JPH02137971A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain extreme high density coloration and to prevent a base surface from staining by a method wherein a specific 1,2-diarylethane is contained in a coloring layer. CONSTITUTION:In a thermal recording material to which a coloring layer generally containing a colorless or light color coloring material and a developer coloring said material when heated is provided, 1,2-diarylethane represented by the general formula (I) of a 1.5mum or less mean particle size is made to be contained in the coloring layer. In the formula, (n) represents 1 to 3. In the case where 1,2-diarylethane having an extremely fine particle size if used, coloring sensitivity and shelf life stability are remarkably improved. Dispersibility is excellently improved because of the fine particle size. Affinity with a dye and/or a developer is extremely improved thereby, and the coloring sensitivity is considered to be improved. Then, there is constant correlation between an effect of improving the coloring sensitivity and an average particle size of a sensitizer, and its inflection is estimated to exist near 1.5 micron.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material characterized in that it contains 1,2-diarylethane having a fine particle size as a sensitizer.

A heat-sensitive recording material is a color-forming system consisting of a usually colorless or light-colored color-forming substance such as a leuco dye, a color developer that develops color when heated, and a sensitizer on a support such as paper, synthetic paper, or resin film. , a heat-sensitive color forming layer in which a binder and other additives are dispersed is provided, and when a heat-generating element such as a thermal head or a thermal pen comes into contact with this recording medium in a recording device, the dye and color developer react with each other. It develops a color such as black and is recorded.

Compared to other recording materials, heat-sensitive recording materials have advantages such as being able to record in a short time, generating less noise, and being inexpensive. It is widely used as a recording material for , telex, ticket vending machines, etc.

Conventionally, as colorless or light-colored color-forming substances, for example, leuco dyes having a lactone, lactam or spiropyran ring have been used, and as color developers, various acidic substances have been proposed, and in particular, phenolic compounds, such as , bisphenol A% p-hydroxybenzoic acid benzyl ester, etc. have been used singly or in combination of several types, but when these phenols are used, it is difficult to achieve high recording speed and high density, and There was a drawback that color unevenness occurred.

Therefore, attempts have been made to achieve higher sensitivity by using a sensitizer, which is a third substance, as a color-forming substance or developer. For example, various waxes, dimethyl phthalate, stearamide, phenyl benzoate, terphenyl,
Bis(vinyloxyethoxybenzene, p-acetyloxybiphenyl, etc.) have been proposed.

However, these sensitizers are not effective unless used in large quantities, and do not fully satisfy the demands for high sensitivity of heat-sensitive recording materials.Furthermore, they may cause fogging or discoloration during storage. However, it has some disadvantages and is not practically satisfactory.

In addition, in Japanese Patent Publication No. 59-25674, melting point 60°
It is proposed to use alkylated biphenyls or substituted biphenyl alkanes between C and 200 °C as sensitizers,
It is described that by using these sensitizers, the color development sensitivity is improved compared to the case where stearic acid amide is used.

The above publication describes 1,2-bis(2,4-dimethylphenyl) as a specific example of the substituted biphenylalkane.
Ethane, 1. 2-bis(2,4,5-trimethylphenyl)ethane and the like are mentioned as suitable compounds.

However, even when these compounds are used, the sensitizing effect is still insufficient and is not practically satisfactory.

As a result of intensive studies to eliminate these drawbacks, the present inventor found that when the particle size of 1,2-bis(7)-trimethylphenyl)ethane used as a sensitizer was made extremely fine, It has been found that the sensitizing effect is remarkable, and not only is color development of extremely high density obtained, but also staining of the background called background fog does not occur.

Sensitizers used in heat-sensitive recording materials are generally finely pulverized and used as aqueous dispersions.
Publication No. 74 also describes that these compounds are used after being ground to 3 microns. However, according to the studies conducted by the present inventors, the effect in the case of an average particle size of 3 microns is unsatisfactory in practice, whereas the effect in the case of an average particle size of 3 microns is
It has been found that the sensitizing effect is significantly exhibited when the particle size is less than microns, more preferably less than 1.0 microns.

