JPH09248964A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium with stable color development density and a high gradation thermal recording medium having stable color development density and low base density by reducing a residual solvent in the medium below an allowable amount within a time causing no problem in production. SOLUTION: In a thermal recording medium in which a recording layer is formed by applying recording layer application liquid comprising at least leuco dye, a developer for heat-coupling the leuco dye, a binder resin as a binding agent, and an organic solvent on a support and drying the liquid, the content of the organic solvent in the dried thermal recording layer is made 500mg/m<2> or less.

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 medium utilizing a color-developing reaction between an electron-donating color-forming compound and an electron-accepting compound, and particularly to a film for a video printer and an image formation for CAD. The present invention relates to a heat-sensitive recording medium useful as an image forming sheet for a projector and an image forming sheet for an overhead projector.

[0002]

2. Description of the Related Art Heat and pressure between a colorless or light-colored electron-donating color-forming compound (hereinafter also referred to as a leuco dye) and an electron-accepting compound (hereinafter also referred to as a color developer) which forms color upon contact. Various recording materials utilizing a color development reaction according to US Pat.

Some of the heat-sensitive recording materials among them do not require frequent processing such as development and fixing, can be recorded in a short time with a relatively simple device, generate little noise, and are cost-effective. It is useful as various recording materials for electronic computers, facsimiles, ticket vending machines, label printers, recorders and the like because of its advantages such as low price.

On the other hand, in recent years, the thermal head has become higher in density, and a resolution of about 600 DPI has been obtained. Therefore, in the fields of medical care, printing, etc., there is an increasing demand for a thermal recording medium capable of high-speed recording and capable of digital image processing with high resolution and high gradation.

Examples of conventional color-forming dyes used in heat-sensitive recording materials include colorless or light-colored leuco dyes having a lactone, lactam or spiropyran ring, and conventional color developers include organic acids and phenolic substances. It is used. Most of the production methods are those in which a developer and a dye are dispersed or dissolved in water or an organic solvent together with a binder resin for production.

The advantage of forming a recording layer using an organic solvent is that the dye is dissolved, so that transparency can be imparted to the recording layer. If the recording layer is formed on a transparent support, It is possible to provide a transparent thermosensitive recording medium.

When a heat-sensitive recording layer is formed using an organic solvent, it is formed by dissolving a suitable resin in an organic solvent, adding a leuco dye and a color developer, dispersing or dissolving the coating liquid, and drying the coating liquid. It Ideally, all the solvent is removed by evaporation at the time of drying, but usually, considering the solvent composition of the coating liquid, coating suitability, productivity, etc., it is not industrially possible to completely remove the solvent. However, it is inevitable that a certain amount of solvent remains in the heat-sensitive recording layer. It is more preferable that the amount of such residual solvent is small, of course, but the problem is how much is allowed.

That is, if the residual solvent is present in excess of the permissible amount, the amount present affects the gamma characteristics, making it difficult to obtain a stable color density. That is, there is a problem in recording of high gradation.

Of course, the above-mentioned problems can be solved by making the drying conditions after coating the coating solution severe, but such a solution causes a background fog due to the drying or takes a considerably long time for the drying. However, there is a problem that it is not realistic industrially.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording medium in which the amount of residual solvent in the heat-sensitive recording medium is kept below the permissible amount within a time that does not cause a problem in production and stable color density is obtained. To provide. That is, it is to provide a thermosensitive recording medium that can obtain stable color density and low background density in order to obtain high gradation.

[0011]

DISCLOSURE OF THE INVENTION As a result of intensive studies on the problems in the above-mentioned thermal recording medium, we have found that at least a leuco dye, a developer that heat-colors the leuco dye, and a binder as a binder. In a heat-sensitive recording medium in which a recording layer coating liquid comprising a resin and an organic solvent is applied and dried on a support to form a recording layer, the amount of residual solvent in the heat-sensitive recording layer is 500 mg / m ² or less. The present invention was found to be effective against the problems, and further studies were conducted to complete the present invention. Further, it has been found that the eutectic starting temperature of the leuco dye and the developer that causes the leuco dye to develop color by heating is 95 ° C. or more, which is particularly effective in eliminating background fog. Eutectic start temperature is 9
When the temperature is 5 ° C. or higher, the recording start temperature can be increased and wasteful color development of the background can be controlled. Also,
By using such a material, the drying temperature in the coating and drying step can be maintained higher, and the amount of residual solvent can be effectively reduced. Further, when forming the protective layer on the recording layer, it has been found to be particularly effective to form the protective layer using a resin liquid which is insoluble in the binder resin of the recording layer. Furthermore, it has been found that it is particularly effective to form a protective layer made of an ultraviolet curable resin as the protective layer on the recording layer. It is particularly preferable that the solid content concentration of the ultraviolet curable resin liquid when forming the protective layer made of the ultraviolet curable resin is 30% or more.

The amount of residual solvent in the recording layer in the present invention is preferably 500 mg / m ² or less. When the amount of the residual solvent exceeds 500 mg / m ² , there is a problem that the color development sensitivity becomes fast and the sensitivity changes after long-term storage.

Therefore, the amount of residual solvent in the recording layer should be 500
It is indispensable to suppress the amount to be less than mg / m ² in order to provide a recording medium with stable color development sensitivity. Therefore, it may be prepared so as to satisfy this condition by the drying temperature, the drying time, the kind of the solvent used for preparing the coating liquid, etc. at the time of forming the recording layer.

The cause of the influence of the residual solvent on the color development sensitivity is that the solvent dissolves the dye, thereby lowering the eutectic starting temperature by lowering the melting point and heating the dye held in the resin network structure. It is considered that the main cause is that the residual solvent occupies the network structure of the resin when it is released from the network structure of the resin, roughens the network structure of the resin, and facilitates release of the dye. However, we do not intend to limit the invention by such theory.

