JPH06219026A - Thermal transfer sheet - Google Patents

Abstract

(57) [Summary] [Objective] Under the storage conditions normally required for thermal transfer sheets, the blocking phenomenon is suppressed without softening, and the multi-time printing performance is impaired even when used as a multi-time thermal transfer sheet. Provided is a thermal transfer sheet capable of increasing the number of printable times. [Structure] A heat-fusible ink layer is provided on one surface of a base film, and a colorant-free uppermost layer formed by mixing carnauba wax and microcrystalline wax is provided thereon.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermal transfer sheet.

[0002]

2. Description of the Related Art Conventionally, when printing an output print of a computer, a word processor or the like by a thermal transfer system, a thermal transfer sheet having a heat-fusible ink layer on one surface of a base film is often used. A conventional thermal transfer sheet uses a base material film such as capacitor paper or paraffin paper having a thickness of about 10 to 20 μm or a plastic film such as polyester or cellophane having a thickness of about 3 to 20 μm. A heat-meltable ink layer is formed by applying a heat-meltable ink in which wax is mixed with a coloring agent such as a pigment or a dye. Then, a predetermined portion is heated and pressed by a thermal head from the back side of the substrate film, and the heat-meltable ink layer at a portion of the heat-meltable ink layer corresponding to the printing portion is transferred to the transfer material to perform printing. . However, in such a conventional thermal transfer sheet, since the ink layer or the ink layer and other layers on the thermal transfer sheet are melted by the thermal energy of the thermal head and printing is performed by pressure-bonding to paper, the ink layer or the ink layer is printed. The other layers were vulnerable to heat, and had a characteristic of poor storage stability at high temperatures as compared with other printing methods. Therefore, in the case of an ink layer or an ink layer and other layers having a low melting point / softening point, under a high temperature condition in a ribbon roll state, a blocking phenomenon in which the ink layer or the ink layer and other layers migrate to the back layer may occur. I was seen.

[0003]

In the conventional thermal transfer sheet, the composition of the ink layer was changed to one having a high melting point and a high softening point to improve the storability, but there was a problem that the printing performance was changed. there were. The present invention has been made in view of such circumstances, and an object thereof is to provide a thermal transfer sheet having good storage stability.

[0004]

In order to achieve such an object, the present invention has a heat-fusible ink layer on one surface of a base sheet, on which carnauba wax and microcrystalline wax are provided. The thermal transfer sheet was provided with an uppermost layer containing no mixed color material.

[0005]

[Function] As the uppermost layer of the thermal transfer sheet, a layer containing no coloring material, which is a mixture of carnauba wax and microcrystalline wax, is formed. The melting point of carnauba wax is about 87 ° C. and is used as the main component of the conventional ink layer. It is much higher than the conventional paraffin wax and does not soften under the storage conditions normally required for thermal transfer sheets, and prevents the back layer and ink layer or ink layer and other layers from sticking to each other and suppresses the blocking phenomenon. To do. Further, even when it is used as the uppermost layer of an ink ribbon which can be printed many times, it has an effect of increasing the number of times printing is possible without impairing the printing performance of many times.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The thermal transfer sheet of the present invention comprises a substrate film, a heat-fusible ink layer formed on one surface of the substrate film, and an uppermost layer. Further, the thermal transfer sheet of the present invention, if necessary, a primer layer for imparting adhesiveness between the base film and the heat-meltable ink layer,
It is also possible to provide a back layer on the other side of the base film. Furthermore, when the thermal transfer sheet of the present invention is used for printing a large number of times, a two-layered thermal melt comprising a first heat-fusible ink layer and a second heat-fusible ink layer provided thereon is formed on a substrate film. A conductive ink layer is provided, and the uppermost layer is formed thereon.

The substrate film used in the present invention may be the same as the substrate film used in the conventional thermal transfer sheet and is not particularly limited. Specific examples of the preferable substrate film include, for example, polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, and ionomer. Examples thereof include plastic films, condenser paper, papers such as paraffin paper, non-woven fabrics, and the like, and a substrate film obtained by combining any of these may be used. The thickness of such a base film can be appropriately selected depending on the material used so that the strength and the thermal conductivity are appropriate, and for example, 2 to 2
It is preferably about 5 μm. It is also possible to provide a slip layer on the back surface of the base film for preventing the thermal head from sticking and improving the slipperiness.

