Classifications

• • 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
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers

Definitions

• This invention relates to novel processes for the treatment of anodised aluminium surfaces by immersing them in aqueous liquors, and to novel compositions for addition to said liquors, and to novel liquors in which the aluminium is immersed.
• the resistance of the surface of aluminium and aluminium alloys to corrosion and abrasion is conventionally improved by subjecting them to anodic oxidation so as to form a substantially anhydrous layer of adherent aluminium oxide.
• Surfaces which have been subjected to this treatment are referred to as having been "anodised”.
• the anodising treatment can be carried out in a variety of ways, for example, by the application of direct current in dilute aqueous solutions of sulphuric acid, or organic acids such as oxalic acid or mixtures thereof with sulphuric acid.
• These coatings can be coloured by immersion in a solution of a suitable dye or by treatment with alternating current in an electrolyte containing metal saltsW-
• the anodising can be carried out in solutions of organic acids such as sulphophthalic acid or sulphosalicylic acid or mixtures thereof with sulphuric acid.
• the oxidised layer formed by these anodising treatments has a porous structure and is insufficiently durable to fully protect the metal surface.
• the anodised metal is usually subjected to a further treatment known as sealing.
• Sealing is usually carried out by immersing the metal in hot or boiling water, which process is believed to cause the hydration of the substantially anhydrous aluminium oxide in the anodised layer thus causing a swelling of that layer which serves to seal the pores in its structure. Whatever the mechanism, the durability of the anodised surfaces is considerably increased by sealing.
• anti-smutting additives are the compounds disclosed in British Patents 1265424, 1302288, 1368336, 1398589,1419597, 1574161 and British Patent Application 2104921.
• our invention provides a method for treating the surface of anodised aluminium which comprises immersing said surface in an aqueous medium having a pH of at least 7.0 and an effective quantity of at least one smut-inhibiting additive.
• the additives which are useful in the processes of this invention are "anti-smutting additives" in that they are selected so as to avoid the formation of smut during the novel alkaline sealing processes. They are distinguished from the known "anti-smutting additives" in that not all of the known additives are effective in the novel alkaline sealing processes and in that the smut-inhibiting additives need not be effective as anti-smutting additives in the acidic sealing processes of the prior art. For reasons of clarity the term "smut-inhibiting additives" will be used hereafter in relation to those additives which are effective in the novel sealing processes of this invention.
• the temperature of the sealing bath will be at least 80°C since the rate of sealing at lower temperatures than this is unacceptably slow.
• the sealing temperature is preferably between 95°C and the boiling point of the bath. Pressurised systems in which the temperature may be above 100°C, e.g. 110 0 C or even 115 0 C may be employed.
• a smut-free product is one upon which no smut is visually detectable. Products which are deemed u smut-free" may carry small particles of smut which are detectable by careful scrutiny, but which do not detract from the appearance of the sealed article as a whole.
• the processes of the present invention are carried out under such conditions so as to seal the product to the desired degree.
• Anodised aluminium which is to be used in architecture and exposed to weathering will normally be sealed as efficiently as is practicable in order to maximise its corrosion resistance.
• the quality of sealing may be evaluated using one or more of three classes of standard tests; the weight loss in acid test, the dyespot test and the conductivity test. These tests can be carried out using the following techniques.
• the criterion used to evaluate the quality of the seal is an at least adequate performance in the weight loss in acid test.
• the pH of the sealing bath is at least 7.0 and more preferably at least 7.5 or 8.0. Higher pH's promote the rapid sealing of the anodised coating but may have detrimental effects upon the quality of that coating and also may encourage the formation of smut.
• the maximum pH of the bath will vary with its composition and the temperature of operation, but will generally be below 10.0, peferably below 9.5 and most preferably below 9.0. Thus, preferably, the pH of the sealing bath will be maintained at a value in the range 7.0 to 9.0, e.g. 7.5 to 8.5.
• the compounds which are effective smut-inhibiting agents in the sealing processes of the present invention must be water soluble and must not adversely effect the quality of the seal.
• Compounds which inhibit crystal growth in alkaline aqueous media when present in threshold quantities e.g. from 1 to 1000 ppm are potentially valuable as smut-inhibiting additives although not all known threshold treatment agents are useful as smut-inhibiting additives in the process of the present invention either because they do not inhibit smut formation or because they retard the sealing process.
• Smut inhibiting additives which may be useful in the processes of the present invention can be selected from the group comprising dextrins (including commercial dextrins, especially those having a viscosity of 50 to 400cP in 50% by weight solution at 20 0 C as measured with a Brookfield rotary viscometer, e.g.
• acrylic acid,methacrylic acid and water soluble polymers derived therefrom especially those polymers having a specific viscosity of up to 0.75cP measured at 20°C in 2N caustic soda and at a concentration of 0.7%, e.g.
• acids such as cycloaliphatic or aromatic polycarboxylic acid having from 4 to 6 carboxylic acid groups per molecule such as benzene penta carboxylic acid, benzene tetracarboxylic acid, benzene hexacarboxylic acid, cyclohexane tetracarboxylic acid and cyclohexane hexacarboxylic acid (in any of their various isomeric forms) or a water soluble salt thereof, e.g.
