JPH0755583B2 - Thermal transfer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an improvement of a heat-sensitive transfer sheet, and more specifically, to a transfer paper having a low surface smoothness, which prevents scumming due to hot-melt ink. The present invention also relates to a heat-sensitive transfer sheet capable of giving high quality printing.

[Conventional technology]

When printing an output print of a computer or a word processor by a thermal transfer method, a thermal transfer sheet having a heat-meltable ink layer on one surface of a base film and a thermal head are used. Conventional thermal transfer sheets use 10 to 20μ thick condenser paper or paraffin paper as the base film, or 3 to 20μ thick plastic film such as polyester or cellophane, and use wax as a pigment. It is manufactured by providing a mixed hot-melt ink layer by coating.

[Problems to be solved by the invention]

When output printing is performed on a transfer paper using a conventional heat-sensitive transfer sheet, the heat-melted and softened ink directly contacts the surface of the transfer paper, and the transfer paper and transfer sheet move at high speed, which causes scumming. It often happened.

Further, although the thermal transfer method can print on plain paper, it cannot necessarily print clearly on all plain paper. When the smoothness of the transferred paper is expressed as Beck's smoothness, the best printing is possible with high-quality paper or coated paper that has been subjected to a calendar process that shows a value of 100 seconds or more. Good print quality. However, if a transfer paper with a low smoothness that does not reach 50 seconds is used, the sharpness of the print will deteriorate. This is because in the case of a paper having a highly uneven surface, the pressure of the thermal head does not allow the ink and the paper to come into complete contact with each other, and the portions that do not come into contact result in poor transfer.

Further, the thermal transfer method has a drawback that the printing speed is slower than that of the impact method, and improvement is desired. In order to increase the printing speed, the level of thermal energy applied to the thermal head must be increased, which may lead to bleeding of the printing, and the above-mentioned background smear is further aggravated. The present invention has been made in view of the above circumstances, and an object thereof is to perform clear printing even on a transfer paper having a low surface smoothness without causing scumming even if a high-speed thermal transfer is performed. The object is to provide a heat-sensitive transfer sheet that can give

[Means for solving problems]

As a result of trial production and testing of heat-sensitive transfer sheets having various configurations, the inventor has found that providing a surface layer having a specific layer thickness on the surface in contact with the transfer paper is effective for achieving the object of the present invention.

That is, in the heat-sensitive transfer sheet of the present invention, a transfer layer consisting of a heat-meltable ink layer and a surface layer for stopping the printed portion during transfer is formed on one surface of the base film. The thermal transfer sheet is characterized in that the surface layer is made of wax and has a thickness of 0.1 μm or more and less than 1 μm.

As an aspect of the present invention, an extender pigment can be included in the surface layer.

In the embodiment of this invention, as the wax, microcrystalline wax, carnauba wax, paraffin wax, Fischer-Tropsch wax, low molecular weight polyethylene, wooden wax, beeswax, spermaceti wax, ivota wax, wool wax, shellac wax, candelilla wax, montan. Waxes, petrolatum, partially modified waxes, fatty acid esters, or amides can be used.

In one aspect of the present invention, silica is used as an extender pigment,
A material selected from talc, calcium carbonate, precipitated barium sulfate, alumina, titanium white, clay, magnesium carbonate and tin oxide can be used.

As one aspect of the present invention, a plastic film may be used as the base film, and a sticking prevention layer may be provided on the surface in contact with the thermal head.

As one aspect of the present invention, a matte layer may be provided between the base film and the heat-fusible ink layer, or the surface of the base film on the transfer film side may be matted.

Base Film As the base film used in the present invention, the conventional base film can be used as it is, and other base films can also be used, and are not particularly limited. As the type of the film, for example, polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride,
There are polyvinyl alcohol, fluororesin, hydrochloric acid rubber, plastics such as ionomers, papers such as condenser paper and paraffin paper, non-woven fabrics, and the like, or a film obtained by combining these.

