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Process for electrochemically roughening aluminum for printing plate supports

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Publication number
CA1209522A
CA1209522A CA 427269 CA427269A CA1209522A CA 1209522 A CA1209522 A CA 1209522A CA 427269 CA427269 CA 427269 CA 427269 A CA427269 A CA 427269A CA 1209522 A CA1209522 A CA 1209522A
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CA
Grant status
Grant
Patent type
Prior art keywords
current
aluminum
alternating
process
aqueous
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
CA 427269
Other languages
French (fr)
Inventor
Engelbert Pliefke
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.)
Hoechst AG
Original Assignee
Hoechst AG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
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Classifications

    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25FPROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00Electrolytic etching or polishing
    • C25F3/02Etching
    • C25F3/04Etching of light metals
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41NPRINTING 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 In this subclass the COPES System is used
    • B41N3/00Preparing for use and conserving printing surfaces
    • B41N3/03Chemical or electrical pretreatment
    • B41N3/034Chemical 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
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S204/00Chemistry: electrical and wave energy
    • Y10S204/09Wave forms

Abstract

ABSTRACT OF THE DISCLOSURE

Disclosed is a process for electrochemically roughening aluminum or alloys thereof, in an aqueous electrolyte, under the action of an alternating current which is generated by superimposing at least two types of alternating current of different frequencies.The materials roughened in this manner are used as supports for radiation sensitive reproduction coatings in the field of manufacturing offset-printing plates. Also disclosed are roughened aluminum supports and printing plates produced by the above process.

Description

s~

PROCESS FOR ELECTROCHEMICALLY ROUGHENING
ALUMINUM FOR PRINTING PLATE SUPPORTS

BACKGROUND OF THE INVENTION

The present invention relates to a process for electrochemically roughening aluminum for use as printing plate supports. In particular, roughening of the aluminum support which is present in an acid and/or salt electrolyte is effected by an alter-nating current.
Printing plates, used herein to refer to offset-printing plates, usually comprise a support and at least one radiation-sensitive (photosensitive) reproduction coating arranged thereon. The reproduc-tion coating is applied to the support either by the user, in the case of plates which are not pre-coated, or by the industrial manufacturer, in the case of pre-coated plates. Aluminum or an alloy thereof has gained acceptance as a support material in the field of printing plates. In principle, it is possible to , .

- - ~ 2~5ZZ

2 ~

use the supports without pretreatment and modification;
however, they are generally modified in or on their surfaces, for example, by a mechanical, chemical and/or electrochemical roughening process, sometimes referred to as graining or etching in liter~ture, a chemical or electrochemical oxidation process and/or a treatment with hydrophilizing agents. In modern continuously working high~speed equipment employed by the manufacturers of printing plate supports and/or pre~coated printing plates, a combination of the aforementioned modifying methods is Erequently used, particularly a combination of electrochemical roughening and anodic oxidation, optionally followed by a hydrophilizing step. Roughening is, for example, carried out in aqueous acids, such as aqueous solu-tions of HCl or HNO3 or in aqueous salt solutions, such as aqueous solutions of NaCl or Al(N03)3, using alternating current. The peak to-valley roughnesses o the roughened surface, which are defined as mean peak-to-valley roughnesses, Rz, are in the range from about 1 to 15 ~m, particularly from 2 to 8 ~m. The peak-to~valley roughness is determined accordLng to DIN 4768, October 1970, as the arithmetic mean of the individual peak-to-valley roughness values oE Eive mutually adjacent lndividual measurement lengths.
Roughening is carried out, inter alia, in order to enhance the adhesion of the reproduction coating to the support and to improve the water acceptance of the printing form, which results from irradiating and developing the printing plate. By irradiating and developing, or decoating in the case of electro-photographically working reproduction coatings, the ink-receptive image areas and the water-retaining non-image areas, the latter generally being the uncovered support surface, are produced on the prlnting plate in the subsequent printing operation, thus producing the actual printing form. The final topography of the aluminum surface which is to be roughened is influenced by various parameters, as is explained, by way of example, in the text which follows.
The paper, "The Alternating Current Etching of Aluminum Lithographic Sheet", by A. J. Dowell, published in Transactions of the Ins-titute of Metal Finishing, 1979, Vol. 57, pages 138 to 144, presents basic comments on the roughening of aluminum in aqueous solutions of hydrochloric acid, based on variations of the following process parameters and an lnvestigation of the corresponding effects. The electrolyte composition is changed during repeated use of the electrolyte, for example, in view of the H (H30+) ion concentration (measurable by means of the pH) and the Al3~ ion concentration. As a result of these changes, influences on the surface topography are observed. Temperature variations do not effect changes until temperatures are 50 C
or higher, ~he effect becoming apparent, for example, as a significant decrease in film formation on the surface. Variations in roughening time between 2 and 25 minutes lead to an increasing metal dissolution 5~2 with increasing duratiorl of action. Variations in current density between about 2 and B A/dm2 result in higher roughness values with rising current density.
If the acid concentration is in the range from about 0.17 to 3.3~ of HCl, only negligible changes in pit structure occur between about 0.5 and 2~ of HCl.
Below 0.5~ of HCl, the surface is only locally attacked and at the high values, an irregular dissolu-tion of A1 takes place. An addition of S042 ions or Cl- ions in the form of salts, e.g~, by adding Al?(SO4)3 or NaCl, can also influence the topography of the roughened aluminum. Rectification of the alternating current shows that both half-wave types are necessary to obtain a uniform roughening. The influence of frequency changes or of superpositions of currents oE di~ferent frequencies ~r-e-~ot investigated;
a constant frequency of about 50 Hz was utilized.
The influence of the ~lectrolyte composition on the quality of roughening is, for example, also ~escribed in the following publications, in which standard alternating current having a frequency from about 50 to 60 H~ is used:

- German Offenlegungsschrift No. 2,250,275 ~ = British Patent No. 1,400,918) specifies aqueous solutions containing from 1.0 to 1.5% by weight of ~NO3 or from 0.4 to 0.~% by weight of HCl and optionally from 0.4 to 0.6% by weight of H3PO4, for use as electrolytes in the roughening of aluminum for printing plate supports by means of an alternating current, - German OffenlegungsschriEt Wo. 2,810,308 ( = UOS. Patent No. 4,072,589) mentions aqueous solutions containing from about 0.2 to 1.0% by weight of HCl and from 0.8 to 6.0~ by weight of HNO3 as electrolytes in the roughening of aluminum with alternating current, - German Auslegeschrift No. 1,238,049 ( = U.S. Patent No. 3,330,743) mentions protective colloids acting as inhibitors, for example, lignin, benzaldehyde, acetophenone or pine needle oil, as additional components in aqueous HNO3 solutions used in the roughening of aluminum for printing plate supports with alternating current, U.S. Patent No~ 3,963,594 specifies aqueous solutions containing HCl and gluconic acid as electrolytes in the electrochemical roughening of aluminum for printing plate supports.

Admittedly, the use of aqueous solu~ions comprising several components to roughen aluminum may lead to more or less uniformly roughened surfaces, but monitoring the bath composition is very expensive, particularly in the case of the presently preferred continuously working high-speed processing equipment for strips. This measure, however, is necessary in practice, since the composition of the electrolyte often changes in the course of the process.

~ll2~522 Another known possibility for improving the uniformity of electrochemical roughening comprises a modification of the type of electric current employed, including, for example, - using an alternating current, in which the anodic voltage and the anodic coulombic input are hiyher than the cathodic voltage and the cathodic coulombic input, according to German Auslegeschrift No. 2,650,762 ( = U.S. Patent No. 4,087,341~, the anodic half-cycle period of the alternating current being generally adjusted to be less than the cathodic half-cycle period. This method is, for example, also referred to in German Offenlegungs-schrift No. 2,912,060 ( = U.S. Patent NoO
4,301,229), German Offenlegungsschrift No. 3,012,135 ( = published UK Patent Appllcation No. 2,047,274) or German Offenlegungsschrift No. 3,030,815 ( = U~S.
Patent No. 4,272,342), - using an alternating current, in which the anodic voltage is markedly increased compared with the cathodic voltage, according to German Offenlegungs-schrift No. 1,446,026 ( = U.S. Patent No. 3,193,485), - interrupting the current flow for 10 to 120 seconds and re-applying current for 30 to 300 seconds, using alternating current and, as the electrolyte, an aqueous solution of 0.75 to 2.0 N HCl, with the addition of NaCl or MgC12, according to ~ritish Patent No. 879,768. A similar process comprising 52;~

an interruption of current flow in the anodic or cathodlc phase is also disclosed in German Offenlegungsschrift No. 3,020,420 ( = U.S~ Patent No. 4,294,672).

