Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
1998-03-06
2002-06-11
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S331000, C430S306000, C430S328000, C252S600000
Reexamination Certificate
active
06403284
ABSTRACT:
This application claims the benefit under 35 U.S.C. §371 of prior PCT International Application No. PCT/JP97/04456 which has an International filing date of Dec. 5, 1997 which designated the United States of America, the entire contents of which are hereby incorporated by references.
TECHNICAL FIELD
This invention relates to a surface-treating solution for a photosensitive resin printing plate which solution comprises a hydrogen-abstracting agent and to a process for producing a photosensitive resin printing plate which is broadly used as a printing plate for letterpress printing in which process the above surface-treating solution is used (said process is referred to as a plate-making process or plate-making in some cases hereinafter).
BACKGROUND ART
A photosensitive resin printing plate is generally obtained by an exposure step in which only the photosensitive layer of a relief portion is cured by a radical polymerization reaction caused by irradiation with active radiation and a development step subsequent to the exposure step, in which the uncured resin in other portions than the relief portion is dissolved in and removed with a given washing solution (developer) or swollen with and dispersed in the washing solution and then removed mechanically, thereby allowing only the cured portion to appear as a relief on the plate surface.
In general, with a photosensitive resin which is cured by a radical polymerization reaction, a vanishment reaction of a radical active species is caused competitively with its propagation reaction. Hence when the reaction rate is increased to heighten the sensitivity of the resin, it becomes difficult to increase the degree of polymerization which is governed by the concentration of an initiator. In order to obtain a relief suitable for printing, and in order to obtain the necessary sensitivity (reaction rate) for efficiently and simply carrying out the plate-making work, it is necessary for the photosensitive resin to contain a given amount of an initiator. However, there is a limit in the degree of polymerization of resin and hence unreacted substance remains even after the resin has been cured, whereby the resulting printing plate surface is tacky.
The production of a photosensitive resin printing plate is generally carried out in four steps of exposure, development, post-exposure and drying. The post-exposure is a step of further irradiating the printing plate with an active radiation in order to cure the unreacted substance present in and on the cured plate obtained after the development, to thereby increase the mechanical strength of the printing plate and reduce the surface tackiness of the printing plate. However, the printing plate even after the post-exposure step is not necessarily sufficiently freed of the surface tackiness.
When a printing plate having a great amount of tackiness is used in printing, there are such problems as poor workability during attaching the plate to and detaching the plate from a plate cylinder; adhesion of plates to each other or attachment of dust to the plates during the storing of the plates; adhesion of paper powder to the plate and paper-picking during the printing; and the like. In particular, when paper powder adhesion and the paper-picking result from the tackiness of the plate during the printing, it is necessary to discontinue the printing and clean the plate, such that working efficiency is remarkably decreased.
As a method of solving problems as mentioned above, there has been adopted a method in which the polymerization of the surface of the cured product of a photosensitive resin is accelerated by immersing the photosensitive resin cured product in a liquid and irradiating the same with an active radiation in the post-exposure step (referred to hereinafter as the post-exposure-in-water method, and in comparison therewith, the post-exposure in the atmosphere is referred to hereinafter as the post-exposure-in-air method) or by effecting the post-exposure in an inert gas; a method in which a coating material such as a rubber latex, a saran latex or the like is coated on the photosensitive resin printing plate to lower the surface tackiness; a method in which an oxidizing agent and a reducing agent are used alone or in admixture to subject the photosensitive resin printing plate to chemical treatment; a method in which the above methods are combined; or the like. As a kind of coating method, there is proposed to utilize a surface tackiness-removing method which, when a higher fatty acid, a higher alcohol or the like is incorporated into the photosensitive resin composition, the said compound is deposited as crystals on the surface of the photosensitive resin printing plate after the plate-making (JP-A-61-120,142).
However, these methods are insufficient in the effect per se, or even though they have any effect, the ease of handling of the reagents used becomes a problem in some cases. Specifically, the following problems are mentioned: (1) The coating method is disadvantageous in that the coating layer is peeled off during the printing, and is insufficient in the maintainability of the effect. (2) With some kinds of photosensitive resin compositions, even when the post-exposure is effected in an atmosphere from which oxygen is excluded such as in a liquid or in an inert gas (referred to hereinafter as poor oxygen post-exposure), the tackiness removal is insufficient in some cases. (3) In the treatment method using an oxidizing agent and a reducing agent, in general, it is necessary to pay attention to the handling of the reagents used and it becomes necessary to subject the apparatus contacting the treating solution to rust prevention processing.
In particular, the poor oxygen post-exposure of (2) is a method in which it is intended that the oxygen be excluded to allow the radical polymerization of the polymerizable double bond in the composition to be efficiently effected, whereby the prepolymer is three-dimensionally cross-linked, the mechanical strength is increased and simultaneously therewith the presence of the unreacted (namely uncross-linked) prepolymer is diminished as much as possible to reduce the tackiness. However, when the photosensitive resin contains a large amount of such a prepolymer that the number of polymerizable double bonds in one molecule is 2 or less, it is confirmed that the mechanical strength of the printing plate obtained from the photosensitive resin is increased by the oxygen-lacking post-exposure, but the tackiness-removal effect is insufficient. Moreover, when the photosensitive resin contains a large amount of such a prepolymer that the number of polymerizable double bonds exceeds 2, it is necessary for the printing plate obtained from the said photosensitive resin to be irradiated with an active radiation for a very long time in order to achieve a sufficient tackiness-removing effect.
That is to say, in the plate-making process at present, it is difficult to allow all the terminal double bonds of the prepolymer to react, and even if all of them should have reacted, a plate quite free of tackiness would not be obtained in many cases. Accordingly, in order to more sufficiently remove the surface tackiness of a printing plate produced from the photosensitive resin composition containing such a prepolymer, it is effective to three-dimensionally cross-link the prepolymer by using the polymerization reaction of the polymerizable double bonds in combination with other methods.
As the three-dimensional cross-linking by other reactions than the reaction of double bonds, JP-B-56-16,182 discloses a method which comprises abstracting hydrogen of the main chain of a prepolymer which has reacted with the unreacted monomer or another prepolymer at the terminal double bonds, thereby producing a radical of the prepolymer, and then cross-linking the main chains of the prepolymers with one another through the reaction of the said radicals. Specifically, the surface layer of a radically polymerizable resin cured product is impregnated with a hydrogen-abstracting agent which can abstrac
Asahi Kasei Kogyo Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Hamilton Cynthia
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