JP2574039B2 - Dye thermal transfer image receiving sheet - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a sheet for receiving and recording a thermally transferred dye image. More specifically, the present invention relates to a full-color printer for thermally transferring an image forming dye such as a sublimable dye, and a dye capable of faithfully receiving a dye image and printing a high-resolution halftone image with high fidelity. The present invention relates to a thermal transfer image receiving sheet.

[Problems to be solved by conventional technologies and inventions]

Recently, a relatively compact color printer capable of printing a clear color image and particularly a dye sublimation type thermal transfer type printer has attracted attention. In such a printer, multicolor printing of yellow, magenta, and cyan dyes is performed on an image receiving sheet, and countless hues and continuous density can be reproduced in each dot to obtain a uniform image.

A dye-sublimation-type thermal transfer printer uses an image receiving sheet having a dye-dyeable image receiving layer on an ink sheet composed of a base film and a sublimation dye layer. The image is formed by superimposing the sublimation dyes in contact with the layer surfaces and transferring the sublimation dye onto the receiving sheet at a required density by heat supplied from a thermal head according to an electric signal corresponding to the image.

Even in the printer of the thermal fusion transfer method, by using a special ink sheet, a predetermined amount of ink is transferred from the ink layer on the ink sheet to the image It is possible to print a full-color image of gradation.

It is known to use paper containing cellulose pulp as a main component, preferably paper having its surface smoothed, as the sheet-like substrate of these image receiving sheets.
However, in order to obtain good printing in continuous tone on the image receiving sheet, if a paper containing wood pulp as a main component is used as a base, even if it has improved its smoothness, The uniformity of the received image was still poor.

In particular, depending on the applied energy of the thermal head,
In a sublimable dye thermal transfer printer that controls the amount of ink transferred, the uniformity of the ink receiving ability of the image receiving layer of the image receiving sheet with the image forming material (dye) has a significant effect on image reproducibility. In the conventional image receiving sheet, density unevenness in a solid portion, unstable transfer of dots, and the like were observed, and a favorable halftone image could not be obtained.

In order to improve these problems, a synthetic paper composed of a multi-layer film including a uniaxially stretched film layer and a biaxially stretched film layer composed mainly of a polyolefin containing an inorganic pigment, for example, polypropylene, is used. Attempts have been made to use it as an image receiving sheet substrate and to provide an image receiving layer thereon.

In the case of an image receiving sheet for a dye sublimation type thermal transfer printer, a dye image receiving layer mainly composed of a polyester resin or the like is coated on a sheet substrate made of the synthetic paper. Such an image receiving sheet is uniform in thickness, flexible, and has advantages such as a lower thermal conductivity than paper made of cellulose pulp due to a void structure peculiar to synthetic paper. For this reason, there is an advantage that a uniform and high-density image can be obtained.

However, when a multi-layer structure film composed of a uniaxially or biaxially stretched film containing polypropylene as a main component is used as a sheet substrate, when the obtained image receiving sheet is recorded using a thermal head, the multi-layer structure film becomes The applied stretching stress is relaxed by heat, whereby the sheet substrate locally undergoes thermal shrinkage, and as a result,
Curls and wrinkles are generated on the image receiving sheet, which causes troubles in running the sheet in the printer, and has a drawback that the commercial value of the obtained print is significantly reduced. In particular, in a printer of a sublimation dye thermal transfer system, this problem is serious because the amount of heat required for transfer is large.

In order to eliminate defects such as image non-uniformity without using the heat-deformable synthetic paper as a sheet base, paper made of cellulose pulp is used as a sheet-like base, and an organic A method of providing a polymer barrier layer (JP-A-62-21590) is disclosed. However, in order to improve the image by this method, if the surface of the image receiving sheet is not highly smooth, there is a problem that the uniformity of the transfer of the ink / colorant becomes poor, and the unevenness appears as density.

In particular, there is a report (USP 4,774,224) that it is important to control the surface roughness of the organic polymer barrier layer of the substrate for the uniformity of the glossiness of the image formed on the image receiving sheet. In practice, it is known that the thermal energy at the time of printing affects the glossiness of a transferred image depending on the glass transition point and the softening temperature of the material forming the image receiving layer. Therefore, the direct correlation between the surface roughness of the organic polymer barrier layer and the uniformity of the glossiness of the image is poor, and if the surface roughness is too small, the surface roughness of the image receiving layer formed on the organic polymer barrier layer is too small. This may cause poor adhesion or generation of streaks in the image receiving layer coating operation.

[Means and actions to solve the problem]

The present inventors have high rigidity of the sheet substrate itself,
The present inventors have found that the adhesion between the image receiving layer and the head is reduced, and that the uniformity of the transferred image is reduced, and the present invention has been completed by solving this problem.

The dye thermal transfer image-receiving sheet of the present invention is a sheet-like substrate containing cellulose pulp as a main component, and a sheet substrate formed on at least one surface thereof and comprising a lower coating layer containing a thermoplastic resin as a main component. An image-receiving layer formed on the lower coating layer, and receiving a thermal transfer image-forming dye, and dyeing, the Bekk smoothness of the surface of the lower coating layer of the sheet substrate is 100 seconds or more, and TAPPI, T
The stiffness in the printing direction of the sheet substrate measured by a method prescribed in EST method, T543, pm84 is 700 mgf or less.

In the thermal transfer image receiving sheet of the embodiment shown in FIG. 1, a sheet-like substrate (paper) 1 is formed and bound on the surface thereof, contains a thermoplastic resin as a main component, and preferably contains a white pigment. A sheet substrate 5 composed of a lower coating layer 2 is formed, and an image receiving layer 3 mainly composed of, for example, a polyester resin or the like capable of dyeing and fixing a dye is formed on the lower coating layer 2. Are bound.

The thermal transfer image receiving sheet of the embodiment shown in FIG. 2 has the same configuration as that shown in FIG. 1, except that a thermoplastic resin is mainly provided on the back surface of the sheet-like substrate 1. A back surface coating layer 4 containing as a component is formed, and the sheet base material, the lower coating layer 2 and the back surface coating layer 4 constitute a sheet substrate.

The thickness of the image receiving sheet of the present invention is appropriately set according to its use, that is, the use such as color printing, computer graphics, labels, and cards, but it is generally preferably 60 to 250 μm.

In the thermal transfer image receiving sheet of the present invention, what is important for realizing the uniformity of the thermal transfer image is that the smoothness and uniformity of the lower coating layer are excellent, and the rigidity of the sheet base material is sufficient for the entire thermal transfer image receiving sheet. To determine the stiffness of the sheet, the stiffness of the sheet substrate must be set so as not to adversely affect the adhesion to the thermal head.

In the above-described image receiving sheet, the smoothness of the surface of the lower coating layer basically does not directly determine the image quality of the transferred image, but in order to improve the smoothness of the image receiving layer and the surface property. Is required that the smoothness of the surface of the lower coating layer is higher than a certain level, and depending on the stiffness of the sheet substrate, the adhesion to the thermal head is insufficient even if the smoothness of the image receiving layer is high. Therefore, it is necessary that the surface of the lower coating layer has a smoothness of a certain level or more and the stiffness of the sheet substrate is controlled to a certain value or less.

The smoothness used in the present invention is defined in JIS P8119. The smoothness can be measured by the method described therein. The stiffness used in the present invention is defined in TAPPI, TEST method, T543, pm84, and can be measured by the method described herein.

Although there is no particular limitation on the type and grade of paper used as the sheet-like substrate, high-quality paper is generally used. The thickness and the like of the sheet substrate are appropriately set depending on the use of the obtained image receiving sheet.

A sheet-like substrate containing cellulose pulp as a main component,
Type of raw pulp, pulp processing method, type of additive chemical,
Depending on the papermaking conditions, post-treatment conditions, etc., the surface and the opposite surface can be smoothed to a certain level, thereby improving the uniformity of the transferred image.

One of the factors that affect the flatness and surface properties of paper used as a sheet-like substrate is the formation of paper. That is, it is necessary to improve the formation, which is the most necessary condition for paper. For this purpose, it is necessary to optimize the pulp concentration, the type and amount of additives, the pH, and the like so as not to agglomerate the fibers in the pulp slurry during papermaking. Further, it is preferable that it does not contain a rigid long fiber or dust that impairs the surface properties of the paper.

It is known that the stiffness of the paper used as the sheet-like substrate in the present invention is generally proportional to the cube of the elastic modulus and the thickness and inversely proportional to the basis weight, but improves the adhesion with the thermal head. As a method of effectively reducing the rigidity of the paper to reduce the paper weight, it is effective to reduce the basis weight of the paper and reduce the thickness of the paper. Further, since the elastic modulus of paper is proportional to the square of its density, it is also an effective means to reduce the density of paper.

The sheet-like substrate used in the present invention is generally 40 to 240 g.
/ m ² preferably having a basis weight of 1
More preferably, it is 70 g / m ² or less.

A lower coating layer containing a thermoplastic resin as a main component and having a surface smoothness of 100 seconds or more is formed on the sheet-like substrate surface. Furthermore, the stiffness of such a sheet substrate is
It is 700 mgf or less.

Generally, when the surface smoothness of the lower coating layer is less than 100 seconds, it is not directly related to the quality of the image received on the image receiving layer, but affects the coatability of the image receiving layer, As a result, the quality of the image received by the image receiving layer may be deteriorated. In addition, the rigidity of the sheet
If it is larger than 0 mgf, the image quality, particularly the uniformity of the image density, is further reduced. Further, even if the surface smoothness of the lower coating layer is 100 seconds or more, the rigidity of the sheet substrate is 700 mgf.
If it is higher, the uniformity of the image density decreases.

As the thermoplastic resin forming the lower coating layer, it is preferable to use a polyolefin-based resin, particularly, polyethylene, polypropylene, polybutene, polypentene,
In addition, it is preferable to be selected from a copolymer or a mixture thereof. Particularly, polyethylene and polypropylene are preferable.

It is preferable that a pigment, particularly a white pigment, is dispersed and contained in a matrix made of a thermoplastic resin in the lower coating layer.

Examples of white pigments include titanium dioxide, zinc sulfide, zinc oxide, calcium sulfate, calcium sulfite, barium sulfate, clay, calcined clay, talc, kaolin, calcium carbonate, silica, and calcium silicate.
It can be freely selected from those conventionally known for blending and kneading with a polyolefin resin.

Depending on the type of white pigment used, it is possible to control the degree of flatness of the surface of the lower coating layer obtained by the melt extrusion laminator to some extent.

Generally, the content of the white pigment in the resin layer is preferably 20% by weight or less. When the content is higher than 20% by weight, the strength of the lower coating layer mainly composed of the laminated polyolefin resin is insufficient, and the film may be cracked,
In some cases, inconveniences such as insufficient adhesion between the sheet-like substrate and the lower coating layer and easy peeling may occur.

The mixture of the polyolefin resin and the white pigment can be coated on the surface of the sheet-like substrate by a melt-extruding laminator, but the resulting lower coating layer has good flatness and good adhesion to the sheet-like substrate. Is preferable.

The lower coating layer on the surface side is formed on the sheet-like substrate, preferably by using a melt extrusion laminator as described above, and the surface thereof has high flatness and high whiteness when containing a white pigment. I have. Such an undercoating layer naturally makes the surface of the image receiving layer highly flat, and thus has excellent high definition,
It becomes possible to receive and fix an image with high sensitivity and high gradation.

Generally undercoat layer preferably has a weight of 5 to 40 g / m ^2.

A resin capable of receiving and fixing the thermal transfer image-forming dye on the lower coating layer as a main component;
An image receiving layer having a thickness of 20 μm, preferably 5 to 10 μm, is formed.

As the resin forming the image receiving layer, a polyester resin, for example, a saturated polyester resin (trademark: Byron 20)
0, manufactured by Toyobo Co., Ltd.), and a polycarbonate resin. If necessary, additives may be added to the dye-receiving resin, for example, a silicone resin (trade name: SH-3746, manufactured by Toray Silicone Co., Ltd.), a modified silicone oil (trade name: SF841)
6, Toray Silicone Co., Ltd.).

By providing a coating layer of a thermoplastic resin also on the back surface of the sheet substrate, curling of the image receiving sheet can be prevented, and water resistance and weather resistance can be imparted.

In the present invention, the thermoplastic resin used for the back coating layer can be selected from the same ones used for the lower coating layer, and may also contain the white pigment used for the lower coating layer.

In addition, when the back surface coating layer is formed into a mat, printing and writing are facilitated. Matting, for example, when extruding and laminating a polyolefin resin on the back of the sheet-like substrate,
The matted irregularities can be embossed by pressing a cooling roll having a surface matted in a desired pattern in advance on the surface of the back surface coating layer.

Generally backcoating layer preferably has a weight of 5 to 40 g / m ^2.

〔Example〕

 The present invention is further described by the following examples.

Example 1 Fine paper having a basis weight of 150 g / m ² and a thickness of 148 μm was used as a sheet-like substrate. On the surface (felt surface) of this substrate, 10
35 g / polyethylene resin layer containing titanium dioxide by weight
The lower coating layer was formed by melt extrusion lamination with an application amount of m ² . Furthermore, 30 g / m ² of polyethylene resin is
The composition was melt-extruded and laminated at a coating amount of 1 to form a back coating layer. The surface of the lower coating layer of the sheet substrate thus obtained was subjected to a corona discharge treatment. The Beck smoothness of the lower coating layer of the sheet substrate was 140,000 seconds or more (measurement range or more), and the rigidity of the sheet substrate was 660 mgf.

Paint-1 having the following composition was coated on this lower coating layer at a solid content of 10 g / m ^{2 by} a doctor blade method and dried to form an image receiving layer to produce a sublimable dye image receiving sheet. .

