JPH01156382A - Ink composition and thermal transfer sheet - Google Patents

Abstract

PURPOSE:To obtain an ink compsn. for thermal transfer sheet capable of giving prints and images having excellent fixing and antifriction properties by compounding a dye as a coloring agent with a low m.p. material so as to exhibit a predetermined melt viscosity. CONSTITUTION:3-10wt.% coloring agent composed of a dye, such as an oil- soluble dye which is pref. ultrafinely dispersible or soluble in a wax, etc., is compounded with a low m.p. material, e.g. composed of a mixture comprising carnauba wax as a main component, another type of wax and at least one member selected from among a drying oil, a resin, a mineral oil, cellulose, a rubber, etc., so as to exhibit a melt viscosity at 100 deg.C of 50cps.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ink composition for a thermal transfer sheet and a thermal transfer sheet using the ink composition, and more specifically relates to a novel ink composition that provides printing with excellent fixing properties and abrasion resistance. The purpose is to provide a thermal transfer sheet.

(Prior Art) Conventionally, when printing output from a computer or a word processor by a thermal transfer method, a thermal transfer sheet having a base sheet with a heat-melting ink layer provided on one side has been used.

This conventional thermal transfer sheet has a thickness of 8 mm as a base sheet.
Using paper such as capacitor paper or paraffin paper with a thickness of 20 μm or plastic film such as polyester or cellophane with a thickness of 3 to 20 μm, coated with a layer of heat-melting ink made by mixing wax with a coloring agent such as pigment or dye. It was prepared and manufactured by.

In printing or images using such a thermal transfer sheet, the sheet is placed on a transfer material such as paper, and the ink layer is transferred by heating with a thermal head from the back side of the thermal transfer sheet. Transfer occurs when the ink layer is melted by the heat of the thermal head, adheres to the paper, and peels off from the thermal transfer sheet.

(Problem to be Solved by the Invention) Since the ink layer of the thermal transfer sheet is made of a low melting point material, the transferred prints or images are simply attached to the ink layer or the surface of the paper. There is a problem with adhesion in that the ink layer easily peels off when it comes into contact with sticky tape or file film containing plasticizer, and wax is soft even at room temperature, so it lacks abrasion resistance and the surface can be rubbed. The problem of contaminating other articles or contaminating the printing surface itself cannot be avoided.

Therefore, it is an object of the present invention to provide a thermal transfer sheet capable of printing or transferring images with excellent fixing properties and abrasion resistance.

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

That is, the present invention consists of two inventions, and the first invention is an ink composition for a thermal transfer sheet comprising a colorant and a low melting point material, in which the colorant is a dye and the melt viscosity at 100°C is 50 cps or less. An ink composition for a thermal transfer sheet characterized by and the melt viscosity of the ink layer at 100°C is 5
This is a thermal transfer sheet characterized in that it has a transfer rate of 0 cps or less.

(Function) By using a dye as a coloring agent in an ink composition and lowering the melt viscosity of the ink, the ink layer becomes as low in viscosity as a liquid during thermal transfer and penetrates into the paper structure. At the same time, since the colorant is a dye, it penetrates into the paper structure and provides prints or images with excellent fixation and abrasion resistance similar to those made with liquid ink, and the ink layer remains intact even when the surface is rubbed. It will not peel off, contaminate other items, or stain the printed surface.

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

The ink composition of the present invention basically consists of a dye, which is a coloring agent, and a wax, which is a low melting point material.

As the dye, any conventionally known dye can be used, but preferred dyes are oil-soluble dyes that are ultrafinely dispersed or dissolved in wax, and most preferably, for example, nigrosine dyes that can be produced by hand under trade names such as Special Black. used. These nigrosine dyes are sufficiently ultrafinely dispersed or dissolved in the wax, and can sufficiently penetrate into the paper structure together with the wax during thermal transfer.

The above dye is about 3 to 10% by weight of the total amount in the ink composition.
%, preferably 5 to 8% by weight. If the amount of dye used is too small, the density of the print will be insufficient, while if the amount used is too large, the solubility of the dye will be insufficient, and coarse particles that cannot penetrate into the paper structure will form in the paper during printing. It will remain on the surface and cause contamination problems.

The low melting point material used in the present invention is mainly composed of wax, and mixtures of wax, drying oil, resin, mineral oil, cellulose, rubber derivatives, etc. are used.

Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. In addition, Fischer-Trobsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolatum, -dairy wax, fatty acid ester,
Various waxes such as fatty acid amides are used.

