JPH066395B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material excellent in light resistance, weather resistance, oil resistance and optical readability in the near infrared region.

(Prior Art) Generally, in a thermal recording paper, a colorless or light-colored basic colorless dye and an organic developer such as a phenolic substance are ground and dispersed into fine particles, respectively, and then the both are mixed to form a binder,
A coating solution obtained by adding fillers, sensitivity improvers, lubricants and other auxiliaries to a support such as paper, synthetic paper, film, plastic, etc., such as hot pens, thermal heads, hot stamps, lasers. Color recording is obtained by an instantaneous chemical reaction caused by heating with light or the like.

These thermal recording papers are applied to a wide range of fields such as measurement recorders, computer terminal printers, facsimiles, automatic ticket vending machines, and bar code labels, but recently, these recording devices have been diversified and improved in performance. Accordingly, the required quality of the thermal recording paper has become higher. For example, with the increase in recording speed, it is required that a clear color image with high density can be obtained even with a small amount of heat energy, and on the other hand, a heat-sensitive recording paper having excellent storage stability such as light resistance, weather resistance and oil resistance is required. Is required.

These thermosensitive recording papers are also used as thermosensitive labels, but since the color development is in the visible region, it is not suitable for reading with semiconductor lasers in the near infrared region, which is widely used as bar code scanners for POS systems and the like. Could not fit.

On the other hand, JP-A-59-199757 and JP-A-60-22
Japanese Patent No. 6871 proposes a thermal recording paper using a fluoran-based leuco dye excellent in color development in the near infrared region and a known developer (acid clay, phenol resin, hydroxybenzoic acid ester, bisphenol A). Has been done.

(Problems to be Solved by the Invention) However, in these thermosensitive recording papers, since the storage stability (light resistance, weather resistance, oil resistance) of the recorded image is extremely poor, the recorded image portion is exposed to light, If left for a long time under environmental conditions affected by heat, humidity, etc., the color density will fade and the image density will decrease, and sometimes the color will completely disappear, resulting in a significant decrease in the optical reading rate in the near infrared region. Resulting in.

Also, sebum components may adhere to the colored image, or plasticizers (DOP, DOA, etc.) contained in wrap films such as PVC films.
Etc.), the image density remarkably decreases and the color disappears, so that the optical reading rate in the near infrared region remarkably decreases. Due to the above difficulties, there is a problem in putting these thermal recording papers to practical use.

An object of the present invention is to provide a heat-sensitive recording material excellent in light resistance, weather resistance, oil resistance, and optical readability in the near infrared region such as a barcode.

(Means for Solving Problems) The present invention relates to 2,4′-dihydroxydiphenyl sulfone or 3,4-dihydroxyphenyl-p which is a specific sulfonylphenol compound as an organic developer in a thermosensitive color developing layer.
By containing tolylsulfone and a fluorane-based leuco dye represented by the following general formula (I) as a basic colorless dye, the above problems are solved all at once.

[In the formula, R ₁ represents a hydrogen atom or an alkyl group, and R ₂ represents a halogen atom or an alkyl group. T ₁ and T ₂ represent a hydrogen atom, an alkyl group or a phenyl group, but T ₁ and T ₂ do not become phenyl groups at the same time. The organic developer 2,4′-dihydroxydiphenyl sulfone used in the present invention has a melting point of 181 to 183 ° C., and the 3,4-dihydroxyphenyl-p-tolyl sulfone has a melting point of 180 ° C. It is a known developer. The structural formulas of these two developers are shown below.

These two color developers are diphenyl sulfone compounds containing two phenolic hydroxyl groups in the molecule, and the effects of the present invention are brought about by their structural characteristics.

That is, conventionally known developers such as bisphenol A, 4,4'-cyclohexylidene bisphenol, 2,
Bisphenol compounds such as 2'-dihydroxydiphenyl, bis (p-hydroxyphenylthioethoxy)-
Sulfur-containing bisphenol compounds such as methylene and 1,2-bis (p-hydroxyphenylthioethoxy) -ethylene, 4-hydroxybenzoic acid esters such as benzyl 4-hydroxybenzoate, 4-hydroxy-4′-methyldiphenyl The present invention includes monohydroxy sulfones such as sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone, and 4-hydroxy-4′-butoxydiphenyl sulfone, and 4-hydroxyphthalic acid diesters such as dimethyl 4-hydroxyphthalate. Even if it is used in combination with the fluoran-based leuco dye represented by the general formula (I), the remarkable effect as obtained in the present invention is not obtained at all.

Among the fluoran-based leuco dyes represented by the general formula (I), the most preferable one is 2-methyl-6-p-represented by the following structural formula (II) in view of productivity, cost and performance.
(P-Dimethylaminophenyl) aminoanilinofluorane (melting point 197 to 203 ° C.), and the following structural formula (III)
2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane (melting point 1
91.5-196 ° C).

