JPS63302089A - Production of thermal transfer sheet - Google Patents

Abstract

PURPOSE:To eliminate irregularities in density or in color forming of transferred images, by applying at least two times a liquid composition comprising a thermally transferable dye, a binder and a liquid medium to the same region of one side of a base sheet, thereby providing a thermally transferable dye layer. CONSTITUTION:A liquid composition comprising a thermally transferable dye, a binder and a liquid medium is applied at least two times to the same region of one side of a base sheet such as a paper, a converted paper and a plastic film to provide a thermally transferable dye layer, thereby producing a thermal transfer sheet. The application of the dye-forming ink (liquid composition) to the surface of the base sheet is preferably carried out by gravure printing using a gravure roll, and the coating weight per one application is preferably about 0.4-1.5 g/m<2> as solid components. The coating weight in the second or latter application is preferably equal to or smaller than that in the first application, and is about 0.3-1.2 g/m<2> as solid components.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more specifically, a dye layer that transfers by heating is provided on a base sheet, and the dye layer is transferred by heating the sheet in an imagewise manner. This invention relates to a thermal transfer sheet for forming an image by transferring dye therein to another transfer material.

(Prior art) Conventionally, a dye layer is formed on a heat-resistant base sheet using a sublimable dye (thermally transferable dye) such as a disperse dye to form a thermal transfer sheet. A method is used in which the thermal transfer sheet is placed on a transferable material that can be dyed and heated from the back side of the thermal transfer sheet using a thermal head, etc. according to the image signal, and the dye on the thermal transfer sheet is thermally transferred to the transferable material to form an image. . This thermal transfer method can easily form a full-color image, and can also form an excellent image comparable to that of a color photograph.

Thermal transfer sheets as described below are generally made by coating one side of a base sheet such as a plastic film with a liquid composition consisting of a heat-transferable dye and an organic solvent containing a binder using various coating methods to form a dye layer. It is done by forming.

The dye layer formed in this way preferably has a high dye concentration and a uniform thickness in order to improve the quality of the transferred image to be formed, and for this purpose, a gravure printing method is generally adopted. ing.

(Problems to be Solved by the Invention) When forming a transferred image on a transfer material using a thermal transfer sheet as described above, there is no major problem if the desired transferred image is a large image. , the desired image is a fine-grained image,
Further, in the case of a detailed full-color image comparable to a photograph, problems such as density unevenness and non-uniformity of color development have arisen in the transferred image.

In addition, the dye liquid used is one in which the dye is finely dispersed in a liquid medium or one in which the dye is dissolved. Average and instability are likely to occur, and furthermore, the dye layer formed is a microscopically heterogeneous phase, so when such a dispersion is used, even if the coating layer itself has a uniform thickness, In fine transferred images, there is a drawback that the above-mentioned density unevenness, spots, uneven color development, etc. occur.

If a soluble dye liquid is used to solve these drawbacks, the solubility of the dye is insufficient in organic solvents suitable for gravure inks, so the dye must be applied at a high concentration. A problem has arisen in that it is difficult to form a dye layer containing the dye, and therefore a transferred image with sufficient density cannot be obtained.

Therefore, there is a demand for a thermal transfer sheet that provides high-quality transferred images with high density and no color unevenness even if the transferred images are fine.

(Means for Solving the Problems) The present inventor completed the present invention as a result of intensive research in order to solve the above problems.

That is, the present invention provides a method for manufacturing a thermal transfer sheet in which a heat-transferable dye layer is formed on one surface of a base sheet, in which a liquid composition consisting of a heat-transferable dye, a binder, and a liquid medium is applied to the same area at least twice. This is a method for producing a thermal transfer sheet, which is characterized by coating.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments of the present invention.

The base sheet used in the method of the present invention may be any conventionally known material having a certain degree of heat resistance and strength, for example, a thickness of about 0.5 to 50 μm, preferably about 3 to 10 μm. They include paper, various processed papers, polyester films, polystyrene films, polypropylene films, polysulfone films, polycarbonate films, polyvinyl alcohol films, cellophane, etc., and polyester films are particularly preferred.

