JPH0264171A - Ink for heat-transfer printing - Google Patents

Abstract

PURPOSE:To provide the subject ink containing a specific PS resin, having excellent gradation and superposition properties and capable of giving a high- density and smooth image in broad color reproduction range in the printing of a color image by a multicolor superposition heat-transfer printing. CONSTITUTION:The objective ink contains 5-50wt.% of a PS resin in the ink layer. A color image can be produced by using a heat-transfer recording medium having three or more kinds of the above inks coated on a substrate along its length and carrying out the superposition transfer of said ink layers.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to ink for use in thermal transfer printers.

[Conventional technology]

Thermal transfer color printers that use a multicolor sequential transfer method, which has recently been actively researched and developed, need to be able to express rich tones and clear images, and solid ←
causing a clear phase change between liquid and solid in a short time;
In addition to performance such as good ink cutting and optimal ink melt viscosity for transfer, the ink was required to have good superimposition characteristics, gradation properties, etc.

In order to satisfy the above required performance, conventional thermal transfer inks are made by dispersing pigments, dyes, or colorants such as carbon black in natural or synthetic waxes mainly composed of hydrocarbons, and then coated with a film. A small amount of synthetic resin or plasticizer was added for the purpose of strengthening, adhesion, flexibility, film-forming properties, etc.

In the ink using the above formulation, sufficient optimization was not achieved regarding the overlapping characteristics and gradation properties of the ink.

[Problem to be solved by the invention]

When three color inks of yellow, magenta, and cyan were created using the above-mentioned prior art ink formulation example and a full-color image was printed by three-color surface sequential thermal transfer, the gradation of the ink was poor and the density was low. Jumps and insufficient low density occur, and furthermore, the overlapping characteristics of the second and third color inks are insufficient, resulting in a narrow color reproduction range and an unclear image.

Methods to solve the above problems include: 1) adding tackifiers, low molecular weight polymers, etc. to the ink layer to improve the tackiness of the ink itself and improving ink gradation and overlapping characteristics; Two methods were considered: lowering the melting point to reduce transfer energy and improve transfer efficiency, and improve gradation and overlay characteristics.

However, both of the above two methods have the fatal disadvantage that blocking tends to occur when the ink is stored as an ink film, and the environmental resistance is poor, so they are not effective means.

Therefore, the present invention aims to improve the gradation properties and ink overlay properties without using the above-mentioned methods. An object of the present invention is to provide a thermal transfer ink which has improved overlapping characteristics and can provide a clear image with a wide range of color expression when a color image is transferred in a multicolor plane sequential manner.

[Means for Solving the Problems] The thermal transfer ink of the present invention contains 5 to 50 wt% of polystyrene resin in the ink layer, and further includes a plurality of the thermal transfer ink layers of at least three colors on a base material. A color image is obtained by overlapping and transferring the ink layers using a thermal transfer recording medium having a structure in which the ink layer is coated along its length.

[Function] According to the thermal transfer ink of the present invention having the above-mentioned characteristics, it is possible to improve gradation and overlay characteristics without using methods such as improving adhesiveness or lowering the melting point of the ink. Therefore, when a color image is transferred, a clear image with a wide color reproduction range can be obtained, and furthermore, harmful effects such as blocking can be prevented.

[Example] Example 1 Table 1 shows ink composition examples of three colors of yellow, magenta, and cyan as an example of the thermal transfer ink of the present invention.
However, the numbers in the table represent parts by weight (the same applies hereinafter). The three-color ink was created according to the following procedure.

First, the dyes and pigments and polystyrene resin shown in Table 1 were added to a toluene solvent, and dispersed in a ball mill for 18 hours. After confirming that the polystyrene resin and dye and pigment were uniformly dispersed, other binders were added and heated to dissolve the ink. And so.

Next, the ink prepared as described above was applied to a base material of 5PET (polyethylene terephthalate) with a thickness of 6 μm as shown in Figure 1.
A thermal transfer recording medium was prepared by coating and drying to form an ink layer 1 (thickness 2 to 3 μm).

Thereafter, the ink manufacturing method and coating method were performed in the same manner.

Example 2 Table 2 shows ink composition examples of three colors, yellow, magenta, and cyan, as an example of the thermal transfer ink of the present invention.

Example 3 Table 3 shows ink composition examples of three colors, yellow, magenta, and cyan, as an example of the thermal transfer ink of the present invention.

Comparative Example 1 Table 4 shows ink composition examples of three colors, yellow, magenta, and cyan, which do not contain polystyrene resin, as a comparative example of the thermal transfer ink of the present invention.

Comparative Example 3 Table 5 shows, as a comparative example of the thermal transfer ink of the present invention, yellow, in which the amount of polystyrene resin added is less than 5 wt%;
Examples of ink compositions for three colors, magenta and cyan, are shown.

Comparative Example 4 Table 6 shows, as a comparative example of the thermal transfer ink of the present invention, yellow in which the amount of polystyrene resin added exceeds 50 wt%,
Examples of ink compositions for three colors, magenta and cyan, are shown.

Table 1 (Example 1) Table 3 (Example 3) Table 4 (Comparative Example 1) Table 2 (Example 2) Table 5 (Comparative Example 2) Table 6 (Comparative Example 3) Next A printing test was conducted using the thermal transfer recording media of the above Examples and Comparative Examples. The printing test was carried out using a three-color superimposed print using a thermal head. Figure 2 shows a schematic cross-sectional view of the state of printing using a thermal head using this thermal transfer recording medium.

