JPH03211084A - Thermal recording material - Google Patents

Abstract

PURPOSE:To reduce the number of background fogs caused by thermal accumula tion with the enhancement of sensitivity and image preservation and the minimi zation of waste sticking to a thermal head by adding a specific compound to a thermal recording material containing a dye precursor and a developer. CONSTITUTION:Compounds shown by formulae (I) and (II) are added to a thermal recording material containing a developer which develops the color of a dye precursor in reaction with the precursor at the time of heating. If the compounds of the formulae (I) and (II) are jointly used, the back-ground fog and waste sticking to a thermal head due to thermal accumulation are minimized with the sensitivity obtained when the compound of the formula (I) is used being maintained at the same leve. 4-phenylphenynol and other chemicals can be used as a developer. However, a compound shown by formula (III) is preferred in terms of image preservation properties. In the formula, R1, R2 are a hydrogen atom, an alkenyl group, an alkyl group, a halogen atom or a hydroxyl; R3 is a hydrogen atom, a hydroxyl, an alkoxy group or an alkyl group. Typically, 4'-dihydroxysulfone and other chemicals are pointed out.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a heat-sensitive recording material that has excellent sensitivity and image storage stability, has less thermal head adhesion residue, and has less background fog due to heat accumulation in the thermal head.

(B) Conventional technology Heat-sensitive recording materials generally have a heat-sensitive recording layer on a support, the main components of which are an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting color developer. It reacts instantaneously with a head, a hot pen, a laser beam, etc., and a recorded image can be obtained.
It is disclosed in the publication number etc. Such heat-sensitive recording materials have the advantage of being able to record with relatively simple equipment, and are used in a wide range of fields such as measurement recorders, facsimile machines, printer/computer terminals, labels, and automatic ticket vending machines. It's being used.

The basic performances required of a heat-sensitive recording material include sufficient color image density and sensitivity, and no deterioration of color images over time. In addition, in recent years, the speed of print recording has been increasing, and as the speed of recording devices themselves has increased, we have also developed recording materials that can cope with this, that is, heat-sensitive recording materials with excellent thermal responsiveness that can produce high-density colored images with low thermal energy. is desired.

Furthermore, as heat-sensitive recording materials became widely used, properties such as image preservation (grease resistance) due to the adhesion of oily substances such as hair products, hand creams, and oils and fats contained in skin sweat were also required. Therefore, there has been a demand for a heat-sensitive recording material that satisfies thermal responsiveness and image storage stability.

Conventionally, methods have been known in which various sensitizers are incorporated into the recording layer in order to obtain colored images with high density.

For example, in Japanese Patent Publication No. 4:3-4160, urea, phthalic anhydride, acetanilide, etc., in Japanese Patent Publication No. 48-19231, natural and synthetic waxes such as beeswax, carnauba wax, paraffin wax, etc.; No. 17748 discloses a method of adding salicylic acid, phthalic acid monobenzyl ester, etc.

However, although the sensitivity is improved by using various sensitizers, other characteristics such as residue adhesion to the thermal head and thermal fog, that is, background fog due to heat accumulation in the thermal head, often deteriorate.

In addition, bisphenol sulfone type color developers have been proposed to improve image storage stability, and bis(3-
Allyl-4-hydroxyphenyl) sulfone
0-208286), 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-138)
No. 52) etc.

Currently, 2°2-bis(4-hydroxyphenyl)propane (hereinafter referred to as BPA) is widely used as a color developer for thermal paper, but compared to thermal paper that uses BPA, these bisphenols Thermal paper using a sulfone type color developer has a drawback in that the image storage stability is greatly improved, but the sensitivity is lowered.

(C) Problems to be Solved by the Invention An object of the present invention is to obtain a heat-sensitive recording material that has excellent sensitivity and image storage stability, has less residue adhering to the heat head, and has less background fog due to heat accumulation in the heat head.