Since the support of the present invention is a support insoluble in the organic solvent, the support hardly contains the organic solvent. Therefore, the content of the organic solvent necessarily represents the content of the organic solvent in the recording layer.

In the present invention, the residual solvent amount in the recording layer is a value including the amount of the support film, which is measured and converted into a value in the recording layer based on the amount of adhesion of the recording layer. The attached amount can be measured using a pyrolysis gas chromatograph (Gas Chromatograph GC17A manufactured by Shimadzu Corporation).

The thermal recording medium of the present invention will be described in detail below. The support used in the present invention is preferably insoluble in the organic solvent. Specific examples thereof include polyester films such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate, polypropylene, polyolefin films such as polyethylene, polystyrene films or films obtained by laminating these, synthetic papers and the like. .

The leuco dye used in the present invention is a compound exhibiting an electron donating property, and is applied alone or as a mixture of two or more kinds, but it is a colorless or light-colored dye precursor per se and is not particularly limited and is conventionally used. Known compounds, for example, triphenylmethanephthalide-based, triallylmethane-based, fluorane-based, phenothidian-based, thioferolane-based, xanthene-based, indophthalyl-based, spiropyran-based, azaphthalide-based, chromenopyrazole-based, methine-based, rhodamine Leuco compounds such as anilinolactam type, rhodamine lactam type, quinazoline type, diazaxanthene type and bislactone type are preferably used. Examples of such compounds include those shown below.

2-anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6
(Di-n-butylamino) fluorane, 2-anilino-
3-methyl-6- (Nn-propyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (N
-Isopropyl-N-methylamino) fluoran, 2-
Anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluoran, 2-anilino-3-methyl-
6- (Nn-amyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (N-sec-butyl-N-ethylamino) fluoran, 2-anilino-
3-methyl-6- (Nn-amyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (N
-Isoamyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluoran, 2-anilino-3-methyl-6- (N-cyclohexyl-N -Methylamino)
Fluoran,

2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-anilino-3
-Methyl-6- (N-methyl-p-toluidino) fluoran, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3- Methyl-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran, 2- (2,4-dimethylanilino)- 3-methyl-6-diethylaminofluoran,
2- (N-ethyl-p-toluidino) -3-methyl-6
-(N-ethylanilino) fluoran, 2- (N-methyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluoran, 2-anilino-6
(Nn-hexyl-N-ethylamino) fluoran,
2- (o-chloroanilino) -6-diethylaminofluoran, 2- (o-bromoanilino) -6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran,

2- (o-Fluoroanilino) -6-dibutylaminofluorane, 2- (m-trifluoromethylanilino) -6-diethylaminofluorane, 2- (p-acetylanilino) -6- (N- n-amyl-N-n-
Butylamino) fluoran, 2-benzylamino-6-
(N-ethyl-p-toluidino) fluoran, 2-benzylamino-6- (N-methyl-2,4-dimethylanilino) fluoran, 2-benzylamino-6- (N-ethyl-2,4-dimethylani Rino) fluorane, 2-dibenzylamino-6- (N-methyl-p-toluidino)
Fluoran, 2-dibenzylamino-6- (N-ethyl-p-toluidino) fluoran, 2- (di-p-methylbenzylamino) -6- (N-ethyl-p-toluidino) fluoran, 2- (α-phenyl) Ethylamino)-
6- (N-ethyl-p-toluidino) fluoran, 2-
Methylamino-6- (N-methylanilino) fluoran, 2-methylamino-6- (N-ethylanilino) fluoran, 2-methylamino-6- (N-propylanilino) fluoran, 2-ethylamino-6- ( N-methyl-p-toluidino) fluoran, 2-methylamino-
6- (N-methyl-2,4-dimethylanilino) fluoran,

2-ethylamino-6- (N-methyl-
2,4-dimethylanilino) fluoran, 2-dimethylamino-6- (N-methylanilino) fluoran, 2-
Dimethylamino-6- (N-ethylanilino) fluoran, 2-diethylamino-6- (N-methyl-p-toluidino) fluoran, 2-diethylamino-6- (N-
Ethyl-p-toluidino) fluoran, 2-dipropylamino-6- (N-methylanilino) fluoran, 2-
Dipropylamino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-methylanilino) fluoran, 2-amino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-propylaniline (Lino) fluorane, 2-amino-6- (N-methyl-p-toluidino) fluoran, 2-amino-6- (N-ethyl-p-toluidino) fluoran, 2-amino-6- (N-propyl-p-toluidino) Fluoran, 2-amino-6
(N-methyl-p-ethylanilino) fluorane, 2-
Amino-6- (N-ethyl-p-ethylanilino) fluoran, 2-amino-6- (N-propyl-p-ethylanilino) fluoran, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluoran 2-amino-6- (N-ethyl-2,4-dimethylanilino) fluoran, 2-amino-6- (N-propyl-2,4-dimethylanilino) fluoran,

2-amino-6- (N-methyl-p-chloranilino) fluorane, 2-amino-6- (N-ethyl-p-chloranilino) fluorane, 2-amino-6
-(N-propyl-p-chloroanilino) fluoran,
2,3-dimethyl-6-dimethylaminofluoran 3-methyl-6- (N-ethyl-p-toluidino) fluoran, 2-chloro-6-diethylaminofluoran,
2-bromo-6-diethylaminofluoran, 2-chloro-6-dipropylaminofluoran, 3-chloro-6
-Cyclohexylaminofluoran, 3-bromo-6-
Cyclohexylaminofluoran, 2-chloro-6
(N-ethyl-N-isoamylamino) fluoran, 2
-Chloro-3-methyl-6-diethylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, 2- (o-chloroanilino) -3-chloro-
6-cyclohexylaminofluoran, 2- (m-trifluoromethylanilino) -3-chloro-6-diethylaminofluoran, 2- (2,3-dichloroanilino)-
3-chloro-6-diethylaminofluoran, 1,2-
Benzo-6-diethylaminofluoran, 1,2-benzo-6- (N-ethyl-N-isoamylamino) fluoran, 1,2-benzo-6-dibutylaminofluoran, 1,2-benzo-6- ( N-ethyl-N-cyclohexylamino) fluoran, 1,2-benzo-6- (N
-Ethyl-toluidino) fluoran and others.

