JPH0274392A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To improve gradation, resolution, high speed recording, preservation stability of a recorded image, and to record a sheet with a low running cost by providing ink particles made by providing a fusion-adherence preventive layer having small affinity to wax around ink made of colorant and wax on a support. CONSTITUTION:As a thermal transfer recording medium, there are compositions in which colorant and wax for forming ink are so provided (a) that a colorant layer is provided outside the wax particles, (b) that with the colorant as nuclei a wax layer is provided outside them, and (c) that the colorant is dispersed or dissolved in the wax. In the composition (a), the particles 22 provided on the surface of a support 21 are formed sequentially of three layers of transparent wax 23, colorant 23 and a fusion-adherence preventive layer 25 having small affinity to the wax. The size of the particle 22 is desirably approx. 0.1-100mum in diameter or 1-20Xm in mean particle size. When the particle sizes are distributed, the smaller the particle size is, the lower the thermal capacity, the faster it is dissolved. Accordingly, a halftone expression can be easily performed.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a recording medium for thermal transfer recording, and particularly to a heat-melting transfer material that is capable of expressing gradations, can print on plain paper, and has a high recording speed. It is.

[Conventional technology]

2. Description of the Related Art There have conventionally been recording apparatuses using many recording methods such as an inkjet method, an electrophotographic method, and a thermal transfer method.

The types of objects required to be recorded by these recording devices are becoming more advanced, from characters to images, and from monochrome to color. High image quality, which is the final form of this requirement, requires achieving not only high resolution but also faithful halftone expression in order to realize a full-color printer.

Regarding this point, in the conventional method described above, binary recording is common in principle, so to express gradation, multiple dots are treated as one unit, and halftones are determined by the on/off ratio of the dots in that unit. A method is used to reproduce halftones in a pseudo manner using an area gradation method such as a dither method.

[Problem to be solved by the invention]

However, when this method is used, the number of dots required per unit increases in order to express many gradations, resulting in a decrease in pixel resolution. For example, in order to obtain an image quality of about 6 pixels/mm with 64 gradations, a recording head resolution of about 48 dots/rats is required.

A thermal printer requires a thermal head of 48 dots/ll1fl+, but such a high-density thermal head cannot be manufactured with current technology. Even if it could be made, it would be impractical because it would require a very large-scale drive circuit to drive a thermal head with a huge number of pixels.

In other words, there is a limit to high-quality gradation recording with binary recording, and if we could somehow perform multi-value recording that expresses the size of one dot in multiple gradations, this problem could be solved. can.

In recording by heat-melting transfer using a thermal head, which is commonly used in the past, density changes due to changes in applied energy are as shown in Figure 2.The slope of recording density with respect to applied energy is large, and the variation is large, so intermediate It was very difficult to get the concentration right. The reason for this will be explained below. In the conventional thermal head shown in FIG. 3(a), the heating element 1 and the voltage V7i2 are shaped to have the same width, so the distribution of the current flowing through the heating element 1 is almost constant everywhere. However, heating element 1
The temperature distribution is slightly higher in the center where less heat is radiated. As shown in Fig. 3(b), the temperature distribution of the heating element is controlled by changing the application time of the pulse voltage applied to the electrode 2.
1a, 12a (the application time is 11a < 12a), the slight difference in the applied energy will determine whether the temperature is higher than the melting point Tm of the thermal transfer ink or not, as shown in Figure 2. It makes a big difference.

In other words, if the applied energy is slightly smaller than the applied energy corresponding to Tn+, the ink will not melt at all, and conversely, if the applied energy is slightly larger than the applied energy corresponding to Tm, most of the ink in contact with the heating element will melt. Become. For this reason, the heat-melting transfer method according to the prior art could practically only perform binary recording.

On the other hand, apart from the above-mentioned thermal melt transfer method, a thermal sublimation transfer method is known. In this sublimation transfer method, the amount of dye transferred changes depending on the amount of thermal energy, so it is a desirable method for obtaining gradation. However, since this method performs recording by sublimating sublimation dye from the recording medium, the required thermal energy is large, making it difficult to increase the speed, and there are problems with the durability, fixability, and other storage properties of recorded images. In addition to being virtually impossible to print on plain paper, it also has drawbacks such as limited sublimation dyes and high costs for consumables.

An object of the present invention is to solve the above-mentioned problems and provide a thermal transfer recording medium that has excellent gradation, resolution, high-speed recording performance, and storage stability of recorded images, has low running costs, and is capable of recording on plain paper. It is in.