(D) Means for Solving the Problems The present inventor has developed a heat-sensitive recording material containing a color developer that reacts with a normally colorless or light-colored dye precursor upon heating to cause the dye precursor to develop a color. ] and the compound of chemical formula [II'l], it was possible to obtain a heat-sensitive recording material which has excellent sensitivity, has less residue adhering to the heat head, and has less background fog due to heat accumulation in the heat head.

The heat-sensitive recording material using the compound of chemical formula H3 showed a superior sensitizing effect compared to conventionally used additives with sensitizing ability, but it also caused background fogging due to heat accumulation in the heat head and scum adhering to the heat head. This made it difficult to use in practice. In addition, when the compound of the chemical formula (III) was used, it was sufficient to reduce the amount of residue adhering to the thermal head, but the sensitivity and background fog due to heat accumulation in the thermal head were insufficient.

If the compounds of chemical formula [I] and [■] are used in combination, there is a drawback while maintaining the sensitivity obtained when using the compound of chemical formula CI). The present invention was based on the discovery that background fogging and deposits on the thermal head due to heat accumulation in the thermal head are reduced.

The color developer used in the present invention includes 4-phenylphenonol, 4-hydroxyacetophenone, 2.2'-dihydroxydiphenyl, 2. 2'methylenebis(4-chlorophenol), 2.2methylenebis(4-methyl-
6-t-butylphenol), 2,2'-bis(4-hydroxyphenyl)propane (also known as bisphenol A)
, 4゜4'-isopropylidene bis(2-chlorophenol), 4.4'-isopropylidene bis(2-
methylphenol), 4,4'-ethylenebis(2
-methylphenol), 4,4'-thiobis(6-
t-butyl-3-methylphenol), King.

1--bis(4-hydroxyphenyl)-cyclohexane, 2,2'-bis(4-hydroxyphenyl)-
n-hebutane, 4. Examples include 4'-cyclohexylidene bis(2-isopropylphenol), salicylic acid anilide, novolak type phenol resin, benzyl p-hydroxybenzoate, etc. Among them, compounds represented by the chemical formula [■] are preferred from the viewpoint of image storage stability. preferable.

R4 (In the formula, R4 and R2 represent a hydrogen atom, an alkenyl group, an alkyl group, a halogen atom, or a hydroxyl group, and R3 represents a hydrogen atom, a hydroxyl group, an alkoxy group, or an alkyl group.) A compound represented by the chemical formula [I[I] Specific examples include bis(3-allyl-4-hydroxyphenyl)sulfone,
3,3'-dimethyl-4,4'-dihydroxyphenylsulfone, 4-hydroxy-4'-propyloxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 3゜4-dihydroxy-41-methyldiphenylsulfone , 3-chloro-4-hydroxy-
4' methyldiphenylsulfone, 4. Examples include 4'-dihydroxysulfone.

A similar effect can be obtained when a compound of the chemical formula [I[) is used as a color developer.

That is, when a heat-sensitive recording material using a compound of chemical formula [I] uses a compound of chemical formula [■] as a color developer, it has superior sensitization compared to conventionally used additives with sensitizing ability. Although it was effective and showed high image storage stability, it was difficult to use in practice due to background fogging and residue adhering to the thermal head due to heat accumulation in the thermal head. Furthermore, when the compound of chemical formula [■] and the compound of chemical formula CIII) are used in combination, the image storage stability and the adhesion of thermal head residue are sufficient, but the sensitivity and background fog due to heat accumulation in the thermal head are insufficient. Ta.

The compound of chemical formula [1[I] has chemical formulas ['I] and [I
If the compound [) is used in combination, there is a drawback while maintaining the sensitivity and high image storage stability obtained when using the compound of the chemical formula CI]. Fog on the skin due to heat accumulation in the heat head and debris adhering to the heat head have been reduced.