Specific examples of other color formers preferably used in the present invention are as follows. 2-anilino-3-methyl-6- (N-2-ethoxypropyl-N
-Ethylamino) fluorane, 2- (p-chloroanilino) -6- (Nn-octylamino) fluorane, 2
-(P-Chloranilino) -6- (N-n-partimylamino) fluorane, 2- (p-chloranilino) -6
-(Di-n-octylamino) fluorane, 2-benzoylamino-6- (N-ethyl-ptoluidino) fluorane, 2- (o-methoxybenzoylamino) -6-
(N-ethyl-p-toluidino) fluorane, 2-dibenzylamino-4-methyl-6-diethylaminofluorane, 2-dibenzylamino-4-methoxy-6- (N
-Methyl-p-toluidino) fluorane, 2-dibenzylamino-4-methyl-6- (N-ethyl-p-toluidino) fluorane, 2- (α-phenylethylamino)
-4-Methyl-6-diethylaminofluorane, 2-
(P-toluidino) -3- (t-butyl) -6- (N-
Methyl-p-toluidino) fluorane,

2- (o-methoxycarbonylanilino)
-6-diethylaminofluoran, 2-acetylamino-6- (N-methyl-p-toluidino) fluoran, 3
-Diethylamino-6- (m-trifluoromethylanilino) fluoran, 4-methoxy-6- (N-ethyl-
p-toluidino) fluoran, 2-ethoxyethylamino-3-chloro-6-dibutylaminofluoran, 2-
Dibenzylamino-4-chloro-6- (N-ethyl-p
Toluidino) fluorane, 2- (α-phenylethylamino) -4-chloro-6-diethylaminofluorane, 2- (N-benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluorane, Two
-Anilino-3-methyl-6-pyrrolidinofluorane,
2-anilino-3-chloro-6-pyrrolidinofluoran, 2-anilino-3-methyl-6- (N-ethyl-N
-Tetrahydrofurfurylamino) fluoran, 2-mesitidino-4 ', 5'-benzo-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3
-Methyl-6-pyrrolidinofluoran, 2- (α-naphthylamino) -3,4-benzo-4′-bromo-6-
(N-benzyl-N-cyclohexylamino) fluorane, 2-piperidino-6-diethylaminofluorane,

2- (N-n-propyl-p-trifluoromethylanilino) -6-morpholinofluorane, 2-
(Di-N-p-chlorophenyl-methylamino) -6
Pyrrolidinofluoran, 2- (Nn-propyl-m-trifluoromethylanilino) -6-morpholinofluoran, 1,2-benzo-6- (N-ethyl-Nn-octylamino) Fluoran, 1,2-benzo-6-diallylaminofluoran, 1,2-benzo-6- (N-ethoxyethyl-N-ethylamino) fluoran, benzolecomethylene blue 2- {3,6-bis (diethylamino) ｝ -6- (o-chloroanilino) xanthyl benzoate lactam, 2-
{3,6-bis (diethylamino)}-9- (o-chloroanilino) xanthylbenzoic acid lactam, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl)-
6-diethylaminophthalide,

3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3- (2-methoxy-4)
-Dimethylaminophenyl) -3- (2-hydroxy-
4,5-dichlorophenyl) phthalide, 3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide, 3- (2-hydroxy-4-dimethoxyaminophenyl ) -3- (2
-Methoxy-5-chlorophenyl) phthalide, 3- (2
-Hydroxy-4-dimethylaminophenyl) -3-
(2-Methoxy-5-nitrophenyl) phthalide, 3-
(2-hydroxy-4-diethylaminophenyl) -3
-(2-methoxy-5-methylphenyl) phthalide,
3,6-bis (dimethylamino) fluorene spiro (9,3 ′)-6′-dimethylaminophthalide, 6′-
Chloro-8'-methoxy-benzoindolino-spiropyran, 6'-bromo-2'-methoxy-benzoindolino-spiropyran and the like.

Next, the color developing agent used in the present invention is an electron-accepting compound, and various conventionally known electron-accepting color developing agents can be used, but the more preferable one in the present invention is It is an electron-accepting color developer containing a long-chain alkyl group in the molecule, which is disclosed in, for example, Kaihei 5-124360.
For example, an organic phosphoric acid compound, an aliphatic carboxylic acid compound or a phenol compound having an aliphatic group having 12 or more carbon atoms, a metal salt of mercaptoacetic acid having an aliphatic group having 10 to 18 carbon atoms, or a metal salt of 5 to 8 carbon atoms And alkyl phosphates of caffeic acid having an alkyl group, and acidic phosphate esters having an aliphatic group having 16 or more carbon atoms. Aliphatic groups include linear or branched alkyl and alkenyl groups,
It may have a substituent such as a halogen, an alkoxy group or an ester. Hereinafter, specific examples of the developer will be described. (A) Organophosphate Compound In the present invention, an organic phosphate compound represented by the following general formula (1) is preferably used.

[0029]

Embedded image (R ₁ represents a straight-chain alkyl group having 12 or more carbon atoms) Specific examples of the organic phosphoric acid compound represented by the general formula (1) include the following. Dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid, hexacosylphosphonic acid, octacosylphosphonic acid and the like. As the organic phosphoric acid compound, α-hydroxyalkylphosphonic acid represented by the following general formula (2) is also preferably used.

