JPH0433632B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal transfer medium used in multi-gradation printing technology that can change printing and print density, and more specifically, the present invention relates to a thermal transfer medium used in multi-gradation printing technology that can change printing and print density. The present invention relates to a multi-tone thermal transfer recording medium used in a multi-tone thermal transfer method for adjusting the density of a transferred image. As a conventional multi-gradation technology using thermal transfer, a method commonly called the 3L method is known (IEICE Techniques published September 25, 1981).
(See IE81-63, pp. 45-52). This 3L method depends on the number of dots in one pixel,
This method attempts to achieve a large number of gradations by combining the reflection density of the thermally transferred ink layer.
In this method, it is extremely difficult to obtain a large number of gradations close to natural gradations with high resolution due to the adjustment limit of the reflection density of the ink layer and the limit to the resolution of the number of dots. On the other hand, if you adjust the print density by overlapping and printing ink layers of the same color with the same or different densities, you can add the number of overlapping prints to the gradation adjustment factor, and the dots per pixel can be adjusted. Even if the number is reduced and the resolution is improved, it is now possible to obtain a sufficiently large number of gradations. However, in multi-gradation recording by overlay printing or printing, the density of the ink layer transferred later in overlay acts more strongly than the density of the ink layer transferred first, making it difficult for additive density increases to occur. Even at the highest reflection density, there was a drawback that the prints tended to be faint and hazy throughout. It is an object of the present invention to eliminate such drawbacks and to enable clear superimposed multi-tone thermal transfer printing. The present invention is an improved thermal transfer ink layer in order to achieve such an object, and an ink layer of at least one color among yellow, magenta, or cyan provided on a base material is thermally transferred for each color to a recording paper. A multi-gradation thermal transfer recording medium used in a multi-gradation thermal transfer method that adjusts the density of a transferred image of each color by overlapping the ink layer multiple times, wherein the ink layer has transparency and coloring. It contains a small amount of a high-power colored pigment that is less than the amount that exhibits the highest reflection density, and the light transmittance of the colored pigment in a non-absorption band is about 65% or more. By overlapping and printing such ink layers, the maximum value of reflection density is extremely high compared to conventional ones, and there is no hazy or blurry appearance when visually inspected, and clear printing, Printing is now available. In the present invention, if the amount of colorant contained in the ink layer is equal to or higher than the maximum reflection density of the printed image of that color, multiple gradations cannot be obtained. It has to be a small amount. In the present invention, the amount of coloring material in the ink layer is expressed by the following formula. Amount of coloring material (g/m ² ) = [Coloring pigment content (weight%)
)×Coating amount (g/m ² )]/100 The maximum reflection density of a printed image for a certain color is the upper limit reflection density at which the reflection density does not increase any further no matter how much the amount of coloring material is increased. means. Furthermore, the light transmittance of the non-absorbing band of the colored pigment is about 65% or more, preferably 70% or more. Approximately 65%
If it is less than that, no density will be achieved even if the ink layers are stacked, and the maximum reflection density of the printed image will not be sufficiently increased.
Since only a hazy printed image can be obtained, a satisfactory gradation cannot be obtained. Note that it is preferable that the light transmittance is as high as possible. Next, the present invention will be explained based on examples. Example 1 As shown in FIG. 1, three partial ink layers Y1, Y with different amounts of coloring materials for each color of cyan (C), magenta (M), and yellow (Y) are formed on one film-like base material 1.
2, Y3; C1, C2, C3; M1, M2, M3
Color Dandara (trademark name of Fuji Kagaku Paper Industries Co., Ltd.)
It is coated in a shape. As the film base material 1, a polyester film having a thickness of 9 μm was used. Further, as the vehicle for the ink layer, a highly transparent vehicle having the following composition was used. Ingredients Weight % Carnauba wax No. 1 20 Parafine wax (melting point 65°C) 35 Ester wax 25 Petroleum resin 10 Spindle oil 10 As the coloring material for the ink layer, for each color,
The following highly transparent colored pigments were used: cyanine blue for cyan, rhodamine lake Y for magenta, and benzidine yellow for yellow. Mixing ratio of vehicle and colored pigment in each partial ink layer and reflection density (ΔOD) of printed image when directly thermally transferred once to plain paper using a thermal printer
(Reflection density of printed area - Reflection density of non-printed area)
Table 1 shows the light transmittance in the non-absorption band, its measurement wavelength, and the maximum absorption wavelength.

