JPH01226392A - Thermal transfer recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal transfer recording medium usable plural times and generating no lowering in the density of a transfer image, by providing an ink layer containing a colorant polyethylene oxide wax and candelilla wax and making the pore size of a microporous layer composed of a resin larger on a base material side but smaller on the surface side of the ink layer. CONSTITUTION:An ink layer 3 wherein thermal transfer ink 2 containing a colorant, polyethylene oxide wax and candelilla wax is contained in a microporous layer 1 composed of a heat resistant resin is provided on a base material 4. By making the pore size of the microporous layer larger on the base material side but smaller on the surface side of the ink layer, ink transfer quantity is made constant regardless of the use number of times to make it possible to obtain a thermal transfer recording medium showing no lowering of image density. It is necessary that the thermal transfer ink is inferior to the compatibility with the heat resistance resin forming the microporous layer at the time of melting by heating as well as at the time of dissolution by a solvent and candililla wax develops large effect in this point and, when the compatibility of the heat resistance resin and the thermal transfer ink is controlled by adding a proper amount of polyethylene oxide wax, the ink transfer amount of every time becomes uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal transfer recording medium used in printers, plotters, etc.

[Prior Art] A thermal recording method using a thermal transfer recording medium is widely put into practical use because of its ease of handling, low cost, and good storage stability. However, with conventional thermal transfer recording media, all of the ink in the printed area is transferred to the transfer target after one use, making it impossible to use the media repeatedly and resulting in high running costs. . In order to solve these drawbacks, Japanese Patent Application Laid-Open No. 54-6
8253@, JP-A No. 55-105579, etc., by using a thermal transfer recording medium in which an ink layer containing a thermal transfer ink in a microporous layer made of a heat-resistant resin is provided on a base material, a plurality of media can be printed. Proposals have been made to enable reuse. However, with these proposed methods, it is difficult to avoid a sudden drop in the density of the transferred image as the same location on the thermal transfer recording medium is used to print twice, thrice, and so on. there were.

[Purpose] The purpose of the present invention is to solve the drawbacks of conventional thermal transfer recording media, and more specifically, to provide a thermal transfer recording medium that can be used multiple times and does not reduce the density of transferred images. It is about providing.

[Structure] In order to achieve the above object, the present invention has a structure in which a heat transferable ink containing a colorant, oxidized polyethylene wax, and candelilla wax is contained in a microporous layer made of resin on a base material. To provide a thermal transfer recording medium provided with an ink layer, characterized in that the pore diameter of the microporous layer made of resin is larger toward the base material and smaller toward the surface of the ink layer. be.

The thermal transfer recording medium of the present invention will be described with reference to FIG. 1. A microporous layer 1 made of a heat-resistant resin contains a thermal transfer ink 2 containing a colorant, oxidized polyethylene wax, and candelilla wax. An ink layer 3 is provided on a base material 4.

The weight ratio of oxidized polyethylene wax and candelilla wax is preferably in the range of 1:2 to 1,
If the amount of oxidized polyethylene wax exceeds this range, not only will the energy required to transfer the thermal transfer ink to the transfer paper increase, but also the microporous layer of heat-resistant resin, which should not be transferred, will be transferred at once. This may cause you to be unable to use it multiple times. Also, if there is a lot of candelilla wax beyond this range,
As printing is repeated two or three times using the same location on the thermal transfer recording medium, the density of the transferred image decreases rapidly.

Heat-resistant resins used in the present invention include nylon resin, polyester resin, phenol resin, Epoquin resin,
Examples include polycarbonate resin, vinyl chloride resin, vinyl chloride vinyl acetate copolymer, and the like. As a coloring agent,
Although various dyes and pigments can be used, in consideration of the fixability of the transferred image, it is preferable to use pigments such as carbon black.

As the base material, conventionally known materials such as various papers, processed papers, and various resin films can be used.

In the conventional thermal transfer recording medium, as shown in FIG. 3, the pore diameter of the microporous layer made of a heat-resistant resin is almost uniform. In this case, the amount of ink transferred at the first use is approximately 1/2 of the total amount.
．． The amount of ink transferred during the second use is about 1/4 of the total amount, which is about 1/2 of the remaining amount after the first use. In this way, as the number of uses increases, the amount of ink transferred decreases, and a decrease in image density is unavoidable.

