JPH0464879B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a thermal transfer recording medium.
Background stains (fogging) on recording sheets such as plain paper
The present invention also relates to a thermal transfer recording medium that can suppress the occurrence of trailing and that enables clear recording (printing).

[Prior Art] A thermal transfer recording medium has been conventionally used as a recording medium for transferring and forming an image on a recording sheet such as plain paper by a thermal printer, a thermal facsimile, or the like. This thermal transfer recording medium has at least one coloring material layer on a support, and the coloring material layer includes, for example, a layer containing a coloring agent made of a dye such as a pigment and a heat-fusible substance. It has been known. In addition, films with excellent surface smoothness and dimensional stability are used as the support in order to obtain good reproducibility of the dye transfer image obtained from the color material layer coated on the support. There is.

When using a thermal printer or thermal facsimile with a thermal head to record a dye transfer image on plain paper or the like using such a thermal transfer recording medium, there should be no background smear (fog) and no trailing. Although it is desired to enable clear recording (printing), conventional thermal transfer recording media have been insufficient.

By the way, JP-A No. 58-36492 discloses a porous base, which is formed on the base, maintains a solid state at room temperature, rapidly decreases in viscosity when heated to a certain temperature, and further decreases in viscosity when heated. An ink donor sheet is disclosed, which is characterized by comprising a heat-fusible ink layer having temperature gradation characteristics that gradually decrease.
It is shown that the viscosity decreases rapidly when the temperature exceeds ℃.

However, although the same publication describes the viscosity change from a semi-molten state to a liquid state, it does not specifically show the viscosity change from a solid state to a semi-solid state or a semi-molten state. Not yet. The publication proposes the use of an ionomer resin as a binder for the coloring material layer, and according to the publication, one of the reasons for selecting the ionomer resin is that it "has a clear melting point, that is, it melts rapidly at a specific temperature."
It points out that it has certain characteristics. In addition, IEICE Technical Report IE-79-58 (IEICE, 1979
(Published in 2010) also states that ``The ink with the L-shaped viscosity curve shown by the thick dotted line in Figure 4 is the ideal ink.'' (Page 36, left column, line 13 of the same document). These known techniques focus on the so-called leg part a that changes from a semi-molten state to a liquid state in a viscosity curve (Fig. 1) showing the relationship with the viscosity of an ink composition (coloring material layer). . As a result of continuing research on these known technologies, the present inventor has discovered that the problem of background stains (fogging)
It has also been found that it is neither possible to prevent trailing nor to improve the resolution of dye transfer images.

[Object of the Invention] An object of the present invention is to provide a thermal transfer recording medium that can suppress the occurrence of background stains (fogging) and trailing.

Another object of the present invention is to provide a thermal transfer recording medium from which a dye transfer image with high resolution can be obtained.

Other objects of the invention will become apparent from the following description of the specification.

[Summary of the Invention] As a result of intensive research, the present inventor has developed a coloring material containing a heat-fusible substance on a support that remains in a solid state at room temperature and whose viscosity rapidly decreases when heated to a certain temperature. In a heat-sensitive transfer recording medium having a layer, the coloring material layer contains a heat-melting substance from which a low molecular weight portion has been purified, and the viscosity of the composition of the coloring material layer is
The temperature difference from 10000 poise to 1000 poise is 3℃
We have discovered that the above object can be achieved by the following, and have arrived at the present invention.

The inventor has discovered that the leg a in the viscosity curve of FIG.
It was found that focusing on the above did not solve the above-mentioned drawbacks, and the reason for this is thought to be as follows. In other words, when heating a thermal head, you should focus on the temperature range from a semi-molten state to a liquid state, but immediately after that, you should focus on the temperature range from a semi-solid state to a solid state. If this temperature range is too wide, unnecessary pressure will cause transfer to plain paper, resulting in background smudges (fogging), and when printing at high speeds, thermal head pressure may damage the undried dye transfer image. It is thought that tailing will also occur. In this respect, the present invention is characterized by the shoulder b in the viscosity curve in FIG.
They focused their attention on this and found that the above objective could be achieved by this method.

[Structure of the invention] The present invention will be described in further detail below.

The thermal transfer recording medium according to the present invention comprises a support coated with at least one heat-melting coloring material layer,
The coloring material layer is a layer containing a heat-fusible substance.

The coloring material layer of the present invention has a characteristic that the temperature difference between the viscosity of 10,000 poise and the viscosity of 1,000 poise (hereinafter referred to as viscosity shoulder temperature difference) is 3° C. or less. If this viscosity shoulder temperature difference exceeds 3°C, the ink layer tends to soften slightly even at room temperature, and unnecessary pressure causes parts other than the print to be transferred to plain paper, causing background smear (fog). Not only does this occur, but also because the viscosity of the dye transfer image increases slowly after heating, tailing occurs in the dye transfer image. In addition, the viscosity of the present invention is a value determined by a flow tester method, for example, a Shimadzu flow tester method.
CFT・500, load 10Kg, heating speed 6℃/min
According to

In the present invention, the means for obtaining a coloring material layer having a viscosity shoulder temperature difference of 3° C. or less is to use a purified heat-melting substance.

