JPS62148293A - Receiving sheet for thermal transfer color printer - Google Patents

Abstract

PURPOSE:To enable reproducibility of dot positions, reproducibility of halftone dots and reproducibility of hues and densities in color superposition, by setting the elongation of the titled sheet under a tensile force and the permanent set of the sheet after removing the tensile force to be not more than predetermined values, respectively. CONSTITUTION:A receiving sheet is so conditioned that the elongation under a tension of 1kg/cm is not more than 0.5% and the permanent set upon removal of the force is not more than 0.2%. If the permanent set is large, the size of a paper differs for different colors, and the positions of dots are deviated, resulting in a different intermediate color reprodcution. Where the reversible elongation is large whereas the permanent set is zero, halftone dots are reproduced at fixed positions for each color although images are distorted due to elongation of the sheet in the vicinity of a head, so that reproducibility of tones can be secured. Thus, the reversible elongation is permitted to a considerable extent. However, the tension on the sheet is not exactly reproduced for each color, and accordingly, the reversible elongation is set to be not more than 0.5% on an empirical basis. The receiving sheet is preferably a biaxially stretched polyolefin sheet comprising an inorganic pigment or a synthetic paper comprising a coated layer on a base material consisting of the polyolefin sheet and has a thickness of not less than 90mum.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a receiving sheet for a thermal transfer color printer. More specifically, it relates to a receiving sheet used in a thermal transfer printer, which uses a thermal head to sequentially transfer images of each color from a multi-colored heat-melting ink sheet to a receiving sheet and superimposes them to form a color image. It is. We provide paper (sheets) that have high dimensional accuracy to maintain color overlay accuracy and can print high-resolution characters and images with good color reproducibility by transferring molten ink sharply. This makes it possible to create a receptor sheet that can be used in a full-color, area-gradation thermal transfer type printer.

(Conventional technology) Recently, the need for color printers has been increasing.

In particular, thermal transfer color printers are attracting attention because they can print on plain paper and produce clear color images at high speed with a relatively compact device.

Among these, printers using the fusion type thermal transfer method include film,
An ink sheet consisting of a base material such as thin paper and a heat-melting ink layer is used. This ink sheet is overlaid with a receiving sheet made of plain paper, such as regular high-quality paper, and heat from the thermal head transfers the heat-melting ink to the receiving paper only in the necessary areas to which the image signal has been applied, forming a recorded image. do. Since pigments can be used as the main component of the colorant in the ink, permanent preservation of prints is possible. However, with such thermal transfer methods, even if it is a plain paper recording method, it is not possible to print images of the same high quality on any type of paper, and the sharpness of the image depends on the smoothness of the receiving paper. Various technologies have been published to provide printing suitability to each printer according to its intended use.

For example, in the case of thermal transfer printer paper, it is known that high-quality paper is smoothed using a super calendar to obtain good printing, and normal high-quality paper has a Beck smoothness of about 10 to 50 seconds. However, it is known that when the time is 100 seconds or more, a particularly clear transferred image can be obtained.

In order to reproduce a full-color image using this type of method, gradation expression is necessary, and normal thermal melting color printers use the area gradation method to express density by combining dots of each color such as halftone dots. express. For accurate color development of intermediate tones, the reproducibility of the dot position and color density of each color on the receiving sheet is important.

However, even if high-quality paper with a Bekk smoothness of 10 or higher is used, colors printed in multiple colors such as yellow, cyan, and magenta, that is, red, blue, violet,
The uniformity of green hue and density is not necessarily good, making it difficult to obtain high-resolution images and characters. Furthermore, improvements in the performance of thermal heads have made it possible to achieve high resolutions of 16 dots/7 mm and 32 dots/mm from a hardware perspective, but the dimensional accuracy of current receiving paper and the uniformity of heat-melting ink sheets are insufficient. These features cannot be fully utilized.

In order to improve the transfer characteristics of thermal transfer printers, a proposal has been made (Japanese Unexamined Patent Publication No. 182487/1987) to obtain a transferred image with even shading by providing an oil-absorbing pigment on a paper base material. Most of the pigments used in coated paper for printing are listed, but even if the reproducibility of single-color halftone dots during thermal transfer is achieved as in this proposal, the expression of intermediate colors that requires overlapping of multiple colors is difficult. In other words, when expressing the halftones of a full-color image, obtaining stable density from low density to high density requires poor microscopic reproducibility of the positions between halftone dots (single color dots) and existing heat-melting ink sheets. This proposal was unsatisfactory because it still had two drawbacks: the uneven accuracy seen in .

(Problems to be Solved by the Invention) There is a demand for small-sized paper for Chinese character printers as the mainstream of thermal transfer systems, especially small-sized non-impact printers. By realizing paper with high resolution and color reproducibility,
It becomes possible to record full-color images using halftones, enabling a wide variety of applications.

SUMMARY OF THE INVENTION An object of the present invention is to provide a receiving sheet having highly accurate color image recording characteristics for a thermal transfer color printer using a multicolor sequential heat-melting ink sheet.

That is, an object of the present invention is to provide a receiving sheet for a full-color printer that is stable from low density to high density, has no density unevenness in halftone dots, and is capable of obtaining clear recorded images with good reproducibility even in intermediate colors. With the goal.

(Means and actions to solve the problem) In view of the current situation, the present inventors have conducted extensive research to improve the above-mentioned drawbacks, and as a result, the elongation due to static tension of the receiving sheet has been reduced to below a certain level. , in a normal color printer, the tension is 1 kg/
By keeping the elongation at crrL to 0.5% or less, and especially the irreversible elongation that remains after the tension is reduced to zero again to 0.2% or less, the reproducibility of dot positions, halftone dots, and color overlap can be improved. It has been found that the reproducibility of hue and density can be improved, and the uniformity of hue and density of full-color images based on the area gradation method can be improved.

This is because when printing an image using the thermal transfer method, the ink sheet and receiving paper are under pressure due to the nip between the platen roll and the thermal head, and the letter and the ink sheet receive different local tensions. This is thought to be because 3 to 4 colors pass through the printing mechanism repeatedly.Also, the tension caused by K (paper feeding inside the printer) acts on the receiving sheet as a tensile force, reducing the reproducibility of dot positions and causing intermediate colors to This is thought to be a factor in the inability to reproduce the density and tone of the image.

For this reason, it can be said that the reason why it is difficult to reproduce full-color tones with the conventional melting type thermal transfer method compared to an inkjet method where the head position of each color is relatively fixed has been found.

It is known that paper made of cellulose fibers deforms irreversibly in response to relatively small stress, and this is also different from synthetic paper made of thermoplastic film.

Although it is currently possible to quantitatively analyze the stresses and reversible and irreversible strains on the receiving paper in a thermal transfer printer mechanism, the Since the response varies depending on the paper and the environment, it has no practical meaning.

The present inventors used a static tension of 1 kg as model parameters for stress and irreversible and reversible deformation within the printer.
We adopted the elongation at /CrrL and the residual elongation when the static tension was completely zero, and since the results matched the experimental halftone reproducibility, we found that we could use this as an index. Ta. Therefore, although these elongation conditions cannot be said to be absolute, they are in good agreement among the design conditions of current general thermal transfer printers, and it is expected that the stress conditions for paper will differ greatly in the future. Even with the advent of printers, the basic idea remains the same.

The tension on the paper in a thermal transfer printer is not strictly static, but it is slow enough in today's printers that print less than a few pages per minute, and rather than specifying a specific speed, it is It can be generalized to the relationship between tension and elongation under so-called static measurement conditions, which can be measured in a range where elongation is no longer dependent on velocity.

A tension of 1 kg/cnl is approximately 20 kg in the vertical direction of A4 paper, which is commonly used, and can be regarded as the maximum tension that will cause the paper to stick with a normal nip. In particular, it is desirable that the irreversible elongation be zero, but in reality, if it is about 0.2% or less, the total length of A4 paper will be 600 μm or less, and the accuracy of the printer can be fully guaranteed.

If the irreversible elongation is large, the dots will be shifted due to the fact that the size of the paper is different for each color, and as a result, intermediate colors will be reproduced differently. Even if the reversible elongation is large, if the irreversible elongation is completely zero, the image will be distorted due to the elongation near the head, but the halftone dots of each color will be reproduced at a fixed position, and color reproducibility will be guaranteed. . For this reason, reversible stretch is quite acceptable, but since the tension is not exactly reproduced for each color, experimentally it has been found that if it exceeds 0.5%, it will be difficult to reproduce precise images. .

The breaking strength due to tensile stress also needs to have a certain natural yield strength, which is higher than normal high-quality paper, for example, 3kl? /
cIn is preferred.

The thermal transfer color printer receiving sheet of the present invention has a tension of 1 to 9 /cm no matter what material is used.
It is acceptable as long as it satisfies the conditions that the elongation when adding the inner row tension deer is 0.5% or less, and the irreversible elongation after removing the inner row tension deer is 0.2% or less.

However, a biaxially oriented polyolefin sheet containing an inorganic pigment or a so-called synthetic paper whose surface is coated using this sheet as a base material is preferred. In the case of such synthetic paper, the thickness is 9
It is preferable that the thickness is 0 μm or more.

For general high-quality paper and coated paper, these conditions can be achieved by increasing the basis weight and thickness.

However, sheets based on thermoplastic synthetic resins achieve this goal because they have a small irreversible elongation curve. Particularly preferred is a biaxially oriented polyolefin sheet having a thickness of 90 μm or more and containing an inorganic pigment, or a so-called synthetic paper car whose surface is coated using this sheet as a base material.

Biaxially oriented polyolefin sheets containing these inorganic pigments or sheets with surface coatings on these sheets are known as synthetic papers and are used for high-grade printing papers, etc.
It is not yet known to uniformly improve the transfer density of heat-melting ink.1. Furthermore, it is not known that the reproducibility of the focus position during multicolor overlapping thermal melt transfer can be improved.

(Example) Next, the thermal transfer color printer paper of the present invention will be described with reference to Examples.

Example 1 When a static tensile force of 1 kg/Cr/L is applied, the elongation is 0.60%, the irreversible elongation is 0.08%, and the tensile strength at break is 3! ? /(m or more paper (synthetic paper YUPO FPG1
50 Oji Yuka Synthetic Paper (150 μTn) was used as a receiving sheet.

The tensile test was conducted using a Tensilon tensile tester (manufactured by Toyo Baldwin) with a length of 100 mm.

The test was carried out by pulling a sample with a width of 10 mm at a constant speed of 10 m1/min.

Example 2 A sheet of synthetic paper Yubo FPG110 (manufactured by Tamago Yuka Synthetic Paper Co., Ltd.) was coated with 209/rii'' paint consisting of 100 parts of calcium carbonate and 20 parts of SBR latex as a pigment, and then dried. A receiving paper sheet was manufactured by smoothing a cotton roll with a super calender using an elastic roll at a linear pressure of 30 kg/cm. Ta.

Static tensile force 1k of the same sheet measured in the same manner as Example 1
The elongation when g/CrrL is added is 0.45%, the irreversible elongation is 0.16%, and the tensile strength at break is 6kg/
It was more than cm.

Example 3 A paint consisting of 100 parts of kaolin and 18 parts of SBR latex was coated at 25 g/m on high-quality paper (OKFlo 128 parts m'') and smoothed under the same conditions as in Example 2. The Bekk smoothness (Ouken method) of the coated surface of the sheet was 8000 seconds.

Static tensile force 1k of the same sheet measured in the same manner as Example 1
The elongation when adding g/CIrL is 0.28%, the irreversible elongation is 0.10%, and the tensile strength at break is 6 kg/
It was more than cm.

Comparative example: Elongation is 0 when static tensile deer 1 kg/cIrL is applied.
．． 57%, irreversible elongation of 0.28%, and tensile strength at break of 1.7 kip/c7rL (commercially available word processing paper (70,!i'/m"))
was used to make a receiving sheet. The tensile test was conducted in the same manner as in Example 1.

The following evaluations were performed on the receiving sheets of each Example and Comparative Example using a thermal transfer printer. In other words, a thermal transfer printer uses a three-color surface-printing ink sheet, writes an image of each color with a thermal line head while feeding the ink sheet and receiving paper at a constant speed, and then reverses the image of each color to its original position. I sent it in and layered the colors. The evaluation results are summarized in Table 1.

Excellent ones were marked as [phase], average ones as ○, slightly inferior ones as △, and poor ones as ×.

Table 1 Example 1 ◎ ◎ (O) ◎Example 2 ◎ ◎ ◎ ○Example 6 0 0
△ ○ Comparative example ○ ○ △ × (Effect of the invention) Judging from the above examples and comparative examples, the receiving paper for thermal transfer color printers of the present invention has good reproducibility of intermediate color tone and density, and can produce precise images. It is a promising technology for use in full-color printers that can reproduce images, and it will greatly contribute to industry by making it possible to create a compact full-color thermal transfer printer system that overcomes the drawbacks of conventional technology.

Claims (1)

[Claims] 1. The elongation is 0 when a static tensile force of 1 kg/cm is applied.
．． 5% or less, and irreversible elongation after removing the inner tensile force is 0.2% or less. 2. The receiving sheet for a thermal transfer color printer according to claim 1, which is made of a biaxially oriented polypropylene sheet containing an inorganic pigment and having a thickness of 90 μm or more and optionally surface-coated.