Painting pre-treatment processes with low environments impact, as an alternative to conventional phosphating treatments

Abstract

Disclosed is a process alternative to the zinc phosphating and phosphodegreasing processes, which comprises: >Zinc phosphating replacement a. a step of alkaline degreasing of the article to be phosphated; b. a first wash with tap water; c. a second wash with demineralized water; d. a conversion treatment in a bath containing zirconium salts, phosphates, fluoride complexes, ammonia, at least one corrosion inhibitor, at least one process accelerator, at least one sequestering agent, a reaction sludge thickening system, and optionally, titanium and vanadium compounds; e. a final wash before treatment of the article in the oven. >Phosphodegreasing process replacement a. a conversion treatment in a bath containing zirconium salts, phosphates, fluoride complexes, ammonia, at least one corrosion inhibitor, at least one process accelerator, at least one sequestering agent, at least one surfactant, a reaction sludge thickening system, and optionally, titanium and vanadium compounds; b. a wash with tap water; c. a wash with demineralized water before treatment of the article in the oven.

Claims

1. A process comprising: applying a conversion treatment to a metal, the treatment comprising phosphates in a concentration of 10 mg/L to 500 mg/L, at least one corrosion inhibitor, at least one sequestering agent, a process accelerating agent, a reaction sludge thickening system, and zirconium salts; wherein the process accelerating agent is selected from the group consisting of ammonium nitrate, nitroguanidine derivatives, benzene derivatives, and combinations thereof; wherein the corrosion inhibitor is hexamethylenetetramine; and wherein a conversion layer is formed on the metal.

2. The process of claim 1, wherein the zirconium salts are selected from the group consisting of fluorozirconic acid, ammonium zirconium carbonate, potassium fluorozirconate, and combinations thereof.

3. The process of claim 2, wherein the conversion treatment is applied in a bath.

4. The process as claimed in claim 1, wherein the phosphates are selected from the group consisting of orthophosphates, ammonium polyphosphates, and combinations thereof.

5. The process according to claim 1, the treatment further comprising titanium compounds.

6. The process of claim 5, wherein the titanium compounds are selected from the group consisting of fluorotitanic acid, titanium oxalate, titanium oxide, potassium fluorotitanate; and combinations thereof.

7. The process according to claim 1, wherein the reaction sludge thickening system consists of a combination of a polysaccharide and a glycol.

8. The process of claim 1, the treatment further comprising fluoride complexes.

9. The process of claim 1, the treatment further comprising ammonia.

10. The process of claim 1, the treatment further comprising titanium compounds.

11. The process of claim 1, the treatment further comprising vanadium compounds.

12. The process of claim 1, further comprising alkaline degreasing the metal before applying the conversion treatment.

13. The process of claim 12, further comprising conducting a first wash of the metal after the alkaline degreasing.

14. The process of claim 13, wherein the first wash includes washing the metal with tap water.

15. The process of claim 13, further comprising conducting a second wash of the metal after the first wash.

16. The process of claim 15, wherein the second wash includes washing the metal with demineralised water.

17. The process of claim 1, further comprising conducting a final wash of the metal after applying the conversion treatment.

18. The process of claim 1, wherein the conversion treatment further comprises a real-time indicator.

19. The process of claim 1, wherein the conversion treatment further comprises an indicator that comprises a color of the conversion layer.

20. The process of claim 19, wherein the color ranges from iridescent yellow to dark red or blue.

21. The process of claim 1, wherein the conversion treatment is applied by a spray.

22. The process of claim 1, wherein the process is a zinc phosphating substitute process.

23. The process of claim 1, wherein the process is a phosphodegreasing process substitute.

24. A process which can be used as a substitute for phosphodegreasing processes, comprising: a. applying a conversion treatment to a metal in a bath, the treatment containing zirconium salts, phosphates in a concentration of 10 mg/L to 500 mg/L, fluoride complexes, ammonia, at least one corrosion inhibitor, at least one process accelerating agent, at least one sequestering agent, at least one surfactant, a reaction sludge thickening system, and optionally, titanium and vanadium compounds, wherein a conversion layer is formed; b. washing the metal with tap water; and, c. washing the metal with demineralised water before treating the metal in an oven, wherein the process accelerating agent is selected from the group consisting of ammonium nitrate, nitroguanidine derivatives, benzene derivatives, and combinations thereof; wherein the corrosion inhibitor is hexamethylenetetramine; and wherein an indicator indicates the existence of the conversion layer.

Description

DESCRIPTION OF THE INVENTION

(1) The invention relates to a phosphating process for multi-metal pre-painting surface treatments which, with different application procedures, provides an alternative to traditional zinc phosphating processes and phosphodegreasing processes.