The heat-transferable dye layer provided on the surface of the base sheet as described above is a layer in which the following heat-transferable dye is supported by an arbitrary binder resin.

As the dye to be used, any dye used in conventionally known thermal transfer sheets can be effectively used in the present invention.
Not particularly limited. For example, some preferred dyes include Sumiplus Red 301, PTR as a red dye;
-51, Seriton Red 5F-7864, Sumiplast Red B1 Mihara Oil Red, and yellow dyes include PTY-51 and ICl-C-5G.

Examples include Miketon Polyester Yellow YL, and
Examples of the blue dye include Kayaset Blue A-2R, Diaresin Blue N, PTB-76, and PTV-54.

As the binder resin for supporting the heat-transferable dye as described above, any conventionally known binder resin can be used, and preferred examples include ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl cellulose, methyl cellulose, Examples include cellulose resins such as cellulose acetate and cellulose acetate, and vinyl resins such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinylpyrrolidone, and polyacrylamide. Among these, polyvinyl butyral and polyvinyl acetal are heat-resistant. This is preferable from the viewpoints of properties, dye migration properties, and the like.

In the present invention, as the ink solvent for dissolving or dispersing the above-mentioned dye and binder resin, any conventionally known ink solvent can be used.Specifically, alcohol-based ink solvents include methanol, ethanol, isopropyl alcohol, butanol, and isobutanol. Ketones such as methyl ethyl ketone, medyl isobutyl ketone, cyclohexanone, etc., aromatic systems such as toluene, xylene, etc., halogen systems such as dichloromethane, trichlorothane, dioxane, tetrahydrofuran, etc., formamide, dimethylformamide, dimethyl sulfoxide, or the above solvents. Mixtures may be mentioned. These solvents are preferably selected and used so that the dye to be used has a predetermined concentration or higher and the binder resin is sufficiently dissolved or dispersed. For example, it is preferable to use the solvent in an amount of about 200 to 5 times the total weight of the dye and binder resin.

The heat-transferable dye layer of the thermal transfer sheet used in the present invention is basically formed from the above-mentioned materials, but may also contain various conventionally known additives as required.

Such a heat-transferable dye layer is preferably prepared by adding the heat-transferable dye, binder resin, and other optional components to a suitable solvent and dissolving or dispersing each component to prepare an ink for forming the dye layer. This is formed by coating and drying this on the above base sheet.

Although any conventionally known method may be used for applying the ink, a preferred method is a gravure printing method.

The heat-transferable dye layer formed in this way has a thickness of about 0.2 to 5.0 μm, preferably about 0.4 to 2.0 μm, and the heat-transferable dye in the dye layer is 5 to 70% by weight of the layer, preferably 10 to 60% by weight
Suitably, it is present in an amount of .

The method of the present invention is characterized in that when forming a thermal transfer sheet by coating one side of the base sheet with the ink as described above, the ink is applied at least twice to the same area. .

In the prior art, ink was generally applied only once, but when ink is applied only once, especially when gravure printing is used as the coating method,
From a microscopic perspective, coating unevenness was caused by the uneven surface of the gravure plate. If the desired image is relatively large and rough, such coating unevenness does not cause any problems with the resulting image, but if the desired image is high-quality, such as a color photograph, In order to ensure quality, the non-uniformity of the ink layer thickness is reflected in the rolled image.

In the present invention, it has been found that the above-mentioned coating unevenness can be easily solved by an overprinting method in which ink is applied at least twice. In the method of the present invention, the number of times of printing only needs to be two or more, and although it is also possible to print three or more times, a sufficiently uniform coating layer is usually formed with two times of printing.

The ink coating method used in the method of the present invention may be any conventionally known coating method and is not particularly limited, but a preferred method is a gravure printing method using a gravure roll. Regarding the particularly preferred gravure roll and coating amount, the number of lines of the gravure roll used initially is 4.
It is preferably about 0 to 100 lines/cm, and the plate depth is about 15 to 50 μm, and the solid content is about 0 to 5 to 15 g/rn'-wet per coating.
It is preferable to have a coating characteristic of 64 to 1.5 g/rn2. The coating amount of the gravure roll used for the second and subsequent coatings is preferably the same as or smaller than that of the first gravure roll, for example, about 12 to 40 g/rlf-
The wet and solid content is preferably about 0.3 to 1.2 g/rn'.