• alkali metal, alkaline earth metal ammonium and alkanolamine salts especially those described in British Patent 1574161, certain hydroxy carboxylic acids for example gallic acid and saccharic acid; the reaction products of one or more sulphonated aromatic compounds with an aldehyde and/or dimethylol urea or a mixture of formaldehyde and urea (including all those which are described or disclosed in British Patent Application 2104921).
• Other compounds which may be useful as smut-inhibiting additives include water-soluble phosphonic acids or one or more water-soluble salts of such acid each of which acid or salt forms one or more complexes with a divalent metal.
• water-soluble phosphonic acids or one or more water-soluble salts of such acid each of which acid or salt forms one or more complexes with a divalent metal.
• a relatively large number of phosphonic acids are known which form complexes with divalent metals.
• hydroxyalkanediphosphonic acids of Formula 1 which may be used are 1 - hydroxypropane -, 1 - hydroxybutane -, 1 - hydroxypentane - and 1 - hydroxyhexane - 1,1 - diphosphonic acid as well as 1 - hydroxy - 1 - phenylmethane - 1,1 - diphosphonic acid and preferably 1 - hydroxyethane - 1,1 - diphosphonic acid.
• Especially valuable smut-inhibiting additives for use in the present invention are the phosphonic acids, especially ethylenediaminotetramethylenephosphonic acid, hexamethylenediaminetetra-(methylene phosphonic) acid, n-propyliminobis(methylene phosphonic) acid and benzene hexacarboxylic acid and salts thereof and the reaction products of sulphonated aromatic compounds with an aldehyde and/or dimethylolurea or a mixture of formaldehyde and urea especially those products formed by the reaction of the sulphonation products of diphenyl, phenyltoluene, dimethyldiphenyl, diphenylether, diphenylsulphide, diphenylsulphoxide, dihydroxydiphenylsulphone, diphenylene oxide, diphenylene sulphide and bis phenol with an aldehyde and/or dimethylolurea or a mixture or formaldehyde and
• the preferred sulphonated aromatic compounds are sulphonated diphenyl, dimethyldiphenyl, diphenyl ether and additionally, when reacted with dimethylolurea (or a mixture of formaldehyde and urea), unsubstituted phenol and cresol.
• Preferred aldehydes used in the preparation of the reaction product are acetaldehyde and formaldehyde, more preferably formaldehyde.
• the reaction product is formed with a mixture of formaldehyde and urea
• the molar ratio of formaldehyde to urea is at leat 2:1.
• Preferred reaction products are those formed by the reaction of formaldehyde with a compound containing no halogen or hydroxyl groups, or the reaction of sulphonated phenols with dimethylolurea. More preferred is the reaction product of formaldehyde with a compound of formula Y in which R represents a hydrogen atom an alkyl group having 1 to 4 carbon atoms, a hydroxyl group or a halogen atom X represents a direct bond or a group of the formula and n has an average val ue in the range 1 to 4.
• the sulphonated aromatic compounds are known and may be made according to known methods.
• reaction of a compound of formula V with formaldehyde or dimethylolurea is known and may be carried out in accordance with known methods.
• the phosphonic acid smut-inhibiting additives must be used in combination with a divalent metal ion M 2+ in a molar ratio of at least 2M 2+ : 1 phosphonate group in order to be effective, i.e. the molar proportion of divalent metal ions must be at least sufficient as is theoretically required to form a complex with all of the phosphonate groups present. If the necessary quantity of divalent metal ions is not present in the sealing bath, e.g. in the form of calcium and magnesium salts dissolved in tap water, it is necessary to add a sufficient quantity of a soluble salt of a divalent metal to raise the molar ratio of metal ions to phosphonate groups to at least 2 : 1. Preferably the molar ratio of divalent metal ions to phosphonate group is at least 4 : 1.
• divalent metal ions appear to deactivate the phosphonate. Where this effect is observed a sufficient quantity of phosphonate can be added which will form a complex with the deactivating metal ion. Thereafter the addition of a further quantity of phosphonate together with the appropriate quantity of a salt of an acceptable divalent metal will be effective in inhibiting smut formation.
• salts of calcium magnesium, nickel or cobalt are examples of ions which may be deactivate the phosphonate and whose presence is thereby less preferred.
• ferric ions and cupric ions are ferric ions and cupric ions.
• ions which complex strongly with the phosphonate appear to deactivate it as a smut-inhibiting agent and their presence is correspondingly less preferred.
• the use of ethylenediamino tetramethylene phosphonic acid or its water soluble salts as a smut-inhibiting agent especially its magnesium salt is particularly preferred.
• the quantity of anti-smutting agent which is present in the bath varies with the nature of that agent.
• the quantity which is sufficient to suppress smut formation in a particular sealing process and the minimum effective quantity will normally be determined empirically.
• the formation of a sealed anodised surface of a satisfactory quality is accompanied by the formation of smut it is necessary to adjust one or more of the parameters which effect the efficiency of the bath, e.g. by increasing quantity of smut-inhibiting additive in the bath or to select a more effective smut-inhibiting additive.
• the quantity of some of the preferred anti-smutting agents e.g. benzene hexacarboxylic acid, 1-hydroxyethane-1-1 diphosphonic acid, and ethylenediaminotetramethylenephosphonic acid will be in the range 1 to 500ppm of the bath, e.g. 2 to 300 and more preferably 5 to 200 ppm of the bath.
• the reaction product of sulphonated aromatic compounds with an aldehyde and/or dimethylolurea (or a mixture of formaldehyde and urea) will preferably be present in a quantity of from 0.01 to 5.0 gms/litre of the bath.
