CA2041892C - Formation of conversion coatings on surfaces of zinc or zinc alloys - Google Patents
Formation of conversion coatings on surfaces of zinc or zinc alloys Download PDFInfo
- Publication number
- CA2041892C CA2041892C CA002041892A CA2041892A CA2041892C CA 2041892 C CA2041892 C CA 2041892C CA 002041892 A CA002041892 A CA 002041892A CA 2041892 A CA2041892 A CA 2041892A CA 2041892 C CA2041892 C CA 2041892C
- Authority
- CA
- Canada
- Prior art keywords
- process according
- solution
- post
- rinsing solution
- zinc
- 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 - Fee Related
Links
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
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
-
- 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
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
-
- 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
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
-
- 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
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/82—After-treatment
- C23C22/83—Chemical after-treatment
Abstract
In a process of forming conversion coatings on surfaces of zinc and zinc alloys, in which the surfaces are contacted in a first stage with a solution which contains at least two different polyvalent metal ions and also contains such an amount of complexing agent that the polyvalent metal ions are kept in solution, and which has a pI3 value of,at least 11, and the surfaces are treated in a succeeding stage with a post rinsing solution, a succeeding stage comprises a treatment with a post rinsing solution which contains aluminum, zirconium and fluoride and has been adjusted to a pH value not in excess of five.
According to desirable features of the process the total concentration of Al + Zr + F is adjusted to a value between 0.1 and 8.0 g/l, preferably between 0.2 and 5.0 g/l, and the Al : Zr : F mole ratio is adjusted to (0.15 to 8.0) : 1 : (5 to 52) or to (0.15 to 0.67) :
1 : (5 to 7).
The treatment is suitably carried out for 1 to 120 seconds preferably 1 to 30 seconds, and at a temperature of 20 to 80°C, preferably 20 to 50°C.
The process can desirably be used for a pretreatment before a succeeding painting, film laminating or adhesive coating operation.
According to desirable features of the process the total concentration of Al + Zr + F is adjusted to a value between 0.1 and 8.0 g/l, preferably between 0.2 and 5.0 g/l, and the Al : Zr : F mole ratio is adjusted to (0.15 to 8.0) : 1 : (5 to 52) or to (0.15 to 0.67) :
1 : (5 to 7).
The treatment is suitably carried out for 1 to 120 seconds preferably 1 to 30 seconds, and at a temperature of 20 to 80°C, preferably 20 to 50°C.
The process can desirably be used for a pretreatment before a succeeding painting, film laminating or adhesive coating operation.
Description
This invention relates to a process of forming conversion coatings on surfaces of zinc and zinc alloys, comprising a first stage of contacting the surfaces with a solution containing at: least two different polyvalent metal ions and complexing agent in such an amount that the polyvalent metal ions are kept in solution, and a pH value of at least 11, and a following stage of rinsing the surfaces with a post rinsing solution, wherein the post rinsing contains aluminum, zirconium, and fluoride having a Al . Zr . F molar ratio of (0.15 to 8) . 1 . (5 to 52) and a pH value not i:n excess of 5.
Such a process of forming a conversion layer is known from DE-C-1 521 854 published on 15 July 1971 particularly as a pretreatment before a painting or film laminating operation.
Such a process of forming a conversion layer is known from DE-C-1 521 854 published on 15 July 1971 particularly as a pretreatment before a painting or film laminating operation.
The layer is Formed on the surface of zinc or zinc alloy by a treatment with aqueous alka-line solutions, which contain so-called non-alkali metal ions consisting of ions of one or more of the metals silver, magnesium, cadmium, aluminum, tin, tita-nium, antimony, molybdenum, chromium, cerium, tungsten, manganese, cobalt, iron, and nickel. It has been empha-sized that particularly suitable solutions contain non-alkali metal ions consisting of ions of iron or of cobalt together with another of tre stated metals. mhe solutions also contain organic complexing agents in an amount which is 7ufficient to keep the non-alkali metal ions in solution. The conversion coatings formed by means of said ions will increase the resistance to corrosion and will improve the adhesion of subsequently applied organic coatings.
'fhe resistance to corrosion and the bond strength will be further improved if -the surfaces on which the conversion layer has been formed are post-rinsed with an ~zd solwtion which contains hexavalent chromium and optionally contains also trivalent chro-mium.
