JPH03166991A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To enable an image to be formed with high print quality even on a comparatively coarse paper by forming a transfer ink layer, a thermal adhesive layer and a filler layer sequentially on one surface of a base film. CONSTITUTION:A thermal transfer sheet consists of a transfer ink layer 2, a thermal adhesive layer 3 and a filler layer 4 sequentially on one surface of a base film 1. The thermal adhesive layer 3 is formed with an adhesive layer with a melt index of 15 to 1,200. In addition, the viscosity of each layer during melting is arranged so that it increases in the ink layer 2 and the thermal adhesive layer 3 in that order. Further, a heat-resistant lubricative layer 5 is provided if necessary. Under this constitution, the filler layer becomes soft to be least viscous and thereby the coarse pores of a paper to which an image is transferred, is filled. In this case, no interlayer separation occurs between the filler layer and the ink layer as the thermal adhesive layer is present. If the ink layers is formed with a comparatively hard vehicle, the ink layer allows ink to be transferred uniformly. Subsequently, it is possible to form an image with excellent print quality even on a paper of coarse texture.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more specifically, a thermal transfer sheet that can form an image with excellent print quality even if the receiving paper is relatively coarse plain paper. Regarding the seat.

(Prior Art and its Problems) Conventionally, when output prints from a computer or a word processor are printed by a thermal transfer method, a thermal transfer sheet is used, in which a transfer ink layer is provided on one side of a base film.

The above conventional thermal transfer sheet has a thickness of 1 as a base film.
Using paper such as capacitor paper or paraffin paper with a thickness of 0 to 20 μm, or plastic film such as polyester or cellophane with a thickness of 3 to 20 μm, coating with a transfer ink layer made of wax mixed with colorants such as pigments and dyes. It was manufactured by installing.

One drawback of the above-mentioned thermal transfer sheet is that because the transfer ink layer is formed from a relatively soft wax with a low softening point, the abrasion resistance of the transferred image is poor, and it can be easily rubbed against other objects. The image is distorted, the print quality is degraded, and the margins are contaminated and other objects are contaminated. A known method to solve this drawback is to form the ink layer with relatively hard wax.
In this case, the melt viscosity of the ink layer is high, so if such a thermal transfer sheet is used to print on relatively coarse paper such as plain paper, the ink transfer will be insufficient, resulting in so-called missing spots and chips. There is a problem that a large number of characters are printed, and a high-quality image cannot be formed. As a method to solve such problems, a method is known in which a sealing layer made of a colorless wax with a low softening point is formed on the surface of the ink layer. This is used to seal the transfer paper, but in this case, peeling occurs between the ink layer and the sealing layer during transfer, and only the sealing layer is transferred, resulting in poor transfer of the ink layer. There is a problem that arises.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks and provide a thermal transfer sheet capable of forming images with excellent print quality even on relatively coarse paper. (Means for solving the problems) The above object is achieved by the present invention as described below.

That is, the present invention is a thermal transfer sheet characterized in that a transfer ink layer, a heat-sensitive adhesive layer, and a sealing layer are sequentially formed on one surface of a base film.

(Function) The transfer layer of the thermal transfer sheet has a three-layer structure of an ink layer, a heat-sensitive adhesive layer, and a sealing layer, and preferably the heat-sensitive adhesive layer is formed of an adhesive having a melt index of 15 to 1,200,
In addition, by configuring each of the above layers so that the viscosity when melted increases in the order of the filler layer, the ink layer, and the heat-sensitive adhesive layer, the filler layer softens to the lowest viscosity during transfer and can be easily transferred. Cover the rough edges of the transfer paper. In this case, since the heat-sensitive adhesive layer is present, there is no delamination between the sealing layer and the ink layer, and even if the ink layer is formed from a relatively hard vehicle, the ink layer can be transferred uniformly. Therefore, even on coarse paper, it is possible to print an image with excellent print quality.