In the present invention, we have improved this point by making the pore diameter of the microporous layer made of heat-resistant resin larger toward the base material and smaller toward the surface of the ink layer, so that the amount of ink transferred remains constant regardless of the number of times it is used. A thermal transfer recording medium with no decrease in image density was obtained.

FIG. 2 is a schematic cross-sectional view of a thermal transfer recording medium of the present invention, and FIG. 4 is a schematic cross-sectional view of a conventional thermal transfer recording medium. The amount of ink to be transferred is 1/2 of the depth from the surface to the bottom for the first time.
Assuming that the second time is 1/4 of the depth, and the third time is 1/8 of the depth, and the total amount of ink is 100, comparing the amount of ink transferred each time, in Figure 4, the first time, 5012th time, 25.3rd time. 12.5, whereas in Figure 2 it is 12.5 for the first time.
5. Second time 29.7. Third time 24.8 The amount of ink transferred each time becomes uniform.

Roughly speaking, in the present invention, since the thermal transfer ink has a composition containing a colorant, oxidized polyethylene wax, and candelilla wax, the amount of ink transferred each time becomes more uniform.

The thermal transfer ink needs to have poor compatibility with the heat-resistant resin forming the microporous layer when it is dissolved by heating or by a solvent, and candelilla wax is very effective in this respect.

However, if a thermal transfer ink consisting only of a colorant and candelilla wax is used, the amount of ink transferred cannot be prevented from decreasing as the number of uses increases. Therefore, by controlling the compatibility between the heat-resistant resin and the thermal transfer ink by adding an appropriate amount of oxidized polyethylene wax, the amount of ink transferred each time can be made uniform.

Next, the method for manufacturing the thermal transfer recording medium of the present invention will be explained.

In order to form an ink layer on a base material in which a heat-transferable ink is contained in a microporous layer made of a heat-resistant resin, a solution containing a heat-resistant resin and a foaming agent is applied onto the base material and dried. Heat-resistant resin can be obtained by foaming a foaming agent by heating, or by coating a base material with a solution containing a water-soluble powder such as salt or starch and a heat-resistant resin, drying it, and then washing with water to wash away the water-soluble powder. The thermal transferable ink may be heated and melted and soaked into the microporous layer, or the ink may be dissolved in a solvent and soaked, and then the solvent may be evaporated. In addition, a solution in which the heat-resistant resin and the heat-transfer ink are dissolved or dispersed in a mixed solvent of a good solvent and a poor solvent for the heat-resistant resin, or a solution in which the heat-resistant resin and the heat-resistant resin are poorly compatible with each other, The thermal transfer recording medium of the present invention can also be obtained by applying and drying a solution in which a thermal transfer ink using a melting point material is dissolved or dispersed in a solvent onto a substrate.

In order to make the pore diameter of the microporous layer made of a heat-resistant resin larger toward the base material and smaller toward the ink layer surface, there is a method of laminating microporous layers with different pore diameters. In order to increase the pore size of the microporous layer, if a blowing agent or water-soluble powder is used, it is sufficient to increase the amount of the blowing agent or water-soluble fine powder relative to the heat-resistant resin. When using a mixed solvent of and a poor solvent, or when using a low melting point material that has poor compatibility with heat-resistant resin, a solution in which the heat-resistant resin and thermal transfer ink are dissolved or dispersed in a solvent is applied onto the base material. The solvent may be evaporated slowly at a low temperature during coating and drying.

The present invention can be achieved by forming an ink layer containing a heat transferable ink in a microporous layer with a large pore diameter on a base material, and then forming an ink layer containing a heat transferable ink in a microporous layer with a small pore diameter thereon. A thermal transfer recording medium is obtained. It is more preferable to increase the number of laminated layers so that the pore diameter of the microporous layer is larger on the base material side and gradually becomes smaller.

[Example] Next, the present invention will be explained with reference to Examples.

Example 1 3 parts by weight of carbon black, 9 parts by weight of candelilla wax, 3 parts by weight of oxidized polyethylene wax, 2 parts by weight of toluene
5 parts by weight and 60 parts by weight of MEK were mixed and dispersed in a ball mill for 15 hours to obtain a thermal transfer ink liquid. A resin liquid prepared by dissolving 8 parts by weight of vinyl chloride-vinyl acetate copolymer in 32 parts by weight of MEK was mixed with a thermal transfer ink liquid to obtain a coating liquid.

