JP3357961B2 - Thermal transfer sheet - Google Patents

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.
In particular, with regard to thermal transfer sheets of thermal transfer printers used as hard copy output devices such as personal computers and word processors, it is possible to form images with excellent print quality even if the paper is not as rough and smooth as plain paper. Thermal transfer sheet.

[0002]

2. Description of the Related Art Conventionally, when a hard copy such as a personal computer or a word processor is printed by a thermal transfer method, a material having a heat-fusible ink layer provided on one side of a base film is often used as a thermal transfer sheet. Conventional thermal transfer sheets have a thickness of 10 to 2 as a base film.
Using a paper such as a condenser paper or a paraffin paper of about 0 μm, or a plastic film such as a polyester or cellophane having a thickness of about 3 to 20 μm, a coloring material such as a pigment or a dye is added to wax on the base film. The mixed ink was applied by a coating device. Then, a predetermined position is heated and pressed by a thermal head from the back side of the base film, and the hot-melt ink layer is transferred to a heat transfer material such as paper to perform printing.

However, in such a conventional thermal transfer sheet, when the surface smoothness of the paper is good, clear and high-density printing which is an advantage of the thermal transfer sheet can be performed. When printing on paper having rough surface smoothness, the transfer of ink is insufficient, resulting in so-called printing with many omissions and chipping, resulting in poor quality.

In order to solve such a problem, it has been considered that a wax having a low melt viscosity is selected as a wax which is a component of the ink layer to form a thermal transfer sheet. Is effective when the printing energy is at a low level, but when the printing energy is at a high level, there is also a problem that the printing is liable to be missed or chipped and the quality is inferior. When the printing density was measured by changing the printing energy from a low level to a high level using plain paper as the paper, and the printing density was measured, as shown at 203 in FIG. On the contrary, it can be seen that the print density decreases at the level. This addresses the above problem. It is considered that the tendency as indicated by 201 in FIG. 2 is due to the fact that the transferred ink layer is cut due to unevenness of the paper surface as shown in FIG. Therefore, conversely, it was considered to select a wax having a high melt viscosity as a wax that is a component of the ink layer to make a thermal transfer sheet.However, this time, at a low printing energy level, printing with a lot of omissions and chippings occurred,
There was a problem of poor quality. The measured results are shown in FIG.
202 indicates that the print density is low at a low print energy level.

[0005] Such a problem is also caused by forming a filling layer made of colorless wax on the surface of the ink layer.
It was an unsolved problem.

[0006]

The problem to be solved by the present invention is to solve the above-mentioned drawbacks of the prior art and to print even on a relatively coarse paper such as plain paper. Another object of the present invention is to provide a thermal transfer sheet capable of stably forming an image having excellent print quality even when a thermal transfer printer having a large fluctuation range of printing energy is used.

[0007]

Means for Solving the Problems In order to achieve such an object, the present inventors have conducted intensive studies and as a result, formed a thermal transfer ink layer on a base sheet, and provided a surface layer on the thermal transfer ink layer. In the formed thermal transfer sheet, the thermal transfer ink layer is composed of at least a colorant, a thermoplastic resin, and a wax, and the surface layer is composed of at least a thermoplastic resin and a wax.
High, that is, the difference in melting point between the thermal transfer ink layer and the surface layer is 0
-10 ° C or less, viscosity of the surface layer at 100 ° C is 1000-20,000 mpas, and melting of the ink layer
The present inventors have found that it can be achieved by making the composition higher than the viscosity , and solved the problem.

[0008]

When printing is performed on plain paper with the thermal transfer sheet of the present invention, even if a thermal transfer printer having a large fluctuation range of printing energy is used, an image having excellent printing quality can be stably obtained. Could be formed. When the print density when the print energy was changed from a low level to a high level was measured, the characteristic of 201 in FIG. 2 was obtained, and an image having a high print density was obtained regardless of the fluctuation of the print energy. It was clear from the data. The reason why such characteristics were obtained is that the surface layer of the thermal transfer sheet of the present invention is more excellent in transferability to paper than the ink layer, and has a high film strength and a high melt viscosity. It is considered that the ink layer transferred at the large uneven portion of the paper is not cut as described above, and the large uneven portion as shown in FIG. 4 can be covered.

