Incremental printing of symbolic information – Thermal marking apparatus or processes
Reexamination Certificate
2001-09-13
2003-04-29
Hilten, John S. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Reexamination Certificate
active
06556230
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heat meltable ink image-receiving sheet used in an image forming method wherein a thermal transfer sheet with a heat meltable ink on a substrate is brought into contact with an ink-receiving layer of the image-receiving sheet so as to face the ink side of the thermal transfer sheet, and the ink is melted with heat from a printing head of a thermal transfer printer from the back side of the thermal transfer sheet and penetrated into pores of the ink-receiving layer. The present invention also relates to an image forming method using the image-receiving sheet.
In forming a high-definition image using a thermal transfer printer, it was known to form a color image wherein using an image-receiving sheet with a porous ink-receiving layer and to perform a melting transfer from thermal transfer sheets in yellow, magenta and cyan (black etc. if required) by penetrating heat meltable inks in a molten state into pores of the porous ink-receiving layer. See, ITE (The Institute of Image Information and Television Engineers) Technical Report, Vol. 17, No. 27 (May, 1993), pages 19-24.
Furthermore, as methods for forming a porous layer, the following methods are known:
a wet coagulation method, wherein a sheet coated with a solution of a resin in dimethylformamide is dipped into water and the dimethylformamide is replaced with water to form a porous layer (JP, B, 49-25430 and JP, A, 5-155163);
a mechanical agitation foaming method, wherein after a resin is foamed by mechanical agitation and the foamed resin is applied onto a sheet to form a porous layer (JP, A, 7-32753 and JP, A, 7-309074);
a pigment addition method, wherein a porous layer of a resin is formed by utilizing the oil absorbing property of a porous pigment incorporated in the resin (JP, A, 3-98333 and Japanese Patent No. 2,535,371);
a solvent dissolving method or a dry method, wherein a resin is dissolved into a mixture of a good solvent having a lower boiling point and a poor solvent having a higher boiling point, the resulting solution is applied onto a sheet and then dried to form a porous layer having a porous structure composed of pores resulting from the poor solvent with a slower rate of drying (JP, A, 4-82790, and JP, A, 6-166283);
a foaming agent method, wherein a porous layer of a resin is formed by incorporating into the resin a foaming agent that generates a gas upon heating, and then foaming the resin (JP, A, 2-3396); and
a soluble particles-dissolving-off method, wherein a resin containing soluble particles is formed into a film and the soluble particles contained in the film are off by washing to form a porous layer (JP, A, 6-171250).
However, in all the above-described porous layer forming methods, it is difficult to control the state of a porous structure, which is recognized to be the most important factor in a thermal transfer involving penetrating ink into pores of the porous ink-receiving layer. As a result, when the number of minute pores in the receiving layer is small, not enough penetration is achieved, and when the pore size is large, an adverse effect results upon the transfer of minute dots.
Among the above-described porous layer forming methods, the wet coagulation method is the one that can relatively easily form a large number of minute pores in the ink-receiving layer. In the wet coagulation method, various types of methods have been examined. Particularly, methods of incorporating a filler component into a resin component to improve a film strength are reported in JP, B, 49-25430 (a wet coagulation method using a mixture of a styrene resin, a plasticizer and a filler), and JP, B, 5-18332 (a wet coagulation method using a mixture of a polyester resin, a plasticizer and a filler). However, in the porous layers formed by these methods, the pore size in the porous layer is large and the porous structure is in a coarse state. Consequently, in thermal transfer printing, it is difficult to form dots of uniform shape because of an insufficient ink penetration. Especially in the case of printing a full-color image, a transfer failure of a second color or subsequent colors to be superimposed on the first color occurs, and hence it is difficult to form a high-definition image.
The present inventors have evaluated various porous sheets prepared according to known technologies as porous image-receiving sheets. The characteristics of porous sheets prepared by the mechanical agitation foaming method and the wet coagulation method, which are considered to be extensively improved in the formation of a high-quality image as compared to conventional image-receiving sheets, are summed as follows:
In the case of an image-receiving sheet having a porous ink-receiving layer formed by the mechanical agitation foaming method, a water-based coating can be used and an image-receiving sheet can be produced by the drying process only after the coating process. Therefore, it is possible to use a paper sheet as a substrate. This is advantageous because a wide selection of substrates for the image-receiving sheet can be used. On the other hand, the obtained porous ink-receiving layer has a wide variation of open pore diameter and a high proportion of pores with large diameter. As a result, there are the following disadvantages: It is difficult to obtain sharp dots. Grainy appearance of small dots is conspicuous in a highlight region. A maximum density (saturated density) of a high level is difficult to be obtained. The gloss of the image obtained is poor.
On the other hand, in the case of an image-receiving sheet having a porous ink-receiving layer formed by the wet coagulation method, pure paper cannot be used as a substrate because of its manufacturing process and high cost. From the viewpoint of formation of a high-definition image, however, the porous ink-receiving layer has a narrow variation of open pore diameter and a low proportion of pores with large diameter as compared with the porous ink-receiving sheet prepared by the mechanical agitation foaming method, resulting in sharply improved performances. However, in order to obtain an image quality comparable to or superior to the image quality achieved by a sublimation transfer method, it must be improved still more. Furthermore, the present inventors have evaluated the superimposing performance of a second color and subsequent colors by using an image-receiving sheet having a porous ink-receiving layer formed by the wet coagulation method disclosed in JP, A, 62-197183 in the image forming method disclosed in JP, A, 6-286181. The results show a defect in that a lot of ink flows and dot lacks are observed, especially in a region from intermediate tone to shadow tone in the resulting image. In order to obtain a high-definition color image, not only the performance of a first color but also the superimposing performance of a second color or subsequent colors is important. However, in the prior art, there are no disclosures mentioning this, as far as the present inventors know.
The water vapor permeability of an ink image-receiving sheet is described in Japanese Patent No. 2,966,901. However, this patent mentions only that the writing property with writing devices, such as a pencil and various pens, is improved by limiting the thickness of the porous ink-receiving layer to a range of 3 to 50 &mgr;m and a water vapor permeability to a range of 1,000 to 9,000 g/(m
2
·hour). Moreover, the patent does not mention the production of an image-receiving sheet, which is used in an image formation method using a heat-meltable ink, the transfer of which is performed by melting the heat-meltable ink with heat provided from a printer head in thermal transfer to penetrate the ink into a porous structure of the receiving sheet, and which is superior in dot shape reproducibility and gradation reproducibility including variable printing performance, and color clearness, especially, dot reproducibility of second color and subsequent color in a color image, which is the object of the present invention.
Furthermore, although the pat
Cai Zheng Long
Fukui Takuto
Shinozaki Fumiaki
Yamane Toshiyuki
Feggins K.
Fish & Neave
Fujicopian Co. Ltd.
Hilten John S.
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