JPH0767831B2 - Thermal transfer recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive transfer recording medium that transfers a recorded image by heating a thermal head, a laser, or the like.

BACKGROUND ART Conventionally, as a thermal transfer recording medium, a transfer sheet having a thermally sublimable dye layer provided on a support or a transfer sheet having a heat-fusible substance and a pigment provided on a support has been known. Used to form an image on a receiving sheet.

However, the method using the heat sublimable dye is excellent in expressing the gradation of the image, but has the drawback that the heat sensitivity is low and the storability of the image is inferior. Further, the heat fusible substance and the pigment are used. The method is excellent in heat sensitivity and storability, but has a drawback that it cannot express gradation.

The present invention aims to remedy the above-mentioned drawbacks of the prior art.
It is an object of the present invention to provide a heat-sensitive transfer recording medium which is excellent in thermal sensitivity, and in particular can obtain a high-density image excellent in gradation.

Composition The present invention provides a thermal transfer recording in which a thermal transfer ink layer comprising a fine porous resin and a thermal fusible ink component containing a thermofusible substance solid at room temperature and a colorant as main components is provided on a support. In particular, the medium is a thermal transfer recording medium in which the resin is cellulose acetate butyrate in which the ratio of butyryl groups to the total of acetyl groups and butyryl groups is 38% or less.

In the present invention, the colorant in the hot-melt ink is held together with the hot-melt substance by the network structure in the fine porous structure of the resin. This colorant is leached from the fine porous structure of the resin together with the heat-melting substance melted by heating with a thermal head or the like, and is gradually transferred onto the receiving sheet. The amount of the transferred colorant varies depending on the amount of heat energy applied by a thermal head or the like. Therefore, by controlling the applied thermal energy, it is possible to change the amount of the colorant transferred, and it is possible to obtain an image in which the gradation is represented faithfully and widely.

The reason why the cellulose acetate butyrate porous resin used in the present invention has not been clarified yet is that it has been surface-chemically balanced in relation to a heat-melting substance such as oil or wax which is a heat-melting ink component. It is immiscible, and as a result, the hot melt ink component is uniformly dispersed in the resin porous structure and forms a fine porous structure. It is also thermally stable and has a relatively high melting point.

Therefore, when the heat-melting substance such as the wax is melted by applying heating energy, the coloring agent is leached from between the network structure composed of the fine porous structure of the cellulose acetate butyrate resin and is transferred to the receiving sheet side. .

The cellulose acetate butyrate used in the present invention is a mixed ester of cellulose having an acetyl group and a butyryl group.

There are the following three types of commercially available acetate butyrate having different butyryl group contents.

(1) Low butyryl group (16-17%) melting point 210 ° C or higher (2) Medium butyryl group (27-38%) melting point 155-210 ° C (3) High butyryl group (50%) melting point 110-160 ° C That is, The higher the butyryl group content, the lower the melting point, and the lower the butyryl group content, the higher the melting point.

Therefore, as the microporous resin used in the present invention, a medium butyryl group or low butyryl group cellulose acetate butyrate is preferable as a resin that can withstand heating energy. More desirable is cellulose acetate butyrate having a low butyryl group.

Here, the level of the heating energy varies depending on the type of each material and the ink layer thickness, and is a relative value. As the support used in the present invention, a conventionally known film or paper can be used as it is. For example, a film of a relatively heat-resistant plastic such as polyester, polyamide, polycarbonate, triacetyl cellulose, nylon, or polyimide, cellophane, condenser paper, or sulfuric acid paper can be preferably used. The thickness of the support is preferably about 2 to 15 μm when a thermal head is considered as a heat source for heat transfer, but a heat source capable of selectively heating a heat transferable ink layer such as laser light is used. There is no particular limitation in this case. When using a thermal head, the surface of the support that comes into contact with the thermal head has a silicone resin, a fluorine resin, a polyimide resin, an epoxy resin, a phenol resin,
By providing a heat-resistant protective layer made of melamine resin, nitrocellulose or the like, the heat resistance of the support can be improved, or a support material which has been heretofore unusable can be used.

The method for producing the thermal transfer ink layer having the above structure is not particularly limited, but the following method is generally used. That is, a colorant, a heat-fusible substance, and other components that are added as necessary are mixed and dispersed with a suitable organic solvent using a dispersing device such as an attritor and a ball mill, and an ink dispersion liquid (solution). But it's okay). Separately, a solution of the resin of the present invention dissolved in an organic solvent is obtained, and this solution is mixed with the above ink dispersion liquid and uniformly dispersed by a mixer such as a ball mill. Then, the obtained dispersion is applied onto a support and dried to obtain the thermal transfer ink layer having the fine porous structure as described above. A wetting agent, a dispersant or the like may be added to the dispersion liquid in order to improve the dispersion of the colorant and the heat-meltable substance.
Further, if necessary, a filler usually used in this type of resin coating can be added.

