Dry lubricant for zinc coated steel

Abstract

The present invention relates to the use of an alkaline, aqueous coating composition for coating of zinc or zinc alloy coated steel substrates, comprising one or more alkaline sulfates, and one or more alkaline carbonates, wherein the pH of the composition ranges from 9-12. The present invention also defines a method for the non-reactive coating of zinc or zinc alloy coated steel substrates by use of said compositions and further relates to the application of said method as a surrogate for pre-phosphating of zinc or zinc alloy coated steel substrates in industrial applications.

Claims

1. A method for coating zinc or zinc alloy coated steel substrates, comprising: contacting a zinc or zinc alloy coated steel substrate with an aqueous composition comprising: (i) one or more alkaline sulfates selected from the group consisting of sodium sulfate, potassium sulfate, ammonium sulfate, and mixtures thereof, (ii) one or more alkaline carbonates selected from the group consisting of alkaline metal carbonates, ammonium carbonate, and mixtures thereof, and (iii) 0 to less than 1 g/l of water soluble inorganic phosphate salts calculated as PO.sub.4; wherein pH of the composition ranges from 9-12; drying the aqueous composition on the zinc or zinc alloy coated steel substrate without intermediate rinsing, thereby forming a coating having a coating weight after drying of 0.05 to 1.0 g/m.sup.2.

2. The method of claim 1, wherein the total alkaline sulfate concentration of the aqueous coating composition is 7-100 g/l.

3. The method of claim 1, wherein the one or more alkaline carbonates in the aqueous coating composition are selected from the group consisting of sodium carbonate, ammonium carbonate, and mixtures thereof.

4. The method of claim 1, wherein the total alkaline carbonate concentration of the aqueous coating composition is 0.5-40 g/l.

5. The method of claim 1, wherein the coating composition additionally comprises chelating agents selected from ?-hydroxy-carboxylic acids.

6. The method of claim 5, wherein the weight fraction of chelating agents in the form of their sodium salts is at least 0.5 wt. %, but less than 10 wt. % based on a total dry salt concentration of the coating composition.

7. The method of claim 1, wherein the coating composition additionally comprises silicates.

8. The method of claim 7, wherein the silicates are contained in the coating composition in an amount that gives rise to an elemental loading of less than 2.0 mg/m.sup.2, but at least 0.1 mg/m.sup.2 with respect to the element Si.

9. The method according to claim 1, wherein the aqueous coating composition has a total dry salt concentration in a range of 14-200 g/l.

10. A method for coating of zinc or zinc alloy steel substrates, wherein the method comprises: (a) coating a zinc or zinc alloy coated steel substrate with a wet film of an aqueous coating composition having a pH of 10.2-11.5 and comprising: (i) 7-100 g/l of one or more alkaline sulfates selected from the group consisting of sodium sulfate, potassium sulfate, ammonium sulfate, and mixtures thereof; (ii) 0.5-40 g/l of one or more alkaline carbonates selected from the group consisting of alkaline metal carbonates, ammonium carbonate, and mixtures thereof; and (iii) 0 to less than 1 g/l of water soluble inorganic phosphate salts calculated as PO.sub.4; (b) drying the coated wet film on the zinc or zinc alloy coated steel substrate at temperatures in a range of 40-100? C.

11. The method according to claim 10, wherein the temperature of the aqueous coating composition during step (a) lies in a range of 15-35? C.

12. The method according to claim 10, wherein subsequent to step (b) a phosphating step (c) is conducted.

13. The method according claim 12, wherein subsequent to step (b) the surfaces of the zinc coated steel substrates are loaded with an oil film, prior to any phosphating step (c).

14. The method according to claim 1, wherein components (i), (ii) and (iii) are selected such that the coating composition has an etching rate of less than 0.01 g/m.sup.2 per hour with respect to the element Zn.

15. The method according to claim 10, wherein the coating composition of step (a), additionally comprises: (iv) chelating agents selected from ?-hydroxy-carboxylic acids present in a weight fraction in the form of their sodium salts of at least 0.5 wt. %, but less than 10 wt. % based on a total dry salt concentration of the coating composition; and (v) silicates present in an amount that gives rise to an elemental loading of less than 0.8 mg/m.sup.2, with respect to the element Si; and final coating weight after drying step (b) is 0.1 g/m.sup.2 and an absolute amount of the element Si on top of the zinc coated substrate being at least 0.1 mg/m.sup.2 and less than 0.8 mg/m.sup.2.

