Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
2000-08-11
2003-03-11
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S531000, C430S619000, C396S575000, C396S577000
Reexamination Certificate
active
06531268
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermally developable photothermographic materials and a processing method thereof.
BACKGROUND OF THE INVENTION
Plate-making work has undergone remarkable changes from manual work to electronic stripping. In such a trend, plotters such as an image setter have rapidly come into wide use. A processing machine for conventional silver salt photographic materials is connected on line to such a precision instrument, producing problems that gas or moisture from the processing solution causes the substrate to corrode, resulting in an increase of troubles in expensive instruments.
In conventional silver salt photographic materials, water supply piping is needed for dilution of developer and fixer solutions as well as washing and recovery of processing effluents by dealers requires much time and labor.
A dry processing system without using water is expected from such a background. Among various dry processing systems, thermal processing is most suitable for practical use in terms of manufacturing cost and performance. However, photothermographic materials are sensitive to variations of temperature in the thermal processing section. Maintaining a uniform temperature of the heated drum surface leads to enhanced quality of finished prints, as is disclosed in JP-A 9-297384 and 9-297385 (hereinafter, the term, JP-A refers to an examined and published Japanese Patent Application).
In this technique, however, maintaining a uniform surface temperature of the drum results in non-uniformity in thermal expansion or shrinkage of the photographic material, leading to the distorted photographic material after thermal processing and producing a problem that moiré images tend to occur after thermal processing, which are not suited to the use for plate-making. Specifically, in cases when used in color printing, such a problem is marked.
Thermal plastic resin, specifically, polyethylene terephthalate (also simply denoted as PET) is employed as a support material for photothermographic materials, in terms of low cost and superior film-making property. However, the use of such a support often causes moiré. The glass transition point (Tg) of such a resin is ca. 80° C. and the photothermographic materials are thermally processed usually at a temperature of 100° C. or higher. It is assumed that such moiré is caused by deformation of the photographic material accompanied with shrinkage or elongation of the support. Thus, it is contemplated that deteriorated dimensional stability causes moiré images. To enhance dimensional stability, it has been attempted to improve thermal variation of the ratio of the dimension in the winding direction to that in the width direction (MD/TD) in the course of preparing the support, e.g., as disclosed in JP-A 10-10676 and 10-10677. However, there was not obtained sufficiently satisfactory stability only by such a technique.
SUMMARY OF THE INVENTION
As a result of the inventors' study, it was proved that deformation caused by distortion markedly affects dimensional stability and that the distortion (or deformation) of a support could not be definitely determined by taking the distance between two points corresponding to the perpendicular direction and the parallel direction to the width of the film support. When a support such as PET base is subjected to biaxial stretching in the preparation thereof, for example, the MD direction is cooled and fixed while being stretched. When developed at a temperature higher than the glass transition point (Tg), the support is softened and tends to shrink in the MD direction and elongate in the TD direction. There have been known a trial of reducing the thermal dimensional change in the MD and TD directions, as afore-mentioned. However, superior quality print images cannot be obtained by only such a technique. In cases when deformed in such a manner as shown in
FIG. 1-2
, for example, although no dimensional change occurs in either the MD or the TD direction, the square still is deformed, i.e., distortion is caused. The fact that the dimensional change (MD/TD) is small but the printed images are nevertheless inferior is presumed to be due to occurrence of the distortion described above. The thus produced distortion appears as a phenomenon of so-called moiré, resulting in deterioration of printed images. Thus, the present invention was achieved based on noting that the dimensional stability of the photothermographic material could not be enhanced to sufficiently satisfactory levels without improvements not only in the MD/TD but also in the distortion of the photothermographic material.
It is an object of the present invention to improve distortion of the photothermographic material. It was proved that when the distortion was represented as an angle and the difference in angle between before and after being processed with respect to three corners of the square being within 0.03°, deterioration of printed images was not visually detected.
It was noted that achievement of holding the distortion of the photothermographic material to within 0.03 degree includes an approach of devising installation of heaters or a heating procedure in a thermal processing apparatus, and an approach of improving the photothermographic material itself, whereby improvements of a thermal processing apparatus, a thermal processing method and a photothermographic material were accomplished. It was further proved that in the case of improving the photothermographic material, an improvement in the support largely affected the distortion angle and improvement in an image forming layer or a constituting layer also affected the distortion angle.
When angles at three corners of a 10 cm square, as shown in (a), (b) and (c) of
FIG. 1
are measured before and after being thermally processed, the distortion defined in this invention refers to the maximum of the values at the three corners with respect to the difference in angle between before and after being thermally processed. The distortion can be determined in such a manner that 10 cm squares are measured as many as possible, in the width direction of the photothermographic material (preferably, in the perpendicular direction to the transport direction of the photothermographic material in the thermal processing apparatus, and more preferably in the width direction of the support roll; herein), and judgment is made based on whether the distortion is within 0.03° or not. In the case of 590 mm of the width of a photothermographic material, for example, five pieces of a 10 cm square are cut from the width direction of the unprocessed photothermographic material. With regard to each of these squares, the difference in angle between before and after being thermally processed, at the three corners (i.e., a, b and c) is within 0.03° (and preferably within 0.017°). Since fluctuation is negligible in the transport direction, there is no need of plural sampling in the transport direction. Herein, the width direction refers to the laterally stretching direction in the biaxial stretching of the support and the transport direction refers to the longitudinally stretching direction.
When 10 cm squares are samples from a few locations within the size of a newspaper sheet and the difference in angle was measured, for example, if no variation in the angle occurs (i.e., in the case of being a similar figure), the overall space is said not to be distorted, though the size of the squares may differ. However, such a case almost never occurs. The distortion occurs non-uniformly so that it can be determined by measuring the angle at each of these three points.
FIG. 1-1
illustrates distortion as defined in this invention, in which the variation in angle between before and after being processed may be within 0.03° at the three points a, b and c.
Accordingly, it is an object of the present invention to provide photothermographic materials exhibiting improved dimensional stability and no moiré images after being processed, a processing method and a thermal processing apparatus by the use ther
Bierman, Muserlian and Lucas
Chea Thorl
Konica Corporation
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