[0030]

Embedded image (However, R ₂ is an aliphatic group having 11 to 29 carbon atoms.) Specific examples of the α-hydroxyalkylphosphonic acid represented by the general formula (2) include α-hydroxydodecylphosphonic acid and α-hydroxytetracarboxylic acid. Examples thereof include decylphosphonic acid, α-hydroxyhexadecylphosphonic acid, α-hydroxyoctadecylphosphonic acid, α-hydroxyeicosylphosphonic acid, α-hydroxydocosylphosphonic acid, and α-hydroxytetracosylphosphonic acid. Also,
As the organic phosphoric acid compound, an acidic organic phosphoric acid ester represented by the following general formula (3) is also preferably used.

[0031]

Embedded image (In the formula, R ₃ represents an aliphatic group having 16 or more carbon atoms, and R ₄ represents a hydrogen atom or an aliphatic group having 1 or more carbon atoms.) An acidic organic phosphoric acid ester represented by the general formula (3) Specifically, dihexadecyl phosphate, dioctadecyl phosphate, dieicosyl phosphate, didocosyl phosphate, monohexadecyl phosphate,
Monooctadecyl phosphate, monoeicosyl phosphate, monodocosyl phosphate, methyl hexadecyl phosphate, methyl octadecyl phosphate, methyl eicosyl phosphate, methyl docosyl phosphate, amyl hexadecyl phosphate, octyl hexadecyl phosphate, lauryl hexadecyl phosphate, etc. Can be

(B) Aliphatic carboxylic acid compound In the present invention, as the aliphatic carboxylic acid compound, α-hydroxy fatty acids represented by the following general formula (4) are preferably used.

[0033]

Embedded image (However, R ₅ represents an aliphatic group having 12 or more carbon atoms.) Examples of the α-hydroxy aliphatic carboxylic acid compound represented by the general formula (4) include the following.
α-hydroxydecanoic acid, α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, α
-Hydroxytetracosanoic acid, α-hydroxyhexacosanoic acid, α-hydroxyoctacosanoic acid, etc.

As the aliphatic carboxylic acid compound,
An aliphatic carboxylic acid compound having an aliphatic group having 12 or more carbon atoms and substituted with a halogen element, and having at least the carbon atom at the α-position or the β-position with the halogen element is also preferably used. Specific examples of such a compound include the followings. 2-bromohexadecanoic acid, 2-bromoheptadecanoic acid, 2-bromooctadecanoic acid, 2-bromoeicosanoic acid, 2-bromodocosanoic acid, 2-bromotetracosanoic acid, 3-bromooctadecanoic acid, 3-bromoeicosanoic acid 2,2-dibromooctadecanoic acid, 2-fluorododecanoic acid, 2-fluorotetradecanoic acid, 2-fluorohexadecanoic acid, 2-fluorooctadecanoic acid, 2-fluoroeicosanoic acid, 2-
Fluorodocosanoic acid, 2-iodohexadecanoic acid, 2-
Iodooctadecanoic acid, 3-iodohexadecanoic acid, 3
-Iodooctadecanoic acid, perfluorooctadecanoic acid and the like.

The aliphatic carboxylic acid is an aliphatic carboxylic acid compound having an aliphatic group having a carbon number of 12 or more and having an oxo group in carbon, and at least the carbon at the α-position, β-position or γ-position is oxo. The base material is also preferably used. Specific examples of such compounds include, for example, the following. 2-oxododecanoic acid, 2-oxotetradecanoic acid, 2-oxohexadecanoic acid, 2-oxooctadecanoic acid, 2-oxoeicosanoic acid, 2-oxotetracosanoic acid, 3-oxododecanoic acid, 3-oxotetradecanoic acid, 3-oxohexadecanoic acid, 3-oxooctadecanoic acid, 3-oxoeicosanoic acid, 3-oxotetracosanoic acid, 4-oxohexadecanoic acid, 4-oxooctadecanoic acid, 4-oxodokosanoic acid and the like. Further, as the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (5) is also preferably used.

[0036]

Embedded image (However, R ₆ represents an aliphatic group having 12 or more carbon atoms,
X represents an oxygen atom or a sulfur atom, and n represents 1 or 2. Specific examples of the dibasic acid represented by the general formula (5) include:
For example, the following are mentioned. Dodecyl malate, tetradecyl malate, hexadecyl malate, octadecyl malate, eicosyl malate, docosyl malate, tetracosyl malate, dodecyl thiomalate, tetradecyl thiomalate, hexadecyl thiomalate,
Octadecylthiomalic acid, eicosylthiomalic acid,
Docosylthiomalic acid, tetracosylthiomalic acid, dodecyldithiomalic acid, tetradecyldithiomalic acid,
Eicosyldithiomalic acid, docosyldithiomalic acid,
Tetracosyldithiomalic acid, etc. Furthermore, as the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (6) is also preferably used.

[0037]

[Chemical 6] (However, R ₇ , R ₈ , and R ₉ represent hydrogen or an aliphatic group, at least one of which is an aliphatic group having 12 or more carbon atoms.) Specific examples of the dibasic acid represented by the general formula (6) For example,
For example, the following are mentioned. Dodecyl butane diacid,
Tridecyl butane diacid, tetradecyl butane diacid, pentadecyl butane diacid, octadecyl butane diacid, eicosyl butane diacid, docosyl butane diacid, 2,3-dihexadecyl butane diacid, 2,3-dioctadecyl Butanedioic acid, 2-methyl-3-dodecylbutanedioic acid, 2-methyl-3-tetradecylbutanedioic acid, 2-methyl-3-hexadecylbutanedioic acid, 2-ethyl-3-dodecylbutanedioic acid, 2-propyl-3-dodecyl butane diacid, 2-octyl-3-hexadecyl butane diacid, 2-tetradecyl-3-octadecyl butane diacid, and the like. Further, as the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (7) is also preferably used.

