Aqueous acidic composition for treating metal surfaces, treating method using this composition and use of treated metal surface

Abstract

An aqueous acidic composition for treating metal surfaces, the composition including the following components: a) at least one water soluble or water dispersable anionic polyelectrolyte; b) at least one organofunctional silane including one or more reactive functional groups selected from the group including amino, mercapto, methacryloxy, epoxy and vinyl; c) at least one water dispersible solid wax
wherein the weight ratio between components a:b is in the range of 1:2-4:1, based on dry matter; the weight ratio between components (a+b):c is in the range of 1:3-3:1, based on dry matter, and wherein components a and b may be present—at least partially—as their graft reaction product. Another aspect is a treating method using this composition and use of the thus treated metal surface.

Claims

1. An aqueous acidic composition for treating metal surfaces, said composition comprising the following components: (a) at least one water soluble or water dispersable anionic polyelectrolyte; (b) at least one organofunctional silane comprising one or more reactive functional groups selected from the group comprising amino, mercapto, methacryloxy, epoxy and vinyl; (c) at least one water dispersible solid wax; wherein the weight ratio between components a:b is in the range of 1:2-4:1, based on dry matter; the weight ratio between components (a+b):c is in the range of 1:3-3:1, based on dry matter, wherein the at least one anionic polyelectrolyte has an acid value of at least 400 mg KOH/g, wherein the aqueous acidic composition is free from inorganic compound particles.

2. The aqueous acidic composition according to claim 1, wherein the at least one anionic polyelectrolyte has an acid value of at least 600 mg KOH/g.

3. The aqueous acidic composition according to claim 1, wherein the at least one anionic polyelectrolyte has an acid value of at least 700 mg KOH/g.

4. The aqueous acidic composition according to claim 1, wherein the at least one anionic polyelectrolyte is present in an amount of 0.6-40 g/L.

5. The aqueous acidic composition according to claim 4, wherein the at least one anionic polyelectrolyte is present in an amount of 1.6-20 g/L.

6. The aqueous acidic composition according to claim 1, wherein the at least one organofunctional silane is present in an amount of 0.3-40 g/L.

7. The aqueous acidic composition according to claim 6, wherein the at least one organofunctional silane is present in an amount of 0.8-20 g/L.

8. The aqueous acidic composition according to claim 1, wherein the at least one water dispersable wax is present in an amount of 1.5-30 g/L.

9. The aqueous acidic composition according to claim 8, wherein the at least one water dispersable wax is present in an amount of 4-15 g/L.

10. The aqueous acidic composition according to claim 1, wherein the ratio of components a:c is less than 1.

11. The aqueous acidic composition according to claim 1 having a pH in the range of 1.2-6.

12. The aqueous acidic composition according to claim 11 having a pH in the range of 1.6-3.5.

13. The aqueous acidic composition according to claim 1, wherein the composition further comprises at least one fluoride compound.

14. The aqueous acidic composition according claim 13, wherein the at least one fluoride compound comprises a fluoacid having at least 4 F atoms and one or more elements selected from the group consisting of Si, Ti, Zr and Al.

15. The aqueous acidic composition according to claim 13, wherein the at least one fluoride compound is present in a total amount of F− anions 0.1-1.5 g/L.

16. The aqueous acidic composition according to claim 1, wherein the composition further comprises one or more complexing agents and/or surfactants.

17. A method of treating a metal surface, comprising a step of applying the aqueous acidic composition according to claim 1 on the metal surface.

18. The method according to claim 17, wherein the metal surface is a zinc or zinc alloy coated steel strip.

19. The method according to claim 17, further comprising a step of drying the applied aqueous acidic composition, at elevated temperature.

20. The aqueous acidic composition according to claim 1, wherein the water soluble anionic polyelectrolytes are selected from polyacrylic acid, polysulphonic acid, phosphorylated polyvinylalcohol, polymethacrylic acid, polymaleic acid, polyvinylphosphonic acid, and polyvinylsulphonic acid, copolymers of methylvinylether and maleic acid, copolymers of methylvinylether and acrylic acid, copolymers of vinylphosphonic acid and acrylic acid, copolymers of maleic acid and acrylic acid, copolymers of ethylene-acrylic acid and sulphonic acid.

21. The method according to claim 20, wherein the step of drying the applied aqueous acidic composition is performed at a Peak Metal Temperature in the range of 35-80° C.