'Whereas chat kno~avn process produces good. results as regards the resistance to corrosion and the bond strength, the use of triZalent chromium ions and particularly of hexavalent chromitun ions i: the pa.ssivatin~; post rinse solution is most undesirable _3_ because hexavalent chromium is toxic and requires a special disposalo It is an object of the invention zo provic;e far the formation cf conversion coatings on surfaces of zinc or zinc alloys a process by which the disadvantages of ~he known Frocess are avoided and, in particular, the environment is not polluted or is only very slightly ,polluted and which produces at least equally good results as regards the resistance to corrosion and the adhesion of paint, Tha t object is accomplished in that the process of the kind described first hereinbef ore is carried out in such a manner in accordance with tl~ in-vention that the solution used for post rinsing contains aluminum, zirconium, and fluoride and has been adjusted to a pH value not in excess of 5 0 ''he process in accordance with the in-ventior~ can be used to treat all surfaces which contain zinc or zinc alloys, such as materials of massive zinc or massive zinc alloys, but also to treat surfaces which have been =~la~ted vrith zinc or zinc alloys electrolyti-cally, by deposition from the gas phase or by hot dip coating. Elements which can be alloyed with zinc include particularly aluminum, silicon, lead, iron, r.ickel~ cobalt and manganese, Sheet materials may be plated with zinc or :with a zinc alloy on one side or on both sidesm ~~~~~~a .I.~ the surface of zinc or zinc alloy is only slightly greased or soiled, there may be no need for a preceding cleaning and degreasing of the surface.
In said cases, surfactants may b~ added in the first stage so that the cleaning and degreasing are effected witYx the treating sclution used also to form the con-version coatingo Thai embodiment affords mainly the ad-vantage that the entire pretrearmenr c.t the sr_2rf_a.ce can be carried out in fewer stages because ~'he separate cleaning and the associated rinsing with water are omittedo The alkaline solution used in the first stage may be applied, e.g., by spraying, dipping or f lOOdin f, a It has been found that alkaline solu-tions which contain iron(III) ions and additionally contain cobalt ions and/or nickel ions and/or chromium (III) ions and/or aluminum ions in a total content bet-ween Oo3 and 3 g/1, preferably betwesn G.4 and 1.2 g/l, ire part,icula 1y suitable. The polyvalent metal ions may be used as salts of inorganic acids, such as nitric acid, or as salts of organic acids, such as formic acid and particularly also of acetic acid. It is also possible to use salts of such organic acids which also serve as complexing agents. Ampho~eric metals, such as aluminum, may b~ dissolved in the form of the hydroxy complex even without an additional anion or complexing agento ~~~~l~a C;~ ~:~ :,~
->_, Due to the pickling attack during t he treatment in the first stage, additional polyvalewt cations, which are .pr-~sent .i.r, the surface to be treated and are not contained in the freshly prepared bath solu-tion, may enter the treating solutian from 'the surface of zinc or zinc alloy. On surfaces plated with zinc by hot dipping such cations consist of e.g. zinc, aluminium and lead. The total concentration of such cations may increase up to a few grams per liter and in general this.will not disturb the format~.on of the conversion coating.
Suitable complexing agents. include parti-cularly organic chelatin~, agents of various kinds, for instance, dicarboxylic acids (malonic acid, fumaric acid etc.); amino acids (e. g., glycine); hydroxycarboxylic acids (e. g., citric acid, glad onic acid, lactic acid);
1,3-diketones (e. g., acet~laaetoine); aliphatic polyal-cohols (e. go, sobitol, 1,2-ethamediol); aromatic carbo~cy-lic acids (e. g., salicylic acid, phthalic acid); amino-carboxylic acid (e. g., ethylenediamine-tetraacetic acid).
Other complexing agents, such as methanephosphonic acid diethanolamide, may also be used, The amount of the complexing agent conta~.ned in the solution must be suffi-cient for a complex binding of all polyvalent metal ions which are present. For this reason the ccntent of complex-ing agent must be increased too when the content of poly-valent metal fans in :,he solution increases. Because in-creasing amounts of certain complexing agents, which are inherently acidic, ma;~ decrease the alkalinity of the solution, it is preferred to use complexing agents in the form of neutral salts, particularly of the alkali metal salts. It has been found that no advantage will be afforded by the use of co:mplexing agents in a surplus.
Particularly desirable results will be produced by the use of complexing agents consisting of salts of gluconic acid, ;particularly of hexahydroxyheptanoic acid.
The solution should contain complexing agents in an amount between 0.05 and 10 g,~l, in most cases between 1.5 and 5.5 g/1 (based on th~~ sodium salt of hexahydroxyheptanoic acid) The aqueous solution must have a pH value of at least 11. Best results will be produced with pH values in the range from 12.2 to 13.3. The pH value may be adjusted, e.g., by triethanolamine, alkali hydroxides, alkali carbonates, al~:ali phosphates, alkali polyphosphates, alkali pyrophosphates, alkali borates, alkali silicates or mixtures thereof. But the use of alkali hydroxides, particularly sodium hydroxide, is most desirable.
The temperature of the solution used in the first stage may generally lie between 20 and 90°C. The preferred temperature range is about 45 to 65°C.
The treating time is generally about 2 to 60 seconds, as a rule, and preferably 5 to 30 seconds. It will depend, inter al:ia, on the application _~_ technology that is employed. For instance, the treat-ing time will be shorter in a spraying process than in a dipping process under conditions which are equal in other respectso In general, solutions having a lower metal ion concentration must be used at higher tempe-ratures and for longer treating times than solutions having a higher metal ion concentration.
