JPH04347689A - Ink composition for thermal transfer recording - Google Patents

Abstract

PURPOSE:To provide an ink composition for thermal transfer recording which is excellent in heat sensitivity by improving mechanism strength of an ink layer before transfer without causing 'Tomoochi phenomenon', so called, wherein a portion of a non-image area is transferred. CONSTITUTION:An ink composition for thermal transfer recording has a thermal plastic resin particle, a wax particle, a color agent and liquid humectant as main components. Herein, instead of the thermal plastic resin particle and the wax particle, solid solution particle containing those thermal plastic resin and wax may be used.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION This invention relates to an ink composition for thermal transfer recording, and more particularly to an ink composition for forming an ink layer that has good transferability and provides clear print on a thermal transfer recording medium. relating to things.

0002

2. Description of the Related Art Thermal transfer recording media are used in word processors, computer output, and many other fields, and research is being conducted to improve printing quality. Some of the thermal transfer recording media and ink compositions used therein are listed below.

For example, (1) an ink composition consisting of a thermoplastic resin and/or wax, a colorant, a softener, and a polyhydric alcohol (Japanese Patent Publication No. 1-31793); (2) a colorant and a melting point or softening point; An ink composition mainly composed of resin particles having a temperature of 60 to 140°C, a wax having a melting point or softening point of 70 to 130°C, and a water-soluble resin (Japanese Patent Laid-Open No. 63-4
5091), (3) providing a colorless release layer between the ink layer made of the ink composition of (2) above and the support (Japanese Unexamined Patent Publication No. 63-51180), (4) melting point or softening. Solid solution particles mainly composed of a resin having a point in the range of 60 to 130°C and a wax having a melting point or softening point in the range of 70 to 130°C, and a dye and/or pigment;
(5) a first transfer layer containing styrene resin particles and wax as main components, a coloring agent, and a tackifying resin; A second transfer layer mainly composed of particles and wax is laminated on a support (Japanese Patent Laid-Open No. 63-84981).
(6) An ink composition comprising particles of a colorant and a thermoplastic resin, wax particles, and a water-soluble resin (Japanese Unexamined Patent Publication No. 89383/1983).

[0004] However, in the method (1) above, since heating coating is performed to provide the ink composition on the support, the various materials are mixed and the ink layer becomes a continuous layer with no gaps. Therefore, although polyhydric alcohols and softeners can improve the transfer rate and resolution, the thermal energy required for transfer is large;
When excessive energy is applied, the image tends to become thicker. That is, since the image becomes thicker due to a slight change in thermal energy, fine energy control is required in the printing device in order to always obtain a constant image.

On the other hand, in the methods (2) to (6) above, by making each material particulate, the boundary between the printed area and the non-printed area can be clearly defined, and the transfer layer becomes easy to break during transfer. , the resolution has been improved. Further, the thermal energy required to start the transfer is low, and the transfer area changes gradually depending on the thermal energy. Therefore, if there is a slight change in thermal energy with respect to appropriate thermal energy, the image will hardly become thicker or thinner. In addition, the composition ratio of resin can be increased without deteriorating thermal sensitivity.
The mechanical strength of the transferred layer is increased, and the abrasion resistance of the image is improved. However, since the transfer layer is formed by granulating each material, voids exist. For this reason, if a portion of the layer has a weak mechanical strength and the pressure with which the thermal head presses the ribbon is high, a portion of the non-image area will be transferred, resulting in a so-called drop-off phenomenon. If a binder is used to improve this, the thermal sensitivity will deteriorate.

In addition, in the products listed in (2) to (6) above, the composition ratio of resin to wax is higher than that of general wax-based thermal transfer recording inks, so it may vary depending on the material to be transferred. The wettability of the ink is poor, and additional thermal energy must be applied to improve fixing properties. In order to improve the fixing properties, it is necessary to improve the wettability to the transfer target during transfer. For this purpose, it is necessary to lower the viscosity during melting and softening, and generally, the viscosity can be lowered by adding a plasticizer or oils such as mineral or vegetable oils. However, since they generally have good compatibility with wax, there are disadvantages in that the wax becomes plasticized, making it easier to transfer under pressure and causing scumming.

