Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-10-26
2004-02-03
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S272100, C430S273100, C430S434000, C430S494000, C430S944000, C430S945000, C101S463100, C101S467000
Reexamination Certificate
active
06686127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plate-making method for producing a waterless lithographic printing plate by processing a high-sensitivity lithographic printing plate precursor capable of being processed to form an image thereon through heat-mode recording with laser rays. The waterless lithographic printing plate means that it does not require dampening water for use in printing systems for producing prints.
2. Description of the Related Art
In conventional printing systems that require dampening water, the delicate balance of dampening water and ink is difficult to control, ink is often emulsified, and dampening water is often polluted with ink. Therefore, the systems involve some serious problems in that the ink concentration fluctuates, the background area in the printed matters is stained, and paper loss increases. Contrary to such systems, waterless printing systems in which the lithographic printing plates used do not require dampening water have many advantages.
On the other hand, the recent progress in pre-press systems and other output systems such as image setters and laser printers is remarkable. With that, novel plate-making methods for producing printing plates have been proposed. In these, the images to be printed are converted into digital data, and formed on printing plates in a mode of computer-to-plate or computer-to-cylinder plate-making technique. For such printing systems, printing materials of a novel type are desired and are being developed.
Some laser writing systems for forming waterless lithographic printing plates have been proposed, for example, as in JP-B 21879/1967; JP-A 158405/1975, 94008/1993, 55723/1994, 186750/1994, 314934/1995; U.S. Pat. No. 5,353,705; WO-9401280; and JP-A 91257/1999. These describe the possibility of waterless printing. Concretely, in these, a printing plate precursor is fabricated by forming an ink-repellent silicone rubber layer on a layer that contains a laser ray-absorbing agent such as carbon black and a binder or a thin metal layer, or that is, on such a layer having the ability to convert light into heat (hereinafter referred to as a photo-thermal conversion layer), and this is exposed to laser rays to thereby remove the silicone rubber layer in the exposed area to form an ink-receiving region (image region), while the non-exposed, silicone rubber-remaining region forms an ink-repellent region (non-image region). The thus-completed printing plate enables waterless printing.
Of those, the waterless lithographic printing plate precursor, for which a coating liquid prepared by dissolving or dispersing a photo-thermal converting agent such as carbon black in other components is used for forming the photo-thermal conversion layer, is inexpensive. In this, in addition, since the photo-thermal conversion layer in the laser-exposed area is ablated for image formation, the vapor generated through exposure to laser pushes up the silicone rubber layer in the laser-exposed area to facilitate the removal of the silicone rubber layer in the laser-exposed area in the subsequent step of development (that is, the developability of the precursor is good). This is another advantage of the waterless lithographic printing plate precursor of that type.
The waterless lithographic printing plate precursor of this type requires good adhesiveness between the silicone rubber layer and the photo-thermal conversion layer and between the photo-thermal conversion layer and the support in order that they are well handled in the process of producing the precursor, that they are durable to laser exposure and development in the process of processing into a printing plate, and that the resulting printing plate has good printing durability. The adhesiveness between them is greatly influenced especially by the composition of the photo-thermal conversion layer. In general, when a polyurethane is added to the photo-thermal conversion layer, the adhesiveness of the layer to the silicone rubber layer is improved. In this case, however, if a plastic film of, for example, polyethylene terephthalate is used for the support, the adhesiveness of the support to the photo-thermal conversion layer is often poor; and if so, the photo-thermal conversion layer will peel from the support. This is one problem with this case.
In general, providing an undercoat layer between the support and the photo-thermal conversion layer is effective for solving the problem of poor adhesiveness between them. For the undercoat layer for that purpose, for example, a photosensitive polymer layer is formed on a support and cured thereon by exposing it to light, before the photosensitive layer is formed on the support, as in JP-A 22903/1985; an epoxy resin is thermo-set as in JP-A 50760/1987; or gelatin is cured as in JP-A 133153/1988.
However, the adhesiveness between the polyurethane-containing photo-thermal conversion layer and the support could not be improved sufficiently, depending on the composition of the undercoat layer.
Through our previous studies, we, the present inventors have already found that, when a coating liquid that contains at least a water-soluble or water-dispersible polymer in a solvent of water is coated and dried (this is hereinafter referred to as aqueous coating) on a support to form an undercoat layer thereon, then the adhesiveness between the polyurethane-containing photo-thermal conversion layer and the support is improved. However, in the waterless lithographic printing plate precursor which has the undercoat layer formed in such an aqueous coating method and of which the photo-thermal conversion layer in the laser-exposed area is ablated for image formation, there occurs a problem in that the ink adhesion to the laser-exposed image area of the printing plate is not good and the image density of the printed matters could not increase.
For the waterless lithographic printing plate precursor which is processed for image formation thereon through ablation of the laser-exposed photo-thermal conversion layer, no one knows an effective method of ensuring good adhesiveness between the support and the photo-thermal conversion layer and ensuring good ink adhesion to the image area of the printing plate.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a plate-making method for producing a waterless lithographic printing plate having the advantage of good ink adhesion thereto, which is applicable to a precursor of the printing plate having an undercoat layer formed by aqueous coating with a water-soluble or water-dispersible polymer and having a polyurethane-containing photo-thermal conversion layer formed on the undercoat layer, and therefore having improved interlayer adhesiveness of the constitutive layers.
Through our studies, we, the present inventors have found that the failure in ink adhesion to the image area of a waterless lithographic printing plate is caused by the existence of the undercoat layer formed by aqueous coating with a water-soluble or water-dispersible polymer and exposed out in the image area though exposure to laser rays to remove the overlying silicone rubber layer. Based on this finding, we have further studied how to prevent the undercoat layer from being exposed out in the image area of the printing plate, and have at last found that it can be attained by a specific constitution described below. On the basis of this finding, we have completed the present invention.
Specifically, the plate-making method for producing a waterless lithographic printing plate of the invention comprises (I) an exposing step of imagewise exposure of the precursor with a laser with a such condition that a portion of a laser-exposed area in a photo-thermal conversion layer in the precursor remains in the photo-thermal conversion layer of the finished printing plate; and (II) a developing step of removing a silicone rubber layer in the laser-exposed area to form an image on the printing plate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is described in detail here
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
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