The aforementioned methods may lead to relatively uniormly roughened aluminum surfaces, but each requires a comparatively great equipment expen-diture and, in addition, are applicable only within closely limited parametersO

SU~MARY OF THE INVENTION

It is therefore an object of the present invention to provide a process for electrochemically roughening aluminum, which is carried out using an alternating current and which leads to a roughening structure oE a uniformity such that the aluminum can be used as a printing plate support It is another object oE the present invention to provide a process for producing a printing plate having a uniformly roughened aluminum support.
It is yet another object of the present invention to provide a process for electrochemically roughening aluminum which can be performed in various electrolytes.
It is still another object of the present invention to provide a process for electrochemically roughening aluminum which can be performed using alternating currents having widely varying frequencies.

According to one aspect of -the present invention there is provided a process for electrochemically roughening aluminum or alloys thereof for use as printing plate supports, comprising -the step of elec-trochemically roughening aluminum or an aluminum alloy in an aqueous electrolyte with an alternating current genera-ted by superimposing at least two types of alternating current having different frequencies, wherein said frequency or frequencies of said higher~frequency superimposed al-terna-ting current(s) is/are from 3 to 100 times greater than said frequency of said super-imposed alternating current having the lowest frequency and theratio of the amplitudes of said higher-frequency superimposed alternating current(s) to said lowest-frequency superimposed alternating current ranges between about 0.1 and 10.
In accordance with another aspect of the present inven-tion, there has been provided a roughened aluminum support produced by the above-mentioned process.
In accordance with still another aspect of the present invention, there has been provided a process for producing printing plates, comprising the steps of providing an aluminum or aluminum alloy support, contacting the support with an aqueous electrolyte, applying to the support an alternating current generated by superimposing at least two types of alternating curren-t having different frequencies to produce a roughened alumi-num support, and coating the roughened support with a radiation-sensitive reproduc-tion coa-ting, wherein the frequency or frequen-cies of the higher-frequency alternating current is/are from 3 to 100 times greater than the frequency or frequencies of the lower-S~2 - 8a -frequency alternating current, the ratio of amplitudes of the higher and lower frequency alternating curren-ts is -from 0.1 -to 10 and the current density is between 3 and 100 A/dm2.
In accordance with yet another aspect of the present invention, there has been provided a printing plate produced by the above-mentioned processO
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments which follows.

DETAILED _ SCRIPTION OF PREE'ERRED EMBODIMENTS
The process of the invention can be carried out either continuously or discontinuously; however, a continuous process is preferred. The process utili-zes strips of aluminum or aluminum alloys. In continuous processes, the process parameters during roughening are generally within the following ranges: tempera-ture of the electrolyte between about 20 and 60C, electrolyte (acid and/or salt) concentration between about 1 and 250 g/l, particularly between about 5 and 100 g/l, current density between about 3 and 130 A/dm , dwell time of a ma-terial spot to be roughened in the electrolyte between about 10 and 300 seconds, and rate of flow of the electrolyte on the surface of the material to be roughened between about 5 and 100 cm/second. As mentioned above, the ratio of the amplitudes of the higher-frequency superimposing alternating current(s) to the lowest-frequency al-ternating current ranges between about 0.1 and 10, particularly between about 0.2 and 2.

_ 9 _ ~,2~ 2 - 9a -Appropriately, only two alternating currents with different frequencies are superimposed upon each other in the process of the invention. The type of alternating current used may have a rectangular, trapezoidal or sinusoidal shape, a combination of rectangular shape for the alternating current having the lower frequency and sinusoidal shape for the alternating current having the higher frequency being preferred in the process according to the invention. In discontinuous processes, the required current densities are in the lower region and the dwell times in the upper region of the ranges indicated in each case.
Additionally, a flow of the electrolyte can even be dispensed with in these processes. In addition to the electrolytes, for example aqueous solutions of HCl and/or HNO3, which have been previously mentioned, it is also possible to use aqueous salt solutions, for example, as described in German Patent No. 2,537,724 ( = British Patent No. 1,532,303) 5~Z

or in German Patent No. 2,527,725 ( = U.S. Patent No.
4,166,015). Suitable apparatus for t'ne continuous performance of the process according to the invention are, for example, disclosed in German Patent No.
2,234,365 ( = U.S. Patent No. 3,880,744) or in German Patent No. 2,234,424 ( = UOS. Patent No. 3,871,982).
The following materials which may be in the form of a sheet, a foil or a strip and which were employed in the examples which follow are, for example, used for roughening in the process of the invention:

- "Pure aluminum" (DIN Material No. 3.0255), i.eO, composed of not less than 99.5~ Al, and the following permissible admixtures (maximum total 0.5~) of 0.3~ Si, 0.4% Fe, 0O03~ Ti, 0.02% Cu, 0.07~ Zn and 0.03~ of other substances, or - "Al-alloy 3003" (comparable to DIN Material No.

3.0515), i.e, composed of not less than 98.5~ Al, O to 0.3~ Mg and 0.8 to 1.5% Mn, as alloying constituents, and 0.5~ Si, 0.5~ Fe, 0.2~ Ti, 0.2 Zn, 0.1% Cu and 0015% of other substances, as permissible admixtures.

The electrochemical roughening process according to the present invention may be followed by an anodic oxidation of the aluminum in a further pro-cess step, in order to improve, for example, the abra-sive and adhesive properties of the surface of the _ 1 _ support material. Conventiorlal electrolytes, such as H2SO~, H3P04, H~C2O4, amidosulfonic acid, sulfosuc-cinic acid, sulfosalicylic acid or mixtures thereof~
may be used for the anodic oxidation. The following are standard methods for the use of aqueous, H2SO4-containing electrolytes for the anodic oxidation of aluminum (see, in this regard, e.g. M. Schenk, Werkstoff Aluminium und seine anodische Oxydation (The Material Aluminum and its ~nodic Oxidation), Francke Verlag, Bern, 194B, pa~e 760; Praktische Galvanotechnik (Practical Electroplating), Eugen G.
Leuze Verlag, Saulgau, 1970, pages 395 et seq., and pages 518/519; W. Huebner and C.T. Speiser, Die Praxis der anodischen Oxidaticn des Aluminiums (Practical Technolog~ of the Anodic Oxidation of Aluminum), Aluminium Verlagr Duesseldorf, 1977, 3rd Edition, Qages 137 et seq.):

- The direct current sulfuric acid process re~ers to a process in which anodic oxidation is carried out in an aqueous electrolyte which conventionally contains approximately 230 g of H2SO4 per 1 liter of solution, for 10 to 60 minutes at 10 to 22C, and at a current density of 0.5 to 2.5 A/dm2. In ~his process, the sulfuric acid concentration in the aqueous electrolyte solution can also be reduced to 8 to 10% by weight of H2SO~ (about 100 g of H2S04 per liter~, or it can also be increased to 30% by weight (365 g of H2SO4 per liter), or more.

52~

- The "hard-anodizing process" is carried out using an aqueous electrolyte, containing H2SO4 in a con-centration of 166 g of H2SO~ per liter (or about 230 g Oe ~2SO4 per liter), at an operating tem-S perature of 0 to 5C, and at a current density of 2 to 3 A/dm2, for 30 to 200 minutes, at a voltage which rises from approximately 25 to 30 V at the beginning of the treatment, to approximately 40 to 100 V toward the end of the treatment.

In addition to the processes for the anodic oxidation of printing plate support materials which have already been mentioned in the preceding paragraph, the following processes can, for example, also be used: the anodic oxidation of aluminum in an a~ueous, H2SO4-containing electrolyte, in which the content of A13~ ions is adjusted to values exceeding 12 g/l (according to German OffenlegungsschriEt No~
2,811,39fi = U.S. Patent No 4,211,61g), in an aqueous electrolyte containing H2SO4 and H3PO4 (according to German Offenlegungsschrift No. 2,707~810 = U.S. Patent No. 4,049,504), or in an aqueous electrolyte containing H2SO4, H3PO~ and A13~ ions (according to German OffenlegungsschriEt No~ 2,836,803 - U.S. Patent No.