Alternatively, a substance that is incompatible with the resin that forms the porous structure and is soluble in a solvent that does not dissolve the resin is kneaded with the resin, and the mixture is applied onto a support to form a resin layer, and then the resin layer is formed. A thermal transfer ink layer having the above-mentioned structure can be obtained by a method of dissolving a substance in a solvent as described above to form a porous resin structure and then filling the porous structure with a heat-meltable ink component. .

In the present invention, a gradation control agent may be added in order to improve gradation. The gradation control agent has better wettability with a resin than a heat-melting substance such as oil or wax which is a heat-melting ink component, and has good compatibility, and is firmly held in a fine porous structure, and by its presence, Finely adjust the pore size of the porous tissue to make it smaller. Therefore,
It itself is not transferred even when heat energy is applied, is retained in the porous structure, and acts as a good gradation control agent of adjusting the transfer amount of the heat-meltable ink component existing in the periphery. .

Examples of the gradation control agent include the following materials which have already been applied.

1) Needle crystal pigment (Japanese Patent Application No. 60-38868) 2) Azo pigment (Japanese Patent Application No. 60-192098) 3) Phthalocyanine pigment (Japanese Patent Application No. 60-168562) Coloring dye And a coloring pigment, but a dye gives a more preferable gradation image.

Examples of such dyes include the following direct dyes, acid dyes, basic dyes, mordant dyes, sulfur dyes, vat dyes, azoic dyes, oil dyes, and heat sublimable disperse dyes.

1) Direct dyes: direct sky blue, direct black W, etc.

2) Acid dyes: Tartrazine, Acid Violet 6
B, Acid Fast Red 3G, etc.

3) Basic dyes: safranine, auramine, crystal violet, methylene blue, rhodamine B, Victoria blue B and the like.

4) Mordant dyes: Sanchromin First Blue MB, Eriochrome Azurol B, Alizarin Yellow B, etc.

5) Sulfur dyes: Sulfur Brilliant Green 4G, etc.

6) Vat dye: Indanthrene blue, etc.

7) Azoic dyes: Naphthol AS, etc.

8) Oily dyes: Nigrosine, Spirit Black EB, Varifast Orange 3206, Oil Black 215, Butter Yellow, Sudan Blue, Oil Red B, Rhodamine B and the like.

9) Thermally sublimable disperse dye (9-1) Monoazo disperse dye: Dispers First Yellow G, Dispers First Yellow 5G, Dispers First Yellow 5R, Dispers Red R and the like.

(9-2) Anthraquinone type disperse dyes: Dispers First Violet OR, Dispers First Violet B, Dispers Blue Extra, Dispers First Brilliant Blue B and the like.

(9-3) Nitrodiphenylamine-based disperse dyes: Dispers First Yellow RR, Dispers First Yellow GL and the like.

The particle size of these dyes may be smaller than that of the gradation control agent having a network structure, and preferably in a dissolved state.

Examples of the color pigment include a fine particle pigment (Japanese Patent Application No. 60-166020) and a monoazo pigment (Japanese Patent Application No. 60-253723), which have already been proposed by the present applicant.

The colorant proposed above is selected not only to have an excellent function as a colorant, but also to have excellent storage stability of image quality and weather resistance.

As the heat-meltable ink component other than the colorant, any liquid, semi-solid, or heat-meltable solid may be used as long as it is incompatible with the fine porous resin and is non-volatile. As the heat-melting substance, a heat-melting substance that constitutes a heat-melting ink component in a normal heat-sensitive transfer material can be used, and for example, carnauba wax, paraffin wax,
Waxes such as sazol wax, microcrystalline wax, and castor wax; stearic acid, palmitic acid, lauric acid, aluminum stearate, lead stearate, barium stearate, zinc stearate,
Higher fatty acids such as zinc palmitate, methyl hydroxystearate and glycerol monohydroxystearate or their metal salts, derivatives such as esters; polyethylene, polypropylene, polyisobutylene, polyethylene wax, polyethylene oxide, polytetrafluoroethylene,
A thermoplastic resin composed of an olefin homopolymer or copolymer such as an ethylene-acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-vinyl acetate copolymer, or a derivative thereof is used. If necessary, animal and vegetable oils such as cottonseed oil, rapeseed oil and whale oil, mineral oils such as motor oil, spindle oil and dynamo oil, lanolin, petrolatum, lard and the like are used. These heat-fusible substances and the like are used alone or in a mixture of two or more kinds in a proportion of 50 to 200 parts with respect to 100 parts of the resin constituting the fine porosity of the thermal transfer ink layer.

In addition, it is possible to previously provide an intermediate adhesive layer on the support in order to more strongly retain the network structure of the porous resin structure.

Examples of the intermediate adhesive layer include so-called plastic resins and plastic resins to which a filler is added.

The receiving sheet may be plain paper or synthetic paper, but if necessary, the above resin or a material containing a filler such as TiO ₂ , silica, or ZnO may be coated on plain paper to form a colorant. It is also possible to devise to facilitate the transfer.

Next, examples and comparative examples will be described. All parts are parts by weight.