[0038]

Embedded image (However, R ₁₀ and R ₁₁ represent hydrogen or an aliphatic group, at least one of which is an aliphatic group having 12 or more carbon atoms.) Specific examples of the dibasic acid represented by the general formula (7) include ,
For example, the following may be mentioned. Dodecylmalonic acid, tetradecylmalonic acid, hexadecylmalonic acid, octadecylmalonic acid, eicosylmalonic acid, docosylmalonic acid, tetracosylmalonic acid, didodecylmalonic acid,
Ditetradecylmalonic acid, dihexadecylmalonic acid, dioctadecylmalonic acid, dieicosylmalonic acid, didocosylmalonic acid, methyloctadecylmalonic acid, methyldocosylmalonic acid, methyltetracosylmalonic acid, ethyl octadecylmalonic acid, ethyl Eicosylmalonic acid, ethyldocosylmalonic acid, ethyltetracosylmalonic acid and the like. Furthermore, as the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (8) is also preferably used.

[0039]

Embedded image (However, R ₁₂ represents hydrogen or an aliphatic group, n represents 0 or 1, m represents 1, 2 or 3, and when n is 0, m is 2 or 3 and n is 1 If m is 1 or 2
Specific examples of the dibasic acid represented by the general formula (8) include:
For example, the following may be mentioned. 2-dodecyl-
Pentanedioic acid, 2-hexadecyl-pentanedioic acid, 2-
Octadecyl pentanedioic acid, 2-eicosyl-pentanedioic acid, 2-docosyl-pentanedioic acid, 2-dodecyl-hexanedioic acid, 2-pentadecyl-hexanedioic acid, 2-octadecyl-hexanedioic acid, 2-eicosyl-hexane. Diacid, 2-docosyl-hexanedioic acid and the like. Further, as the aliphatic carboxylic acid compound, a tribasic acid such as citric acid acylated by a long-chain fatty acid is preferably used. Specific examples include the following. O-palmityl citric acid

[0040]

Embedded image O-stearyl citric acid

[0041]

Embedded image O-eicosilicenoic acid

[0042]

Embedded image (C) Phenol compound In the present invention, a compound represented by the following general formula (9) is preferably used as the phenol compound.

[0043]

Embedded image (Where Y is -S-, -O-, -CONH- or -C
OO—, R ₁₃ represents an aliphatic group having 12 or more carbon atoms, and n is an integer of 1, 2, or 3.) Specific examples of the phenol compound represented by the general formula (9) include the following. Such a thing is mentioned. p- (dodecylthio) phenol, p- (tetradecylthio) phenol, p- (hexadecylthio) phenol, p- (octadecylthio) phenol, p- (eicosylthio) phenol, p- (docosylthio) phenol, p- (tetracosyl) Ruthio) phenol, p- (dodecyloxy) phenol, p- (tetradecyloxy) phenol, p- (hexadecyloxy) phenol, p- (octadecyloxy) phenol, p- (eicosyloxy) phenol, p- ( Docosyloxy)
Phenol, p- (tetracosyloxy) phenol,
p-dodecylcarbamoylphenol, p-tetradecylcarbamoylphenol, p-hexadecylcarbamoylphenol, p-octadecylcarbamoylphenol, p-eicosylcarbamoylphenol, p-docosylcarbamoylphenol, p-tetracosylcarbamoylphenol, hexa gallic acid Decyl ester,
Octadecyl gallate, eicosyl gallate, docosyl gallate, tetracosyl gallate and the like. As the phenol compound, caffeic acid alkyl esters represented by the following general formula (10) can also be used.

[0044]

Embedded image (Where R ₁₄ is an alkyl group having 5 to 8 carbon atoms) Specific examples of the caffeic acid alkyl ester represented by the general formula (10) include caffeic acid-n-bentyl, caffeic acid-n-hexyl, and caffeic acid. Acid-n-octyl and the like. (D) Metal salt of mercaptoacetic acid In the present invention, as the metal salt of mercaptoacetic acid, a metal salt of an alkyl or alkenyl mercaptoacetic acid represented by the general formula (11) can be preferably used.

[0045]

Embedded image (However, R ₁₅ represents an aliphatic group having 10 to 18 carbon atoms, and M represents tin, magnesium, zinc or copper.) Specific examples of the metal mercaptoacetate represented by the general formula (11) include the following. And the like.
Decylmercaptoacetic acid tin salt, dodecylmercaptoacetic acid tin salt, tetradecylmercaptoacetic acid tin salt, hexadecylmercaptoacetic acid tin salt, octadecylmercaptoacetic acid tin salt, decylmercaptoacetic acid megnesium salt, dodecylmercaptoacetic acid magnesium salt, tetradecylmercaptoacetic acid magnesium salt , Hexadecylmercaptoacetic acid magnesium salt, octadecylmercaptoacetic acid magnesium salt, decylmercaptoacetic acid zinc salt, dodecylmercaptoacetic acid zinc salt, tetradecylmercaptoacetic acid zinc salt, hexadecylmercaptoacetic acid zinc salt, octadecylmercaptoacetic acid zinc salt, decylmercaptoacetic acid copper salt Salt, dodecyl mercapto acetic acid copper salt, tetradecyl mercapto acetic acid copper salt, hexadecyl mercapto acetic acid copper salt, octadecyl mercapto acetic acid copper salt Etc..

Further, in the present invention, the color developer is not limited to the above compounds, and various other compounds having an electron accepting property can be used. In the heat-sensitive recording medium of the present invention, the developer is used in an amount of 1 to 20 per part of the color former.
Parts, preferably 2 to 10 parts, are used. The color developer can be used alone or in combination of two or more kinds, and also in the case of the color developer, it can be applied alone or in combination of two or more kinds.

In the present invention, the combination of the leuco dye and the color developer is particularly preferably one in which the eutectic starting temperature of the leuco dye and the color developer is 95 ° C. or higher. When the eutectic initiation temperature is high, when the drying temperature is high and the amount of residual solvent is the same, the fog on the background is small. The eutectic onset temperature can be examined by measuring the color development temperature at which the leuco dye and the color developer are mixed and heated and melted by differential scanning calorimetry (DSC) or differential thermal analysis (DTA).