Any of the above waxes can be used in the present invention, but
The ink of the present invention needs to be adjusted to have a melt viscosity of 50 cps or less at 100°C when containing the dye described above; if the melt viscosity exceeds the above range, the permeability of the melted ink to paper during thermal transfer will be poor. This becomes insufficient, making it difficult to achieve the objective of the present invention. The most preferred melt viscosity is 20 to 40 cps at 100°C and 15 cps at 120°C.
The range is from 25 cps to 25 cps.

Furthermore, in the present invention, it is preferable that the wax has a high hardness when solidified by cooling while having the above viscosity range, and a wax suitable for such a purpose is a mixture containing carnauba wax as a main component and other waxes. I found out. The amount of carnauba wax in the mixed wax is 60% by weight or more, preferably 70 to 95% by weight in the ink.

The above are the essential components of the ink composition of the present invention, but other optional additives such as various low melting point materials, lubricants, antioxidants, etc. as described above can be used within the range that does not interfere with achieving the objectives of the present invention. Of course.

The ink composition of the present invention may be produced by a method known per se, and can be easily obtained by mixing and kneading the necessary components.

The thermal transfer sheet according to the second aspect of the present invention may have the same structure as a conventionally known thermal transfer sheet, except that the ink layer is formed from the ink composition of the present invention, and is not particularly limited.

That is, the base sheet used in the present invention is
The same base sheet used in conventional thermal transfer sheets can be used as is, and other base sheets can also be used without any particular limitation.

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

In particular, when carnauba wax is used as the main component as the wax in the present invention, if a plastic sheet is used as the base sheet, the adhesion of the ink layer will be poor, resulting in peeling of the ink layer during printing, staining, and unclear characters. Since this may occur, it is necessary to pay attention to the adhesion. In this respect, capacitor paper is most suitable because it does not cause such a risk.

The thickness of this base sheet 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, 3 to 25 μm.
It is. In the case of capacitor paper, a thickness of 10 to 15 μm is preferable.

Methods for directly or indirectly forming the above-mentioned hot-melt ink layer on the base sheet include coating with a hot-melt coating liquid, gravure coating, gravure reverse coating, and coating liquid in which a solvent is added and dissolved by heating or at room temperature. Examples include coating methods, roll coating, and many other methods.

The thickness of the ink layer formed should be determined to balance the required optical density and thermal sensitivity, and is in the range of 0.1 to 10 μm, preferably in the range of 1 to 5 μm.

The above is the basic structure of the thermal transfer sheet of the present invention, but in a preferred embodiment of the present invention, a surface layer may be provided on the surface of the uppermost ink layer, and an anti-sticking layer may be provided on the back surface of the base sheet. can. Furthermore, a layer having fine irregularities may be provided on the surface of the base sheet so as to obtain matte printing.

In the present invention, the surface layer formed on the ink layer forms a part of the uppermost transfer film, forms the surface in contact with the transfer paper, and seals the printed portion of the transfer paper during transfer, or,
It has the function of preventing background smearing and improving the adhesion of the ink layer to the transfer paper.

The above surface layer may be formed using a wax melt, an organic solvent solution, or an aqueous dispersion, and may further include a thermoplastic resin, extender pigment, or other arbitrary additives as necessary. good.

The wax used to form the surface layer is the same as the wax used in the hot-melt ink layer described above. The thickness of this layer is preferably between 0.1 μm and 5 μm.

When a heat-resistant material is used for the base sheet, it is preferable to provide a layer on the surface in contact with the thermal head to prevent sticking of the thermal head. The anti-sticking layer basically includes a heat-resistant resin and a substance that functions as a heat release agent or a lubricant. Heat-resistant resins include synthetic resins with a glass transition point of 60°C or higher, or thermoplastic resins with hydroxyl groups or carboxyl groups, which are slightly crosslinked and cured by adding a compound having two or more amino groups, or diisocyanate or triisocyanate. Preferably, those that cause Thermal mold release agents or lubricants include waxes, amides, esters, and salts of higher fatty acids that melt when heated, and powders of organic substances such as fluororesin and powders of inorganic substances. Some are useful while remaining solid.

By providing such an anti-sticking layer, it is possible to perform thermal printing without causing sticking even on thermal transfer sheets based on heat-sensitive plastic films, and it is possible to print them thermally without causing sticking, thereby reducing the resistance to cutting and ease of processing that plastic films have. You can take advantage of the advantages of

The thermal transfer sheet of the present invention as described above is capable of good printing on conventionally known transfer materials such as plastics, paper, metals, and any other transfer materials, but is particularly suitable for transfer materials that require abrasion resistance. It is made of a material such as paper or a surface-treated plastic sheet, and is suitable for printing on commuter passes, cards, packaging materials with bar codes, etc.

