JPH0564982A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To provide a thermal transfer recording medium which is capable of maintaining print at high density level, even if thermal transfer printing is performed many times and visualizing a sharp image. CONSTITUTION:The subject thermal transfer recording medium consists of the first ink layer of coarse porous branches resin structure 12 impregnated with thermal fusible ink 11 as a thermal transfer ink layer and the second ink layer 2 containing mainly thermal fusible ink 21 formed on the first ink layer, both layers being laminated sequentially on a heat-resistant base 3. In addition, the interface between the first ink layer and the second ink layer has mold lubrication effects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording medium capable of recording many times, particularly to a thermal transfer recording medium excellent not only in maintaining image density but also in resolution of initial printing.

[0002]

2. Description of the Related Art Printers such as printers and facsimiles, which utilize a thermal transfer recording system, are widely used because they can be downsized, reduced in price, and reduced in maintenance. A thermal transfer recording medium used in a thermal transfer recording apparatus is generally one in which a thermal transferable ink layer is simply provided on a base material, and therefore, the heated portion of the ink layer is completely transferred by one use and repeatedly used. However, there was a problem in terms of running cost. Therefore, the appearance of a thermal transfer recording medium that can be used repeatedly has been demanded, and various thermal transfer recording media have been proposed so far.

Some of them are (1) JP-A-54.
-68253, JP-A-55-105579, and the like, in which a fine porous ink layer is provided on a substrate so that the heat-meltable ink is gradually leached, 2) A method in which a porous film is provided on an ink layer on a substrate to control the outflow amount of ink, as disclosed in JP-A-58-2129993, and (3) JP-A-60- No. 127191, JP-A-60-1271
As disclosed in Japanese Patent Laid-Open No. 92, etc., there is proposed a method in which an ink layer is provided via an adhesive layer and the ink layer is peeled off little by little and transferred.

However, in the thermal transfer recording media of the above (1) and (2), the heat-meltable ink exudes from the holes and is transferred. Image resolution has the drawback that it depends on the size and distribution of the holes, or the smoothness of the receiving paper. Further, the thermal transfer recording medium of the above (1) has a drawback that it is difficult to seep out the ink with repeated use and the print density gradually decreases. The thermal transfer recording medium (2) has a drawback that the mechanical strength is lowered and the ink layer is peeled off when the pore diameter of the porous film is increased in order to increase the printing density.

The thermal transfer recording medium of (3) above has an excellent image resolution because the non-transfer portion is not contained in the ink layer, but the ink transfer is performed by utilizing the cohesive failure of the ink. The position of cohesive failure in the ink layer is not constant due to changes in printing conditions such as printing speed and energy applied from the thermal head, and it is difficult to say that it can be applied to all wide thermal transfer printing devices.

Most of the conventional thermal transfer recording media are compatible with a serial thermal head used in a recording device such as a word processor, and are not printed by a line thermal head used in a recording device such as a facsimile or a bar code printer. Bar code printing or gradation expression using dots is used, and there is a strong demand for improvement in reproducibility of thin lines.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a thermal transfer recording medium which maintains high printing density even when thermal transfer printing is performed a number of times, records an image with little density decrease, and is excellent in fine line reproducibility. Is what you are trying to do.

[0008]

The constitution of the present invention for solving the above-mentioned problems is a first structure of a coarse porous branched resin structure in which a heat transfer ink layer on a heat-resistant substrate is impregnated with a hot-melt ink.
A thermal transfer recording medium comprising an ink layer and a second ink layer on the surface of which is composed mainly of a heat-fusible ink, and the branched resin structure of the first ink layer is partially bonded to a substrate. And a thermal transfer recording medium having a releasing action between the first ink layer and the second ink layer.

