Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
1999-07-30
2001-12-04
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
C347S056000, C347S171000
Reexamination Certificate
active
06326989
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a so-called thermal transfer printer head for transferring ink to a transfer member, such as printing paper, by heating and discharging ink and to a printer.
DESCRIPTION OF THE RELATED ART
In recent years, a color image processed by a personal computer or the like or a color image photographed by an electronic still camera or the like has been printed out for the purpose of appreciating the image. Therefore, there arises a need for a printer with which a full color image exhibiting a high quality can be obtained. In particular, there arises a need for a relatively low-cost and personal use printer oriented to a small-size office, for example, a “small office” or a “home office”.
Color printing methods have been suggested which include a dye-sublimation thermal transfer method (or a dye diffusion thermal transfer method), a melt thermal transfer method, an ink jet method, an electronic photography method, a thermal development silver-salt method and so forth. Among the foregoing methods, the dye diffusion thermal transfer method and the ink jet method are methods with which a high-quality image can easily be output with a relatively simple structure.
The dye diffusion thermal transfer method has a step of applying an ink layer, in which a high-concentration transfer dye is dispersed in appropriate binder resin, to an ink ribbon or a sheet. Then, the ink ribbon or the sheet is brought into intimate contact with so-called thermal transfer paper coated with dye resin for accepting transferred dye. Then, heat is applied to the surface of the ink ribbon or the sheet from a heat sensitive head (a thermal head). Thus, the transfer dye is thermally transferred from the ink ribbon or the sheet to the thermal transfer paper in accordance with the quantity of heat.
The above-mentioned process is repeated for an image signal decomposed into yellow (Y), magenta (M) and cyan (C) which are three primary colors of subtractive color mixture. Thus, a full color image having a continuous gradient can be obtained.
FIG. 25
is a diagram showing the structure of a portion including a thermal head of a printer adapted to the above-mentioned method.
A thermal head
101
is disposed opposite to a platen roller
102
. An ink sheet
103
having a base film
103
b,
on which an ink layer
103
a
is formed, and thermal transfer paper
104
incorporating paper
104
b
coated with a dye resin layer (a dye acceptance layer)
104
a
are moved between the thermal head
101
and the platen roller
102
. During the movement, the ink sheet
103
and the thermal transfer paper
104
are pressed against the thermal head
101
by the rotating platen roller
102
.
In accordance with an image which must be printed, ink contained in the ink layer
103
a
selectively heated by the thermal head
101
is, by heat, dispersed in the dye resin layer
104
a
in the thermal transfer paper
104
brought into contact with the ink layer
103
a
and thus heated. Thus, transfer in the form of a dot pattern is performed.
The dye diffusion thermal transfer method is an excellent technique because the size reduction and maintenance of the printer can easily be performed, immediacy is realized and an image equivalent to a silver salt color photograph can be obtained. The foregoing method, however, suffers from a problem of a large quantity of a waste caused from the disposable ink ribbon or the sheet and an excessively high running cost. Moreover, the thermal transfer paper must be used, causing another problem to arise in that the cost cannot be reduced.
Although the melt thermal transfer method is able to transfer an image to plain paper, use of the ink ribbon or the sheet raises similar problems of the large quantity of waste caused from the disposable ink ribbon and the sheet and the high running cost. A problem exits in that the quality of the printed image is inferior to that obtainable from the silver salt photograph.
Although the thermal development silver salt method is able to form a high quality image, similar problems arise in that the running cost cannot be reduced because dedicated photographic paper and disposable ribbon or sheet are used. Another problem is that the above-mentioned method utilizes a costly apparatus.
As disclosed in, for example Japanese Patent Publication No. 61-59911 and Japanese Patent Publication No. 5-217, the ink jet method is adapted to any one of an electrostatic attraction method, a continuous oscillation generation method (a piezoelectric method) and a thermal method (a bubble jet method). A small droplet of ink is jetted out from a nozzle provided for a printer head to allow the droplet to adhere to printer paper or the like so as to print an image.
Therefore, transfer to plain paper is permitted. In addition, the running cost can be reduced because the ink ribbon is not used. Moreover, waste caused from use of the ink ribbon or the like can substantially be prevented. Recently, the thermal method has widely been used because a color image can easily be printed.
However, the ink jet method encounters a difficulty in realizing a gradient in the density in a pixel because of the principle of the method. Therefore, an image having a high quality equivalent to that of the silver salt photograph obtainable from the dye diffusion thermal transfer method cannot be reproduced in a short time. That is, the conventional ink jet method, with which one droplet of ink forms one pixel, cannot easily realize a gradient in a pixel because of the principle of the method. Therefore, a high-quality image cannot be formed. Although an attempt using the high resolution has been made to realize pseudo gradient by a dither method, a quality of an image equivalent to that obtainable from the dye diffusion thermal transfer method cannot be obtained. What is worse, the transfer rate is excessively reduced.
Recently, an ink jet method has appeared which uses diluted ink to obtain two- or three-step gradient. However, quality of an image equivalent to that obtainable from the silver salt photograph or the dye diffusion thermal transfer method cannot be realized in a case of an image, such as a natural image.
On the other hand, the electrophotographic method, which is able to reduce the running cost and realize a high transfer rate, cannot print an image having a quality equivalent to that obtainable from the silver salt photograph. Moreover, an excessively high cost is required for the apparatus.
That is, any one of the foregoing methods cannot simultaneously satisfy the requirements for realizing a high image quality, a low running cost, a low apparatus cost and a short transfer time.
As a color printing method which is able to satisfy all of the above-mentioned requirements, a so-called dye-vaporization thermal transfer method has been suggested (refer to, for example, Japanese Patent Laid-Open No. 7-89107 and Japanese Patent Laid-Open No. 7-89108).
The foregoing method has the step of heating ink in a transfer portion of a printer head to discharge ink by vaporization or ablation. Thus, ink is allowed to adhere to the surface of a transfer member, such as printing paper, disposed at an opposite position through a gap of about 50 &mgr;m to about 100 &mgr;m so that ink is transferred.
The transfer portion incorporates an ink holding structure having an irregular portion which incorporates a multiplicity of columnar members. Each of the columnar members has a width of, for example, about 2 &mgr;m and a height of, for example, about 6 &mgr;m. The columnar members are stood erect and positioned apart from one another at small intervals of about 2 &mgr;m. A heater is disposed below the ink holding structure. Thus, a vaporizing portion is constituted.
Since the above-mentioned ink holding structure is provided for the transfer portion, the following effects (1) to (4) can be obtained:
(1) The capillary phenomenon allows ink to spontaneously be supplied to the vaporizing portion.
(2) A large surface area enables ink to efficiently be heated.
(3) When the height of each
Hirano Hideki
Kohno Minoru
Feggins K.
Le N.
Sonnenschein Nath & Rosenthal
Sony Corporation
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