Specific examples of the combination of the leuco dye and the color developer include octadecylphosphonic acid and 2- (o-chloroanilino) -6-dibutylaminofluorane (eutectic starting temperature, 96.0 ° C.), octadecylphosphone. Acid and 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane (eutectic onset temperature, 9
6.0 ° C), octadecylphosphonic acid and 2-anilino-
3-methyl-6- (N-ethyl-N-ptoluidino)
Fluoran (eutectic starting temperature, 96.2 ° C.) and the like can be mentioned. Of course, the present invention is not limited to these combinations.

Next, various known resins can be used as the binder resin in the thermosensitive coloring layer used in the present invention.
For example, polyacrylamide, maleic acid copolymer, polyacrylate, polymethacrylate,
Vinyl chloride / vinyl acetate copolymer, styrene copolymer,
Polyester, polyurethane, polyvinyl butyral,
Ethyl cellulose, polyvinyl acetal, polyvinyl acetoacetal, polycarbonate, epoxy resin,
Polyamide etc. can be mentioned.

The specific examples of the leuco dye, the color developer and the binder resin which are the main components in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention have been described above, but these are merely examples and the present invention is not limited thereto. It is not something that can be done. Further, known fillers, pigments, surfactants, and heat-fusible substances can be added, if necessary.

The heat-sensitive recording layer of the present invention is prepared by uniformly dispersing or dissolving a color former and a developer together with a binder resin in an organic solvent, coating this on a support, and drying it. Not limited. When a dispersion liquid in which a color developer is dispersed is used as a recording layer coating liquid, the particle size of the color developer has a large influence on the surface roughness of the protective layer and, in the case, dot reproducibility during printing, the particle size is 0. It is preferably 0.5 μm or less.
The film thickness of the recording layer is about 1 to 50 μm, preferably about 3 to 20 μm, depending on the composition of the recording layer and the use of the thermal recording medium. Various additives such as conventionally known surfactants can be added to the coating solution for the recording layer, if necessary, for the purpose of improving coatability or recording characteristics.

In the present invention, a layer containing a pigment, a binder, a heat-fusible substance or the like as an intermediate layer is optionally provided between the support and the thermosensitive coloring layer to improve smoothness. Can be provided.

In the present invention, a protective layer is provided on the thermosensitive color developing layer in order to improve chemical resistance, water resistance, abrasion resistance, light resistance and head matching with a thermal head.

For the protective layer used in the present invention, a conventionally known water-soluble resin, hydrophobic resin, ultraviolet curable resin or electron beam curable resin can be used.

The residual solvent in the recording layer is also generated when the solvent at the time of forming the protective layer penetrates into the recording layer, so that the protective layer is formed by using a resin liquid which is insoluble in the binder resin of the recording layer. Is particularly preferable to obtain a stable color density. It is also particularly preferable to form the protective layer using an ultraviolet curable resin in order to obtain a stable color density. The coating method of the protective layer is not particularly limited, and can be applied by a conventionally known method. The preferred protective layer thickness is 0.1 to 2
It is 0 μm, more preferably 0.5 to 10 μm. If the thickness of the protective layer is too thin, the function of the recording medium as a protective layer such as storability and head matching is insufficient, and if it is too thick, the thermal sensitivity of the recording medium decreases, which is also disadvantageous in terms of cost.

In the present invention, it is particularly desirable to form the protective layer using an ultraviolet curable resin. The type of the ultraviolet curable resin is not limited, and various conventionally known resins can be used. As a solvent for this resin, an organic solvent such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, isopropyl alcohol, ethyl acetate, butyl acetate, toluene or benzene is preferably used. Further, instead of these solvents, a liquid photopolymerizable monomer can be used as a reactive diluent for easy handling. Liquid photopolymerizable monomers include 2-ethylhexyl acrylate, cyclohexyl acrylate, butoxyethyl acrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol. Examples thereof include triacrylate and ethyl methacrylate.

The UV-curable resin used for forming the protective layer is a monomer or oligomer (or prepolymer) which undergoes a polymerization reaction upon irradiation with UV rays and is cured to become a resin.
If so, all can be used. Such monomers or oligomers include (poly) ester acrylate, (poly) urethane acrylate, epoxy acrylate, polybutadiene acrylate, silicone acrylate,
Examples include melamine acrylate and polyphosphazene methacrylate. (Poly) ester acrylate is 1,6-
A polyhydric alcohol such as hexanediol, propylene glycol (as polypropylene oxide), or diethylene glycol is reacted with a polybasic acid such as adipic acid, phthalic anhydride, or trimellitic acid, and acrylic acid. Examples of the structure are shown in (a) to (c).

(A) Adipic acid / 1,6-hexanediol / acrylic acid

[0059]

Embedded image (B) Phthalic anhydride / Propylene oxide / Acrylic acid

[0060]

Embedded image (C) trimet acid / diethylene glycol / acrylic acid

[0061]

Embedded image

The (poly) urethane acrylate is obtained by reacting a compound having an isocyanate group such as tolylene diisocyanate (TDI) with an acrylate having a hydroxyl group. An example of the structure is shown in FIG.
HEA is 2-hydroxyethyl acrylate, H
DO is an abbreviation for 1,6-hexanediol, and ADA is an abbreviation for adipic acid. (D) HEA / TDI / HDO / ADA / HDO / TD
I / HEA

[0063]

Embedded image

Epoxy acrylates are roughly classified into bisphenol A type, novolac type and alicyclic type, and the epoxy group of these epoxy resins is esterified with acrylic acid to make the functional group an acryloyl group.
Examples of the structure are shown in (e) to (g). (E) Bisphenol A-epichlorohydrin type / acrylic acid

[0065]

Embedded image (F) phenol novolak-epichlorohydrin type /
Acrylic acid

[0066]

Embedded image (G) Alicyclic type / acrylic acid

[0067]

[Chemical 21]

Polybutadiene acrylate has a terminal OH
Isocyanate or 1,2 polybutadiene
-Mercaptoethanol or the like is reacted, and then acrylic acid or the like is further reacted. Its structural example (h)
Shown in (H)

[0069]

Embedded image The silicone acrylate is, for example, methacryl-modified by a condensation reaction (de-methanol reaction) between an organofunctional trimethoxysilane and a silanol group-containing polysiloxane, and a structural example thereof is shown in (i). (I)

[0070]

Embedded image

When an ultraviolet curable resin is used for the protective layer, the solid concentration of the ultraviolet curable resin liquid is particularly preferably 30% or more for the purpose of preventing the solvent from penetrating into the recording layer during coating.