(Preferred Embodiments) Next, the present invention will be explained in more detail with reference to preferred embodiments. As shown in the first figure, the thermal transfer sheet of the present invention is characterized by sequentially forming a transfer ink layer 2, a heat-sensitive adhesive layer 3, and a sealing layer 4 on one surface of a base film 1, preferably The heat-sensitive adhesive layer 3 has a melt index of 15 to 1.2.
00 adhesive, and the viscosity of each of the above layers when melted increases in the order of block layer 4, ink layer 2, and heat-sensitive adhesive layer 3, and if necessary, a heat-resistant slippery layer is added to the back surface. It has a structure with 5 layers. 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 is no particular restriction.

Specific examples of preferred base films include polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride,
Boristyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber,
Examples include plastic films such as ionomers, papers such as condenser paper and paraffin paper, nonwoven fabrics, and base films made of composites of these materials.

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 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.

In the thermal transfer sheet of the present invention, the transfer ink layer 2 consists of a colorant and a vehicle, and may further contain various additives as required. The colorant is preferably an organic or inorganic pigment or dye that has good properties as a recording material, for example, one that has sufficient color density and does not discolor due to light, heat, temperature, etc. Alternatively, it may be a substance that is colorless when not heated but develops color when heated, or a substance that develops color when it comes into contact with something coated on the transfer target. In addition to the colorants forming cyan, magenta, yellow, and black, colorants of various other colors can also be used.

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, and paraffin wax. 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.

Further, in order to provide the transfer ink layer with good thermal conductivity and melt transferability, a thermally conductive substance can be blended into the heat melt ink. Examples of such substances include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

The thickness of the ink layer 2 to be formed should be determined so as to balance the required concentration and thermal sensitivity. For example, in the case of one-time printing, the thickness of the ink layer 2 should be approximately 2 to 7 μm. On the other hand, in the case of multiple printing, the thickness of the ink layer is preferably in the range of about 5 to 20 um. The melt viscosity of such an ink layer is 50 to 3.0 at 100°C.
A range of 00 cps is preferred. In the present invention, a layer 3 made of a heat-sensitive adhesive, that is, a thermoplastic resin having a relatively low melting point, is formed on the surface of the ink layer 2. Examples of such heat-sensitive adhesives include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylate copolymer (EEA), bolybdenum, petroleum resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, and the like. The ink layer 2 is formed from a resin having a higher melt viscosity than the vehicle used to form the ink layer 2. In addition, this heat-sensitive adhesive layer 3
may be colored similarly to the ink layer 2. The thickness of the heat-sensitive adhesive layer 3 to be formed is as thin as possible, for example, 0.5, as long as the ink layer 2 and the sealing layer 4 described below are sufficiently bonded together.
It may be about 2 μm to 2 μm. The melt viscosity of such a heat-sensitive adhesive layer is preferably in the range of 15 to 1,200 in terms of melt index.

Methods for forming the ink layer 2 and the heat-sensitive adhesive layer 3 include hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods.

In the present invention, a sealing layer 4 is further formed on the surface of the heat-sensitive adhesive layer 3. This sealing layer 4 is formed by selecting a wax having a lower melt viscosity than the vehicle used to form the ink layer 2, and this sealing layer 4 seals the rough surface of the transfer material during printing.

The sealing layer 4 may be formed by the same method as the ink layer 2 and heat-sensitive adhesive layer 3, or may be formed by using an aqueous emulsion containing wax. . For example, by coating a water emulsion of wax on a heat-sensitive adhesive layer and drying it at a temperature below the melting point of the wax, a sealing layer is formed while the wax retains its particle shape.

In the present invention, the sealing layer formed as described above preferably has a thickness of O. It is 1 μm or more and less than 5 μm. The melt viscosity of such a sealing layer is preferably in the range of 5 to 40 CpS at 100°C.

When a heat-sensitive material is used as the base film, a heat-resistant slipping layer 5 is provided on the surface in contact with the thermal head to improve the slipperiness of the thermal head and prevent sticking.
It is preferable to provide The basic components of the heat-resistant slipping layer are a heat-resistant resin and a substance that functions as a heat release agent or a lubricant. By providing such a heat-resistant slipping layer 5, thermal printing is possible without sticking even on a thermal transfer sheet based on a heat-sensitive plastic film, and it is possible to perform thermal printing without causing sticking, which reduces the difficulty of cutting and processing of plastic films. Benefits such as ease of use can be taken advantage of.