Further, according to detailed research by the present inventor, the recesses A on the plate surface of the gravure roll used are continuous and open in one direction, preferably in the direction perpendicular to the rotational direction of the roll, as shown in the first figure. It has been found that a dye layer of this type can form a dye layer of better uniformity. For kneading, it can be used even when the four parts of the plate are not continuous with the four adjacent parts as shown in the second figure, but it is inferior to the one shown in the first figure in terms of uniformity of the coating layer. It was something.

The transfer material used to form an image using the thermal transfer sheet as described above may be any material as long as its recording surface has dye receptivity to the above-mentioned dyes. If the material is paper, metal, glass, synthetic resin, etc. that does not have any properties, a dye-receiving layer may be formed on at least one surface thereof.

Examples of transfer materials that do not require a special dye-receiving layer include polyolefin resins such as polyethylene and polypropylene, halogenated polymers such as polyvinyl chloride and polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl alcohol. Vinyl polymers such as acrylic ester, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polystyrene resins,
Polyamide resins, copolymer resins of olefins such as ethylene and propylene and other vinyl monomers, ionomers, cellulose resins such as cellulose diacetate and cellulose triacetate, polycarbonates, polysulfones, polyimides, etc., 1am, woven fabrics, and films. , sheets, molded products, etc. Particularly preferred are sheets or films made of polyester, or processed paper provided with a polyester layer.

Furthermore, in the present invention, a solution or dispersion of the above-mentioned dyeable resin is applied and dried on the recording surface of paper, metal, glass, or other transfer material that is adhesive to the bridge of the nose. By laminating a resin film, it can be used as a transfer material. Furthermore, even if the transfer material has the dyeability described above, a dye-receiving layer may be formed on the surface thereof from a resin having better dyeability, as in the case of the paper described above.

The dye-receiving layer thus formed may be formed from a single material or from a plurality of materials, and may also contain various additives within the range that does not impede the purpose of the present invention. Of course.

Such a dye-receiving layer may be of any thickness, but typically has a thickness of 5 to 50 μm. Although such a dye-receiving layer is preferably a continuous coating, it may also be formed as a discontinuous coating using a resin emulsion or resin dispersion.

The thermal energy key application means used when performing thermal transfer using the above thermal transfer sheet and the above transfer material are as follows:
Any conventionally known application means can be used, and for example, by controlling the recording time using a recording device such as a thermal printer (for example, Toshiba ■, Thermal Printer TN-5400), 5 to 100 mJ/mrI can be applied.
A desired image is formed by applying thermal energy of about I'.

(Functions and Effects) According to the present invention as described above, the following effects are achieved compared to conventional methods.

(]) Since the dye layer formed on the base sheet has a uniform thickness, it is possible to provide a high-quality transferred image without uneven density or uneven color development.

(2) When using dye-soluble ink, even if the dye concentration in the ink used is low, by overprinting two or more times, the dye layer containing a high concentration of dye can be formed. Therefore, a high-density transferred image can be provided.

Next, the present invention will be explained in more detail with reference to Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 Eρ no Riko MS Red G 2.8
Part 6 Macrolex Red Violet, R1
, 56 parts Polybutyral resin 4.32 parts Methyl ethyl ketone 43.34 parts Toluene 42.92 parts Cyclohexanone 5.00 parts An ink having the following composition was prepared, and this ink was used to initially print a line width of 54 lines/cm. , the dry coating amount is approximately 0.6 using a gravure roll with a plate depth of 36 μm.
g/rn' on a 9 μm thick polyethylene terephthalate film with a heat-resistant treatment on the back side of the plastic, and then dried, followed by a second coating with the same gravure roll and the same coating amount. A dye layer having a total thickness of 1.1 μm was formed to obtain a thermal transfer sheet. Examples 2-9
and Comparative Examples 1 to 3 Thermal transfer sheets of the present invention and comparative examples were obtained in the same manner as in Example 1 except that the gravure roll shown in Table 1 below was used in place of the gravure roll in Example 1.

