JPH01214478A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To obtain a clear print with high density, by a method wherein the pigment concentration per unit area of a heat-fusible ink layer of a thermal transfer sheet used in an N-times mode process is set to a concentration represented by a specified formula. CONSTITUTION:An N-times mode process is a thermal transfer process in which the feeding velocity (N) of a transfer recording material is set to be greater than the feeding velocity (N') of a thermal transfer sheet when thermal transfer by a thermal head is conducted by superposing the sheet and the recording material on each other. The pigment concentration per unit area, P(g/m<2>), of a heat-fusible ink layer of the thermal transfer sheet used for the N-times mode process is set to be P'XN/N', where P' (g/m<2>) is the pigment concentration per unit area of an ink layer of an ordinary thermal transfer sheet. For example, where N/N'=2, P is set to 2P'. By this, high-density printing can be performed even in the N-times mode process. The pigment concentration of the ink layer can be enhanced by a method wherein the concentration of a pigment in a wax ink is preliminarily enhanced, or a method wherein the thickness of the ink layer itself is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to improvements in thermal transfer sheets, and more specifically to a general thermal transfer method and a thermal transfer method in which the conveyance speed of the transfer material is higher than the conveyance speed of the thermal transfer sheet. The present invention relates to a thermal transfer sheet capable of printing with high density in the 8x mode method (hereinafter simply referred to as the 8x mode method).

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

This conventional thermal transfer sheet uses a paper such as capacitor paper or paraffin paper with a thickness of 10 to 20 μm, or a plastic film such as polyester or cellophane with a thickness of 3 to 20 μm as a base film, and contains pigments, dyes, etc. in wax. This product is manufactured by coating a layer of hot-melt ink mixed with a coloring agent.

In the 8x mode method using these thermal transfer sheets, the conveyance speed of the transfer material is N, and the conveyance speed of the thermal transfer sheet is N'.
and NUN'', the printing distance is N, but
Since the consumption distance of the thermal transfer sheet is N', there is an advantage that the consumption amount of the thermal transfer sheet can be saved relative to the printing distance, but the problem is that the print density is approximately N'/N, which inevitably lowers the print density. There is.

The present invention was made against the background of the above-mentioned circumstances,
The purpose is to provide a thermal transfer sheet that can provide clear printing with high density even when thermal transfer is performed using the N-times mode method.

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

That is, the present invention provides a thermal transfer method in which, when a thermal transfer sheet and a material to be transferred are stacked and thermal transfer is performed using a thermal head, the conveyance speed (N) of the material to be transferred is set higher than the conveyance speed (N') of the thermal transfer sheet. This thermal transfer sheet is characterized in that the pigment concentration (P) per unit area of the heat-fusible ink layer is expressed by the following formula (g/rn').

P=P'×N/N' However, P' in the above formula is the pigment concentration (g/rn2) per unit area of the ink layer in the case of NUN', and N/N'
>1.3.

(Function) When forming a heat-fusible ink layer, assuming a thermal transfer method using the N-fold mode method, and assuming that the pigment concentration per unit area of the ink layer of a normal thermal transfer sheet is P', the ink layer By setting the pigment concentration P per unit area to P'XN/N', high-density printing is possible even in the N-fold mode method.

(Preferred Embodiments) Next, the present invention will be explained in more detail with reference to preferred embodiments.

The heat-sensitive transfer sheet of the present invention has a heat-melting ink layer on one surface of a base film, and further has a surface layer made of wax formed thereon as required.

As the base film used in the present invention, the same base film used in conventional thermal transfer sheets can be used as is, and other base 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, fluororesin, chlorinated rubber, ionomer, etc. Examples include plastics, papers such as condenser paper and paraffin paper, and nonwoven fabrics, and base films made of composites of these materials 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 25 μm.
It is m.

The heat-melting ink layer provided on the base film is composed of a pigment and a vehicle, and may further contain various additives as required.

The pigment is preferably an organic or inorganic pigment that has good properties as a recording material, for example, one that has sufficient color density and does not change color or fade due to light, heat, temperature, etc.