The thickness of this base film can be appropriately changed depending on the material so that its strength and thermal conductivity are appropriate, but the thickness is, for example, 3 to 25 μm.

Heat-meltable ink layer The heat-meltable ink used in the present invention may be composed of a colorant and a vehicle, and may further contain various additives if necessary.

The colorant is preferably an organic or inorganic pigment or dye having good characteristics as a recording material, for example, a pigment having a sufficient coloring density and not discolored by light, heat, humidity or the like.

Further, it may be a substance which is colorless when not heated but develops a color when heated, or a substance which develops a color when contacted with a substance applied to a transfer target. In addition to the colorants forming cyan, magenta, yellow and black, colorants of various other colors can be used. That is, in the hot-melt ink, carbon black or various dyes and pigments are selected and added as a colorant according to the color to be given to the ink.

Waxes, drying oils, resins, mineral oils, cellulose and rubber derivatives and the like and mixtures thereof are used as the vehicle.

Here, typical examples of the wax include microcrystalline wax, carnauba wax, and paraffin wax. In addition, Fischer-Tropsch wax, various low molecular weight polyethylene, wood wax, beeswax, whale wax, ivowa wax, wool wax, shellac wax, candelilla wax, petrolatum, partially modified wax,
Various waxes such as fatty acid esters or amides are used.

Here, as the resin, for example, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polyethylene, polystyrene, polypropylene, polybutene, petroleum resin, vinyl chloride resin, polyvinyl alcohol, chloride Vinylidene resin, methacrylic acid,
Polyamide, polycarbonate, fluororesin, polyvinyl formal, polyvinyl butyral, acetyl cellulose, nitrocellulose, polyvinyl acetate, polyisobutylene, ethyl cellulose, polyacetal or the like is used.

Here, in order to impart good thermal conductivity and melt transferability to the ink layer, a thermal conductive substance can be added to the ink. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, molybdenum dioxide and the like.

The direct or indirect coating of the heat-meltable ink layer on the base film can be carried out by hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating and many other means. The thickness should be determined so as to balance the required printing density and thermal sensitivity, and is in the range of 0.1 to 30 .mu.m, preferably 1 to 20 .mu.m.

Surface Layer In the present invention, the surface layer forms a part of the transfer film, forms a surface on the side in contact with the transfer paper, and serves to stop the printed portion of the transfer paper at the time of transfer and also to prevent scumming. Have.

In the present invention, the surface layer is made of wax, and may have an extender pigment and other optional additives added as necessary. Typical examples of this wax are microcrystalline wax, carnauba wax, paraffin wax and the like. Further, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes and some modified waxes, fatty acid esters, amides, waxes, beeswax, spermaceti wax, ibota wax, wool wax, shellac wax, candelilla wax, petrolatum are also used. be able to.

The wax used in the surface layer is the same as or different from the wax used in the heat-meltable ink layer. As a preferred embodiment of the present invention, both waxes can be different from each other as follows. That is, a surface layer is provided on the heat-meltable ink layer, a vehicle such as wax having a relatively low melting point is used for both, and that of the heat-meltable ink has a relatively low melting point, for example, 40 to 80 ° C. The high thermal sensitivity of the ink enables high-speed thermal transfer. On the other hand, the surface layer in contact with the transfer paper has a relatively high melting point, for example, 50 to 100 ° C. However, the occurrence of printing blurring is reduced. Therefore, an appropriate combination can be determined so that the above-mentioned melting point range and melting point difference, for example, 10 to 60 ° C. are satisfied.

It is recommended to add an appropriate amount of extender pigment to the surface layer. This is because bleeding and tailing of the print can be prevented.

The particle size of the extender pigment is not suitable if it is too large.
Suitable as extender pigments are inorganic fillers such as silica, talc, calcium carbonate, precipitated barium sulfate, alumina, titanium white, clay, magnesium carbonate, carbon black or tin oxide.

When the amount of the extender pigment is small, the effect is poor. On the other hand, when the amount is large, the dispersibility is lowered to make it difficult to adjust the ink.
The coated product may easily fall off the base film, so it is recommended to add it in the range of 0.1 to 60% by weight.