[0072]

The present invention will be described below in detail with reference to examples. In the following, all parts and percentages are based on weight.

Example 1 The following composition was pulverized and dispersed by a ball mill to a particle size of 0.3 μm to prepare a developer dispersion. [Liquid A] Octadecylphosphonic acid 6 parts 10% Polyvinyl butyral resin solution (solvent: methyl ethyl ketone) 10 parts (Denka Butyral # 3000-2 manufactured by Denki Kagaku Kogyo Co., Ltd.) Toluene 17 parts Methyl ethyl ketone 7 parts

Next, [B liquid] prepared with the following composition was sufficiently stirred to prepare a recording layer coating liquid. [Liquid B] Developer dispersion [Liquid A] 20 parts 2-anilino-3-methyl-6-diethylaminofluorane 1 part 10% polyvinyl butyral resin solution (solvent: methyl ethyl ketone) 10 parts (Sekisui Chemical Co., Ltd.) , S-REC BX-1)

A thickness of 7 after coating prepared as described above is obtained.
A 5 μm polyester film was coated with a wire bar and dried at 60 ° C. for 2 minutes to form a 10 μm thick thermosensitive recording layer. When the amount of residual solvent in the recording layer of this sample immediately after coating the recording layer was measured, it was 860 mg / m 2.
^{Was 2} .

Next, this sample was aged for 4 hours, 24 hours, and 360 hours in a 40 ° C. dry thermostat to measure the amount of residual solvent in the recording layer. The results are shown in Table 1. These samples after aging were printed with a thermal head (printing energy: 10.7 mj / mm ² ) and the transmission density of the printed portion was measured by X-Rite 309TR (XR
It was measured with a transmission densitometer (manufactured by ITE COMPANY). The results are shown in Table 1.

Example 2 A coating solution was prepared in the same manner as in Example 1, coated on a 75 μm-thick polyester film with a wire bar, and then dried at 75 ° C. for 3 minutes to obtain a heat-sensitive coating having a thickness of 10 μm. A recording layer was formed. Immediately after coating the recording layer of this sample, the amount of residual solvent in the recording layer was measured and printing was performed with a thermal head (printing energy: 10.7 mj / mm ² ), and the transmission density of the printed portion and the background portion was measured by X-Rite 309TR (XRITE). C
It was measured with a transmission densitometer (manufactured by OMPANY). The results are shown in Table 2.

Example 3 The leuco dye of Example 2 was treated with 2-anilino-3-methyl-6.
A recording layer was prepared in the same manner as in Example 2 except that -diethylaminofluorane was replaced with 2-anilino-3-methyl-6- (N-ethyl-N-ptoluidino) fluorane.
Immediately after coating the recording layer, the amount of residual solvent in the recording layer was measured and printing was performed with a thermal head (printing energy: 10.7 mj / mm ² ), and the transmission density of the printed portion and the background portion was measured by X-Rite 30.
It was measured with a 9TR (manufactured by XRITE COMPANY) transmission densitometer. The results are shown in Table 2.

Example 4 The leuco dye of Example 2 was prepared from 2-anilino-3-methyl-6.
-Diethylaminofluorane to 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino)
A recording layer was prepared in the same manner as in Example 2 except that fluoran was used, and the amount of residual solvent in the recording layer immediately after coating the recording layer was measured and the thermal head (printing energy: 10.7 mj / mm).
² ) Print and print the transmission density of the printed area and the background area with X-Rit.
It was measured with a transmission densitometer of e309TR (manufactured by XRITE COMPANY). The results are shown in Table 2.

Example 5 After forming a thermosensitive recording layer on a polyester film in the same manner as in Example 1, aging was carried out at 40 ° C. for 24 hours. Next, a liquid having the following composition was prepared and dispersed by a ball mill so as to have an average particle diameter of 0.6 μmΦ to obtain a liquid [C].

[Liquid C] Aluminum hydroxide 10 parts 10% PVA318 aqueous solution (itaconic acid modified PVA) 1 part

Next, a liquid having the following composition was prepared and used as a protective layer coating liquid. [C liquid] 50 parts Water 86 parts 10% PVA318 aqueous solution 100 parts Zinc stearate (Hydrin Z-7-30 manufactured by Chukyo Yushi Co., Ltd.) 4 parts 25% Polyamide epichlorohydrin aqueous solution 12 parts

The protective layer coating liquid thus prepared was coated with a 0.3 mm wire bar and dried at 60 ° C. for 3 minutes to form a protective layer. Print this sample with a thermal head (printing energy: 10.7 mj / mm ² ),
X-Rite 309TR for the transmission density of the printed area and the background area
It was measured with a transmission densitometer (manufactured by XRITE COMPANY). The results are shown in Table 3.

Example 6 After forming a protective layer in the same manner as in Example 5, the sample was aged at 40 ° C. for 24 hours and then printed in the same manner as in Example 5 to determine the transmission density of the printed portion and the background portion. It was measured. The results are shown in Table 3.

Example 7 After forming a thermosensitive recording layer on a polyester film in the same manner as in Example 1, aging was carried out at 40 ° C. for 24 hours. Next, a protective layer coating solution having the following composition was used to coat a protective layer on the recording layer using a wire bar, and the protective layer was coated at 70 ° C. for 5 minutes.
After drying for 1 minute, under a 1.5 kw mercury lamp, 8 m / mi
n. After forming a protective layer of about 3 μm,
Print evaluation was performed in the same manner as in Example 5. The results are shown in Table 3.