A 3.5 μm thick polyester film coated with a silicone resin on the surface was used as a base film, and the coating solution was applied using a wire bar, followed by air drying to give an ink layer thickness of 4 μm. Roughly apply the coating liquid on top of it with a wire bar and dry at 120℃ to obtain an ink layer thickness of 4μm and a total of 8μm.
The thermal transfer recording medium of the present invention was obtained in such a way that the temperature was 100 m.

Japanese word processor JP50D manufactured by Ricoh Co., Ltd.
When printing was repeated three times using the same location on the thermal transfer recording medium, the transferred image density each time was 1.
It was 17.1.03.0.93.

Example 2 A polyester film with a thickness of 3.5 μm coated with silicone resin on the back side was used as a base film, and the above coating solution C was applied.
was coated with a wire bar, dried at 120'C and coated with 3μ
An ink layer having a thickness of m was formed. Roughly coat the above coating solution B with a wire bar, dry at 120°C, and apply 2μ
An ink layer having a thickness of m was formed. Roughly coat the above coating solution A with a wire bar and dry at 120'C.
A μm thick ink layer was formed. In this way, a thermal transfer recording medium was obtained in which an 8 μm thick ink layer was formed on the base film. When the same location was repeatedly printed using this thermal transfer recording medium in the same manner as in Example 1, the image density each time was 1.15 for the first time, 1.05 for the second time, and 0.98 for the third time. .

Comparative Example 1 The same coating solution as in Example 1 was applied using a wire bar using a 3.5 μm thick polyester film coated with silicone resin on the back side as a base film, and dried at 120° C. to form a 4 μm thick ink layer. Formed. Furthermore, the same coating solution as in the example was applied again using a wire bar.
A thermal transfer recording medium having a total ink layer thickness of 8 μm was obtained by drying at °C to form an ink layer with a thickness of 4 μm.

When this thermal transfer recording medium was used to repeatedly print the same location as in Example 1, the image density each time was 1.15 for the first time, 0.89 for the second time, and 0.55 for the third time. There was a noticeable decrease in image density each time the images were stacked.

Comparative Example 2 Candelilla Wax 9 of the thermal transfer ink liquid of Example 1
All parts by weight, except that 3 parts by weight of oxidized polyethylene wax was replaced with 12 parts by weight of candelilla wax.
In the same manner as above, when the same location of the obtained thermal transfer recording medium was repeatedly printed, the transferred image density each time was 1.24 at the first time, 0.87 at the second time, and 0.45 at the third time.
It was noticeable that the image density decreased with each use.

Comparative Example 3 Candelilla Wax 9 of the thermal transfer ink liquid of Example 1
parts by weight, 923 parts by weight of oxidized polyethylene straw, 6 parts by weight of candelilla wax, 6 parts by weight of oxidized polyethylene wax
When printing was carried out repeatedly on the same location on the obtained thermal transfer recording medium in the same manner as in Example 1 except that the parts by weight were changed, only a very blurred transferred image was obtained using the same energy as in Example 1. First, when the energy was increased by 20%, the ink layer was transferred along with the microporous layer in one transfer.

[Effect] Using the thermal transfer recording medium of the present invention, it is possible to perform multiple transfers using the same ink sheet.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the thermal transfer recording medium of the present invention, FIG. 2 is a schematic cross-sectional view showing the amount of ink that is expected to be transferred during 1st to 3rd printing of the thermal transfer recording medium of the present invention, and FIG. 3 is a diagram illustrating the thermal transfer recording medium of the present invention. FIG. 4, an explanatory diagram of a conventional thermal transfer recording medium, is a schematic cross-sectional view also showing the amount of ink that is expected to be transferred during one to three printings of a conventional thermal transfer recording medium. 1... Microporous layer made of heat-resistant resin 2... Thermal transferable ink 3... Ink layer 4... Base material

Claims (1)

[Claims] In a thermal transfer recording medium in which an ink layer is provided on a base material, the microporous layer made of resin contains a heat transferable ink containing a colorant, oxidized polyethylene wax, and candelilla wax. A thermal transfer recording medium characterized in that the pore diameter of the transparent layer is larger toward the substrate and smaller toward the surface of the ink layer.