Examples of the fluoran-based leuco dye used in the present invention include the following, but the invention is not limited thereto.

2-methyl-6-p- (p-dimethylaminophenyl)
Aminoanilinofluorane, 2,3-dimethyl-6-p
-(P-Dimethylaminophenyl) aminoanilinofluorane, 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-chloro-3-
Methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane,
2,3-Dimethyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 3-methyl-6-p
-(P-Phenylaminophenyl) aminoanilinofluorane, 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane.

In the present invention, a black-coloring fluoran-based leuco dye may be used in combination for the purpose of complementing the visible color development in the visible region, and specific examples thereof are shown below.

3-Diethylamino-6-methyl-7-anilinofluorane 3- (N-ethyl-p-toluidino) -6-methyl-7
-Anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 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-Nn-dibutylamino-7- (o-chloroanilino) fluorane 3- (N-ethyl-N- Tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3- (N-methyl-N-propylamino)- 6-Methyl-7-anilinofluorane 3-diethylamino-6-chloro-7-anilinofluorane 3-dibutylamino-7- (o-chloroanilino) fluorane 3-diethylamino-7- (o-chloroanilino) fluorane As a sensitizer, fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamido ,
Montan wax, polyethylene wax, terephthalic dibenzyl, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, p-benzyl biphenyl, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy- It is also possible to add 2-naphthoic acid phenyl ester or the like.

By adding a halogen-substituted zinc benzoate derivative as a stabilizer, the effects of the present invention can be further improved, and the following can be exemplified.

In the present invention, in order to prevent the heat-sensitive color developing layer on the support from being peeled off by wetting with water or being damaged by physical impact, the heat-sensitive layer and the back of the support are covered with a transparent thin film such as polyester or polypropylene. It is also possible to laminate with a resin film.

The binder used in the present invention has a degree of polymerization of 200.
~ 1900 fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl 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, polyacrylamide, polyacrylic acid ester, polyvinyl butyral polystyrol and Examples thereof include copolymers, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins and coumarone resins. These polymeric substances are used by dissolving them in solvents such as water, alcohols, ketones, esters, hydrocarbons, etc., or in the state of being emulsified or pasty dispersed in water or other medium, depending on the required quality. It can also be used together.

The amount of organic developer and basic colorless dye used in the present invention,
The types and amounts of other various components are determined according to the required performance and recording suitability, and are not particularly limited, but usually, 1 part of the basic colorless dye to 1 to 8 parts of the organic developer, 1 to 20 parts of filler is used, and 10 to 25% by weight of the total solid content of the binder is suitable.

The desired thermosensitive recording medium can be obtained by applying a coating solution having the above composition to an arbitrary support such as paper, synthetic paper, film and plastic.

The above-mentioned organic developer, basic colorless dye and materials to be added as necessary are atomized to a particle size of several microns or less by a grinder such as a ball mill, attritor, or sand grinder or an appropriate emulsifying device, and a binder. Also, various kinds of additive materials are added according to the purpose to prepare a coating liquid.

In this coating liquid, a filler, a release agent for preventing sticking of fatty acid metal salts, a fatty acid amide, an ethylene bisamide, a montan wax, a lubricant for preventing pressure coloration of polyethylene wax, sodium dioctylsulfosuccinate, Sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, sodium salt,
Alginate and other dispersants, benzophenone-based and triazole-based UV absorbers, other defoamers, fluorescent brighteners,
A waterproofing agent and the like can be added.

As the filler used in the present invention, all inorganic organic fillers used in the field of ordinary paper processing can be used, and examples thereof include clay, talc, silica, magnesium carbonate, alumina, aluminum hydroxide, and hydroxide. Magnesium, barium sulfate, kaolin, titanium oxide, zinc oxide,
Examples of the fine particles include calcium carbonate, aluminum oxide, urea / formalin resin, polystyrene, and phenol resin.

(Function) The reason why the thermal recording paper of the present invention is excellent in optical readability in the near infrared region is explained as follows. A recorded image using a conventional recording material using an electron-donating color former such as a fluoran leuco dye does not absorb light in the near infrared region at all. However, when the specific fluoran-based leuco dye used in the present invention causes a heat-melting reaction with the specific electron-accepting substance (developing agent) used in the present invention to develop a color, a near infrared region (particularly 700 to 1500 nm) is used. Light in the near infrared region) is very efficiently absorbed.

Further, the recorded image of the thermal recording paper of the present invention has light resistance, weather resistance,
The extremely high stability in terms of 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 these basic colorless dyes and the color developer is an acid-base reaction based on electron donation / acceptance, whereby a metastable "charge transfer complex" is formed and a color image is obtained. .

