JPH02214692A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To form a recording image excellent in color reproducibility by using a dye having a narrow absorbing width as the dye having main absorption max. on the shortest wavelength side among two or more kinds of the cyan dyes contained in a dye layer. CONSTITUTION:A sublimable dye layer is a layer wherein cyan dyes are supported by an arbitrary binder resin and said cyan dyes are used as a mixture of two or more kinds of cyan dyes. As one of the cyan dyes, a dye (I) having main absorption max. on a relatively long wavelength side, that is, on the side of a wavelength region of 660nm or more when a color is developed on a receiving sheet. The dye of this kind is low in the absorption of a wavelength of 540nm or less becoming a green component. As the other cyan dye (II), one wherein main absorption max. is at 650nm or less and the main absorption peak in an absorption spectrum is sharp and a wavelength width at 50% absorbency is within a range of 50-120nm is pref. When the wavelength width becomes wider than the above mentioned range, it is not pref. because the skirt on the short wavelength side of an absorption curve becomes large in a range of 540nm or less. When these dyes (1), (2) are used in a mixed state, a high density cyan color can be developed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal transfer sheet, and more specifically, an object of the present invention is to provide a thermal transfer sheet that can form a recorded image with excellent color reproducibility of an original.

(Prior art) Various thermal transfer methods have been known in the past, among which a sublimable dye is used as a recording agent, this is supported on a base sheet such as a polyester film to form a thermal transfer sheet, and a sublimable dye is used as a recording agent to form a thermal transfer sheet. 2. Description of the Related Art Various methods have been proposed for forming a full-color image on an image-receiving sheet in which a dye-receiving layer is formed on a dyeable transfer material, such as paper or a plastic film.

In the above-mentioned full-color thermal transfer method, thermal transfer sheets of three or four colors of yellow, magenta, and cyan (and black), or dye layers of these three or four colors, are often formed surface-sequentially on a continuous base sheet. Using a thermal transfer sheet, the thermal head is actuated by an electrical signal that separates the original into three colors or envelopes, and the three or four colors are printed in alignment on two thermal transfer image-receiving sheets, producing a full-color image on the image-receiving sheet. It is intended to reproduce.

The images formed in this way are very clear because the coloring material used is dye, and they have excellent transparency, so the images obtained have excellent intermediate color reproducibility and gradation, and are It is possible to form high-quality images that are similar to images produced by offset printing or gravure printing, and comparable to full-color photographic images.

(Problem to be solved by the invention) When forming a color image from the three primary colors mentioned above, each color should have highly pure spectral characteristics, and in particular, in the case of cyan dye, it should absorb at around 540 nm or less. Ideally, it would have a block-type absorption curve that absorbs wavelengths longer than that.

However, existing cyan dyes exhibit a so-called bell-shaped absorption curve, and the short wavelength side of the absorption curve is 540 nm.
There is a problem in that the brightness and chroma of the cyan image produced by this absorption of 540 nm or less decreases.

These problems become more noticeable as the image density increases, and since components below 540 nm are in the green light range,
There is a problem in that intermediate colors such as green, which are produced when primary colors such as yellow dye are mixed during image formation, become unclear.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermal transfer sheet capable of solving the above-mentioned problems and forming a recorded image with excellent color reproducibility of an original.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides a thermal transfer sheet in which at least a cyan dye layer is formed on one side of a base sheet,
A thermal transfer sheet characterized in that the dye included in the dye layer is composed of two or more types of cyan dyes, and among the cyan dyes, the dye having a main absorption maximum on the shortest wavelength side is a dye with a narrow absorption width. It is.

(Function) By forming the cyan dye layer of the thermal transfer sheet from two or more types of cyan dyes, and using the dye with the main absorption maximum on the shortest wavelength side among the cyan dyes as the dye with the narrowest absorption width. , it is possible to develop a cyan color with few absorption components below 540 nm even at high density, and the recorded image has excellent color reproducibility of not only the cyan color of the original but also intermediate colors synthesized with the cyan color and other colors. Provided is a thermal transfer sheet capable of forming.

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

The base sheet of the thermal transfer sheet 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. paper, various processed papers, polyester film, polystyrene film, polypropylene film, polysulfone film, aramid film, polycarbonate film, polyvinyl alcohol film, cellophane, etc., and particularly preferred is polyester film.

When the base sheet as described above has poor adhesion to the dye layer formed on the surface, it is preferable to subject the surface to a primer treatment or a corona discharge treatment.