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 products such as Fischer-Tropsch wax, various low-molecular-weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolactam, polyester wax, assorted waxes, fatty acid esters, fatty acid amides, etc. Wax is used. Furthermore, a thermally conductive substance can be blended into the hot-melt ink in order to provide the hot-melt ink layer with good thermal conductivity and melt transferability. This substance includes carbonaceous substances such as carbon black, aluminum,
Examples include copper, tin oxide, and molybdenum dioxide.

Methods for directly or indirectly forming a hot-melt ink layer on the base film include applying the above-mentioned ink by hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods. There are methods etc.

In the present invention, when forming an ink layer as described above, the pigment concentration P of the ink layer is set to about 0.06 to 1 g/rn per area of the ink layer, whereas the pigment concentration P' of the conventional thermal transfer sheet is about 0.06 to 1 g/rn per area of the ink layer.
', but in order to fit the N-fold mode method,
In relation to N and N' in the above definition, P'×N/N
', for example, N/N'-2
If so, the concentration is 2P'.

There are two methods for increasing the pigment concentration in the ink layer: increasing the pigment concentration in the wax ink in advance, and increasing the thickness of the ink layer itself. Either method may be used in the present invention. . When N/N' is a value of 1.5 or more, it is practically difficult to increase the pigment concentration of the ink corresponding to this value, so the thickness of the ink layer may be reduced without increasing the pigment concentration too much. It is preferable to increase the amount. According to this method, even if the value of N/N' is 2 or more, it can be satisfactorily handled. In reality, N/N′ in the N-fold mode method
Since the value of is about 1.4 to 10, the pigment concentration of the ink layer in the present invention is - number Generally 0.06 to 1g/
rr+', the concentration is generally multiplied by N/N', for example, 0.08 to 10 g/d. Also, if the pigment concentration in the ink is the same as the conventional concentration, the thickness of the conventional ink layer is about 2 to 5 μm, so the thickness multiplied by N/N', for example, 2.6 ~2
A thickness of 0 μm is common.

In the present invention, the surface layer formed on the ink layer forms a part of the transfer film, and forms the surface in contact with the transfer paper to prevent scumming during transfer, and also prevents the ink layer from forming on the transfer paper. It has the function of improving adhesiveness.

The wax used to form the surface layer may be the same as the wax used in the hot-melt ink layer described above.

Further, a thermoplastic resin can be used in combination with the surface layer to improve adhesion. Examples of such thermoplastic resins include ethylene-vinyl acetate copolymer (EV8),
Ethylene-acrylic acid ester copolymer (EE8), polyethylene, polystyrene, polypropylene, polybdenum, petroleum resin, vinyl chloride resin, vinyl chloride-vinyl acetate resin, polyvinyl alcohol, vinylidene chloride resin,
Methacrylic resin, polyamide, polycarbonate fluororesin, polyvinyl formal, polyvinyl butyral, acetyl cellulose, nitrocellulose, polyvinyl acetate, polyisobutylene, ethyl cellulose, polyacetal, etc. are used, especially those with low softening properties compared to conventional heat-sensitive adhesives. Those having a softening point of, for example, 50 to 80°C are preferred.

The surface layer made of the wax (and thermoplastic resin) is
It is formed by applying and cooling a molten liquid containing these mixtures, applying and drying an organic solvent solution containing the above mixture, and further applying and drying an aqueous dispersion containing particles of the above mixture.

The coating of the surface layer, as well as the formation of the ink layer, can also be done by various techniques. In the present invention, the thickness of this layer is preferably 0.5 mm to prevent insufficient sensitivity even when printing energy is low as in high-speed printers.
It is 1 μm or more and less than 5 μm. If the thickness is less than 0.1 μm, there is a risk that the transfer paper and the ink layer will rub against each other, resulting in scumming.

It is recommended that an appropriate amount of extender pigment be added to the surface layer. This is because bleeding and trailing of printed characters can be better prevented.

As described above, the surface layer may or may not contain a colorant, if necessary. If a coloring agent is used, it overlaps with the coloring agent of the hot-melt ink layer to provide a recording of sufficient density,
If only a colorless vehicle is used, it is possible to prevent background smudges due to rubbing between the transfer paper and the heat-fusible ink layer.

