JPH0439092A - Ink sheet for thermal transfer printer - Google Patents

Abstract

PURPOSE:To prevent the release of an ink layer and to enhance transfer density by laminating an ink layer to a sheet like support through an intermediate layer based on a polyester resin having specific glass transition temp. CONSTITUTION:An ink layer is laminated to a sheet like support through an intermediate layer. As the sheet like support, a film composed of polyester or polycarbonate and paper such as condenser paper or tissue paper are pref. The polyester resin used in the intermediate layer is a polycondensation product of at least one kind of a diol component and at least one kind of a dicarboxylic acid component and an amorphous linear saturated polyester resin having glass transition temp. of 50 deg.C or lower, low in crystallinity, soluble in an org. solvent and having excellent adhesiveness is pref. The ink layer is based on wax, fatty acid amide, a dye and a filler and, if necessary, a dispersant is added.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an ink sheet for thermal transfer printers, and more particularly to an intermediate layer provided between a base material and an ink layer of an ink sheet for thermal transfer printers, and This relates to an ink sheet that does not peel off the ink layer, the transferred image is sharp, and can print high-resolution characters and images uniformly.This relates to an ink sheet that can be used with thermal transfer type Kanji printers, color printers, etc. be.

[Prior art and issues to be solved] Recently, the need for color printers has increased, and their development and commercialization are progressing. In particular, full-color printers using the melt/sublimation thermal transfer method are attracting attention because they can print clear color images with relatively compact equipment.

A melt-type thermal transfer printer uses a thermal transfer ink sheet consisting of a base material such as a film or thin paper and a heat-meltable ink layer.

By overlapping this thermal transfer ink sheet and receiving paper and applying heat from a thermal head in response to an electric signal, ink is transferred from the heat-melting ink layer to the receiving paper to form a monochrome or color image on the receiving paper. According to this recording method, since pigments can be used as the main component of the coloring material in the ink, prints can be stored for a long time, unlike conventional thermal paper that uses leuco dyes.

Such thermal transfer printers are characterized by being able to print on any receiving paper, but for full-color images with intermediate densities, such as photographs, halftone images are formed using the dither signal processing method, resulting in lower resolution and lower image quality. There are drawbacks to it.

Further, printers using a sublimation type thermal transfer method use a sublimation transfer ink sheet consisting of a base material such as a film or thin paper and a sublimable dye layer. This sublimation type thermal transfer ink sheet and a receiving paper whose surface has been treated with dyeable resin such as polyester resin are superimposed, and printing is performed in the same manner as in the melting type thermal transfer method. The transfer amount of the image can be continuously controlled at the molecular level of the sublimation dye by the energy applied from the thermal head, so the density of the image changes continuously, resulting in a high-quality full-color image similar to that of a photograph. Is possible.

However, the sublimation transfer method requires a special receiving paper whose surface is treated with dyeable resin such as polyester resin, and the coloring agent is a sublimable dye, which has the disadvantage that the image has poor storage stability against light and heat.

In order to compensate for these drawbacks, a melt density gradation type thermal transfer method has been developed. This method uses sublimation transfer onto an ink sheet that contains heat-melting ink using dyes with high fastness in a stone wall structure made of pigments such as carbon black and calcium carbonate, and a microporous network structure made of a resin matrix. Similar to the method, by applying thermal energy from the thermal head, the molten ink is transferred from the microporous according to the amount of heat, making it possible to continuously control the amount of ink transferred, and the amount of transferred image is It is possible to vary the concentration continuously.

Therefore, since continuous gradation can be obtained for each dot, similar to the sublimation type thermal transfer recording method, there is no reduction in image resolution. Furthermore, since ink containing a dye and a vehicle such as a fatty acid amide is transferred, printing is possible even on high-quality paper, and full-color images comparable to high-quality printing can be obtained.

For example, Japanese Patent Application Laid-open No. 60-54894 is known as a melt density gradation type thermal transfer technique for obtaining such an ink sheet. Although the resolution of the transferred image was better than that of ordinary thermal transfer recording methods, the maximum transfer density was insufficient compared to ordinary printed matter. In addition, the ink sheet is a base material,
It consists of an intermediate layer and an ink layer.The material used for the intermediate layer is an intermediate product obtained in the process of forming polyester resin, which has a high viscosity between solid and liquid phases at room temperature. The problem of thermal properties affecting the adhesion and transfer density of the ink layer remains unsolved.

[Problem to be solved by the invention]

The present invention solves the drawbacks of the prior art and uses a specific material as the intermediate layer of the ink sheet, thereby preventing peeling of the ink layer and improving the transfer density of the image. The purpose is to provide sheets.

[Means for Solving the Problem] As a result of intensive research to improve the defects on the ridges, the present inventors have developed a thermal transfer printer in which an ink layer is laminated on a sheet-like support via an intermediate layer. In the ink sheet,
With the ink sheet for thermal transfer printers in which the intermediate layer is mainly composed of a polyester resin having a glass transition temperature of 50° C. or lower, the ink layer does not peel off from the base material.
The sheet-like support of the present invention, which was discovered to enable high-density and high-quality printing on receiving paper, and which led to the present invention, is made of thick materials such as polyester, polycarbonate, triacetylcellulose, nylon, and polyimide. Sa3~3
It is preferable to use a film with a thickness of 0 μm or paper with a thickness of 7 to 30 μm such as capacitor paper, thin paper, electrically insulating paper, parchment paper, etc. The thickness of the film that is the sheet-like support is 3
If the thickness of the paper is less than 7 μm, the strength will be insufficient and practicality will be a problem. Also, the thickness of the film or the thickness of the paper is 3
If it is thicker than 0 μm, the sensitivity decreases and a large amount of energy is required for transfer, which is not preferable.

In the film of the sheet-like support, the side opposite to the ink layer, that is, the side in direct contact with the thermal head, is heated above the melting point of the film, so a so-called stick phenomenon occurs in which the thermal spatula and the film are thermally fused. To avoid this phenomenon, a heat-resistant protective layer is provided on the film. The heat-resistant protective layer may be formed by applying a highly heat-resistant material such as silicon to about lttm.

The polyester resin used in the intermediate layer of the present invention is a polycondensation product of at least one diol component and at least one dicarboxylic acid component, and has a glass transition temperature of 5.
General-purpose organic solvents with low crystallinity or amorphous at 0°C or below, such as toluene, benzene, xylene, methanol,
Ethanol, acetone, MEK, ethyl acetate, THF
Linear saturated polyester resins are preferred, as they are soluble in esters and have excellent adhesive properties.

Diol components constituting such polyester resins include, for example, ethylene oxide adducts to bisphenol, which is an aromatic diol, and aliphatic glycols other than aromatic diols such as propylene glycol, l, 3
-Propanediol, 1.4-butanediol, 1.5
-bentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, and 1.
Cycloaliphatic glycols such as 4-cyclohexylmethane can also be used.

As the dicarboxylic acid component, aromatic dicarboxylic acids such as terephthalic acid, orthophthalic acid, and 2゜6-naphthalene dicarboxylic acid are used, but dicarboxylic acids other than aromatic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, Aliphatic dicarboxylic acids such as sebacic acid, dodecanedioic acid, and dimer acid, and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid may also be used.

If a polyester resin having a glass transition temperature of 50° C. or more is used for the intermediate layer, the adhesion between the ink layer and the ink sheet substrate will deteriorate, causing the ink layer to peel off during transfer.

The thickness of the intermediate layer is preferably in the range of 1-10 μm. When the thickness is less than 1 μm, the effect of adhering the base material and the ink layer becomes weak, causing peeling of the ink layer. If it is thicker than 10 .mu.m, the thermal efficiency decreases, resulting in low sensitivity, gradation deterioration, blocking, and is uneconomical.

The ink layer of the present invention includes wax, fatty acid amide, dye,
The main component is filler.

Other ingredients such as a dispersant can be added in required amounts as necessary.

As the wax, for example, paraffin wax, microcrystalline wax, ester wax, carnauba wax, Fischer-Tropsch wax, etc. can be used. When storing an ink sheet in roll form, the melting point must be 40°C or higher to prevent blocking, and the melting point must be 200°C or lower to maintain fluidity that does not affect transfer. desirable.

The fatty acid amide of the present invention is a component for dissolving the dye, but at the same time it must not impair fluidity upon heating. Examples of fatty acid amides include erucic acid amide, oleic acid amide, and stearic acid amide.

Examples of the colorant used in the present invention include methanol,
Examples include organic complex dyes, oil-soluble dyes, and disperse dyes that have high solubility in ethanol, acetone, MEK, ) toluene, and ethyl acetate, and have high fastness.

