the heat-sensitive recording material is maintained and the undercoat layer exhibits appropriate elasticity, so that the adhesion with the thermal head becomes good. The printed image has excellent definition.

Further, in the present invention, in order to improve the heat insulating property of the hollow resin fine particles, the specific gravity thereof is 0.21 g.
/ Cm ³ or less, preferably 0.08 to 0.14 g / cm ³ .

Since most of the ordinary resin hollow fine particles have water in their voids and water evaporates to form hollow fine particles, the ordinary resin hollow fine particles have poorer drying efficiency than non-hollow fine particles. On the other hand, since the hollow fine particles used in the present invention are already in a hollow state at the stage of the undercoat liquid, the drying efficiency is not changed as compared with the undercoat liquid using the non-hollow particles, and the heat insulating property is much higher. Will be excellent.

Examples of the thermoplastic resin as the shell of the hollow fine particles include styrene resins such as polystyrene, poly-α-methylstyrene and poly-β-α-methylstyrene, polymethyl methacrylate, polyethyl methacrylate, poly Acrylic resins such as isopropyl methacrylate, polyisobutyl methacrylate, polyacrylonitrile, polymethacrylonitrile, polyvinyl chloride, polytetrafluoroethylene, polyvinyl alcohol, poly-o-vinylbenzyl alcohol, poly-m-vinylbenzyl alcohol, Poly-p-vinylbenzyl alcohol, polyvinyl formal, polyvinyl acetal, polyvinyl propional, polyvinyl butyral, polyvinyl isobutyral, polyvinyl tert-butyl ether,
Examples thereof include polyvinylpyrrolidone, polyvinylcarbazole, cellulose acetate, cellulose triacetate, polycarbonate, and copolymers thereof.

Among these, hollow fine particles made of vinylidene chloride-acrylonitrile copolymer resin are particularly preferably used as a material suitable for high sensitivity because they are excellent in heat insulation and adhesion.

In order to provide the above-mentioned undercoat layer on the support, the resin hollow fine particles are mixed with a conventionally known water-soluble polymer,
Dispersed in water with a binder such as an aqueous polymer emulsion,
It is obtained by applying this on the surface of a support and drying. In this case, the coating amount of the hollow resin fine particles is at least 1 g, preferably about ^{2 to} 15 g per 1 m ² of the support,
The coating amount of the binder may be such that the undercoat layer is strongly bonded to the support, and is usually 2 to 50% based on the total weight of the hollow resin particles and the binder.

In the present invention, the binder used in forming the undercoat layer is appropriately selected from conventionally known water-soluble polymers and aqueous polymer emulsions. Specific examples thereof include water-soluble polymers such as polyvinyl alcohol, starch and derivatives thereof, methoxycellulose,
Cellulose derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer,
Examples thereof include acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride terpolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein. Examples of the aqueous polymer emulsion include latex such as styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic acid copolymer,
Examples include styrene / acrylic acid ester copolymers, emulsions of acrylic acid ester resins, polyurethane resins and the like.

In the above-mentioned undercoat layer, auxiliary auxiliary components commonly used in this type of heat-sensitive recording material, such as a filler, a heat-soluble substance, and a surfactant, are used together with the resin hollow fine particles and the binder, if necessary. You can do it.

Further, in order to make the surface of the undercoat layer formed on the support as described above smoother, the flat surface may be smoothed by calendering after the undercoat layer is formed.