16. A method for coating zinc or zinc alloy coated steel substrates, comprising the steps of: (a) coating a zinc or zinc alloy coated steel substrate with a wet film of an aqueous composition having pH from 9-12 and temperature from 15-35? C. consisting of: (i) 7-100 g/l of one or more alkaline sulfates selected from the group consisting of sodium sulfate, potassium sulfate, ammonium sulfate, and mixtures thereof, (ii) 0.5-40 g/l of one or more alkaline carbonates selected from the group consisting of alkaline metal carbonates, ammonium carbonate, and mixtures thereof, (iii) 0 to less than 1 g/l of water soluble inorganic phosphate salts calculated as PO.sub.4, (iv) less than 0.1 g/l of a total amount of Zr, Ti, Mo, and Cr, (v) optionally, a weight fraction between 0.5 wt % and 10 wt. % based on the total dry salt concentration of the coating composition of a water soluble sequestrant selected from the group consisting of ethylenediaminetetraacetic acitd (EDTA), ?-hydroxy-carboxylic acids, nitrilodiacetic acid (NTA), gluconate sodium gluconate, and mixtures thereof, and (vi) optionally, an amount of silicates that results in an elemental loading on the substrate of less than 2.0 mg/m.sup.2 but at least 0.1 mg/m.sup.2 with respect to the element Si; wherein the aqueous coating composition has a total dry salt concentration in a range of 14-200 g/l; and (b) drying the coated wet film on the zinc or zinc alloy coated steel substrate at temperatures in a range of 40-100? C., such that the dried film has a final coating weight; wherein the final coating weight after drying is 0.05 to 1.0 g/m.sup.2.

Description

EXAMPLES

(1) Part 1: Corrosion Resistance

(2) Zinchot dipped galvanized (HDG) steel panels (20?10 cm) were treated according to the following sequence: cleaning dip rinse (tap water) drying (compressed air) coating: 25? C., 5 seconds, dip squeezing to 4 ml/m.sup.2 drying (oven, 80? C., 900 seconds) surface loading with 1 g/m.sup.2 of RP 4107 S (oil commercially available from Fuchs Petrolub SE)

(3) TABLE-US-00001 TABLE 1a Solution A1 A2 B1 B2 Na.sub.2SO.sub.4 9.7 g/l 19.4 g/l 10.7 g/l 21.4 g/l K.sub.2SO.sub.4 26.4 g/l 52.8 g/l 28.7 g/l 57.4 g/l Na.sub.2CO.sub.3 5.5 g/l 11.0 g/l 7.2 g/l 14.4 g/l Sodium 0.2 g/l 0.4 g/l 1.2 g/l 2.4 g/l gluconate Coating 0.15 g/m.sup.2 0.3 g/m.sup.2 0.15 g/m.sup.2 0.3 g/m.sup.2 Weight 1 1 The coating weight is determined by measuring the weight difference between the sample after step 6 and the same sample after the following treatment: dip in deionized water (? < 1 ?Scm?1) at 50? C. for 10 minutes; remove and rinse with deionized water (? < 1 ?Scm?1) at 20? C. for 10 seconds; and blowing clean compressed air to remove adherent wet film; and drying at 80? C. under 1 atm. for 15 minutes

(4) Table 1a depicts the recipes for each coating composition being tested under step 3 of the above-mentioned process sequence as well as the yielded coating weights after step 6 of the above-mentioned process sequence.

(5) After treatment the steel panels were evaluated according to the DIN 50 017-KTW test:

(6) Test specimens were placed in an enclosed chamber, and exposed to a changing climate that comprised the following two part repeating cycle:

(7) 8 hours exposure to a heated, saturated mixture of air and water vapor at temperatures of +40? C. and a relative humidity of 100% RH followed by 16 hours exposure to room temperature (+18 to +28? C. according to DIN 50 014) whilst the relative humidity is maintained at 100% RH.

(8) Table 1b shows the degree of corrosion after 5 cycles of the above-mentioned test procedure.

(9) TABLE-US-00002 TABLE 1b Sample Coating Corrosion % 0 none 10 1 A1 3 2 A2 2 3 B1 2 4 B2 1
Part 2: Lubricity

(10) Zinc coated steel stripes (40?5 cm) were coated and subsequently charged with 1.0 g/m.sup.2 of a certain lubricative oil commercially available from Fuchs Petrolub SE (see table 2a). While for panel sample EG-1 a dry-in-place coating based on a commercial available reactive coating composition from Henkel AG & Co. KGaA was applied, the other samples were coated according to this invention.

(11) The zinc coated steel stripes were processed according to the following sequence:

(12) 1. cleaning

(13) 2. dip rinse (tap water)

(14) 3. drying (compressed air)

(15) 4. coating: 25? C., 5 seconds, dip

(16) 5. squeezing to 1 ml/m.sup.2 (C1; C2) or 1.5 ml/m.sup.2 (C3; C4)

(17) 6. drying (oven, 80? C., 900 seconds)

(18) 7. oil deposition

(19) Table 2a lists the recipes of the coating compositions applied in step 4 of the above-mentioned process sequence, while Table 2b depicts the coating weight yielded after step 6 of the above-mentioned process sequence as well the type of oil loaded to each dried steel strip.