• the effective quantity will vary according to the anti-smutting agent which is selected and will normally be determined empirically under the conditions which are to be employed in the sealing process.
• the quantity will be from 5 to 500 ppm in the case of benzene hexacarboxylic acid, from 5 to 100 ppm in the case of ethylenediaminotetramethylenephosphonic acid.
• the use of excessive quantities of anti-smutting additives may have a detrimental effect upon the quality of the anodised coating and is thereby preferably avoided. Where the pH of the bath is relatively high the maximum amount of a particular anti-smutting agent which may be tolerated without damage to the anodised coating will be increased.
• the preferred bases for present use are Lewis bases. Examples of suitable bases are triethanolamine, sodium borate, sodium carbonate, sodium bicarbonate, mono-ethanolamine, diethanolamine and hexamine or mixtures thereof. The most preferred base for present use is triethanolamine. Commercial grades of triethanolamine which contain minor quantities of diethanolamine and monoethanolamine may be used if desired. The addition of a base which might inhibit the sealing process should preferably be avoided. Thus, bases which liberate phosphate silicate and fluoride ions on dissolution in water are preferably not employed.
• the sealing processes of the present invention may be carried out in demineralised wateror in tap water.
• demineralised water is advantageous in that the sealing process is more likely to proceed without complication.
• the bath will inevitably become contaminated by the carry-over of material from previous processing steps, e.g. the anodising bath and subsequent rinsing steps. Although a certain amount of this contamination may be tolerated the efficiency of the sealing process is decreased and eventually the bath must be discarded.
• the use of tap water to make up the bath may be disadvantageous in that the minerals which are dissolved in it may affect the efficiency of the sealing process.
• the presence of dissolved minerals may also lead to the precipitation of solid material in the sealing bath which can form an unsightly crusted coating upon the anodised surface.
• This tendency is most common when the anti-smutting agent comprises a phosphonic acid or a phosphonate as hereinbefore described.
• the deposited solids can usually be removed by rinsing with water, it is preferred to operate the sealing bath under such conditions as will avoid the need for such a rinsing step. We have discovered that this tendency to the formation of solid material can be reduced by the addition of a surface active agent to the bath.
• the quantity of such a compound may vary through a wide range say lppm to lOgms/litre.
• the preferred additive is carboxymethylcellulose, hereinafter referred to as CMC.
• CMC carboxymethylcellulose
• the addition of from 5ppm to 100ppm of CMC will often be sufficient to prevent the formation of solid material in the bath.
• the sealing bath may also contain conventional additives e.g. additives which are known to inhibit the leaching of dye such as nickel acetate.
• the bath may also advantageously contain a wetting agent, the presence of which enhances the efficiency of the sealing process. Relatively small quantities of wetting agent, say wetting agent, say from 2.0 to 2000 ppm of the bath may be employed.
• wetting agent say wetting agent
• the efficient operation of the bath may be prolon ged by the addition of an agent which is capable of complexing with the metal.
• An example of a suitable agent is citric acid.
• Such agents may be effective when present in quantities which are significantly less than would be required to complex the metal ions which are present in the bath.
• the baths may also advantageously contain a buffering agent to assist the control of the pH.
• Suitable buffering agents include salts of acetic acid and formic acid.
• the various ingredients of the sealing bath may be added separately if so desired. It is preferred by way of convenience to formulate the various additives as a separate concentrate and then add that concentrate to the bath. Concentrates which, when added to water, form a sealing bath useful in the processes of the present invention are believed to be novel and form another aspect of our invention.
• Such concentrates comprise at least one anti-smutting agent, as hereinbefore defined, and at least one base, as hereinbefore defined.
• Optional ingredients include salts of organic acids such as acetic acid to regulate the pH thereof, other additives such as nickel acetate and any other compatible ingredients of the bath.
• Additives such as nickel acetate are preferably solubilised in the concentrate e.g. by the addition of triethanolamine to form a water soluble complex.
• sealing baths were assessed using the methods hereinbefore described and in addition by.visually inspecting the sealed product the visible presence of any velvety bloom being regarded as unsatisfactory.
• the pieces used were formed of Type 6063 aluminium alloy which had been alkaline etched (5% NaOH + additives) and anodised in sulphuric acid (175gms/litre at 18-20°C and 1.5A/ dm2) to provide an anodic film of 20 microns thickness.
• Demineralised water with mellitic acid (benzene hexacarboxylic acid) added in the quantities shown.
• the pH of the bath was raised by the addition of triethanolamine.
• the first two results illustrate comparative procedures.
• the seal obtained in-the time used is not of adequate quality.
• the third result is an Example according to the invention showing satisfactory sealing is obtained in a significantly shorter time.
• results at a concentration of 60mg/litre illustrate the reduction of the quality of the seal produced by excessive quantitites of smut-inhibitor and how this effect can be overcome by raising the pH of the bath.
• the sealing time was 1 min/micron.
• ANODAL SH1 is an aqueous solution comprising a reaction product of a sulphonated aromatic compound with an aldehyde or dimethylolurea (or a mixture of formaldehyde and urea).

