JPH04101890A - Manufacture of ink sheet for thermal transfer printer - Google Patents

Abstract

PURPOSE:To reduce a dispersing time and dispersing energy by preparing a low viscosity ink layer coating having good coating properties and to enhance the transfer density and uniformity of an image by dispersing waxes of an ink layer using lanolin fatty acid ester. CONSTITUTION:At the time of the manufacturing of an ink sheet for thermal transfer printer formed by providing an ink layer based on fatty acid amide, waxes, a filler and a dye on a sheet-like support through an intermediate layer, the waxes of the ink layer are dispersed using lanolin fatty acid ester, lanolin fatty acid ester is obtained by reacting hard lanolin fatty acid containing a large amount of 20 or more C fatty acids among 9-34C fatty acids obtained by purifying wool grease collected from wool with polyhydric alcohol, for example, pentaerythritol.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an ink sheet for thermal transfer printers, and more specifically, a method for dispersing waxes in an ink layer provided on a sheet-like substrate coated with an intermediate layer. Regarding this, the waxes in the ink layer paint can be uniformly dispersed, and as a result, the ink layer paint has a lower viscosity and improved fluidity, making it possible to prepare it uniformly, and the resulting ink layer is uniform. Therefore, the transferred image is sharp and can be used for multiple printing with thermal transfer type kanji printers, color printers, etc., which can uniformly print high-resolution characters and images, and the ink sheet has excellent density and gradation printing performance. It relates to a manufacturing method.

[Prior art and problems 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.

BACKGROUND ART Melting-type thermal transfer printers used in color copiers, word processors, facsimile machines, etc. use thermal transfer ink sheets consisting of a base material such as film or thin paper and a heat-melting 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, forming 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 have the characteristic that they can print on any receiving paper, but the fusion type thermal transfer method expresses a binary density per dot depending on the presence or absence of ink, and for full-color images with intermediate density such as photographs, it is difficult to use dither. Since a halftone image is formed by a signal processing method such as a method that combines a plurality of dots to obtain density gradation, there is a drawback that the resolution decreases and the quality of the image is impaired.

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 a dyeable resin such as polyester resin are overlapped, and printing is performed in the same manner as in the melting type thermal transfer method.

The resulting image is created by continuously controlling the energy applied from the thermal head to change the amount of sublimation dye transferred at the molecular level, resulting in a high-quality, full-color image with continuously changing density, similar to a photograph. I can do it.

However, the sublimation transfer method requires a special receiving paper whose surface is treated with a dyeable resin such as polyester resin, and since the coloring agent is a sublimable dye, the resulting image may change color or fade due to light or heat. There are drawbacks such as:

In order to compensate for these drawbacks, a melt density gradation type thermal transfer system has been developed. This method uses an ink sheet that contains heat-melting ink by dissolving 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 sublimation transfer method, by applying heat energy corresponding to the image signal from the thermal head, the amount of molten ink transferred from the microporous material is continuously controlled according to the amount of heat, thereby increasing the density of the transferred image. can be changed continuously.

Therefore, like the sublimation thermal transfer recording method, continuous gradation can be obtained for each dot, so the resolution of the image does not decrease, and a high-resolution, full-color image comparable to high-end printing can be obtained.

As a technique for obtaining such a melt density gradation type thermal transfer ink sheet, for example, Japanese Patent Application Laid-Open No. 60-54894 is known. Printing using this method transfers ink containing a dye and a vehicle such as a fatty acid amide, so printing is possible even on high-quality paper, and the use of dyes with high fastness makes the image long-lasting. .

However, the waxes used in the ink layer of melt density gradation type thermal transfer ink sheets, which are mainly composed of fatty acid amides, waxes, fillers, and dyes, are chemically stable and insoluble in water and general solvents. It is difficult to disperse uniformly due to its softness.

Therefore, it was difficult to prepare a uniform, low-viscosity ink coating, the transfer was uneven, and the maximum transfer density was insufficient compared to binary thermal transfer images and general printed matter.

[Problem that the invention seeks to solve]

In order to overcome the drawbacks of the prior art, the present invention creates an ink layer paint that has low viscosity and is easy to coat by dispersing the waxes used in the ink layer of the ink sheet in a solvent with a specific material. An object of the present invention is to provide a method for producing a melt density gradation type thermal transfer ink sheet that can significantly reduce the time and energy for dispersion, improve the transferred image density, and improve the uniformity of the transferred image. It is said that

[Means to solve the problem]

As a result of extensive research to improve the above-mentioned drawbacks, the inventors of the present invention formed an ink layer containing fatty acid amide, waxes, fillers, and dyes as main components on a sheet-like support via an intermediate layer. In the method for producing an ink sheet for a thermal transfer printer, the wax of the ink layer is dispersed with lanolin fatty acid ester.

The lanolin fatty acid ester in which the waxes contained in the ink layer of the present invention are dispersed in the ink coating is one of the fatty acids with 9 to 34 carbon atoms obtained by refining wool grease obtained from wool. , is an ester obtained by reacting a hard part lanolin fatty acid containing a large amount of fatty acids having 20 or more carbon atoms with a polyhydric alcohol, such as pentaerythritol.

Examples of the sheet-like support of the present invention include films of 3 to 30 μm thick such as polyester, polycarbonate, diacetylcellulose, nylon, and polyimide, or 7 to 30 μm thick films such as capacitor paper, thin paper, electrically insulating paper, parchment paper, etc.
Preferably, 30 μm paper is used. If the thickness of the film serving as the sheet-like support is less than 3 μm or the thickness of the paper is less than 7 μm, the strength will be insufficient and practicality will be a problem.

Further, if the thickness of the film or the paper is thicker than 30 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 surface that is in direct contact with the thermal head on the opposite side of the ink layer is heated to a temperature above the melting point of the film for a short period of time, so a so-called stick is formed in which the thermal head and the film are thermally fused. This phenomenon occurs. 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 a thickness of about 1 μm.

The polyester resin used as the intermediate layer of the present invention is a polycondensation product of at least one type of diol component and at least one type of dicarboxylic acid component, and has a glass transition temperature of 50°C or lower and has low crystallinity or has no crystallinity. Preferable is a linear saturated polyester resin that is soluble in regular, general-purpose organic solvents such as toluene, benzene, xylene, methanol, ethanol, acetone, MEK, ethyl acetate, THF, etc., and has excellent adhesive properties.

Examples of diol components constituting such polyester resins include ethylene oxide adducts of bisphenol A, which is an aromatic diol, and aliphatic glycols other than aromatic diols such as propylene glycol, 1,3-
Propanediol, 1,4-butanediol, 1,5-
Bentanediol, 1.6-hexanediol, diethylene glycol, dipropylene glycol, and 1.4
- It is also possible to use cycloaliphatic glycols such as cyclohexane dimetatool.

As the dicarboxylic acid component, aromatic dicarboxylic acids such as terephthalic acid, orthophthalic acid, and 2.6-naphthalene dicarboxylic acid are used, and dicarboxylic acids other than aromatic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedioic acid. , aliphatic dicarboxylic acids such as dimer acid, and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid.

If a polyester resin having a glass transition temperature of 50° C. or higher is used for the intermediate layer, the adhesion between the ink layer and the ink sheet base material will be insufficient, causing peeling of the ink layer during transfer.

The thickness of the intermediate layer is preferably in the range of 1 to 10 μm. When the thickness is less than 1 μm, the effect of adhering the ink layer to the base material becomes weak, causing the ink layer to peel off. 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 ingredient 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 ink sheets in roll form, it is necessary to use a wax with a melting point of 40°C or higher to prevent blocking, and to maintain fluidity that does not affect transfer, the melting point must be 200°C or lower. is desirable.

The fatty acid amide of the present invention is a component for dissolving the dye, and at the same time must not impair fluidity upon heating. Examples of the fatty acid Tamide 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 the filler of 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.

When the fatty acid amide, wax, filler, and dye of the ink layer coating of the present invention are dispersed in a solvent such as acetone or MEK using a paint shaker, the fatty acid amide and dye are easily dissolved, and the filler is also dissolved. Can be easily dispersed. However, it is extremely difficult to disperse waxes alone.

As a result of intensive research, the inventors of the present invention have prepared a low-viscosity wax dispersion liquid by using a small amount of lanolin fatty acid ester as a dispersant for dispersing waxes, thereby dissolving other components in the ink layer. By mixing the ink and the dispersion liquid, a uniform and low viscosity ink layer paint was created.

The blending ratio of lanolin fatty acid ester to waxes is preferably 0.1 to 5% by weight.

If it is less than 0.1% by weight, the dispersion effect will be insufficient, and if it is more than 5% by weight, the effect will be saturated, and the viscosity of lanolin fatty acid ester in the molten state will be higher than that of waxes, resulting in a lower transfer density. This may lead to a decrease in

Dissolution and dispersion are not limited to paint conditioners; depending on the ink layer being manufactured and the dispersion equipment that can be used, uniform dispersion can be achieved using general dispersion equipment such as ball mills, sand mills, basket mills, dispersers, etc. be.

In the present invention, dispersion can be performed well, and as a secondary effect, it has become possible to significantly shorten dispersion time and save energy compared to the prior art.

The thicker the ink layer, the more ink layers are 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, resulting in insufficient density gradation reproducibility, and There are drawbacks such as increased peeling.

Furthermore, when the ink layer is thin, the gradation becomes better, but there is a drawback that the transfer density becomes lower because there is less ink layer to be transferred. In the present invention, the thickness of the ink layer is 5
~15 μm is preferred.

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, which is used in general coated paper.
Uses one or more types of pigments such as light or heavy calcium carbonate, clay, calcium silicate, alumina, titanium dioxide, etc., water-soluble adhesives such as PVA, starch, casein, and acrylic-styrene copolymer, styrene-butadiene. It is constructed using one or more types of emulsions such as copolymers.

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

If the coating amount is less than 5g/m2, ink absorption will be poor,
Transfer density decreases and image fixability becomes insufficient. Furthermore, if the coating amount is more than 40 g/m2, cracking of the ink-receiving layer and peeling of the ink-receiving layer due to a decrease in adhesive strength are likely to occur, and it is also uneconomical.

As the receiving paper provided with such an ink-receiving layer, commercially available pigment-coated synthetic papers such as PFK and 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 coated with a bar to a thickness of 3 μm.

Intermediate layer> Byron 30SS (manufactured by Toyobo: Tg = 6°C, molecular weight = 2
0000 to 25000, concentration 15%, MEK/) luene = 2/8) After coating the intermediate layer, the solvent was dried, and 7 μm of paint 1, which had been dispersed with paint conditioner for 30 minutes, was applied thereon using a bar.

<Paint 1: Composition of ink layer> Paint A.

acetone 5th part Paint B.

1 part of 40 (Japanese pear type) was separately dispersed in Carbon Black Kayaset BL^CK 149 for 30 minutes and mixed to obtain an ink layer coating.

The coated ink sheet was dried at 100° C. for 5 minutes.

The 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 millisecond step, and a duration of 1 to 20 milliseconds.

The evaluation results are shown in Table 1.

The maximum density was 8.5V, and the printed area was measured for 20 milliseconds using a Macbeth densitometer.

The gradation and the state of peeling of the ink layer were visually evaluated.

Example 2 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, Table 1: Evaluation of ink sheets for thermal transfer printers was used as the lanolin fatty acid ester in the paint.

Comparative Example 1 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, lanolin fatty acid ester was used in the paint instead.

Comparative Example 2 A thermal transfer ink sheet was obtained in the same manner as in Example 1. However, the lanolin fatty acid ester was not used in the paint, and a paint in which paraffin 135 was dispersed only in acetone was used.

〔Effect of the invention〕

The present invention has a melt density gradation system that enables thermal transfer printing with excellent image quality, which has good image storage stability, image resolution, and density gradation, and improves image uniformity and low transfer density, which are disadvantages of conventional methods. This paper relates to a method for producing thermal transfer ink sheets, and will greatly contribute to the industrial world.

Claims (1)

[Claims] In a method for producing an ink sheet for a thermal transfer printer, in which an ink layer containing fatty acid amide, waxes, fillers, and dyes as main components is provided on a sheet-like support via an intermediate layer,
A method for producing an ink sheet for a thermal transfer printer, comprising dispersing wax in the ink layer with lanolin fatty acid ester.