JP2994397B2 - Thermal recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thermosensitive recording medium, and more particularly, to a thermosensitive coloring layer containing a colorless or slightly pale leuco dye and a developer which causes the leuco dye to develop color when heated. The present invention relates to an improvement in a thermosensitive recording medium in which is provided on an undercoat layer.

(Prior art and problems to be solved) A thermosensitive recording system using a colorless or slightly light-colored leuco compound and a color developer which causes the leuco dye to develop a color when heated does not require a development step, and requires hardware maintenance. Since it has features such as easiness, it is widely used for various printers, facsimile machines, recorders of measuring instruments, and the like. With the increase in the speed of these devices, there is a demand for a thermosensitive recording medium that can perform high-speed recording with low energy and has excellent coloring properties. Providing an undercoat layer on a support and further providing a thermosensitive coloring layer thereon to meet such a demand has already been disclosed in JP-A-54-23545 and JP-A-53-86229. ing.

By the way, it has been found that when a pigment having a large oil absorption determined by the JIS K-5101 method is used, the sensitivity of the thermal recording medium is improved, and the adhesion of scum to the head is greatly improved (Japanese Patent Application Laid-Open No. 53-86229).

However, when the thermosensitive coloring liquid is supplied on the undercoat layer using the pigment having a large oil absorption, the aqueous solution portion such as the water-soluble binder liquid in the thermosensitive coloring liquid is rapidly absorbed into the undercoat layer. As a result, the amount of the water-soluble binder in the thermosensitive coloring liquid decreases rapidly, or the concentration of the thermosensitive coloring liquid increases. The water-soluble binder transferred to the undercoat layer fills the voids of the undercoat layer, reduces the scum absorption inherent in the pigment, and further reduces the surface strength of the thermosensitive coloring layer itself as the binder amount of the thermosensitive coloring layer decreases. This causes a tendency to cause color fouling due to pressure fog and scratches. Moreover, if an extra binder is added to the heat-sensitive coloring solution to prevent this, the coating solution concentration of the heat-sensitive coloring solution increases, the color sensitivity decreases, and streaking may occur in bar coating. In blade coating, however, there has been a problem that the heat-sensitive coloring solution reaches an immobilization point between the time when the heat-sensitive coloring solution is applied and the time when the excess coating solution is scraped off, so that streaks and scratches are easily generated.

(Objects of the Invention) Accordingly, the present invention provides a thermosensitive recording medium having improved surface strength and reduced adhesion of scum by reducing the absorptivity of the aqueous solution portion in the thermosensitive coloring solution to the undercoat layer. The purpose is to:

The present inventors have conducted intensive studies to achieve the above object, and as a result, by reducing the migration of the aqueous solution portion of the thermosensitive coloring material to the undercoat layer, that is, the support having the undercoat layer is made of J.TAPPI paper. Pulp test method No.51−
0.40 ml / m ² · m about the absorption coefficient Ka for water by the Bristow method according to 87 (hereinafter simply referred to as the Bristow method)
It s ^1/2 or less, yet by a 0.10ml / m ² · ms ^1/2 or more the absorption coefficient Ka for linseed oil by Bristow method, found that the above object can be achieved, which was led to the present invention is there.

(Means for Solving the Problems) Hereinafter, the present invention will be described in detail.

As the support, various sheet-like materials such as paper, synthetic paper, and plastic film are generally used.

Examples of pigments for the undercoat layer include aluminum oxide, titanium oxide, hydrous silicic acid, calcium silicate, sodium aluminosilicate, magnesium aluminosilicate, calcined kaolin, diatomaceous earth, silicic anhydride, aluminum silicate, magnesium silicate, and the like. Are used.

As a binder of the undercoat layer, a water-soluble binder, for example, starches, hydroxyethyl cellulose,
Water-soluble binders such as methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer Latex water-soluble binders such as polymers and methyl acrylate-butadiene copolymer are exemplified.

The amount of the binder used is determined in consideration of the strength of the undercoat layer. Usually, it is used in a ratio of 10 to 100 parts by weight in terms of solid content with respect to 100 parts by weight of the pigment.