According to the results of research conducted by the present inventors, as shown in FIG. 1, a heat-fusible ink is formed on a first ink layer 1 composed of a heat-fusible ink and a branched resin structure having holes on a substrate. When the second ink layer 2 is formed, the heat-meltable ink that does not include the non-transferable portion of the second ink layer 2 is transferred in a large number of times of printing, especially in the first printing, so that the fine line reproducibility of the image is excellent. Had found it. However, when the thermal transfer is repeatedly performed using the line type thermal head and the thermal transfer recording medium, the ink transfer is always performed near the interface between the first ink layer 1 and the second ink layer 2 due to the change of the printing speed or the printing energy. However, depending on the conditions, cohesive failure may occur in the second ink layer 2 or may occur in the first ink layer 1 or at the interface between the ink layer 1 and the substrate (so-called total transfer). It was practically difficult to make the transfer amount constant.

Therefore, the present inventors proceeded with further studies and
It was confirmed that the above problems can be achieved if the thermal transfer recording medium is devised so as to have a releasing action between the ink layer 1 and the second ink layer.

Releasability is imparted in the present invention by a method of imparting releasability to the resin of the ink layer 1 with the heat-meltable ink, or imparting releasability to the heat-meltable ink itself of the ink layer 1 or 2. The method is taken.

Here, as a component having a releasing action which is preferably used, a low surface energy substance such as a modified silicone resin, a silicone resin or a modified fluororesin is used alone or in a mixture of two or more kinds. Alternatively, a suitable coarse-pore forming resin or heat-meltable ink may be blended with the substance having a low surface energy. Further, a mold releasing property may be imparted by compounding using a reactive silicone resin or the like.

As the modified silicone resin and modified fluororesin, various kinds are used for the purpose of improving the adhesiveness and mechanical strength and enhancing the affinity with other matrix forming resins. As a modification method, conventionally known acrylic modification, urethane modification, alkyd modification, epoxy modification, higher fatty acid modification, carnauba modification and the like are used. A polyorganosiloxane part having a low surface energy and a di-, tri-, tetra-, or fluorinated ethylene part are bonded to these resins in a block or graft form.

As the reactive silicone resin, one or both ends of polyorganosiloxane is substituted with a reactive functional group such as an epoxy group, a carboxyl group, a hydroxy group or an amino group. Is used.

Next, a specific method for preparing the thermal transfer recording medium according to the present invention will be described.

It can be obtained by mixing, coating and drying a resin having a coarse branched resin structure for forming the first ink layer 1 and an ink obtained by gelating a heat-meltable ink. Further, by adding a foaming agent and foaming after coating and drying, a coarser branched resin structure closer to the ideal can be formed. In this drying step, the temperature of the layer is raised to near the softening point temperature of the branched resin, so that the branched resin and the support are connected. Furthermore, the second ink layer 2 is formed by applying a heat-meltable ink on the layer and drying it.

The support 1 used in the present invention is a conventionally known material having heat resistance, for example, plastic film such as polyester, polycarbonate, triacetyl cellulose, nylon, polyimide, cellophane, sulfuric acid paper,
Capacitor paper etc. can be used. The thickness of the substrate is thermal sensitivity,
Considering the mechanical strength, it is desirable that the thickness is about 2 to 15 μm. Further, by providing a heat-resistant protective layer 5 made of silicone resin, fluororesin, polyimide resin, epoxy resin, phenol resin, melamine resin, nitrocellulose or the like on the surface of the heat-resistant substrate that contacts the thermal head, the heat resistance of the substrate is improved. Can be further improved.

The heat-meltable ink or the heat-meltable ink immiscible with the branched resin or the fine porous resin held in the first ink layer 1 and the second ink layer 2 which are the ink stocks of the present invention is It consists of a colorant and a vehicle component.

The colorant can be appropriately selected from conventionally known pigments and dyes. Carbon black and phthalocyanine pigments are preferably used as the pigment, and the dyes are direct dyes, acid dyes, basic dyes and dispersions. Dyes and oil-soluble dyes are preferably used.

