JPH05262048A - Thermal recording sheet - Google Patents

Abstract

PURPOSE:To obtain a thermal recording sheet having high sensitivity and excellent in heat resistance and water resistance by providing a thermal color forming layer based on a specific fluorane leuco dye and a specific diphenylsulfone derivative on a support. CONSTITUTION:Specified amounts of 3-diethylamino-6-methyl-7-(m-methylanilino) fluorane represented by formula II, a diphenylsulfone derivative represented by formula I (wherein R is a propyl group, an isopropyl group or a butyl group) and, if desired, other additive are finely ground by a grinder such as a ball mill and a binder is compounded with the ground mixture to prepare a coating solution for a thermal color forming layer. This coating solution is applied to a support such as paper, synthetic paper or a plastic film and dried to form the thermal color forming layer to produce a thermal recording sheet. Further, an overcoat layer composed of a polymeric substance containing a filler can be provided on the thermal color forming layer for the purpose of enhancing preservability.

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 sheet excellent in heat resistance, water resistance and oil resistance.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording sheet is generally prepared by grinding and dispersing a colorless or light-colored basic colorless dye and an organic color developer such as a phenolic substance into fine particles, and then mixing them together to form a binder and filling. A coating solution obtained by adding agents, sensitivity enhancers, lubricants and other auxiliaries to a support such as paper, synthetic paper, film, plastic, etc., such as hot pens, thermal heads, hot stamps, laser light. Color recording is obtained by an instant chemical reaction due to heating such as.

These thermal recording sheets are used for measuring recorders, computer terminal printers, facsimiles,
It has been applied to a wide range of fields such as automatic ticket vending machines and bar code labels, but recently, with the diversification and high performance of these recording devices, the quality requirements for thermal recording sheets have become higher. .. For example, it is required that a high-density and clear color image can be obtained even with minute heat energy as recording speed increases, and light resistance on the other hand,
A heat-sensitive recording sheet having excellent storage stability such as weather resistance and oil resistance is required.

As a conventional example of the heat-sensitive recording sheet, for example, Japanese Patent Publication No. 43-4160 or Japanese Patent Publication No. 45-1403.
The heat-sensitive recording material disclosed in Japanese Patent No. 9 is mentioned, but such a conventional heat-sensitive recording material has a low thermal response, for example, and sufficient color density cannot be obtained during high-speed recording.

As a method of improving such a defect, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane is used as a leuco dye (JP-A-49-109120), 3- Dibutylamino-
A high-sensitivity dye using 6-methyl-7-anilinofluorane (JP-A-59-190891) has been developed, and a substance having a good color forming property 1,7-
Bis (4-hydroxyphenylthio) -3,5-dioxaheptane (JP-A-59-106456), 1,
By using 5-bis (4-hydroxyphenylthio) -3-oxaheptane (JP-A-59-116262) and 4-hydroxy-4'-isopropoxydiphenyl sulfone (JP-B-63-46067). Techniques for achieving high speed and high sensitivity have been disclosed.

[0006]

However, these heat-sensitive recording sheets have high sensitivity, but generally have a problem in heat resistance such that the image density is lowered when they are stored at a high temperature.

Further, the storage stability of the recorded image is remarkably poor, so that water or sebum components adhere to the color image or contact with a plasticizer (DOP, DOA, etc.) contained in a wrap film such as a vinyl chloride film. Then, there are still drawbacks such as a remarkable decrease in image density and decoloring.

An object of the present invention is to provide a thermosensitive recording sheet having high sensitivity and excellent heat resistance, water resistance and oil resistance.

[0009]

The present invention provides 3-diethylamino represented by the following formula (II) as a basic colorless dye in which a specific diphenyl sulfone derivative is contained as an organic developer in the thermosensitive color developing layer. -6-methyl-7- (m
By containing -methylanilino) fluorane, the above problems are solved all at once.

[Chemical 3]

In the present invention, other fluorane type leuco dyes can be used in combination within the range of not impairing the effects of the present invention, and specific examples thereof are shown below.

3-Diethylamino-6-methyl-7-anilinofluorane 3- (N-ethyl-p-toluidino) -6-methyl-
7-anilinofluoran 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluoran 3 -Pyrrolidino-6-methyl-7-anilinofluorane 3-piperidino-6-methyl-7-anilinofluorane 3- (N-cyclohexyl-N-methylamino) -6-
Methyl-7-anilinofluorane 3-diethylamino-7- (m-trifluoromethylanilino) fluorane 3-dibutylamino-6-methyl-7-anilinofluorane 3-diethylamino-6-chloro-7-ani Rinofluorane 3-dibutylamino-7- (o-chloroanilino) fluorane 3-diethylamino-7- (o-chloroanilino) fluorane

Similar to the dyes, other developers may be added to the organic developers as long as the effects of the present invention are not impaired.