The present invention has been made based on the above findings, and provides a heat-sensitive recording material provided with a color-forming layer containing a normally colorless or light-colored color-forming substance and a color developer that causes the substance to develop color when heated. In the coloring layer, an average particle size of 1. The present invention provides a heat-sensitive recording material characterized by containing 1,2-diarylethane represented by the following general formula (1) of 5 microns or less.

(In the above formula, n represents 1 to 3) 1,2- with extremely fine particle size used in the present invention
It is not clear why diarylethane significantly improves color development sensitivity and storage stability compared to 1,2-diarylethane, which has a relatively large particle size. It is thought that the dispersibility was significantly improved, and thereby the affinity with the dye and/or the color developer was significantly improved, resulting in the improvement in coloring sensitivity. There is a certain correlation between the effect of improving color development sensitivity and the average particle size of the sensitizer, which is 1.5
It is estimated that the inflection point exists near microns.

Hereinafter, the present invention having the above-mentioned summary will be explained in more detail.

The 1,2-diarylethane represented by the general formula (1) used in the present invention is 1°2-bis(2
-methylphenyl)ethane, 1. 2-bis(3-methylphenyl)ethane, 1,2-bis(4-methylphenyl)ethane, 1,2-bis(2,3-dimethylphenyl)ethane, 1,2-bis((2,4- dimethylphenyl)ethane, 1,2-bis(2,5-dimethylphenyl)
Ethane, 1,2-bis((2,6-dimethylphenyl)
Ethane, l, 2-bis(3,4-dimethylphenyl)ethane, 1,2-bis(3,5-dimethylphenyl)ethane, 1,2-bis(2,3,4-trimethylphenyl)
Ethane, 1.2-bis(2゜3.5-trimethylphenyl)ethane, 1.2-bis(2,3,6-trimethylphenyl)ethane, 1.2-bis(2,4,5-)dimethyl phenyl)ethane, 1,2-bis(2,4,6-)dimethylphenyl)ethane, 1,2-bis(3,4,5-
An example is trimethylphenyl)ethane.

The above diarylethane compound has an average particle size of 1.

5 microns or less, more preferably 1. It is necessary to use it as extremely fine particles of 0 microns or less,
If particles with a larger size are used, the coloring sensitivity and storage stability will be poor, and this will not be practically satisfactory.

Various dyes are well known as the usually colorless or light-colored color-forming substances used in the present invention, and there are no particular limitations as long as they are used in general pressure-sensitive recording paper, heat-sensitive recording paper, etc. .

