Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/32—Alkaline compositions
  • C23F1/36—Alkaline compositions for etching aluminium or alloys thereof

Definitions

• An alkali etching composition for aluminum is comprised of an aqueous solution of alkali metal hydroxide, hexavalent chorium ion, chelating agent, and a minor pro portion of fluoroalkyl surfactant. The composition provides more eflicient alkali consumption and a longer bath life.
• This invention pertains to compositions for the etching of aluminum and aluminum alloys. More particularly, this invention concerns an alkali composition which, as an aqueous alkali etching solution for aluminum, provides more efiicient alkali consumption and longer bath life due to the incorporation therein of a specifically defined minor proportion of fluoroalkyl surfactant.
• Industrial aluminum finishers usually process their product in an aqueous alkaline etching bath to remove surface imperfections and generally to enhance the appearance of the aluminum or aluminum alloy product. In such operations it is desirable for obvious economic reasons to produce good finishes with the smallest possible consumption of etching chamicals while endeavoring to employ the etchant baths over an extended period of time without the need for frequent costly dumping and recharging.
• the conventional, previously used, alkaline etching compositions suffer from deficiencies in these areas in the following respects.
• Conventional alkaline etchant systems such as that disclosed in my US. Pat. 3,314,890, generally involve the removal of a relatively large amount of metal from the surface of the treated aluminum object to produce an acceptable finish.
• the novel aqueous etching solution of this invention produces a desired architectural finish on aluminum and aluminum alloys that may be described as an etched finish, gray white to white in color, having a non-metallic appearance, having a low or matte reflectance, having a uniform fine grained appearance independent of any underlying aluminum grain boundaries and having what is known in the trade as an excellent hide, that is, all extrusion, die marks and scratches are completely hidden.
• the etchant consumption is significantly reduced to the extent that there is about 10% to 25% less consumption of the etchant chemicals than that incurred using the conventional etching compositions to accomplish an equivalent amount of surface finishing.
• the bath life is appreciably extended because the solution can be used without causing product surface defects until the specific gravity of the bath is increased by dissolved aluminum to a value of from about 1.35 to 1.50, compared to a specific gravity of 1.20 for the previously known baths at which point dumping would be required to avoid defective etching.
• This invention provides an alkali etching composition for aluminum and aluminum alloys comprised of an aqueous solution containing (A) from 3.75 to 209 grams per liter of alkali metal hydroxide, (B) water-soluble hexavalent chromium ion ranging in amount of at least 0.035% by weight of the alkali metal hydroxide content and no greater than 11 grams per liter, (C) chelating agent ranging in amount of at least 3% by weight of the alkali metal hydroxide content and no greater than 44 grams per liter and (D) fluoroalkyl surface active agent ranging in amount of at least 0.0002% by wegiht of the alkali metal hydroxide content and up to 0.44 gram per liter.
• A from 3.75 to 209 grams per liter of alkali metal hydroxide
• B water-soluble hexavalent chromium ion ranging in amount of at least 0.035% by weight of the alkali metal hydroxide content and no greater than 11 grams
• an embodiment of the invention comprises the solid granular compositions which are capable of forming the foregoing aqueous solutions by mixing in water.
• the components are present in the following ranges in percents by weight: (A) from 80% to 95% of alkali metal hydroxide, (B) from 0.035% to 5% of water-soluble hexavalent chromium, (C) from 3% to 20% of chelating agent, and (D) from 0.0002% to 0.2% of fluoroalkyl surfactant, said percentages of (B), (C) and (D) based on the weight of the alkali metal hydroxide (A).
• the total of the four components will, of course, be 100%.
• the composition of this invention can also be conveniently handled as a liquid concentrate comprised of from 15 to 60 weight percent of the aforesaid granular composition and from 40 to weight percent water.
• Sodium hydroxide is the principal source of the alkali metal hydroxide because it is inexpensive as compared to potassium or lithium hydroxide. However, potassium hydroxide or other alkali metal hydroxides are equally efficient in these compositions.
• the source materials for the hexavalent chromium ion are one or more of the wellknown water-soluble ionizable chromium containing compounds. They may beselected from the group which includes sodium dichromate, potassium dichromate, ammonium dichromate, sodium chromate, potassium chromate, chromic anhydride, sodium chrom glucosate and potassium chrom glucosate.