As sensitizers, fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montan wax, polyethylene wax, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate. , P-benzylbiphenyl, phenyl α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-
2-naphthoic acid phenyl ester, 1,2-di- (3-
Methylphenoxy) ethane, di (p-methylbenzyl) oxalate, β-benzyloxynaphthalene, 4-biphenyl p-tolyl ether and the like can also be added.

As the binder used in the present invention, a fully silicified polyvinyl alcohol having a polymerization degree of 200 to 1900, a partially silicified polyvinyl alcohol, a carboxy modified polyvinyl alcohol, an amide modified polyvinyl alcohol, a sulfonic acid modified polyvinyl alcohol, and a butyral modified polyvinyl are used. Alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer and ethyl cellulose, cellulose derivatives such as acetyl cellulose, polyvinyl chloride, polyvinyl acetate,
Examples thereof include polyacrylamide, polyacrylic acid ester, polyvinyl butyral polystyrol and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin and coumarone resin. These polymeric substances are water, alcohol, ketones,
In addition to using it by dissolving it in a solvent such as ester or hydrocarbon,
It may be used in a state of being emulsified in water or another medium or dispersed in a paste form and used together depending on the required quality.

In the present invention, a known stabilizer p-nitrobenzoic acid metal salt (Ca, Zn) or phthalic acid monobenzyl ester metal salt (Ca, Zn) is used within a range that does not impair the effects of the present invention. It is also possible to add.

The filler used in the present invention is silica,
Examples thereof include inorganic or organic fillers such as calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, tanks, titanium oxide, and aluminum hydroxide.

In addition to the above, a releasing agent such as a fatty acid metal salt, a lubricant such as waxes, a UV absorber such as a benzophenone-based or triazole-based UV absorber, a waterproofing agent such as glyoxal, a dispersant, an antifoaming agent, etc. should be used. You can

The amounts of the stabilizer and basic colorless dye used in the present invention, and the types and amounts of various other components are determined according to the required performance and recording suitability, and are not particularly limited, but usually a base is used. 1 to 8 parts of an organic color developer and 1 to 20 parts of a filler are used per 1 part of a water-soluble colorless dye, and the binder is preferably 10 to 25% of the total solid content.

The desired heat-sensitive recording sheet can be obtained by applying the coating liquid having the above composition to any support such as paper, synthetic paper, film, plastic and the like.

Further, an overcoat layer of a polymeric substance containing a filler or the like may be provided on the thermosensitive color developing layer for the purpose of improving storage stability.

An undercoat layer containing an organic filler or an inorganic filler may be provided below the thermosensitive color developing layer for the purpose of enhancing the storage stability and sensitivity.

The above-mentioned organic color developer, basic colorless dye and materials to be added as necessary are finely divided by a pulverizer such as a ball mill, attritor or sand grinder or an appropriate emulsifying device until the particle diameter becomes several microns or less. Then, the binder and various additives according to the purpose are added to obtain a coating liquid.

[0023]

The reason why the effect of the present invention is obtained when the specific developer and the specific dye are combined in the present invention is considered as follows.

First, what is excellent in the ability of dynamic coloring is
This is because the dye has a large melt-dissolution diffusion rate and saturation solubility with respect to the developer of the present invention, and a recorded image can be instantaneously formed by instantaneous contact of a high-heat thermal head.

The reason why the recorded image is extremely stable in terms of water resistance and oil resistance is explained as follows. Generally, a thermal recording paper is composed of a basic colorless dye as an electron donor and an organic acidic substance such as a phenol compound, an aromatic carboxylic acid or an organic sulfonic acid as an electron acceptor. The heat-melting reaction between the basic colorless dye and the color developer causes the donation of electrons.
It is an acid-base reaction that is based on acceptance, whereby a metastable "charge transfer complex" is formed and a color image is obtained.

When the specific diphenyl sulfone derivative of the present invention is used as an organic developer, the chemical bonding force between the diphenyl sulfone derivative and the specific fluoran leuco dye, which is a basic colorless dye, in the color developing process. Is a developer other than the present invention (for example, benzyl 4-hydroxybenzoate, 1,7-di (4-hydroxyphenylthio)-
3,5-dioxaheptane, 4,4'-dihydroxydiphenylsulfone) and the fluorane-based leuco dye have a stronger specific bond compared to the chemical bond, so that they are not affected by environmental conditions such as water and oil. Even if it is exposed for a long time, its chemical bond is not broken, and the stability of the color image is maintained.

