Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-03-09
2002-02-05
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S303000, C101S457000, C101S456000, C101S467000
Reexamination Certificate
active
06344306
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a printing plate precursor which allows printing without using dampening water, especially a directly imageable waterless planographic printing plate precursor which can be directly processed by a laser beam.
The processing method of producing an offset printing plate directly from an original without using a process film, so-called direct processing begins to be used also in the fields of general offset printing and gravure printing, as well as in the light printing industry, because of such features as simplicity requiring a little skill, speediness in obtaining a printing plate in a short time, and rationality of selectability adapted to desired quality and cost from a variety of systems.
Especially recently, in response to the rapid progress of output systems such as prepress systems, image setters and laser printers, new types of various planographic printing plate materials are being developed.
The processing methods for these planographic printing plates include methods of irradiating with a laser beam, methods of writing by a thermal head, methods of partially applying a voltage by a pin electrode, methods of forming an ink repellent layer or an ink acceptable layer by ink jet, etc.
Among them, the methods of using a laser beam are more excellent than the other methods in resolution and processing speed, and are diverse.
Especially usefulness of the heat mode type methods is being reviewed recently because of its advantage of handling in a daylight room and the sudden progress of semiconductor lasers used as the light source.
For example, Japanese Patent Laid-Open (Kokai) No. Hei6-199064, U.S. Pat. Nos. 5,339,737, 5,353,705, EP 0580393, etc. describe directly imageable waterless planographic printing plate precursors using a laser beam as the light source, and processing methods thereof.
The heat sensitive layer of any of these heat destructive planographic printing plate precursors uses mainly carbon black as a laser beam absorbing compound and nitrocellulose as a thermally decomposable compound. The laser beam absorbed by carbon black is converted into heat energy, and the heat destroys the heat sensitive layer. Finally, the destroyed area is removed by development, to simultaneously remove the silicone rubber layer on the surface, and an ink acceptable layer remains.
However, such a printing plate has a problem that since the heat sensitive layer is destroyed to form an image, the ditch cells of the image area become deep, to lower the ink acceptability at very small half tone dots, shortening the ink mileage. Furthermore, since the heat sensitive layer has a crosslinked structure formed to allow easier thermal destruction, the printing plate is poor in printing durability disadvantageously. If the heat sensitive layer is softened, the sensitively declines extremely. So, it is difficult to soften the heat sensitive layer.
Furthermore, the printing plate also has a problem that since the sensitivity is low, a laser beam with a high intensity must be used for destroying the heat sensitive layer.
Japanese Patent Laid-Open (Kokai) No. Hei9-239942 proposes a printing plate of peel-apart type with a laser beam sensitive layer containing a substance capable of generating an acid and a macromolecular compound capable of being decomposed by the action of the acid, but it requires two steps of laser beam irradiation and heating and has a problem peculiar to the peel-apart type that the reproducibility of fine half tone dots is poor.
Japanese Patent Laid-Open (Kokai) No. Hei6-55723, EP 0573091 and U.S. Pat. No. 5,378,580 also have another problem that a large-scale exposure apparatus is required since they use an Nd-YAG laser as the light source.
In addition to the above mentioned planographic printing plates using a laser beam, a thermal bonding type directly imageable waterless planographic printing plate can be considered as a directly imageable waterless planographic printing plate.
In this type of printing plate, the silicone rubber layer remains selectively at the laser beam irradiated area, to function as a non-image area. As for the mechanism, the laser beam irradiation improves the bonding strength between the silicone rubber layer and the laser beam sensitive layer, or the bonding strength between the laser beam sensitive layer and the underlying substrate anyway, and as a result, the silicone rubber layer or the silicone rubber layer and the laser beam sensitive layer are removed selectively at the non-irradiated area by subsequent treatment.
The printing plates proposed in Japanese Patent Laid-Open (Kokai) No. Hei9-120157 and U.S. Pat. No. 5,786,125 use the acid generated by laser beam irradiation as a catalyst to promote the reaction of the photosensitive layer, for reproducing the image. However, to promote the reaction after acid generation, a step of heat treatment is necessary. Furthermore, since the time till heat treatment after acid generation affects the image reproducibility, the image reproducibility becomes unstable disadvantageously.
The printing plate proposed in Japanese Patent Laid-Open (Kokai) No. Hei9-300837 has a foamable layer, and the foamable layer is foamed by irradiation with a laser beam, to give expanding strain to the silicone rubber layer laminated on the foamable layer. Subsequently the base film is removed to form a deep etched plate. However, foaming so much as to give expanding strain to the silicone rubber layer requires enormous energy, and the formation of a deep etched plate by removing the base film causes the silicone rubber layer to remain partially, and a good plate cannot be obtained at low energy.
SUMMARY OF THE INVENTION
This invention improves the disadvantages of the prior art, and provides a direct imageable waterless planographic printing plate having good image reproducibility without requiring any complicated process after laser beam irradiation.
To solve the above problems, this invention is constituted as follows.
A directly imageable waterless planographic printing plate precursor, in which at least an ink acceptable layer and a silicone rubber layer are laminated in this order on a substrate, wherein when the printing plate precursor is measured by TG-GC/MS in a helium current at a heating rate of 10° C./min, a decomposition product is generated in a temperature range of 100° C. to 200° C. by 0.001 g/m
2
to 1 g/m
2
per plate area.
A directly imageable waterless planographic printing plate precursor, in which at least an ink acceptable layer and a silicone rubber layer are laminated in this order on a substrate, wherein a decomposition product is produced between the ink acceptable layer and the silicone rubber layer by exposure to a laser beam.
A directly imageable waterless planographic printing plate precursor, in which at least an ink acceptable layer and a silicone rubber layer are laminated in this order on a substrate, wherein when the surface of the ink acceptable layer is measured by ESCA after exposure to a laser beam, the increase of C—O component is observed compared to the value measured before exposure to a laser beam.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, “directly imageable” means that an image is formed on the printing plate directly from a recording head without using a negative or positive film at the time of exposure. This invention is described below in detail.
If the directly imageable waterless planographic printing plate precursor of this invention is irradiated with a laser beam, a decomposition product is generated on the surface of the ink acceptable layer. If the decomposition product is precipitated between the ink acceptable layer and the silicone rubber layer, or if the outermost surface of the ink acceptable layer in contact with the silicone rubber layer is foamed by a generated decomposition product, the bonding strength between the silicone rubber layer and the ink acceptable layer is weakened. So, it can be considered that if a physical rubbing force is given from the surface of the printing plate
Fujiyoshi Kunitaka
Goto Kazuki
Nagase Kimikazu
Ohbayashi Gentaro
Hamilton Cynthia
Morrison & Foerster / LLP
Toray Industries Inc.
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