(20) TABLE-US-00003 TABLE 2a Solution C1 C2 C3 C4 Na.sub.2SO.sub.4 11.6 g/l 23.1 g/l 8.9 g/l 17.8 g/l K.sub.2SO.sub.4 32.0 g/l 55.8 g/l 23.9 g/l 47.8 g/l Na.sub.2CO.sub.3 6.7 g/l 13.3 g/l 6.0 g/l 12.0 g/l Sodium gluconate 0.4 g/l 0.7 g/l 1.0 g/l 2.0 g/l

(21) TABLE-US-00004 TABLE 2b Sample Coating Coating weight Oil for forming 0 none // PL 3802-39 S EG-1 Granodine? 5895 0.2 g/m.sup.2 PL 3802-39 S EG-2 C1 0.05 g/m.sup.2 PL 3802-39 S EG-3 C2 0.1 g/m.sup.2 PL 3802-39 S GA-4 C2 0.1 g/m.sup.2 PL 3802-39 S HDG-1 C3 0.05 g/m.sup.2 RP 4107 S HDG-1 C4 0.11 g/m.sup.2 RP 4107 S EG Electrogalvanized Steel GA Galvannealed Steel HDG Hot Dip Galvanized Steel

(22) The test stripes were then evaluated with a tribometric test using QUIRY HYDROMAXE 2B machine:

(23) The sample was coated with a lubricant. While the sample was squeezed horizontally between two flat dies, a vertical traction device pulled it up. The friction coefficient (?) of the lubricant is the ratio of the traction force to the pressing force.

(24) Parameters of the Test:

(25) Pressing force, daN: 500 (see Table 2c); 0-800 (see Table 2d) Pressing force gradient, daN/s: constant Speed, mm/min: 20 Number of cycles: up to 10

(26) Table 2c lists the corresponding tribometric test results with regard to the friction coefficient at different pressing forces while Table 2d resembles the test results with regard to the maximum friction coefficient.

(27) TABLE-US-00005 TABLE 2c friction coefficient (?) at different pressing forces Sample Coating 200 daN 400 daN 600 daN 800 daN HDG-0 none 0.153 0.129# 0.096 0.078 HDG-1 E1 0.096 0.079 0.064 0.058 HDG-2 E2 0.101 0.082 0.069 0.063 HDG Hot Dip Galvanized Steel #sticking and overheating - trial stopped

(28) TABLE-US-00006 TABLE 2d Max friction coefficient (?) during different cycles Sample Coating Cycle 2 Cycle 4 Cycle 6 Cycle 10 EG-0 none 0.279 0.514# // // EG-1 Granodine 0.183 0.202 0.248# // 5895 EG-2 C1 0.105 0.123 0.174 0.206 EG-3 C2 0.091 0.093 0.094 0.105 GA-1 C2 0.108 0.125 0.172 0.249 EG Electrogalvanized Steel GA Galvannealed Steel #sticking and overheating - trial stopped
Part 3: Dissolution Tests on Zinc Coated Steel Alloys

(29) The effect of certain coating compositions on the zinc dissolution rate is shown in Table 3a.

(30) The evaluations were made putting hot dipped galvanized (HDG) steel panels in contact with the respective coating composition for 24 hours as well as 48 hours at two different temperatures (25? C. and 40? C.). For each contact time, a different solution/panel was used. At the evaluation time, the panel was gently rinsed and removed; the solution was acidified with HCI 1:1 to dissolve possible precipitates formed and the dissolved zinc was then measured with ICP-OES.

(31) TABLE-US-00007 TABLE 3a T = 25? C. T = 40? C. t = 24 h t = 48 h t = 24 h t = 48 h Zn, Zn, Zn, Zn, Solution composition, g/l. mg/m.sup.2 mg/m.sup.2 mg/m.sup.2 mg/m.sup.2 1 K.sub.2SO.sub.4, 52/Na.sub.2SO.sub.4, 19 227 570 442 2075 2 K.sub.2SO.sub.4, 51/Na.sub.2SO.sub.4, 19/ 212 495 370 2137 Na.sub.2CO.sub.3, 1 3 K.sub.2SO.sub.4, 50/Na.sub.2SO.sub.4, 18.5/ 152 277 235 572 Na.sub.2CO.sub.3, 2.5 4 K.sub.2SO.sub.4, 48/Na.sub.2SO.sub.4, 17.5/ 185 148 85 190 Na.sub.2CO.sub.3, 5 5 K.sub.2SO.sub.4, 45/Na.sub.2SO.sub.4, 16.5/ 55 123 157 152 Na.sub.2CO.sub.3, 9.5 10 K.sub.2SO.sub.4, 26/Na.sub.2SO.sub.4, 9.5/ 85 62 82 85 Na.sub.2CO.sub.3, 35.5 11 Na.sub.2CO.sub.3, 71 177 265 237 231