Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/02—Etching
  • C25F3/04—Etching of light metals
• • 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

Definitions

• This invention relates in general to the treatment of aluminum surfaces and in particular to the treatment of aluminum sheet material to render it suitable for use in the production of lithographic printing plates. More specifically, this invention relates to an improved process for carrying out
• the art of lithographic printing is based upon the immiscibility of oil and water, wherein the oily material or ink is preferentially retained by the image area and the water or fountain solution is preferentially retained by the non-image area.
• the background or non-image area retains the water and repels the ink while the image area accepts the ink and repels the water.
• the ink on the image area is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth and the like.
• ink is transferred to an intermediate material called the blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
• Aluminum has been used for many years as a support for lithographic printing plates. In order to prepare the aluminum for such use, it is typical to subject it to both a graining process and a subsequent anodizing process.
• the graining process serves to improve the adhesion of the subsequently applied radiation-sensitive coating and to enhance the water- receptive characteristics of the background areas of the printing plate.
• the graining affects both the performance and the durability of the printing plate, and the quality of the graining is a critical factor determining the overall quality of the printing plate. A fine, uniform grain that is free of pits is essential to provide the highest quality performance.
• electrolytic graining which is also referred to in the art as electrochemical graining or electrochemical roughening, and there have been a great many different processes of electrolytic graining proposed for use in lithographic printing plate manufacturing. Processes of electrolytic graining are described, for example, in U. S. patents 3,755,116, 3,887,447, 3,935,080,
• the aluminum is treated, so as to increase its surface area and create a specific surface structure, by passing an electric current - - usually an alternating electric current - - from an electrode through an acid
• the aluminum that is conveyed through the electrolyte solution is in the form of a thin continuous web that may have a width of as much as two or more meters. It is desirable to grain the surface with a high efficiency in regard to both electric power and chemical consumption, while at the same time achieving proper grain morphology without excessive formation of adhering reaction by-products, commonly referred to as "smut".
• smut adhering reaction by-products
• the presence of smut can necessitate an aggressive etch treatment, following the graining operation, which can further modify the surface in an unwanted manner. It is therefore highly desirable to operate the process in such a way that a minimal amount of smut is formed, and that which is formed is loosely bound and easily removed.
• hydrochloric acid in admixture with the respective aluminum salt thereof.
• Other acids and many other types of chemical agents are also known for use in electrolytic graining baths.
• Electrodes most commonly formed of graphite, are positioned to oppose the aluminum web at a distance ranging from about one-half centimeter to several centimeters. Either single phase or three phase alternating current is passed through the electrolyte so that at the interface between the solution and the aluminum, a displacement reaction occurs whereby aluminum is oxidized to form either the chloride or nitrate salt which is soluble in the solution. By removing aluminum with the use of an electric current, a specific surface structure is obtained. Parameters such as temperature, electrolyte concentration, flow rates and electrode spacing are important in determining the characteristics of the surface structure produced.
• Q 1 , Q 2 , and Q 3 represent, respectively, the quantity of electricity per unit area of application during the first one-third period, the intermediate one-third period and the final one-third period of the total electrolytic graining time. This method of control of current density distribution is said to reduce the total quantity of electricity required and to provide improvement in the quality of grain
• an improved two-stage process i.e., a process employing first and second stages in which treatment conditions are different -- for the electrolytic graining of the surface of aluminum.
• the aluminum is immersed in an acidic electrolyte solution while it is subjected to an alternating electric
• D 1 and D 2 respectively represent current density in amps/dm 2 in the first and second stages
• t 1 and t 2 respectively represent treatment time in seconds in the first and second stages
• Q 1 and Q 2 respectively represent current consumption in coulombs/dm 2 in the first and second stages.
• the invention also includes within its scope an aluminum article, such as aluminum sheet material, having a surface which has been electrolytically grained by the two-stage process and a lithographic printing plate comprising a support composed of such grained aluminum sheet material and at least one radiation-sensitive layer capable of forming a
• current density is at least as great and preferably substantially greater in the first stage than in the second stage, whereas time is longer in the second stage than in the first stage.
• Current density and time in each stage must not only satisfy the ratios specified above, but must be so selected that Q 1 (which is equal to the product of D 1 and t 1 ) is less than Q 2
• aluminum as used herein is intended, as the context requires, to include both pure aluminum and aluminum alloys, which are capable of being grained electrolytically. Suitable alloys of aluminum include alloys containing minor amounts of any of silicon, iron, copper, manganese, magnesium, zinc, titanium, chromium, nickel and the like.
• the surface of the aluminum Prior to electrolytic graining, the surface of the aluminum is cleaned to remove oil, dirt and grease therefrom. Suitable solvents and/or caustic solutions for carrying out such cleaning are well known in the art.
• the two-stage electrolytic graining process of this invention is a process which can be carried out in a batch, semi-continuous or continuous manner.
• the aluminum article in a batch operation, can be immersed in a suitable electrolyte solution and an alternating electric current, at an appropriate current density, can be supplied for a sufficient time to complete stage one.
• the current density can then be decreased by appropriate control of the voltage applied and the appropriate time can be selected to complete stage two.
• the process is a continuous one in which aluminum in the form of a continuous web is unwound from a roll and passed successively through the first and second stages of the process, whereupon it is subjected to further treatment such as an anodization process.
• the aluminum can be rewound or it can be subjected to an in-line coating process in which one or more
• radiation-sensitive layers are coated thereon to
• the process of this invention is one in which aluminum articles of any shape or form are subjected in any suitable manner to the two-stage treatment described herein.
• the process of this invention preferably utilizes alternating electric current. Either single phase alternating current or three phase alternating current can be utilized, and alternating current of any suitable wave form can be usefully employed. Direct current can be used, if desired, but it typically provides a less uniform grain.
• the two-stage electrolytic graining process described herein provides a remarkably improved grained surface.
• it provides a fine uniform grain that is essentially free of pits.
• the grained surface is especially well adapted for use as a support for lithographic printing plates.
• the total current consumption i.e., the sum of the current consumed in both stages, is in the range of from about
• D 1 and D 2 respectively represent current density in amps/dm 2 in the first and second stages of the two-stage process.
• t 1 :t 2 is in the range of from about 1:2 to about 1:15, more preferably in the range of from about 1:3 to about 1:10; and most preferably in the range of from about 1:4 to about 1:8; where t 1 and t 2
• treatment time refers to the time that the aluminum is immersed in the electrolyte while disposed opposite the electrode from which it receives the current.
• Q 1 which is the product of D 1 and t 1 and represents current consumption in coulombs/dm 2 is less than Q 2 , which is the product of
• the first stage employs much higher current density and much shorter treatment time, and the second stage employs much lower current density but much longer treatment time.
• the treatment time in each stage is the time that the aluminum article being treated is allowed to remain immersed in the
• travelling at a speed of one hundred meters per minute through a stage that is twenty meters long would be subjected to a treatment time of 12 seconds.
• the first and second stages can be represented by different tanks, or by separate compartments of a single tank, or by zones within a single tank whose length is defined by the electrode or electrodes characterizing that stage.
• the independent variables which are controlled in the process of this invention are time and current density. Voltage is a dependent variable.
• densities for the first stage are in the range of from about 50 to about 100 amps/dm 2
• preferred current densities for the second stage are in the range of from about 15 to about 40 amps/dm 2
• Preferred treatment times for the first stage are in the range of from about 3 to about 10 seconds
• preferred treatment times for the second stage are in the range of from about 20 to about 50 seconds.
• the acidic electrolyte solution used in the electrolytic graining process of this invention can be any electrolyte solution known to be useful in the art.
• Typical solutions include nitric acid in admixture with aluminum nitrate arid hydrochloric acid in admixture with aluminum chloride.
• the acidic electrolyte solution can be maintained at any suitable temperature.
• Typical temperatures are in the range of from about 10°C to about 75°C, and more preferably in the range of from about 20°C to about 50°C.
• a preferred electrolyte solution is a
• hydrochloric acid Typical concentrations for the hydrochloric acid are in the range of from about 0.1 grams per liter to about 30 grams per liter, more preferably from about 1 gram per liter to about 20 grams per liter, and most preferably from about 5 grams per liter to about 15 grams per liter.
• Typical concentrations for the aluminum chloride are from about 1 gram per liter to about 50 grams per liter, more preferably from about 2 grams per liter to about 35 grams per liter, and most preferably from about 4 grams per liter to about 25 grams per liter.