For the transfer sheets of Examples 1 to 9 above, the coating surface was examined with an optical microscope to check the uniformity of the dye layer. △ for uniform and X for non-uniform
It is shown in Table 1 as follows.

Next, synthetic paper (Yupo FP manufactured by Tamago Yuka Co., Ltd.) was used as a base sheet.
G #l50), apply a coating liquid with the following composition to one side at a rate of 4.5g/rn2 when dry,
The material to be transferred was obtained by drying at 00° C. for 30 minutes.

Polyester resin (Vylon200, manufactured by Toyobo) 11
．． 5 parts Vinyl chloride-vinyl acetate copolymer (VY, manufactured by IIcc) 5.0 parts Amino-modified silicone oil (F-393, manufactured by I3-Koshi Chemical Industry Co., Ltd.) 1.2 parts Epoxy-modified silicone oil (X -22-343,
Shin-Etsu Chemical Co., Ltd.) 1.2 parts Methyl ethyl ketone/toluene/cyclohexanone (weight ratio 4:4:2) 102 parts The magenta dye layer of the thermal transfer sheet and the transfer material,
The magenta dye layer and the dye-receiving surface are stacked facing each other,
The width is 0 with the thermal head under the conditions of 10V applied voltage to the head from the back of the thermal transfer sheet, printing time 4.0 m5ec,
．． A continuous line of 1 mm was transferred to obtain a magenta line image.

Observe these transferred line images with an optical microscope. If the line is continuous with uniform density, it is ◎. If there is some shading, but the line is sufficiently continuous, the O1 line is continuous or has clear shading. Those with a number of wire breaks are indicated as △, and those with multiple disconnections are indicated as X.

〜U 1 -1ゝI I-AI-A -00 211-A II-A II-A ◎ O3
l11-A m-A m-A ◎ O4
1V-A IV-A TV-A ◎
O5V-A I-A -〇 06V-
AIV-A -◎ ◎7I-BI-A
-○ 0 8 I-B II-A -○ 0
9V-BV-B -Δ Δ Comparative Example I I -A --X X2U-B-xx 3 III -B --x In the above, I to V, A and B are as follows.

■ = Number of lines 54/cm, plate depth 36 μm II: Number of lines 607 cm, plate depth 30 μm ■ Number of double lines 70/cm, plate depth 20 μm ■: Number of lines 8 o'/cm, plate depth 14 μm ■ = Number of lines 40
7cm, plate depth 45μm A: Concave portions on the plate surface are continuous. B: Concave portions on the plate surface are discontinuous.

[Brief explanation of the drawing]

FIG. 1 shows a part of the plate surface of a gravure roll in which the concave portions of the plate surface are continuous, and FIG. 2 shows a part of the plate surface of a gravure roll in which the concave portions of the plate surface are discontinuous. A: Concave portion B: Convex portion Fig. 1 Fig. 2

Claims (6)

[Claims] (1) In a method for manufacturing a thermal transfer sheet in which a heat-transferable dye layer is formed on one side of a base sheet, a liquid composition consisting of a heat-transferable dye, a binder, and a liquid medium is applied to the same area at least twice. A method for producing a thermal transfer sheet, characterized by: (2) The method for producing a thermal transfer sheet according to claim (1), wherein the coating method is a gravure printing method. (3) The method for producing a thermal transfer sheet according to claim (1), in which the first coating and subsequent coatings are performed using a gravure roll with the same coating amount. (4) The method for producing a thermal transfer sheet according to claim (2), wherein the coating amount of the gravure roll from the second time onwards is smaller than the coating amount of the first time. (5) The method for manufacturing a thermal transfer sheet according to claim (2), wherein the concave portions of the plate surface of the gravure roll are connected in a direction perpendicular to the printing direction. (6) The method for producing a thermal transfer sheet according to claim (1), wherein the liquid composition is a dye solution containing a binder.