[0027]

EXAMPLES The present invention will be described below with reference to examples and comparative examples. In the description, parts indicate parts by weight. [Examples 1 to 3] Liquid A (dye dispersion) Dye (see Table 1) 2.0 parts 10% aqueous polyvinyl alcohol solution 4.6 parts water 2.5 parts Liquid B (developer dispersion) Diphenyl sulfone derivative (See Table 1) 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts water 11.2 parts Each solution of the above composition was ground to a particle size of 1 micron with a sand grinder. Then, the dispersion liquids are mixed in the following proportions to prepare a coating liquid. Liquid A (dye dispersion) 9.1 parts Liquid B (developer dispersion liquid) 36.0 parts Kaolin clay (50% dispersion liquid) 12.0 parts Each of the above coating liquids on one side of 50 g / m ² base paper Apply amount to 5.0
The sheet was coated and dried so as to have g / m ² , and this sheet was treated with a super calendar so as to have a smoothness of 400 to 500 seconds to obtain a black color thermosensitive recording paper.

[Comparative Examples 1 to 3] Thermal recording papers were obtained in the same manner as in Example 1 except that the dyes of the liquid A were replaced with the dyes shown in Table 1.

[Comparative Examples 4 to 7] Liquid C (dye dispersion) Dye (see Table 1) 2.0 parts 10% polyvinyl alcohol aqueous solution 4.6 parts water 2.5 parts D liquid (developing agent dispersion) Developer (see Table 1) 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts water 11.2 parts Each liquid of the above composition was ground to a particle size of 1 micron with a sand grinder. Then, the dispersion liquids are mixed in the following proportions to prepare a coating liquid. Liquid C (dye dispersion) 9.1 parts Liquid D (developer dispersion) 36.0 parts Kaolin clay (50% dispersion) 12.0 parts Each of the above coating liquids on one side of 50 g / m ² base paper Apply amount to 5.0
The sheet was coated and dried so as to have g / m ² , and this sheet was treated with a super calendar so as to have a smoothness of 400 to 500 seconds to obtain a black color thermosensitive recording paper.

The thermal recording papers obtained in the above Examples and Comparative Examples were subjected to the following quality performance tests, and the results are shown in Table 1.

Note (1) Dynamic color density; manufactured by Tokyo Shibaura Electric Co., Ltd.
Thermal fax KB-4800 is used and the applied voltage is 1
The image density recorded at 8.03 V and a pulse width of 3.2 milliseconds was measured with a Macbeth densitometer (RD-914, using an amber filter. The same applies hereinafter). Note (2) Heat resistance: The uncolored sample was allowed to stand under high temperature drying conditions at 60 ° C for 24 hours, and the background color density was measured with a Macbeth densitometer. Note (3) Water resistance: The thermal paper sample dynamically recorded by the method of Note (1) was immersed in cold water at 20 ° C. for 24 hours, dried, and the recorded portion was measured with a Macbeth densitometer. The residual rate is calculated from the following formula.

[Equation 1] Note (4) Oil resistance: Tokyo Shibaura Denki-Thermal facsimile K
The image density recorded with B-4800 at an applied voltage of 18.03 V and a pulse width of 3.2 milliseconds was measured by a Macbeth densitometer (using an RD-914 amber filter), and the untreated density was obtained. Then, drop the salad oil on the color-developed area, lightly wipe it with filter paper after 10 seconds, and let it stand at room temperature for 1
After leaving for a while, measure the image density with a Macbeth densitometer. The residual rate is calculated from the following formula.

[Equation 2]

[0032]

[Table 1]

[Table 2]

[0033]

【The invention's effect】

(1) Since the thermal response is excellent, a clear high density image can be obtained even at high speed and high density recording. (High sensitivity) (2) Almost no decoloring occurs in the printed part (colored part) even when contacted with a plasticizer, salad oil, vinegar, etc. (Oil resistance) (3) Almost no discoloration of the printed part occurs even when it comes into contact with water. (Water resistance) (4) The ground color is stable even under high temperature conditions. (Heat-resistant)

Claims (1)

[Claims] 1. A thermosensitive recording sheet comprising a support and a thermosensitive color developing layer containing a colorless or light-colored basic colorless dye and an organic developer as main components, wherein the thermosensitive color developing layer is an organic developer. As a basic colorless dye, and a fluoran-based leuco dye represented by the following formula (II) as a basic colorless dye. [Chemical 1] (In the formula, R represents a propyl group, an isopropyl group, or a butyl group.)