Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
1997-10-01
2003-09-02
Ashton, Rosemary (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S325000, C430S348000, C430S401000, C430S272100, C430S273100, C430S945000
Reexamination Certificate
active
06613496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a dampening-waterless lithographic plate capable of performing printing without use of dampening water, through employment of heat mode recording achieved by means of a laser beam.
2. Description of the Related Art
As conventional printing methods, there are known typographic printing, gravure printing, lithographic offset printing, and the like. In recent years, lithographic offset printing has become popular except for special fields. There are known two types of lithographic offset printing: one is wet printing in which an image pattern composed of hydrophilic areas and oleophilic areas is formed at a plate surface and dampening water is used for printing, and the other is waterless printing in which an image pattern composed of ink-repellent areas and ink-receptive areas is formed at a plate surface and no dampening water is used for printing. The waterless printing has advantages compared to the wet printing, in that skill in printing work is not required since dampening water is not used, and that ink density is constant from the incipient stage of printing and an amount of spoilage is small, which realizes economical printing when the number of copies is relatively small.
Advancement of computer technology has digitized a plate-making process, which is a preparatory process for printing and which had previously been carried out manually, and has enabled recording of print images in the form of digital data. In recent years, a technique for directly forming a plate from this digital data without use of lith-type film (computer-to-plate technique) has been developed. However, in many cases, such techniques are intended to form wet plates, and techniques for forming waterless plates are rarely known.
Japanese Patent Application Publication (JP-B) No. 42-21879 provides the earliest disclosure of a technique for forming a waterless plate through use of laser for writing. According to the publication, an ink-repellent silicone layer which is an outermost layer of a plate is removed imagewise through irradiation with a laser beam, thereby forming imagewise ink-receptive areas and thus forming a plate for a waterless printing. However, this technique has involved problems in that silicone removed by irradiation with a laser beam scatters over the entire plate, causing problems during printing, and in that a portion of the silicone layer, which portion has been irradiated with a laser beam but has not been completely remove, peels off as printing continues, resulting in an increase in the size of ink-receptive areas (dot gain).
Japanese Patent Application Laid-Open (JP-A) No. 50-158405 discloses a method for forming a waterless plate in which a dampening-waterless lithographic blank plate (hereinafter referred to as waterless blank plate) having a silicone rubber surface layer is irradiated with a YAG laser beam (an infrared laser beam) and subsequently a portion, irradiated with a laser beam, of the silicone layer is removed through solvent (naphtha) processing to thereby form a waterless plate.
Further, European Patent No. 573,091 discloses a method for forming a waterless plate in which a plate having a silicone rubber surface layer is irradiated with a YAG laser beam, and subsequently the silicone rubber surface layer is partially rubbed off under dry conditions in which no solvent is used or is partially rubbed off using a solvent which does not swell the silicone rubber, to thereby form a waterless plate.
However, in these methods, silicone rubber in non-image areas may be scratched by rubbing during the removal of silicone rubber from areas exposed to a laser beam. Also, it is difficult to completely remove, from the plate surface, silicone rubber which has been removed from exposed areas. Accordingly, when printing is carried out by use of the waterless plates formed by these methods, drawbacks such as dropout in the image areas, tinting due to the scratching of the non-image areas, and the like arise.
As described above, the methods for forming a waterless plate through the use of a laser have failed to achieve both complete removal of a silicone layer from exposed areas (developing performance) and excellent printing performance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for forming a waterless plate which enables laser recording and provides satisfactory removal of an ink-repellent layer from exposed areas, as well as satisfactory printing performance.
Another object of the present invention is to provide a method for forming a waterless plate, which method does not involve the formation of scratches in non-image areas and thereby prevents tinting in non-image areas during printing, and which method also does not involve the re-adhesion of removed pieces of the ink-repellent layer to the plate surface and thereby prevents dropout in image areas.
The inventors of the present invention carried out extensive studies on a method for forming a waterless plate which can be written with a laser, and as a result, found that the above objects were achieved by a method for forming a dampening-waterless lithographic plate, comprising an irradiation step of irradiating a dampening-waterless lithographic blank plate imagewise with a laser beam, the blank plate comprising a support, a photothermal conversion layer provided on the support for converting laser beam energy to heat, and an ink-repellent layer provided on the photothermal conversion layer, a first rubbing step of rubbing the surface of the ink-repellent layer without use of a liquid so as to remove at least a portion of the ink-repellent layer in areas irradiated with a laser beam and a second rubbing step of rubbing the surface of the partially removed ink-repellent layer through use of a liquid.
As used herein, a dampening-waterless lithographic blank plate (or a waterless blank plate) means a plate in which an image pattern composed of ink-receptive areas and ink-nonreceptive areas is not formed, while a dampening-waterless lithographic plate (or a waterless plate) means a plate in which an image pattern is formed and which can be used for printing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described.
Method for Forming a Waterless Plate:
A waterless blank plate used in the present invention includes a support, a photothermal conversion layer provided on the support for converting laser beam energy to heat, and an ink-repellent layer provided on the photothermal conversion layer.
When the waterless blank plate is irradiated with a laser beam which the photothermal conversion layer can absorb, the photothermal conversion layer absorbs the laser beam energy and sharply increases in temperature and thus undergoes, partially or entirely, a chemical reaction or a physical change, such as combustion, fusion, decomposition, vaporization, or ablation. As a result, adhesion between the support and the ink-repellent layer decreases, so that the ink-repellent layer peels off easily from the support. Since such decrease in adhesion occurs only in the areas irradiated with a laser beam, the ink-repellent layer can be selectively removed.
The laser used in the present invention for exposing a waterless blank plate is not particularly limited so long as it can provide an exposure amount such that the adhesion between an exposed portion of the ink-repellent layer and the support is reduced and the exposed portion of the ink-repellent layer and the support is reduced and the exposed portion can be peeled off from the support, without the exposed portion of the ink-repellent layer being scattered and the unexposed portion of the ink-repellent layer being damaged. Such lasers include gas lasers such as an Ar laser and a carbon dioxide laser, solid lasers such as a YAG laser, and semiconductor lasers. Usually, the present invention requires a laser having an output power of 100 mW or higher. From practical aspects such as maintenance
Fukaya Masahiko
Inno Toshifumi
Yokoya Hiroaki
Ashton Rosemary
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
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