[0009]

Now, the present invention will be described in further detail with reference to preferred embodiments. As shown in FIG. 1, the thermal transfer sheet of the present invention has a thermal transfer ink layer 1 on one surface of a base film 101.
02 and the surface layer 103 are sequentially formed, the difference between the melting points of the thermal transfer ink layer 102 and the surface layer 103 is within 0 to 10 ° C., and the melt viscosity of the surface layer 103 is higher than that of the thermal transfer ink layer 102. High at 100 ° C
2,000 to 20,000 mpas.

The substrate film 101 used in the present invention may be the same as the substrate film used in the conventional thermal transfer sheet, and is not particularly limited. Specific examples of preferred base film include, for example, polyester, polypropylene, cellophane, polycarbonate, cellulose acetate,
Polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, plastic films such as ionomers, condenser paper, paper such as paraffin paper, non-woven fabrics, and the like. May be a composite substrate film. The thickness of the base film 101 can be appropriately selected so that the strength and the thermal conductivity are appropriate according to the material to be used. For example, the thickness is preferably about 2 to 25 μm.

The thermal transfer ink layer 102 formed on the surface of the base film 101 contains a colorant and a vehicle as main components, and can further add various additives as needed. The thickness of the ink layer 102 to be formed can be determined so that the required density and thermal sensitivity can be harmonized,
Usually, the range of about 1 to 10 μm is preferable.

The colorant can be appropriately selected from known organic or inorganic pigments or dyes.
For example, it has a sufficient coloring density, discolors due to light, heat, etc.
Those that do not fade are preferred. Further, it may be a substance that develops color by heating or a substance that develops color when it comes into contact with a component applied to the surface of the transfer-receiving body. Further, the color of the colorant is not limited to cyan, magenta, yellow, and black, and various colors of colorants can be used.

As the vehicle, a mixture of wax and a derivative of a drying oil, a resin, a mineral oil, cellulose, rubber and the like is used. Representative examples of the wax include microcrystalline wax, carnauba wax, and paraffin wax. Further, waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti, ibota wax, wool wax, shellac wax, candelilla wax, petrolactam, partially modified wax, fatty acid ester, fatty acid amide and the like are used. . Of these, waxes having a solidification point of 45 to 85 ° C and a viscosity at 100 ° C of 10 to 200 mPas are particularly preferred.

When the adhesiveness between the base film 101 and the thermal transfer ink layer 102 is insufficient, the thermal transfer ink layer 102 may be formed via an adhesive layer. The adhesive layer can be formed of an acrylic resin, a nylon resin, a vinyl chloride copolymer, a polyester resin, a urethane resin, or the like, and preferably has a thickness of about 0.1 to 0.2 μm.

In the present invention, a surface layer 103 is formed on the thermal transfer ink layer 102. The components of the surface layer 103 include:
Basically, it may be similar to the thermal transfer ink layer 102 component. For example, if a colorant such as that used in the thermal transfer ink layer 102 is used as one of the components of the surface layer 103, the effect of increasing the print density can be obtained. However, the present invention is not limited to this. However, it is necessary to select components so that the melt viscosity of the surface layer 103 is higher than that of the thermal transfer ink layer 102. Its viscosity is 1000-20 at 100 ° C.
000mpas is appropriate. Viscosity is 1000mpas
Below this, if the transfer film strength is low, and if the printing energy is high, the loss or chipping shown in FIG.
If it exceeds 0 mpas, the viscosity is too high and transfer cannot be performed well. The thermal transfer sheet of the present invention is characterized in that the difference between the melting points of the ink layer and the surface layer is within 0 to 10C.
Thereby, it is possible to improve the transfer efficiency in the two-layer configuration of the surface layer and the thermal transfer ink layer, and a good printed matter can be obtained even with a relatively low print energy.