Example 1 Neozapon Blue 807 (coloring dye) (manufactured by BASF) 10 parts 2,7-bis [2-hydroxy-3- (2-chlorophenylcarbamoyl) naphthalen-1-ylazo] -9-fluorenone (tone control agent) ) 10 parts Modified lanolin oil 30 parts Carnauba wax 20 parts Paraffin wax 20 parts Dispersant 0.5 part Liquid paraffin 5 parts Methyl ethyl ketone 10 parts at 68 ℃
Approximately 48 with a ball mill together with a mixed solution of 0 parts and 130 parts of toluene.
Disperse enough for time.

Next, a 10% by weight reagent cellulose acetate butyrate (Kanto Kagaku: butyl group 17% melting point 230-240 ° C) solution (10 parts resin, 20 parts toluene, 20 parts methyl ethyl ketone) 300
Parts were added to the above ink dispersion and dispersed by a ball mill for about 1 hour to prepare a coating composition for the heat-sensitive transfer composition.

This coating material is applied to the surface of a polyester film having a thickness of 6 μm with a heat resistant silicone resin layer on the back side using a wire bar and dried at a drying temperature of 100 ° C. for 1 minute to form a thermal transfer ink layer having a thickness of about 5 μm. Formed.

When the ink layer of the thermal transfer recording medium thus obtained was superposed so as to face the synthetic paper as the receptor, and the heating energy was changed by the thermal head from the back side of the transfer medium to perform image recording, as shown in the drawing. A cyan tone characteristic curve was recorded on.

It can be seen that in the present embodiment, the image density changes gently according to the change in heating energy, and the gradation reproduction is further expanded. Furthermore, the density of the recorded image remained almost unchanged after the recorded image was stored in a constant temperature bath at 60 ° C for 50 hours and after being irradiated with light for 24 hours using a fade meter.

Example 2 All were carried out under the same conditions except that the coloring dye of Example 1 was changed to Spilon Red GRLT Special (manufactured by Hodogaya), and the image recording results were recorded with a magenta gradation characteristic curve as shown in the figure. Was done.

From the above results, it can be seen that gradation reproduction is further expanded in this embodiment. Further, as a result of weather resistance and storability tests using a fade meter, the density of the recorded image hardly changed.

Example 3 The same procedure as in Example 1 was repeated except that Neozapon Yellow R (manufactured by BASF) was used as the coloring dye. The result is shown by the yellow tone characteristic curve shown in the figure.

Example 4 Neozapon Black RE (manufactured by BASF) 8 parts Heltogen Blue D 7030 (manufactured by BASF) 15 parts Machine oil 20 parts Carnauba wax 20 parts Castor wax 20 parts Dispersant 0.4 parts Liquid paraffin 4 parts Carry out the above hot melt ink properties Disperse well in the same manner as in Example 1, and similarly perform cellulose acetyl butyrate resin (CAB-3
81-0.5; manufactured by Eastman Kodak; butyryl group 37%, melting point 155-
(165 ° C.) resin solution was added and dispersed in the same manner to prepare a coating material for the heat-sensitive transfer composition.

Then, coating is performed in the same manner as in Example 1 to a thickness of about 4 μm.
m thermal transfer ink layer was formed.

Next, when image recording was performed in the same manner as in Example 1, the black gradation characteristic curve shown in FIG. 1 was recorded.

From the above results, it is clear that the gradation reproduction is further expanded in this embodiment.

The weather resistance and storability test results were also good.

Below, the results of experiments are shown as comparative examples.

Comparative Example As a comparative example, a sheet was prepared under the same conditions as in Example 1 except that the resin for forming a porous layer of Example 1 was replaced with the following resins, and image recording was performed. The results are shown in the table. .

Comparative Example 1. Polyester resin (Vylon 200; manufactured by Toyobo) Comparative example 2. Polycarbonate resin (GELEXAN141-111; manufactured by Engineering Plastics Co., Ltd.) Comparative example 3. Styrene-acrylic copolymer resin (RTR-28; manufactured by Fujikura Kasei) Comparison Example 4. Nitrocellulose resin (DN type; manufactured by Daicel Chemical) Comparative Example 5. Vinyl chloride-vinyl acetate copolymer (VYHH; manufactured by Union Carbide) Effect As is clear from the above description, in the heat-sensitive transfer recording medium of the present invention, the ink oozes out from between the porous resins and is transferred to the receiving sheet surface according to the magnitude of heating energy.
Therefore, by controlling the heating energy at the time of transfer, it is possible to obtain a transferred image with excellent gradation expression (wide gradation reproduction), and the image has good storage stability and weather resistance. A full color image can be obtained by selecting a dye.

[Brief description of drawings]

The drawings are graphs showing the relationship between image density and recording energy using the heat-sensitive transfer recording medium of the embodiment of the present invention.

Claims (1)

[Claims] 1. A heat-sensitive transfer recording medium comprising a support and a thermal transfer ink layer comprising a fine porous resin and a heat-meltable ink component containing a heat-meltable substance solid at room temperature and a colorant as main components. 2. The heat-sensitive transfer recording medium according to, wherein the resin comprises cellulose acetate butyrate in which the proportion of butyryl groups to the total of acetyl groups and butyryl groups is 38% or less.