(Coating liquid for protective layer) 30% ethyl acetate solution of urethane acrylate-based UV curable resin 667 parts (Unidec C7-157 manufactured by Dainippon Ink and Chemicals, Inc.) 6% 52% xylene solution of silicone resin 6 parts (Big Kimmy Japan Co., Ltd.) Manufactured BYK-344)

Example 8 After forming a protective layer in the same manner as in Example 7, the sample was aged at 40 ° C. for 24 hours, and then printed in the same manner as in Example 7, and the transmission density of the printed portion and the background portion was measured. It was measured. The results are shown in Table 3.

Example 9 A recording medium was prepared and evaluated in the same manner as in Example 7, except that the coating solution for protective layer in Example 7 was changed to the following composition. The results are shown in Table 3.

(Protective Layer Coating Liquid) Urethane acrylate UV curable resin 25% ethyl acetate solution 800 parts (Dainippon Ink and Chemicals Co., Ltd. Unidec C7-157) Silicone resin 52% xylene solution 6 parts (Big Kimmy Japan Co., Ltd. Manufactured BYK-344)

Example 10 After a protective layer was formed in the same manner as in Example 9, the sample was aged at 40 ° C. for 24 hours, and then printed in the same manner as in Example 9, and the transmission density of the printed portion and the background portion was measured. It was measured. The results are shown in Table 3.

Comparative Example 1 A thermal recording layer was formed on a polyester film in the same manner as in Example 1 and then aged at 40 ° C. for 24 hours. Next, the volume average particle size of the following composition was measured with a ball mill.
Dispersion liquid (D liquid) for coating liquid for protective layer by pulverizing and dispersing to 0 μm
Was produced.

[Liquid D] Silica 30 parts (P-832 manufactured by Mizusawa Industry Co., Ltd.) Polyvinyl acetoacetal resin solution 30 parts (KS-1, 10% MEK solution manufactured by Sekisui Chemical Co., Ltd.) Methyl ethyl ketone 140 parts Furthermore, the following composition Was sufficiently stirred to prepare a protective layer coating solution.

[Solution E] Solution D 100 parts Silicon modified polyvinyl butyral resin 60 parts (Dainichi Seika Co., SP-712, solid content, 12.5%) Methyl ethyl ketone 70 parts Toluene 52 parts

The coating solution for protective layer prepared as described above was applied onto the thermosensitive recording layer obtained above and dried to prepare a protective layer having a thickness of 3 μm. This sample was printed with a thermal head (printing energy: 10.7 mj / mm ² ) and the transmission density of the printed area and the background area was measured by X-Rite 309T.
R (manufactured by XRITE COMPANY) was measured with a transmission densitometer. The results are shown in Table 3.

Comparative Example 2 After the protective layer was formed in the same manner as in Comparative Example 1, the sample was heated at 70 ° C. for 10 hours.
After heating for a minute, printing was performed in the same manner as in Comparative Example 1, and the transmission densities of the printed portion and the background portion were measured. The results are shown in Table 3.

Comparative Example 3 After forming the protective layer in the same manner as in Comparative Example 1, the sample was placed at 40 ° C. for 24 hours.
After time aging, printing was performed in the same manner as in Comparative Example 1,
The transmission density of the printed part and the background part was measured. The results are shown in Table 3.

[0097]

[Table 1]

[0098]

[Table 2]

[0099]

[Table 3]

[0100]

As described above in detail and concretely,
The heat-sensitive recording medium of the present invention can obtain a stable color density by controlling the amount of the residual solvent in the recording layer to the allowable amount or less, and the eutectic starting temperature of the leuco dye and the color developer is 95 ° C.
By the above, less background fog and stable color density can be obtained, and further, a protective layer made of a resin liquid insoluble in the binder resin of the recording layer or a protective layer made of an ultraviolet curable resin is used. In this way, it is possible to produce an extremely excellent effect that a thermosensitive recording medium having stable color density and high practicality is manufactured.

Claims (7)

[Claims] 1. A recording layer comprising at least a leuco dye, a developer for heating and coloring the leuco dye, a binder resin as a binder and an organic solvent to form a recording layer coating solution on the support to dry the recording layer. The thermal recording medium to be formed is
500 m of organic solvent was added to the thermosensitive recording layer formed after drying.
A heat-sensitive recording medium containing g / m ² or less. 2. A recording layer is formed by coating and drying on a support a coating solution for a recording layer comprising at least a leuco dye, a developer that heat-colors the leuco dye, and a binder resin as a binder. A thermal recording medium, wherein the eutectic starting temperature of the leuco dye and the color developer is 95 ° C. or higher. 3. A heat-sensitive recording medium, characterized in that a leuco dye and a developer that heat-colors the leuco dye have a eutectic starting temperature of 95 ° C. or higher. 4. A recording layer is formed by coating and drying on a support a recording layer coating liquid comprising at least a leuco dye, a developer that heat-colors the leuco dye, a binder resin as a binder and an organic solvent. The heat-sensitive recording medium according to claim 1 or 2, wherein the protective layer is formed on the recording layer by using a resin liquid insoluble in the binder resin of the recording layer. 5. A recording layer coating liquid comprising at least a leuco dye, a color developer that heat-colors the leuco dye, a binder resin as a binder, and an organic solvent is applied on a support to dry the recording layer. 3. The thermosensitive recording medium according to claim 1, wherein the thermosensitive recording medium is formed and a protective layer made of an ultraviolet curable resin is formed on the recording layer. 6. The heat-sensitive recording medium according to claim 5, wherein the solid content concentration of the ultraviolet curable resin liquid when the protective layer made of the ultraviolet curable resin is formed is 30% or more. 7. The thermal recording medium according to claim 1, wherein the thermal recording medium is a transparent thermal recording medium.