The hot-melt ink layer contains a wax component as a binder and a colorant, and further contains various additives as required. Examples of the wax component include microcrystalline wax, carnauba wax, paraffin wax, Fischer-Tropsch wax, various low molecular weight polyethylenes, waxes,
Waxes such as beeswax, whale wax, ivowa wax, wool wax, shellac wax, candelilla wax, petrolactam, partially modified wax, fatty acid ester and fatty acid amide are used. Among these, especially the freezing point is 50 to 7
0 ° C. and a melt viscosity at 100 ° C. of 10 to 200
Waxes in the mPas range are preferred.

The colorant can be appropriately selected from known organic or inorganic pigments or dyes,
For example, it has a sufficient coloring density and discolors due to light, heat, etc.
Those that do not fade are preferred. Further, it may be a substance that develops a color by heating or a substance that develops a color by coming into contact with a component applied to the surface of the transfer target. Furthermore, the color of the colorant is not limited to cyan, magenta, yellow and black, and colorants of various colors can be used.

When the adhesiveness between the base film and the heat-meltable ink layer is insufficient, the heat-meltable ink layer may be formed via a primer layer. The primer layer can be formed of acrylic resin, nylon resin, vinyl chloride copolymer, polyester resin, urethane resin, or the like, and the thickness is preferably about 0.1 to 0.5 μm.

When used in a thermal transfer sheet for multi-use printing, a second ink layer composed of a supercooling component and a colorant is formed on the hot melt ink layer. The resin used as a binder in the second ink layer is a supercooling component which is incompatible with the wax component used in the heat-meltable ink layer and has a melting point of 58 to 70 ° C and a freezing point of 20 to 50 ° C. Some are preferred. More specifically, the average molecular weight is 1,000 to 40,000, preferably 7,000 to 3,000.
The melt viscosity at 100 ° C. is 100 to
30,000 mPas, preferably 100-20000 m
In the range of Pas, polyester such as polycaprolactone or polyethylene glycol, or a silicone modified product of these is considered. Examples of the colorant used in the second ink layer include those used in the above first ink layer.

To form such an ink layer, first, a wax component, which is a binder of the heat-meltable ink layer, is heated and melted, and a coating liquid having a colorant dispersed therein is applied onto a substrate by a hot melt coating method. Coating is performed to form a heat-meltable ink layer having a thickness of 3 to 7 μm. Further, when it is used for a thermal transfer sheet for printing many times, a second layer is formed on the heat-meltable ink layer.
A supercooling component and a colorant, which are the binder of the ink layer, are dissolved in a solvent having a low solubility in wax of the above-mentioned heat-meltable ink layer such as methyl ethyl ketone and ethyl acetate, and the coating solution is applied by a gravure coating method and dried. It is necessary to form a second ink layer having a thickness of 2 to 7 μm.

In the present invention, carnauba wax is suitable as the component of the uppermost layer as an anti-blocking layer formed on these ink layers, because it has a high melting point and a strong coating film when applied. As a coating method, the cost is low and the coating amount is relatively small (0.3 to 3 g / m ² ).
It is suitable to apply an ink in which carnauba wax is dispersed in water, which can be stably applied, by a gravure coating method. However, carnauba wax is difficult to disperse in water by itself. Therefore, as a substance to be mixed with carnauba wax for dispersion, microcrystalline wax is suitable because it does not inhibit the effect as the anti-blocking layer.
Therefore, the uppermost layer is 35 parts by weight of carnauba wax,
It is formed by applying a coating solution in which 5 parts by weight of microcrystalline wax is mixed by a gravure coating method to a thickness of 0.3 to 3 g / m ² on the hot-melt ink layer.