In the present invention, a purified thermofusible substance refers to an unpurified thermofusible substance obtained by purifying means such as extraction, column chromatography, thin layer chromatography, recrystallization, reprecipitation, or fractional distillation. refers to a heat-melting substance that has been purified by heat treatment to remove low-molecular-weight parts.

In the present invention, unrefined heat-melting substances to be purified include, for example, paraffin waxes such as beeswax, paraffin wax, and microcrystalline wax, carnauba wax, and Hoechst wax F (manufactured by Hoechst Co., Ltd.). ), oxidized waxes such as NPS-9210 (manufactured by Nippon Seiro Co., Ltd.), and amide waxes such as Amide O (manufactured by Kao Soap Co., Ltd.).

The purified heat-melting substance used in the coloring material layer of the present invention is not limited to a single use, but may be used in combination of two or more kinds, or may be used in combination with an unrefined heat-melting substance.

When used in combination with an unrefined thermofusible substance, it is sufficient if the purified thermofusible substance accounts for 20% or more (by weight, the same applies hereinafter) of the total thermofusible substance, but preferably 30% or more of the total thermofusible substance.
% or more, more preferably 50% or more, is a purified thermofusible substance.

The colorant to be contained in the color material layer of the present invention may be appropriately selected from conventionally known dyes, for example, direct dyes, acid dyes, basic dyes, disperse dyes, oil-soluble dyes, etc. .

The dye used in the color material layer of the present invention may be any pigment that can be transferred (transferred) together with the purified heat-fusible substance of the present invention, and thus may be a pigment in addition to the above.

It is preferable that the color material layer of the present invention contains a resin. The resin used in the present invention preferably has a softening point (measured by the ring and ball method) of 40 to 200°C, and either a hydrophilic polymer or a hydrophobic polymer can be used. Examples of hydrophilic polymers include gelatin, gelatin derivatives, cellulose derivatives, proteins such as casein, natural products and natural product derivatives such as polysaccharides such as starch, water-soluble nylon, polyvinyl alcohol, polyvinylpyrrolidone, and acrylamide polymers. synthetic water-soluble polymers such as polyvinyl compounds;
Examples include vinyl-based and polyurethane-based polymer latexes. Examples of hydrophobic polymers include U.S. Pat.
Examples include the synthetic polymers described in No. 3220844, No. 3287289, and No. 3411911. Preferred polymers include polyvinyl butyral, polyvinyl formal, polyethylene, polypropylene, polyamide, ethyl cellulose, cellulose derivatives such as cellulose acetate, polystyrene, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl acetate, vinyl chloride-vinyl acetate. Copolymers, vinyl chloride-vinyl acetate-maleic acid terpolymers, acrylic resins such as polymethyl methacrylate, polyisobutylene, rosin derivatives such as ester gums, petroleum resins, coumaron indene resins, cyclic rubbers, chlorinated rubbers, etc. It will be done. In the present invention, one or a combination of two or more of these resins may be used.

Although the composition ratio of the coloring material layer of the present invention is not limited,
For the total amount of color material layer 100 parts (parts by weight, the same applies hereinafter),
20-80 parts of purified thermofusible substance, 5-30 parts of colorant
parts, resin is 5 to 30 parts.

The color material layer of the present invention may contain various known additives. For example, antioxidants, softeners, color tone regulators, etc. may be added. In the present invention, it is not necessary to add a thermally conductive substance, but it may be added.

In the thermal transfer recording medium of the present invention, techniques suitable for applying the coloring material layer to a support such as a polymer film are known in the art, and these techniques can also be used in the present invention. For example, the coloring material layer is a layer formed by hot melt coating the composition or by solvent coating a coating solution prepared by dissolving or dispersing the composition in an appropriate solvent. As a method for applying the coloring material layer of the present invention, any known technique can be employed, such as a reverse roll coater method, an extrusion coater method, a gravure coater method, and a wire bar coating method.

The coloring material layer of the present invention has a thickness of 15 μm or less, preferably 1 μm or less.
It may be set to 5 μm.

The thermal transfer recording medium of the present invention includes other constituent layers such as an undercoat layer (for example, a layer for improving film adhesion), an intermediate layer, and an overcoat layer (for example, a layer made of a purified thermofusible substance). may have.

