Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
2000-06-05
2002-04-09
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C101S462000
Reexamination Certificate
active
06367383
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solution for the use of the same receiving element in combination with different writing heads.
More specifically the invention is related to a receiving element that can be imaged with heat and with ink jet.
BACKGROUND OF THE INVENTION
In computer to plate lithography, there exist different recording techniques for imaging a printing plate such as a laser, a thermal head, an ink jet printing head, etc. . . .
The imaged printing plates can then be used as printing elements without any processing step or alternatively after some kind of processing. Such printing elements can allow recording on press.
It is a very desirable property of the printing press that it can be used with an imaging element that can be imaged with different writing heads; those different heads can all be present on the press and can be used for recording separately or in any combination.
EP-A-770 497 discloses a method for making a lithographic printing plate comprising the steps of: (1) image-wise exposing to light an imaging element comprising (i) on a hydrophilic surface of a lithographic base an image forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and (ii) a compound capable of converting light to heat, said compound being comprised in said image forming layer or a layer adjacent thereto; (2) and developing a thus obtained image-wise exposed imaging element by rinsing it with plain water or an aqueous liquid.
A method wherein an image or non-image portion is directly formed on a substrate by ink-jet printing is known to the art. The ink-jet printing system is a relatively rapid image output system and has a simple construction because it does not require any complex optical system. Therefore, the printing system makes an apparatus for making printing plates simple and the cost for making printing plates can be reduced since the maintenance labor is largely reduced.
As examples of the methods for preparing printing plates by using the ink-jet printing system, Japanese Kokai Publication 113456/1981 proposes the methods for preparing printing plates wherein ink-repelling materials (e.g. curable silicone) are printed on a printing plate by ink-jet printing. The printing plate obtained by this method is an intaglio printing plate in which the ink-repelling material formed on the surface of the substrate serves as a non-image part. As a result, the resolution of the printed images at shadow area or reversed lines is not so good. Moreover, a large amount of ink is needed in this method because the ink-repelling material must be deposited on the whole non-image part which occupies most of the surface of the printing plate, thereby delaying the printing process.
U.S. Pat. No. 5,511,477 discloses a method for the production of photopolymeric relief-type printing plates comprising: forming a positive or a negative image on a substrate by ink-jet printing with a photopolymeric composition, optionally preheated to a temperature of about 30°-260° C., and subjecting the resulting printed substrate to UV radiation, thereby curing said composition forming said image.
The receiving layer is not specified.
U.S. Pat. No. 5,312,654 discloses a method for making lithographic printing plates comprising: forming an image on a substrate having an ink absorbing layer and a hydrophilized layer between the substrate and absorbing layer by ink-jet printing using a photopolymerizable ink composition, and exposing it to an active light in the wavelength region for which said ink composition is sensitized to cure the image. The printing endurance of said printing plates is low.
Japanese Kokai Publication 69244/1992 discloses a method for making printing plates comprising the steps of forming a printed image on a recording material subjected to a hydrophilic treatment by ink-jet printing using a hydrophobic composition containing photocurable components; and exposing the whole surface to an active light. However, the surface of the substrate to be used for the lithographic plate is usually subjected to various treatments such as a mechanical graining, an anodizing or a hydrophilic treatment to obtain good hydrophilic property and water retention property. Therefore, even the use of an ink composition having a very high surface tension results in a poor image on the surface of the substrate because of ink spreading and low printing endurance.
EP-A-533 168 discloses a method for avoiding said ink spreading by coating the lithographic base with an ink absorbing layer which is removed after ink printing. This is an uneconomical and cumbersome method.
Research Disclosure 289118 of May 1988 discloses a method for making printing plates with the use of an ink jet wherein the ink is a hydrophobic polymer latex. However said printing plates have a bad ink acceptance and a low printing endurance.
EP-A-003 789 discloses a process for the preparation of offset printing plates by means of an ink jet method with oleophilic compositions. There is not indicated how said compositions are made but from the examples it is clear that it concerns artificial lattices, which are difficult to prepare. The receiving layer is not specified.
JN-57/038142 discloses a method of preparing a printing plate by forming an ink image on a blank printing plate, and also by fixing this image thermally by making toner adhere to this image-formed area. The composition of the ink is not mentioned, only the composition of the toners is disclosed.
JN-07/108667 discloses a plate-making method forming an ink image containing a hydrophilic substance on a conductive support whose surface layer is made hydrophilic according to an electrostatic attraction type ink set system to dry or cure the same, by applying bias voltage to the conductive support at the time of ink jet writing. This is a cumbersome process.
U.S. Pat. No. 5,213,041 discloses a method for preparing a re-usable printing plate for printing, projecting an imaging deposit on the plate surface by jet printing using an ejectable substance containing a heat fusible component. The image forms an imaging deposit, which is fused to the surface of the printing plate using a variable frequency and variable power induction heater. This is a cumbersome method.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a method for preparing a printing plate by ink jet, using a receiving element that is also usable as imaging element in direct thermal or heat mode writing.
It is also an object of the present invention to provide a method for preparing a printing plate with a good ink acceptance and a good printing endurance.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method for preparing a lithographic printing plate, comprising the step of dispensing in a predetermined pattern a hydrophobic or hydrophobizing composition onto a receiving element comprising on a support a layer comprising hydrophobic thermoplastic polymer particles dispersed in a hardened hydrophilic binder.
DETAILED DESCRIPTION OF THE INVENTION
The advantage of using a receiving element according to the invention for ink jet printing lies in the fact that a part of the image can be made by contact with a thermal head or by irradiation with a laser (heat-mode).
The imaging element according to the present application comprises (i) on a support an image forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hardened hydrophilic binder and preferably (ii) a compound capable of converting light to heat, said compound being comprised in said image forming layer or a layer adjacent thereto.
Specific examples of hydrophobic polymer particles for use in connection with the present application have a Tg above 80° C.
Preferably the polymer particles are selected from the group consisting of polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole etc., copolymers or mixtures thereof. Most preferably used are polystyrene, polymethylmethacrylate or co
Leenders Luc
Vermeersch Joan
Agfa-Gevaert
Breiner & Breiner L.L.C.
Funk Stephen R.
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