~Nhen a conversion coating has. been form-ed, any surplus treating solution should be removed as completely as possible from the surface of zinc or zinc alloy. That may be effected, e.g., by dripping, squee gee-ing, blasting or rinsing with water or with an aqueous solution, which may have been acidified, e.g., by an in-organic of organic acid (hydrofluoric acid, boric acid., nitric acid, formic acid, acetic acid, etc.).
The post rinse solution mar be applied, e.g., by dippin~;~, flooding, spraying or roller coating.
In a preferred embodiment of the inven-tion the solution employed f or the aftertreatment contains aluminum,, zirconium and fluoride in a total concentra-tion of A1 -~ Zr a- F between 0.1 and 8 g/1 preferably between 0.2 and 5 g/1> The Al ; Zr s F mole ratios should desirably be adjusted to (0.15 to 8) . 1 : (5 to 52), particularly to (0.15 t o 2.0) . '1 . (5 to 16). In a particularly preferred embodiment of the process the Al . Zr . F ratio in the post rinsing solution is (0.15 to 0.67) . 1 . (5 to T). According to a further preferred feature of the invention the pH value should be adjusted to 2 to 5.
The post rinsing solutions used in the process in accordance with the invention contain, inter alia, acid aluminum fluoride zirconates and in case of a surplus of aluminum additionally contain other salts of aluminum, such as fluorides, t:etraf_Luoroborates, nitrates. They may be produced, e.g., in that zirconium metal or zirconium carbonate is initially dissolved in aqueous hydrofluoric acid to form complex fluoro'zirconium acid. Aluminum metal or aluminum hydroxide or an aluminum salt, such as the nitrate, fluoride, tEa rafluoborate, formate, acetate, is then added, preferably in dissolved form, and is optionally dissolved. A possible slight cloudiness of the solution will not adversely affect its effectiveness. Whereas the preparation is preferably effected on the described route, the solutions ma.y alternatively be prepared in a different manner.
The pH value of the solution is preferably adjusted with c:ations of volatile bases. These include particularly ammonium, ethanolammonium and di- and triethanolammoni~am. The adjustment particularly to relatively high pH value in the stated pH range and to relatively high concentrations in the range stated for rL J c.~ ~J
the total concentration of A1 + Zr + F may result in a cloudiness of the solution but this wily not adversely affect the effectiveness of the process.
Accordinc; to a further desirable feature of the invention the surfaces provided with, a conversion coating are rinsed with an aqueous solution which additionally contains at ~e'st one of thn anions benzoate, caprylate, ethyl hexoate, salicyate9 preferably in a total concentration of C~.05 to 0~5 g/1.
This will further increase the bare corrosion protection. The anions may be introduced by means of the corresponding acids or their saltso According to a further desirable feature of the invention the post rinsing ~ solution is applied for betvJeen about 1 .and 1?_~ seconds, particularly for between 1 and j0 seconds. The solution may be applied at a temperature between 20oC and about 80°C. 'i'e:~~;sr:~.tnarF:;
between 20 and 50 °C are preferred.
Deionized ~Yvater or low-salt water is preferably used to prepare the .post rinsing bath. 'hater having a high salt content is less suitable for the pre-paration of the bath.
After zhe passivating aftertreatment the surface may be dried, e.g., on the air or in an oven and optionally may be rinsed befora with deionized water.
Acco~~ding to a preferred embodiment of the invention the surface which has been subjected to the passivating after-~!~ ~.~a' -lo-treatment is subjected to an accelerated drying, e.g., with hot air or by infrared radiation.
The process in accordance with the in-vention serves primarily to pretreat surfaces of zinc or zinc alloys before they are painted' laminated with a f i1m or coated with an adhesive. It will improve the ad-hesion of the organic films on the metallic substrate and will also improve their resistance to a f ormat'._on of blisters under corrosive action and will inhibit subsur-face carrosion proceeding from ~.efects f.n the film.
The .process in accordance with the in-vention,will be explained more in detail. and by way of example with reference to the following example.
Example fo forn a conver~;~ion coating on cleaned and degreased sheets of hot galvanized steel they -,were dipped for 30 seconds into a solution which w~:s a~ a temperature of 55°C and had the following composition:
0~3 g/1 Fe5+ 0.2 g/1 rd03 1 ~ 3 g/1 sodium Salt of hexahydroxyhepta-noic acid 2~2 g/1 NaOH 2~.4 g/1 Thereafter the sheets were rinsed with ..x. ',l ."..~ Vo' water and were then subjected to a passivating af-ter-treatment. To that end the sheets were dipped into 'the post rinse solution for 5 seconds and were subse-quently squeegeed for a removal of surplus solution.
After a drying at 75°C in an oven operated with circulat-ing air for 0.5 minute the pretreated sheets were painted with an epoxy .primer and an acrylate top coat, The total coating had a thickness of about 25 dam.