(2) The process of the invention offers, for both applications: Low environmental impact, due to the elimination of heavy metals; Simplification of the process in engineering terms, due to the drastic reduction in the number of steps required; Energy saving, in view of the possibility of working at lower operating temperatures; A reduction in the number of products involved in the treatment; A drastic reduction, estimated at a minimum of 90%, in the quantity of reaction sludge, which is very friable, and consequently easier to remove; A reduction in deposits/encrustations in the feed pipes and heat exchangers; The formation of a coloured conversion layer which gives the operatives on the production line an immediate idea in real time of the operation of the line, with no need to wait for the results of destructive tests.

(3) This aspect appears particularly important, and constitutes an important innovation compared with other products alternative to the conventional zinc phosphating and phosphodegreasing products currently used, paving the way for their industrial use. While conventional products, due to the colour acquired by the conversion layer obtained, immediately show whether the quality of the coating is good or not, the alternative products applied to date on industrial production lines give a colourless or slightly yellowish coating, the colour of which can easily be mistaken for rust, which means that it is very difficult, if not impossible, to evaluate the quality correctly.

(4) The process according to the invention therefore produces a significant reduction in operating costs, greater operational safety, and is more environment-friendly.

(5) The process can be applied, by spray or immersion, to all types of substrate, such as cold-rolled steel (CRS), electrogalvanised steel (EG), hot-dip galvanised steel (HDG) or aluminium (AL), and is compatible with the subsequent application of all the main painting processes now known (electrophoresis, powder paints and liquid paints).

(6) The mechanical performance and corrosion resistance of these products are at least comparable to those obtained with conventional cycles.

(7) In a first embodiment thereof, the invention provides a process that replaces zinc phosphating, comprising: a) a step of alkaline degreasing of the article to be phosphated; b) a first wash with tap water; c) a second wash with demineralised water; d) a conversion treatment in a bath containing zirconium salts, phosphates, fluoride complexes, ammonia, at least one corrosion inhibitor, at least one process accelerator, at least one sequestering agent, and optionally, titanium and vanadium compounds; e) a final wash before treatment of the article in the oven.

(8) Degreasing (step a) serves to eliminate all trace of oils, fats, cleaning paste, oxides and any other impurities from the coil surface, in order to leave a perfectly clean metal surface ready for subsequent treatments.

(9) Normally, said degreasing is performed with liquid products in aqueous solution at an alkaline pH (10-14). The use concentration is between 1% and 10%, and the temperature of the working bath between 50 C. and 70 C., for a treatment time of between 30 and 120 seconds.

(10) The degreasing bath typically contains 2 to 20 g/l of KOH or NaOH, 2 to 20 g/l of P.sub.2O.sub.5, 200 to 3000 ppm of surfactants, and 1 to 10 g/l of sequestering additives.

(11) P.sub.2O.sub.5 is present in the form of sodium or potassium orthophosphates (monosodium, disodium or trisodium phosphate) or polyphosphates (tripolyphosphate or neutral pyrophosphate).

(12) The surfactants most commonly used are selected from ethoxylated and/or ethoxy-propoxylated fatty alcohols with C9-C11, C12-C13 or C12-C18 alcohol chain, with different degrees of ethoxy-propoxylation.

(13) The sequestering additives are preferably selected from nitriloacetic acid, sodium gluconate, gluconic acid, ethylenediaminetetraacetic acid disodium, ethylenediaminetetraacetic acid trisodium, phosphonates, acrylates and polyacrylates.

(14) The wash with tap water (step b) serves to eliminate all trace of the preceding step; the temperature is normally between 30 C. and 60 C., with times ranging between 15 and 60 seconds.

(15) Washing with demineralised water (step c) completes the action of the preceding step, and the operating conditions are the same; the temperature ranges between 30 C. and 60 C. for times of 15 to 60 secs.

(16) The conversion treatment (step d) is the characteristic feature of the invention. It is usually performed at a temperature of between 15 C. and 50 C., for times ranging between 20 a 120 seconds, depending on the speed of the line, the type of application (spray or immersion) and the quality/reactivity of the metal. The treatment is normally performed with the bath described above, based on zirconium salts and phosphates with a pH of between 4 and 5, used at concentrations of between 10 and 30 g/1.

(17) The zirconium salts are usually present in concentrations of 100 to 5000 mg/l, and are preferably selected from fluorozirconic acid, ammonium zirconium carbonate and potassium fluorozirconate.

(18) The phosphates, typically present in concentrations of 10-500 mg/l, are ammonium orthophosphates (monosodium, disodium or trisodium phosphate) or polyphosphates (tripolyphosphate or neutral pyrophosphate).

(19) The fluoride complexes are present in concentrations of 100-10000 mg/l, while ammonia is present in concentrations of 100-1000 ppm.

(20) The titanium compounds comprise, for example, fluorotitanic acid, titanium oxalate, titanium oxide and potassium fluorotitanate, and can be present in concentrations of 100-5000 mg/l.

(21) Other metals, such as vanadium, molybdenum and antimony, can be present in acid or salified form in concentrations of between 10 and 10000 mg/l.

(22) The corrosion inhibitor, present in concentrations of 100-500 ppm, can be a more or less branched amine, an alkine derivative or a thiourea derivative, and has the basic function of preventing the appearance of oxidative phenomena during accidental or intentional stoppages of the treatment line.

(23) The process accelerator is typically a donor compound of inorganic NO.sub.3, such as ammonium nitrate, or nitrogen organic compounds such as nitroguanidine or benzene derivatives, used alone or mixed together, in concentrations of 100-1500 ppm.

(24) The system that limits the quantity of sludge and makes it friable, and therefore easily removable, consists of a suitably balanced combination of a polysaccharide and a glycol.

(25) The sequestering agents are selected from those specified above for the degreasing bath, at concentrations of 10-5000 ppm.

(26) The morphology of the phosphate coating obtained, mostly consisting of zirconium and/or titanium phosphates, is compact, uniform and highly insoluble. Depending on the type of application (spray or immersion) and the type of metal, the thickness of the phosphate coating layer can range between 50 and 200 nm, and the colour of the layer can vary from iridescent yellow to dark red or blue.

(27) In a second embodiment thereof, the invention provides a process that replaces phosphodegreasing, comprising: a) a conversion treatment in a bath containing zirconium salts, phosphates, fluoride complexes, ammonia, at least one corrosion inhibitor, at least one process accelerator, at least one sequestering agent, at least one surfactant, and optionally, titanium and vanadium compounds; b) a wash with tap water; c) a wash with demineralised water before treatment of the article in the oven.

(28) Step a) is similar to step d) described above, in terms of the components and their concentrations, with the sole difference that the conversion bath also contains at least one surfactant able to eliminate traces of oils, fats, cleaning paste, oxides and all other impurities from the surface of the material. The same surfactants as described above for the degreasing step can conveniently be used.

(29) Similarly, washing steps b) and c) are performed under the same conditions as for the corresponding washing steps of the zinc phosphating replacement process described above.

(30) The invention is described in greater detail in the examples below.

Example 1Replacement of Zinc Phosphating Processes

(31) TABLE-US-00001 Element Concentration Degreasing KOH 4 g/l P.sub.2O.sub.5 from neutral potassium pyrophosphate 5 g/l Surfactants with chain C9-C11 + 5 and 6 moles of OE 500 ppm Sodium gluconate 3 g/l Use concentration of product 3-5% Temperature 50-60 C. Treatment time 30 sec. Spray pressure 2 bars First wash Continuously renewed tap water Temperature 30 C. Treatment time 30 sec. Spray pressure 2 bars Second wash Continuously renewed demineralised water Temperature 30 C. Treatment time 30 sec. Spray pressure 2 bars Conversion treatment Zr (from fluorozirconic acid) 500 mg/l P.sub.2O.sub.5 (from dibasic ammonium phosphate) 25 mg/l NH.sub.3 50 ppm Total fluorides 200 ppm Nitrogen organic accelerator 750 ppm Hexamethylenetetramine (inhibitor) 300 ppm Polysaccharide/glycol mixture 500 ppm Phosphonate 1000 ppm Vanadium salts 10 ppm Use concentration of immersion product 3% Use concentration of spray product 1% Temperature Ambient Spray treatment time 20 sec. Immersion treatment time 60 sec. pH 4.5

Example 2Replacement of Phosphodegreasing Processes

(32) TABLE-US-00002 Element Concentration Conversion treatment Zr (from fluorozirconic acid) 500 mg/l P.sub.2O.sub.5 (from dibasic ammonium phosphate) 25 mg/l NH.sub.3 50 ppm Total fluorides 200 ppm Nitrogen organic accelerator 750 ppm Hexamethylenetetramine 300 ppm Phosphonate 1000 ppm Surfactants with chain C9-C11 + 4-5 moles of OE/5-4 300 ppm moles of OP Polysaccharide/glycol mixture 500 ppm Vanadium salts 10 ppm Use concentration of spray product 1 to 3% Temperature 30 to 50 C. Treatment time 120 sec. pH 4.5 First wash Continuously renewed tap water Temperature 30 C. Treatment time 30 sec. Spray pressure 2 bars Second wash Continuously renewed demineralised water Temperature 30 C. Treatment time 30 sec. Spray pressure 2 bars

Example 3Laboratory Tests and Results

(33) The laboratory tests were conducted so as to compare the results obtained with those of conventional cycles.