The ink layer 102 and the surface layer 103 contain a thermoplastic resin. The purpose is to use the ink layer 102
The purpose is to improve the durability of the foil between the substrate layer and the base film, and to improve the transferability of the surface layer 103 to paper. As such a thermoplastic resin, for example, ethylene vinyl acetate copolymer, ethylene acrylate copolymer, polybutene, petroleum resin, vinyl chloride vinyl acetate copolymer, polyvinyl acetate and the like are used, and particularly preferred thermoplastic resin is It is an ethylene vinyl acetate copolymer. For the surface layer 103, a resin having the same or higher melt viscosity than the vehicle used for forming the ink layer 102 is used. Furthermore, the amount of the thermoplastic resin contained in the surface layer 103 depends on the amount of the ink layer 10.
When the content is increased by 5 to 20% as compared with 2, the printing performance is further improved.

The thickness of the surface layer 103 to be formed is preferably as thin as possible, as long as it has a sufficient coloring power, for example, about 0.3 to 2 μm. If the thickness is too large, sensitivity and foil breakage become insufficient. As a method for forming the ink layer 102 and the surface layer 103, a hot lacquer coat, a gravure coat, a gravure reverse coat, a roll coat, and many other known methods can be applied in addition to the hot melt coat.

In the present invention, a background stain prevention layer made of a colorless wax may be further formed on the surface of the surface layer 103. When a heat-sensitive material is used as the base film, it is preferable to provide a heat-resistant lubricating layer 104 on the surface in contact with the thermal head for improving the slipperiness of the thermal head and preventing sticking. Needless to say, the present invention can be applied to a thermal transfer sheet for color printing, and a multicolor thermal transfer sheet is also included in the scope of the present invention. The type of the thermal transfer printer is not limited, and the present invention can be applied to a serial type printer, a line type printer, and the like.

Hereinafter, the present invention will be described with reference to more specific examples. In the following description, parts and% are by weight unless otherwise specified. Example 1 A composition for a thermal transfer ink layer having the following composition was kneaded for 6 hours while heating to 90 ° C. using a sand mill. Thermal transfer ink layer composition Paraffin wax (HNP-10) 68 parts Ethylene vinyl acetate copolymer (Smitate KC-10) 17 parts Carbon black 15 parts At this time, the thermal transfer ink layer has a melting point of 72 ° C and a viscosity of 100.
It was 500 mpas at ° C. Further, a surface layer composition having the following composition was kneaded for 6 hours while being heated to 90 ° C. using a sand mill. Composition for surface layer Paraffin wax (HNP-10) 58 parts Ethylene vinyl acetate copolymer (Smitate KC-10) 27 parts Carbon black 15 parts At this time, the melting point of the surface layer is 72 ° C, and the viscosity is 5000 mpas at 100 ° C. there were. A hot lacquer obtained by adding xylene to the above composition for a thermal transfer ink layer and heating to a temperature of 75 ° C. was applied by a roll coating method at a coating amount of 4.0 g / m ^2.
To form a thermal transfer ink layer on the surface of the substrate film. As the base film, a 3.5 μm-thick polyester film (trade name Lumirror, manufactured by Toray) having a heat-resistant lubricating layer formed on the back surface was used. Next, the surface layer composition was coated on the surface of the thermal transfer ink layer in the same manner as the thermal transfer ink layer composition so that the coating amount was 0.5 g / m ² to form a surface layer. The thermal transfer sheet of the present invention was obtained. (Example 2) A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Surface layer composition paraffin wax (HNP-10) 58 parts Ethylene vinyl acetate copolymer (Evaflex 410) 27 parts Carbon black 15 parts At this time, the melting point of the surface layer was 72 ° C and the viscosity was 5000 mpas at 100 ° C. Was. Example 3 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Surface layer composition paraffin wax (HNP-10) 56 parts Ethylene vinyl acetate copolymer (Evaflex 210) 29 parts Carbon black 15 parts At this time, the melting point of the surface layer was 72 ° C. and the viscosity was 5000 mpas at 100 ° C. Was. Example 4 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Surface layer composition paraffin wax (HNP-10) 58 parts Ethylene vinyl acetate copolymer (Evaflex 460) 27 parts Carbon black 15 parts At this time, the melting point of the surface layer was 72 ° C, and the viscosity was 15,000 mpas at 100 ° C. Was. Example 5 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Composition for surface layer Paraffin wax (HNP-10) 43 parts Ethylene vinyl acetate copolymer (Smitate KC-10) 17 parts Carbon black 40 parts At this time, the melting point of the surface layer is 72 ° C, and the viscosity is 15000 mpas at 100 ° C. there were. Example 6 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Composition for surface layer Paraffin wax (HNP-10) 59 parts Ethylene vinyl acetate copolymer (Evaflex 210) 40 parts Carbon black 1 part At this time, the melting point of the surface layer was 72 ° C, and the viscosity was 1200 mpas at 100 ° C. Was.