The treated sheets were subsequently subjected to the following testss The adhesion of paint was determined by the T-Bend Test, in which the sheets were bent through 180° and the various radii of curvature (Tn) were stated as amounting to n times the sheet metal thickness (n==, '1,2 ...). The test result is stated as the percentage of the flaked-off paint surface area in the total curved surface area.
In other treated sheets, scratches ex-tending as far as to the metal sub~rate were made by means of a metal needle and the sheets were formed with a cut edge by plate shears. Thereafter the sheets were sub-jected to the salt spray test in accordance with DIN 50021 SS for 1008 hours. The test result was stated as the extent in mm of the migration under the paint from the crack or the cut edge.
To prepare the post rinsing solution to be employed, 1,6 g/1 and ZO g/1 respectively of an aqueous concentrate, which contained _ 12--0.855% by weight A1 and 8.62% by weight Zr and 10.'7/
by weight F, was diluted with deionized watertp yield post rinsing solution A
and post rinsing solution B. Both solutions ware adjusted with ammonia to a pH value of about 3.6.
F'or comparison, a post rinsing solution C was employed, which contained Cr('VI) arid Cr(IIT) and had a pH value o2 about 3.3.
The post rinsing solutions had the following composityons:
Post rinsing solution A:
A1 0.014 g/1 Zr 0.14 g/1 F o.17 g/1 NH4 0.016 g/1 Post rinsing solution B:
Al Ool? U/1 Zr 1.?2 g/1 y F 2.14 g/1 NHS 0.40 g/1 .
Post rinsing solution C:
Cr6~ 2.0 g/1 Cr~+ G.8 g/1 F 0.2 g/1 Zn 0.3 g/1 ~~~~~i _13_ The test results are stated in the follow-ing Tables.
Table 1: Paint adhesion in T-Bend Test Post rinsing Flaked off surface area (/) in Solution case of radius of curvature Tn A (invention) 100 55 15 5 B (invention) 100 65 25 5 C (comparison) 100 80 30 5 Table 2: Resistance to corrosion in salt spray test Post rinsing solution migration under paint (mm) after 1008 h at the scratch at the edge A (invention) z1 to 1 8 to g B (invention) 0 to 1 C (comparison) 1 to 3 g to 10 A comparison of the tabulated data reveals that the data obtained with the process in accordance with the invention are just as good or better than those of the also tested comparison process in which an post rinsing solution waa used that contained Cr(VI) and Cr(III).
'fhe resistance to corrosion and the bond strength will be further improved if -the surfaces on which the conversion layer has been formed are post-rinsed with an ~zd solwtion which contains hexavalent chromium and optionally contains also trivalent chro-mium.
'Whereas chat kno~avn process produces good. results as regards the resistance to corrosion and the bond strength, the use of triZalent chromium ions and particularly of hexavalent chromitun ions i: the pa.ssivatin~; post rinse solution is most undesirable _3_ because hexavalent chromium is toxic and requires a special disposalo It is an object of the invention zo provic;e far the formation cf conversion coatings on surfaces of zinc or zinc alloys a process by which the disadvantages of ~he known Frocess are avoided and, in particular, the environment is not polluted or is only very slightly ,polluted and which produces at least equally good results as regards the resistance to corrosion and the adhesion of paint, Tha t object is accomplished in that the process of the kind described first hereinbef ore is carried out in such a manner in accordance with tl~ in-vention that the solution used for post rinsing contains aluminum, zirconium, and fluoride and has been adjusted to a pH value not in excess of 5 0 ''he process in accordance with the in-ventior~ can be used to treat all surfaces which contain zinc or zinc alloys, such as materials of massive zinc or massive zinc alloys, but also to treat surfaces which have been =~la~ted vrith zinc or zinc alloys electrolyti-cally, by deposition from the gas phase or by hot dip coating. Elements which can be alloyed with zinc include particularly aluminum, silicon, lead, iron, r.ickel~ cobalt and manganese, Sheet materials may be plated with zinc or :with a zinc alloy on one side or on both sidesm ~~~~~~a .I.~ the surface of zinc or zinc alloy is only slightly greased or soiled, there may be no need for a preceding cleaning and degreasing of the surface.