It goes without saying that the present invention can be applied to thermal transfer sheets for color printing, so multicolor thermal transfer sheets are also included within the scope of the present invention. Furthermore, it can be applied to either line or serial type thermal transfer printers. (Effects) According to the present invention as described above, the transfer layer of the thermal transfer sheet has a three-layer structure of an ink layer, a heat-sensitive adhesive layer, and a sealing layer, and preferably the heat-sensitive adhesive layer has a melt index of 15 to 1.
, 200 adhesive, and by configuring each of the above layers so that the viscosity when melted increases in the order of the sealing layer, the ink layer, and the heat-sensitive adhesive layer, the sealing layer can be easily removed during transfer. It softens to the lowest viscosity and easily closes the rough edges of the transfer paper. In this case, since the heat-sensitive adhesive layer is present, there is no peeling between the sealing layer and the ink layer, and even if the ink layer is formed from a relatively hard vehicle, the ink layer can be transferred uniformly. Therefore, it is possible to form images with excellent print quality even on coarse paper. (Example) Hereinafter, 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 1 A transfer ink composition having the composition shown below was kneaded for 6 hours while heating to 90° C. using a blade doubler. Ink Invarafin wax 8 parts Carnauba wax 2 parts Ethylene/vinyl acetate copolymer 1 part Carbon black
Heating 2 parts of the above ink composition at a temperature of 100°C,
A 6.0 um thick polyester film with a heat resistant layer formed on the back using a hot melt roll coating method (
The amount applied to the surface of the product (product name: "Lumirror" manufactured by Toray ■) is approximately 4g.
A thermal transfer ink layer was formed by applying the ink so that it was lrd. The melt viscosity of this ink layer at 100°C is 100
It was cps. Next, the following composition was applied to the surface of the ink layer in the same manner as the ink layer at a coating amount of 1 g/ITiI to form a heat-sensitive adhesive layer. The melt index of this heat-sensitive adhesive layer was 400. Feeling 1' Ethylene/vinyl acetate copolymer (Evaflex 410
) 8 parts carbon black
Part 2 Next, carnauba wax was coated on the surface of the heat-sensitive adhesive layer at a rate of 0.5 g/nf to form a sealing layer or to obtain a heat transfer sheet of the present invention.

The melt viscosity of this sealing layer at 100°C is 28 cp.
It was s. Example 2 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1, except that the heat-sensitive adhesive layer in Example 1 had the following composition. Feeling ′゛Ethylene/vinyl acetate copolymer (MB-850)
Part 6 carbon black
4 parts (melt index=800) Example 3 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the heat-sensitive adhesive layer in Example 1 had the following composition.

Feeling. 1. Ethylene/vinyl acetate copolymer (Evaflex 420
) 7 parts carbon black
3 parts (melt index = 150
) Example 4 A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the heat-sensitive adhesive layer in Example 1 had the following composition.

#4 1. Ethylene/vinyl acetate copolymer (Evaflex 450
) 6 parts carbon black
4 parts (melt index = 15) Comparative Example 1 A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that the heat-sensitive adhesive layer was not formed in Example 1. Usage 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 stain resistance, abrasion resistance, and printing quality were evaluated, and the results are shown in Table 1 below. I got it. Equipment used: Toshiba simulator equipped with a thin-film thermal head Printing energy: 0.8mJ/dot (constant)
Photography: Plain paper (Beck smoothness 20, 25, 30 and 5)
4 types of 0 seconds) (below margins) 1! Printing was visually inspected for chipping.

O: No missing print is observed: Δ: Some parts of the print are missing.

×: Missing of printing is observed throughout.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a cross section of the thermal transfer sheet of the present invention. 2. Base film 2: Ink layer 3: Heat-sensitive adhesive layer 4: Sealing layer 5: Heat-resistant slipping layer

Claims (3)

[Claims] (1) A thermal transfer sheet, characterized in that a transfer ink layer, a heat-sensitive adhesive layer, and a sealing layer are sequentially formed on one side of a base film. (2) The thermal transfer sheet according to claim 1, wherein the heat-sensitive adhesive layer has a melt index of 15 to 1,200. (3) The thermal transfer sheet according to claim 1, wherein the viscosity of each layer increases in the order of the filler layer, the ink layer, and the heat-sensitive adhesive layer.