Arc-grained lithoplate

• US 5,187,046 A
• Filed: 03/18/1991
• Issued: 02/16/1993
• Est. Priority Date: 03/18/1991
• Status: Expired due to Fees

• Current Assignee: Alcoa Incorporated (Howmet Aerospace, Inc.)
• Original Assignee: Aluminum Company of America (Howmet Aerospace, Inc.)
• Inventors: Patrick, Edward P., Pajerski, A. Victor
• Primary Examiner(s): BRAMMER, JACK
• Application Number:
  US07/670,576
• Time in Patent Office: 701 Days
• Field of Search: 430/278, 430/302, 428/632, 428/609, 428/550, 204/33, 204/129.75, 204/129.8, 156/665, 101/459, 101/463.1
• US Class Current: 430/278.1
• CPC Class Codes: B21B 2001/383 Cladded or coated products
• CPC Class Codes: B22D 11/008 of clad ingots, i.e. the molten metal being cast against a continuous strip forming part of the cast product
• CPC Class Codes: B23K 35/0238 layered
• CPC Class Codes: B23K 35/286 Al as the principal constituent
• CPC Class Codes: B32B 15/016 all layers being formed of aluminium or aluminium alloys
• CPC Class Codes: B41N 1/083 made of aluminium or aluminium alloys or having such surface layers B41N1/086 takes precedence
• CPC Class Codes: B41N 3/032 Graining by laser, arc or plasma means
• CPC Class Codes: Y10T 428/12042 Porous component
• CPC Class Codes: Y10T 428/12451 Macroscopically anomalous interface between layers
• CPC Class Codes: Y10T 428/12611 Oxide-containing component

Abstract

An essentially flat "arc-grained" surface of a sheet of aluminum alloy is produced with a coarse and non-uniform microstructure which, after it is coated with a durable phosphate-free coating, provides excellent lithoplate. Though such arc-grained microstructure is much coarser than an electrochemically etched surface typically used on lithoplate, the very coarse surface is peculiarly well-adapted to provide durable lithoplate after it is coated with a phosphate-free protective surface. After the coated surface is coated with a photoresist the excellent resolution of prints is maintained over a large number of repeated uses in an off-set printing press. A method of producing lithoplate comprises, controlledly rastering an A-C, or D-C reverse polarity plasma-generating electric arc on an aluminum sheet less than 30 mils thick, kept distortion-free on a mounted surface such as on a cylindrical drum; then coating the arc-grained surface with a hard and durable, inert phosphate-free coating while maintaining a capillary microstructure in the surface adapted to provide a support for a photoresist for use in lithographic printing of adequate resolution.

Claims

1. In a coated lithoplate of aluminum sheet, the improvement comprising, said lithoplate having an overall thickness in the range from 5 miles to 30 mils and a surface having a non-uniform microstructure having a roughness in the range from 0.1μ

to 1.5μ

[RA, including a profusion of craters having a diameter in the range from 1μ

to 10μ

, peripherally surrounded by petal-like projections with from about 30% to about 80% terminating in peaks packed closely enough to provide a capillary uptake of water and printing ink in separately identifiable zones;

a coating of aluminum oxide or boehmite on said non-uniform microstructure, said aluminum oxide having a thickness in the range from 1.2μ

to 3μ

, and said boehmite having a thickness in the range from 0.6μ

to 3μ

; and

,

a light-sensitive resist deposited on said coating.

2. The lithoplate of claim 1 wherein said surface is anodized to produce an oxide coating formed in an amount in the range from about 100 to about 500 mg/ft².

3. The lithoplate of claim 1 wherein said aluminum alloy is selected from the group consisting of 1050, 1100, 3003, and 5×

×

×

alloys including 5005 and 5052.

4. The lithoplate of claim 1 wherein said boehmite is a non-porous gamma-alumina hydrate.