Specific examples of these dyes include (1) triarylmethane compounds; for example, 3.3-bis(P-dimethylaminophenyl)-6-dimethylaminophthalide (commonly known as crystal violet lactone), 3-( p-dimethylaminophenyl)-3=(1,2-dimethyl-3-indolyl)phthalide, 3-(p-dimethylaminophenyl)-3(2-phenyl-3-indolyl)phthalide,
3゜3-bis(9-ethyl-3-carbazolyl)-5-
Dimethylaminophthalide, 3.3-bis(2-phenyl-3-indolyl)-5-dimethylaminophthalide, etc.
(2) Diphenylmethane compounds; e.g., 4,4-bis(dimethylamino)benzhydrin benzyl ether, N-2,4,5-trichlorophenylleukoolamine, etc.; (3) Xanthine compounds; e.g., rhodamine- β-anilinolactam, 3-dimethylamino-7-methoxyfluoran, 3-dimethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-dimethylamino-7-chlorofluoran, 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-7dibenzylaminofluorane, 3-diethylamino-7-
N-methyl-N-benzylaminofluorane, 3-diethylamino-6-methyl-7=xylidinofluorane,
3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p- ) luidino) fluoran, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-
Anilinofluoran, 3-diethylamino-6-chloro-7-(β-ethoxyethylamino)fluoran, 3-
Diethylamino-7-(2-carbomethoxyphenylamino)fluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane, 3-
(N-methyl-N-n-amylamino)-6=methyl-
7-anilinofluorane, 3-(N-ethyl-N-n-amylamino)-6-methyl-7-anilinofluorane,
3-(N-methyl-Nn-hexylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-
n-hexylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-β-ethylhexylumino)-6-methyl-7-anilinofluorane, 3-
dibutylamino-6-methyl-7anilinofluorane,
3-dibutylamino-7-(2-chloroanilino)fluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3(N-ethyl-p-1-luidino-6-methyl-7-anilinofluoran) Oran, 3-pyrrolidino-6methyl-7-anilinofluorane, 3-pyrrolidino-6-
Methyl-7-P-butylphenylaminofluorane, 3
-(N-cyclohexyl-N-methylamino)-6-methyl-7-aniritefluorane, 3-(N-isopropyl-N-ethylamino)-6-methyl-7-aniritefluorane, 3-diethylamino -6-chloro-7-7-
(4) Thiazine compounds such as chloropropylaminofluorane; for example, benzoylleucomethylene blue p-
nitrobenzoylleucomethylene blue, etc., (5) spiro-based compounds; for example, 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho(3-methoxybenzo)spiropyran, etc. These dyes can also be used in combination.

Furthermore, the color developer used in the present invention includes, for example, p
-octylphenol, p-tert-butylphenol, p
-Phenylphenol, P-hydroxyacetophenone, α-naphthol, β-naphthol, p-tertiary octylphenol, 2゜2″-dihydroxybiphenyl, bisphenol A, 1.1-bis(p-hydroxyphenyl)butane, 2.2 -bis(4-hydroxyphenyl)hebutane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3゜5-dimethyl-
4-hydroxyphenyl)propane, 2,2-bis(3
, 5-dichloro-4-hydroxyphenyl)propane,
Bis(4-hydroxyphenyl)sulfone, bis(3,
4-dihydroxyphenyl) sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4″-isopropoxydiphenyl sulfone, 1.1
-Bis(4-hydroxyphenyl)cyclohexane, bis(4-hydroxyphenyl)ether, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, bis(4- hydroxyphenyl)acetic acid butyl ester, 1,1°3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1. l, 3-1 phenols such as lis(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, bis(2-(4-hydroxyphenylthio)ethoxycomethane, 4-hydroxyphthalic acid dimethyl ester); Aliphatic carboxylic acids such as oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid, stearic acid, behenic acid; benzoic acid, tert-butylbenzoic acid, phthalic acid, gallic acid, salicylic acid, isopropyl salicylic acid, phenyl salicylic acid, 3 , 5-di-tert-butylsalicylic acid, 3-methyl-5-benzylsalicylic acid, 3.5-di(α-methylbenzyl)salicylic acid, 3-
Aromatic carboxylic acids such as phenyl-5-(α,α-dimethylbenzyl)salicylic acid and polyvalent metal salts of these aromatic carboxylic acids such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; acidic White clay, activated clay, attapulguide, bentonite, colloidal silica, aluminum silicate, magnesium silicate,
Examples include inorganic color developers such as zinc silicate, tin silicate, calcined kaolin, and talc.

1 represented by the general formula (summer) used in the present invention,
The 2-diarylethane compound is pulverized using a grinder such as a ball mill, atlyzer, or sand grinder, or a suitable emulsifier until the average particle size becomes 1.5 microns or less.

Further, a color-forming colorless dye, a color developer, and various other additive materials as required are atomized using a similar device, and these are combined to form a coating liquid.

This coating liquid usually contains polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, polyacrylamide polymer, starch, styrene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, styrene-butadiene copolymer, etc. Alternatively, binders such as modified products thereof, fillers such as silane, kaolin, diatomaceous earth, talc, titanium dioxide, calcium carbonate, magnesium carbonate, aluminum hydroxide, and melamine are blended.