[0014]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples.
A more specific description will be given. In the text, "part" or "%" means
Unless otherwise specified, it is based on weight. Example 1 Primer layer having the following composition, ink for the first ink layer, Mogami
The layer ink was adjusted. (Composition of ink for primer layer) Melamine resin filler (Nippon Shokubai Eposta S) 15 parts Polyester resin (Unitika Elitel 3200) 15 parts Toluene 48 parts MEK 22 parts (Ink composition for first ink layer) Carbon black (Mitsubishi Chemical manufactured diamond black) 10 parts Ethylene / vinyl acetate copolymer 10 parts Carnauba wax 9 parts Paraffin wax (freezing point 64 ° C, melt viscosity 80 mPas) 70 parts (composition of ink for the uppermost layer) carnauba wax 35 parts Microcrystalline wax 5 parts Water 60 parts Next, as a base film, a polyethylene film having a thickness of 6 μm is used.
The back layer is formed on one side of the rephthalate film, and the other
On the surface of the ink for the primer layer and the ink for the first ink layer.
Ink in this order and dry to form a thermal transfer sheet.
Formed. The primer layer and the top layer are gravure coat.
Coating amount of 0.3 g / m ² , 0.3 g /
m ² The first ink layer is hot melt low
Coating amount of 4.5 g / m ² Applied at the ratio of
Was formed, and this was designated as sample 1. Example 2 A primer layer having the same composition as in Example 1 and an ink for the first ink layer
Ink for the top layer and ink for the second ink layer with the following composition
I adjusted the tank. (Composition of ink for the second ink layer) Carbon black (Mitsubishi Black manufactured by Mitsubishi Chemical) 12 parts Supercooling component (Plaxel H1P, freezing point 30 ° C) 80.4 parts Ethylene / vinyl acetate copolymer 6.6 parts MEK 276 parts Next, a polyethylene film having a thickness of 6 μm was used as a base film.
The back layer is formed on one side of the rephthalate film, and the other
On the surface of the ink for the primer layer and the ink for the first ink layer.
Ink and the ink for the second ink layer in this order and dry.
When dried, a primer layer and a two-layer heat-meltable ink layer
Was formed to obtain a thermal transfer sheet. The primer layer,
2 For ink layer and top layer, use the gravure coating method
Dry coating amount 0.3g / m ² , 2 g / m ² , 1 g / m
² The first ink layer is a hot melt roll.
Dry coating amount by coating method 3g / m ² Apply at the ratio of
It was formed, and this was made into sample 2. Example 3 With the same layer configuration as in Sample 2, the coating amount of the uppermost layer was 0.5 g / m.
² Was used as Sample 3. Comparative Example 1 Further, Comparative Example 1 was obtained by omitting the uppermost layer of Sample 2. (Storage test conditions) Temperature 50 ° C Humidity 80% Storage time 24 hours Storage test result

[0015]

[Table 1]

[0016]

As described in detail above, according to the present invention, a layer containing no coloring material, which is a mixture of carnauba wax and microcrystalline wax, is formed as the uppermost layer of the thermal transfer sheet, and the melting point of carnauba wax is formed. Is about 87 ° C
It is much higher than paraffin wax that has been conventionally used as the main component of the ink layer, and does not soften under the storage conditions normally required for thermal transfer sheets, and the back layer and ink layer or the ink layer and other layers Prevents close contact and suppresses the blocking phenomenon. Further, even when it is used as the uppermost layer of a multi-time printable thermal transfer sheet, it has the effect of increasing the number of printable times without impeding the multi-time printing performance.

Claims (3)

[Claims] 1. A base sheet having a heat-fusible ink layer on one side thereof, and a colorant-free uppermost layer formed by mixing carnauba wax and microcrystalline wax is provided on the heat-meltable ink layer. A thermal transfer sheet. 2. The coating amount of the uppermost layer containing no coloring material, which is a mixture of carnauba wax and microcrystalline wax according to claim 1, is 0.3 to 3 g / m ^2. Thermal transfer sheet. 3. A base film having a first heat-meltable ink layer and a second heat-meltable ink layer containing a supercooling component on one surface of the base film, and carnauba wax and microcrystalline wax on the first heat-meltable ink layer. A thermal transfer sheet that can be printed many times, which is provided with an uppermost layer that does not contain a coloring material, which is obtained by mixing