However, the 2,4′-dihydroxydiphenyl sulfone and 3,4-dihydroxyphenyl-p-tolyl sulfone of the present invention are diphenyl sulfone compounds containing two phenolic hydroxyl groups in the molecule, and they are used as an organic color developer. When used, 2,4'-in the coloring process
The chemical bond between dihydroxydiphenyl sulfone or 3,4-dihydroxyphenyl-p-tolyl sulfone and a specific fluoran-based leuco dye, which is a basic colorless dye, has been known to be a known developer (bisphenol A, p-hydroxyl). Benzyl benzoate, 4-hydroxy-4'-isopropoxydiphenyl sulfone) and fluorane-based leuco dyes have a strong specific bond compared with the chemical bond strength,
Chemical bond that does not break even when exposed to environmental conditions affected by heat, humidity, etc. for a long time, the color image is stable, and the optical readability of the recorded image in the near infrared region does not deteriorate. it is conceivable that.

(Example) Hereinafter, the present invention will be described with reference to Examples.

In the description, parts indicate parts by weight.

[Examples (Test Nos. 1 to 4)] Liquid A (dye dispersion liquid) Solution B (Developer dispersion) Each liquid of the above composition was ground with an attritor to a particle size of 3 microns. Then, the dispersion liquids are mixed in the following proportions to prepare a coating liquid.

6.0 g / m ² of the above coating liquid on one side of 50 g / m ² base paper
^It was coated and dried so as to be ² , and this sheet was treated with a super calendar so that the smoothness was 200 to 600 seconds to prepare a thermal recording paper.

[Comparative Example (Test Nos. 5 to 8)] C liquid (dye dispersion liquid) Liquid D (Developer dispersion) Each liquid of the above composition was ground with an attritor to a particle size of 3 microns. Then, the dispersion liquids are mixed in the following proportions to prepare a coating liquid.

6.0 g / m ² of the above coating liquid on one side of 50 g / m ² base paper
^It was coated and dried so as to be ² , and this sheet was treated with a super calendar so that the smoothness was 200 to 600 seconds to prepare a thermal recording paper. Quality performance tests were conducted on all the thermal recording papers of Examples and Comparative Examples, and the results are shown in Tables 1 and 2.

Note (1) Static color density; 10g on hot plate heated to 150 ℃
Measured with a Macbeth densitometer (RD-914, amber filter used; the same applies hereafter) after pressing for 5 seconds at a pressure of / cm ² to develop color.

Note (2) Dynamic color density: Measured with Macbeth densitometer, image density recorded with applied voltage of 18.03V and pulse width of 3.2 milliseconds using KB-4800 manufactured by Tokyo Shibaura Denki.

Note (3) Infrared reflectance (%); Infrared reflectance of the image portion recorded by the method of Note (1) was measured with a spectrophotometer (wavelength 940 nm).

Note (4) The image density dynamically recorded by the method of Note (2) was taken as the untreated density, and the density after the color-developed portion was irradiated with light for 2 hours by the fade meter was taken as the processed density. The residual rate is calculated from the following formula.

The infrared reflectance is a measured value of the image portion after the light processing.

Note (5) Oil resistance: The image density dynamically recorded by the method of Note (2) is taken as the unprocessed density, and castor oil is dropped on the color-developed part to
After 0 seconds, it was lightly wiped off with a filter paper, and the density after standing for 24 hours at room temperature was taken as the density after treatment. The residual rate is calculated from the following formula.

The infrared reflectance is a measured value of the image portion after the oil treatment.

Note (6) Weather resistance: The thermosensitive recording paper sample dynamically recorded by the method of Note (2) is left under the condition of 25 ° C and 50% RH, and the density of the recorded part after one week is measured with a Macbeth densitometer. . The residual rate is calculated from the following formula.

The infrared reflectance of the processed image portion is measured by a spectrophotometer (wavelength 94
0 nm).

(Effects of the Invention) The effects of the present invention are as follows.

(1) Excellent optical readability in the near infrared region.

(2) It is excellent in stability such as light resistance, oil resistance, and weather resistance and, as a result, long-term storage stability.

(3) Due to the effect of (2) above, it can withstand use under severe conditions such as barcode labels.

Claims (2)

[Claims] 1. A thermosensitive recording material comprising a support and a thermosensitive coloring layer containing a colorless or light-colored basic colorless dye and an organic developer as main components, wherein the thermosensitive coloring layer is an organic developer. 2,4'-dihydroxydiphenyl sulfone or 3,4-dihydroxyphenyl-p-tolyl sulfone as the basic compound, and a fluoran leuco dye represented by the following general formula (I) as the basic colorless dye. Heat sensitive recording material [In the formula, R ₁ represents a hydrogen atom or an alkyl group, and R ₂ represents a halogen atom or an alkyl group. T ₁ and T ₂ represent a hydrogen atom, an alkyl group or a phenyl group, but T ₁ and T ₂ do not become phenyl groups at the same time. ] 2. A fluorane-based leuco dye represented by the general formula (I) is 2-chloro-3-methyl-6-p- (p-
The heat-sensitive recording material according to claim 1, which is phenylaminophenyl) aminoanilinofluorane or 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane.