JPS61192597A - Thermal transfer medium - Google Patents

Abstract

PURPOSE:To enhance heat sensitivity and storage stability and to improve the gradation expression of image density, in a thermal transfer medium consisting of a transfer sheet having a transfer layer containing a leuco dye and a receiving sheet having a receiving layer containing a coupler, by containing a specific amount of a polyester resin and a phenol resin in the transfer layer of the transfer sheet. CONSTITUTION:The titled medium consists of a transfer sheet having a transfer layer containing a leuco dye and a receiving sheet having a receiving layer based on a coupler to the leuco dye. A mixture of 30-70wt% of a polyester resin and 70-30wt% of a phenol resin is contained in the transfer layer of the transfer sheet. By containing the polyester resin and the phenol resin in the transfer layer as mentioned above, the release of the leuco dye layer of the transfer sheet from a support is prevented and, because the phenol resin has coupling function, the heat sensitivity of the leuco dye is promoted and the enhancement of heat sensitivity and the rapid thermal transfer onto the receiving sheet are achieved and a sharp high density image can be formed. As the polyester resin, one having physical properties, such that MW is 5,000-15,000, a glass transition point is 30-55 deg.C and melt viscosity at 150 deg.C is 100-1,000cp, is pref. used.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a thermal transfer medium comprising a transfer sheet having a transfer layer containing a leuco dye and a receiving sheet having a receiving layer containing the leuco dye. .

[Prior art]

Conventionally, thermal transfer methods use a transfer sheet in which a heat-sublimable dye is provided on a support, or a transfer sheet in which a heat-fusible substance and a pigment are provided on a support, and a receiving sheet is placed on top of this.
Methods of forming transferred images on receiving sheets by thermal printing are known. However, when using a transfer sheet in which a heat sublimable dye is provided on a support, although it has excellent gradation expression of image density, it has the disadvantages of low heat sensitivity and poor storage stability. Thermal transfer sheet 1-, in which a thermofusible substance and a pigment are provided on a support, has excellent heat sensitivity and storage stability, but has the drawback of not being able to express gradation in one image density.

〔the purpose〕

The present invention has excellent heat sensitivity and storage stability.

An object of the present invention is to provide a heat-sensitive transfer medium that has excellent gradation expression of image density.

〔composition〕

According to the present invention, the transfer sheet includes a transfer sheet having a transfer layer containing a leuco dye as a main component, and a receiving sheet having a receiving layer containing a color developer as a main component for the leuco dye, and in the transfer layer of the transfer sheet. There is provided a thermal transfer medium characterized in that it contains a mixture of 30 to 70% by weight of a polyester resin and 70 to 30% by weight of a phenolic resin.

The thermal transfer medium of the present invention is a transfer sheet.

The receiving sheets are stacked so that the receiving layer is in contact with the transfer layer of the transfer sheet, and a desired colored image is formed on the surface of the receiving sheet by thermal printing from the back side of the transfer sheet.
In the present invention, since the transfer layer contains polyester resin and phenol resin as described above, the leuco dye layer of the transfer sheet does not peel off from the support, and the phenol resin has a color developing function. This promotes thermal sensitivity with the leuco dye, achieving improved thermal sensitivity and rapid thermal transfer onto the receiving sheet, making it possible to form clear and high-density images.

Furthermore, by controlling the heating energy during thermal transfer, it is possible to obtain a gradation expression with a certain degree of accuracy in one image.

In the present invention, as the polyester resin used for the transfer layer, both saturated polyester resin and unsaturated polyester resin can be used, but representative examples include XTP, TP, and SP type products manufactured by Nippon Gosei ■. Examples include Byron products manufactured by Toyobo ■ and Plaxel products manufactured by Daicel ■. The polyester resin used in the present invention has a molecular weight of 5,000 to 15,000 and a glass transition point of 30.
~55°C and melt viscosity at 150°C 100-10
It is preferable to use one having physical properties of 00 cp. When the molecular weight is less than 5,000, the sheet expands and contracts significantly, and on the other hand, when it is greater than 15,000.

The adhesive strength to the sheet becomes stronger and the thermal sensitivity decreases. Also, if the glass transition point (g) is low, the raw storage stability of the transfer sheet will be poor, whereas if it is high, the thermal sensitivity will be decreased. Furthermore, if the melt viscosity is low, the raw storage stability of the transfer sheet will be poor, while if it is high, the compatibility with the phenol resin will be poor, and not only will thermal sensitivity be lowered, but uniform image formation will not be obtained.

The phenolic resin used in the present invention includes phenols (phenol, catechol, ethylphenol, L-butylphenol, cyclohexylphenol, resorcinol, cresol, xylenol, 7-octylcresol, resorcinol, pyrogallol, cycloamyl cresol, etc.) and aldehydes ( It is a resin obtained by condensing formaldehyde, acetaldehyde, acrolein, crotonaldehyde, furfural, paraformaldehyde, etc.) with acid or alkali. When condensed using an acid, a novolac type resin is obtained,
This can be further hardened by adding an excess of formaldehyde, paraformaldehyde, hexamethylenetetramine, etc. When condensation is carried out using an alkali, resol, resitol,
Becomes legit.

Phenol resin can also be dissolved in a solvent such as alcohol or drying oil to form a festival.

Furthermore, the phenolic resin used in the present invention may be a mixture of phenol resins condensed with one or more types of phenols and one or more types of aldehydes, or a mixture of two or more different phenol resins further condensed. But that's fine.

In the present invention, the polyester resin and phenol resin are contained in the transfer layer as a mixture of 30 to 70% by weight of the polyester resin and 70 to 30% by weight of the phenolic resin.

The transfer sheet used in the present invention is a support 1, for example.

For the surface of paper, synthetic paper, especially plastic film,
A transfer layer containing leuco dye as a main component is provided.

As the leuco dye in this case, any of those conventionally used for pressure-sensitive paper and thermal paper can be used, including triphenylmethane, fluoran, phenothiazine, and auramine.

Spiropyran type substances are preferably used. Specific examples of these leuco dyes are shown below.

3.3-bis(p-dimethylami, nophenyl)-phthalide, 3.3-bis(p-dimethylami, nophenyl)-6-
Dimethylaminophthalide (also known as crystal violet lactone), 3.3-His(P-dimethylaminophenyl)-6-diethylaminophthalide.

3,3-bis(P-dimethylaminophenyl)-6-chlorphthalide.

3.3-bis(P-dibutylaminophenyl)phthalide.

3-cyclohexylamino-6-chlorofluorane, 3-dimethylamino-5,7-dimethylfluorane.

3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane.

3-diethylamino-7,8-benzfluorane, 3-
Diethylamino-6-methyl-7-chlorofluorane, 3-(N-p-tolyl-N-dithylamino)-6-methyl-7-anilinofluorane.

3-pyrrolidino-6-methyl-7-anilinofluorane, 2-(N-(3'-trifluoromethylphenyl)amino)-6-dinithylaminofluorane, 2-(3,
6-bis(diethylamino)-9-(o-chloroanilino)xantylbenzoic acid lactam).

3-diethylamino, no 6-methyl-7-(m-trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran.

3-Dibutylamino-7-(o-chloroanilino)fluoran.

3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane.

3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N,N-diethylamino)-5- Methyl-7-(
N.

N-dibenzylamino)fluoran, benzoylleucomethylene blue, 6'-bromo-3'-methoxy-benzoindolino-pyrylosbilane.

3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-Methoxy-51-nitrophenyl)phthalide.

3-(2'-Hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide.

3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-
Methylphenyl) phthalide.

In the present invention, the leuco dye is
Usually 0.3-30g/i, preferably 0.5-20α/
It is used to a certain extent.

The receiving sheet used in the present invention is one in which a receiving layer containing a color developer for the leuco dye as a main component is provided on a support such as synthetic paper or plastic film. In this case, as the color developer, an electron-accepting substance such as a phenolic substance, an organic acid or a salt or ester thereof is used, and from the viewpoint of practicality, one with a melting point of 200°C or less is preferably used. 1 Specific examples of the color developer preferably applied in the present invention are shown below. Note that the numbers in parentheses indicate the melting point.

4-7 ert-butylphenolsidiphenyl ether (84), l-naphthol (98
), 2-naphthol (121), methyl-4-hydroxybenzoate (131), 4-hydroxyacetophenone (109), 2,2'-dihydroxydiphenyl ether (79), 4-phenylphenol (166)
), 4 tart-octylcatechol diphenyl (103), 4.4'-methylenebisphenol (160), 2.2'-methylenebis(4
-chlorophenol) (164), 2.2'-methylenebis(4-methyl-6-t.ert-butylphenol) (125), 4.4'-isopropylidenediphenol (156), 4.4'-isopropylene Redenbis(2-chlorophenol) (90), 4,4'
-isopropylidene bis(2,6-dibromophenol) (172), 4.4'-isopropylidene bis(
2-tarL-butylphenol) (110), 4,4
′ -isopropylidene bis(2-methylphenol)
(136), 4,4'-isopropylidene bis(2,
6-dimethylphenol) (168), 4.4'-
5ee-butylidene diphenol (119), 4.4'
-5ec-butylidenebis(2-methylphenol)
(142), 4,4'-cyclohexylidene diphenol (180), 4,4'-cyclohexylidene bis(2-methylphenol) (184), salicylic acid (
163), salicylic acid methalyl ester (74),
Salicylic acid phenacyl ester (110), 4-hydroxybenzoic acid methyl ester (131), 4-hydroxybenzoic acid ethyl ester (116), 4-hydroxybenzoic acid propyl ester (98), 4-hydroxybenzoic acid isopropyl ester (86) ), 4-hydroxybenzoic acid butyl ester (71), 4-hydroxybenzoic acid isoamyl ester (50), 4-hydroxybenzoic acid phenyl ester (178), 4-hydroxybenzoic acid benzyl ester (111), 4-hydroxybenzoic acid acid cyclohexyl ester (119),
5-hydroxysalicylic acid (200), 5-chlorsalicylic acid (172), 3-chlorsalicylic acid (178),
Thiosalicylic acid (164), 2-chloro-5-nitrobenzoic acid (165).

4-methoxyphenol (53), 2-hydroxybenzyl alcohol (87), 2,5-dimethylphenol (75), benzoic acid (122), orthotoluic acid (107), metatoluic acid (111), paratoluic acid (181) , orthochlorobenzoic acid (142),
Metaoxybenzoic acid (200), 2,4-dihydroxyacetophenone) (97), resorcinol monobenzoate (135), 4-hydroxybenzophenone (135), 2,4-dihydroxybenzophenone (1)
44), 2-Naphtoic Acid (184), ■-
Hydroxy-2-naphthoic acid (195),
3.4-dihydroxybenzoic acid ethyl ester (12
8), 3,4-dihydroxybenzoic acid phenyl ester (189), 4-hydroxypropiophenone (is
o), salicyl salicylate (148), phthalic acid monobenzyl ester <107).

Further, in the present invention, a phenolic compound represented by the general formula (wherein R is an alkylene group containing 1 to 5 ether bonds) can be used as a color developer. This phenolic substance is produced in high yield and purity by reacting monothiohydroquinone with the corresponding dihalogenoalkyl ether under alkaline conditions.
Moreover, it can be synthesized relatively inexpensively.

In the phenolic substance represented by the above general formula, R
is an alkylene group containing 1 to 5 ether groups; in this case, the ether group may be present in the main chain of the alkylene group or may be present in the side chain. The number of carbon atoms contained in this ether group-containing alkylene group is usually in the range of 2 to 15. Preferred ether group-containing alkylene groups are:
It contains 1 to 3 ether bonds and has 2 to 7 carbon atoms.

In the present invention, the receiving layer and/or the transfer layer has an oil absorption amount of 50 m Q /100 g (JIS K 510
1 method) or more preferably 150 m Q / 100 g
It is preferable to contain the above porous filler. The porous filler contained in the receptor layer is 0.01 parts by weight or more, usually 0.05 to 10 parts by weight, per 1 part by weight of the color developer.
Parts by weight, preferably in the range of 0.1 to 3 parts by weight. When incorporated in the transfer layer, 0.01 to 1 part by weight, preferably 0.03 to 0.5 parts by weight, per 1 part by weight of the leuco dye.
Parts by weight. Specific examples of porous fillers include:
Silica, aluminum silicate, alumina, aluminum hydroxide, magnesium hydroxide, urea-formalin resin,
Examples include inorganic and organic fine powders such as styrene resin.

Further, in the present invention, a thermofusible substance having a melting point of 200° C. or less, preferably 150° C. or less can be added to the transfer layer or the receiving layer. The amount used is 0.1 to 50 parts by weight per 1 part by weight of the leuco dye. The thermofusible substances preferably used in the present invention are as follows.

(1) Fatty acid amides RlNHCOR” represented by the following general formula (I) or (If)
In the formula, R2 is an alkyl group having 1 to 30 carbon atoms, R1°R3
is an alkyl group having 10 to 30 carbon atoms, and R4 and Rs are hydrogen or a lower alkyl group.) Specific examples of such fatty acid amides include the following.

decyl acetamide, decyl propionamide, undecyl acetamide, undecyl propionamide, lauryl acetamide, lauryl propionamide, tridecyl acetamide, tridecyl propionamide, myristyl acetamide, myristyl propionamide, pentadecyl acetamide, pentadecyl propionamide, palmityl Acetamide, palmitylpropionamide, palmitic acid amide, heptyl acetamide, heptyl propionamide, stearyl acetamide, stearyl propionamide 5 stearyl butyramide, stearyl valeramide, stearyl capronamide, stearyl lauramide, stearyl palmitin amide, stearyl sudearin amide , nonadecylacetamide, nonadecylpropionamide, behenylacetamide, behenylpropionamide, behenylstearamide 6-undecanoic acid methylamide, undecanoic acid ethylamide, lauric acid methylamide, lauric acid ethylamide, tridecanoic acid methylamide, tridecanoic acid ethylamide, myristic acid methylamide, myristin Acid ethylamide, pentadecanoic acid methylamide, pentadecanoic acid ethylamide.

Palmitic acid methylamide, palmitic acid dimethylamide, palmitic acid butyramide, stearic acid methylamide, stearic acid ethylamide.

Stearic acid propylamide, stearic acid butylamide, stearic acid dimethylamide, stearic acid diethylamide, stearic acid dibutylamide, nonadecanoic acid methyl amide, nonadecanoic acid ethylamide, behenic acid methylamide, oleic acid methylamide, oleic acid ethylamide (2) The following general Aromatic carboxylic acid amides represented by formula (m) (wherein R' is an alkyl group having 1 to 30 carbon atoms, R7゜R
(8 is hydrogen, halogen, lower alkyl group or lower alkoxy group, n is 0 or l) Specific examples of such compounds include those shown below.

N-stearinbenzamide, N-palmityl-2-chloropenzamide, N-stearyl-2-methoxybenzamide, N-stearyl-4-methylbenzamide,
N-palmityl-2,4-dimethylbenzamide, N-
Behenylbenzamide, N-behenyl-2-methylbenzamide, N-stearylphenylacetylamide, N
-Behenylphenylacetylamide.

(3) Amides having a cyclohexyl ring represented by the following general formulas (IV) and (V) (wherein R9 is an alkyl group having 1 to 30 carbon atoms or a substituted or unsubstituted aryl group, R10 is hydrogen, halogen or a lower alkyl group) In formula C, H41 is an alkyl group having 1 to 30 carbon atoms, R12
is hydrogen, halogen or a lower alkyl group) Specific examples of such compounds include those shown below.

N-cyclohexyl acetamide, N-cyclohexylpropionamide, N-cyclohexyl stearin amide, N-cyclohexylbenzamide, N-cyclohexyl-2-methylbenzamide, N-cyclohexyl-2-chlorobenzamide, N-cyclohexyl-2,
4-dimethylbenzamide.

N-cyclohexylpalmitic acid amide, N-(chlorohexyl) palmitic acid amide, N-(2-methylcyclohexyl) stearic acid amide, N-stearylhexahydrobenzamide.

(4) Phenyl esters of hydroxybenzoic acid represented by the following general formula (VI) (wherein, group, substituted or unsubstituted aryloxy or aralkyloxy group, carboxylic acid group or hydroxyl group, n is 0, 1.2 or 3, m is 1, 2 or 3) Specific examples include those shown below.

4-Hydroxybenzoic acid phenyl ester, 4-hydroxybenzoic acid (2-methoxyphenyl) ester, 4-
Hydroxybenzoic acid (2-methoxy-4-methylphenyl) ester, 4-hydroxybenzoic acid (3,5-dioxyphenyl) ester, 3-hydroxybenzoic acid (4
-carboxyphenyl) ester, 4-hydroxybenzoic acid (4-butoxyphenyl) ester, 4-hydroxybenzoic acid (4-chlorophenyl) ester, salicylic acid (2-chlorophenyl) ester, salicylic acid (4-
chlorophenyl) ester, salicylic acid (2,3-dichlorophenyl) ester, salicylic acid (2,6-dichlorophenyl) ester, salicylic acid (2,4,6-trichlorophenyl) ester, salicylic acid (2-bromophenyl) ester, salicylic acid (4) -bromophenyl)
ester, salicylic acid (2,4-dibromophenyl) ester.

Salicylic acid (2,4,6-tribromophenyl) ester, salicylic acid (3-methylphenyl) ester.

Salicylic acid (4-tert-butylphenyl) ester, salicylic acid (4-tert-amylphenyl) ester, salicylic acid (2-methoxyphenyl) ester, salicylic acid (2-ethoxyphenyl) ester, salicylic acid (3-methoxyphenyl) ester, salicylic acid (4
-hydroxyphenyl) ester, salicylic acid (4-benzylphenyl) ester.

Salicylic acid (4-benzoinphenyl) ester.

Salicylic acid (2-methoxy-4-allylphenyl) ester, salicylic acid (alpha naphthyl) ester.

Salicylic acid (beta naphthyl) ester, salicylic acid (
4-chloro-3-methylphenyl) ester, salicylic acid (3-hydroxyphenyl) ester, salicylic acid (
4-propenylphenyl) ester, 5-chlorosalicylic acid (3-methylphenyl) ester, 3,5-dichlorosalicylic acid (2-methoxyphenyl) ester.

(5) Convex benzoic acid phenyl esters represented by the following general formula (■) (wherein R13 is hydrogen, an alkyl group or alkoxy group having 1 to 30 carbon atoms, a halogen, or a nitro group).

nitrile group, acyloxy group, substituted or unsubstituted aryl or aralkyl group, substituted or unsubstituted aryloxy or aralkyloxy group, R14 is hydrogen,
An alkyl group or alkoxy group having 1 to 3 carbon atoms, a halogen, a nitro group, a nitrile group, an acyloxy group, a substituted or unsubstituted aryl or aralkyl group, a substituted or unsubstituted aryloxy or aralkyloxy group, or an acyl group. Specific examples of such compounds include those shown below.

Benzoic acid phenyl ester, benzoic acid-4-methylphenyl ester, benzoic acid-2,4-dichlorophenyl ester, benzoic acid-2,4,6-trichlorophenyl ester, benzoic acid-2-methyl-4-chlorophenyl ester ester, benzoic acid-3-bromphenyl ester, benzoic acid-4-nitrylphenyl ester, benzoic acid-2,
4-dibromphenyl ester, benzoic acid-3-iodophenyl ester, benzoic acid-3-ditrophenyl ester.

Benzoic acid-4-methyl-2,6-dichlorophenyl ester, benzoic acid W! -4-isopropylphenyl ester, benzoic acid-4-butylphenyl ester, benzoic acid-4-benzylphenyl ester, benzoic acid-4-(
1-naphthyl) phenyl ester, benzoic acid-2-benzoyloxyphenyl ester, benzoic acid-4-(2-
methyl) diphenyl ester, benzoic acid #-2-phenylethyloxyphenyl ester, benzoic acid-2-acetoxyphenyl ester, benzoic acid-4-methoxyphenyl ester, benzoic acid-4-(4-methyl)phenoxyphenyl ester, 4- Methylbenzoic acid phenyl ester, 4-methoxybenzoic acid phenyl ester, 4-phenoxybenzoic acid phenyl ester, 4-acetoxybenzoic acid phenyl ester, 4-methoxybenzoic acid-4-methoxyphenyl ester, 2-acetoxybenzoic acid phenyl ester, 2-benzoyloxybenzoic acid phenyl ester, 2-nitrobenzoic acid-4-methylphenyl ester, 4-nitrobenzoic acid-4-methylphenyl ester, 4-benzoyloxybenzophenone, 2-benzoinoxy-4-methylbenzophenone.

