JPH0768947A - Heat transfer sheet - Google Patents

Abstract

PURPOSE:To provide a heat transfer sheet wherein a dye layer is easily formed and dye transferring characteristics is excellent and a printed image with excellent coloring density, clarity and durability is provided. CONSTITUTION:A dye layer consisting of a dye and a binder is provided on a base film and the dye layer contains 0.001-5% high b.p. polar org. solvent with a b.p. of 80-190 deg.C and a dielectric const. epsilon of 10<=epsilon<=50 to the wt. of the dye layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer sheet, and more specifically, it is useful for a thermal transfer system using a sublimable dye (thermal transferable dye), and has excellent dye transferability during thermal transfer and excellent image density. The purpose is to provide a thermal transfer sheet capable of giving a heat transfer.

[0002]

2. Description of the Related Art Inkjet systems, thermal transfer systems, etc. have been developed as a method for simply and rapidly providing an excellent monocolor or full-color image in place of conventional general printing methods and printing methods. , The so-called sublimation heat transfer method, which uses a sublimable dye, has the best continuous gradation and gives a full-color image comparable to a color photograph. The thermal transfer sheet used in the sublimation type thermal transfer system described above forms a dye layer composed of a sublimable dye and a binder on one surface of a substrate film such as a polyester film, and, on the other hand, in order to prevent the thermal head from sticking. A substrate having a heat-resistant layer provided on the other surface of the substrate film is generally used. The dye layer surface of such a thermal transfer sheet is superposed on a transfer material having an image receiving layer made of polyester resin or the like, and the dye in the dye layer is transferred to the transfer material by imagewise heating with a thermal head from the back surface of the thermal transfer sheet. The desired image is formed by shifting.

[0003]

In the thermal transfer system as described above, only the dye migrates from the dye layer to the material to be transferred, and the binder remains on the base film side. On this occasion,
The better the transferability of the dye, the clearer and the higher the density of the image is formed. As a method for improving the transferability of the dye,
There is a method of using a dye having a relatively low molecular weight and good solubility in a solvent as a dye, a method of increasing the dye content of the dye layer, and the like, but the image formed by the former method is clear and beautiful. However, there are problems that the light resistance and bleeding resistance of the image are poor and an image having excellent fastness is not formed, and that the dye bleeds out on the surface during storage of the thermal transfer sheet. Also, when a dye having good solubility is dissolved in a general-purpose solvent at a high concentration to form a dye layer, the dye in the coating liquid may be deposited on the doctor part or the plate surface during coating due to the high volatility of the general-purpose solvent. However, there is a problem that a uniform dye layer is not formed. Further, in the latter method, it is essential to increase the dye concentration in the coating liquid used for forming the dye layer, but when the dye has low solubility in a general-purpose solvent, the dye concentration in the dye layer is increased. Is difficult. In particular, a dye having a relatively high molecular weight and a rigid dye having a large number of polar groups (generally having good fastness) are not sufficiently dissolved in a general-purpose solvent.

Further, when a black dye layer is prepared by mixing three color dyes, the solubility of each dye in a general-purpose solvent is different, so that a part of the dye precipitates in the state of the coating liquid,
There is a problem that a dye layer having a desired composition cannot be formed.
In order to solve these problems, it is possible to use a solvent having a high solubility for the dye, but in this case, the boiling point of the solvent used is high, and the drying step after forming the dye layer becomes a problem, and, A relatively large amount of residual solvent remains in the formed dye layer, and the resulting thermal transfer sheet has problems of blocking and storage stability. Therefore, the object of the present invention is to easily form a dye layer, and also excellent in dye transferability, color density,
It is an object of the present invention to provide a thermal transfer sheet which gives an image excellent in sharpness and durability.

[0005]

The above object can be achieved by the present invention described below. That is, the present invention is a substrate film provided with a dye layer comprising a dye and a binder,
The dye layer has a boiling point of 80 to 190 ° C. and a dielectric constant ε of 10 ≦.
It is a thermal transfer sheet characterized by containing a high boiling point polar organic solvent with ε ≦ 50 in the range of 0.001 to 5% by weight of the dye layer.