Sublimation property (thermal migration property) formed on the base sheet as above
The dye layer is a layer in which cyan dye is supported by an arbitrary binder resin.

The cyan dye used in the present invention may be a dye known for dye sublimation type thermal transfer, and any known cyan dye can be used. In the present invention, two or more of these cyan dyes are used as a mixture, and at least one of them has a relatively long wavelength side, that is, when developed on an image receiving sheet, 6
A dye (I) having a main absorption maximum at 60 nm or more is used. Since the main absorption maximum of such a dye is on the long wavelength side, there is little absorption below 540 nm, which is the green component.

Preferred specific examples of such dye (I) include dyes having the following structure.

etc. Any of these dyes (I) can be used alone or as a mixture.

Other cyan dyes (
II) has a main absorption maximum below 650 nm, and the main absorption peak in its absorption spectrum is sharp;
The top of the peak in the absorption spectrum is 100% absorbance.
Where, the wavelength width at 50% absorbance is preferably in the range of 50 to 120 nm. When the wavelength width becomes wider than the above range, the short wavelength side of the absorption curve becomes 540
It becomes large in the range of nm or less, which is not preferable for achieving the object of the present invention.

Preferred examples of the dye (II) include the following. Any of these dyes (II) can be used alone or as a mixture.

The preferred mixing ratio of dye (I) and dye (If) as described above is 5:95 to 95. :5 weight ratio.

The feature of the present invention is that the dye (I) and dye (2) as described above are used in a mixed manner, thereby producing an ideal cyan color with a high concentration and a small amount of absorption components below 540 nm. I can do it. On the other hand, when dye (I) is used alone, the color reproduction gamut is narrow;
) If used alone, the color density will be low and the hue will deviate from the ideal cyan color, resulting in insufficient reproduction of excellent cyan colors and intermediate colors.

As the binder resin for supporting the above-mentioned heat-transferable dye, any conventionally known binder resin can be used, and preferred examples include ethyl cellulose, droxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl cellulose, Cellulose resins such as methylcellulose, cellulose acetate, and cellulose acetate, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinylpyrrolidone,
Vinyl resins such as polyacrylamide, polyesters, etc. may be mentioned, and among these, cellulose-based, acetar-based, polyester-based, butyral-based, polyester-based, etc. are particularly preferred.

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

Preferably, such a dye layer is prepared by adding the above-mentioned sublimable dye, binder resin, and other optional components in a suitable solvent, dissolving or dispersing each component, and preparing a paint or ink for forming the dye layer, which is then added to the above-mentioned solvent. It is formed by coating and drying it on a base sheet. .

The dye layer thickness formed in this way is 0.2 to 5.0 μm,
The thickness is preferably about 0.4 to 2.0 μm, and the sublimable dye in the dye layer is about 5 to 90 μm of the weight of the dye layer.
Suitably it is present in an amount of 10% to 70% by weight.

The thermal transfer sheet of the present invention as described above may be provided with a heat-resistant layer on its back surface in order to prevent the adverse effects of the heat of the thermal head.

The above is the basic structure of the thermal transfer sheet of the present invention. However, the thermal transfer sheet of the present invention may be a monochrome sheet having only the cyan dye layer. In this case, when forming a full color image, yellow, magenta (and Use a thermal transfer sheet of another color (black). Further, in a preferred embodiment of the present invention, a thermal transfer method is employed, in which each of yellow and magenta (and black) dyes is provided on a continuous base sheet, along with the cyan dye layer, sequentially, for example, alternately at intervals of 30 cm width. It can be made into a sheet.

The image-receiving sheet used to form an image using the thermal transfer sheet as described above may be of any type as long as its recording surface has dye-receptive properties for the above-mentioned dyes. In the case of paper, metal, glass, synthetic resin film or sheet, etc., which do not have a dye-receiving property, a dye-receiving layer may be formed on at least one surface thereof from a resin having excellent dye-receptivity. In addition, such a dye-receiving layer may contain solid waxes such as polyethylene wax, amide wax, and Teflon powder, which are known as release agents, fluorine-based or phosphate-based surfactants, silicone oil, etc. preferable.

As the means for applying thermal energy during thermal transfer used in the present invention, any conventionally known applying means can be used. By controlling the recording time, 5 to 100 mJ/
The intended purpose can be fully achieved by applying thermal energy of the order of mtn'.

