Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-12-06
2003-10-28
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S278100, C430S284100, C430S286100, C430S287100, C430S288100, C430S348000, C430S434000, C430S494000
Reexamination Certificate
active
06638687
ABSTRACT:
DETAILED EXPLANATION OF THE INVENTION
1. Industrial Field of the Invention
The present invention relates to a method for preparing a lithographic printing plate. More specifically, the present invention pertains to a method for processing a lithographic printing plate, which can control the reduction of developing properties due to the elapse of time and/or the repeated use, hardly forms any sludge even when developing a large number of printing plates, can ensure a good ability of developing nonimage areas and can provide a printing plate free of any scumming during printing operations. Moreover, the present invention further relates to a method for processing a lithographic printing plate, which never causes any trouble or accident such as blinding, scarcely damages image areas during development, can provide an image having high strength and is capable of realizing high printing durability.
2. Prior Art
The negative-working presensitized plate for use in making a lithographic printing plate, which has widely been used, comprises a hydrophilized aluminum plate provided thereon with a diazo resin layer and therefore, an organic solvent should be used as a developing liquid. For this reason, the developing waste liquor must be post-treated and it would be feared that the waste liquor might adversely affect the environment. Alternatively, the positive-working presensitized plate for use in making a lithographic printing plate comprises, in its light-sensitive layer, an o-quinone diazide compound in combination with a novolak resin and accordingly, the developer therefor comprises an aqueous alkaline silicate solution capable of dissolving the novolak resin. However, the pH value of the solution capable of dissolving the novolak resin is on the order of about 13. A developer having such a high pH value is highly irritative when it is adhered to the skin or the mucous and therefore, sufficient care should be necessary when handling the same.
On the other hand, there has also been used a photopolymerizable presensitized plate for use in making a lithographic printing plate comprising an aluminum substrate provided thereon with a photopolymerizable light-sensitive layer and there have been proposed, as a developer therefor, aqueous solutions of, for instance, silicates, phosphates, carbonates and hydroxides of alkali metals and organic amine compounds.
For instance, Japanese Un-Examined Patent Publication (hereunder referred to as “J.P. KOKAI”) No. Hei 8-248643 discloses a developer containing an alkali silicate and an amphoteric surfactant and having a high pH value of not less than 12 and J.P. KOKAI No. Hei 11-65129 discloses a developer containing an alkali silicate having a pH value of not more than 12, in which the ratio: SiO
2
/M
2
O (M represents an alkali metal) is specified.
The former suffers from such a problem that image areas are susceptible to damages during development because of the high pH value of the developer in addition to the foregoing problem of handling and the latter suffers from a problem in that the silicate is insolubilized through gelation due to only a slight pH reduction of the developer during using the same.
As developers free of any alkali silicate, J.P. KOKAI No. Sho 61-109052 disclosed those comprising, for instance, alkaline agents, chelating agents, anionic surfactants, emulsifying agents and n-alkanes and West German Patent No. 1,984,605 disclosed those comprising alkaline agents, chelating agents, anionic surfactants, amyl alcohol and N-alkoxyamines. However, the developers have extremely high pH values and contain organic solvents. Therefore, image areas would be greatly damaged and there are some problems to be solved in order to obtain sufficient printing characteristics such as printing durability.
As developers having a relatively low pH values (not more than 12) and free of any alkali silicate, J.P. KOKAI No. 2000-81711 discloses a developer consisting of an aqueous potassium hydroxide solution containing an anionic surfactant and J.P. KOKAI No. Hei 11-65126 discloses a developer consisting of an aqueous solution of an alkali metal carbonate having a pH value ranging from 8.5 to 11.5.
However, such a developer having a relatively low pH value is fundamentally insufficient in the ability of solubilizing the photopolymerizable light-sensitive layer and therefore, problems arise such that undeveloped residue remains on the printing plate after the development since the development does not sufficiently proceed when using a printing plate material stored over a long period of time prior to the development and that sludge is generated during the development. Some consideration is needed to solve these problems. For instance, the developing ability should be improved by increasing the acid value of a polymeric binder incorporated into the light-sensitive layer of the plate material or a monomer carrying an acidic group is used in combination. If such a binder having a high acid value is used, however, problems concerning printing frequently arise such that ink is not adhered to the printing plate in the course of the printing operation (a problem of blinding) and that image areas are damaged by the action of the developer to thus reduce the printing durability of the resulting printing plate.
PROBLEMS THAT THE INVENTION IS TO SOLVE
Accordingly, it is an object of the present invention to provide a method for processing a lithographic printing plate, which makes use of an alkaline developer having a low pH value favorable from the viewpoint of the environmental protection and safety, which is not accompanied by the formation of any sludge in the developer even if the developer is used over a long period of time, which ensures a good ability of developing nonimage areas, which can provide a printing plate free of any scumming in printing operation and never accompanied by any trouble such as blinding during printing operations, which scarcely damages image portions during development, which can provide images having high strength and which can provide a printing plate having high printing durability.
MEANS FOR SOLVING THE PROBLEMS
The inventors of this invention have conducted various studies to solve the foregoing problems associated with the conventional techniques, have found that if an alkali solution having a relatively low pH value is used in combination with a nonionic surfactant having a specific structure and a salt concentration in the developer is adjusted, the unexposed area of a photopolymerizable light-sensitive layer comprising a polyurethane resin binder is dissolved at an improved dissolution speed, while the penetration of the developer into the exposed portion or the portion crosslinked through photopolymerization is conversely inhibited and have thus completed the present invention.
According to the present invention, there is thus provided a method for preparing a lithographic printing plate comprising the steps of subjecting, to imagewise exposure, a presensitized plate for use in making a lithographic printing plate comprising an aluminum substrate provided thereon with a light-sensitive layer formed from a photopolymerizable light-sensitive composition, which comprises a compound having an ethylenically unsaturated double bond, a photopolymerization initiator and a polyurethane resin binder and then developing the image-exposed plate with a developer containing an inorganic alkaline agent and a nonionic surfactant, carrying a polyoxyalkylene ether group, and having a pH value ranging from 10.0 to 12.5 and an electrical conductivity ranging from 3 to 30 mS/cm.
The present invention thus permits the stable production of a printing plate, which comprises unexposed areas free of any scumming and exposed areas having a high printing durability.
BEST MODE FOR CARRYING OUT THE INVENTION
The method for processing a lithographic printing plate according to the present invention will hereunder be described in more detail.
We first describe the novel developer used in the processing method of the present invention. The use of such
Higashi Tatsuji
Okamoto Yasuo
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
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