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
2002-07-22
2004-04-06
Huff, Mark F. (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
C430S270100, C430S302000, C101S453000, C101S459000
Reexamination Certificate
active
06716567
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a support for a lithographic printing plate and a presensitized plate. More particularly, the invention relates to a positive working presensitized plate having a photosensitive layer that can become alkali-soluble by photothermal conversion by a laser beam, and a support for a lithographic printing plate used for the same.
BACKGROUND ART
With development of image formation technology in recent years, it has come to be possible to perform direct plate making by scanning narrow focused laser beams on the printing plate to form a manuscript of letters, images and the like directly on the plate without using a film manuscript.
In a presensitized plate of a so-called thermal positive working type for causing photothermal conversion in a photosensitive layer by laser beam irradiation to make the photosensitive layer alkali soluble, and thus forming a positive image, a subtle change in interaction of binder molecules contained in the photosensitive layer by laser beam exposure is utilized as an image forming principle. Accordingly, a difference in ON/OFF levels of alkaline solubility between exposed and unexposed portions is reduced. Therefore, for the purpose of obtaining clear discrimination to be put to practical use, use has been made of means for forming a photosensitive layer structure by providing a surface slightly soluble layer in developer as an uppermost layer of the photosensitive layer, and suppressing developer solubility of the unexposed portion.
However, when the surface slightly soluble layer is damaged for some reason, even a portion intended as an image area is made easily soluble in the developer. In other words, a printing plate produced is damaged very easily from a practical standpoint. Thus, scratch-shaped non-image portion is brought about by subtle contacts such as clashing in handling of the printing plate, subtle rubbing of an interleaving sheet, contact of fingers with the plate surface or the like.
For example, in the presensitized plate, paper called an interleaving sheet for protecting the plate surface is normally provided on the surface of the photosensitive layer. This interleaving sheet is electrostatically adsorbed on the plate surface, thereby becoming difficult to be peeled off. At present, automatic feeding of the presensitized plate by a machine is generally carried out, and the interleaving sheet adsorbed on the plate surface is also removed mechanically. In this case, however, friction between the interleaving sheet and the photosensitive layer may cause scratching.
Therefore, the above-described presensitized plate of the thermal positive working type is still difficult to be handled in printing plate work. For the purpose of improving the tendency to be damaged, a layer of fluorine-containing surfactant or wax agent has been provided on the surface of the photosensitive layer to reduce a friction coefficient. However, no satisfactory measures have been taken.
Furthermore, the above-described scratch-like non-image portion caused by contact or the like has also been a problem even in the case of a presensitized plate provided with a photosensitive layer which doesn't have a surface slightly soluble layer.
DISCLOSURE OF THE INVENTION
Objects of the present invention are to provide a positive working presensitized plate of a thermal type, which has damage resistance, and which is handled easily in conventional operation, high in sensitivity and excellent in press life when used as a lithographic printing plate, and to provide a support for a lithographic printing plate, which is suitably used for the same.
The inventors conducted serious studies in order to achieve the foregoing objects, and accordingly completed a support for a lithographic printing plate of a first aspect of the present invention.
That is, the first aspect of the present invention provides a support for a lithographic printing plate obtained by performing graining treatment, alkali etching treatment and anodizing treatment on an aluminum plate, wherein a ratio of a real area of a surface thereof to an apparent area of the surface set larger by 1.3 to 1.8 times, comprising a pit having an average diameter of 0.3 to 1.0 &mgr;m and a micro grained structure inside (also referred to as “grained structure with small undulation” hereinafter) on the surface, wherein a ratio of an apparent area of the pits to the apparent area of the surface is 90% or more.
In this case, “ratio of a real area of a surface thereof to an apparent area of the surface” means a value obtained by dividing a real area of a surface of the support for the lithographic printing plate by an apparent area of the surface, wherein the real area of the surface includes a pit surface area but not a surface area of the pit micro grained structure, while the apparent area represented by an area of a drawing of projecting the surface of the support for the lithographic printing plate on a surface parallel to the support. Specifically, when a surface shape of the support for the lithographic printing plate is measured by using an atomic force microscope (AFM) under conditions of horizontal (X, Y) resolution 0.1 &mgr;m, and a measuring area of 100 &mgr;m-square, a surface area obtained by an approximate three-point method is set as a real area, an upper projected area is set as an apparent area and, then, it can be obtained by dividing the real area with the apparent area.
Moreover, “ratio of an apparent area of the pits to the apparent area of the surface” means a value obtained by dividing a pit apparent area represented by an area of a drawing projecting the pits on the surface of the support for the lithographic printing plate on a surface parallel to the support with a surface apparent area of the support for the lithographic printing plate.
Roughness caused by asperities on the support surface is present on a photosensitive layer surface of a positive working presensitized plate of a thermal type. When the photosensitive layer is brought into contact with an object or the like, if the surface of the photosensitive layer is rubbed by the object or the like, a top part of a micro convex portion is slightly rubbed off, fracturing a surface slightly soluble layer, and even the support may be partially exposed. In development, developer easily infiltrates an interface between the support and the photosensitive layer from the fractured portion of the surface slightly soluble layer. Accordingly, the photosensitive layer starts dissolving from near the interface with the support. In other words, development is started preferentially from the rubbed place. Thus, a scratched portion is observed as a white line from a macroscopic standpoint.
The inventors obtained the foregoing knowledge as a result of serious studies. The inventors conducted further serious studies on measures to reduce a level of fine asperities on the surface of the photosensitive layer. As a result, it was discovered that a surface asperity shape on the surface of the support itself decided fine asperities on the surface of the photosensitive. It was also discovered that it was possible to reduce the level of fine asperities on the photosensitive layer surface without deteriorating press life thereof or the like by setting a ratio of a real area to a apparent area of the surface of the support in a specified range, specifying a pit structure, and setting a ratio of a pit apparent area to the surface apparent area in a specified range. Accordingly, the support for the lithographic printing plate capable of forming a photosensitive layer which has damage resistance was realized.
That is, an effective way to realize a flat photosensitive layer surface is to make a surface shape of the support flat as much as possible. However, since adhesion is lowered between the photosensitive layer and the support if the surface shape of the support is made simply flat, press life of the lithographic printing plate is deteriorated, peeling easily occurs between the photosensitive layer and the support, and damaged
Endo Tadashi
Hotta Hisashi
Miwa Hideki
Teraoka Katsuyuki
Yasutake Teruyoshi
Burns Doane Swecker & Mathis L.L.P.
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
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