(34) Cold-rolled steel plates (CRS), electrogalvanised steel (EG), hot-dip galvanised steel (HDG) and aluminium (AL) were tested; after the cycles, they were painted with 2 types of paint for both cases of pre-treatment, according to the normal conditions of industrial application.

(35) The treated and painted plates were subjected to corrosion-resistance tests in a salt spray (fog) chamber, in accordance with Standard ASTM B 117. Panels on which a deep cross-cut was made down to the basic metal, with protected edges, were inspected for the appearance of the first signs of corrosion.

(36) For convenience, Table 1 shows the ways in which the various cycles tested were distinguished. The results obtained are expressed as hours of exposure in the salt spray chamber until the appearance of the first signs of oxidation, such as sub-corrosion or flaking of the paint at a distance of >1 mm from the cut.

(37) TABLE-US-00003 TABLE 1 PROCESS SUBSTRATE PAINT CODE RESULTS Zinc phosphating CRS 1 ZSTC1 700 conventional spray 2 ZSTC2 850 process EG 1 ZSTE1 1000 2 ZSTE2 1000 HDG 1 ZSTH1 800 2 ZSTH2 800 AL 1 ZSTA1 1000 2 ZSTA2 1000 Process alternative CRS 1 ZSIC1 700 to conventional zinc 2 ZSIC2 900 phosphating spray EG 1 ZSIE1 1000 process 2 ZSIE2 1000 HDG 1 ZSIH1 800 2 ZSIH2 800 AL 1 ZSIA1 1000 2 ZSIA2 1000 Zinc phosphating CRS 1 ZDTC1 700 conventional immersion 2 ZDTC2 850 process EG 1 ZDTE1 1000 2 ZDTE2 1000 HDG 1 ZDTH1 800 2 ZDTH2 800 AL 1 ZDTA1 1000 2 ZDTA2 1000 Process alternative to CRS 1 ZSIC1 700 conventional zinc 2 ZSIC2 900 phosphating immersion EG 1 ZSIE1 1000 process 2 ZSIE2 1000 HDG 1 ZSIH1 800 2 ZSIH2 800 AL 1 ZSIA1 1000 2 ZSIA2 1000 Phosphodegreasing CRS 1 FTC1 500 conventional spray 2 FTC2 600 process EG 1 FTE1 600 2 FTE2 600 HDG 1 FTH1 700 2 FTH2 750 AL 1 FTA1 600 2 FTA2 600 Process alternative CRS 1 FIC1 700 to conventional zinc 2 FIC2 900 phosphating spray EG 1 FIE1 800 process 2 FIE2 800 HDG 1 FIH1 800 2 FIH2 800 AL 1 FIA1 600 2 FIA2 600

(38) In view of the results obtained, the two alternative processes were further tested to evaluate the quantity of sludge formed, which was compared, once again, with that obtained in the corresponding conventional processes. The results are shown in Table 2 below.

(39) TABLE-US-00004 TABLE 2 QUANTITY OF SLUDGE PROCESS Values not absolute, but relative Conventional zinc phosphating 100 Process alternative to conventional 15 zinc phosphating process Conventional phosphodegreasing 100 Process alternative to conventional 10 phosphodegreasing

Evaluation of Technical and Economic Benefits

(40) When the laboratory tests had been performed, and the very good results objectively evaluated, it was necessary to ensure that after industrialisation, the process would guarantee the same performance on the production line.

(41) For this purpose, the product according to the invention was tested confidentially, for a period required to assess its real benefits, on two production lines in the field of household appliances; the first used traditional trication multi-metal zinc phosphating, and the second used normal multi-metal phosphodegreasing.

(42) In all cases it was found that compared with conventional cycles: the quality of the treated products was equal, if not better; there is a real 90% reduction in sludge on the production line, which in both cases was removed very easily, with no problems; the coloured conversion layer gives operators an idea of the operation of the line in real time, immediately showing whether the quality of the coating is good or poor, thus allowing an instant, correct quality assessment; the presence of the inhibitor prevented the appearance of oxidative phenomena on the surfaces of the article, even in the event of lengthy stoppages of the production lines; the process of the invention is simpler to perform, thus improving user safety.

(43) The product is cheaper, guaranteeing lower electricity consumption, less maintenance of the tanks, and lower logistical and waste water disposal costs.