METHOD FOR APPLYING A CORROSION-RESISTANT COATING TO A METAL PART, AQUEOUS COATING COMPOSITION, CORROSION-RESISTANT COATING FOR METAL PARTS AND COATED METAL PART

Abstract

The invention relates to a method for applying a corrosion-resistant coating to a metal part by immersing/withdrawing said part in/from an aqueous paint bath. The invention is characterized in that the aqueous paint bath includes water, a binder and cellulose microfibrils, and in that the coated metal part is subjected to vibrations when removed from the bath.

The invention also relates to an aqueous coating composition including water, a binder, metal particles and CMNFs.

The invention also relates to a corrosion-resistant coating for metal parts that is characterized in that it is obtained by the method according to the invention, the coating layer subsequently being subjected to a curing operation preferably at a temperature of between 70 C. and 350 C.

Lastly, the invention relates to a metal part provided with a corrosion-resistant coating according to the invention.

Claims

1.-17. (canceled)

18. A method for applying a corrosion-resistant coating to a metal part by immersing/withdrawing said part in/from an aqueous paint bath, wherein the aqueous paint bath includes water, a binder and cellulose microfibrils or nanofibrils (CMNFs), and the coated metal part is subjected to vibrations when removed from the bath.

19. The method according to claim 18, wherein the CMNFs have a length less than 100 m and a diameter less than 100 nm.

20. The method according to claim 19, wherein the CMNFs have a length ranging from 1 to 2 m and a diameter varying from 20 to 70 nm.

21. The method according to claim 18, wherein the CMNFs are in a tile-form of a maximum average dimension of at least 10 microns and a minimum average dimension less than 1 micron.

22. The method according to claim 18, wherein the aqueous paint bath includes 0.2 to 8% by weight, compared to the total weight of the bath, of cellulose microfibrils.

23. The method according to claim 18, wherein the bath includes 3 to 50% by weight, compared to the total weight of the bath, of binder.

24. The method according to claim 18, wherein the binder is selected from binders based on silane, binders based on titanate, binders based on zirconate, binders based on silicate, binders based on cross-linked phenoxy resins in aqueous phase.

25. The method according to claim 18, wherein the bath includes from 30 to 85% by weight, compared to the total weight of the bath, of water.

26. The method according to claim 18, wherein the bath includes from 10 to 40% by weight, compared to the total weight of the bath, of particulate metal.

27. The method according to claim 26, wherein the particulate metal is in lamellar form.

28. The method according to claim 26, wherein the particulate metal is selected from zinc, aluminium, chromium, manganese, nickel, titanium, alloys and intermetallic mixtures thereof, and mixtures thereof.

29. The method according to claim 18, wherein the bath also includes one or more of the following compounds: a. 1 to 30% by weight of organic solvent or a mixture of organic solvents, compared to the total weight of the bath, b. 0.1 to 7% by weight of molybdenum oxide, compared to the total weight of the bath, c. 0.5 to 10% by weight, compared to the total weight of the bath, of a corrosion-resistance performance enhancer selected from the group constituted of yttrium, zirconium, lanthanum, cerium, praseodymium, in the form of oxides or salts, d. 0.2 to 4% by weight, compared to the total weight of the composition, of a corrosion inhibiting pigment such as aluminium triphosphate, e. A silicate of sodium, potassium or lithium.

30. The method according to claim 29, wherein the corrosion-resistance performance enhancer is Y.sub.2O.sub.3.

31. The method according to claim 18, wherein acceleration of the vibrations varies from 10 m/s.sup.2 to 100 m/s.sup.2.

32. An aqueous coating composition including water, a binder, metal particles and CMNFs.

33. A corrosion-resistant coating for metal parts, wherein it is obtained by the method according to claim 18, the coating layer subsequently being subjected to a curing operation.

34. The corrosion-resistant coating for metal parts according to claim 33, wherein the curing operation is carried out at a temperature of between 70 C. and 350 C.

35. The corrosion-resistant coating for metal parts according to claim 33, wherein prior to the curing operation, the coated metal parts are subjected to a drying operation.

36. The corrosion-resistant coating for metal parts according to claim 35, wherein the drying operation is carried out at a temperature of between 60 C. and 80 C.

37. The corrosion-resistant coating for metal parts according to claim 33, wherein it is applied to the metal parts to protect, with a uniform thickness of between 5 and 100 m.

38. The corrosion-resistant coating for metal parts according to claim 33, wherein it is applied to the metal parts to protect, with a uniform thickness of between 10 and 30 m.

39. A metal part provided with a corrosion-resistant coating according to claim 33.

Description

EXAMPLE N.SUP.O .1

[0102] In the example that follows, different rheology agents were dispersed in baths of standard composition (CStd):

[0103] Bath according to the invention: [0104] A: CStd+0.5% by weight (of dry matter) of Curran THIX 5000 of the Cellucomp Company.