(Effects) According to the present invention as described above, by using a dye as a colorant in an ink composition and lowering the melt viscosity of the ink, the ink layer becomes as low in viscosity as a liquid during thermal transfer, and it penetrate into the organization. At the same time, since the colorant is a dye dissolved in the ink, it penetrates into the paper structure and provides prints or images with excellent fixation and abrasion resistance similar to liquid ink prints or images, and can be rubbed against the surface. The ink layer will not peel off, nor will it contaminate other items, nor will the printed surface become dirty.

(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.

Examples 1 to 2 and Comparative Example 1 Ink compositions A and B for thermal transfer sheets of the present invention and ink composition C of comparative example having the following compositions were prepared, and each of these inks had a film thickness of 3 μm when dried. Thermal transfer sheets A, B, and C of the present invention and comparative examples were obtained by forming the thermal transfer sheets A, B, and C of the present invention and comparative examples on one side of a 12 μm thick capacitor paper using a conventional method.

Special Black EB (Orient Chemical, Nigrosine dye) 6.0 parts Carnauba wax 1
No. (natural ester wax)
75.0 parts Paraffin 135°F (manufactured by Nippon Seiro, petroleum wax) 15.0 parts Mark AO-50 (manufactured by Adeka Argus, antioxidant) 0.2
Bufu 2 Hiki 1 bottom m Special Black EB (Orient Chemical, Nigrosine dye) 5.0 parts Carnauba wax No. 1 (natural ester wax)
76.0 parts Parafiiso HNPIO (manufactured by Hiki Seiro, petroleum wax) 15.0 parts Lubricant (VLZ200, manufactured by Yoken Fine Chemicals, stearic acid) 2.0 parts To the mark 〇-5
0 (manufactured by Adeka Argus, antioxidant) 0.2 parts Non-λhikumisaiyudany Special Black EB (manufactured by Orient Chemical, nigrosine dye) 5.0 parts Carnauba wax 1
No. (natural ester wax)
40.0 parts Parafiiso HNPIO (manufactured by Nippon Seiro, petroleum wax) 40.0 parts Behenic acid (manufactured by Dai-ichi Croda Chemical) 10.0 parts Sumirard KCl0 (manufactured by Sumima Kagaku Kogyo, ethylene vinyl acetate copolymer) 10.0 Department mark AO-
50 (manufactured by Adeka Argus, antioxidant) 0.2 parts The melt viscosity (cps) of the above ink composition was as shown in Table 1 below.

Using the above three types of thermal transfer sheets A, B, and C, and using plain paper as the transfer paper, thermal transfer was performed using a commercially available thermal head, and the fixability of the resulting printed matter was investigated. It was as shown in Table 1.

Table 1 Ink A Ink B Ink C Melt viscosity 100℃ 35 35 135120℃
20 20 85 Fixing property OOX The fixing property was measured using a rotary ablation tester using abrasion wheel C3-10 with a load of 500 gf and a rotation speed of 70
The sample was rotated 10 times under the condition of rpm, and the degree of contamination of the non-printed area was visually compared, and those with little contamination were marked as O1, and those with severe contamination were marked with X.

Claims (9)

[Claims] (1) In an ink composition for a thermal transfer sheet consisting of a colorant and a low melting point material, the colorant is a dye and
An ink composition for thermal transfer sheets, characterized in that it has a melt viscosity of 50 cps or less. (2) Claim No. (1) in which the dye is an oil-soluble dye
The ink composition described in . (3) The ink composition according to claim (1), wherein the dye is nigrosine black. (4) The ink composition according to claim (1), wherein the low melting point material contains carnauba wax as a main component. (5) In a thermal transfer sheet having a heat-melting ink layer made of a colorant and a low-melting point material on one side of a base sheet, the colorant is a dye and the melt viscosity of the ink layer at 100°C is 50 cps or less. A thermal transfer sheet characterized by: (6) Claim No. (5) in which the dye is an oil-soluble dye
Thermal transfer sheet described. (7) The thermal transfer sheet according to claim (5), wherein the dye is nigrosine black. (8) The thermal transfer sheet according to claim (5), wherein the low melting point material contains carnauba wax as a main component. (9) The thermal transfer sheet according to claim (5), wherein the base sheet is a capacitor paper.