In said cases, surfactants may b~ added in the first stage so that the cleaning and degreasing are effected witYx the treating sclution used also to form the con-version coatingo Thai embodiment affords mainly the ad-vantage that the entire pretrearmenr c.t the sr_2rf_a.ce can be carried out in fewer stages because ~'he separate cleaning and the associated rinsing with water are omittedo The alkaline solution used in the first stage may be applied, e.g., by spraying, dipping or f lOOdin f, a It has been found that alkaline solu-tions which contain iron(III) ions and additionally contain cobalt ions and/or nickel ions and/or chromium (III) ions and/or aluminum ions in a total content bet-ween Oo3 and 3 g/1, preferably betwesn G.4 and 1.2 g/l, ire part,icula 1y suitable. The polyvalent metal ions may be used as salts of inorganic acids, such as nitric acid, or as salts of organic acids, such as formic acid and particularly also of acetic acid. It is also possible to use salts of such organic acids which also serve as complexing agents. Ampho~eric metals, such as aluminum, may b~ dissolved in the form of the hydroxy complex even without an additional anion or complexing agento ~~~~l~a C;~ ~:~ :,~
->_, Due to the pickling attack during t he treatment in the first stage, additional polyvalewt cations, which are .pr-~sent .i.r, the surface to be treated and are not contained in the freshly prepared bath solu-tion, may enter the treating solutian from 'the surface of zinc or zinc alloy. On surfaces plated with zinc by hot dipping such cations consist of e.g. zinc, aluminium and lead. The total concentration of such cations may increase up to a few grams per liter and in general this.will not disturb the format~.on of the conversion coating.
Suitable complexing agents. include parti-cularly organic chelatin~, agents of various kinds, for instance, dicarboxylic acids (malonic acid, fumaric acid etc.); amino acids (e. g., glycine); hydroxycarboxylic acids (e. g., citric acid, glad onic acid, lactic acid);
1,3-diketones (e. g., acet~laaetoine); aliphatic polyal-cohols (e. go, sobitol, 1,2-ethamediol); aromatic carbo~cy-lic acids (e. g., salicylic acid, phthalic acid); amino-carboxylic acid (e. g., ethylenediamine-tetraacetic acid).
Other complexing agents, such as methanephosphonic acid diethanolamide, may also be used, The amount of the complexing agent conta~.ned in the solution must be suffi-cient for a complex binding of all polyvalent metal ions which are present. For this reason the ccntent of complex-ing agent must be increased too when the content of poly-valent metal fans in :,he solution increases. Because in-creasing amounts of certain complexing agents, which are inherently acidic, ma;~ decrease the alkalinity of the solution, it is preferred to use complexing agents in the form of neutral salts, particularly of the alkali metal salts. It has been found that no advantage will be afforded by the use of co:mplexing agents in a surplus.
Particularly desirable results will be produced by the use of complexing agents consisting of salts of gluconic acid, ;particularly of hexahydroxyheptanoic acid.
The solution should contain complexing agents in an amount between 0.05 and 10 g,~l, in most cases between 1.5 and 5.5 g/1 (based on th~~ sodium salt of hexahydroxyheptanoic acid) The aqueous solution must have a pH value of at least 11. Best results will be produced with pH values in the range from 12.2 to 13.3. The pH value may be adjusted, e.g., by triethanolamine, alkali hydroxides, alkali carbonates, al~:ali phosphates, alkali polyphosphates, alkali pyrophosphates, alkali borates, alkali silicates or mixtures thereof. But the use of alkali hydroxides, particularly sodium hydroxide, is most desirable.
The temperature of the solution used in the first stage may generally lie between 20 and 90°C. The preferred temperature range is about 45 to 65°C.
The treating time is generally about 2 to 60 seconds, as a rule, and preferably 5 to 30 seconds. It will depend, inter al:ia, on the application _~_ technology that is employed. For instance, the treat-ing time will be shorter in a spraying process than in a dipping process under conditions which are equal in other respectso In general, solutions having a lower metal ion concentration must be used at higher tempe-ratures and for longer treating times than solutions having a higher metal ion concentration.
~Nhen a conversion coating has. been form-ed, any surplus treating solution should be removed as completely as possible from the surface of zinc or zinc alloy. That may be effected, e.g., by dripping, squee gee-ing, blasting or rinsing with water or with an aqueous solution, which may have been acidified, e.g., by an in-organic of organic acid (hydrofluoric acid, boric acid., nitric acid, formic acid, acetic acid, etc.).
The post rinse solution mar be applied, e.g., by dippin~;~, flooding, spraying or roller coating.
In a preferred embodiment of the inven-tion the solution employed f or the aftertreatment contains aluminum,, zirconium and fluoride in a total concentra-tion of A1 -~ Zr a- F between 0.1 and 8 g/1 preferably between 0.2 and 5 g/1> The Al ; Zr s F mole ratios should desirably be adjusted to (0.15 to 8) . 1 : (5 to 52), particularly to (0.15 t o 2.0) . '1 . (5 to 16). In a particularly preferred embodiment of the process the Al . Zr . F ratio in the post rinsing solution is (0.15 to 0.67) . 1 . (5 to T). According to a further preferred feature of the invention the pH value should be adjusted to 2 to 5.
The post rinsing solutions used in the process in accordance with the invention contain, inter alia, acid aluminum fluoride zirconates and in case of a surplus of aluminum additionally contain other salts of aluminum, such as fluorides, t:etraf_Luoroborates, nitrates. They may be produced, e.g., in that zirconium metal or zirconium carbonate is initially dissolved in aqueous hydrofluoric acid to form complex fluoro'zirconium acid. Aluminum metal or aluminum hydroxide or an aluminum salt, such as the nitrate, fluoride, tEa rafluoborate, formate, acetate, is then added, preferably in dissolved form, and is optionally dissolved. A possible slight cloudiness of the solution will not adversely affect its effectiveness. Whereas the preparation is preferably effected on the described route, the solutions ma.y alternatively be prepared in a different manner.