In addition, metal soaps, amides, waxes,
Light stabilizers, waterproofing agents, dispersants, antifoaming agents, etc. can be used, and sensitivity and storage stability can be improved by using zinc soaps and amides such as zinc stearate and stearamide. It is often done.

By applying this coating liquid to paper and various films, the desired heat-sensitive recording material can be obtained.

1 represented by the general formula (1) used in the present invention,
The amount of the 2-diarylethane compound is not particularly limited, as it varies depending on the required performance and recording suitability, as well as the type and amount of other additives used together, but it is usually about 1 part of the color-forming dye. 0.1 to 10 parts are used.

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

Example-1 20 g of 3-(N-ethyl-N-isopropylamino)=6-methyl-7-anilite fluorane and 100 g of a 10% polyvinyl alcohol aqueous solution were thoroughly ground to obtain a dye dispersion (liquid A). Ta.

20 g of bisphenol A and 100 g of a 10% polyvinyl alcohol aqueous solution were sufficiently ground to obtain a color developer dispersion (liquid B).

20 g of zinc stearate and 100 g of a 10% polyvinyl alcohol aqueous solution were sufficiently ground to obtain a dispersion (liquid C).

Further, sensitizer dispersions (liquid B) having different average particle sizes were obtained by the following operation.

20 parts by weight of a sensitizer and 100 parts by weight of a 10% polyvinyl alcohol aqueous solution were placed in a polyethylene container, and glass beads with a diameter of 2 m+a were added thereto, and the mixture was shaken at room temperature using a shaker made by Thermonix. When the average particle size was measured over time, it was about 6 microns after 6 hours, about 3 microns after 12 hours, and about 2 microns after 24 hours, and the particle size did not become smaller even if it was continued beyond that.

To prepare a dispersion with an average particle size of 1.5 microns or less, use a dispersion with an average particle size of about 2 microns, replace the glass piece with one with a diameter of IW+, and shake for 3 hours to obtain an average particle size of about 1 micron, Approximately 0.7 micron after 6 hours,
Approximately 0.5 micron after 12 hours, approximately 0.3 micron after 18 hours
It became a micron.

Liquids A, B, C, B and finely powdered silica were mixed at a weight ratio of 1:2:O14:2:0.5171 and sufficiently dispersed to obtain a coating liquid.

This coating liquid was applied to a thickness of 28 μm on a 50 g/rd base paper and dried to form a heat-sensitive recording material.

Using the obtained thermal paper, a thermal printing device (TH-PMD
: manufactured by Okura Electric Co., Ltd.), and the color density of the recorded image printed by changing the pulse width was measured using a Macbeth densitometer (model RD-933, manufactured by Macbeth Co., Ltd.).

The results are shown in Table 1.

As is clear from the results in Table 1 Continued Table 1, there is a tendency that the finer the particle size of the sensitizer used, the better the coloring sensitivity is. So the average particle size is 2. The improvement effect is small when the average particle size is 1.5 microns or less, especially when the particle size is 1.5 microns or less.
．． In the case of 0 micron or less, a remarkable effect of improving the coloring sensitivity is observed, and almost no background capri is observed.

On the other hand, when metaterphenyl was used, no such peculiar effect depending on the particle size was observed, and the finer the particle size, the more background fogging occurred.

From this result, the effect of using a sensitizer with a specific particle size can be seen from 1. of the present invention. This is considered to be a unique effect that is observed only when a 2-diarylethane compound is used.

1 continuation

Claims (1)

[Scope of Claims] A heat-sensitive recording material provided with a color-forming layer containing a normally colorless or light-colored color-forming substance and a color developer that causes the substance to develop color when heated, wherein the color-forming layer contains particles with an average particle size of 1. A heat-sensitive recording material characterized by containing 1,2-diarylethane represented by the following general formula (I) having a size of .5 microns or less. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (In the above formula, n indicates 1 to 3.)