Specifically, the Ka for water in the Bristow method is 0.40 ml.
It is obvious to those skilled in the art that the method of reducing the thickness to / m ² · ms ^1/2 or less is performed, for example, by adding a sizing agent having a size effect to the undercoat layer. Examples of the substance exhibiting a size effect include, for example, an acidic sizing agent and a neutral sizing agent.Examples of the acidic sizing agent include rosin, modified rosin, rosin emulsions, rosin-based sizing agents, and neutral sizing agents. A self-fixing cationic sizing agent such as a petroleum resin type or an acrylic type and a reactive sizing agent such as an alkenyl succinic anhydride or an alkyl ketene dimer are exemplified. The amount used is generally in the range of 0.01 to 20 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the pigment. Also, adjustment of the oil absorption coefficient is obvious to those skilled in the art,
For example, it can be easily adjusted by using a pigment having a large oil absorption.

The undercoat layer is applied on a support using an air knife coater, a bar coater, a blade coater, a rod coater or the like.

The heat-sensitive coloring layer usually contains a leuco compound, a color developer for causing the leuco compound to develop color when heated, a binder, and a pigment.

As the leuco compound, a substance which is usually colorless or pale in color and which develops a color by reacting with a developer is preferable. For example, various derivatives such as triphenylmethane, triphenylmethanephthalide, fluoran, leuco auramine, diphenylmethane, phenothiazine, phenoxazine, spiropyran, indoline, and indigo derivatives may be mentioned. Specifically, the following can be exemplified.

Crystal violet lactone (blue), 3-diethylamino-6-methyl-7-anilinofluoran (black), 3- (N-ethyl-P-toluidino) -6-methyl-7-anilinofluoran (black) , 3-diethylamino-6-methyl-7- (ortho-, para-dimethylanilino) fluoran (black), 3-pyrrolidino-6
-Methyl-7-anilinofluoran (black), 3-piperidino-6-methyl-7-anilinofluoran (black), 3- (N-cyclohexyl-N-methylamino)
-6-methyl-7-anilinofluoran (black), 3-
Diethylamino-7- (ortho-chloroanilino) fluoran (black), 3-diethylamino-7- (meta-trifluoromethylanilino) fluoran (black), 3-
Diethylamino-6-methyl-chlorofluoran (red), 3-diethylamino-6-methyl-fluoran (red), 3-cyclohexylamino-6-chlorofluoran (orange), 3- (N-isoamyl-N-ethyl) Amino) -6-methyl-7-anilinofluoran (black), 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9 '-Xanthen] -2'-ylamino] phenyl} propane (black) and the like.

The developer is a solid at room temperature, and is a substance that softens or dissolves when heated and contacts the leuco compound to develop a color. For example, 4-tertiary butyl phenol, 4-phenyl phenol, bisphenol, 4-hydroxy di- Phenoxide, α-naphthol, β-naphthol, methyl-4-hydroxybenzoate, 4′-hydroxyacetophenone, 4-tertiaryoctylcatechol, 2,
2'-dihydroxydiphenyl, 2,2'-methylenebis (4-chlorophenol), 4,4'-secondary butylidene diphenol, 4,4'-isopropylidenebis (2
-Methylphenol), 4,4'-isopropylidenebis (2,6-dimethylphenol), penzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, dibenzyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, benzyl- 4-hydroxyphenyl acetate or resorcinol monobenzoate.

As the binder, conventionally known binders that are used in the thermosensitive coloring layer can be widely used. Further, it may be the same as the binder of the undercoat layer.

80ml / 100g oil absorption as specified in JIS K-5101
Although the above is preferred, the pigment is not limited thereto, and pigments used in conventional thermosensitive recording media such as calcium carbonate, barium sulfate, and aluminum hydroxide can be used.

Various auxiliary components can be added to the heat-sensitive coloring layer as needed. Such additives include, for example, head abrasion inhibitors, anti-sticking agents such as zinc stearate and higher fatty acid metal salts such as calcium stearate, and waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearic amide, and caster wax. Further, as a sensitivity improver, fatty acid amides such as stearic acid amide, metaterphenyl, parabenzyl biphenyl, esters of hydroxynaphthoic acid, tribenzylamine naphthalene derivatives and dibenzyl terephthalate, and the like. Agents, phenolic resins, dispersants such as sodium dioctylsulfosuccinate, benzophenone-based and benzotriazole-based ultraviolet absorbers, surfactants, and fluorescent dyes.

The heat-sensitive coloring layer is prepared by preparing a heat-sensitive coloring solution containing the above components in the same manner as in the preparation of the undercoat layer.
The application of the thermosensitive coloring solution is preferably performed in a continuous process subsequent to the application of the undercoat layer, but is not limited thereto.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

However, all parts and percentages shown in the examples are on a weight basis.