[0105] BathsComparative Examples: [0106] B: CStd+0.5% by weight (of dry matter) of xanthan gum (Rhodopol 23, supplier: Rhodia) [0107] C: CStd+0.7% by weight (of dry matter) of conventional cellulosic thickener (CELLOSIZE QP4400, supplier: Dow Chemical) [0108] D: CStd+1% by weight (of dry matter) of an organophilic clay (Bentone EW, supplier: Elementis Specialties) [0109] E: CStd+0.75% by weight (of dry matter) of a polyurea (BYK420, supplier: BYK-Chemie GmbH)

[0110] The standard reference composition corresponds to:

TABLE-US-00004 De-ionized water 39.06% DPG 10.29% Synperonic 13/6.5 3.15% Silquest A 187 8.66% Zinc* 32.12% Aluminium** 5.08% Schwego foam 0.4% Nipar S10 0.71% Aerosol TR70 0.53% *Zinc in the form of a paste at around 95% in white spirit **Aluminium in the form of a paste at around 70% in DPG (dipropylene glycol) Synperonic 13/6.5: polyoxyethylene (6.5) isotridecanol surfactant Silquest A187: gamma-glycidoxypropyltrimethoxyysilane Schwego foam: anti-foaming agent Nipar S10: 1-nitropropane Aerosol TR70: anionic surfactant, sodium bistridecyl sulfosuccinate.

[0111] To assist the reader, the curing conditions may be defined as below: [0112] Pre-drying: 15 min plateau at 70 C. by convection [0113] Curing T, duration: 25 min plateau at 310 C. by convection

[0114] Table 1 below shows that, in the absence of vibrations applied to a part withdrawn at 1 m/min: [0115] A part withdrawn from bath A, then cured for 25 min at 310 C., does not run, has a high average dry film thickness (62 microns), does not have a uniform appearance. [0116] The parts withdrawn from baths B or C, then cured for 25 min at 310 C., have numerous appearance defects (accumulation of coating at the bottom of the plate, disbonding of the film after curing). [0117] A part withdrawn from bath D, then cured for 25 min at 310 C., has low average thickness and appearance defects. [0118] A part withdrawn from bath E, then cured for 25 min at 310 C. has a low average thickness.

TABLE-US-00005 TABLE 1 Comparison, in the absence of vibrations, of the films obtained after curing of parts withdrawn from CStd baths containing different types of thickening agents Acc. Speed Displ. Frequency Thickness (m) Bath m/s.sup.2 mm/s mm Hz Flow Upper Lower Average Observations A 0 0 0 0 No 62 64 62 Non-uniform appearance B 0 0 0 0 Yes 60 85 72 Delamination at bottom of plate C 0 0 0 0 Yes 35 61 48 Delamination at Lot bottom of plate D 0 0 0 0 Yes 14 22 18 Bubbling + grains E 0 0 0 0 Yes 12 13 12 ok

[0119] Table 2 below shows that, in the presence of vibrations applied to a withdrawn part, parallel to the direction of immersing/withdrawing the part in/from the bath, only the part withdrawn from a CStd bath+0.5% (of active material) of CMNF (bath A), then cured for 25 min at 310 C., has a uniform appearance and an average thickness approximately of 33 microns. The application of vibrations to a part withdrawn from the other baths did not influence the appearance and the deposited thickness.

TABLE-US-00006 TABLE 2 Comparison, in the presence of vibrations of around 36 Hz (acceleration of around 18-20 m/s.sup.2, amplitude of around 1.2-1.3 mm), of films obtained after curing of parts withdrawn from CStd baths containing different types of thickening agents Acc. Speed Displ. Frequency Thickness (m) Bath m/s.sup.2 mm/s mm Hz Flow Upper Lower Average Observations A 19.6 90.4 1.219 37 non 27 39 33 Significant effect of vibrations B 19.8 92.3 1.231 37 yes 64 83 73.5 Lots of bubbles + flake off C 19.7 92.8 1.246 37 yes 46 72 59 Lots of bubbles + flake off D 18.1 92.8 1.295 36 yes 13 22 17.5 Lots of bubbles + grains E 18.2 88.4 1.241 36 yes 13 14 13.5 Ok

[0120] Table 3 below shows that, in the presence of vibrations applied to a withdrawn part, parallel to the direction of immersing/withdrawing the part in/from the bath, of a higher frequency or amplitude than in table 2, only the part withdrawn from a CStd bath+0.5% (of active material) of CMNF (bath A), then cured for 25 min at 310 C. continues to influence significantly the thickness of the uniform film deposited (33 microns on average for an acceleration of around 18-19 m/s.sup.2 vs. 25.5 microns for an acceleration of around 29-30 m/5.sup.2).