(6) Benzoyloxybenzoic acid esters represented by the following general formula (■) (wherein R''+! Hydrogen flame alkyl group or alkoxy group or halogen with 1 to 30 carbon atoms, R18 is a carbon number of 1 to 30)
Specific examples of such compounds (30 argyl groups, substituted or unsubstituted aryl or aralkyl groups) include, for example.

Examples include those shown below.

4-benzoyloxybenzoic acid methyl ester, 4-benzoyloxybenzoic acid ethyl ester, 4-benzoyloxybenzoic acid-n-propyl ester, 4-benzoyloxybenzoic acid benzyl ester, 4-benzoyloxybenzoic acid phenyl ester, 2- Benzoyloxybenzoic acid phenyl ester, 4-(4'-methylbenzoyloxy)benzoic acid ethyl ester, 4-(4'
-Methoxybenzoyloxy)benzoic acid ethyl ester, 4-(4'-chlorobenzoyloxy)benzoic acid ethyl ester.

When a receptive layer is provided on the receptive sheets 1 to 1, a conventional binder is used. For example, polyvinyl alcohol, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch. ,
Water-soluble materials such as gelatin, polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc.
Those soluble in organic solvents or those capable of forming aqueous emulsions can be used. When a receptor sheet is prepared using these resins as a binder, the receptor layer forming liquid can be applied by any of a solvent coating method, a hot melt coating method, or an aqueous emulsion coating method.

Furthermore, in the present invention, in order to obtain a transfer medium with higher thermal sensitivity, the transfer layer and/or the receiving layer containing the thermofusible material is formed by using the thermofusible material during or after the layer formation. It is advantageous to thermally melt the thermofusible substance once by applying heat treatment to a temperature higher than the melting point of
When forming a transfer layer containing a leuco dye, it is also a preferable means to use a coating liquid containing the leuco dye in a dissolved state.

Furthermore, the surface smoothness (Beckman smoothness, J'l5-P81L9) of the transfer layer and/or the receiving layer is 200 to
It is also effective to adjust the time to 10,000 seconds.

The thermal transfer medium of the present invention is prepared by dispersing and dissolving the above-mentioned layer-forming components together with a solvent such as water using a pulverizing and mixing means such as a ball mill or an attritor to prepare a layer-forming liquid, which is then dried and adhered onto each support. Amount 0.3~30 (H/rr
It can be obtained by coating and drying so that -.

In the transfer sheet 1- used in the present invention, the transfer layer provided on the surface thereof may be a so-called plain (no image) layer provided uniformly over the entire surface of the support;
It may be provided in advance in the form of a desired image. A transfer sheet having an image-free transfer layer can be obtained by simply applying a transfer layer forming liquid to the surface of a support. On the other hand, those having an image-like transfer layer can be obtained by applying a transfer layer-forming liquid onto the surface of a support in the form of a desired image (including letters) by letterpress printing or gravure printing. Alternatively, paper, synthetic paper,
Appropriate supports such as plastic films are stacked one on top of the other, and the image is pressed from the support side or the transfer sheet side using a suppressing means such as a typewriter or iron pen, or a heating suppressing means such as a thermal head or a thermal pen to transfer the image. An imageless transfer layer of the sheet can be obtained by imagewise application to the surface of another suitable support.

To carry out the thermal transfer of the present invention, for example, when using a transfer sheet having an image-shaped transfer layer, a receiving sheet 1- is placed on the surface of this transfer layer so that the receiving layer is in contact with the surface of the transfer sheet. This can be done by passing it between heated rolls,
On the other hand, when using a transfer sheet with a transfer layer without an image, the receiving layer of the receiving sheet is superimposed on the transfer layer surface of the transfer sheet, and thermal printing is performed directly from the back side of the transfer sheet 1 using a thermal printer. This can be done by:

In addition, when obtaining multicolor copies, transfer sheets are prepared using leuco dyes of different tones as main coloring components, for example, a transfer sheet using a blue leuco dye and a transfer sheet using a red leuco dye are prepared.