Examples of the vehicle component include beeswax, carnauba wax, whale wax, tree wax, candelilla wax, natural wax such as wax, montan wax, paraffin wax, microcrystalline wax, oxidized wax, ozokerite, ceresin, ester wax and the like. Be done. Besides, higher fatty acids such as margaric acid, lauric acid, myristic acid, palmitic acid, stearic acid, frommenic acid and behenic acid, higher alcohols such as stearyl alcohol and behenyl alcohol, esters such as fatty acid esters of sorbitan, stearamide, oleinamide. And other amides.

When the hot-melt ink itself has releasability, it is selected from a modified silicone or a modified fluororesin having a high compatibility with a vehicle component such as higher fatty acid-modified or carnauba-modified silicone oil.

The heat-meltable gelled ink in the first ink layer is roughly classified into a solvent dispersion method, a hot melt dispersion method, and an ink gelling agent.
Use it by selecting it arbitrarily.

First, in the case of the solvent dispersion method,
The ink composition is obtained by dispersing the ink composition in a suitable solvent in a high temperature atmosphere and cooling to room temperature. Specifically, it is desirable that the dispersion temperature range is 25 to 40 ° C.
If the temperature is 25 ° C or lower, the gelation effect is not obtained and the transfer ability is not improved, and if it is 40 ° C or higher, it is not preferable in terms of safety. The cooling is performed by leaving it at room temperature.

The gelation of the ink may also be carried out by adding an appropriate gelling agent such as glycerin fatty acid esters. At this time, the addition amount of the gelling agent is preferably in the range of 5 to 50% by weight based on the total solid content of the heat-meltable ink.

When the hot melt dispersion method is used,
For example, it is dispersed in a high temperature atmosphere by a roll mill, a sand mill, an attritor, etc., but a dispersion method using a sand mill is more uniform and preferable. Specifically, the above colorant and the vehicle component are mixed and then dispersed under high shear in a vessel set at 10 to 20 ° C. higher than the melting temperature of the vehicle component. After dispersing for an arbitrary time, the mixture is left to cool at room temperature, or a suitable diluent solvent and an arbitrary vehicle component that have been melted are added, and then redispersed at 25 to 35 ° C. Adjust.

The heat-melting wax of the second ink layer is appropriately selected and used from the vehicle components constituting the heat-melting ink of the first ink layer. At this time, the waxes are not particularly required to be gelled, and are not limited as long as they are preferable for dispersion of the colorant such as dispersion method and temperature conditions.

Various resins having a glass transition point higher than the melting point of the heat-meltable ink of the present invention can be used as the branched resin of the first ink layer of the present invention. For example, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, polyester resin, epoxy resin, polycarbonate resin, phenol resin, polyimide resin, resin such as cellulose,
Examples thereof include polyamide resin and acrylic resin.

When the branched resin has a releasing property with respect to the hot-melt ink of the second ink layer, the above-mentioned releasing property imparting method may be adopted. Further, in the case of imparting releasability using a reactive silicone resin or the like, it is necessary to select a branched resin composition having a reactive functional group.

Further, the above-mentioned foaming agent which facilitates the formation of the resin structure is preferably an azo compound which disperses upon heating to form pores in the entire layer, and examples thereof include azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile and diazoa. Examples include fuminobenzene and barium diazocarboxylate. Further, in order to control the foaming temperature and foaming efficiency of the foaming agent, a foaming aid such as zinc oxide, various stearates or palmitates, and a plasticizer such as DOP may be added. Although the amount of the foaming agent is not particularly limited, it is preferably added in an amount of 5 to 30% with respect to the total solid content of the resin matrix and the heat-meltable gelled ink in the first ink layer. If the content of the foaming agent is less than the above range, the pores necessary for increasing the transfer ability cannot be sufficiently obtained, and conversely, if it is more than the above range, the mechanical strength is lowered, which is not preferable.