22. The method according to claim 17, wherein the coating weight (dry solids) is in the range of 0.001 g/m2-1.5 g/m2.

23. The method according to claim 22, wherein the coating weight (dry solids) is in the range of 0.004-0.2 g/m2.

24. The method according to claim 17, wherein the coating weight (dry solids) is component a) polyelectrolyte: 0.3-320 mg/m2; component b) silane: 0.15-320 mg/m2; component c) wax: 0.75-240 mg/m2.

25. The method according to claim 24, wherein the coating weight (dry solids) is component a) polyelectrolyte: 0.8-80 mg/m2; component b) silane: 0.4-80 mg/m2; component c) wax: 3-60 mg/m2.

26. The method according to claim 17, further comprising the step of applying a lubricant.

27. The method according to claim 26, wherein the lubricant is applied in a coating weight of 0.2 to 3.0 g/m2.

28. A method of use of a coated metal surface, in particular a zinc or zinc alloy coated steel sheet, treated according to claim 17 in the production of an automotive component comprising at least one step selected from the group of forming, joining and painting.

29. The method of use according to claim 28, wherein the coated metal surface is a zinc or zinc alloy coated steel sheet.

30. The method of use according to claim 28 at least comprising the steps of forming, joining and painting.

31. The aqueous acidic composition according claim 1, wherein the at least one water dispersable wax is present in an amount of 4-15 g/L.

32. The method according to claim 17, further comprising a step of drying the applied aqueous acidic composition, at a Peak Metal Temperature in the range of 35-80° C.

33. The aqueous acidic composition according to claim 1, wherein components (a) and (b) are at least partially present as their graft reaction product.

Description

EXAMPLES

(1) Polyelectrolyte Component a1

(2) A commercial grade random copolymer of polyvinylphosphonic-co-acrylic acid solution (based on 30 mol % vinylphosponic acid and 70 mol % acrylic acid and a solid content of 38 wt. %). The acid value is 769 mg KOH/g.

(3) The acid value was determined by dissolving a predetermined amount of the polyelectrolyte sample in a suitable solvent, i.c. water because this polyelectrolyte is water soluble. Then the aqueous solution thus obtained was titrated with a solution of potassium hydroxide having a known concentration. Phenolphtalein was used as color indicator.

(4) Polyelectrolyte Component a2

(5) A water-soluble co-polymer, which is the reaction product from vinyl ether and maleic anhydride with a molecular weight Mw of 220.000 g/mol. The anhydride was converted into the acid form by hydrolysis. In order to dissolve and hydrolyse the polymer was dispersed in warm water. The polyelectrolyte solution was diluted with water to obtain a solid weight concentration of 21 wt. %. The acid value of component a2 is 852 mg KOH/g.

(6) Organofunctional Silane Component b

(7) Two commercial available organofunctional silane oligomers, a partially hydrolysed and condensed epoxy silane wt. 10% and a fully hydrolyzed aminoalkylsilane 30 wt. %, were mixed for 1 hour with 8 wt. % phosphoric acid. Then water was added 52 wt. % and the solution was kept for 8 hours at 50° C. The final silane solution had a solid content of 31 wt. %. As hardly no alcohols are released during hydrolysis there is no need for an additional distillation step to make the product VOC free.

(8) Graft Reaction Product Ab

(9) Polyelektrolyte component a2 was blended with 3-glycidoxy propyl trimethoxy silane in a dry weight ratio of 2:1. Hydrolysis and reaction were carried out during 3 hours at 50° C. The resulting product after vacuum distillation to remove alcohol was diluted with water to a solid weight concentration of 17.5 wt. %. This graft reaction product has an acid value of 396 mg KOH/g.

(10) Wax Component c

(11) Non-ionic stabilized water-dispersed montan-ester wax (solids 30 wt. %)

Example Ex1

(12) 3 Wt. % of the organofunctional silane component b and 2.4 wt. % polyelectrolyte component a1 were added to demineralised water. The final mixture contained 9.1 g/L of the polyelectrolyte (dry solid weight) and 9.3 g/L of the silane. (dry solid weight). Finally the wax component c was added in a concentration of 2.4 wt. %, amounting to 7.2 g/L of wax. Total Solids: 25.6 g/L; pH=2.1 and 1.8 g/L phosphates (derived from the organofunctional silane component b). Weight ratio polyelectrolyte:silane=1:1.3, polyelectrolyte:wax=1:0.8 and ((polyelectrolyte+silane):wax=1:0.4.

Example Ex2

(13) To 2.4 wt. % of the above graft reaction product ab (resulting in 2.8 g/L of polyelectrolyt), 11 g/L of HEDP (60 wt. %) as a complexing agent was added, before 19 g/L hexafluorotitanium acid (50 wt. %) and 6 g/L aluminium orthophosphate (48 wt. %) were added. Finally 2.4 wt. % wax component c was added (7.2 g/L of wax). Example 2: ratio A:B=1:0.5 and ratio (A+B):C=1:1.7 Weight ratio polyelectrolyte:silane=1:0.5, polyelectrolyte:wax=1:1.7 and ((polyelectrolyte+silane):wax=1:0.6.

Comparative Example CEx1

(14) A metal treatment aqueous solution was prepared that contained zinc bis-hydrogenphosphate (8.6 g/L of phosphate and 3 g/L of zinc) and 24 g/L of wax component c. Total solids 18.8 g/L. pH=2.1.

Comparative Example CEx2

(15) This solution contained 46 g/L of aluminium ortho phosphate (dry solids), an emulsion acrylate co-polymer 8.6 g/L (dry solids) and 24 g/L of wax component c. Total solids 61.8 g/L; pH=1.9. The acid value of the acrylate co-polymer is 4 mg KOH/g.

Comparative Example CEx3

(16) A metal treatment aqueous solution of polyelectrolyte component a2 (30 g/L) and wax component c (24 g/L) was prepared. Total solids 13.5 g/L; pH=2.2. Weight ratio polyelectrolyte:wax=1:1.1.

Comparative Example CEx4

(17) This composition contained silane component b (200 g/L) and wax component c (24 g/L). Total solids 69 g/L; pH=3.

Comparative Example CEx5

(18) A composition containing 8.6 g/L emulsion acrylate co-polymer (acid value: =4 mg KOH/g), 4.3 g/L silane and 0.2 g/L of wax component c 7.2 g/was prepared.

(19) The above aqueous metal treatment compositions as summarized in Table 1 were applied to HDG steel (grade BH180) having a thickness of 0.6 mm using a ChemCoater. The wet film had a coating weight of 2 g/m.sup.2 before drying. The samples were dried at a PMT of 70° C.

(20) Table 1 summarizes the compositions.

(21) TABLE-US-00001 TABLE 1 Compositions of examples (Ex) and comparative examples (CEx) Polymer/ Grafted Complexing Sample Polyelectrolyte Silane product Wax Fluoride Phosphate agent CEx1 c Zn phosphate CEx2 Acrylic c Al copolymer phosphate CEx3 a2 c CEx4 b c CEx5 Acrylic b c copolymer Ex1 a1 b c Ex2 ab c TiF.sub.6 Al HEDP phosphate

(22) Each of the samples was subjected to various tests including:

(23) Lubricity

(24) Linear friction test: Galling

(25) Force 5 kN, 20 mm/min, test length 55 mm, tools Ra=0.4

(26) Visual inspection after 6 strokes CoF=coefficient of friction before and after 6 strokes
After application of the compositions of Table 1, the thus treated samples were loaded with 1 g/m.sup.2 per side prelube oil PL61 (Zeller+Gmelin).
Adhesive Bonding
Adhesive bonding tests: lapshear with and without ageing (VDA 621-415) according to SEP 1220-6.
After application of the compositions of table 1, the thus treated samples were loaded with 3 g/m.sup.2 per side prelube oil PL 3802-39 S (Fuchs) and tested with two commercially available structural adhesives, i.e. Betamate (Dow) and M91 Failure mode: adhesive/cohesive, cohesive is the desired failure mechanism.
Weldabiliy
Spot welding performance was tested according to SEP 1220/2.
Material was welded to itself, as well as in combination with HDG and EG coated materials. Standard welding parameters as specified in SEP1220-2 were used. Tests that have been performed: Welding current range window: Electrode life test Additionally the electrode sticking behaviour was assessed.
Testing of Removability (Suitable for Standard E Coat Process)
For subsequent trouble free process steps like phosphatizing, painting and similar or alternative steps, the forming auxiliaries (metal treatment composition/lubricant) should be removed, as much as possible in the alkaline cleaning step. VDA 230-213 (ch.5.10) water break test XRF measurement of coating weight (removal)

(27) Table 2 summarizes the result in qualitative way. For comparison test results of phosphatized EG, commercially available inorganic treated NIT on GI and T-treated (Zn phosphate) on GA and GI reference are also incorporated.

