JPH04251792A - thermal transfer sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 particularly to a thermal transfer sheet capable of forming an image with excellent print quality even when the paper to be transferred is relatively coarse plain paper or the like.

0002

2. Description of the Related Art Conventionally, when output prints from a computer or word processor are printed by a thermal transfer method, a thermal transfer sheet having a transfer ink layer provided on one side of a base film is used. The conventional thermal transfer sheet described above uses paper such as capacitor paper or paraffin paper with a thickness of 10 to 20 μm, or a paper with a thickness of 3 to 20 μm as a base film.
It is manufactured by coating a plastic film such as polyester or cellophane with a transfer ink layer made of wax mixed with a coloring agent such as a pigment or dye.

0003

[Problems to be Solved by the Invention] The advantage of the above-mentioned thermal transfer sheet is that it provides clear and high-density printing, but one major drawback is that it cannot be used on relatively rough receiving paper such as plain paper. When printing, the ink transfer is insufficient, resulting in printing with many so-called missing spots and chips, which makes it impossible to form a high-quality image. This problem can be solved to some extent by forming the ink layer from wax with a relatively low melt viscosity, but in the case of such an ink layer, the printing energy is large. In this case, there is a problem in that blanks and chips occur, and the print density decreases. This problem is unique to coarse-grained plain paper, and when printing density is measured while gradually increasing the printing energy, the maximum density is reached at a certain energy level as shown in Figure 2a, and the density decreases at higher energy levels. On the contrary, it decreases. This tendency is due to the fact that when the melt viscosity of the ink is low and the printing energy is high, the transferred ink layer is cut by the large depressions and protrusions of the paper, as shown in Figure 3, and the white surface of the underlying paper is exposed. It seems to be.

In order to solve this problem, if the melt viscosity of the ink layer is increased, the transferability at a low energy level decreases as shown in FIG. 2b. The above problem is particularly noticeable in the case of serial printers where the contact time of the thermal head and the contact time between the ink layer and the paper are short, and the print density changes due to fluctuations in the applied energy during printing, making it difficult to obtain high quality prints. The problem is that there is no. Such problems cannot be solved by forming a sealing layer made of colorless wax on the surface of the ink layer. Therefore, it is an object of the present invention to solve the above-mentioned drawbacks and to provide excellent printing quality even on relatively coarse paper and even when used with a serial printer where printing energy tends to fluctuate. It is an object of the present invention to provide a thermal transfer sheet capable of stably forming images.

[0005]

[Means for Solving the Problems] The above object is achieved by the following present invention. That is, the present invention is a thermal transfer sheet comprising a transfer ink layer and a surface layer formed on one side of a base film, characterized in that the surface layer is formed from a colored thermoplastic resin. .

[0006]

[Operation] When printing by forming a surface layer made of a colored thermoplastic resin on the surface of the ink layer, this surface layer has higher coating strength and higher melt viscosity than the ink layer whose main component is wax. Even when the paper has large irregularities as in No. 4, it is not cut, and the irregularities can be covered. Therefore, the ink layer transferred thereon will not be cut off by the uneven portions, and a continuous ink layer can be maintained. In addition, even if the printing energy is high and the ink layer melts to a low viscosity, the uneven parts of the paper are covered with a colored surface layer as shown in Figure 4, so the paper surface is not exposed and the print density decreases. There is no. The relationship between the printing energy and the printed image of the thermal transfer sheet of the present invention as described above is a curve as shown in FIG. 2c, and an image with high printing density can be obtained despite fluctuations in the printing energy.

[0007]

[Preferred Embodiments] The present invention will now be explained in more detail with reference to preferred embodiments. The thermal transfer sheet of the present invention is shown in Figure 1.
The transfer ink layer 2 and the surface layer 3 are sequentially formed on one side of the base film 1 as shown in FIG.
00 ethylene/vinyl acetate copolymer. As the base film 1 used in the present invention, the same base film used in conventional thermal transfer sheets can be used as is, and other films can also be used, and there are no particular limitations. Specific examples of preferred base films include polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol,
Examples include plastic films such as fluororesin, chlorinated rubber, and ionomer, papers such as condenser paper and paraffin paper, and nonwoven fabrics, and base films made of composites of these may also be used. The thickness of this base film can be changed as appropriate depending on the material so that its strength and thermal conductivity are appropriate, but the thickness is preferably, for example, 2 to 2.
It is 25 μm.

In the present invention, a transfer ink layer 2 is formed on the surface of the base film 1 using an ink containing necessary materials. The transfer ink layer 2 in the thermal transfer sheet of the present invention consists of a colorant and a vehicle, and may further contain various additives as required. The colorant is preferably an organic or inorganic pigment, and the concentration is preferably in the range of 5 to 20% by weight. The vehicle used includes wax as a main component, and mixtures of wax with drying oil, resin, mineral oil, cellulose, rubber derivatives, and the like. Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. Furthermore, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolactam, partially modified wax, fatty acid ester, fatty acid amide, etc. used. The thickness of the ink layer 2 to be formed should be determined to balance the required concentration and thermal sensitivity, and should be approximately 1 to 10 μm thick.
A range of is preferred.