The pH value of the solution is preferably adjusted with c:ations of volatile bases. These include particularly ammonium, ethanolammonium and di- and triethanolammoni~am. The adjustment particularly to relatively high pH value in the stated pH range and to relatively high concentrations in the range stated for rL J c.~ ~J
the total concentration of A1 + Zr + F may result in a cloudiness of the solution but this wily not adversely affect the effectiveness of the process.
Accordinc; to a further desirable feature of the invention the surfaces provided with, a conversion coating are rinsed with an aqueous solution which additionally contains at ~e'st one of thn anions benzoate, caprylate, ethyl hexoate, salicyate9 preferably in a total concentration of C~.05 to 0~5 g/1.
This will further increase the bare corrosion protection. The anions may be introduced by means of the corresponding acids or their saltso According to a further desirable feature of the invention the post rinsing ~ solution is applied for betvJeen about 1 .and 1?_~ seconds, particularly for between 1 and j0 seconds. The solution may be applied at a temperature between 20oC and about 80°C. 'i'e:~~;sr:~.tnarF:;
between 20 and 50 °C are preferred.
Deionized ~Yvater or low-salt water is preferably used to prepare the .post rinsing bath. 'hater having a high salt content is less suitable for the pre-paration of the bath.
After zhe passivating aftertreatment the surface may be dried, e.g., on the air or in an oven and optionally may be rinsed befora with deionized water.
Acco~~ding to a preferred embodiment of the invention the surface which has been subjected to the passivating after-~!~ ~.~a' -lo-treatment is subjected to an accelerated drying, e.g., with hot air or by infrared radiation.
The process in accordance with the in-vention serves primarily to pretreat surfaces of zinc or zinc alloys before they are painted' laminated with a f i1m or coated with an adhesive. It will improve the ad-hesion of the organic films on the metallic substrate and will also improve their resistance to a f ormat'._on of blisters under corrosive action and will inhibit subsur-face carrosion proceeding from ~.efects f.n the film.
The .process in accordance with the in-vention,will be explained more in detail. and by way of example with reference to the following example.
Example fo forn a conver~;~ion coating on cleaned and degreased sheets of hot galvanized steel they -,were dipped for 30 seconds into a solution which w~:s a~ a temperature of 55°C and had the following composition:
0~3 g/1 Fe5+ 0.2 g/1 rd03 1 ~ 3 g/1 sodium Salt of hexahydroxyhepta-noic acid 2~2 g/1 NaOH 2~.4 g/1 Thereafter the sheets were rinsed with ..x. ',l ."..~ Vo' water and were then subjected to a passivating af-ter-treatment. To that end the sheets were dipped into 'the post rinse solution for 5 seconds and were subse-quently squeegeed for a removal of surplus solution.
After a drying at 75°C in an oven operated with circulat-ing air for 0.5 minute the pretreated sheets were painted with an epoxy .primer and an acrylate top coat, The total coating had a thickness of about 25 dam.
The treated sheets were subsequently subjected to the following testss The adhesion of paint was determined by the T-Bend Test, in which the sheets were bent through 180° and the various radii of curvature (Tn) were stated as amounting to n times the sheet metal thickness (n==, '1,2 ...). The test result is stated as the percentage of the flaked-off paint surface area in the total curved surface area.
In other treated sheets, scratches ex-tending as far as to the metal sub~rate were made by means of a metal needle and the sheets were formed with a cut edge by plate shears. Thereafter the sheets were sub-jected to the salt spray test in accordance with DIN 50021 SS for 1008 hours. The test result was stated as the extent in mm of the migration under the paint from the crack or the cut edge.
To prepare the post rinsing solution to be employed, 1,6 g/1 and ZO g/1 respectively of an aqueous concentrate, which contained _ 12--0.855% by weight A1 and 8.62% by weight Zr and 10.'7/
by weight F, was diluted with deionized watertp yield post rinsing solution A
and post rinsing solution B. Both solutions ware adjusted with ammonia to a pH value of about 3.6.
F'or comparison, a post rinsing solution C was employed, which contained Cr('VI) arid Cr(IIT) and had a pH value o2 about 3.3.
The post rinsing solutions had the following composityons:
Post rinsing solution A:
A1 0.014 g/1 Zr 0.14 g/1 F o.17 g/1 NH4 0.016 g/1 Post rinsing solution B:
Al Ool? U/1 Zr 1.?2 g/1 y F 2.14 g/1 NHS 0.40 g/1 .
Post rinsing solution C:
Cr6~ 2.0 g/1 Cr~+ G.8 g/1 F 0.2 g/1 Zn 0.3 g/1 ~~~~~i _13_ The test results are stated in the follow-ing Tables.