This was an unexpected effect from the combination of commonly known sensitizers. Furthermore, it has been found that this effect varies depending on the amount added, and that there is an optimum amount for each.

In the present invention, the preferred addition amounts of the compounds of the chemical formulas [E] and (II) are 25 to 75% by weight of the compound of the chemical formula [I] and 50 to 100% of the compound of the chemical formula (It, ) based on the developer. %, and the total amount of the compound of chemical formula [I] and the compound of chemical formula (II) is 7% relative to the color developer.
5 to 175% by weight, and particularly preferred addition amounts are 35 to 65% by weight of the compound of chemical formula CIE and 60 to 90% by weight of the compound of chemical formula [11] to each color developer; The total amount of the compound of I) and the compound of the chemical formula [I, I is 95 to 155% by weight.

If the amount of the compound of chemical formula [I] added is less than 25% by weight of the color developer, the sensitivity will not be sufficient, and if the amount added is more than 75% by weight, the background capri will decrease due to thermal head deposits and heat accumulation in the thermal head. I can't see it.

Also, the amount of the compound of chemical formula [■] added is 5% to the color developer.
If it is less than 0% by weight, there will be a lot of debris attached to the thermal head.
If the amount added is greater than % by weight, sufficient sensitivity may not be obtained.

The main components used in the heat-sensitive recording material of the present invention will be specifically explained below, but are not limited thereto.

Examples of the dye precursor include triphenylmethane-based, fluoran-based, diphenylmethane-based, thiazine-based, and spiropyran-based compounds. For example, crystal violet lactone, 3-diethyl-1-amino-7-methylfluorane, 3-diethylamino-
6-chloro-7-methylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-
7-(2-chloroanilino)fluoran, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3-
Diethylamino-7-(3-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-
Methyl-7-anilinofluorane, 3-(N-methylcyclohexylamino)-3-methyl-7-anilinofluorane, 3-piperidino-3-methyl-7-anilinofluorane, 3-dibutylamino- 6-Methyl-7-anilinofluorane, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluorane, 3(N-
Ethyl-N-isopropyl)amino-6-methyl-7-
Examples include anilinofluorane, 3-(N-ethyl-N-tetrahydrofurfuryl)amino-69-monomethyl-7-anilite fluorane, and the like.

Examples of binders include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, water-soluble binders such as styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, etc. Latex-based water-insoluble binders such as copolymers, acrylonitrile-butadiene copolymers, and methyl acrylate-butadiene copolymers may be mentioned.

Examples of pigments include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and the like.

In addition, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide, and castor wax are used to prevent head wear and stickiness. Examples include dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, surfactants, and fluorescent dyes.

Paper is mainly used as the support for the heat-sensitive recording material of the present invention, but various nonwoven fabrics, plastic films, synthetic papers, metal foils, etc., or composite sheets made of combinations thereof can also be used as desired.

(E) Examples The present invention will be explained in detail by way of examples.

(Example 1) 30 g of 3-dibutylamino-6-methyl-7-anilinofluorane was ground with a paint conditioner together with 70 g of water containing 1.5 g of polyvinylal=r-L. Meanwhile, 40g of bis(3-allyl-4hydroxyphenyl)sulfone was added to 6g of water containing 2g of polyvinyl alcohol.
It was ground with paint conditioner along with 0g. Furthermore, 15 g of the compound of the chemical formula CI) was ground with 50 g of water containing 0.75 g of polyvinyl alcohol, and 35 g of the compound of the chemical formula (II'l) was ground with 117 g of water containing 1.75 g of polyvinyl alcohol. I got it.

After mixing these four types of dispersions, 4
Add 75g of 0% dispersion, and add 40g of zinc stearate.
% dispersion 25g, 10% polyvinyl alcohol aqueous solution 1
60 g and 170 g of water were added and thoroughly stirred to obtain a coating liquid.