In the present invention, a surface layer 3 made of a colored thermoplastic resin is formed on the surface of the ink layer 2. Examples of such thermoplastic resins include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid ester copolymer (EEA), polybutene, petroleum resin, and vinyl chloride.
Vinyl acetate copolymer, polyvinyl acetate, etc. are used, and the ink layer 2 is formed from a resin having a higher melt viscosity than the vehicle used for forming the ink layer 2. A particularly preferred thermoplastic resin is an ethylene-vinyl acetate copolymer. Note that this surface layer 3 needs to be colored in the same hue as the ink layer 2. The melt viscosity of the resin forming such surface layer 3 is preferably in the range of 100 to 600 in terms of melt index. If the melt index exceeds 600, the strength of the transfer film will be low, and if the printing energy is high, chipping or missing spots as shown in Figure 3 will occur, and if it is less than 100, the ink layer will break and the heat sensitivity will increase. descend.

The thickness of the surface layer 3 to be formed is preferably as thin as it has sufficient coloring power, for example, about 0.3 to 2 μm; if it is too thin, it will be difficult to maintain print density; If it is too thick, sensitivity and foil cutting will be insufficient. Also, for the same reason, the pigment concentration in the surface layer 3 should be higher as the coating is thinner, and a concentration of 20 to 40% by weight is preferred. If the pigment concentration is too low, the printing density will be low, while if it is too high, the film strength and adhesion to the paper will be insufficient.Methods for forming the ink layer 2 and surface layer 3 include hot melt coating, hot melt coating, etc. Examples include lacquer coating, gravure coating, gravure reverse coating, roll coating and many other methods.

In the present invention, a scumming prevention layer made of colorless wax may be further formed on the surface of the surface layer 3. Further, when a heat-sensitive material is used as the base film, it is preferable to provide a heat-resistant slipping layer 4 on the surface in contact with the thermal head to improve the slipperiness of the thermal head and prevent sticking. Since it goes without saying that the present invention can be applied to thermal transfer sheets for color printing, multicolor thermal transfer sheets are also included within the scope of the present invention. Furthermore, the thermal transfer printer is not limited to serial type printers, but can also be applied to line type printers.

0012

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. In the text, parts or percentages are based on weight unless otherwise specified. Example 1 A transfer ink composition having the following composition was prepared using a sand mill.
It was prepared by kneading for 6 hours while heating to 90°C. Ink layer ink carnauba wax (HNP-10)

68 parts ethylene/vinyl acetate copolymer (
KC-10)
20 parts carbon black

12 parts Add xylene to the above ink composition, heat it at 75°C, and form a 3.5 μm thick polyester film (trade name "Lumirror", Toray Co., Ltd.) with a heat-resistant slipping layer on the back side by roll coating with hot lacquer. Approximately 4.5g/approx.
A thermal transfer ink layer was formed by coating the ink in an amount of m2. Next, the following composition was applied to the surface of the ink layer in the same manner as for the ink layer at a coating amount of 0.5 g/m2 to form a surface layer, thereby obtaining a thermal transfer sheet of the present invention. . Coating liquid for surface layer Ethylene/vinyl acetate copolymer (Evaflex 4
10, MI400, vinyl acetate 19%)

70 copies
Carbon black

30 copies

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. Coating liquid for surface layer Ethylene/vinyl acetate copolymer (Evaflex 4
20, MI150, vinyl acetate 19%)

60 copies
Carbon black

40 parts 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. Coating liquid for surface layer Ethylene/vinyl acetate copolymer (Evaflex 2
10, MI400, vinyl acetate 28%)

70 copies
Carbon black

30 parts 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. Coating liquid for surface layer Vinyl chloride/vinyl acetate copolymer (manufactured by Union Carbide, VYHD)


70 parts carbon black

30 copies

Comparative Example 1 A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the surface layer was not formed in Example 1. Use Example 1 Using the thermal transfer sheets of Examples 1 to 4 and Comparative Example 1, printing was carried out under the following printing conditions, and the print density was evaluated to obtain the results shown in Table 1 below. Printing conditions Equipment used: Sharp word processor WD-2 equipped with a thin-film thermal head 70H printing energy: Table 1 below Transferred material: Plain paper

[0015] (Measurement using a Macbeth reflection densitometer)

[0016]

[Effect] According to the present invention as described above, images with excellent print quality can be stably produced even on relatively coarse paper or when used with a serial printer where printing energy tends to fluctuate. A thermal transfer sheet that can be formed is provided.

[0017]

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a cross section of a thermal transfer sheet of the present invention.

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

FIG. 3 is an imaginary diagram of ink dots.

FIG. 4 is an imaginary diagram of ink dots.

[Explanation of symbols] 1: Base film 2: Ink layer 3: Surface layer 4: Heat-resistant slippery layer 5: Transfer material (paper)

Claims (3)

[Claims] 1. A thermal transfer sheet comprising a transfer ink layer and a surface layer formed on one side of a base film, wherein the surface layer is formed from a colored thermoplastic resin. [Claim 2] The thermoplastic resin has a melt index of 1.
The thermal transfer sheet according to claim 1, which is an ethylene/vinyl acetate copolymer having a molecular weight of 00 to 600. [Claim 3] Claim 1 for use in a serial printer.
Thermal transfer sheet described in .