EP0007234B1 - A process for the anodic treatment of a continuous web of aluminium foil, foil so obtained and its application as a lithographic printing plate - Google Patents

A process for the anodic treatment of a continuous web of aluminium foil, foil so obtained and its application as a lithographic printing plate Download PDF

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Publication number
EP0007234B1
EP0007234B1 EP79301378A EP79301378A EP0007234B1 EP 0007234 B1 EP0007234 B1 EP 0007234B1 EP 79301378 A EP79301378 A EP 79301378A EP 79301378 A EP79301378 A EP 79301378A EP 0007234 B1 EP0007234 B1 EP 0007234B1
Authority
EP
European Patent Office
Prior art keywords
bath
aluminium foil
foil
printing plate
continuous web
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP79301378A
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German (de)
French (fr)
Other versions
EP0007234A3 (en
EP0007234A2 (en
Inventor
Alan Thomas
David Philip Rowlands
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Balfour Beatty PLC
Original Assignee
BICC PLC
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Publication date
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Application filed by BICC PLC filed Critical BICC PLC
Priority to AT79301378T priority Critical patent/ATE885T1/en
Publication of EP0007234A2 publication Critical patent/EP0007234A2/en
Publication of EP0007234A3 publication Critical patent/EP0007234A3/en
Application granted granted Critical
Publication of EP0007234B1 publication Critical patent/EP0007234B1/en
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
    • B41N3/00—Preparing for use and conserving printing surfaces
    • B41N3/03—Chemical or electrical pretreatment
    • B41N3/034—Chemical or electrical pretreatment 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/12—Anodising more than once, e.g. in different baths

Definitions

  • This invention relates to the anodic treatment of foil of aluminium (including its alloys) in continuous web from Primarily, but not exclusively, it is concerned with the pretreatment of aluminium foil that is subsequently to be coated with photosensitive material to make a presensitised lithographic printing plate.
  • Aluminium foil for this purpose is almost always anodised, generally using a bath based on sulphuric acid, though phosphoric acid is used by at least one manufacturer.
  • Sulphuric acid gives a hard, adherent and abrasion- resistant coating, but there are problems in getting satisfactory adhesion of some attractive sensitive coatings (for example polyvinyl cinnamate among negative-based resists amongst positive-working coatings).
  • Phosphoric acid anodising gives much better adhesion with these and some other coatings, but the anodic coating is much softer and tends to abrade away during printing to an extent that may limit the number of copies that can be taken off the plate.
  • aluminium foil that has been anodised in sulphuric acid has been treated subsequently with phosphoric acid, and this has been found to give a useful improvement in adhesion while retaining part of the advantages of the use of sulphuric acid for anodising, but this prevents obvious difficulties in control of the operation.
  • DE-A 2557222 illustrates the use of an auxiliary electrolytic cell as a mere means for introducing current into a web of aluminium foil for the purpose of anodising it
  • US-A 3929591 describes a process in which, prior to being anodised, an aluminium foil is etched in an entirely separate A.C. anodising process.
  • the invention is based in part on the realisation that anodic oxidation takes place at the surface of the metal, not of the coating, and that it will not of itself destroy the existing exposed surface of the coating.
  • a continuous web of aluminium foil is passed through a first bath containing phosphate ions and a second bath containing sulphate ions and is anodised by passing alternating current between a first electrode immersed in the first bath and a second electrode immersed in the second bath.
  • the phosphate and sulphate ions may be the only anions present to any substantial extent in the respective baths, but other anions that are inert or that modify, rather than radically alter, the effect of the treatment may be present.
  • the presence of minor amounts of sulphate in the phosphate bath and/or of phosphate in the sulphate bath is not excluded.
  • the associated cations should be wholly or mainly hydrogen ions, but neutral or alkaline salt solutions may be suitable in some cases.
  • the method of the invention avoids the need for rectification equipment and yet allows both positive and negative half-cycles to be used in anodising; because of the superior combination of good adhesion and abrasion resistance, only thin coatings are required for lithographic printing plates, and this avoids any significant difficulty from migration of dye when a coloured sensitive coating is used to obtain a visible image on development.
  • Aluminium foil web is continuously advanced through the apparatus, and is first slurry-grained in the usual way, etched in a bath comprising 5 9/1 sodium hydroxide and 5 g/I sodium gluconate at 20°C, dwell time in the bath being four minutes; then washed in de-ionised water for four minutes; and the treated for four minutes in a bath containing 22.5 g/I of a brightening agent sold under the designation "Aluminux no. 1 Etch" at 20°C and again washed in de-ionised water for four minutes.
  • the web 1 is now passed through a first bath 2 containing 45% ortho phosphoric acid and a second bath 3 containing 15% sulphuric acid. Each bath is at 20°C and the dwell time is 4 minutes in each bath. Alternating electric current is supplied to two inert electrodes 4 and 5, one immersed in each bath, the web 1 providing the electrical connection between the two baths.
  • the current density referred to the area of web (one side) facing the electrode in each bath, is 200 Nm2 at 21 V.
  • a bright and very hydrophilic anodised finish is obtained, which can be coated with conventional photolithographic coatings to give a plate with an excellent combination of coating adhesion and abrasion resistance (press life).
  • a proprietary positive-working lithographic resist comprising a resin sensitised with the 2,4 dihydroxybenzophenone ester of 1, 2, 5 diazo naphthol sulphonic acid and coloured with a blue dye yields presensitised plates that were in a satisfactory condition after exposure at 35°C to a relative humidity of 85%; conventional sulphuric acid anodising of comparable thickness gave a plate that became unsuable after about two weeks.