Landscapes

• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Rigid Containers With Two Or More Constituent Elements (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Sealing Material Composition (AREA)
• Catalysts (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Road Signs Or Road Markings (AREA)
• Resistance Heating (AREA)
• Casings For Electric Apparatus (AREA)
• Gasket Seals (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

Family

ID=10540815

Family Applications (1)

Country Status (10)

Cited By (7)

Families Citing this family (3)

Family Cites Families (12)

• 1983
  • 1983-04-08 GB GB838309571A patent/GB8309571D0/en active Pending
• 1984
  • 1984-04-06 EP EP84302358A patent/EP0122129B1/de not_active Expired
  • 1984-04-06 GB GB08408870A patent/GB2139646B/en not_active Expired
  • 1984-04-06 ES ES531380A patent/ES8608589A1/es not_active Expired
  • 1984-04-06 AT AT84302358T patent/ATE45396T1/de not_active IP Right Cessation
  • 1984-04-06 DE DE8484302358T patent/DE3479324D1/de not_active Expired
  • 1984-04-06 CA CA000451431A patent/CA1251416A/en not_active Expired
  • 1984-04-09 BR BR8401643A patent/BR8401643A/pt not_active IP Right Cessation
  • 1984-04-09 AU AU26718/84A patent/AU579098B2/en not_active Ceased
  • 1984-04-09 JP JP59069284A patent/JPS59197594A/ja active Pending
  • 1984-04-09 ZA ZA842624A patent/ZA842624B/xx unknown

Also Published As

Similar Documents

Legal Events