TABLE-US-00007 TABLE 3 Comparison, in the presence of vibrations of around 43 Hz (acceleration of around 29-30 m/s.sup.2, amplitude of around 1.3-1.5 mm), of films obtained after curing of parts withdrawn from CStd baths containing different types of thickening agents Thickener Acc. Speed Displ. Frequency Thickness (m) family m/s.sup.2 mm/s mm Hz Flow Upper Lower Average Observations A 29.4 116.3 1.368 43 no 19 32 25.5 Significant effect of vibrations Large difference lower/upper B 29.3 117.3 1.329 44 yes 63 78 70.5 Lots of bubbles + flake off C 29.3 123 1.48 42 yes 46 100 73 Lots of bubbles + flake off D 30.8 119 1.34 44 yes 14 18 16 Lots of bubbles + grains E 30.1 113.7 1.289 44 yes 11 13 12 Ok

[0121] FIG. 1 shows that the vibration (measurable notably via its frequency or its acceleration or instead its amplitude) imposed on the part emerging from the bath A makes it possible to adjust the thickness of the uniformly deposited coating.

[0122] FIG. 1: Evolution of the thickness deposited as a function of the acceleration (parallel vibration) as a function of the nature of the rheological agent of the CStd bath (from left to right: Fibre A=NMFC, Rhodopol 23=xanthan gum, QP4400=conventional cellulosic thickener, Bentone EW=organophilic clay, BYKE 420=thickener of the BYK company of polyurea type).

[0123] Grey: acceleration 0 m/s.sup.2; dots: acceleration 18 m/s.sup.2; dashes: acceleration 30 m/s.sup.2.

EXAMPLE N.SUP.O .2

[0124] In the example that follows, two different concentrations of CMNF (of dry matter) were dispersed in the CStd bath: [0125] CStd+0.3% by weight (of dry material) of CMNF (Exilva of the Borregaard Company [0126] CStd+0.5% by weight (of dry material) of CMNF (Exilva of the Borregaard Company)

[0127] 3 parts were immersed then withdrawn in/from each bath at a speed of 1 m/min. 3 vibrations, parallel to the direction of immersing/withdrawing the part in/from the bath, of different acceleration, were imposed on each part before curing: [0128] Vibration of 20 m/5.sup.2 [0129] Vibration of 47 m/5.sup.2 [0130] Vibration of 85 m/5.sup.2

[0131] Table 4 clearly shows that, after curing, the combination of the concentration of CMNF, in the bath, and the type of vibration imposed on the withdrawn part, makes it possible to adjust the thickness of the deposited coating.

TABLE-US-00008 TABLE 4 Influence of the concentration of CMNF and vibration on the deposited thickness Average thickness (microns) Acceleration m/s.sup.2 0.3% CMNF 0.5% CMNF 20 31 57 47 22 31 85 11 16

EXAMPLE N.SUP.O .3

[0132] In the example that follows, other bath compositions were tested: [0133] Silicate: aqueous composition (77% by weight of water, compared to the total weight), sodium silicate binder (23% by weight, compared to the total weight). No metal particles. [0134] Phenoxy: aqueous composition (69% by weight of water, compared to the total weight), phenoxy binder, melamine cross-linked (25% by weight, compared to the total weight), talc (6% by weight compared to the total weight). No metal particles. [0135] Silane/titanate: aqueous composition (69% by weight of water, compared to the total weight), 15% of organic solvents compared to the total weight, silane-titanate binder (15% by weight, compared to the total weight, 50:50 silane/titanium weight ratio), MoO.sub.3 (1% by weight, compared to the total weight). No metal particles. [0136] Silane: aqueous composition (45% by weight of water, compared to the total weight), silane binder (7% by weight, compared to the total weight, organic solvents (18% by weight compared to the total weight), metal particles including zinc (30% by weight, compared to the total weight)

[0137] To these baths were added CMNFs (Exilva sold by Borregaard) at the concentrations expressed in the following table (% by dry weight, compared to the total dry matter).

[0138] The parts were immersed in these baths at an immersion speed of 1 m/min. Vibrations were applied, parallel to the direction of immersing/withdrawing the part in/from the bath.

The results are given in the following table:

TABLE-US-00009 TABLE 5 Lamellar % Acceleration (m/s.sup.2) Type of binder Zn? CMNF 0 15 30 70 Silane + Titanate No 1 47 m 62 m 29 m 11 m Silicate No 0.6 92 m 63 m 47 m 20 m Phenoxy melamine No 0.6 104 m 98 m 53 m 27 m Silane Yes 0.50% >100 m 33 m 25 m 20 m

[0139] These results demonstrate that the same effect is obtained with other binder technologies.