As fillers in the present invention, various carbon blacks widely used in the field of conventional monochrome melt-type thermal transfer inks and carbon copying papers, and commonly used pigments such as calcium carbonate, silica, and clay can be used without any special restrictions. It is possible.

The thicker the ink layer, the larger the amount of ink transferred and the higher the transfer density, but on the other hand, the temperature of the ink sheet is less likely to rise, making it difficult to transfer low density images and resulting in poor gradation.
Further, there is a drawback that the ink layer is likely to peel off.

Furthermore, when the ink layer is thin, the gradation is improved, but the amount of ink to be transferred is reduced, so there is a drawback that the transfer density is low.

In the present invention, it is preferable that the thickness of the ink layer is 5 to 15 μm so that no adverse effects are likely to occur.

The receiving paper used in the print evaluation of the present invention is a pigment-coated synthetic paper in which an ink-receiving layer containing pigment and adhesive as main components is provided on synthetic paper. The ink-receiving layer is made of silica, light/bicarbonate calcium, clay, etc. used in general coated paper.
At least one pigment such as calcium silicate, alumina, titanium dioxide, etc., a water-soluble adhesive such as PVA, starch, casein, and an emulsion such as an acrylic-styrene copolymer or a styrene-butadiene copolymer. It is composed of more than one type.

The coating amount of the ink receiving layer is preferably 5 to 40 g/m2.

If the coating amount is less than 5 g/l112, ink absorbency will be poor, transfer density will decrease, and image fixability will deteriorate. Moreover, if the coating amount is more than 4.0 g/m', the ink-receiving layer is likely to crack or peel off due to a decrease in adhesive strength, and it is also uneconomical. An example of a receiving paper provided with such an ink receiving layer is PFK.

Commercially available pigment-coated synthetic paper such as PFI (manufactured by Tamago Oil Synthetic Paper) can be used.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

Example 1 On the opposite side of a 6 μm polyester film provided with a heat-resistant layer on one side, the following intermediate layer paint was applied to a thickness of 3 μm using a bar #6.

[Middle layer]

Byron 30SS (manufactured by Toyobo: Tg = 6°C, molecular weight = 20000-25000, concentration 15%, MEK/
) Luene = 2/8) After coating the intermediate layer, the solvent was dried, and Paint 1, which was dispersed for 30 minutes with a paint conditioner, was applied to a thickness of 7 μm using a bar #20.

[Paint 1: Ink layer composition] Paraffin wax 135 Melting point 58°C (Japanese Ruso) 1 part fatty acid amide P-10 Melting point 78-85°C (NOF Department) 2
Part Carbon Black Kayaset BLAC 149-40 (Nippon Kayaku) 1 Part Dye Kayasef) BL^CK K-R
(Made by Nippon Kayaku) 1 part A7ton
After drying the solvent of the ink layer, the ink sheet coated with 30 parts was heat-treated at 100° C. for 5 minutes.

The above ink sheet was printed on coated synthetic paper (PFK90: manufactured by Tamago Yuka Synthetic Paper) using a thermal transfer tester.

The printing conditions were a voltage of 8.5 V, a pulse width of 1 msec step, and a duration of 1 to 20 msec. The evaluation results are shown in Table 1. The highest density as an evaluation item was 8.5 cm, and the portion printed in 20 msec was measured using a Macbeth densitometer.

The gradation was evaluated visually.

The state of peeling of the ink layer was visually evaluated.

Example 2 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, the middle layer is Byron 60SS (manufactured by Toyobo: Tg=
47°C, molecular weight = 9000-12000).

Comparative Example 1 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, for the middle class, Byron 20SS (manufactured by Toyobo: 'rg
= 67°C, molecular weight = 15,000 to 20,000).

Comparative Example 2 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, the middle layer is Byron 29SS (manufactured by Toyobo: Tg=
77°C, molecular weight = 20,000 to 25,000).

Table 1 Evaluation of ink sheet for thermal transfer printers [Effects of the invention] The ink sheet for thermal transfer printers of the present invention has no peeling of the ink layer, good density gradation, and improves low transfer density, which is a drawback of conventional methods. This technology enables thermal transfer printing with excellent image quality, and will greatly contribute to industry.

Claims (1)

[Claims] 1. An ink sheet for thermal transfer printers comprising an ink layer laminated on a sheet-like support via an intermediate layer, in which the intermediate layer is mainly composed of a polyester resin having a glass transition temperature of 50° C. or lower. sheet.