The leuco dyes used in the heat-sensitive recording layer of the present invention are applied singly or as a mixture of two or more kinds. As such leuco dyes, those applied to this kind of heat-sensitive material are arbitrarily applied. For example, leuco compounds of dyes such as triphenylmethane type, fluorane type, phenothiazine type, auramine type, spiropyran type and indolinophtalide type dyes are preferably used. Specific examples of such leuco dyes include 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-chlorofluorane, 3-dimethylamino-5,7 -Dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-
Diethylamino-7,8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
(Np-tolyl-N-ethylamino) -6-methyl-
7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2- {N- (3'-trifluoromethylphenyl) amino} -6-diethylaminofluorane, 2- {3. 6-bis (diethylamino)-
9- (o-chloroanilino) xanthylbenzoic acid lactam}, 3-diethylamino-6-methyl-7- (m-trichloromethylanilino) fluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-di- n-Butylamino-7- (o-chloroanilino) fluorane, 3-N-methyl-N, n-amylamino-6-
Methyl-7-anilinofluorane, 3-N-methyl-N
-Cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N, N-diethylamino) -5
-Methyl-7- (N, N-dibenzylamino) fluorane, benzoyl leuco methylene blue, 6'-chloro-
8'-methoxy-benzoindolino-spiropyran, 6 '
-Bromo-3'-methoxy-benzoindolino-spiropyran, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-chlorophenyl) phthalide, 3- (2 '-Hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-nitrophenyl) phthalide, 3- (2'-hydroxy-4'-diethylaminophenyl) -3- (2'-methoxy -5'-
Methylphenyl) phthalide, 3- (2'-methoxy-4 '
-Dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-methylphenyl) phthalide, 3-
(N-ethyl-N-tetrahydrofurfuryl) amino-
6-methyl-7-anilinofluorane, 3-N-ethyl-N- (2-ethoxypropyl) amino-6-methyl-
7-anilinofluorane, 3-N-methyl-N-isobutyl-6-methyl-7-anilinofluorane 3-morpholino-7- (N-propyl-trifluoromethylanilino) fluorane, 3-pyrrolidino- 7-m-trifluoromethylanilinofluorane, 3-diethylamino-5
-Chloro-7- (N-benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7- (di-p-
Chlorophenyl) methylaminofluorane, 3-diethylamino-5-chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino)
-7- (α-phenylethylamino) fluorane, 3-
Diethylamino-7- (o-methoxycarbonylphenylamino) fluorane, 3-diethylamino-5-methyl-7- (α-phenylethylamino) fluorane, 3
-Diethylamino-7-piperidinofluorane, 2-chloro-3- (N-methyltoluidino) -7- (pn-
Butylanilino) fluorane, 3- (N-methyl-N-)
Isopropylamino) -6-methyl-7-anilinofluorane, 3-di-n-butylamino-6-methyl-7-
Anilinofluorane, 3,6-bis (dimethylamino)
Fluorene spiro (9,3 ′)-6′-dimethylaminophthalide, 3- (N-benzyl-N-cyclohexylamino) -5,6-benzo-7-α-naphthylamino-4 ′
-Bromofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-
Methyl-7-mesitidino-4 ', 5'-benzofluorane, 3-N-methyl-N-isopropyl-6-methyl-
7-anilinofluorane, 3-N-ethyl-N-isoamyl-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (2 ', 4'-dimethylanilino) fluorane etc.

As the color developer used in the heat-sensitive recording layer of the present invention, various electron-accepting compounds that cause the leuco dye to develop color upon contact, or oxidizing agents are used. Such a material is conventionally known, and specific examples thereof include the following.

4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis (o-methylphenol), 4,4'-secondary butylidene bisphenol 4,4'-isopropylidene bis (2-tertiary) Butylphenol), zinc p-nitrobenzoate,
1,3,5-Tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 2,2- (3,4′-dihydroxydiphenyl) propane, bis (4-hydroxy-3) -Methylphenyl) sulfide, 4- {β- (p-methoxyphenoxy) ethoxy} salicylic acid, 1,7-bis (4-hydroxyphenylthio) -3,5-dioxaheptane, 1,5-bis (4- Hydroxyphenylthio) -5-oxapentane, phthalic acid monobenzyl ester monocalcium salt,
4,4'-Cyclohexylidene diphenol, 4,4 '
-Isopropylidene bis (2-chlorophenol),
2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (6-
Tert-butyl-2-methyl) phenol, 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-methyl) phenol, 4,4'-diphenol sulfone, 4-isopropoxy-4'-hydroxydiphenyl sulfone, 4-benzyloxy-4'-hydroxydiphenyl sulfone, 4,4 '-Diphenol sulfoxide, isopropyl P-hydroxybenzoate,
Benzyl P-hydroxybenzoate, benzyl protocatechuate, stearyl gallate, lauryl gallate, octyl gallate, 1,3-bis (4-hydroxyphenylthio) -propane, N, N′-diphenylthiourea,
N, N′-di (m-chlorophenyl) thiourea, salicylanilide, methyl bis- (4-hydroxyphenyl) acetate, bis- (4-hydroxyphenyl) benzyl acetate, 1,3-bis (4-hydroxycumyl) )benzene,
1,4-bis (4-hydroxycumyl) benzene, 2,
4'-diphenol sulfone, 2,2'-diallyl-4,
4'-diphenol sulfone, 3,4-dihydroxyphenyl-4'-methyldiphenyl sulfone, 1-acetyloxy-2-naphthoate zinc, 2-acetyloxy-
Zinc 1-naphthoate, zinc 2-acetyloxy-3-naphthoate, α, α-bis (4-hydroxyphenyl)-
α-Methyltoluene, zinc thiocyanate antipyrine complex, tetrabromobisphenol A, tetrabromobisphenol S, 4,4′-thiobis (2-methylphenol), 4,4′-thiobis (2-chlorophenol) and the like.

In the heat-sensitive recording layer of the present invention, various conventional binders may be appropriately used for coating the leuco dye and the color developer on the undercoat layer, and specific examples thereof are as described above. The same as those exemplified in the undercoat layer coating of 1.

Further, in the heat-sensitive recording material of the present invention, a protective layer may be provided on the heat-sensitive color developing layer for the purpose of improving the matching property of a thermal head or the like and further improving the storability of recorded images. In this case, the above-mentioned filler, binder, surfactant and heat-fusible substance can also be used as the component constituting the protective layer. The heat-sensitive recording material of the present invention includes, for example, a paper,
It is produced by coating on a suitable support such as synthetic paper or plastic film and drying, and is applied to various heat-sensitive recording fields.

[0022]

EXAMPLES Next, the present invention will be described in detail with reference to Examples and Comparative Examples.

Example 1 [Liquid A] 3- (N-methyl-3-cyclohexyl) amino-6-methyl-7-anilinofluorane 20 wt% Polyvinyl alcohol 10 wt% Aqueous solution 20 wt% Water 60 wt% [Liquid B] p -Benzyl hydroxybenzoate 10 wt% Polyvinyl alcohol 10% Aqueous solution 25 wt% Calcium carbonate 15 wt% Water 50 wt% Mixtures of the above compositions each having an average particle size of 2 μm.
[Solution A] and [Solution B] were prepared by dispersing using a sand mill as follows. [Liquid C] Resin-based (vinylidene chloride-acrylonitrile copolymer) fine hollow particles having a shell wall (solid content 17.8%, specific gravity 0.08, particle diameter 2.55 μm) 40 wt% styrene-butadiene copolymer Latex (solid content 47%) 10 wt% water 50 wt% A mixture consisting of the above components was stirred and dispersed with a disper to prepare an undercoat liquid, which was applied to the surface of commercially available high-quality paper (basic weight 52 g / m ² ). An undercoat paper was obtained by dry coating so that the dry weight was 6 g / m ² . Next, the above [solution A] and [solution B] were mixed and stirred in a weight ratio of 1: 8 to prepare a thermosensitive recording layer-forming liquid, which was dried on the above undercoated paper. After coating and drying so as to have a weight of 7 g / m ² , a thermosensitive recording layer was provided, and then supercalendering was performed so that the Beck smoothness was 500 to 600 seconds to obtain a thermosensitive recording material of the present invention. ..

Example 2 [Liquid C] of Example 1 had an average particle size of 3.43 μm,
A thermosensitive recording material of the present invention was obtained in the same manner as in Example 1 except that hollow fine particles having a partition wall of the same material having a specific gravity of 0.14 were used.