• the type and concentration of the electrolyte solution and the temperature are advantageously, but not necessarily, the same in both stages of the
• the preferred electrolyte solution for use in the process of this invention is a solution containing hydrochloric acid and aluminum chloride. Incorporation of either boric acid or phosphoric acid or both in this electrolyte solution is optional, but preferred. Boric acid and phosphoric acid both act as corrosion inhibitors and serve to provide finer grain structure when utilized in such electrolyte solutions.
• Boric acid is advantageously employed in an amount of from about 0.5 grams per liter up to its saturation point, more preferably in an amount of from about 3 grams per liter to about 13 grams per liter, and most preferably in an amount of from about 5 grams per liter to about 10 grams per liter.
• Phosphoric acid is advantageously employed in an amount of from about 1 gram per liter to about 35 grams per liter, more preferably in an amount of from about 5 grams per liter to about 20 grams per liter, and most preferably in an amount of from about 7.5 grams per liter to about 15 grams per liter.
• the aluminum can be etched with a mild caustic solution to brighten the surface and then desmutted by treatment with a suitable acid such as nitric acid or sulfuric acid.
• the electrolytic graining process is typically followed by an anodizing process, utilizing an acid such as sulfuric or phosphoric acid, and the anodizing process is typically followed by a process which renders the surface hydrophilic such as a process of thermal silication or electrosilication.
• anodization step serves to provide an anodic oxide layer and is preferably controlled to create a layer of at least 0.3 g/m 2 .
• Processes for anodizing aluminum to form an anodic oxide coating and then hydrophilizing the anodized surface by techniques such as silication are very well known in the art, and need not be further described herein.
• the two-stage electrolytic graining process of this invention is particularly advantageous for preparing aluminum supports for use in lithographic printing plates.
• Such plates comprise at least one radiation-sensitive layer overlying the support. They can be either negative-working or positive-working.
• radiation-sensitive layer is suitable, which after exposure and any necessary developing and/or fixing provides an area in imagewise distribution which can be used for printing.
• Useful negative-working compositions include those containing diazo resins, photocrosslinkable polymers and photopolymerizable compositions.
• Useful positive-working compositions include aromatic diazooxide compounds such as benzoquinone diazides and naphthoquinone diazides.
• Radiation-sensitive materials useful in lithographic printing plates include silver halide emulsions; quinone diazides (polymeric and non- polymeric), as described in U. S. Patent 4,141,733 (issued February 27, 1979 to Guild) and references noted therein; light sensitive polycarbonates, as described in U. S. Patent 3,511,611 (issued May 12, 1970 to Rauner et al) and references noted therein;
• a particularly important class of negative- working lithographic printing plates are those based on the use of diazo resins.
• the radiation-sensitive layer is typically comprised of the diazo resin, a polymeric binder and other ingredients such as colorants,
• Particularly useful diazo resins include, for example, the condensation product of p-diazo diphenyl amine and paraformaldehyde, the condensation product of 3-methoxy-4-diazo diphenylamine and paraformaldehyde, and the diazo resins of U. S. patents 3,679,419,
• Particularly useful polymeric binders for use with such diazo resins are acetal polymers as described, for example, in U. S. patents 4,652,604, 4,741,985 and 4,940,646.
• a second particularly important class of negative-working lithographic printing plates are those based on the use of radiation-sensitive photocrosslmkable polymers.
• a typical example of such a photocrosslmkable polymer is the polyester prepared from diethyl p-phenylenediacrylate and 1,4- bis ( ⁇ -hydroxyethoxy) cyclohexane, which is comprised of recurring units of the formula :
• Particular useful polymers of this type are those which incorporate ionic moieties derived from monomers such as dimethyl-3,3'-[(sodioimino) disul- fonyl]dibenzoate and dimethyl-5-sodiosulfoisophthalate.
• polymers examples include poly [1,4-cyclo- hexylene-bis (oxyethylene)-p-phenylenediacrylate]-co- 3,3'-[sodioimino)disulfonyl] dibenzoate and poly[1,4- cyclohexylene-bis (oxyethylene)-p-phenylenediacrylate]- co-3,3'-[sodioimino)disulfonyl]dibenzoate-co-3- hydroxyisophthalate.
• a third particularly important class of negative-working lithographic printing plates are the so-called "dual layer" plates.
• a radiation-sensitive layer containing a diazo resin is coated over an anodized aluminum support and a radiation-sensitive layer containing a photocrosslmkable polymer is coated over the layer containing the diazo resin.