Abstract

Aluminium web (1) is passed through a first bath (2) containing phosphate ions and a socond bath (3) containing sulphate ions and is anodised by passing alternating current between electrodes (4, 5) immersed one in each bath. The product is especially suitable for use as a base for a presensitised lithographic printing plate.

Description

  • This invention relates to the anodic treatment of foil of aluminium (including its alloys) in continuous web from Primarily, but not exclusively, it is concerned with the pretreatment of aluminium foil that is subsequently to be coated with photosensitive material to make a presensitised lithographic printing plate.
  • Aluminium foil for this purpose is almost always anodised, generally using a bath based on sulphuric acid, though phosphoric acid is used by at least one manufacturer. Sulphuric acid gives a hard, adherent and abrasion- resistant coating, but there are problems in getting satisfactory adhesion of some attractive sensitive coatings (for example polyvinyl cinnamate among negative-based resists amongst positive-working coatings). Phosphoric acid anodising gives much better adhesion with these and some other coatings, but the anodic coating is much softer and tends to abrade away during printing to an extent that may limit the number of copies that can be taken off the plate.
  • In some cases aluminium foil that has been anodised in sulphuric acid has been treated subsequently with phosphoric acid, and this has been found to give a useful improvement in adhesion while retaining part of the advantages of the use of sulphuric acid for anodising, but this prevents obvious difficulties in control of the operation.
  • DE-A 2557222 illustrates the use of an auxiliary electrolytic cell as a mere means for introducing current into a web of aluminium foil for the purpose of anodising it, and US-A 3929591 describes a process in which, prior to being anodised, an aluminium foil is etched in an entirely separate A.C. anodising process.
  • The invention is based in part on the realisation that anodic oxidation takes place at the surface of the metal, not of the coating, and that it will not of itself destroy the existing exposed surface of the coating.
  • In accordance with the invention, a continuous web of aluminium foil is passed through a first bath containing phosphate ions and a second bath containing sulphate ions and is anodised by passing alternating current between a first electrode immersed in the first bath and a second electrode immersed in the second bath.
  • The phosphate and sulphate ions may be the only anions present to any substantial extent in the respective baths, but other anions that are inert or that modify, rather than radically alter, the effect of the treatment may be present. In particular the presence of minor amounts of sulphate in the phosphate bath and/or of phosphate in the sulphate bath is not excluded. We prefer that the associated cations should be wholly or mainly hydrogen ions, but neutral or alkaline salt solutions may be suitable in some cases.
  • The method of the invention avoids the need for rectification equipment and yet allows both positive and negative half-cycles to be used in anodising; because of the superior combination of good adhesion and abrasion resistance, only thin coatings are required for lithographic printing plates, and this avoids any significant difficulty from migration of dye when a coloured sensitive coating is used to obtain a visible image on development.
    • Example
  • The accompanying drawing shows the distinctive part of apparatus for the manufacture of printing plates in accordance with the invention.
  • Aluminium foil web is continuously advanced through the apparatus, and is first slurry-grained in the usual way, etched in a bath comprising 5 9/1 sodium hydroxide and 5 g/I sodium gluconate at 20°C, dwell time in the bath being four minutes; then washed in de-ionised water for four minutes; and the treated for four minutes in a bath containing 22.5 g/I of a brightening agent sold under the designation "Aluminux no. 1 Etch" at 20°C and again washed in de-ionised water for four minutes.
  • Referring now to the drawing, the web 1 is now passed through a first bath 2 containing 45% ortho phosphoric acid and a second bath 3 containing 15% sulphuric acid. Each bath is at 20°C and the dwell time is 4 minutes in each bath. Alternating electric current is supplied to two inert electrodes 4 and 5, one immersed in each bath, the web 1 providing the electrical connection between the two baths. The current density, referred to the area of web (one side) facing the electrode in each bath, is 200 Nm2 at 21 V.
  • After washing in de-ionised water for a further four minutes, a bright and very hydrophilic anodised finish is obtained, which can be coated with conventional photolithographic coatings to give a plate with an excellent combination of coating adhesion and abrasion resistance (press life). Using a proprietary positive-working lithographic resist comprising a resin sensitised with the 2,4 dihydroxybenzophenone ester of 1, 2, 5 diazo naphthol sulphonic acid and coloured with a blue dye yields presensitised plates that were in a satisfactory condition after exposure at 35°C to a relative humidity of 85%; conventional sulphuric acid anodising of comparable thickness gave a plate that became unsuable after about two weeks.
  • It is believed that the benefits of the invention are attributable partly to modification of the pore structure of the anodic oxide coating and partly to the incorporation into the coating of small quantities of phosphate ions.