Note that the support used as a base material for the thermal transfer recording medium of the present invention is preferably a support that has heat-resistant strength, high dimensional stability, and high surface smoothness.
Heat resistance strength requires strength and dimensional stability to maintain the toughness of the support without becoming softened or plasticized by the heating temperature of a heat source such as a thermal head, and surface smoothness requires heat melting on the support. It is desired that the coloring material layer containing a coloring substance has sufficient smoothness to exhibit a good transfer rate. The smoothness is preferably 100 seconds or more in a smoothness test using a Beck tester (JIS P 8119), and when it is 300 seconds or more, images with better transfer rate and reproducibility can be obtained. Materials include, for example, papers such as plain paper, condenser paper, laminated paper, and coated paper; resin films such as polyethylene, polyethylene terephthalate, polyester, polystyrene, polypropylene, and polyimide; paper-resin film composites; and aluminum foil. Metal sheets such as the following are preferably used. The thickness of the support is preferably about 60 μm or less, particularly 2 to 20 μm, in order to obtain good thermal conductivity.

Furthermore, in the thermal transfer recording medium of the present invention, the structure of the back side of the support is arbitrary.

[Operations and Effects of the Invention] According to the present invention, in a thermal transfer recording medium having a coloring material layer containing a heat-melting substance on a support, the coloring material layer contains a purified heat-melting substance, and the coloring material Since the temperature difference when the viscosity of the layer changes from 10,000 poise to 1,000 poise is 3°C or less, the above-mentioned object of the present invention can be achieved, and in particular, the coloring material layer shows rapid softening instead of slow softening. Therefore, background smear (fogging) can be suppressed, and since the viscosity increases rapidly after heating, there is no trailing in the dye transfer image, and a high resolution dye transfer image can be obtained.

[Example] Examples are given below, but the embodiments of the present invention are not limited thereto. Note that "parts" used below indicate "parts by weight."

Example 1 10 parts of beeswax was subjected to alkaline hydrolysis in a 10% sodium hydroxide solution at 30°C for 1 hour, and then extracted with chloroform. After drying, the solution was dissolved in 2 parts of chloroform, passed through a silica gel column, and eluted with hexane. Next, components remaining in the column were eluted using benzene. Two parts of the heat-melting substance [A] which was decomposed and purified by evaporation was obtained.

The following composition for a coloring material layer was kneaded at 120°C for 2 hours to prepare. The temperature difference from 10,000 poise to 1,000 poise in this colorant layer composition was 3°C. This colorant layer composition was coated on a polyethylene terephthalate film support with a thickness of 6 μm using a wire bar to obtain a thermal transfer recording medium sample of the present invention having a colorant layer with a thickness of 3.2 μm after drying. Ta.

Composition for coloring material layer Heat-melting substance [A] 2 parts beeswax 2 parts petroleum resin (Petrozin #80, manufactured by Mitsui Petrochemicals)
0.8 parts Carbon black 1.2 parts Comparative example 1 Beeswax 4 parts Petroleum resin (Petrogin #80, manufactured by Mitsui Petrochemicals)
0.8 parts Carbon black 1.2 parts The colorant layer composition having the above composition was kneaded at 120° C. for 2 hours to prepare. The temperature difference from 10,000 poise to 1,000 poise in this colorant layer composition was 7°C. This composition was applied using the same method as in Example 1 to obtain a comparative thermal transfer recording medium sample having a colorant layer with a dry film thickness of 3.2 μm.

Comparative Example 2 Carnauba wax 20 parts Ester wax 40 parts Castor oil 10 parts Other additives (EVA) 10 parts Carbon black 20 parts The colorant layer composition described in JP-A-58-36492 was heated at 120°C. The mixture was prepared by kneading for 2 hours.

The temperature difference from 10,000 poise to 1,000 poise in this colorant layer composition was 6°C. This composition was applied using the same method as in Example 1 to obtain a comparative thermal transfer recording medium sample having a colorant layer with a dry film thickness of 3.2 μm.

The thermal transfer recording medium sample ~ obtained as described above was printed using a thermal printer (heating element density: 8 dots/
A prototype machine equipped with a thin film type line thermal head of mm. ) was used to transfer and record onto plain paper in the range of 0.5 mJ to 1.2 mJ per element.

(Resolution) A checkered pattern was printed on plain paper with a Beck smoothness of 550 seconds and observed with a magnifying glass. As a result, the sample exhibited a checkered pattern, while the sample was "squashed."

(Fog and trailing) Various kanji characters were printed on plain paper with a Beck smoothness of 300sec, and stains and trailing outside of the printed areas were observed using a magnifying glass. As a result, although some stains and trailing occurred between the letters in the sample, no stains or trailing were observed in the sample.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the viscosity curve of the coloring material layer composition.

Claims (1)

[Claims] 1. In a thermal transfer recording medium having a coloring material layer on a support containing a heat-melting substance that remains in a solid state at room temperature and whose viscosity rapidly decreases when heated to a certain temperature, the composition of the coloring material layer is A thermal transfer recording medium characterized in that the temperature difference between the viscosity from 10,000 poise to 1,000 poise is 3°C or less.