As described above, the surface layer may optionally include a colorant,
Or configure without adding. If a colorant is used, it overlaps with the colorant in the ink layer to give a sufficient density of recording, and if only a colorless vehicle is used, it is possible to prevent the transfer paper and the ink layer from rubbing and causing scumming.

The coating of the surface layer can also be done by various techniques.
The thickness of this layer is 0.1 μm or more and less than 1 μm in the present invention so that the sensitivity is not insufficient even when the printing energy is low as in a high-speed type printer. If the thickness is less than 0.1 μm, the ink layer on the paper to be transferred may be rubbed to cause scumming.

Sticking Prevention Layer When a heat-sensitive material is used for the base film, it is preferable to provide a layer for preventing sticking to the thermal head on the surface in contact with the thermal head. The sticking prevention layer has a heat-resistant resin and a substance acting as a thermal release agent or a lubricant as basic constituent components. As a heat-resistant resin, a synthetic resin having a glass transition point of 60 ° C or higher, a thermoplastic resin having an OH group or a COOH group, a compound having two or more amino groups, or a diisocyanate or triisocyanate to be crosslinked to some extent Those that have been cured are preferred. Thermal release agents or lubricants, such as waxes and amides, esters and salts of higher fatty acids, which act by melting when heated, and fluororesins and inorganic substance powders remain solid. Some are useful.

By providing such a sticking-preventing layer, thermal printing can be performed without sticking even on a heat-sensitive transfer sheet using a plastic film that is weak against heat as a base material, and the plastic film has a difficulty in cutting and processing. You can take advantage of advantages such as ease of use.

Matte layer / Matte processing Thermal transfer is generally glossy and beautiful, but on the other hand,
Matte printing may be desirable because it can make documents difficult to read. In such a case, for example, as proposed by the applicant (Japanese Patent Application No. 58-208306), a base film is coated with a dispersion of inorganic pigments such as silica and calcium carbonate in an appropriate solvent. It is advisable to form a heat-sensitive transfer sheet by coating the heat-fusible ink on the mat layer. Alternatively, the base film itself may be matted before use (the technique of Japanese Patent Application No. 58-208307 proposed by the applicant).

Needless to say, the present invention can be applied to a heat-sensitive transfer sheet for color printing, so that a multicolor heat-sensitive transfer sheet is also included in the scope of the present invention.

[Operation and effect of the invention]

In the thermal transfer sheet of the present invention, the surface layer is made of wax and the thickness thereof is set to 0.1 μm or more and less than 1 μm. Although the mechanism by which this sheet is effective for achieving the object of the present invention is not logically clear, it is considered as follows. That is, the surface layer on the heat-meltable ink layer is heated by the thermal head and migrates onto the transfer paper together with the ink layer. At that time, it is considered that the surface layer prevents direct contact between the ink layer and the paper surface to prevent the background stain. In addition, the surface layer transferred to the transfer paper fills the irregularities on the surface of the transfer paper to improve the smoothness. The same high quality printing as when transferring to existing paper is realized.

In any case, the following effects can be obtained by the present invention.

(A) It is possible to prevent scumming on the transfer paper even at high speed thermal transfer printing, not to mention low speed.

(B) High-quality printing can be performed even under the severe conditions of high-speed heat-sensitive transfer and the transfer paper being rough paper with low surface smoothness.

〔Example〕

 The present invention will be specifically described by the following examples.

Example 1 A 3.5 μm-thick polyethylene terephthalate film was used as a base film, and a heat-meltable ink and a surface layer material having the following composition (“parts” were parts by weight, the same applies hereinafter) were prepared on one side thereof. The coating was carried out by the means additionally described.

Heat-fusible ink layer Carbon black “Dia Black G” (Mitsubishi Kasei) 15
Part Ethylene / vinyl acetate copolymer "EVA Flex 310" (Mitsui Polychemicals) 8 parts Paraffin wax "Paraffin 150 ° F" (Nippon Seiwa)
50 parts Carnauba wax 25 parts Kneading at 120 ℃ for 6 hours using an attritor, 3.5g / m by 120 ℃ hot melt roll coating method
Apply at a rate of ² (dry state).