Claims (4)

1. A method of anodically treating a continuous web of aluminium foil comprising passing it through a first bath containing phosphate ions and a second bath containing sulphate ions and anodising it by passing alternating current between a first electrode immersed in the first bath and a second electrode immersed in the second bath.
2. Anodised aluminium foil anodised by the method claimed in Claim 1.
3. A method of making a presensitised lithographic printing plate comprising anodising a continuous web of aluminium foil and subsequently applying a lithographic photosensitive coating to it, characterised in that the web is anodised by the method claimed in Claim 1.
4. A presensitised lighographic printing plate made by the method claimed in Claim 3.
EP79301378A 1978-07-13 1979-07-12 A process for the anodic treatment of a continuous web of aluminium foil, foil so obtained and its application as a lithographic printing plate Expired EP0007234B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT79301378T ATE885T1 (en) 1978-07-13 1979-07-12 PROCESS FOR THE CONTINUOUS ANODISING OF ALUMINUM FOIL, ALUMINUM FOIL OBTAINED IN THIS WAY AND ITS USE AS A LITHOGRAPHIC PLATE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB2970678 1978-07-13
GB7829706 1978-07-13

Publications (3)

Publication Number Publication Date
EP0007234A2 EP0007234A2 (en) 1980-01-23
EP0007234A3 EP0007234A3 (en) 1980-02-06
EP0007234B1 true EP0007234B1 (en) 1982-04-21

Family

ID=10498400

Family Applications (1)

Application Number Title Priority Date Filing Date
EP79301378A Expired EP0007234B1 (en) 1978-07-13 1979-07-12 A process for the anodic treatment of a continuous web of aluminium foil, foil so obtained and its application as a lithographic printing plate

Country Status (4)

Country Link
EP (1) EP0007234B1 (en)
AT (1) ATE885T1 (en)
DE (1) DE2962554D1 (en)
ES (1) ES482399A1 (en)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2088901B (en) * 1980-10-23 1983-12-07 Vickers Ltd Anodised aluminium sheet for lithographic printing plate production
DE3206470A1 (en) * 1982-02-23 1983-09-01 Hoechst Ag, 6230 Frankfurt METHOD FOR THE PRODUCTION OF CARRIER MATERIALS FOR OFFSET PRINTING PLATES
DE3206469A1 (en) * 1982-02-23 1983-09-01 Hoechst Ag, 6230 Frankfurt METHOD FOR THE PRODUCTION OF CARRIER MATERIALS FOR OFFSET PRINTING PLATES
DE3312497A1 (en) * 1983-04-07 1984-10-11 Hoechst Ag, 6230 Frankfurt TWO-STAGE METHOD FOR THE PRODUCTION OF ANODICALLY OXIDIZED FLAT MATERIALS FROM ALUMINUM AND THE USE THEREOF IN THE PRODUCTION OF OFFSET PRINTING PLATES
DE3328048A1 (en) * 1983-08-03 1985-02-21 Hoechst Ag, 6230 Frankfurt METHOD FOR THE TWO-STAGE ANODIC OXIDATION OF CARRIER MATERIALS MADE OF ALUMINUM FOR OFFSET PRINTING PLATES
CN105624757B (en) * 2016-03-18 2018-01-05 西安交通大学 A kind of industrial frequency AC anodizing of aluminium electrolutic capacitor anode aluminium foil
CN105803505B (en) * 2016-03-18 2018-01-05 西安交通大学 A kind of frequency-changing AC anodizing of aluminium electrolutic capacitor anode aluminium foil

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1621115C3 (en) * 1967-10-17 1981-06-25 Metalloxyd GmbH, 5000 Köln Process for the production of an aluminum support for lithographic printing plates
US3929591A (en) * 1974-08-26 1975-12-30 Polychrome Corp Novel lithographic plate and method
CA1112600A (en) * 1975-11-13 1981-11-17 Shyoichi Anada Electrolytically treating aluminium surface in bath of hydroxide or salt with acid

Also Published As

Publication number Publication date
EP0007234A3 (en) 1980-02-06
DE2962554D1 (en) 1982-06-03
ATE885T1 (en) 1982-05-15
EP0007234A2 (en) 1980-01-23
ES482399A1 (en) 1980-04-01

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