(Means for Solving the Problems) The present invention provides a thermal transfer method in which ink particles comprising an ink consisting of a coloring agent and a wax and an anti-fusing layer having a low affinity with the wax are provided on a support. This is a recording medium that solves the above problem.

Examples of the above structure include the colorant and wax that make up the ink: (a) a colorant layer is provided on the outside of the wax particles; and (b) a colorant layer is provided on the outside of the colorant as a core. (C) has a structure in which a coloring agent is dispersed or dissolved in wax, and in both cases, the ink component is coated with an anti-fusing layer. Figure 1 shows (a) above.
1 is a schematic cross-sectional view of a thermal transfer recording medium of the present invention having the configuration shown in FIG. That is, the ink particles 22 provided on the surface of the support 21 are sequentially coated with transparent wax 239, coloring agent 24, and so on from the inside.
It is composed of three layers including an anti-fusing layer 25 which has a low affinity with transparent wax.

The anti-fusing layer serves to prevent ink particles from sticking to each other, and has a low affinity with transparent wax.

The configurations (a) to (C) and the like have the following effects.

First, the wax in the ink particles placed on the support is melted by heating with a thermal head or the like, and the molten wax dissolves or disperses the colorant and incorporates it into the wax. Next, this colorant-containing molten wax breaks through the outer anti-fusing layer and is transferred to the transfer medium due to the pressure between the platen and the head. At this time, if the ink particles adjacent to the molten ink particles are not heated, the adjoining ink particles will not be pulled by the molten ink particles and transferred because the fusion prevention layer is formed on the outside, resulting in what is called a clean transfer. becomes possible. For this reason, when a so-called concentrated heating type thermal head is used, variations in the transfer area are reduced, gradation is greatly improved, resolution is excellent, and recording on plain paper is possible due to wax transfer. Furthermore, since the energy required for recording is mainly the energy for thermally melting the wax in the ink particles, unlike sublimation transfer recording, less energy is required, which is a factor in producing high-speed recording performance.

In the structure (a) above, in which the colorant layer is on the outside of the wax particles, the wax melted by heating from a thermal head, etc. dissolves or disperses the colorant inside the ink particles, and This is preferable because the coloring agent leaches into the medium, resulting in excellent colorant transfer to the transfer medium, and furthermore, it is relatively easy to form ink particles. Also, the above (b)
In the configuration in which the colorant is the core and a wax layer is provided on the outside, the wax first melts by heating with a thermal head, etc., and while the colorant is dissolved or dispersed, it leaks out to the outside of the ink particles. Since the rate at which the colorant spreads throughout the wax changes depending on the heating energy, the reproducibility of intermediate tones is better. Other Makoto (C)
The present invention can be carried out satisfactorily even in a wax having a composition in which a coloring agent is already dispersed or dissolved.

In the third aspect of the present invention, the adhesion prevention layer plays a role of preventing ink particles from sticking to each other and has a low affinity with transparent wax. Specifically, fluorosilicone oil, epoxy-modified silicone oil, etc. , dimethyl silicone oil, alkyl-modified silicone oil, various glycols,
Alkylbenzene, alkylnaphthalene, phosphoric acid ester, silicone resin, etc. can be used. The thickness of the anti-fusing layer may be about 1:10 (10 to 1:!) in weight ratio to the ink components (colorant and wax).

On the other hand, in order to prevent the ink particles from peeling off from the support before heating, an adhesive layer may be provided between the support and the ink particles, or a binder may be used to form the ink particles, but if the thickness is too large, heat conduction It is desirable that the thickness be as thin as possible, and 0.01 to 20% per ink particle weight.
Good condition. Polyamide resin, polyester resin, etc. are suitable for the adhesive layer, and polyvinyl butyral and vinyl chloride-vinyl acetate copolymer can be used as the binder.

Next, other components according to the present invention will be explained.

Approximately 2 of paper, plastic, metal, etc. can be used as a support.
Suitable materials are those that do not soften or change in quality when heated to about 00° C. for a short period of time, and among these, polyethylene terephthalate, aromatic polyamide films, etc. are particularly preferred.

The thickness is desirably about 2 to 20 .mu.m, but more preferably about 3 to 10 .mu.m in view of ease of application and thermal conductivity during coating of one colorant layer. If sticking or the like is likely to occur due to the heat of the thermal head, a heat-resistant protective layer may be provided on the back surface of the support as a backside treatment.

As the heat-resistant protective layer, silicone resins, epoxy resins, polyimide resins, unsaturated aldehyde resins, acrylate resins, etc. are preferable.
13359. The thickness of these films is not particularly limited, but generally they can be applied uniformly from 0.1 μl to 3 μl and have excellent thermal conductivity. Further, by mixing a metal or an inorganic filler into this protective layer, effects of heat resistance and slipperiness can be expected. As the fine particles, amorphous silica, carbon black, alumina, titanium oxide, etc. are useful. Furthermore, it is also useful to apply a liquid lubricant to the back surface of the support to prevent sticking. For example, fluorine silicone oil.

Examples include dimethyl silicone oil, various modified silicone oils (epoxy modified, alkyl modified, etc.), phosphoric acid esters, synthetic oils such as polyalkylene gelcol oil, and the like.

The ink for thermal transfer recording is structured on a support in the form of ink particles. The transparent wax may be one that can dissolve or disperse the coloring agent during hot melting, is transparent, white, or nearly colorless, and is solid at room temperature; it does not need to be a wax, but may have similar characteristics. Good. Specifically, ester waxes (carnauba wax, montan wax, synthetic ester waxes), oxidized waxes (oxidized paraffin waxes, microcrystalline waxes, etc.), low-molecular polyethylene waxes, acid waxes, and other waxes include polyvinyl alcohol, Polystyrene, polyvinyl chloride, polyester, polycarbonate, polyethylene, polyamide, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, and the like are suitable.

The coloring agent can be any coloring agent as long as it dissolves or disperses in the transparent wax when it is heated and melted, and various dyes or pigments can be used, so the storage stability of recorded images is excellent and running costs are kept low. You can also do that.

The size of ink particles composed of these elements is preferably about 0.1 to 100 μm in diameter, more preferably 1 to 20 μm in diameter.
It is more preferable that the average particle size of the ink particles is about μm. Furthermore, if the particle size is distributed, small particles have a small heat capacity and begin to melt quickly, making it easier to express intermediate tones. The particle size distribution may be a normal distribution with a standard deviation of about 20 parts or a mixture of particles with several types of particle sizes, but the particle size range of small particles and large particles is generally set at about 30 to 200% of the average particle size. do it.

In order to create the ink particles according to the present invention, commonly known creating means can be used. In other words, the header (
In the configuration a), the wax component is made into fine particles in water, a coloring agent is added thereto, the mixture is dried, and an anti-fusing layer is spray-coated. In the above (b), both the wax and the anti-fusing layer can be spray coated, and in the above (C) etc., the wax component and the coloring agent are made into an emulsion, dried, and then the anti-fusing layer is spray coated. The ink component may be formed so as to have a structure covered with an anti-fusing layer, such as can be obtained by using an anti-fusing layer. The particle size can be adjusted simply by mixing particles of different particle sizes at a predetermined ratio, or by adjusting the stirring state of a mixer or the like when producing ink particles.

The obtained ink particles may be provided on a support with an adhesive layer and sprinkled thereon, or coated as a paint with a binder to form a thermal transfer recording medium.

(Example) The present invention will be explained below with reference to Examples. Note that parts are parts by weight.

Example! Paraffin wax surfactant water 50 parts 1 part 49 parts Total 100 parts The mixed solution of the above recipe was heated to 90° C. and stirred and mixed in a homomixer to obtain a mixed solution A. This mixture A contained dispersed wax particles having a particle size of 5μl±3μ.

Five parts of water-soluble blue dye was added to mixture A, stirred, and dried to obtain fine particles. These fine particles were spray-coated with fluorosilicone oil to obtain ink particles.

To create an ink sheet, polyethylene terephthalate (PET) with a thickness of 6 μm was used as a support, and a solution prepared by mixing polyester resin in toluene as a solvent for 8 hours in a ball mill was coated on this support to a thickness of about 1 μm using a bar coater to form an adhesive layer. . The ink particles prepared above were sprinkled on the adhesive layer before it was dry. After removing excess ink particles that did not adhere to the adhesive layer, it was sufficiently dried to obtain a thermal transfer recording medium.

When this thermal transfer recording medium was subjected to a printing test on plain paper using a 6 dat/mm thermal head, a clear transferred image was obtained. Also, the pulse width is 1Ills, 1.511s
.

2ms, 2.5[+13.3ms, 3.5ms,
When recording is performed with a change of 4tns (applied voltage 12V), the recording density is 0.10°0.30.0.52.0
．． 73.0.90.1.05.1. J9, and was able to record halftones with good reproducibility.

Example 2 Carnauba wax 50 parts Surfactant 1 part Water 49 parts Total
100 parts of the above-mentioned mixed solution were heated to 90° C. and stirred and mixed in a homomixer to obtain a mixed solution B. Wax particles having a particle size of 5 μm±3 μm were dispersed in this mixed liquid B. 10 parts of carbon black was added to mixture B, stirred, and then dried to obtain fine particles. These fine particles were spray-coated with dimethyl silicone oil to obtain ink particles. A thermal transfer recording medium was obtained in the same manner as in Example 1 using these ink particles.

Using this thermal transfer recording medium, the same evaluation as in Example 1 was carried out, and it was possible to record halftones with good reproducibility at recording densities of 0.1 to 1.20.

Example 3 Paraffin wax 50 parts Oil-soluble blue dye 5 parts Surfactant 1 part Water 44 parts Total
A mixture C of 100 parts of the above recipe was stirred and mixed in a homomixer while being heated to 90° C. to obtain a mixture C. Wax particles having a particle size of 5 μm±3 μm were dispersed in this mixed liquid C. Mixture C was dried to obtain fine particles.

These fine particles were spray-coated with fluorosilicone oil to obtain ink particles. A thermal transfer recording medium was obtained in the same manner as in Example 1 using these ink particles. This embodiment has the advantage that the method for producing ink particles is simple.

When the same evaluation as in Example 1 was carried out using this thermal transfer recording medium, it was possible to record halftones with good reproducibility at recording densities of 0.1 to 1.15.

Example 4 Paraffin wax: 50 parts Toluene: 50 parts Total: 100 parts A wax solution with the above composition was sprayed onto a water-soluble black dye (particle size: 5 μm ± 3 μm) at room temperature, and then dried to form a composition with a wax layer around the colorant. Fine particles were obtained. These fine particles were spray-coated with fluorosilicone oil to obtain ink particles. A thermal transfer recording medium was obtained in the same manner as in Example 1 using these ink particles. In this embodiment, by changing the energy used to heat the ink particles using a thermal head, etc., the rate at which the colorant spreads over the wax changes, which changes the recording density, which has the advantage of excellent midtone reproducibility. be.

When the same evaluation as in Example 1 was carried out using this thermal transfer recording medium, it was possible to record halftones with good reproducibility up to a recording density of 0.1-1.17.

Comparative Example The liquid mixture C obtained in Example 3 was dried and the resulting fine particles were used as ink particles. Example 1 using these ink particles
A thermal transfer recording medium was obtained in the same manner as described above.

When the same evaluation as in Example 1 was performed using this thermal transfer recording medium, good recording was performed when the applied energy was large, but when the applied energy was small, ink particles fused together, and Unheated ink particles may also be transferred, resulting in uneven transfer and failure to reproduce halftones well.

(Effects of the Invention) As is clear from the above description, according to the thermal transfer recording medium of the present invention, by using ink particles in which an anti-fusing layer is provided around colorant-containing wax particles (ink), gradation can be improved. It has excellent performance, resolution, high-speed recording performance, and storage stability of recorded images, has low running costs, and enables recording on plain paper.

Furthermore, by appropriately setting the composition of the ink, it is possible to improve the reproducibility of halftone expression, simplify the production process, and furthermore, it is possible to set the particle size distribution of the ink particles to be relatively wide. This is extremely useful, as it allows for better halftone expression.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing one configuration of the thermal transfer recording medium of the present invention, FIG. 2 is a diagram showing the relationship between applied energy and recording density of a thermal head according to the prior art, and FIG. 3 is a diagram showing a thermal head according to the prior art. FIG. 3 is a diagram showing the temperature distribution in the heating element of FIG. 1 Heat generating element 2 Electrode 3 Current flow method 11a, 12a Temperature distribution of heat generating element 21 Support Ink particle wax colorant fusion prevention layer Patent applicant Canon Co., Ltd.

Claims (4)

[Claims] (1) A thermal transfer recording medium characterized in that ink particles comprising an ink consisting of a colorant and a wax and an anti-fusing layer having low affinity with the wax are provided on a support. (2) The thermal transfer recording medium according to claim 1, wherein the ink particles have a layer of the colorant on the outside of the wax particles, and the anti-fusing layer is provided on the outside of the colorant layer. (3) The thermal transfer recording medium according to claim 1, wherein the ink particles have the wax layer on the outside of the colorant and the anti-fusing layer on the outside of the wax layer. (4) The thermal transfer recording medium according to any one of claims 1 to 3, wherein the particle size of the ink particles is not uniform but varies.