Example 1 Formation of Undercoat Layer Amorphous silica (Mizukasil P52 manufactured by Mizusawa Chemical Industry Co., Ltd.)
7) 100 parts by weight of 333.3 parts by weight of 12% aqueous solution of PVA
3.4 parts by weight and 4 parts by weight of a styrene-maleic acid-based sizing agent (Sunsizer SA501) as a sizing agent were added, and the mixture was dispersed for 10 minutes with a Coreless disperser. ^The composition was coated on a high-quality paper having a basis weight of ^{2 so} as to have a coating amount of 6 g / m ^2, and dried to form an undercoat layer on the support.

Formation of thermosensitive coloring layer The following liquid A and liquid B were prepared respectively.

To 50 parts by weight of Solution A, 50 parts by weight of an acrylic amide-based water-soluble resin (TY-121, solid content 20%) manufactured by Showa Denko KK and 30 parts by weight of a 30% zinc stearate aqueous dispersion were added. Mix and add amorphous silica (oil absorption 150ml / 100g)
20 parts by weight were gradually added and mixed. Next, add B
150 parts by weight of the liquid was added, and 35 parts by weight of water was further added to obtain a thermosensitive coloring liquid.

Solution A Color-forming leuco dye (3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran)
[S-205 by Yamada Chemical] 10 parts by weight Polyvinyl alcohol (12% aqueous solution) 30 parts by weight Polystyrene ammonium acrylate (20% aqueous solution) 2 parts by weight Water 8 parts by weight The average particle diameter of the above components is 1 μm with a sand grinder.
It was prepared by dispersing until it became.

Solution B Bisphenol A 18 parts by weight Meta-terphenyl 22 parts by weight Polyvinyl alcohol (12% aqueous solution) 50 parts by weight Polystyrene ammonium acrylate (20% aqueous solution) 3 parts by weight Water 57 parts by weight The above components are averaged with a sand grinder. Is 1 μm
It was prepared by dispersing until it became.

The thermosensitive coloring solution prepared as described above was coated on a support provided with an undercoat layer with a test blade coater so that the coating layer was 5 g / m ² . Next, let it dry,
By further performing a calendering process, a thermosensitive recording medium having a recording surface with a Bekk smoothness of 600 seconds was obtained.

Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that the pigment of the undercoat layer was changed to calcined kaolin (Ansiles).

Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that PVA was replaced with casein and a sizing agent was not used.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the sign sizer SA501 was not used.

Comparative Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the undercoat pigment was changed to carbon carbon PC.

○ Evaluation (1) Support with undercoat layer Bristow method (J. Tappl paper pulp test method No. 51-87)
The absorption coefficient for water and linseed oil was measured in accordance with the following.

(2) Printing characteristics Thermal facsimile tester (MF-Matsushita Electronic Parts Co., Ltd.)
Type 1), applied voltage 20.0V, pulse width 0.8ms and 1.
The color density obtained by printing in 4 ms is measured by Macbeth densitometer RD5.
Measured at 14.

(3) Surface Strength The surface strength was examined using a commercially available cellophane tape (cellopel test).

(4) Adhesion of Head to Head Using a thermal tester MF-1 type, 500 lines were continuously printed under the conditions of an applied voltage of 20.0 V and a pulse width of 1.4 ms, and the head residue was observed.

The results are shown in Table 1 below.

As can be seen from Table 1, the water absorption coefficient Ka of the support having the undercoat layer based on the Bristow method was 0.40 ml / m2.
With a ² · ms ^1/2 or less, and the absorption coefficient Ka for linseed oil law 0.15ml / m ² · ms ^1/2 or more, while maintaining the surface strength, moreover head without degrading the sensitivity An excellent heat-sensitive recording medium was obtained in which the adhesion of scum to the recording medium was prevented.

Claims (1)

(57) [Claims] 1. A thermosensitive recording medium comprising a support and an undercoat layer containing a pigment and a binder, and a thermosensitive coloring layer provided thereon, wherein the support having the undercoat layer is formed by a Bristow method. (J.TAPPI paper pulp test method N
0.40 ml for the absorption coefficient Ka for water according to o.51-87)
/ m ²・ ms ^1/2 or less and absorption coefficient for linseed oil
A thermosensitive recording medium having a Ka of 0.10 ml / m ² · ms ^1/2 or more.