[0006]

[Function] When forming the dye layer, a solvent having a good drying property is added.
When a dye layer is prepared by using a mixed solvent prepared by mixing a small amount of a specific polar solvent having high dye solubility, the dye is well dissolved in the mixed solvent, and it is easy to form a dye layer having a high dye concentration. . Further, by positively leaving a small amount of a polar solvent in the dye layer formed in this way, the precipitation or aggregation of the dye in the dye layer is eliminated, and at the time of thermal transfer, the action of the polar solvent causes the dye to heat up. The transferability is improved. Therefore, even if a high-molecular weight dye having a relatively low solubility, a dye having a low molecular weight but a low solubility, a mixed dye, or a high concentration of a dye is used, the formation of the dye layer is easy, and
It is possible to provide a thermal transfer sheet which is excellent in heat transfer property of a dye, gives an image excellent in color density, sharpness and various durability and is also excellent in storability.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. The thermal transfer sheet of the present invention,
Basically, a dye layer is formed on a substrate film as in the prior art, but the dye layer is characterized by containing a small amount of a high boiling polar organic solvent. The substrate film of the thermal transfer sheet of the present invention as described above may be any one as long as it has a conventionally known degree of heat resistance and strength, for example, 0.5 to 50 μm, preferably 3 to 10 μm. Paper having a certain thickness, various processed papers, polyester film, polystyrene film, polypropylene film, polysulfone film, aramid film, polycarbonate film, polyvinyl alcohol film, cellophane, etc. are particularly preferable. These substrate films may be of single-wafer type or continuous film, and are not particularly limited.

The dye layer formed on the surface of the base film is a layer in which a dye is carried by an arbitrary binder resin. As the dye to be used, any of the dyes used in conventionally known thermal transfer sheets can be used in the present invention, but in the present invention, a relatively low solubility high molecular weight dye represented by the following formula, When a dye having a low molecular weight but low solubility, or a mixed dye thereof is employed, or when these dyes are used after being dissolved in a high concentration, a remarkable effect can be obtained. That is, these dyes have a high affinity with polar solvents, the dyes are well dissolved, and the polar solvent exists in the dye layer in a state of being associated with dye molecules in the dye layer.
Therefore, the precipitation or aggregation of the dye in the dye layer does not occur,
In addition, during thermal transfer, the polar solvent accelerates the heat transfer property of the dye.

[0009]

[Chemical 1]

As the binder resin for supporting the dye as described above, any conventionally known binder resin can be used, and preferred examples include ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxycellulose, hydroxypropyl cellulose, methyl cellulose and acetic acid. Cellulose, cellulosic resins such as cellulose acetate butyrate,
Polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone, vinyl resins such as polyacrylamide, polyesters, and the like. Among these, cellulose-based,
Acetal-based, butyral-based, polyester-based and the like are preferable from the viewpoints of heat resistance, dye migration, and the like. Further, the dye layer may further contain various conventionally known additives such as a release agent and an ultraviolet absorber, if necessary.

The dye layer is preferably methyl ethyl ketone, which is widely used in the fields of gravure ink and coatings.
Using a general-purpose low boiling point solvent such as methyl isobutyl ketone, ethyl acetate, toluene, xylene or a mixture thereof as a main solvent, the boiling point is 80 to 190 ° C. and the dielectric constant ε is 10 ≦ ε ≦ 5.
A high boiling polar organic solvent having a boiling point of 0, for example, dimethylformamide, dimethylsulfoxide, cyclohexanone, or a mixed solvent of a mixture thereof is added with the sublimable dye, the binder resin and other optional components, and each component is added. It is dissolved to prepare a dye layer-forming coating material or ink, which is applied onto the above-mentioned substrate film and dried to form it. The ratio of the mixed solvent used at this time is preferably 1 to 10 parts by weight of the high boiling point solvent per 100 parts by weight of the low boiling point solvent. If the amount of the high-boiling point organic solvent used is too large, a large amount of the high-boiling point solvent remains in the dye layer, which causes a problem in the storage stability of the thermal transfer sheet. On the other hand, when the amount used is too small, the solubility of the dye and the content of the organic solvent in the dye layer are low, which makes it difficult to achieve the object of the present invention.

The dye layer thus formed has a thickness of 0.2 to
It has a thickness of about 5.0 μm, preferably 0.4 to 2.0 μm, and the sublimable dye in the dye layer is 5 to 90% by weight, preferably 10 to 70% by weight of the weight of the dye layer. It is preferably present in an amount. The dye layer to be formed is formed by selecting one color from the above dyes when the desired image is a mono color image, and when the desired image is a full color image, for example, a suitable cyan, magenta and Select yellow (and black if necessary) to select yellow,
Dye layers of magenta and cyan (and optionally black) are formed on the substrate sheet in a frame-sequential manner.

The amount of the high-boiling-point organic solvent left in the dye layer formed as described above is 0.001 to the weight of the dye layer.
The range of 5% by weight and 0.5 to 5% by weight is preferable, and the range of such content can be arbitrarily adjusted by the mixing ratio of the solvent used, the drying temperature and the drying time of the coated dye layer.
If the content of the high boiling point organic solvent is too large, problems such as storage stability (blocking) of the thermal transfer sheet occur, while if the content is too small, precipitation or aggregation of the dye in the dye layer occurs, or The effect of improving the heat transfer property of the dye at the time of thermal transfer is small, and a thermal transfer sheet giving an image excellent in color density and sharpness cannot be obtained.