Comparative Example 1 A thermal transfer sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that the surface layer in Example 1 was not formed. Comparative Example 2 A thermal transfer sheet of Comparative Example 2 was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Surface layer composition carnauba wax 58 parts Ethylene vinyl acetate copolymer (Smitate KC-10) 27 parts Carbon black 15 parts At this time, the melting point of the surface layer was 83 ° C, and the viscosity at 100 ° C was 5000 mpas. Comparative Example 3 A thermal transfer sheet of Comparative Example 3 was obtained in the same manner as in Example 1 except that the surface layer in Example 1 had the following composition. Surface layer composition paraffin wax (HNP-10) 58 parts Ethylene vinyl acetate copolymer (MB080) 22 parts Carbon black 15 parts At this time, the melting point of the surface layer was 72 ° C and the viscosity was 800 mpas at 100 ° C. Comparative Example 4 A thermal transfer sheet of Comparative Example 4 was obtained in the same manner as in Example 1, except that the surface layer in Example 1 had the following composition. Surface layer composition paraffin wax (HNP-10) 55 parts Ethylene vinyl acetate copolymer (Evaflex 460) 30 parts Carbon black 15 parts At this time, the melting point of the surface layer was 72 ° C, and the viscosity at 100 ° C was 30,000 mpas. Was.

Using the thermal transfer sheets of Examples 1 to 6 and Comparative Examples 1 to 4, printing was performed under the following printing conditions, and the print density and void were evaluated. The results shown in Table 1 below were obtained. (Printing conditions) Apparatus used: Word processor WD-A300 manufactured by Sharp Corporation equipped with a thin-film thermal head Printing energy: Table 1 below Paper: PPC paper (M paper)

[Table 1]

[0022]

As described above, according to the present invention, even if the paper is relatively coarse, such as plain paper, or if it is used in a thermal transfer printer in which the printing energy tends to fluctuate, it is excellent. Transfer sheet capable of forming a printed image of high quality.

[0023]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a thermal transfer sheet of the present invention.

FIG. 2 is a diagram showing a relationship between printing energy and printing density.

FIG. 3 is a diagram showing a state in which an ink layer is cut by irregularities of a transfer-receiving sheet.

FIG. 4 is a diagram showing a state in which the ink layer can be covered without being cut by the unevenness of the sheet to be transferred.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Base film 102 Thermal transfer ink layer 103 Surface layer 104 Heat-resistant lubricating layer 105 Adhesive layer 201 Thermal transfer sheet of the present invention 202 High melt viscosity wax composition thermal transfer sheet 201 Low melt viscosity wax composition thermal transfer sheet

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/38-5/40

Claims (3)

(57) [Claims] 1. A thermal transfer sheet having a thermal transfer ink layer formed on a base sheet and a surface layer formed on the thermal transfer ink layer, wherein the thermal transfer ink layer comprises at least a colorant, a thermoplastic resin, and a wax, surface layer at least a thermoplastic resin, made of wax, high 0 ° C. the melting point of the surface layer from the thermal transfer ink layer, i.e. thermal transfer Lee
The difference between the melting points of the ink layer and the surface layer is within 0 to 10 ° C.
The viscosity at 100 ° C. of the face layer is 1,000 to 20,000 m
a thermal transfer sheet, which is higher than the melt viscosity of the ink layer . 2. The amount of the thermoplastic resin contained in the surface layer is more than the amount of the thermoplastic resin contained in the thermal transfer ink layer by weight%.
2. The thermal transfer sheet according to claim 1, wherein the thermal transfer sheet is 5 to 20% higher. 3. The thermal transfer sheet according to claim 1, wherein the surface layer is colored.