Composition ingredients of the paint -1 weight saturated polyester resin 100 (trademark: Byron 200, Toyobo Co., Ltd.) Silicone resin 5 Trademark: SH-3746, manufactured by Toray Silicone Co.) Toluene 500 Methyl ethyl ketone 100 Performance Testing of the thickness of 6μm polyester Contact each of the yellow, magenta and cyan ink sheets provided with an ink layer containing a sublimable dye together with a binder on a film with an image receiving sheet and heat them stepwise by a thermal head of a commercially available thermal transfer printer. , A predetermined image was thermally transferred to an image receiving sheet, and an image of a halftone single color and a superimposed image of each color was printed. The image transferred onto the image receiving sheet was visually evaluated for image clarity, dot uniformity, solid portion uniformity, and curl due to heat.

 The test results are evaluated in five stages and are shown in Table 1.

Example 2 The same operation as in Example 1 was performed. However, after a lower coating layer having an application amount of 20 g / m ² was provided on the high quality paper, a polyethylene resin layer having an application amount of 18 g / m ² was melt-extruded and laminated on the opposite surface (wire surface) of the high quality paper. The surface smoothness of the lower coating layer is
It was 70,000 seconds, and the rigidity of the sheet substrate was 610 mgf.

 Table 1 shows the test results.

Example 3 The same operation as in Example 1 was performed. However, coated paper having a basis weight of 64 g / m ² and a thickness of 57 μm was used as a sheet-like substrate. A lower coating layer having a coating amount of 30 g / m ² was formed on the surface (felt surface) of the sheet-like substrate in the same manner as in Example 1, and the coating amount was coated on the opposite surface (wire surface) of the sheet-like substrate. A back surface coating layer of 28 g / m ² was formed. An image receiving layer was formed on the lower coating layer by a die coating method in the same manner as in Example 1. The Beck smoothness of the lower coating layer surface was 140,000 seconds or more (measurement range or more), and the rigidity of the sheet substrate was 90 mgf.

 Table 1 shows the test results.

Example 4 The same operation as in Example 1 was performed. However, at the time of melt extrusion lamination for forming the lower coating layer, by using an emboss roll and cooling, the Beck smoothness of the lower coating layer surface was set to 3,000 seconds. Further, the rigidity of the sheet substrate was 660 mgf.

 Table 1 shows the test results.

Comparative Example 1 The same operation as in Example 1 was performed. However, high quality paper having a basis weight of 180 g / m ² and a thickness of 237 μm was used as the sheet-like substrate. The Beck smoothness of the surface of the lower coating layer was 140,000 seconds or more (measurement range or more), but the stiffness of the sheet substrate was 1,550 mgf.

 Table 1 shows the test results.

Comparative Example 2 The same operation as in Example 1 was performed. However, the high-quality paper described in Comparative Example 1 was used as the sheet-like substrate, and the coating amount of the lower coating layer was 8 g / m ² and the coating amount of the back coating layer was 7 g / m ² . The Beck smoothness of the surface of the lower coating layer of the obtained sheet substrate was 76 seconds, and the stiffness of the sheet substrate was 1,550 mgf.

 Table 1 shows the test results.

Comparative Example 3 The same operation as in Example 1 was performed. However, the same lower coating layer and back coating layer as in Example 3 were formed to prepare a receiving sheet substrate. The Beck smoothness of the lower coating layer surface of the sheet substrate was 30 seconds, and the stiffness of the sheet substrate was 550 mgf.

 Table 1 shows the test results.

[Effects of the Invention] The dye thermal transfer image receiving sheet of the present invention is excellent in image gradation, low density, and high density uniformity, has less thermal curl after printing, and has a clear image. It is excellent in all of the bulk, the whiteness of the background, and the natural feeling, and enables a high quality thermal transfer printer which has solved the drawbacks of the conventional method.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are cross-sectional explanatory views each showing an example of the configuration of a material thermal transfer image receiving sheet of the present invention. DESCRIPTION OF SYMBOLS 1 ... Sheet base, 2 ... Lower coating layer, 3 ... Image receiving layer, 4 ... Back coating layer, 5 ... Sheet base material.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kenji Yasuda 1-10-6 Shinonome, Koto-ku, Tokyo Oji Paper Co., Ltd. Product Research Institute (56) References JP-A-62-21590 (JP, A) 61-144394 (JP, A)

Claims (1)

(57) [Claims] 1. A sheet substrate comprising a sheet-like substrate containing cellulose pulp as a main component, a lower coating layer formed on at least one surface thereof, and containing a thermoplastic resin as a main component, and the lower coating layer And an image receiving layer for receiving and dyeing a thermal transfer image forming dye, and having a Beck smoothness of 100% on the surface of the lower coating layer of the sheet substrate.
A dye thermal transfer image receiving sheet, wherein the stiffness in the printing direction of the sheet substrate is 700 mgf or less as measured by a method specified in TAPPI, TEST method, T543, pm84.