• dual layer plates are described, for example, in British Patent No. 1 274 017. They are advantageous in that radiation-sensitive layers containing diazo resins adhere much more strongly to most anodized aluminum supports than do radiation-sensitive layers containing photocrosslmkable polymers. Thus, the enhanced performance provided by photocrosslmkable polymers is achieved without sacrificing the excellent adhesive properties of diazo resin compositions.
• the 1050 alloy contains a minimum of 99.50 % aluminum and minor amounts of silicon, iron, copper, manganese, magnesium, zinc and titanium.
• the 3103 alloy contains
• the 5XXX alloy contains approximately 98.5 % aluminum and minor amounts of silicon, iron, copper and magnesium, as described, for example, in United States patent 4,818,300.
• the objective of this invention is to produce an aluminum surface with a fine uniform grain that is free of pits.
• measurements were made for the following parameters, all of which are defined in ANSI/ASME Standard B46.1 -
• R a which is the roughness average and is also known as the center line arithmetic average, is the arithmetic average of the absolute values of the measured profile height deviations taken within the sampling length and measured from the graphical center line.
• R q which is the root-mean-square roughness, is the root-mean-square deviation from the center line.
• R z which is the ten-point height, is the average distance between the five highest peaks and the five deepest valleys within the sampling length
• the value of the optical density is indicative of the amount of smut on the grained
• a white surface would typically have an optical density of about 0.1 or 0.2 while a dark gray or black surface would have an optical density of about 1.3.
• An aluminum web having a thickness of 0.20 millimeters was subjected to a continuous two-stage electrolytic graining process in accordance with this invention.
• the aluminum was 1050 alloy, except as otherwise indicated.
• the electrolyte solution contained hydrochloric acid and aluminum chloride in concentrations as indicated in Table I.
• the aluminum was immersed in a caustic solution to remove oil and dirt from its surface, rinsed, treated with acid to remove metal salts adhering to the surface, rinsed again, and then grained.
• the two-stage graining process utilized three-phase 60 cycle alternating current with values for D 1 , D 2 , t 1 , t 2 , Q 1 and Q 2 as indicated in Table I.
• D 1 and D 2 are in amps/dm 2
• t 1 and t 2 are in seconds
• Q 1 and Q 2 and Q are in coulombs/dm 2 .
• R z and R q are in micrometers.
• the two-stage process of this invention provides fine grain as indicated by R a values of less than 0.5 and very uniform grain as indicated by R q /R a values that are typically less than 1.5 and often 1.3 or less.
• the two-stage process of this invention typically provides R a values of less than about 0.7 and frequently of less than 0.5 .
• a value of less than 0.5 for R a is indicative of very fine grain structure. It also typically provides low R q /R a values of less than about 1.5, which is indicative of uniform grain
• a desired very high degree of uniformity of grain structure, which provides optimum performance in lithographic printing plates, is achieved when the R q /R a value is equal to or less than 1.3.
• the two-stage process of this invention provides many important advantages as compared to prior processes for electrolytic graining of aluminum.
• a very fine grain structure and very large surface area can be obtained which provides excellent adhesion for radiation-sensitive coatings that are subsequently applied and good resolution during the printing process.
• the grain structure is outstanding.
• the grain structure is non-directional in nature. A grained surface having a low smut level is produced, and the smut is only loosely bound and easily removed, thereby requiring less etching and reducing the chance that the grain structure will be adversely affected by a harsh etching process.
• the three-dimensional grain structure that is produced by the two-stage process is capable of creating an optimum ink/water balance, as desired for high quality printing.
• the two-stage graining process also provides good power efficiency and low chemical consumption, yet attains the grain morphology that is critical to the lithographic printing process.
• lithographic printing plates and has been described herein with particular reference to such utility, it can be used for the graining of any aluminum article, regardless of its size, shape or purpose, whenever it is desired to provide a surface with a fine uniform grain.
• the process is beneficial in the production of decorative architectural aluminum and in the production of aluminum foil for electrolytic capacitors.

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• 1992
  • 1992-07-21 EP EP92916680A patent/EP0596005A1/de not_active Withdrawn
  • 1992-07-21 WO PCT/US1992/006011 patent/WO1993001942A1/en not_active Ceased
  • 1992-07-21 JP JP5502994A patent/JPH06509754A/ja active Pending
  • 1992-07-21 CA CA 2111195 patent/CA2111195A1/en not_active Abandoned

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