[0007]

[Problems to be Solved by the Invention] An object of the present invention is to form an ink layer (transfer layer) using a particulate material, while taking advantage of the ease of tearing the transfer layer during transfer. An object of the present invention is to provide an ink composition for thermal transfer recording in which scumming can be prevented by improving the mechanical strength of the transfer layer. Another object of the present invention is to reduce the viscosity of the melting/softening of the transfer layer during transfer, improve wettability to a transfer target such as paper, improve thermal sensitivity, and improve image fixability. The present invention provides an ink composition for thermal transfer recording.

[0008]

[Means for Solving the Problems] The first ink composition for thermal transfer recording of the present invention is characterized by containing thermoplastic resin particles, wax particles, a colorant, and a liquid humectant as main components. The second thermal transfer recording ink composition of the present invention comprises solid solution particles containing a thermoplastic resin and a wax;
It is characterized by containing a colorant and a liquid humectant as its main ingredients.

The present invention will be explained in more detail below. As the "liquid moisturizer" commonly used in the first and second inventions of the present invention, any one such as polyhydric alcohol can be used, but among them, ethylene glycol, glycerin, diethylene glycol, propylene glycol can be used. , triethylene glycol, 1,2,6-hexanetriol, and dipropylene glycol have high moisturizing properties and are particularly effective. These humectants can be used alone or in combination of two or more.

[0010] Although it has not necessarily been clarified what kind of function such a liquid humectant plays in the ink composition of the present invention, it is thought to be roughly as follows. That is, general plasticizers and mineral or vegetable oils dissolve or soften some of the thermoplastic resins and waxes, so these oils are not used in thermal transfer recording ink compositions. In this case, background stains occur due to melting or softening of the material (resin, wax, etc.). On the other hand, liquid moisturizers have little ability to dissolve or soften thermoplastic resins or waxes. Therefore, even if a liquid humectant is added, scumming will not occur. When an ink layer is formed using an ink composition for thermal transfer recording to which a liquid humectant is added, the liquid humectant is present between the thermoplastic resin particles, wax particles, and colorant. When an ink layer is superimposed on a transfer target such as paper and thermal energy is applied, the liquid moisturizer on the surface of the ink layer first transfers and penetrates into the paper, helping the transfer of resin particles, wax particles, and colorant. Furthermore, the humectant inside the ink layer is thought to have the function of lowering the viscosity of the melted and softened resin or wax and improving transferability. In addition, thermoplastic resins include rosin resin, terpene resin, styrene resin,
When using a sticky resin such as petroleum resin or chroman-indene resin, stickiness may develop at room temperature. Liquid humectants also have the function of suppressing the development of stickiness at room temperature.

[0011] The liquid humectant is added in an amount of 1 to 5 to the ink composition.
It is preferable to add it in a proportion of 0% by weight, preferably 10 to 30% by weight. Since a thermal transfer recording medium using an ink containing a liquid humectant has less static electricity, it is thought that the humectant also has an antistatic function.

[0012] As the thermoplastic resin particles in the first ink composition of the present invention, various resins having a melting point or softening point in the range of 70 to 140°C can be used. Examples include acrylic resin, methacrylic resin, styrene resin, vinyl acetate resin, vinyl chloride resin, vinylidene chloride resin, petroleum resin, novolak resin, olefin resin, polyester resin, polyacetal resin, or copolymers containing heavy bodies of these resins. . If the melting point or softening point is lower than 70°C, the abrasion resistance of the transferred image in a high temperature environment (30 to 60°C) will be poor. On the other hand, if the temperature is higher than 140° C., high energy is required during thermal transfer recording, resulting in problems such as slow recording speed and shortened thermal head life.

The wax used in the first ink composition of the present invention is a wax having a melting point or softening point of 70 to 130° C. and is used in the form of particles. Further, the particulate wax preferably has a penetration degree (at 25° C.) of 1 or less. If the melting point or softening point of this wax is lower than 70° C., the applied thermal energy is consumed to melt the wax, resulting in insufficient energy to soften the resin particles. Therefore, only the wax is preferentially transferred, and the transfer of the transfer layer becomes insufficient, causing blurring of the transferred image and deterioration of sharpness. Further, if the temperature is higher than 130° C., high thermal energy is required for transfer. Specific examples of waxes that satisfy the above conditions include carnauba wax, polyethylene wax, Fischer-Trobsch wax, montan wax derivatives, hydrogenated castor oil, rice wax, candelilla wax, montan wax, ozokerite, ceresin, paraffin wax, and microcrystalline. Examples include wax, petrolactam, paraffin wax derivatives, and microcrystalline wax derivatives.

Both the thermoplastic resin and the wax used in the first aspect of the present invention are used in the form of fine particles, and the average particle size in the transfer layer is about 0.1 to 10 μm, preferably about 0.1 to 5 μm. . The smaller the average particle size, the better the thermal sensitivity and resolution, but if it is too small, the abrasion resistance will deteriorate, making it impossible to obtain sufficient blocking resistance. Moreover, if it is too large, thermal sensitivity and resolution will deteriorate.

The transfer layer may contain other water-soluble resins as binders, and specific examples of these water-soluble resins include polyvinyl alcohol, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, and polyacrylamide. , starch, gelatin, etc.

As dyes and pigments, inorganic or organic dyes and pigments used in printing inks, paints, etc. can be used. Specific examples include carbon black, Disazo Yellow, Brilliant Carmine 6B, Lake Red C, Phthalocyanine Blue, Kayaset Black KR (manufactured by Nippon Kayaku Co., Ltd.), Oil Yellow 3G (manufactured by Orient Chemical Co., Ltd.),
Kayaset Red K-BE (manufactured by Nippon Kayaku Co., Ltd.), Kayaset Blue KFL (manufactured by Nippon Kayaku Co., Ltd.), and the like.

The second ink composition of the present invention is similar to the first ink composition of the present invention in terms of the materials of the thermoplastic resin and wax, which are essential components, but The difference is that solid solution particles are formed by mixing. The size of the solid solution particles is an average particle diameter of 0.1 to 10 μm, preferably 0.1 to 5 μm.
The thickness is preferably about 1 to 3 μm. If it is less than 0.1 μm, sticking will easily occur during transfer;
If it exceeds μm, thermal sensitivity and resolution tend to deteriorate.

In order to actually produce a thermal transfer recording medium using the ink composition according to the present invention, a transfer layer (ink layer) may be coated on a support directly or via a release layer. Note that an adhesion-retaining layer may be provided between the release layer and the support.

As the support, various conventionally known supports can be used as appropriate. Specifically, polyester film, polyamide film, polyvinyl chloride film, polyethylene film, polypropylene film,
Examples include plastic films such as polyimide film, polysulfone film, and polycarbonate film, and condenser paper. The thickness of the support is preferably about 2 to 15 μm when considering a thermal head as a heat source during thermal transfer, but when using a heat source that can selectively heat the thermal transfer ink layer, such as a laser beam, for example. There are no particular restrictions.

When using a thermal head, a heat-resistant protective layer made of silicone resin, silicone rubber, fluororesin, polyimide resin, epoxy resin, phenol resin, melamine resin, nitrocellulose, etc. is placed on the surface of the support that comes into contact with the thermal head. By providing this, the heat resistance of the support can be improved, or a base material that could not be used conventionally can be used.

[0021] The peeling layer has a melting point or softening point of 60 to 150°C.
Advantageously, it is formed by a colorless layer (thickness approximately 2 μm) based on a thermoplastic resin and/or wax in the range of . Thermoplastic resin/wax weight ratio is 7/3 to 0
/10 can be selected. Some or all of the materials used here may overlap those used in the ink layer.