[Table] * As the amount of colorant decreases, the light transmittance in the non-absorbing band increases.
Next, overlapping printing of each color of the ink layer of each portion was performed using a thermal printer. The relationship between the reflection density of the obtained printed image and the amount of coloring material is shown in a graph in FIG. In Figure 2 (the same applies to Figures 3 and 4), the printed image obtained by one transfer of Y1 and the printed image obtained by multiple overlapping transfers of Y1 are indicated by ○ marks, and the printed image obtained by one rotation of Y2 The printed images obtained by copying and the printed images obtained by multiple overlapping transfers of Y2 are indicated by ●, and the printed images obtained by one transfer of Y3 and the printed images obtained by multiple overlapping transfers of Y3 are indicated by ●. The resulting printed image is indicated by a ▲ mark. C1, C2,
The same applies to C3 and M1, M2, and M3. As shown in FIG. 2, when the amount of colorant for each color exceeded a certain value, the reflection density of the printed image obtained by increasing the amount of colorant did not exceed a certain value. In addition, printed images of about 10 gradations were obtained for each color, and all printed images were extremely clear. Example 2 A multi-tone thermal transfer recording medium was prepared in the same manner as in Example 1 by further mixing 0.5 parts by weight of titanium oxide with 1 part by weight of the colored pigment used in Example 1, and using this, Example 1 Printing was carried out in the same manner. The relationship between the reflection density of the obtained printed image and the amount of coloring material is shown in a graph in FIG. The light transmittance in the non-absorption band is approximately 70% for the layer corresponding to the Y1 ink layer, approximately 76% for the layer corresponding to the C1 ink layer, and approximately 76% for the layer corresponding to the M1 ink layer. It was 73%. As is clear from FIG. 3, a maximum reflection density value almost as high as that of Example 1 was obtained for all colors. Further, printed images of approximately 8 gradations were obtained for each color, and all printed images were extremely clear. Comparative Example 4 parts by weight of titanium oxide was added to 1 part by weight of the colored pigment used in Example 1, and the light transmittance in the non-absorption band was approximately 45 in the layer corresponding to the ink layer of Y1.
%, about 49% in the layer corresponding to the ink layer of C1,
A thermal transfer recording medium for comparison was prepared with a layer corresponding to the M1 ink layer having a thickness of about 47%. Printing was carried out in the same manner as in Example 1 using this. The relationship between the reflection density of the obtained printed image and the amount of coloring material is shown in a graph in FIG. As is clear from Figure 4, in this comparative example, the reflection density was significantly reduced in all colors compared to Examples 1 and 2, and even if the ink layers were stacked, only a hazy printed image could be obtained. It was not possible to obtain clear gradation colors. In the above comparison, since different colored pigments have different hues and are difficult to compare, the transmittance was deliberately reduced by titanium oxide and the effect of transmittance was confirmed. In Figs. 2 to 4 above, ◇ indicates the print density of an ink layer formed with an ink coating amount of 2 g/m ² having the same coloring pigment content as that corresponding to ▲. ing. As is clear from FIGS. 2 to 4, the reflection density (ΔOD) varies depending on the amount of coloring material. In most cases, the thickness of the ink layer is preferably set so that the total thickness resulting from overlapping printing is about 35 μm or less. In addition to the above examples, when using the following highly transparent vehicles and coloring pigments,
Almost the same tendency as in the above example was shown. However, although variations occurred in the maximum reflection density, the light transmittance in the non-absorption band, and the amount of coloring material when the reflection density was reached depending on each material, it was possible to achieve a maximum density higher than the maximum density visually observed. Naphthol Yellow S, Hansa Yellow 5G, Permanent Yellow as yellow coloring pigments
When one type or a mixture of two or more types of pigments such as NCG and quinoline yellow lake were used, excellent effects similar to those in Example 1 were obtained. Magenta coloring pigments include Brilliant Fast Curly, Brilliant Carmine BS, Permanent Carmine FB, Resole Red, Permanent Red F5R, Brilliant Carmine 6B,
One or two pigments such as Pigment Scarlet 3B, Rhodamine Lake B, Alizarin Lake, etc.