4,229,226). Direct current is preferably used for the anodiG oxidation, but it is also possible to u~e alternating current or a combination of these types of current (for example, direct current with superimposed alternating current). The layer weights of aluminum oxide range from about 1 to 10 g/m2~ which corresponds ~A~ ~ 5 2 to layer thicknesses from about 0.3 to 3.0 ~m. After the electro-chemical roughening s-tep and prior to an anodic oxidation step, an abrasive modification of the roughened surface may additionally be performed, as described, for example, in German Offenlegungs-schrift No. 3,009,103 (Filed: March 10, 1980, Published:
September 24, 1981, Applicant: ~OECHST AKTIENGSELLSCHAFT, Inven-tor: Frass et al). A modifying intermediate treatment of this kind can, inter alia, enable the formation of abrasion-resistant oxide layers and reduce the tendency to scumminy in the subsequent printing operation.
The anodic oxidation of the aluminum support material for printing plates is optionally followed by one or more post-treating stepsO Post-treating is particularly understood to be a hydrophilizing chemical or electrochemical treatment of the alumi-num oxide layer, for example, an immersion treatment of the material in an aqueous solution of polyvinyl phosphonic acid according to German Patent No. 1,621,478 ( = British Patent No. 1,230,447), an immersion treatment in an aqueous solution of an alkali-metal silicate according to German Auslegeschrift No. 1,471,707 ~= U.S. Patent No. 3,181,461), or an electrochemical treatment ~anodiza-tion) in an aqueous solution of an alkali-metal silicate according to German OffenlegungsschriEt No. 2,532,769 ~=
U.S. Patent No. 3,902,976). These post-treatment steps serve, in particular, to even further improve the hydrophilic properties of the aluminum oxide layer, which are already sufficient for many fields of application, while maintaining the other well-known properties of the layer.

52~:

Suitable photosensitive reproduction coatings hasically comprise any coatings which, after exposure, optionallv followed hy development and/or fixins, yield a surface in image con~iguration, which can be used for printing and/or which represents a relief image of an original. The coatings are applied to one of the support materials roughened according to the present invention, either by the manuEacturers of presensitized printing plates or so-called dry resists or directly by the user. The photosensltive reproduc-tion coatings include those which are described, for example, in "Light-Sensitive Systems", by Jaromir Kosar, published by John Wiley & Sons, New York, 1965.
These include coatings containing unsaturated compounds, which, upon exposure, are isomerized, rearranged, cyclized, or cross-linked (Kosar, Chapter 4); coatings containing compounds; e.g. monomers or prepolymers, which can be photopolymerized, which, on being ex~osed, undergo polymerization, optionally with the aid o an initiator (Kosar, Chapter 5); and coatings containing o-diazoquinones, such as naphthoquinone-diazides, p-diazoquinones, or condensation products of diazonium salts (Kosar, Chapter 7)~
Other suitable coatings include the electro-photographic coatings, i.e. coatings which contain an inorganic or organic photoconductor. In addition to the photosensitive substances, these coatings can~ of course, also contain other constituents, such as for example, resins, dyes, pigments, wetting agents, sensitizers, adhesion promoters, indicators, plasticizers or other conventional auxiliar~ agents.

In particular, the following photosensitive composi-tions or compounds can be employed in -the coating of support materials:
positive-working o-quinone diazide compounds, preferably o-naphthoquinone diazide compounds, which are clescribed, Eor example, in German Patents No. ~54,890, ~o. 865,109, No. 879,203, No. 894,959, No. 938,233, No. 1,109,521, ~o. 1,144,705, No. 1,118,606 No. 1,120,273 and ~o. 1,124,817:
negative-working condensation products from aromatic diazo-nium salts and compounds with active carbonol groups, preferablycondensation products formed from diphenylaminediazonium salts and formaldehyde, which are described, for example, in German Patents NoO 596,731, No. 1,138,399, No. 1~138,400, No. 1,138,401, ~o. 1,142,871, and ~o. 1,154,123, U.S. Patents No. 2,679,498 and No. 3,050,502 and British Patent No. 712,606;
negative-working co~condensation products of aromatic dia.æo~
nium compounds, for example, according to German Offenlegungs-schrift ~o. 2,024,244 (Filed: 05/19/1970; Published: 11/26/1970;
Applicant: Azoplate Corporation; Inventor Teuscher), which possess, in each case at least one unit of the general types A(-D)n and B, connected by a divalent linking member derived from a carbonyl compound which is capable of participating in a condensation reaction. In this context, these symbols are defined as follows: A is the radical of a compound which contains at least two aromatic carbocyclic and/or heterocyclic nuclei, and which is capable, in an acid medium, of participating in a condensation reaction with an active carbonyl compound, at one or more positions.

~'~ 1 ~
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D is a diazonium salt group which is bonded to an aromatic carbon atom of A; n is an integer from 1 to 10, and B is the radi-cal of a compound which con-tains no diazonium yroups and which is capable, in an acid medium, o-E participating in a condensation reaction with an active carbonyl compound, at one or more posi-tions on the molecule;
posi-tive-~orking coatings according to German Offenlegungs-schrift No. 2,610,842 (Filed: 03/15/1976; Published: 09/30/1976, Applicant: Hoechst AG; Inventor: Buhr et al), which contain a 10 compound which, on being irradiated, splits off an acid, a compound which possesses at least one C-O-C group, which can be split off by acid (e.g., an orthocarboxylic acid ester yroup, or a carboxamide-acetal group), and, if appropriate, a bindex;
negative-working coatings, composed of photopolymeri7able monomers, photo-initiators, binders and, if appropriate, further additives. In these coatings, for example, acrylic and methacryl-ic acid esters, or reaction products of diisocyanates with partial esters of polyhydric alcohols are employed as monomersi as described, for example, in U.S. Patents No. 2,760,863 and 20 Mo. 3,060,023, and in German Offenlegungsschrift No. 2,064,079 (Filed: 12/28/1970; Published: 07/13/1972; Applicant: Kalle AG;
Inventor: Faust) and No. 2,361,041 (Filed: 12/07/1973; Published:
06/12/1975, Applican-t: Hoechst AG; Inventor: Faust). Suitable photo-initiators are inter alia, benzoin, benzoin ethers, poly-nuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives, or synergistic mix-tures of various ketones. A large number of soluble organic polymers can be employed as binders, for example, polyamides, polyesters, alk~d resins, polyvinyl alcohol, polyvinyl-pyrroli-done, polyethylene oxide, gelatin or cellulose ethers;
negative-working coatings according to German Offenle~ungs-schrift No. 3,036,077 (Filed: 09/25/1980, Applicant: Hoechst AG;
Inventor: Bosse et al), which contain, as the photosensitive compound, a diazonium salt polycondensation product, or an organic azido compound, and which contain, as the binder, a high-molecular weight polymer with alkenylsulfonylurethane or cycloalkenylsulfon-ylurethane side groups.
It is also possible to apply photo-semiconducting coa-tings to the support materials, such as described, ~or example, in German Patents No. 1,117,391, No. 1,522,~97, No. 1,572,312, ~o.
2,322,046 (Filed: 05/02/1973; Published: 11/07/1974; Applicant:
Hoechst AG; Inventor: Lind et al) and No. 2,322,047 (Filed:
05/02/1973; Published: 11/07/1974; Applicant: Hoechst AG, Inven-tor: Lind et al), as a result of which highly photo-sensitive electrophotographic coatings are produced.
The materials for printing plate supports, which have been roughened according to the process of the invention, exhibit a uniform topography, which positively influences the stability of print runs and -the water acceptance during printing with printing forms manufactured from these supports. Compared with the use of only one type of alternating current, "pitting" (pronounced depressions, in comparison to the surrounding roughening) occurs less fre~uently and can even be completely suppressed. These surface characteristics can be produced without great equipment S2~
- 17a -expenditure and without continuously monitoring the quality and quantity of the bath. Possibly, the formation of a more uniform roughening can be ascribed to the fact that the gas bubbles which are formed on the aluminum surface in the electrochemical reaction can more easily detach from the surface.

5~

The present invention is explained in further detail by the following non-limiting examples wherein percentages denote percentages by weight, unless otherwise stated. Parts by weight are related to parts by volume as the g is related to the cm3.