The material forming the adhesion-retaining layer (thickness: approximately 0.5 μm) is the same as the release layer (having a melting point or softening point of 6.0 μm).
(mainly containing thermoplastic resin and/or wax in the range of 0 to 150°C) is used. The weight ratio of thermoplastic resin/wax can be selected from 3/7 to 10/0.

Furthermore, part or all of the resin component of the release layer and/or the adhesion-retaining layer may be replaced with a rubber-based elastomer (
Butadiene rubber, styrene-butadiene rubber, nitrile rubber, nitrile-butadiene rubber, high styrene rubber,
The adhesive strength can be increased by using synthetic rubber such as isoprene rubber, acrylic rubber, epichlorohydrin rubber, butyl rubber, ethylene-propylene rubber, natural rubber, etc.).

The ink composition of the present invention can be prepared and used to produce a thermal transfer recording medium by, for example, the following method. (2) In the first ink composition of the present invention, the above-mentioned ink layer forming components are mixed with water or a solvent that does not dissolve the resin particles, and the average particle size of the resin particles is Disperse the resin particles so that they are 0.1 to 10 μm in size, and apply them on a support so that the total solid content is 1 to 10 g/m2. Dry at a temperature below the softening point of. ■ In the ink composition according to the second aspect of the present invention, the resin and wax are heated to a hot molten state, mixed uniformly, and cooled to obtain a solid solution. A solution is prepared by uniformly mixing binder, dye and/or pigment dispersed so that the particle size is 0.1 to 10 μm, and this is coated on a support with a total solid content of 1.
It is applied at a density of ~10 g/m2 and dried at a low temperature (below 50°C) to prevent the solid solution particles from fusing.

[0025]

[Example] Next, an example will be shown. Both parts and percentages herein are based on weight.

Examples 1 to 12 (1) Preparation of carbon black dispersion Carbon black

20 parts surfactant

Part 2 Water

78 parts of these mixtures were dispersed in a ball mill for 24 hours.

(2) Preparation of resin particle dispersion

[Table 1] Table 1
The material described in 1. was dispersed in a ball mill for 24 hours to obtain a dispersion of resin particles with an average particle size of about 2 μm.

(3) Preparation of wax dispersion

[Table 2] The materials listed in Table 2 above were dispersed in a ball mill for 24 hours to obtain a dispersion of wax particles having an average particle size of about 3 μm.

(4) Next, these (1) (2) (3)
The dispersion liquid having the composition shown in Table 3 below was mixed uniformly using a stirrer to prepare an ink liquid (transfer layer forming liquid).

[Table 3]

(5) Preparation of stripping solution As shown in Table 4 below, No. 11, No. 12 and no. As the stripping solution in No. 13, the wax dispersion itself was used. No. 14, No. 15 and no. Stripping solutions No. 16 were prepared by uniformly mixing the respective compositions using a stirrer.

[Table 4]

(6) Preparation of thermal transfer recording media Twelve types of thermal transfer recording media according to the present invention were prepared by providing an ink layer on the substrate either directly or via a release layer (Table 5).

[Table 5] For Examples 1 to 6, the ink layer forming liquid was applied onto a polyester film with a thickness of about 6 μm using a wire bar so that the amount of adhesion after drying was about 4 g/m2, and then heated. It was air dried (50°C). For Examples 7 to 12, a release layer was provided on a polyester film with a thickness of about 6 μm so that the amount of adhesion after drying was about 1.5 g/m2 (However, in Examples 7 to 9, coating with a wire bar, Example 1
0 to 11 were applied by hot melt coating), and then on top of this, an ink layer forming liquid was applied using a wire bar so that the amount of adhesion after drying was approximately 2.5 g/m2, and hot air was applied ( 40
~50°C).

As shown in Table 6 below, a comparative thermal transfer recording medium was prepared in exactly the same manner as in the corresponding example except that the humectant was removed from the ink layer.

[Table 6]

Comparative Example 7 A comparative thermal transfer recording medium was prepared in exactly the same manner except that a polyhydric alcohol derivative of castor oil (HYRIC AQ350, manufactured by Ito Seyu Co., Ltd.) was used in place of the humectant in Example 1.

Examples 13 to 17 First, the following three types of solid solution particle liquids (A), (B), and (C) were prepared. (A) Polystyrene (softening point 80°C)
12 parts carnauba wax (melting point 83°C)
Eight parts were heated to 100°C, melted, mixed uniformly, and then cooled to room temperature to form a solid solution. 20 parts of this solid solution, 10 parts of polyvinyl alcohol (10% aqueous solution), and 70 parts of water were dispersed in a ball mill for 24 hours to obtain a solid solution particle liquid (A) having an average particle size of 3 μm. (B) Styrene/acrylic resin (softening point 100°C)
10 parts rice wax (melting point 80°C) 10 parts A solid solution particle liquid (B) was obtained in the same manner as in the above (A) using these. (C) Petroleum resin (softening point 70°C)
10 parts polyethylene wax (softening point 128°C)
Using 10 parts of these, prepare a solid solution particle liquid (C
) was obtained.

Using these solid solution particle liquids, thermal transfer recording media according to the present invention were prepared in the same manner as in Examples 1 to 6 (Table 7).

[Table 7]

Comparative Examples 8 to 12 Comparative Example 8 is from Example 13, Comparative Example 9 is from Example 14, Comparative Example 10 is from Example 15, Comparative Example 11 is from Example 1.
6 and Comparative Example 12, comparative thermal transfer recording media were prepared in exactly the same manner as in Example 17 except that the humectant was removed.

The transfer layer of these thermal transfer recording media (
The ink layer) was brought into close contact with the surface of the high-quality paper, and printing was performed using a thermal transfer printer. The image density of the printed image, presence of scumming, and thermal sensitivity were examined. The results are shown in Table 8.

[Table 8] (Note 1) Image density: Reflection density of the solid printed area (by Magbeth reflection densitometer) (Note 2) Thermal sensitivity: Decoding rate of printed vertical barcode (parallel bar) by LASERCHEC
K 28 11 (manufactured by Symbol Tephrosies), and is expressed as the minimum printing energy whose value is 90 or more. The unit is mj/mm2. (Note 3) Friction resistance: Number of frictions: 100 reciprocating loads
100g/cm2 room temperature
20°C, 50°C Good...No change, slightly bad...A little ink was removed from the printed area and a little adhered to the non-printed area. Bad: A lot of ink is removed from the printed area and a lot of ink sticks to the non-printed area. (Note 4) Scratch resistance: The transferred image was rubbed with a Ben scanner to see how much ink was removed from the printed area. Good...No change Bad...Ink is removed and lines are cut.

[0038]

[Effects of the Invention] As is clear from the description of the examples, when the ink composition of the present invention is used in a thermal transfer recording medium, the thermal sensitivity is extremely good, and in addition, the fixing property is good. With this, a transferred image without background stains can be obtained.

Claims (7)

[Claims] 1. An ink composition for thermal transfer recording, comprising as main components thermoplastic resin particles, wax particles, a colorant, and a liquid humectant. 2. The ink composition according to claim 1, wherein the thermoplastic resin particles and wax particles both have an average particle size of 0.1 to 10 μm. 3. An ink composition for thermal transfer recording, comprising as main components solid solution particles containing a thermoplastic resin and wax, a colorant, and a liquid humectant. 4. The ink composition according to claim 3, wherein the solid solution particles containing the thermoplastic resin and wax have a diameter of 0.1 to 10 μm. 5. The ink composition according to claim 1, wherein the thermoplastic resin has a melting point or softening point in the range of 70 to 140°C. 6. The melting point or softening point of the wax is 70.
The ink composition according to claim 1 or 3, wherein the ink composition has a temperature in the range of -130C. 7. The content of the liquid humectant is 1 to 50% by weight of the total amount of the ink.
The ink composition described.