The material to be transferred used for forming an image using the above-mentioned thermal transfer sheet may be any material as long as its recording surface has dye acceptability for the above dye, and In the case of paper, metal, glass, synthetic resin or the like having no dye-receptive property, the dye-receptive layer may be formed on at least one surface thereof. The thermal energy applying means used when performing thermal transfer using the thermal transfer sheet and the recording material as described above, any conventionally known applying means can be used, for example, a thermal printer (for example, manufactured by Hitachi, Video printer VY-100)
A desired image is formed by applying a thermal energy of about 5 to 100 mJ / m ² by controlling the recording time with a recording device such as the above.

[0015]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the text, parts and% are based on weight unless otherwise specified. Example 1 A 6 μm thick polyethylene terephthalate film having a heat-resistant back surface on which a dye layer was formed as a base film was coated with the following ink composition for forming a dye layer to a dry thickness of 1.0 g / m 2. ^A dye layer was formed by applying gravure printing and drying so as to obtain 2, and a thermal transfer sheet of the present invention was obtained. Ink composition (yellow) : Yellow dye (Formula 1) 3.0 parts Polyvinyl acetal resin (S-REC KS-5, Sekisui Chemical Co., Ltd.) 3.5 parts Methyl ethyl ketone 45.5 parts Toluene 46.0 parts Dimethylformamide (ε = 37) , Bp = 153 ° C.) 2.0 parts

Example 2 Instead of the ink composition for forming a dye layer in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (magenta) : Magenta dye (Formula 2) 3.0 parts Polyvinyl acetal resin (ESREC KS-5) 3.5 parts Methyl ethyl ketone 44.0 parts Toluene 44.5 parts Dimethylformamide 3.0 parts

Example 3 Instead of the ink composition for forming a dye layer in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (cyan): Cyan dye (Formula 3) 3.0 parts Polyvinyl acetal resin (ESREC KS-5) 3.5 parts Methyl ethyl ketone 44.0 parts Toluene 44.5 parts Dimethyl sulfoxide (ε = 45, bp) . = 189 ° C.) 3.0 parts

Example 4 Instead of the dye layer forming ink composition in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (black): Yellow dye (Formula 4) 1.6 parts Magenta dye (Formula 5) 1.6 parts Cyan dye (Formula 6) 5.2 parts Polyvinyl acetal resin (ESREC KS-5) 3. 8 parts Methyl ethyl ketone 40.8 parts Toluene 41.0 parts Dimethylformamide 1.0 parts Cyclohexanone (ε = 18, bp = 156 ° C.) 5.0 parts

Example 5 Instead of the ink composition for forming a dye layer in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (yellow): Yellow dye (Formula 1) 3.0 parts Ethyl cellulose resin (manufactured by Hercules) 3.0 parts Methyl ethyl ketone 46.0 parts Toluene 46.0 parts Dimethylformamide 2.0 parts

Example 6 Instead of the ink composition for forming a dye layer in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (magenta) : Magenta dye (Formula 2) 5.0 parts Ethyl cellulose resin (manufactured by Hercules) 3.0 parts Methyl ethyl ketone 44.5 parts Toluene 44.5 parts Dimethylformamide 3.0 parts

Example 7 Instead of the dye layer forming ink composition in Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (cyan) : Cyan dye (Formula 3) 3.0 parts Ethyl cellulose resin (manufactured by Hercules) 3.0 parts Methyl ethyl ketone 44.5 parts Toluene 44.5 parts Dimethylformamide 5.0 parts

Example 8 Instead of the dye layer forming ink composition of Example 1,
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (black): Yellow dye (Formula 4) 1.6 parts Magenta dye (Formula 2) 1.6 parts Cyan dye (Formula 5) 5.2 parts Ethyl cellulose resin (Hercules) 3.3 parts Methyl ethyl ketone 41.0 parts Toluene 41.3 parts Dimethylformamide 1.0 parts Cyclohexanone 5.0 parts

Comparative Example 1 Instead of the dye layer forming ink composition of Example 1,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (yellow) : Yellow dye (Formula 1) 3.0 parts Polyvinyl acetal resin (ESREC KS-5) 3.5 parts Methyl ethyl ketone 46.5 parts Toluene 47.0 parts

Comparative Example 2 Instead of the ink composition for forming a dye layer in Example 1,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (magenta): Magenta dye (Formula 2) 5.0 parts Polyvinyl acetal resin (ESREC KS-5) 3.5 parts Methyl ethyl ketone 45.5 parts Toluene 46.0 parts