Examples l to 35 and Com~arative Examples C1 to C8 In the examples and comparative examples which follow, the alternating carrier current used was, with the exception of Example 7, a rectangular current and the superimposing alternating current was a sinusoidal current. In Example 7 a sinusoidal current was also used as the alternating carrier current.
An aluminum sheet was Eirst pickled in an aqueous solution containing 20 g/l of NaOH, at room temperature, for a duration of 60 seconds, and was then freed from any alkaline residue which may have been present, by briefly dipping into a solution corresponding to the electrolyte used for roughening.
Roughening was carried out in the specified electrolytes, either with galvanostatic or potentio-static control, in the latter case, the reference electrode was either the saturated system Ag/AgCl (Examples 32, C8, 34 and 35) or the counter electrode (Example 33). Examples l to 31 and Cl to C7 were galvanostatically controlled (Table I) and Examples 32 to 35 and C8 (Table II) were potentiostatically controlled.

~2~$5~2 Classification into quality grades (surface topography) was made by visual assessment under a microscope, a homogeneously roughened surface which was free from pitting was assigned quality grade "ln.
A surface with severe pitting of a size exceeding 100 ~m or with an extremely nonuniformly roughened surface was assigned quality grade "10". The electro-lytes used in the examples had the following compositions:

10 Electrolyte A: 1.0 part by weight oE HNO3 and . .
5.0 parts by weight of Al(NO3)3 9 H2O per 100 parts by volume of aqueous solution;

ElectrolYte B: 1.5 parts by weight of HNO3 and 7.0 parts by weight o:E Al(NO3)3~9 H2O
per 100 parts by volume of aqueous solution;

Electrolyte C: 2.0 parts by weight of HNO3 and 9.0 parts by weight of Al(NO3j3~9 H2O
per 100 parts by volume of aqueous solution;

Electrolyte D: ~3~ strength aqueous soluton of HCl;

Electrolyte E: 3% strength aqueous solution of HCl containing 1.0 part by weight of AlC13 per 100 parts by volume oE
solution and Electrolyte F: 5% strength aqueous solution of HCl.

i2Z

-- ~o --Electrolysis was started with the electro-lyte being at room temperature. A comparison of suraces treated with an alternating current comprising a carrier current and superimposing current o~ higher frequency with surfaces treated with only one type of alternating current of uniform frequency, under process conditions which are otherwise iden-tical, clearly showed a more homogeneously roughened surface in the former surface.

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~1.21:!$S~2 - 2~ -Example 36 An aluminum sheet which had been roughened in accordance with Example 2 was anodically oxidized in an electrolyte comprising H2S04 and A12(S04)3, as specified in German Offenlegungsschrift No. 2,811,396, until a 2.8 ~m thick oxide layer was obtained. The roughened and anodically oxidized aluminum support was then coated with the following negative-working photo-sensitive coating.

0.70 part by weight of the polycondensation product of 1 mole of 3-methoxy diphenylamine-4-diazonium sulfate and 1 mole of 4,4'-bis-methoxymethyl-diphenyl ether r precipitated as the mesitylene sulfonate, 3.40 parts by weight of 85% strength H3P04, 3.00 parts by weight of a modified epoxide resin, obtained by reacting 50 parts by weight of an epoxide resin having a molecular weight of less than 1,000 and 12.8 parts by weight of benzoic acid in ethylene glycol monomethyl ether, in the presence of benzyltrimethylammonium hydroxide, 0.44 part by weight of finely-ground Heliogen Blue G (C.I. 74 100), 62.00 parts by volume of ethylene glycol monomethyl ether, 30.hO parts by volume of tetrahydrofuran, and 8.00 parts by volume of butyl acetate.

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- ~.5 -~fter imagewise exposure, the coating was developed with a solution of 2.80 parts by weight of Na2SO4.10~2O, 2.80 parts by weight of MgSO4.7H2O, 0.90 part by weight of 85~
stren~th H3PO~, 0.08 part by weight oE H3PO3, 1.60 parts by weight of a non-ionie wetting agent, 10.00 parts by weight of benzyl alcohol, 20.00 parts by weiqht of n-propanol, and 60.00 parts by weight o water.

It was possible to print 125,000 copies from this printing form.

_ompaLative Example C9 A printing plate which was anodically oxi-dized and coated as specified ln Example 36~ but which was roughened at 50 Hz, upon development, resulted in a printing form which yielded a print run o only 75,000 copies.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for electrochemically roughening aluminum or alloys thereof for use as printing plate supports, comprising the step of electrochemically roughening aluminum or an aluminum alloy in an aqueous electrolyte with an alternating current generated by superimposing at least two types of alternating current having different frequencies, wherein said frequency or frequencies of said higher-frequency superimposed alternating current(s) is/are from 3 to 100 times greater than said frequency of said superimposed alternating current having the lowest frequency and the ratio of the amplitudes of said higher-frequency superimposed alternating current(s) to said lowest-frequency superimposed alternating current ranges between about 0.1 and 10.
2. A process as claimed in claim 1, wherein said ratio ranges between about 0.2 and 2.
3. A process as claimed in claim 1, wherein, when super-imposing two types of alternating current, said lower-frequency superimposed alternating current comprises a rectangular shape and said higher-frequency superimposed alternating current comprises a sinusoidal shape.
4. A process as claimed in claim 1, wherein said aqueous electrolyte solution comprises HCl.
5. A process as claimed in claim 1, wherein said aqueous electrolyte solution comprises HNO3.
6. A process as claimed in claim 1, wherein said process is continuously performed.
7. A process as claimed in claim 1, wherein said process is discontinu-ously performed.
8. A process as claimed in claim 1, further comprising the step of anodic-ally oxidizing said aluminum support to produce an aluminum oxide layer.
9. A process as claimed in claim 8, further comprising the step of post-treating said support.
10. A process as claimed in claim 9, wherein said post-treating step com-prises a hydrophilizing treatment of said aluminum oxide layer.
11. A process as claimed in claim 10, wherein said hydrophilizing treatment comprises a chemical treatment.
12. A process as claimed in claim 10, wherein said hydrophilizing treatment comprises an electrochemical treatment.
13. A process as claimed in claim 8, further comprising the step of abrasi-vely modifying said roughened surface prior to said anodically oxidizing step.
14. A process as claimed in claim 1, wherein the temperature of said elec-trolyte ranges from about 20 to 60°C.
15. A process as claimed in claim 1, wherein said support is uniformly roughened.
16. A roughened aluminum support produced by the process defined by claim 1.
17. A process for producing printing plates, comprising the steps of:
providing an aluminum or aluminum alloy support;
contacting said support with an aqueous electrolyte;
applying to said support an alternating current generated by superimpo-sing at least two types of alternating current having different frequencies to produce a roughened aluminum support; and coating said roughened support with a radiation-sensitive reproduction coating, wherein the frequency or frequencies of the higher-frequency alternating current is/are from 3 to 100 times greater than the frequency or frequencies of the lower-frequency alternating current, the ratio of amplitudes of the higher and lower frequency alternating currents is from 0.1 to 10 and the current density is between 3 and 100 A/dm2.

18. A printing plate produced by the process defined in
claim 17.
CA 427269 1982-05-10 1983-05-03 Process for electrochemically roughening aluminum for printing plate supports Expired CA1209522A (en)

Priority Applications (2)

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DE19823217499 DE3217499A1 (en) 1982-05-10 1982-05-10 Process for the electrochemical roughening of aluminum for druckplattentraeger
DEP3217499.3 1982-05-10

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CA1209522A true CA1209522A (en) 1986-08-12

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JP (1) JPH0568560B2 (en)
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JPH0517876B2 (en) * 1985-10-04 1993-03-10 Fuji Photo Film Co Ltd
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JP3117322B2 (en) * 1993-04-05 2000-12-11 富士写真フイルム株式会社 Method for producing a photosensitive planographic printing plate and its support
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US5500101A (en) * 1993-12-28 1996-03-19 Nihon Chikudenki Kogyo Kabushiki Kaisha Method of etching aluminum foil for electrolytic capacitor
EP0689096B1 (en) 1994-06-16 1999-09-22 Kodak Polychrome Graphics LLC Lithographic printing plates utilizing an oleophilic imaging layer
US20030032879A1 (en) * 1997-07-07 2003-02-13 Steven Quay Microbubble formation using ultrasound
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EP0093961A1 (en) 1983-11-16 application
JPH0568560B2 (en) 1993-09-29 grant
JPS58207374A (en) 1983-12-02 application
CA1209522A1 (en) grant
DE3217499A1 (en) 1983-11-10 application
US4468295A (en) 1984-08-28 grant
EP0093961B1 (en) 1987-06-10 grant
JP1853801C (en) grant

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