Table 1: Paint adhesion in T-Bend Test Post rinsing Flaked off surface area (/) in Solution case of radius of curvature Tn A (invention) 100 55 15 5 B (invention) 100 65 25 5 C (comparison) 100 80 30 5 Table 2: Resistance to corrosion in salt spray test Post rinsing solution migration under paint (mm) after 1008 h at the scratch at the edge A (invention) z1 to 1 8 to g B (invention) 0 to 1 C (comparison) 1 to 3 g to 10 A comparison of the tabulated data reveals that the data obtained with the process in accordance with the invention are just as good or better than those of the also tested comparison process in which an post rinsing solution waa used that contained Cr(VI) and Cr(III).
Claims (14)
1. A process of forming conversion coatings on surfaces of zinc and zinc alloys, comprising a first stage of contacting the surfaces with a solution containing at least two different polyvalent metal ions and complexing agent in such an amount that the polyvalent metal ions are kept in solution, and a pH value of at least 11, and a following stage of rinsing the surfaces with a post rinsing solution, wherein the post rinsing solution contains aluminum, zirconium, and fluoride having a Al : Zr : F
molar ratio of (0.15 to 8) : 1 : (5 to 52) and a pH value not in excess of 5.
molar ratio of (0.15 to 8) : 1 : (5 to 52) and a pH value not in excess of 5.
2. A process according to claim 1, wherein the post rinsing solution contains aluminum, zirconium and fluoride in a total concentration of Al + Zr + F between 0.1 and 8 g/l.
3. A process according to claim 2, wherein the total concentration of Al + Zr + F is between 0.2 and 5 g/l.
4. A process according to any one of claims 1 to 3, wherein the post rinsing solution has a Al : Zr : F
molar ratio of (0.15 to 0.67) : 1 ; (5 to 7).
molar ratio of (0.15 to 0.67) : 1 ; (5 to 7).
5. A process according to any one of claim 1 to 4, wherein the pH value of the post rinsing solution has been adjusted to 2 to 5.
6. A process according to any one of claims 1 to 5, wherein the pH value of the post rinsing solution has been adjusted with cations of volatile bases.
7. A process according to claim 6, wherein said volatiles bases are selected from the group of consisting of ammonium, ethanolammonium and di- or triethanolammonium.
8. A process according to any one of claims 1 to 7, wherein the post rinsing solution additionally contains at least one of the anions benzoate, caprylate, ethyl hexoate, salicylate, in a total concentration of 0.05 to 0.5 g/l.
9. A process according to any one of claims 1 to 8, wherein the rinsing with the post rinsing solution takes 1 to 120 seconds.
10. A process according to any one of claims 1 to 9, wherein the post rinsing solution has a temperature of 20 to 80°C.
11. A process according to any one of claims 1 to 10, wherein the surface is dried after the post rinsing with the post-rinsing solution.
12. A process according to any one of claims 1 to 11, wherein the rinsing with the post rinsing solution takes 1 to 30 seconds.
13. A process according to any one of claims 1 to 12, wherein the post rinsing solution has a temperature of 20 to 50°C.
14. The use of the process according to any one of claims 1 to 13 as a pretreatment before a painting, film-laminating or adhesive coating operation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4017186A DE4017186A1 (en) | 1990-05-29 | 1990-05-29 | GENERATION OF CONVERSION OVERHEADS ON ZINC OR ZINC ALLOY SURFACES |
| DEP4017186.8 | 1990-05-29 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2041892A1 CA2041892A1 (en) | 1991-11-30 |
| CA2041892C true CA2041892C (en) | 2000-10-03 |
Family
ID=6407363
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002041892A Expired - Fee Related CA2041892C (en) | 1990-05-29 | 1991-05-06 | Formation of conversion coatings on surfaces of zinc or zinc alloys |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0459549B1 (en) |
| JP (1) | JP3083872B2 (en) |
| AU (1) | AU633728B2 (en) |
| BR (1) | BR9102173A (en) |
| CA (1) | CA2041892C (en) |
| DE (2) | DE4017186A1 (en) |
| ES (1) | ES2057734T3 (en) |
| ZA (1) | ZA914085B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19733972A1 (en) * | 1997-08-06 | 1999-02-11 | Henkel Kgaa | Alkaline band passivation |
| DE102010001686A1 (en) | 2010-02-09 | 2011-08-11 | Henkel AG & Co. KGaA, 40589 | Composition for the alkaline passivation of zinc surfaces |
| ITMI20102198A1 (en) * | 2010-11-26 | 2012-05-27 | Np Coil Dexter Ind Srl | PRE-TREATMENT PROCESS ON GALVANIZED STAINLESS STEEL COIL FREE OF HEAVY METALS |
