CONTINUOUS TONE LITHOGRAPHIC PLATE AND METHOD OF MAKING

• US 3,861,917 A
• Filed: 08/03/1973
• Issued: 01/21/1975
• Est. Priority Date: 02/22/1972
• Status: Expired due to Term

• Current Assignee: W.R. Grace & Co.-Conn. (WR Grace & Company)
• Original Assignee: Arthur D. Ketley, Frank Magnotta, Suzanne E. Matheson
• Inventors: Ketley, Arthur D., Magnotta, Frank, Matheson, Suzanne E.
• Primary Examiner(s): Torchin, Norman G.
• Assistant Examiner(s): SuroPico, Alfonso T.
• Application Number:
  US05/385,261
• Time in Patent Office: 536 Days
• Field of Search: 96/35.1,33,86P,115P,115R,86R 204/129.1
• US Class Current: 430/305
• CPC Class Codes: B41N 3/034 characterised by the electrochemical treatment of the aluminum support, e.g. anodisation, electro-graining; Sealing of the anodised layer; Treatment of the anodic layer with inorganic compounds; Colouring of the anodic layer

Abstract

This invention relates to a continuous tone lithographic printing plate comprising a treated anodized aluminum surface having thereon an ink-receptive, image-forming layer of a photosensitive composition capable of forming photographic films that can be exposed and processed to give images having a gamma in the range 0.3-2.5.

Claims

2. A method for preparing a continuous tone lithographic printing plate which comprises a. electrochemically graining the surface of an aluminum or aluminum alloy sheet at a temperature in the range between 15* and 36*C using line AC current and a voltage between 8.5 and 12 volts in a bath consisting of 0.1-1.0 Baume HCl with a spacing between the aluminum sheets between 1 and 3 inches for a period ranging up to 30 minutes to obtain a depth variation of 1-15 microns;

b. anodizing the grained sheet in a 5-30% aqueous solution of sulphuric acid as the electrolyte at a current density in the range 8-55 amperes/ft.2 at a temperature in the range 10*-40*C for a period ranging from 1-10 minutes;

c. sealing the anodized sheet in boiling deionized water until it has an electrical impedance in the range 6-12 kiloohms; and

d. coating the thus sealed sheet with a negative-working photosensitive material.

3. The method according to claim 2 wherein the photosensitive material is a photocurable composition capable of forming an image having a gamma in the range 0.3 to 2.5 consisting essentially of (1) 2 to 98 parts by weight of an ethylenically unsaturated polyene containing two or more reactive unsaturated carbon to carbon bonds per molecule;

(2) 98 to 2 parts by weight of a polythiol containing at least 2 thiol groups per molecule, the total combined functionality of the carbon to carbon bonds per molecule in the polyene and the thiol groups per molecule in the polythiol being greater than 4 and (3) 0.0005 to 50 parts by weight based upon 100 parts by weight of (1) and (2) of a photocuring rate accelerator.

4. The method according to claim 2 wherein the photosensitive material is a diazo material capable of forming an image having a gamma in the range 0.3 to 2.5.

5. A method for preparing a continuous tone lithographic printing plate which comprises a. electrochemically graining the surface of an aluminum or aluminum alloy sheet at a temperature in the range between 15* and 36*C using line AC current and a voltage between 8.5 and 12 volrs in a bath consisting of 0.1 to 1.0 Baume HCl with a spacing between the aluminum sheets between 1 and 3 inches for a period ranging up to 30 minutes to obtain a depth variation of 1-15 microns;

b. anodizing the grained sheet in a 5-30% aqueous solution of sulphuric acid as the electrolyte at a current density in the range 8-55 amperes/ft.2 at a temperature in the range 10*-40*C for a period ranging from 1-10 miinutes;

c. sealing the anodized sheet in boiling deionized water until it has an electrical impedance in the range 6-12 kiloohms;

d. coating the thus treated sheet with a negative-working photosensitive diazo material;

e. exposing said diazo material imagewise through a continuous tone, image bearing transparency to ultraviolet radiation whereby the exposed area of the diazo material is insolubilized; and

f. removing the unexposed diazo material thereby uncovering portions of the sheet and forming an image having a gamma in the range 0.3-2.5.

6. A method for preparing a continuous tone lithographic printing plate which comprises a. electrochemically graining the surface of an aluminum or aluminum alloy sheet at a temperature in the range between 15* and 36*C using line AC current and a voltage between 8.5 and 12 volts in a bath consisting of 0.1 to 1.0 Baume HCl with a spacing between the aluminum sheets between 1 and 3 inches for a period ranging up to 30 minutes to obtain a depth variation of 1-15 microns;

b. anodizing the grained sheet in a 5-30% aqueous solution of sulphuric acid as the electrolyte at a current density in the range 8-55 amperes/ft.2 at a temperature in the range 10*-40*C for a period ranging from 1-10 minutes;

c. sealing the anodized sheet in boiling deionized water until it has an electrical impedance in the range 6-12 kiloohms;

d. coating the thus treated sheet with a negative-working photocurable composition consisting essentially of (1) 2 to 98 parts by weight of an ethylenically unsaturated polyene containing two or more reactive unsaturated carbon to carbon bonds per molecule;

(2) 98 to 2 parts by weight of a polythiol containing at least 2 thiol groups per molecule, the total combined functionality of the carbon to carbon bonds per molecule in the polyene and the thiol groups per molecule in the polythiol being greater than 4 and (3) 0.0005 to 50 parts by weight based upon 100 parts by weight of (1) and (2) of a photocuring rate accelerator, e. exposing said photocurable composition imagewise through a continuous tone, image bearing transparency to ultraviolet radiation whereby the exposed area of the photocurable composition is insolubilized; and

f. removing the unexposed photocurable composition thereby uncovering portions of the sheet and forming an image having a gamms in the range 0.3-2.5.