On the other hand, after stirring a mixture of 100 g of calcined kaolin and 200 g of an aqueous solution of 10% polyvinyl alcohol on paper with a basis weight of 42 g/n, the mixture was coated to a solid content of 5 g/n and dried to form a support. The previously obtained coating solution was applied onto the support obtained so that the solid content coating amount was 4 g/rrf and dried.

This was treated with a calendar to obtain a heat-sensitive recording material.

(Example 2) R A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the compound of formula CI used in Example 1 was 25 g, and the compound of formula [■] was 25 g.

(Example 3) A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the compound of formula CI used in Example 1 was used in 10 g, and the compound of formula [■] in 40 g.

(Example 4) A thermosensitive recording material was obtained in the same manner as in Example 1 except that the compound of chemical formula [I] used in Example 1 was 30 g and the compound of chemical formula [II] was 20 g.

(Comparative Example 1-) A thermosensitive recording material was obtained in the same manner as in Example 1, except that 50 g of the compound of chemical formula [I] was used instead of 15 g of chemical formula CI) and 35 g of the compound [■] used in Example 1. .

(Comparative Example 2) A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 50 g of the compound of chemical formula [■] was used instead of 15 g of chemical formula (I) and 35 g of the compound of [■] used in Example 1. .

(Comparative Example 3) 5 g of chemical formula [I] used in Example 1, chemical formula [II]
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the amount of the compound was changed to 45 g.

(Example 4) A thermosensitive recording material was obtained in the same manner as in Example 1 except that 40 g of the compound of chemical formula CI) used in Example 1 and 10 g of the compound of chemical formula (n) were used.

(Evaluation) The heat-sensitive recording materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were printed using a G3 FAX tester, and the image densities were compared. The testing machine was manufactured by Taishoku Denki Co., Ltd. (TH-PMD) and used a thermal head with a dot density of 8 dots/mm and a head resistance of 185 Ω. Printing was carried out at a head voltage of 11 μ and a current application time of 5 ms. Regarding image density, Macbeth RI)-51
It was measured using a type 4 reflection densitometer. In addition, the printed samples were left in a constant temperature room at 60° C. for 24 hours, and the image survival rate (%) after processing was compared.

Note that the image survival rate was calculated using the formula shown below.

Image survival rate (%) Optical density of image area after processing Background fog due to heat accumulation in the thermal head was measured by placing a thermal block at 85°C in close contact with thermal paper at 200 g/cnr for 3 seconds and measuring the optical density of the colored area. .

(The smaller the value, the less the background fog due to heat accumulation in the head.) The results of each measurement are shown in Table 1.

(Blank below) (F) Effects of the Invention As shown in Table 1, by using the combination of sensitizers according to the present invention, it is possible to prevent background fogging due to heat accumulation in the thermal head while maintaining the conventional sensitivity and image preservability. It was possible to obtain an excellent heat-sensitive recording material with less residue adhering to the heat head.

Claims (1)

[Scope of Claims] 1. Compounds of chemical formulas [I] and [II] in a heat-sensitive recording material containing a normally colorless to light-colored dye precursor and a color developer that reacts with the dye precursor upon heating to develop color from the dye precursor. A heat-sensitive recording material characterized by containing. ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [I] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [II] 2. The color developer according to claim 1, characterized in that the color developer is a compound of chemical formula [III]. Heat-sensitive recording material. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [III] (In the formula, R_1 and R_2 represent a hydrogen atom, an alkenyl group, an alkyl group, a halogen atom, or a hydroxyl group, and R_3 represents a hydrogen atom, a hydroxyl group, an alkoxy group, or an alkyl group. ) 3. The compounds of chemical formula [I] and [II] are 25 to 75% by weight and 50 to 100% by weight of the color developer, respectively, and the compound of chemical formula [I] and the compound of chemical formula [II] are 3. The heat-sensitive recording material according to claim 1, wherein the total amount of the color developer is 75 to 175% by weight.