Surface layer 155 ° F paraffin wax emulsion "WE-70" (Bond Wax, solid content 40% aqueous emulsion) 10 parts 60% isopropanol aqueous solution 15 parts At a ratio of 0.8 g / m ² (dry state) by gravure coating method Application.

Using the thermal transfer sheets with the ink layer and surface layer thicknesses of 3.5μ and 0.8μ respectively, select several types of high-smooth high-quality paper to low-quality medium paper as the transfer paper, and use a commercially available thermal head. Was used for thermal transfer printing. With the thermal head energy of 0.7 mJ / dot, high-speed printing of 40 characters / sec was achieved with high quality without scumming on all transfer paper.

Example 2 Using the same base film as in Example 1, two layers of the following composition were applied.

Hot-melt ink layer Same as in Example 1.

Surface layer 155 ° F Paraffin wax emulsion "WE-70" (Bond Wax Co., solid content 40%, aqueous emulsion) 70 parts Silane treated silica emulsion "Bond wax WE-"
3 "(Bond Wax Company, solid content 10%) 30 parts 50% isopropanol aqueous solution 50 parts Coated at a rate of 0.5 g / m ² (dry state) by the gravure coating method.

This heat-sensitive transfer sheet in which the thickness of the ink layer was 3.5 μm and the thickness of the surface layer was 0.5 μm, respectively, showed good transfer performance as in Example 1.

Example 3 The same base film as in Example 1 was used to apply two layers of the following composition.

Hot-melt ink layer Same as in Example 1.

Surface layer Carvana emulsion "WE-90" (Bond Wax,
Solid content 40%) 10 parts 70% Isopropanol aqueous solution 10 parts Coated at a rate of 0.3 g / m ² (dry state) by the roll coating method.

The transfer sheet of this example in which the thickness of the ink layer was 3.5 μ and the thickness of the surface layer was 0.3 μ, respectively, also showed good transfer performance without background stains.

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Claims (7)

[Claims] 1. A heat-sensitive transfer sheet in which a transfer layer composed of two layers, a heat-fusible ink layer and a surface layer for blocking a printed portion of a transfer-target paper at the time of transfer, is formed on one surface of a base film. The heat-fusible ink layer comprises a colorant and a vehicle,
The surface layer is made of wax and has a thickness of 0.1 μm
And less than 1 μm, and the melting point of the heat-meltable ink layer is
40 to 80 ° C., the melting point of the surface layer is 50 to 100 ° C., and the melting point of the surface layer is 10 to 60 ° C. higher than the melting point of the heat-meltable ink layer. Thermal transfer sheet. 2. The heat-sensitive transfer sheet according to claim 1, wherein the surface layer contains an extender pigment. 3. The wax is microcrystalline wax, carnauba wax, paraffin wax, Fischer-Tropsch wax, low molecular weight polyethylene,
Claims: At least one selected from the group consisting of wood wax, beeswax, spermaceti wax, ivowa wax, wool wax, shellac wax, candelilla wax, montan wax, petrolatum, partially modified wax, fatty acid ester and amide. The heat-sensitive transfer sheet according to item 1 above. 4. An extender pigment selected from silica, talc, calcium carbonate, precipitated barium sulfate, alumina, titanium white, clay, magnesium carbonate and tin oxide is used. The heat-sensitive transfer sheet described. 5. The heat-sensitive transfer sheet according to claim 1 or 2, wherein a sticking prevention layer is provided on the surface in contact with the thermal head. 6. A matte layer is provided between the base film and the heat-meltable ink layer, and the matte layer is provided.
The heat-sensitive transfer sheet according to item 2 or 5. 7. The heat-sensitive transfer sheet according to claim 1, 2 or 5, wherein the surface of the base film on the transfer film side is matt processed.