Comparative Example 3 Instead of the dye layer forming ink composition of Example 1,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (cyan) : Cyan dye (Formula 3) 3.0 parts Polyvinyl acetal resin (ESREC KS-5) 3.5 parts Methyl ethyl ketone 46.5 parts Toluene 47.0 parts

Comparative Example 4 Instead of the dye layer forming ink composition of Example 1,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (black) : Yellow dye (Formula 4) 1.6 parts Magenta dye (Formula 5) 1.6 parts Cyan dye (Formula 3) 5.2 parts Polyvinyl acetal resin (ESREC KS-5) 3. 8 parts Methyl ethyl ketone 43.8 parts Toluene 44.0 parts Dimethylformamide 5.0 parts Cyclohexanone 5.0 parts

Comparative Example 5 Instead of the dye layer forming ink composition of Example 1,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the following ink composition was used. Ink composition (black) : Yellow dye (Formula 4) 1.6 parts Magenta dye (Formula 5) 1.6 parts Cyan dye (Formula 6) 5.2 parts Polyvinyl acetal resin (ESREC KS-5) 3. 8 parts Methyl ethyl ketone 38.8 parts Toluene 39.0 parts Cyclohexanone 10.0 parts

Next, a synthetic paper (Yupo FPG150, manufactured by Oji Yuka Co., Ltd.) was used as a base film, and one side was coated with a coating solution having the following composition at a rate of 4.5 g / m ² when dried. Then, the dye receiving layer was formed by drying at 100 ° C. for 30 minutes to obtain a transfer material. Coating liquid composition : Polyester resin (Toyobo, Vylon200) 11.5 parts Vinyl chloride-vinyl acetate copolymer (UCC, VYHH) 5.0 parts Amino-modified silicone oil (Shin-Etsu Chemical Co., Ltd., KF393) 1.2 Part Epoxy-modified silicone oil (X-22-343 manufactured by Shin-Etsu Chemical Co., Ltd.) 1.2 parts Methyl ethyl ketone 40.8 parts Toluene 40.8 parts Cyclohexanone 20.4 parts

Thermal Transfer Test The thermal transfer sheets of the above-mentioned Examples and Comparative Examples and the material to be transferred were superposed with the dye layer and the dye receiving layer facing each other, and the thermal head (KMT-85-
6, MPD2), the head applied voltage is 12.0 V,
Applied pulse width 16.0 msec. 1 ms from / line
ec. Step pattern that decreases sequentially every time, 6 line / mm (33.3 msec./line) in the sub-scanning direction
Thermal head recording was carried out under the conditions of the above and the results shown in Table 1 below were obtained.

[0030]

[Table 1]

Measurement of solvent content : Measured by gas chromatography (Shimadzu GL-14A) using a packing material BX-10 at a constant temperature of 150 ° C. Evaluation of print quality : ○ …… Good × …… Poor Evaluation of print quality : ○ …… Good △ …… Slightly bad × …… Poor Evaluation of storability of thermal transfer sheet : 40 ° C., after 2 days storage ○ …… Dye No bleed-out to the surface of the dye. △ …… Some bleed-out to the surface of the dye is present × …… When the residual solvent is 0, the bleed-out to the surface of the dye is remarkable. The adhesion to the material film was poor and blocking occurred during storage. Overall evaluation : ○ …… Good △ …… Slightly bad × …… Poor

[0032]

[Effect] According to the present invention as described above, when forming a dye layer, a dye layer is prepared by using a mixed solvent prepared by mixing a small amount of a specific polar solvent having high dye solubility with a solvent having good drying property. Then, the dye is well dissolved in the mixed solvent, and it is easy to form a dye layer having a high dye concentration. Further, by positively leaving a small amount of a polar solvent in the dye layer formed in this way, the precipitation or aggregation of the dye in the dye layer is eliminated, and at the time of thermal transfer, the action of the polar solvent causes the dye to heat up. The transferability is improved. Therefore, even if a high-molecular weight dye having a relatively low solubility, a dye having a low molecular weight but a low solubility, a mixed dye, or a high concentration of a dye is used, the dye layer can be easily formed and the heat transfer of the dye can be facilitated. It is possible to provide a thermal transfer sheet which is excellent in property, gives an image excellent in color density, sharpness and various durability and is also excellent in storability.

Claims (2)

[Claims] 1. A dye layer comprising a dye and a binder is provided on a base film, and the dye layer has a boiling point of 80.
A thermal transfer sheet comprising a high boiling point polar organic solvent having a dielectric constant ε of 10 ≦ ε ≦ 50 at ˜190 ° C. in an amount of 0.001 to 5% by weight of the dye layer. 2. The thermal transfer sheet according to claim 1, wherein the high-boiling polar organic solvent is dimethylformamide, dimethylsulfoxide or cyclohexanone.