(Effects) According to the present invention as described above, the cyan dye layer of the thermal transfer sheet is formed from two or more types of cyan dyes, and among the cyan dyes, a dye having a main absorption maximum on the shortest wavelength side is used. By using a dye with a narrow absorption width, it is possible to produce a cyan color with few absorption components below 540 nm even at high concentrations, and it is possible to produce a cyan color that has few absorption components below 540 nm, and can be used not only for the cyan color of the original but also for the intermediate color synthesized with the cyan color and other colors. A thermal transfer sheet capable of forming recorded images with excellent color reproducibility etc. is provided.

(Example) Next, the present invention will be explained in more detail by giving examples and comparative examples. In the text, parts or percentages are based on weight unless otherwise specified.

Example An ink composition for forming a dye layer having the following composition was prepared, and applied to a 6 μm thick polyethylene terephthalate film whose back surface was heat-resistant treated so that the dry coating amount was 1.0 g/♂, and dried. Thermal transfer sheets of the present invention shown in Table 1 were obtained.

Polyvinyl butyral resin 4.5 parts Methyl ethyl ketone 46.25 parts Toluene
46.25 parts However, when the dye mixture was insoluble in the above composition, DMF, dioxane, chloroform, etc. were appropriately used as a solvent.

In addition, a yellow thermal transfer sheet was prepared using a yellow dye (Foron Brilliant Yellow S-6GL) as the dye.

Next, synthetic paper (Yubo FP manufactured by Tamago Yuka Co., Ltd.) was used as a base sheet.
G#150), apply a coating liquid with the following composition on one side at a rate of 10.0g/rn' when dry,
It was dried at 00° C. for 30 minutes to obtain a thermal transfer image-receiving sheet.

Polyester resin (Vylon200, manufactured by Toyobo) 11
．． 5 parts vinyl chloride/vinyl acetate copolymer (VYIIH1UCC
5.0 parts amino-modified silicone (F-393, manufactured by Shin-Etsu Chemical) 1.2 parts epoxy-modified silicone (X-22-343, manufactured by Shin-Etsu Chemical) 1.2 parts methyl ethyl ketone/toluene/cyclohexanone (Weight ratio 4:4:2) 102.0 parts The above yellow thermal transfer sheet and the above image receiving sheet were placed one on top of the other with their respective dye layers and dye receiving surfaces facing each other, and a head was applied from the back side of the thermal transfer sheet. Voltage 10V, printing time 4,
Solid printing was performed with a thermal head under the conditions of 0.01 sec, and then the same pattern was printed on the same image receiving sheet using the cyan thermal transfer sheet of the present invention, overlapping the yellow image to form a recorded image. Cyan single-color solid printing was also performed in parallel, and the results shown in Table 1 below were obtained.

70/30 70/30 4 Q/60 80/20 80/20 60/40 60/40 30/70 80/20 7 2 40/fi0 1.83 ◎
◎7 3 50150 1.95
◎ ◎8 3 70/:1G 2.
05 0 ◎8 4 50150
1.95 00 The mixing ratios in the table above are based on weight. Further, the hue of all mixed dyes is cyan.

Comparative Example The dyes shown in Table 2 below were used in place of the dyes in the Examples, and the results shown in Table 2 below were obtained in the same manner as in the Examples.

"2" 6 50150 61 dye: dye (I) @ 2 dye: dye (I) 13 dye: dye (n) 84 dye: dye (n) 15 dye: 1,95 1 of 2 1 of 4 06 Dye: 1'2 ''4 The coloring density mentioned above is a value measured with a densitometer RD-918 manufactured by Macbeth Co., Ltd. in the United States.

Color reproducibility was evaluated visually.

◎: Extremely clear ○：Clear "t 075G Δ: Slightly unclear ×: Unclear Procedural amendment (spontaneous)

Claims (3)

[Claims] (1) In a thermal transfer sheet in which at least a cyan dye layer is formed on one side of a base sheet, the dye included in the dye layer is composed of two or more cyan dyes, and among the cyan dyes, A thermal transfer sheet characterized in that a dye having a main absorption maximum on the shortest wavelength side is a dye having a narrow absorption width. (2) The thermal transfer sheet according to claim 1, wherein one of the dyes has a main absorption maximum on the long wavelength side of 660 nm or more, and the other dye has a main absorption maximum on the long wavelength side of 650 nm or less. (3) The thermal transfer sheet according to claim 1, wherein the dye having a main absorption maximum at 650 nm or less has a wavelength width of 50 to 120 nm at 50% absorbance of the main absorption maximum.