When a heat-resistant material is used for the base film, 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 having OH or COOH groups, and a compound having two or more amino groups, or diisocyanate or triisocyanate added to slightly crosslink and cure. Preferably, those that cause Thermal mold release agents or lubricants include those that melt when heated, such as waxes and amides, esters, and salts of higher fatty acids, and those that remain solid, such as fluororesin and inorganic substance powders. There is something like that.

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, which reduces the difficulty of cutting and processing of plastic films. Benefits such as ease of use can be taken advantage of.

Thermal transfer images generally have glossy and beautiful prints, but the documents may become difficult to read, so matte prints are sometimes desirable. In such a case, for example, as proposed by the applicant (Japanese Patent Application No. 58-20830 [1]), inorganic pigments such as silica, calcium carbonate, etc. are dispersed in a suitable solvent on a base film. A heat-sensitive transfer sheet may be constructed by coating the matte layer with a heat-melting ink layer.

Alternatively, the base film itself may be matted and used.
307 technology).

It goes without saying that the present invention can be applied to heat-sensitive transfer sheets for color printing, and therefore multi-colored heat-sensitive transfer sheets are also included within the scope of the present invention. Further, as a thermal transfer printer, it can be applied to either a line or serial type.

(Effects) According to the present invention as described above, when forming a heat-fusible ink layer, an N-times mode thermal transfer method is assumed, and the pigment concentration per unit area of the ink layer of a normal thermal transfer sheet is reduced. P′
In this case, by setting the pigment concentration P per unit area of the ink layer to P'XN/N', high-density printing is possible even in the N-fold mode method.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 A polyethylene terephthalate film with a thickness of 3.5 μm was prepared as a base film and a heat-melting ink and a surface layer material having the following compositions were prepared on one side of the base film and coated and dried by the methods described respectively. A thermal transfer sheet of the present invention was obtained.

Acute Enemy I 2 Carbon Black (Diablack G, manufactured by Mitsubishi Kasei)
30 parts ethylene/vinyl acetate copolymer (EV Hachiraflex 31O1 manufactured by Mitsui Polychemicals) 5 parts paraffin wax (paraffin 15
50 parts carnauba wax (manufactured by Hiki Seiro) 50 parts carnauba wax 15 parts Attritor was kneaded at 120°C for 6 hours, and 3.
It was applied and dried at a rate of 5 g/rn' (dry state).

Yuketsuya 155F Parafine Wax Emulsion (WE-70
, manufactured by Bond Wax Co., Ltd., solid content 40% aqueous emulsion) 20 parts ionomer resin (Chemivar S-100, manufactured by Mitsui Petrochemicals, solid content 27'l;)
10 parts 60% Impropatool aqueous solution
0.8g/rn" (15 parts by gravure coating method)
(dry state) and dried at 60°C to form a matte surface layer.

The thickness of the ink layer and the surface layer is 3.5 μm and 0.8 μm, respectively.
Thermal transfer printing was carried out using the above-mentioned thermal transfer sheet of 1.m, selecting high-quality paper as the transfer paper, and using a commercially available thermal head. The energy of the thermal head is 0.7 W/dot, the conveying speed of the transfer paper is 40 cm/sec (N), the conveying speed of the thermal transfer sheet is 20 cm/sec (N'), and the N times mode (
When high-speed printing was performed with N/N' = 2), the pigment concentration was 15 copies, and high-density printing without background smearing was possible on the transfer paper, similar to the printing in the case of N/N phrase 1. It was dead.

Example 2 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention.

Shushinenki 42A counterfeit carbon black (Diablack G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EV Hachiraflex 310 manufactured by Mitsui Polychemicals) 8 parts paraffin wax (paraffin 15
50 parts carnauba wax (manufactured by Nippon Sabawa) 50 parts carnauba wax 25 parts Attritor was kneaded at 120°C for 6 hours, and an ink temperature of 7.0 was obtained by hot melt roll coating at 120°C.
g/rr? (dry state) and dried.