Example 3 The present invention was carried out in the same manner as in Example 1 except that in the [C liquid] of Example 1, hollow fine particles having a specific gravity of 0.15 and an average particle diameter of 10.1 μm and having partition walls of the same material were used. A heat-sensitive recording material of was obtained.

Example 4 This example was prepared in the same manner as in Example 1 except that, in the [C liquid] of Example 1, hollow fine particles having a partition wall made of the same material and having a true specific gravity of 0.21 and an average particle size of 18.0 μm were used. A heat-sensitive recording material of the invention was obtained.

Comparative Example 1 A comparison was made in the same manner as in Example 1 except that hollow fine particles having a partition wall made of the same material and having a true specific gravity of 0.33 and an average particle size of 4.45 μm were used in [C liquid] of Example 1. A heat-sensitive recording material for use was obtained.

Comparative Example 2 A comparison was made in the same manner as in Example 1 except that hollow fine particles having a partition wall made of the same material and having a true specific gravity of 0.33 and an average particle size of 8.0 μm were used in [C liquid] of Example 1. A heat-sensitive recording material for use was obtained.

Comparative Example 3 Comparative Example 3 was carried out in the same manner as in Example 1 except that in the [C liquid] of Example 1, hollow fine particles having a partition wall made of the same material and having a true specific gravity of 0.04 and an average particle size of 25.0 μm were used. A heat-sensitive recording material for use was obtained.

Comparative Example 4 An example except that fine particles (specific gravity 1.09) having a styrene-acrylic resin containing water inside the true specific gravity of 0.4 μm as partition walls were used in [C liquid] of Example 1. A thermal recording material for comparison was obtained in the same manner as in 1. The specific gravity of the hollow fine particles was determined by a method of measuring the weight of a dispersion liquid (10 wt%) of hollow fine particles using a pycnometer shown below.

[Usage code]

 W: weight V: volume ρ: density

[Subscript]

F: Hollow fine particles (filler) L: Dispersion liquid W: Water First, empty weight of pycnometer, weight when water is added, 1
The weight when the 0 wt% dispersion liquid was added was measured under the condition of 20 ° C., and the dispersion liquid density ρL was obtained from these values and the water density.

[0031] On the other hand, the following relationship holds. However, since the concentration of the dispersion liquid is 10 wt%, Vw = WL · ρw ·
(1.0-0.1) When VF is calculated by the above equation, Therefore, the density ρw of the micro hollow particles is Note that here, the density of water is 1.00 and the density = specific gravity.

The thermal recording material obtained above was tested for dynamic color density. The results are shown in Table 1. The test was conducted as follows. Head thermal power of 0.45w / dot, 1 line recording time 20ms in a thermal printing experimental device with a thin film head manufactured by Matsushita Electronic Components Co., Ltd.
ec / line scanning line density 8 * 3.85 dots / mm
Pulse widths of 0.3, 0.4, 0.5 and 0.60 under conditions
The print image density printed in msec was measured with a Macbeth densitometer RD-914.

[0033]

From the results shown in Table 1, in the heat-sensitive recording material according to the present invention, the average particle diameter of fine hollow particles having a shell wall such as vinylidene chloride-acrylonitrile copolymer is 2 μm to 20 μm.
Since it is m or less and the true specific gravity of the fine particles is 0.21 or less, it can be seen that the color developing sensitivity is superior to the conventional ones.

[0034]

[Table 1]

Claims (2)

[Claims] 1. A heat-sensitive recording material comprising an undercoat layer provided on a support, and a heat-sensitive recording layer comprising a leuco dye and a color developer capable of coloring the leuco dye when heated as a main component. A heat-sensitive recording material, wherein the fine hollow particles contained in the layer have a particle size in the range of 2 to 20 μm and a specific gravity of 0.21 or less. 2. The heat-sensitive recording material according to claim 1, wherein the material of the shell wall of the hollow microparticles is a vinylidene chloride-acrylonitrile copolymer.