When a mixture of more than one species was used, similar excellent effects as in Example 1 were obtained. As a cyan coloring pigment, one of pigments such as Victoria Blue Lake, metal-free phthalocyanine blue, phthalocyanine blue, Fast Sky Blue, etc.
When the seeds or a mixture of two or more kinds were used, similar excellent effects as in Example 1 were obtained. Regarding the composition of the vehicle, it is preferable to use a solid wax with a penetration degree of 10 to 30 (25°C) as a binder agent in order to improve the heat sensitivity of the resulting ink layer, such as carnauba wax, microcrystalline wax, etc. Waxes such as wax, wood wax, beeswax, ceresin wax, and spermaceti wax are used, and if necessary, easily meltable substances such as low molecular weight polyethylene, oxidized wax, and ester wax are used in combination. May be used. Suitable softeners include substances that can be easily melted by heat, such as petroleum resins, polyvinyl acetate, polystyrene, styrene-butadiene copolymers, cellulose esters, cellulose ethers, and acrylic resins, or lubricating oils. used for. Furthermore, in the present invention, a powdery thermally conductive substance and/or extender pigment may be blended in order to impart good thermal conductivity and melt transferability to the thermally transferable ink layer. Examples of powdered thermally conductive substances include aluminum, copper, tin, and zinc, whose thermal conductivity is 6.0×.
10 ^-4 to 25.0×10 ^-4 cal/sec・cm・℃ is preferably used. As extender pigments, relatively highly transparent ones such as colloidal silica, magnesium carbonate, calcium charcoal, clay, kaolin, calcium silicate, Aerosil, and white carbon are preferably used. These thermally conductive substances and extender pigments are blended in proportions of 0 to 30 parts by weight and 0 to 10 parts by weight, respectively, based on 100 parts by weight of the total ink layer. The combination and amount of each of the components constituting the vehicle must be selected so as not to impair the transparency of the vehicle itself. Base material 1 includes capacitor thin paper, capacitor insulating paper, one-time carbon base paper, parchment paper,
Thin paper such as glassine paper, Indian paper, wax paper, etc., or plastic film such as cellophane, polyester, polyimide, polyvinyl chloride, etc. can be used. Further, the surface of the base material 1 may be coated with a resin to prevent sticking or a highly thermally conductive layer to improve transferability. The arrangement of the ink layer on the substrate 1 is not necessarily the first one.
The arrangement is not limited to the one shown in the figure, but may be arranged in a conventionally known pattern. Furthermore, instead of applying ink layers of different colors to one base material 1, ink layers of each color may be applied to the base material, or the base material may be changed depending on the density.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an example of a multi-tone thermal transfer recording medium of the present invention arranged in a color random pattern, and FIGS. 2 to 4 are images obtained in Examples 1 to 2 and a comparative example, respectively. It is a graph showing the relationship between the reflection density (ΔOD) of a printed image and the amount of coloring material.

Claims (1)

[Scope of Claims] 1. An ink layer of at least one color among yellow, magenta, or cyan provided on a base material is superimposed on a recording paper multiple times by thermal transfer for each color, so that the ink layer of each color obtained is A multi-tone thermal transfer recording medium used in a multi-tone thermal transfer method for adjusting the density of a transferred image, wherein the ink layer comprises:
A thermal transfer for multi-gradation use, which contains a colored pigment with high transparency and coloring power in a small amount less than the amount that exhibits the highest reflection density, and in which the light transmittance of the colored pigment in a non-absorption band is about 65% or more. recoding media. 2. A multi-gradation product according to claim 1, wherein a plurality of ink layers belonging to one color among yellow, magenta, or cyan and having different reflection densities are arranged side by side on a single base material. Thermal transfer recording medium. 3 On a single base material, multiple ink layers that belong to yellow and have mutually different reflection densities, multiple ink layers that belong to magenta and have mutually different reflection densities, and multiple ink layers that belong to cyan and have mutually different reflection densities. The multi-tone thermal transfer recording medium according to claim 1, wherein a plurality of ink layers are arranged side by side.