Surface layer 155F paraffin wax emulsion (WE-70
(manufactured by Bond Wax Co., Ltd., solid content 40% aqueous emulsion) 70 parts EVA resin emulsion (Bond Wax 62-357, made by Bond Wax Co., Ltd., solid content 40%) 10 parts 50% aqueous isopropanol solution 50 parts 0 by gravure coating method It was coated at a rate of .5 g/rn'' (dry state) and dried at 73°C to form a surface layer with a smooth surface.

The thickness of the ink layer and the surface layer is 7.0 μm and 0.5 μm, respectively.
This thermal transfer sheet also showed good transfer performance as in Example 1, with N/N'=1.8.

Example 3 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention.

Carbon black (dia black G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EVAV Rex 310, manufactured by Mitsui Polychemicals) 8 parts paraffin wax (paraffin 15
50 parts carnauba wax (manufactured by Nippon Seiro) 50 parts carnauba wax 25 parts Attritor was kneaded at 120°C for 6 hours, and 10g'
/rn'' (dry state) and dried.

Surface layer carnauba wax 10 parts ethylene/
After melting 2 parts of vinyl acetate copolymer resin (Evaflex 310, manufactured by Mitsui Polychemicals), the resulting emulsion (solid content 20%) was coated with 0.0% by roll coating method.
It was applied at a rate of 3 g/rn' (dry state) and dried at 60°C to form a matte surface layer.

The thickness of the ink layer and the surface layer is 10 μm and 0.3 μm, respectively.
The transfer sheet of this example also showed good transfer performance with N/N' = 2.2 and no scumming.

Example 4 Using a polyethylene terephthalate film with a thickness of 6 μm as a base film, yellow (Y) with the following composition,
An ink layer and a surface layer were formed using heat-melting inks of magenta (M), cyan (C), and black CB) and a surface layer ink to obtain a thermal transfer sheet of the present invention.

Eyebrow pigment (yellow, magenta, cyan or black pigment) 12 parts ethylene/vinyl acetate copolymer (Sumitate Kllney 10, manufactured by Sumitomo Chemical) 5.5 parts oxidized paraffin ester complex compound ( Amide Polymer T-820, made by Denka Polymer) 1
0.5 parts paraffin wax (paraffin 5P-0145, manufactured by Nippon Seiro) 13 parts microcrystalline wax (Himic 2065, manufactured by Nippon Seiro)
Part 8 Improper Tools
5 parts xylene 46
Section: An ink layer was formed by sequentially printing yellow, magenta, cyan, and black in the order of yellow, magenta, cyan, and black by a gravure printing method using the ink compositions of the above four colors. The coating weight at that time was 4 g/rn' (dry).

Blood loss 1 Carnauba emulsion (WE-95, manufactured by Bond Wax Co., Ltd., solid content 40%) 30 parts ethylene/vinyl acetate copolymer emulsion (Polysol EVAAD-
5. Made by Showa Kobunshi, solid content 56%)
10 parts 75% Improper Tool aqueous solution 60 parts Using the above ink composition, apply a dry weight of 0.7 g onto the hot melt ink layer previously printed in yellow, magenta, cyan, and black using a gravure printing method. /r
A surface layer was formed by coating to give n'. The drying conditions at that time were 65°C for 3 seconds.

When the thermal transfer sheet of the present invention prepared through the above steps was used to print with a color thermal printer at N/N'=1.7, printing with sufficient density was similarly possible.

Patent applicant: Dai Nippon Printing Co., Ltd. Agent: Patent Attorney Yoshi 1) Hiroshi Katsuki

Claims (1)

[Claims] (1) Used in a thermal transfer method in which the conveyance speed (N) of the transfer material is higher than the conveyance speed (N') of the thermal transfer sheet when the thermal transfer sheet and the transfer material are stacked and thermal transfer is performed with a thermal head. A thermal transfer sheet, characterized in that the pigment concentration (P) per unit area of the heat-melting ink layer is a concentration (g/m^2) expressed by the following formula. P=P'×N/N' (where P' is the pigment concentration (g/m^2) per unit area of the ink layer when N≒N', and N/N'>1.3 .)