In the first ink layer of the present invention, the resin forming the branched and fine porous particles, the heat-melting gelled ink and the heat-melting wax are highly volatilized together with the method using the foaming agent. It is also possible to use in combination with a method of dissolving in a mixed solvent of an organic solvent and a low volatility solvent and forming a resin porous body by drying.

The thickness of the first ink layer 3 of the present invention can be appropriately set according to the size of the number of times of printing, but it is 3-1.
By setting the thickness to 5 μm, it is possible to obtain excellent thermal sensitivity and repeatable printability. Further, the thickness of the second ink layer 4 may be such that a sufficient density can be obtained by one-time transfer, and is preferably 1 to 5 μm.

[0032]

The present invention will be described in more detail with reference to the following examples. The amounts (parts) of each component described in the examples are parts by weight.

Example 1 A heat-resistant layer made of a silicone resin is formed on one surface of a polyethylene terephthalate film having a thickness of 4.5 μm to prepare a base material.

[Preparation of heat-meltable gelled ink] Carbo black 15 parts Candelilla wax 60 parts Oxidized polyethylene wax 23 parts Terpene resin (dispersant) 2 parts After filling the above components in a sand mill vessel, dispersion at 110 ° C. A uniform ink was obtained. After that, the system is heated to 65 ° C,
10 parts of low melting point oil-soluble dye benzol black and 675 parts of methyl ethyl ketone / toluene (2/1 ratio) were added, and redispersion was carried out at 32 ° C. After dispersion, the mixture was allowed to cool at room temperature to obtain a heat-meltable gelled ink. Using this ink, the following ink layer coating solutions were prepared to prepare an ink layer.

[Preparation of First Ink Layer] Heat-meltable gel ink 10 parts 20% solution of vinyl chloride-vinyl acetate copolymer in methyl ethyl ketone / toluene (2/1 ratio) 3 parts Acrylic-modified silicone resin (polyorgano Siloxane, 20% solution of methylethylketone / toluene (2/1 ratio) of n≈20-40, average amount about 15000) 0.3 parts After mixing the above components, apply on a substrate to a film thickness of 8 μm. The first ink layer was prepared by drying at 110 ° C.

[Preparation of Second Ink Layer] A mixture of carbon black 15 parts, candelilla wax 50 parts, paraffin wax 25 parts, ethylene-vinyl acetate copolymer 10 parts and toluene 700 parts as a heat-meltable ink component is sufficiently dispersed by a ball mill. After that, it is applied on the first ink layer so as to have a dry film thickness of 1.5 μm.
The second ink layer was formed by drying at 0 ° C to obtain a thermal transfer recording medium of the present invention.

Example 2 Of the substances forming the coarse porous resin structure having releasability in the first ink layer of Example 1, an acrylic modified fluororesin (polytetrafluoroethylene (polytetrafluoroethylene A resin obtained by grafting (n≈15 to 20) onto an acrylic vinyl monomer and copolymerizing it with MMA, except that an isopropyl alcohol / methyl ethyl ketone (1/1) 20% solution having an average molecular weight of 35000) was 0.3 part. A thermal transfer recording medium was obtained in the same manner as in 1.

Example 3 [Preparation of First Ink Layer] In Example 1, the coarse porous resin structure was formed only by 3 parts of a 20% solution of a vinyl chloride-vinyl acetate copolymer in methyl ethyl ketone / toluene (2/1 ratio). A first ink layer was formed in the same manner as in Example 1 except for the above.

[Preparation of Second Ink Layer] Carbon black as a heat-meltable ink component 15 parts Candelilla wax 40 parts Paraffin wax 20 parts Ethylene-vinyl acetate copolymer 10 parts Higher fatty acid-modified silicone oil (KF-910 manufactured by Shin-Etsu Chemical Co., Ltd.) ) 15 parts Toluene 700 parts of a mixture was sufficiently dispersed by a ball mill, and then coated on the first ink layer so as to have a dry film thickness of 1.5 μm.
A second ink layer was formed by drying at 0 ° C to obtain a thermal transfer recording medium.

