Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-01-25
2004-11-02
Gilliam, Barbara (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S278100, C430S281100, C430S286100, C430S302000, C430S434000, C430S435000, C101S453000, C101S463100, C101S466000, C101S494000
Reexamination Certificate
active
06811950
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a presensitized plate useful for making a lithographic printing plate (hereinafter referred to as “PS plate”) and a method for making a lithographic printing plate therefrom. More specifically, the present invention relates to a PS plate showing an improved developability (i.e., PS plate can be sufficiently developed by a developer) and a resistance to a damage during development to give a lithographic printing plate which is not easily contaminated during printing process and has a strong image, and relates to a method for making such a lithographic printing plate from the PS plate.
When a lithographic printing plate is used to prepare printings, it is important to obtain printings with no background contamination. Generally, the occurrence of background contamination in printings increases with the storage time of a PS plate after production. In particular, this phenomenon becomes more intense when the PS plate has been stored under a high temperature and high humidity. It is particularly difficult to stably store a PS plate having a photopolymerizable photosensitive layer for a long time since a radical easily generates to initiate a chain polymerization reaction in the photopolymerizable photosensitive layer when the PS plate is exposed to light. Accordingly, there has been a demand to obtain a PS plate that can be stably kept for a long time, especially under a high temperature and high humidity and that can provide a lithographic printing plate which does not cause any background contamination.
Many attempts have been made to eliminate the background contamination. For instance, the following PS plates or methods disclosed in various publications are known; a PS plate comprising a basecoat layer consisting of polyvinylphosphonic acid coated on a surface of an anodized aluminum plate and a photosensitive layer coated thereon comprising a diazo compound (German Patent No. 1,621,478), a PS plate comprising a basecoat layer of polyacrylic acid that is coated on an aluminum substrate and a layer of diazo resin coated on the basecoat layer (German Patent No. 1,091,433), a PS plate comprising a basecoat layer of polyacrylamide and a photosensitive layer coated thereon (U.S. Pat. No. 3,511,661), a method to add an organic acid polymer compound to a photosensitive layer comprising a diazo compound and organic polymer carrier to improve the stability with time of a PS plate comprising the photosensitive layer, thereby inhibiting generation of a background contamination of the PS plate (Japanese Un-examined Patent Publication (hereunder referred to as “J.P. KOKAI”) No. Sho 56-107238). However, these PS plates are still insufficient and a further improvement is required. J.P. KOKAI No. 57-5042 discloses a photo-addition composition comprising a combination of a diazo resin having plural diazonium groups on the side chain and a sulfonated polymer comprising plural sulfonate groups (for example, sulfonated polyurethane and sulfonated polyester). However, the effect of the composition to inhibit the background contamination is not sufficient and further, the utility of the PS plate is restricted since the performance of the plate is highly influenced by the sulfonated polyurethane or sulfonated polyester used in the photosensitive layer.
J.P. KOKAI No. 59-101651 discloses a method to improve the background contamination of a PS plate having a photosensitive layer comprising a diazo compound and a photopolymerizable compound when the plate is kept for a long time, which the method comprises coating a polymer comprising a monomer unit having a sulfonic acid as an intermediate layer. The storage stability of the PS plate was improved by the method when the PS plate has such a poorly sensitive photopolymerizable photosensitive layer that can be treated with a conventional PS plate-exposing device. However, the effect is not sufficient when the PS plate has a highly sensitive photopolymerizable photosensitive layer which is exposed to laser light as used for CTP technique.
The method to deposit a basecoat layer comprising a compound highly soluble in a developer or the method to add such a compound to the photopolymerizable photosensitive layer is effective for improving the background contamination property of a PS plate. But an irradiated portion of the photopolymerizable photosensitive layer of the PS plate is severely damaged by development and the printing durability of the PS plate is also deteriorated.
A conventional negative-working PS plate that has been widely used is such a plate that a diazo resin is coated on an aluminum plate which has been treated so that the surface becomes hydrophilic. In order to develop the plate, a developer containing an organic solvent should be used. However, use of such a developer may cause problems such as disposal of a waste developer and influence of the waste developer on an environment. A positive-working PS plate usually comprises an orthoquinonediazide compound together with a novolak resin. An alkali solution of a silicate salt should be used as a developer for such a plate and the developer should have a pH of around 13 to dissolve the novolak resin. The developer having such a high pH irritates skin and mucous membrane of a worker and thus, such a developer should be carefully treated.
There has been utilized a PS plate comprising a photopolymerizable photosensitive layer on an aluminum substrate. As a developer for the PS plate, an aqueous solution of silicate, phosphate, carbonate or hydroxide of an alkali metal or organic amine compound has been proposed.
For example, J.P. KOKAI No. Hei 8-248643 discloses a developer having a high pH of at least 12 and comprising an alkali silicate and an amphoteric surfactant. J.P. KOKAI No. Hei 11-65129 discloses a developer having a pH of 12 or lower, wherein the ratio SiO
2
/M
2
O (M is alkali metal) is specified.
The former developer having such a high pH has a problem, in addition to the handling problem, that an image area of a PS plate is easily damaged when the PS plate is developed. The latter developer has a problem that the contained silicate easily gels and becomes insoluble due to the decrease of the pH of the developer during the developing process.
A developer comprising no alkali silicate is described, for example, in J.P. KOKAI No. Sho 61-109052 which discloses a developer comprising an alkaline agent, a complexing agent, an anionic surfactant, an emulsifying agent and n-alkanoic acid, and in German Patent No. 1984605 which discloses a developer comprising an alkaline agent, a complexing agent, an anionic surfactant, amyl alcohol, and N-alkoxyamine. However, it is difficult to obtain a good printing performance such as printing durability since both the developers have high pH and comprise an organic solvent which causes damages of image area.
A developer having a relatively low pH (12 or less) with no alkali silicate is described, for example, in J.P.KOKAI No.2000-81711 which discloses a developer comprising an aqueous solution of potassium hydroxide comprising an anionic surfactant, and in J.P. KOKAI No. Hei 11-65126 which discloses a developer comprising an aqueous solution of alkali metal carbonate having pH ranging from 8.5 to 11.5.
However, such a developer having a relatively low pH poorly dissolves photopolymerizable photosensitive layer and thus, may cause problems such as a remain of a film in a non-image area of the photosensitive layer, particularly when the utilized PS plate is an aged one (that is, the plate has been stored for a long time after production). In order to solve the problem, it is necessary to improve the developability by increasing an acid number of a binder polymer in the photosensitive layer of the PS plate, or by use of an additional monomer having an acid group in the binder polymer. But, when such a binder polymer having a higher acid number is used, it often causes a problem in a printing process such as a blinding, that is, an ink does not adhere to the PS plate during the printing proces
Kobayashi Fumikazu
Kondo Shun-ichi
Tsuchiya Mitsumasa
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
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