• the above sources of hexavalent chromium ion are all normally solid materials and of course are useful in preparing the solid granular concentrates which are used in making the etching solutions.
• the third component of the formulation which acts as a surface modifier with respect to the action of the alkali metal hydroxide etchant on aluminum and aluminum al-v loys is a special group of Wellknown surface modifyingg agents of the chelating type which combine with the hexavalent chromium to modify the attack of the caustic soda and to prevent precipitation of aluminum salts from solution.
• Suitable chelating agents include sorbital, mannitol, ascorbic acid, sorbose, tannic acid, ethylene diaminetetraacetic acid, diglycolic acid, picolinic acid, aspartic acid, dithiooxamide, l-rhamnose, b-fructose, glycerol, maleic acid, mannose, succinic acid, sucrose, tartaric acid and the like.
• R is an alkylene group and R is hydrogen or alkyl; the acids and salts of U.S. 2,951,051, i.e.,
• the aluminum or aluminum alloy is first cleaned with a conventional aluminum cleaner which may be of the alkaline or acid type to remove oxides and soil which might obstruct the etching action.
• a conventional aluminum cleaner which may be of the alkaline or acid type to remove oxides and soil which might obstruct the etching action.
• the aluminum is rinsed with water, preferably warm, and is then immersed in or sprayed with the etching solution held at a temperature within the range of 150 to 200 F. However, at temperatures less than 150 F. the solutions are effective in preventing the unwanted effect known in the industry as galvanizing.
• the preferred temperature range for securing the preferred architectural finish is within the range of 160 to 180 F.
• the metal workpiece is allowed to remain in contact with the etchant solution until the desired etch is obtained. Generally this will vary from one to minutes depending on the concentration of the ingredients in the bath and the temperatures used. Suitable etching is often obtained in about 3 to 7 minutes.
• the work piece is then rinsed at least once with water, preferably warm, and then the work piece is desmutted to remove the metal particles which are insoluble in the etching solution. Since the present etching solutions have a considerable concentration of chromium contained therein it is unnecessary to use a chromated desmutter, and in fact, a nonchromated desmutter is preferred.
• tEtchant baths were prepared having the following compositions wherein the proportions are expressed in grams of ingredient per liter of aqueous solution and in weight percent based on a dry composition basis.
• a Bath B type composition was used for two weeks with appropriate replenishment before an unacceptable increase in viscosity and lack of etching efficiency required its disposal.
• a Bath C composition was used for some nine weeks with appropriate replenishment before disposal became necessary.
• a composition for the etching of aluminum and aluminum alloys comprised of an aqueous solution of (A) from 3.75 to 209 grams per liter of alkali metal hydroxide, (B) water-soluble hexavalent chromium ion ranging in amount of at least 0.035% by weight of the alkali metal hydroxide and up to 11 grams per liter, (C) chelating agent ranging in amount of at least 3% by weight of the alkali metal hydroxide and up to 44 grams per liter and (D) fluoroalkyl surfactant ranging in amount of at least 0.0002% by weight of the alkali metal hydroxide and up to 0.44 gramper liter.
• the solid granular composition capable of forming References Cited the aqueous etching solution of claim 1 comprised of (A) UNITED STATES PATENTS from 80% to 95% of alkali metal hydroxide, (B) from 0.002% to 0.2% of fluoroalkyl surfactant, hte precent- 3314890 4/1967 Smlth (C) from 3% to 20% Of chelating agent and (D) from 5 JACOB H STEINBERG i E i 0.0002% to 002% of fluoroalkyl surfactant, the percentages of (B), (C) and (D) being based on the Weight of US. Cl. XJR.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=25086410

Family Applications (1)

Country Status (8)

Cited By (6)

Families Citing this family (1)

• 1968
  • 1968-10-22 US US769755A patent/US3557000A/en not_active Expired - Lifetime
• 1969
  • 1969-10-15 GB GB1227070D patent/GB1227070A/en not_active Expired
  • 1969-10-17 CH CH1553869A patent/CH508739A/fr not_active IP Right Cessation
  • 1969-10-17 DE DE1952425A patent/DE1952425C3/de not_active Expired
  • 1969-10-20 FR FR6935837A patent/FR2021214A1/fr not_active Withdrawn
  • 1969-10-20 JP JP44083298A patent/JPS4843020B1/ja active Pending
  • 1969-10-21 BE BE740553D patent/BE740553A/xx unknown
  • 1969-10-22 NL NL6915915A patent/NL6915915A/xx not_active Application Discontinuation

Also Published As

Similar Documents