| CN108374168A (en) | 2011-02-08 | 2018-08-07 | 汉高股份有限及两合公司 | Method and composition for the corrosive nature for improving the pretreated zinc surface of zirconium oxide |
| PL2503025T3 (en) | 2011-03-22 | 2013-12-31 | Henkel Ag & Co Kgaa | Multi-step corrosion-resistant treatment of metallic workpieces having at least partially zinc or zinc alloy surfaces |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3501352A (en) * | 1965-08-02 | 1970-03-17 | Hooker Chemical Corp | Composition and method for treating zinc surfaces |
| US3695942A (en) * | 1970-12-02 | 1972-10-03 | Amchem Prod | Zirconium rinse for phosphate coated metal surfaces |
| US3852123A (en) * | 1972-11-20 | 1974-12-03 | Pennwalt Corp | Sealing rinses for phosphate coatings on metal |
| JPS6022067B2 (en) * | 1982-09-30 | 1985-05-30 | 日本パ−カライジング株式会社 | Method for forming film on metal surface |
| US4496404A (en) * | 1984-05-18 | 1985-01-29 | Parker Chemical Company | Composition and process for treatment of ferrous substrates |
| US4650526A (en) * | 1986-03-18 | 1987-03-17 | Man-Gill Chemical Company | Post treatment of phosphated metal surfaces by aluminum zirconium metallo-organic complexes |
| DE3924984A1 (en) * | 1989-07-28 | 1991-01-31 | Metallgesellschaft Ag | METHOD FOR PASSIVATING RINSING OF PHOSPHATE LAYERS |
-
1990
- 1990-05-29 DE DE4017186A patent/DE4017186A1/en not_active Withdrawn
-
1991
- 1991-04-29 AU AU76178/91A patent/AU633728B2/en not_active Ceased
- 1991-04-29 DE DE59102544T patent/DE59102544D1/en not_active Expired - Fee Related
- 1991-04-29 ES ES91201020T patent/ES2057734T3/en not_active Expired - Lifetime
- 1991-04-29 EP EP91201020A patent/EP0459549B1/en not_active Expired - Lifetime
- 1991-05-06 CA CA002041892A patent/CA2041892C/en not_active Expired - Fee Related
- 1991-05-28 JP JP03152482A patent/JP3083872B2/en not_active Expired - Fee Related
- 1991-05-28 BR BR919102173A patent/BR9102173A/en unknown
- 1991-05-29 ZA ZA914085A patent/ZA914085B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JP3083872B2 (en) | 2000-09-04 |
| EP0459549A1 (en) | 1991-12-04 |
| BR9102173A (en) | 1991-12-24 |
| ES2057734T3 (en) | 1994-10-16 |
| AU7617891A (en) | 1991-12-05 |
| AU633728B2 (en) | 1993-02-04 |
| DE4017186A1 (en) | 1991-12-05 |
| JPH04231479A (en) | 1992-08-20 |
| DE59102544D1 (en) | 1994-09-22 |
| ZA914085B (en) | 1993-01-27 |
| CA2041892A1 (en) | 1991-11-30 |
| EP0459549B1 (en) | 1994-08-17 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4273592A (en) | Coating solution for metal surfaces | |
| US4148670A (en) | Coating solution for metal surface | |
| US4263059A (en) | Coating solutions of trivalent chromium for coating zinc and cadmium surfaces | |
| EP1433875B1 (en) | Chemical conversion coating agent and surface-treated metal | |
| US4171231A (en) | Coating solutions of trivalent chromium for coating zinc surfaces | |
| KR910003722B1 (en) | Phosphate coating composition and method of applying a zinc-nickel phosphate coating | |
| US5294266A (en) | Process for a passivating postrinsing of conversion layers | |
| US4278477A (en) | Metal treatment | |
| US4419199A (en) | Process for phosphatizing metals | |
| US4313769A (en) | Coating solution for metal surfaces | |
| US5407749A (en) | Iridescent chromium coatings and method | |
| WO1995033869A1 (en) | Composition and method for treating the surface of aluminiferous metals | |
| MXPA05006156A (en) | Treating fluid for surface treatment of metal and method for surface treatment. | |
| WO1985005131A1 (en) | Metal treatment | |
| CA1332910C (en) | Process of phosphating before electroimmersion painting | |
| US4600447A (en) | After-passivation of phosphated metal surfaces | |
| US3929514A (en) | Composition and method for forming a protective coating on a zinc metal surface | |
| KR20040058038A (en) | Chemical conversion coating agent and surface-treated metal | |
| US4775427A (en) | Phosphate conversion coatings for composite metals | |
| US4963198A (en) | Composition and process for treating metal surfaces | |
| CA2057825A1 (en) | Process of postrinsing conversion layers | |
| US5344504A (en) | Treatment for galvanized metal | |
| CA2041892C (en) | Formation of conversion coatings on surfaces of zinc or zinc alloys | |
| US4220486A (en) | Conversion coating solution for treating metallic surfaces | |
| EP0032306B1 (en) | Aluminium-coating solution, process and concentrate |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |