Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-04-17
2003-10-14
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S270100, C430S271100, C430S272100, C430S273100, C430S348000, C430S401000
Reexamination Certificate
active
06632589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing process using a heat-sensitive lithographic printing plate and, more particularly, to a printing process using a lithographic printing plate, in which image recording can be conducted by scanning exposure based on a digital signal and image is formed in a lithographic printing original plate by processing with a simple printing machine, so that a printed matter can be stably obtained without using wetting water.
2. Description of the Related Art
In general, a lithographic printing plate is composed of an oleophilic image portion receiving an ink and a hydrophilic non-image portion receiving wetting water in the printing process. As the lithographic printing plate, a photosensitive (PS) plate composed of a hydrophilic support having thereon an oleophilic photosensitive resin layer has been widely used. In the prepress process using the same, generally, exposure is conducted through an original copy, such as a lith film, and a non-image portion is removed by dissolving with a developing solution, whereby a desired printing plate is obtained.
While such an operation is necessary after exposure that the non-image portion is removed by dissolving in the conventional prepress process using the PS plate, it is one of the problems of the conventional technique demanding to be solved that such an additional wet process is omitted (i.e., replaced by a dry process) or is simplified. Particularly, in recent years, since treatment of waste liquid discharged from the wet process has become a matter of concern to the industrial world, demand for improvement of the process in this respect is being increased.
As one simple prepress process addressing the demand, a process has been proposed that an image recording layer in which removal of a non-image portion of a printing plate original can be conducted through an ordinary printing process is used, and the layer is exposed and then developed on a printing machine, so as to obtain a final printing plate. The prepress process of the lithographic printing plate according to such a process is referred to as an on-machine developing process. Examples of the specific process include the use of an image recording layer that is soluble in wetting water or an ink solvent, and a process conducting mechanical removal by contact with an impression cylinder or a blanket cylinder. However, in the case where a conventional image recording material utilizing an ultraviolet ray or a visible ray is subjected to the on-machine development, because an image recording layer is not fixed even after exposure in such an image recording material, such a complicated operation becomes necessary that, for example, the original plate is stored under a completely light shielding condition or a completely-temperature constant condition until it is loaded on the printing machine.
As another trend in this field of art, a digitalization technique is being widely spread in which image information is electronically processed, accumulated and output provided by using a computer, and various novel image output processes are being subjected to practical use addressing the digitalization technique. According to the trend, a computer-to-plate technique receives an attention in which technique an original plate is exposed by scanning with a radiant ray of high astringency like laser beam carrying digitalized image information, so as to produce a printing plate in a direct manner without using a lith film. Accordingly, it becomes an important technical problem to obtain an original printing plate adapted to such a purpose.
Therefore, demands for simplification, use of a dry process and omission of the process for the prepress operation are being greatly increased from both the standpoints of environment and digitalization.
As a production process of a printing plate of scanning exposure type, which can be easily incorporated in the digitalization technique, a prepress process utilizing a solid laser of high output power, such as a semiconductor laser or a YAG laser, as an image recording means is receiving hopeful attention since the laser is available at low cost. In the conventional prepress process, image recording is conducted in such a manner that imagewise exposure of low or intermediate illuminance is applied to a photosensitive original plate to effect imagewise physical change on the surface of the original plate by a photochemical reaction. In a process using exposure of a high power density by a high output power laser, however, an exposed area is intensively irradiated with a large amount of light energy within a momentary exposure period, so as to effectively convert the light energy to heat energy, and thermal change, such as chemical change, phase change and change in shape and structure, is caused by the heat, so that the change is utilized for image recording. In other words, while the image information is input by light energy, such as laser light, the image recording is effected by a reaction caused by the heat energy. In general, such a recording mode utilizing the heat generation caused by the high power density exposure is referred to as heat mode recording, and the conversion of light energy to heat energy is referred to as photothermal conversion.
A remarkable advantage of the prepress process using the heat mode recording means is that exposure is not effected with an ordinary illuminance level, such as interior illumination, and a fixing operation is not necessary for an image recorded by the high illuminance exposure. In other words, when a heat mode sensitive material is utilized for image recording, it is not exposed by interior illumination, and an image does not have to be fixed after exposure. Therefore, for example, when a prepress process, in which an image recording layer which is made insolubilized or solubilized by the heat mode exposure is used and the exposed image recording layer is imagewise removed to form a printing plate, is conducted by the on-machine developing process, a printing system can be established in which the development (removal of the non-image portion) can be effected so that the image is not adversely affected even when the image is exposed to interior environmental illumination for a certain period after the imagewise exposure.
Therefore, it is expected that a lithographic printing plate original plate that is suitable for the on-machine developing process can be realized by utilizing the heat mode recording.
As one of preferred production processes for a lithographic printing plate based on the heat mode recording, such a process has been proposed that a hydrophobic image recording layer is provided on a hydrophilic substrate, which is subjected to imagewise heat mode exposure to change the solubility and the dispersibility of the hydrophobic layer, followed by removing, depending on necessity, the non-image portion by wet development.
Examples of the original plate of this type include a process for obtaining a printing plate in JP-B-46-27919, in which an original plate is subjected to heat mode recording, the original plate being composed of a hydrophilic support having thereon a recording layer exhibiting the so-called positive effect (where the solubility is increased by heat) a recording layer specifically having a particular composition containing a saccharide and a melamine formaldehyde resin.
However, since the recording layer thus disclosed has insufficient heat sensitivity, the sensitivity to the heat mode scanning exposure is insufficient. Furthermore, it is a practical problem that the discrimination between hydrophobicity and hydrophilicity before and after exposure, i.e., the change in solubility, is small. When the discrimination is poor, it is practically difficult to conduct prepress by the on-machine developing process.
WO98/40212 discloses a lithographic printing plate original that can be subjected to prepress without development, composed of a hydrophilic layer containing a transition metal oxide colloid fo
Akiyama Keiji
Inno Toshifumi
Tachikawa Hiromichi
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbaras
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