Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-07-28
2002-01-08
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S472200, C101S459000, C420S534000, C420S537000, C420S546000, C420S549000
Reexamination Certificate
active
06337136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aluminum alloy support for a lithographic printing plate, prepared by cold rolling while intermediate annealing is omitted and the number of the passes is decreased to simplify the sheet production steps, being extremely excellent in resistance to ink staining in the nonimage areas during printing and having proper strength, and a process for producing a substrate therefore.
2. Description of the Related Art
Conventional aluminum alloy substrates for a support for a lithographic printing plate are generally provided in the form of a 0.1 to 0.5 mm thick sheet made of an aluminum alloy such as JIS A1050. Such aluminum alloy sheets are generally produced by scalping the surface of a semicontinuous-cast slab, homogenization heat-treating the slab, hot-rolling the heat-treated slab, cold-rolling the hot-rolled strip, and further intermediate-annealing and finally cold-rolling to impart a desired strength to the sheet.
The aluminum alloy substrate for a lithographic printing plate thus produced is grained by either one of or a combination of at least two of the following steps: a mechanical step, a chemical step and an electrochemical step. Furthermore, in order to impart wear resistance, water retainability, resistance to staining in nonimage areas and adhesion of a photosensitive layer during printing, the grained aluminum alloy substrate is further anodically oxidized (film thickness of about 0.1 to 1.0 &mgr;m), and optionally subjected to a hydrophilic treatment to give a lithographic printing plate support. The support is further coated with a photosensitive material to form a photosensitive layer, and optionally subjected to a heating and burning treatment so that the photosensitive layer is stengthened, to give a photosensitive lithographic printing plate.
The lithographic printing plate is then successively subjected to preparation treatment such as image exposure, development, water washing and lacquering to give an original printing plate. The photosensitive layer remaining still undissolved after the development is water repellent, and forms image areas as an ink-accepting portion which selectively accepts ink alone. In the portion where the photosensitive layer is dissolved, the surface of the aluminum alloy support under the photosensitive layer is exposed, and the portion becomes a water-accepting portion due to its hydrophilic property and forms nonimage areas as an ink-excluding portion.
When printing is to be carried out, both end portions of the printing original plate are bent, and fixed to the printing drum of a printer. Accordingly, the substrate for a lithographic printing plate is required to have a desired strength from the standpoint of easy handling, durability, etc.
When dampening water is supplied to the surface of the printing original plate thus fixed, the water is retained in nonimage areas alone where the photosensitive layer is removed and a hydrophilic alloy substrate surface is exposed, and it is not held in image areas where a water repellent photosensitive layer surface remains. When ink is supplied to the original plate surface in such a state, the ink adheres to the image areas alone, and is held there. The ink adhering to and being retained in the image areas is further transferred to a bracket drum, and then it is transferred to a surface to be printed such as a paper sheet surface from the bracket drum, whereby printing is conducted.
When ink adheres to the nonimage areas, the printed materials are stained. Accordingly, in order to prevent ink from adhering to the nonimage areas which are exposed portions of the aluminum alloy support surface, it is important that the nonimage areas have water retainability to sufficiently retain dampening water. In order to ensure the water retainability, it is necessary to obtain an excellent uniformity of the grained surface and a defectless anodic oxide film by graining treatment such as electrochemical treatment.
Japanese Unexamined Patent Publication (Kokai) No. 62-148295 proposes a process for producing a lithographic printing plate excellent in resistance to ink staining in nonimage areas during printing, comprising the following procedures: an aluminum alloy slab is homogenization heat-treated at high temperature so that part of Fe forms solid solution, and cooled to precipitate the Si atoms contained in the slab as Al—Fe—Si-based intermetallic compounds and to fix them, thereby decreasing the amount of precipitated Si in the following steps; and the alloy is electrolytically grained to give a uniform grained surface. In addition, the patent publication shows in its example a process wherein intermediate annealing is omitted in the cold rolling step subsequent to hot rolling.
Furthermore, Japanese Unexamined Patent Publication (Kokai) No. 6-192779 proposes a process for producing a lithographic printing plate excellent in resistance to ink staining in nonimage areas during printing, in which precipitation of Si is inhibited in the production steps including casting, homogenization heat treating, hot rolling, cold rolling, intermediate annealing and final cold rolling by allowing the aluminum alloy to contain Mg.
Still furthermore, Japanese Unexamined Patent Publication (Kokai) No. 10-306355 proposes a process for producing a support, comprising starting hot-rolling a slab having been homogenization heat-treated, from given temperatures, finishing hot rolling at given temperatures, subsequently cooling slowly to given temperatures so that streaks are not formed as a fine recrystallized grain structure, and rolling the hot-rolled strip to a sheet having a final thickness at a reduction of at least 60% without subsequent heat treatment, thereby imparting a strength to the support.
The substrate must have a strength sufficient not to form defects such as recesses when it suffers a slight impact during transportation or handling. On the other hand, the support is also required to have a ductility sufficient to ensure bendability at the time when both ends of the original plate are bent and the original plate is fixed to the printing drum of a printing machine. Furthermore, in order to ensure durability to repeated stress during printing, the substrate must have a sufficient fatigue strength, namely, a combination of strength and a toughness. The substrate therefore must have mechanical properties which simultaneously meet these requirements. As a result, the strength of the substrate must be regulated so that it has a tensile strength of from about 145 to 180 MPa.
However, in the production process in which intermediate annealing is not conducted during cold rolling after hot rolling, work hardening caused by cold rolling makes the substrate have an excessively high strength, and imparting a suitable strength to the substrate becomes difficult. In order to lower the degree of work hardening, the following procedure can be conceived of: the final strip thickness is decreased in the hot rolling, and the working degree of the sheet in the following cold rolling is reduced. However, when the thickness of the strip which has become soft due to its high temperature is reduced by hot rolling, a slight strain of the rolling rolls causes nonuniformity in the thickness of the hot-rolled strip. The hot rolling as mentioned above therefore becomes significantly difficult in practice. Consequently, there is actually a lower limit to the thickness of the hot-rolled strip to be provided to cold rolling, and the thickness is about 3 mm even when the strip is made as thin as possible by hot rolling.
The present inventors have discovered the following method as a procedure to solve the problem of an excessive increase in the strength caused by work hardening. When cold rolling is conducted at a high reduction to generate a large amount of heat of working and make the temperature of the sheet being cold-rolled as high as at least the recovery temperature of the sheet, the sheet is softened by the recovery during or after cold rolling
Asahi Tadashi
Mizushima Kazumitsu
Okamoto Ichiro
Sakaki Hirokazu
Sawada Hirokazu
Jones Deborah
McNeil Jennifer
Merchant & Gould P.C.
Nippon Light Metal Company Ltd.
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