Comparative Example 1 The ink layer was composed of a single layer, carbon black 15 parts, candelilla wax 60 parts, polyethylene oxide wax 25 parts, vinyl chloride-vinyl acetate copolymer 100 parts, the above substances were mixed solvent of toluene and methyl ethyl ketone (2/1 Ratio) to a solid content of 15% by weight and sufficiently dispersed in a ball mill in an atmosphere of 30 ° C., and then allowed to stand at room temperature to obtain an ink composition. This dispersion was applied onto a substrate so as to have a dry film thickness of 10 μm and dried at 110 ° C. to obtain a thermal transfer recording medium.

Comparative Example 2 In the same manner as in Example 1 except that the acrylic-modified silicone resin was omitted from the coarse porous resin structure constituents in Example 1, a mold release was performed between the first ink layer and the second ink layer. A thermal transfer recording medium having no effect was obtained.

The five types of thermal transfer recording media prepared as described above were mounted on a line printer, and as a print pattern,
Use the one that includes all solid parts and CODE39 barcode,
The same position on the thermal transfer recording medium was repeatedly printed four times, and the image density at each time was measured by a Macbeth reflection densitometer (RD-914).
Then, read the barcode reading rate (%) by Symbol Tech.
It was measured with a barcode checker 2811 manufactured by Nologies.

[Printing conditions] Thermal head: Thin film head type Platen pressing: 230 gf / cm Clearing angle: 45 ° (for transfer paper) Printing energy: 17 and 22 mJ / mm ² Printing speed: 4 inch / sec Transfer paper : Lightweight coated paper (Beck smoothness of 350 sec) The printing result at 17 mJ / mm ² in FIG. 2 is 22 mJ in FIG.
The printing results (change in image density with respect to the number of printing times) in / mm ² are shown. Table 1 shows the results of bar code reading rate (%) at 22 mJ / mm ² .

[0044]

[Table 1] From Table 1, in Examples 1 to 3 in which the first ink layer and the second ink layer are provided with releasability, the bar code reading rate is high and the fine line reproducibility is excellent. On the other hand, in Comparative Example 1 having no second ink layer, the reading rate was low, and in Comparative Example 2 having no releasability between the first ink layer and the second ink layer, all the ink layers were transferred in the first transfer. It peeled off and was not suitable for printing many times. Further, as shown in FIG. 2 (a), in Comparative Example 2, the image density is low on the contrary in low energy printing, and it is weak against the change of printing conditions, but in Examples 1 to 3, in comparison with energy change,
It can be seen that the stable multi-time printing performance is maintained.

[0045]

As described above, the thermal transfer recording medium of the present invention has a first ink layer mainly composed of a coarse porous resin structure and a heat-fusible ink, and a heat-fusible layer laminated on the first ink layer. By providing a releasing action between the second ink layer composed mainly of ink, it is possible to obtain an image that maintains high printing density even when used many times, has excellent reproducibility of fine lines, and is resistant to changes in printing conditions. ..

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a thermal transfer recording medium of the present invention.

[Fig. 2]

FIG. 3 is a graph showing the relationship between the number of prints and the image density when an image is formed using the thermal transfer recording medium of the present invention and the thermal transfer recording medium of the comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st ink layer 2 2nd ink layer 11,21 Thermofusible ink 12 Coarse porous resin structure 3 Heat resistant base material 4 Heat resistant slipping layer

Claims (1)

[Claims] 1. A first ink layer having a coarse porous branched resin structure in which a heat transfer ink layer on a heat-resistant substrate is impregnated with a heat-fusible ink, and a second ink layer mainly composed of the heat-fusible ink on the surface thereof. And a release resin between the first ink layer and the second ink layer, wherein the branched resin structure of the first ink layer is partially bonded to the substrate. A thermal transfer recording medium comprising: