Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-03-24
2001-09-04
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C101S463100, C430S944000, C430S945000, C430S272100
Reexamination Certificate
active
06284433
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing a directly imageable waterless planographic printing plate directly using a laser beam, particularly a method of producing a directly imageable waterless planographic printing plate which allows printing without using dampening water.
A process of producing an offset printing plate directly from an original without using a plate making film, the so-called directly imageable process (also called direct process) begins to be used also in the fields of general offset printing and gravure printing, as well as in the small-scale printing industry, because of such features as simplicity requiring 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 plates for the direct process 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.
The planographic printing plates using a laser beam include the photon mode type based on photo reaction and the heat mode type in which thermal reaction is caused by light-heat conversion. The heat mode type can be advantageously handled in a daylight room, and its usefulness is being reviewed recently because of the sudden progress of semiconductor lasers used as the light sources.
For producing a planographic printing plate in the heat mode, particularly a waterless planographic printing plate not requiring the use of dampening water for printing, the following methods have been proposed, but they involve various problems.
For example, U.S. Pat. Nos. 5,339,737, 5,353,705, EP 0580393, etc. propose methods for forming a printing plate based on the ablation of the heat sensitive layer. However, these methods have such problems that a high laser energy is necessary for ablating the heat sensitive layer, that a byproduct such as gas is produced by ablation, being likely to adversely affect the optical system, that the residue of ablation must be removed, and that it is difficult to reproduce very small halftone dots.
For producing a printing plate using a developer, the following methods are proposed.
U.S. Pat. No. 5,378,580 proposes to rub the plate surface for development using a solvent (IPA) not swelling the ink repellent layer after laser beam irradiation. However, the use of IPA is unpreferable in view of environmental sanitation.
U.S. Pat. No. 5,849,464 proposes to give a liquid with a surface tension of 25 to 50 dyn/cm
3
(250 to 500 &mgr;N/cm
2
) for rubbing after laser beam irradiation. However, since rubbing is effected with the ink repellent layer swollen, the ink repellent layer is likely to be flawed disadvantageously.
Japanese Patent Laid-Open (Kokai) No. Heill-198335, etc. propose on the removal of the ink repellent layer at the laser beam irradiated area in the presence of, for example, water or water containing a surfactant after laser beam irradiation. However, these methods have such problems that though halftone dots larger than a certain size can be reproduced, very small halftone dots can be reproduced only unstably, and that the ink acceptance of halftone dots is low.
Problems of the conventional waterless planographic printing plates as described above include that it is difficult to reproduce very small halftone dots and that the grooves formed by laser irradiation into which ink is to be accepted, hereinafter called the image ditch cells are deepened.
If the image ditch cells are deepened, the ink is built up to make the prints felt like being coarse. Furthermore, in rotary offset printing, a longer oven must be used, or the printing speed must be lowered to evaporate off the ink solvent. As described above, deep image ditch cells give many disadvantages in the printing process.
SUMMARY OF THE INVENTION
The problem of the present invention is to improve the disadvantages of the prior art by providing a method of producing a directly imageable planographic printing plate with the heat sensitive layer left, having high sensitivity and good image reproducibility.
To overcome the disadvantages of the prior art, this invention provides a directly imageable planographic printing plate with good image reproducibility.
(1) A method of producing a directly imageable waterless planographic printing plate, which has at least a heat sensitive layer and an ink repellent layer in this order on a substrate, comprising a first step of imagewisely irradiating a precursor of the printing plate with a laser beam, a second step of pre-treating the precursor by a pre-treatment liquid containing a glycol compound and/or a glycol ether compound represented by the following general formula (I), or a pre-treatment liquid containing an amine compound by 0.1 to 30 wt % based on the weight of the entire pre-treatment liquid, and a third step of removing the ink repellent layer at the laser beam irradiated area, in this order, to have the heat sensitive layer left at least partially still after completion of the above steps.
R
2
O(—CHR
1
—CH
2
O)
n
—R
3
(I)
(where R
1
denotes a hydrogen atom or alkyl group with 1 to 5 carbon atoms; R
2
and R
3
denote, respectively independently, a hydrogen atom or alkyl group with 1 to 15 carbon atoms; and n denotes an integer of 1 to 12.)
(2) A method of producing a directly imageable planographic printing plate, according to said (1), wherein the light transmittance, in the heat sensitive layer, of the light with the same wavelength as that of the laser beam applied in the first step is less than 20%.
(3) A method of producing a directly imageable planographic printing plate, according to said (1), wherein the heat sensitive layer contains at least a compound (A) capable of absorbing a laser beam for generating heat and a compound (B) capable of causing reaction by heat for improving the dissolvability or swelling rate.
(4) A method of producing a directly imageable planographic printing plate, according to said (3), wherein the compound (B) capable of causing reaction by heat for improving the dissolvability or swelling rate is a combination comprising a metal-containing organic compound and an active hydrogen-containing compound.
(5) A method of producing a directly imageable planographic printing plate, according to said (1), wherein the liquid temperature of the organic solvent used for pre-treatment in the second step is 30 to 60° C. and the pre-treatment time is 10 to 100 seconds.
DESIRABLE EMBODIMENTS
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. The method of producing a directly imageable waterless planographic printing plate of this invention contains a plate processing steps ranging from the exposure step of imagewisely irradiating a planographic printing plate precursor with a laser beam to the development step of patterning the printing plate by developing the exposed planographic printing plate.
The precursor of a directly imageable waterless planographic printing plate used in this invention is described below. The directly imageable waterless planographic printing plate precursor used in this invention has at least a heat sensitive layer and an ink repellent layer in this order on a substrate. A directly imageable waterless planographic printing plate precursor in which the ink repellent layer is mainly made of a silicone rubber is preferable.
<Constitution of Directly Imageable W
Aoki Shingo
Goto Kazuki
Ichikawa Michihiko
Miyaguchi Seigo
Nagase Kimikazu
Hamilton Cynthia
Morrison & Foerster / LLP
Toray Industries Inc.
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