By forming a transfer image on the same receiving sheet by transfer, blue and red colored images can be formed on the same sheet.

〔effect〕

The thermal transfer sheet of the present invention has the above structure, and by performing thermal transfer using this thermal transfer sheet in combination with a receiving sheet, a high density and clear image can be formed, and furthermore, by controlling the heating energy, Since the amount of color development and the amount of leuco dye transfer can be changed, gradation expression of image density can be obtained.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples. Note that all parts and percentages shown below are based on weight.

Example 1 10 parts of 3-N-methyl---dicyclohexylamino-6-methyl 7-anilinofluorane polyester resin (manufactured by Nippon Gosei ■, XTP-2461) (molecular weight 8000. Melt viscosity 300 cp (150°C), glass transition point 45°C) 1 part phenol resin (phenol aldehyde and phenolacetylene polymer) 1 part methyl ethyl ketone
A transfer sheet having a transfer layer having a coating weight of 0.5 g1rd was prepared by applying and drying a composition consisting of 100 parts using a wire bar.

on the other hand.

4-Hydroxybenzoic acid n-butyl ester 20 parts Silica fine particles (oil absorption 200m Q /100g) 1
0 parts polyvinyl alcohol 3 parts water
After dispersing 100 parts of the composition using a ball mill for 24 hours, it was dispersed using a wire bar on high-quality paper (35 g/
rrl') was applied and dried to prepare a receptor sheet having a receptor layer of adhesion capacity/A.

Transfer sheet 1- to receiving sheet 1- thus obtained
When 0.7 mJ of heating energy was applied from the back side of the transfer sheet 1- by a thermal head, a clear black image with an image density of 1.45 was obtained. Further, by controlling the heating energy to 0.3 mJ to 0.7 mJ, an image with gradation expression as shown in Table 1-1 could be formed.

Table-1 Example 2 on a polyester film with a thickness of 6 μm.

3-N-Methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane 10 parts Polyester resin (manufactured by Nippon Gosei@, XTP-2464) (molecular weight 100
00, melt viscosity 500 cp (150°C).

Glass transition point: 50°C) 1 part phenolic resin (phenol aldehyde and phenolic acetylene polymer) 1 part methyl ethyl ketone
A composition consisting of 100 parts was applied and dried in the same manner as in Example 1 to obtain a transfer sheet. Next, the transfer sheet thus obtained and the receiving sheet shown in Example 1 were stacked, and heating energy of 0.7 mJ was applied from the back side of the transfer sheet using a thermal head, resulting in an image density of 1.43. A clear black image was obtained. In addition, by controlling the heating energy to 0.3 mJ to 0.7 ■J,
It showed the same values as in Example 1 and was able to form an image with one gradation expression. Furthermore, this transfer sheet has excellent shelf life and has 6
No problems occurred under the conditions of 0°C and 48 hours.

Comparative example 1 Made of 6μ thick polyester film.

3-N-Methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane 10 parts Polyester resin (manufactured by Nippon Gosei ■, XTP-2461) 2
A composition comprising 100 parts of methyl ethyl ketone was coated using a wire bar and dried to prepare a transfer sheet having a transfer layer with a coating weight of 0.5 H/m.

Comparative Example 2 A thermal transfer sheet was obtained in the same manner as in Comparative Example 1 except that 2 parts of the polyester resin in Comparative Example 1 was replaced with 2 parts of the phenol resin shown in Example 1.

Using the above transfer sheet and the receptor sheet shown in Example 1, image formation was carried out under the same conditions as in Example 1, and the following results were obtained.

Table-2

Claims (2)

[Claims] (1) Consisting of a transfer sheet having a transfer layer containing a leuco dye as a main component, and a receiving sheet having a receiving layer containing a color developer as a main component for the leuco dye, the transfer layer of the transfer sheet contains a polyester resin. 1. A thermal transfer medium comprising a mixture of 30 to 70% by weight of a phenolic resin and 70 to 30% by weight of a phenolic resin. (2) The polyester resin has a molecular weight of 5000 to 150
00, glass transition point 30-55℃, melt viscosity 100-1
The thermal transfer medium according to claim 1, having physical properties of 0.000 cp (150° C.).