The thermal transfer recording medium 5 produced by the above method comes into contact with the heating element 3 of the thermal head on the surface not coated with the thermal transfer ink 1, and the surface coated with the thermal transfer ink comes into contact with the printing paper 4. In this state, the heating element 3 of the thermal head generates heat according to the printing information, and the thermal energy is transmitted to the thermal transfer ink layer 1 via the base material 2, the ink is melted, and the dots 6 are transferred to the printing paper 4, forming an image. It is formed.

The print pattern was a density gradation pattern of 16 horizontal stripes on smooth paper. The printing energy was adjusted so that the 14th gradation reached full density when the first color was transferred, and was set at a constant value such that excess energy was applied to the 15th gradation and above.

Next, as an evaluation of transferability, the transfer density for each gradation was determined by Ko.
l 1Morgan, Macbeth TR-92
7, and the reflection OD value was measured using a complementary color filter.

The overlapping characteristics and gradation of the present example and comparative example were evaluated by the following method.

First, the first color is cyan ink, printed in 16 gradations on paper,
The second color is cyan ink, which is a full-color transfer of the first color yellow, and then a 16-tone print is made, and the third color is a full-color print of yellow as the first color and magenta as the second color, and then a 16-tone print of cyan is made on each. We investigated the transfer density and gradation characteristics with respect to printing energy.

FIG. 3 is a graph showing the transfer characteristics of the three colors of Example 1.

FIG. 4 is a graph showing the transfer characteristics of the three colors of Example 2.

FIG. 5 is a graph showing the transfer characteristics of the three colors of Example 3.

FIG. 6 is a graph showing the transfer characteristics of the three colors of Comparative Example 1.

FIG. 7 is a graph showing the transfer characteristics of the three colors of Comparative Example 2.

FIG. 8 is a graph showing the transfer characteristics of the three colors of Comparative Example 3.

are shown respectively.

As shown in Figures 3 and 4, the inks of Example 1 and Example 2 have excellent gradation and ink overlay characteristics from the low printing energy range to the high printing energy range, and The reflection density at full density also showed a high value.

As shown in FIG. 5, the ink of Example 3 had extremely excellent gradation properties in the first to third colors, with a linear relationship between printing energy and density. However, the density at full density was lower than that of the ink of Example 1.2.

As shown in Figures 6 and 7, the inks of Comparative Example 1 and Comparative Example 2 had a rapid increase in density from the medium density range to the high density range, and the density of the second and third colors was lower than that of the first color. It showed an extremely low value.

As shown in FIG. 8, the ink of Comparative Example 3 had good gradation, but the density at full 4 degrees was extremely low compared to other inks.

Next, we printed a full-color image using the above six types of ink with 64 gradations for each color and three-color overlapping transfer.
Images using the inks of Examples 1 to 3 had a wide range of color expression (also, smooth and clear images were obtained).

Furthermore, images using Comparative Examples 1 to 3 had a narrow color reproduction range, and image deterioration phenomena such as roughness due to density jumps were observed.

From the above results, in order to improve gradation, overlay characteristics, and transfer density (transfer efficiency), and to obtain high image quality with a wide range of vivid brown color reproduction when printing full-color images, it is necessary to It is desirable to contain 5 to 50 wt% of polystyrene resin.

In addition, although this embodiment describes three-color superimposed image printing using a thermal head, the present invention is not limited thereto, and can also be applied to an electric thermal transfer method or other thermal transfer methods.

Furthermore, although this embodiment has described a color image composed of three colors, yellow, magenta, and cyan, the present invention is not limited to this (a full-color printer using four colors including black, or Application to two-color printers is also possible.

[Effect of the invention J As described above, if the thermal transfer ink of the present invention is used,
Because the gradation and overlay characteristics of the ink are improved, when printing color images using the multicolor overlay thermal transfer method, clear images with a wide color reproduction range, smoothness, and high density can be obtained. It has this effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a thermal transfer recording medium according to an example using the thermal transfer ink of the present invention. FIG. 2 is a schematic diagram showing a mechanism for transferring dots onto photographic paper by heat generation from a thermal head using the thermal transfer ink of the present invention. FIG. 3 is a correlation diagram between printing energy and transfer density showing the gradation and overlay characteristics of the ink of Example 1. FIG. 4 is a correlation diagram between printing energy and transfer density showing the gradation and overlapping characteristics of the ink of Example 2. FIG. 5 is a correlation diagram between printing energy and transfer density showing the gradation and overlay characteristics of the ink of Example 3. FIG. 6 is a correlation diagram between printing energy and transfer density showing the gradation and overlay characteristics of the ink of Comparative Example 1. FIG. 7 is a correlation diagram between printing energy and transfer density showing the gradation and overlay characteristics of the ink of Comparative Example 2. FIG. 8 is a correlation diagram between printing energy and transfer density showing the gradation and overlay characteristics of the ink of Comparative Example 3. Heat-generating element Photographic paper support Heat-fused dot Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (and 1 other person) 1... Thermal transfer ink 2... Thermal transfer recording medium Figure 5

Claims (2)

[Claims] (1) 5 to 50 wt% polystyrene resin in the ink layer
A thermal transfer ink characterized by containing: (2) Using a thermal transfer recording medium having a structure in which a plurality of the thermal transfer inks of at least three colors or more are coated on a base material along its length, the thermal transfer ink layers are superimposed and transferred. The thermal transfer ink according to claim 1, wherein a color image is obtained by the method.