(28) After the alkaline cleaning step a standard phosphatizing procedure was followed (activation and phosphatizing). The performance of the thus treated samples was studied visually (using a microscope) and homogeneity, coverage, crystal size and thickness of the phosphate layers were evaluated. If no abnormalities were determined in the phosphate layer compared to the GI reference then the rating “pass” is given, meaning that the thus treated surface is suitable for E coat evaluated by observing the crystal size using a microscope, the coverage and thickness of the phosphate layer.

(29) TABLE-US-00002 TABLE 2 Test results Removability Formability Adhesive bonding composition (<0.15 = pass) (cohesive Welding (>1.2 kA = pass) and lubricant [%] CoF(no. of (=pass)/adhesive(=fail)) Welding Electrode (40-70% = strokes) Structural adhesive current life test moderate; 70%- Phosphatibility CoF Cof Betamate range [no. of 90% = good; (suitable for Sample (1) (6) (Dow) M91 [kA] welds] remark 100% excellent) E coat) EG 0.14 0.1 cohesive cohesive 100 pass Phosphate NIT 0.1 0.16 cohesive cohesive 80 pass T treat 0.13 0.12 adhesive adhesive 2 600 sticking Not determined NA GI reference 0.1 0.25 cohesive cohesive 3 >1000 100 pass CEx1 0.09 0.17 adhesive adhesive 3 >1000 70 pass CEx2 0.1 0.08 adhesive adhesive 1.8 sticking 50 fail CEx3 0.1 0.19 cohesive adhesive 3 100 pass CEx4 0.1 0.11 adhesive adhesive 3 100 pass CEx5 0.1 0.08 adhesive adhesive 1.8 sticking 50 fail Ex1 0.09 0.11 cohesive cohesive 40 fail Ex2 0.09 0.13 cohesive cohesive 2.3 >1000 90 pass

(30) The above results indicate that Example 1 according to the invention has a combination of properties regarding formability, adhesion bonding and welding on HDG steel similar to phosphate EG steel, and better than the commercially available treatments and comparative examples. Example 2 shows the best overall performance regarding all tested properties.

(31) The below table 3 provides further test data regarding adhesive bonding properties for structural adhesives Betamate and M91 tested according to SEP 1220-6 on GI (zinc coated) and MZ (magnesium zinc coated) steel samples after degreasing, treated with 2 mL/m.sup.2 of Cex1, Ex1 and Ex2 and oiled with 3 g/m.sup.2 PL3802-395, respectively.

(32) TABLE-US-00003 TABLE 3 GI MZ Betamate Betamate 1480V203G M91 1480V203G M91 shear shear shear shear strength [N] strength [N] strength [N] strength [N] Degreased 5000 4550 4780 4550 reference CEx 1 4520 4200 4550 4150 Ex 1 4800 4750 4780 4550 Ex 2 4950 4500 4850 4450

(33) The above test results show that the compositions (E×1 and E×2) according to the invention provide a similar or better bonding performance than the degreased (untreated) reference for both types of steel and both types of adhesives, while in all these conditions the comparable example CEx1 performs less than the reference.

(34) The below Table 4 provides further adhesion test data for zinc magnesium alloy coated steel HX460LAD+Z120 (1.5 mm), (indicated as MZ in the table below) with and without post-treatment with the composition according to Ex2 using different adhesives compared to the GI reference DX56MZ140 (1.5 mm). The composition of Ex2 was applied at 2 g/m.sup.2, cured 60 min at 190° C. and oiled with PL61 (3 g/m.sup.2). 100% cohesive failure is considered excellent.

(35) TABLE-US-00004 TABLE 4 Lap Shear test Peel test % cohesive failure mode % cohesive failure mode Teroson RB Teroson RB Betamate Teroson RB Betaguard Teroson RB Adhesives 5194 GB 5191 GB 1485 S 3233AA25 KP75 1248LV25 GI reference 100 100 100 75 100 80 MZ 100 100 80 60 100 70 MZ plus Ex2 100 100 100 100 100 95

(36) FIG. 1 is a diagrammatical view of an embodiment of a steel product treated according to the invention, wherein the reference numerals refer to:

(37) 1=steel strip or sheet;

(38) 2=Zn or Zn alloy coating;

(39) 3=HDG steel strip or sheet;

(40) 4=treatment composition according to the invention;

(41) 5=additional lubricant (oil).

(42) It has been shown that a metal surface treatment composition and treatment method according to the invention provide a balanced improvement of the tribology and adhesion properties allowing welding operations, if required. Therefore the metal surfaces treated according to the invention, in particular zinc or zinc alloy coated surfaces thus treated, are attractive for use in manufacturing processes of articles, such as automotive (body) parts, that involve forming, joining and painting operations.