Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2000-07-26
2002-06-04
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C101S462000, C101S467000, C430S271100, C430S302000
Reexamination Certificate
active
06397749
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-sensitive lithographic printing plate precursor, which enables direct platemaking without requiring development-processing and can ensure a long press life for offset printing plates. More specifically, the invention relates to a lithographic printing plate precursor in which images can be recorded by scanning exposure based on digital signals, and which can be loaded in a printing machine after recording the images and subjected to printing operations without undergoing the development of the recorded images with a conventional liquid developer.
BACKGROUND OF THE INVENTION
In general, the lithographic plate is constituted of a oleophilic image area to receive ink in the printing step and a hydrophilic non-image area to receive fountain solution applied thereto prior to the inking step. For making such a lithographic plate, a presensitized plate (abbreviated as “PS plate” hereinafter) comprising a water-wettable (i.e., a hydrophilic) support and an ink-receptive photopolymer layer provided thereon has been widely used as a plate material. In a conventional method adopted for making the desired printing plate from such a PS plate, the exposure is generally carried out via an original such as a litho film, and then the non-image area is dissolved and removed with a developer.
The conventional process of making a printing plate by the use of a PS plate requires a step of removing the non-image area by dissolution after exposure. Of the improvements expected in the conventional arts, it is one subject to make such an additional wet processing unnecessary or simple. Lately in particular, the disposal of the liquid waste discharged with the progress of wet processing has been a matter of great concern of the whole industrial world from the viewpoint of considering global environment. Therefore, the request for improvements in this respect has become even stronger.
The method proposed as one of simple platemaking methods answering to that request comprises utilizing an image recording layer which makes it possible to remove the non-image areas of a printing plate precursor during the general printing process, and carrying out development on a printing machine after exposure, thereby obtaining the final printing plate. The system for making a lithographic printing plate according to the aforementioned method is referred to as a “on-press development” system. As a specific example thereof, mention may be made of the method in which the image recording layer soluble in a fountain solution or an ink solvent is employed and the non-image areas is removed mechanically by contact with the impression cylinder or the blanket cylinder installed in a printing machine. However, the on-press development system according to the conventional ultraviolet or visible light-utilized image recording method has a drawback that the image-recording layer remains unfixed even after exposure. Therefore, such a system requires taking a troublesome measure such that the printing plate precursor is stored in a completely shaded or thermostated condition till it is loaded in a printing machine.
On the other hand, it is another recent trend in this field that the technology to digitize image information has been widely spreading, wherein the image information is electronically processed, stored and outputted by the use of a computer. And a variety of new image-output systems which can keep up with such digitization technology have become practical. Under these circumstances, considerable attention has been devoted to the computer-to-plate technology which enables the direct platemaking to be performed by exposure-scanning the printing plate precursor with highly directional radiant rays, such as laser beams, carrying the digitized image information, but not using a litho film. And the production of printing plate precursors suitable for such technology has been one of important technical problems.
Accordingly, the needs for simplifying platemaking operations and performing them in a dry process or without processing have become much stronger than usual in both fields of environmental protection and adaptation to digitization.
Of the platemaking methods using scanning exposure in which the digitization techniques are easy to incorporate, the especially promising method is a platemaking method utilizing as an image-recording means a high-output solid-state laser device, such as a semiconductor laser device or a YAG laser device, because such a device has lately become available at a low price. In the conventional platemaking method, the imagewise exposure of low to medium illumination intensity is given to a photosensitive printing plate precursor, and thereby the photochemical reaction is caused imagewise at the printing plate precursor surface. As a result, the printing plate precursor surface causes an imagewise change in physical property to record the image. On the other hand, in the method of using high energy density exposure, such as exposure with a high-output laser device, the area to be exposed undergoes instant concentrated exposure to the light with a large quantity of energy, resulting in efficient conversion of the energy of exposure light to thermal energy. This thermal energy causes various thermal changes, such as chemical change, phase change and changes in form and structure, and these changes are utilized for recording images. In other words, the image information is input with light energy, such as laser beams, but the images are recorded via the reaction caused by thermal energy. In general such a high energy density exposure-utilized recording system is referred to as heat mode recording, and the conversion of light energy to heat energy is referred to as light-heat conversion.
The platemaking method utilizing a heat mode recording means has a great advantage in that the heat mode sensitive materials are in a substantial sense insensitive to light of ordinary illumination intensity and the fixation is not always essential to the images recorded by high illumination intensity exposure. In other words, in a case where the heat mode sensitive materials are used for recording images, they are safe from indoor light before exposure, and besides, they do not always require the fixation of images after exposure. Therefore, if the image recording layer of the type which can be made either soluble or insoluble by heat mode exposure is used and the on-press development system is adopted into the platemaking step of removing imagewise the exposed image recording layer, it becomes possible for the graphic arts system to have recorded images which are not affected by the development (the removal of non-image areas) performed after the exposed image recording layer is exposed to indoor light for a while.
Thus, it is expected that the utilization of heat mode recording makes it possible to design lithographic printing plate precursors suitable for the on-press development system.
As a desirable method of making a lithographic printing plate on a basis of heat mode recording, there is a proposal on the method, wherein the hydrophobic image recording layer provided on a hydrophilic substrate is subjected to heat mode exposure to change its solubility or dispersibility and, if needed, the non-image areas are removed by wet development.
As examples of a lithographic printing plate precursor usable in the method proposed, JP-B-46-27919 (the term “JP-B” as used herein means an “examined Japanese patent publication”) discloses the printing plate precursors for heat mode recording which each have on a hydrophilic support a recording layer whose solubility is heightened by heat, or the so-called positively working recording layer, more specifically a recording layer having a particular composition in which saccharides or melamine-formaldehyde resin is comprised.
However, each of the recording layers disclosed has insufficient thermal sensitivity, and so the sensitivity thereof is insufficient for heat mode scanning exposure. In addition, it has a pract
Akiyama Keiji
Kita Nobuyuki
Oohashi Hidekazu
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Funk Stephen R.
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