Binder composition, a method of manufacturing a corrosion-resistant sacrificial protective coating using said composition, and a support coated with such a coating

Abstract

The present disclosure provides an aqueous binder composition for forming a sacrificial corrosion-protective coating, said composition being free of chromates and also preferably free of borates and molybdates. Said binder composition advantageously has a pH of less than 6 and comprises a binder, particles of at least one metal oxide and at least one metallic phosphate, said binder comprising a hydrolyzed organosilane oligomer. In addition, the proportion by weight of said particles of at least one metal oxide relative to the total dry weight of said binder composition is greater than or equal to 75%.

Claims

1. An aqueous binder composition for manufacturing a sacrificial corrosion-protective coating, said composition being free of chromates, wherein said aqueous binder composition has a pH of less than 6 and comprises a binder, particles of at least one metal oxide, and at least one metallic phosphate, said binder comprising a hydrolyzed organosilane oligomer, and wherein the proportion by weight of said particles of at least one metal oxide relative to the total dry weight of said aqueous binder composition is greater than or equal to 75%.

2. The aqueous binder composition according to claim 1, wherein said at least one metal oxide is selected from the group consisting of aluminum oxide, zinc oxide, a mixed zinc-magnesium oxide, a mixed aluminum-zinc oxide, and mixtures thereof.

3. The aqueous binder composition according to claim 1, wherein the hydrolyzed organosilane oligomer represents in the range 5% to 30% by weight of the total dry weight of said aqueous binder composition.

4. The aqueous binder composition according to claim 1, wherein said aqueous binder composition comprises an acidic catalyst selected from the group consisting of p-toluene sulfonic acid, phosphoric acid, boric acid, acetic acid, and mixtures thereof.

5. The aqueous binder composition according to claim 1, wherein the particles of the at least one metal oxide have a granulometric distribution for 10% to 90% by weight of said particles in the range of 2 m to 30 m.

6. The aqueous binder composition according to claim 1, wherein said composition is free of borates and molybdates.

7. The aqueous binder composition according to claim 1, wherein the hydrolyzed organosilane oligomer is selected from: an epoxy dialkoxysilane, an epoxy trialkoxysilane, a vinyldialkoxysilane, or a vinyl trialkoxysilane.

8. The aqueous binder composition according to claim 1, wherein the hydrolyzed organosilane oligomer represents in the range 5% to 15% by weight of the total dry weight of said aqueous binder composition.

9. The aqueous binder composition according to claim 1, wherein said at least one metallic phosphate is selected from the group consisting of zinc phosphate (Zn.sub.3(PO.sub.4).sub.2), manganese phosphate (Mn.sub.3(PO.sub.4).sub.2), aluminum phosphate (Al.sub.5PO.sub.4), aluminum tripolyphosphate (Al.sub.5(P.sub.3O.sub.10).sub.3), aluminum and zinc phosphate, and mixtures thereof.

10. The aqueous binder composition according to claim 9, wherein said at least one metallic phosphate is selected from the group consisting of zinc phosphate (Zn.sub.3(PO.sub.4).sub.2), aluminum tripolyphosphate (Al.sub.5(P.sub.3O.sub.10).sub.3), and mixtures thereof.

11. The aqueous binder composition according to claim 1, wherein the proportion by weight of the particles of the at least one metal oxide is greater than or equal to 80% relative to the total dry weight of said aqueous binder composition.

12. The aqueous binder composition according to claim 11, wherein the proportion by weight of the particles of the at least one metal oxide is greater than or equal to 85% relative to the total dry weight of said aqueous binder composition.

13. The aqueous binder composition according to claim 1, wherein the proportion by weight of the at least one metallic phosphate is more than 1 and less than or equal to 15% relative to the total dry weight of said aqueous binder composition.

14. The aqueous binder composition according to claim 13, wherein the proportion by weight of the at least one metallic phosphate is greater than or equal to 3% and less than or equal to 10%, relative to the total dry weight of said aqueous binder composition.

15. The aqueous binder composition according to claim 1, wherein said organosilane oligomer has the following formula (I), [R.sub.4(SiR.sub.1R.sub.2R.sub.3)].sub.n, in which n is an integer with 2n100 and R4 is a non-hydrolyzable group, and wherein at least one group from R1, R2, and R3 is a hydrolyzable group.

16. The aqueous binder composition according to claim 15, wherein R4 represents a non-hydrolyzable group selected from: a C1-C20 alkyl group or C3-C10 cycloalkyl group substituted with one or more epoxy group(s), said epoxy(s) group being mono, di, tri or tetravalent; a glycidoxy group; a C1-C20 alkyl group substituted with a glycidoxy group; a vinyl group (CH2=CH); a C1-C20 alkyl group substituted with a vinyl group (CH2=CH); a C1-C20 alkyl group substituted with a primary amine and/or a secondary amine and/or a tertiary amine; a primary amine; a secondary amine; a tertiary amine; a C1-C20 alkyl group substituted with a thiol group; a thiol group; a urea group; a C1-C20 alkyl group substituted with a urea group; an isocyanate group; or a C1-C20 alkyl group substituted with an isocyanate group; and wherein at least one of R1, R2, or R3 represents, as the hydrolyzable group, a C1-C10 alkoxy group; a C3-C10 cycloalkyloxy group; a C5-C10 aryloxy group, or a C1-C5 acyloxy group.

17. The aqueous binder composition according to claim 16, wherein at least one of R1, R2, or R3 represents a non-hydrolyzable group selected from: a C1-C20 alkyl group or C3-C10 cycloalkyl group substituted with one or more epoxy group(s), said epoxy(s) group being mono, di, tri or tetravalent; a glycidoxy group; a C1-C20 alkyl group substituted with a glycidoxy group; a vinyl group (CH2=CH); a C1-C20 alkyl group substituted with a vinyl group (CH2=CH); a C1-C20 alkyl group substituted with a primary amine and/or a secondary amine and/or a tertiary amine; a primary amine; a secondary amine; a tertiary amine; a C1-C20 alkyl group substituted with a thiol group; a thiol group; a urea group; a C1-C20 alkyl group substituted with a urea group; an isocyanate group; or a C1-C20 alkyl group substituted with an isocyanate group.

18. The aqueous binder composition according to claim 15, wherein R.sub.4(SiR.sub.1R.sub.2R.sub.3) of the organosilane oligomer with formula (I) is selected from a list (IIa): gamma-glycidoxypropyltrimethoxysilane; gamma-glycidoxypropyltriethoxysilane; gamma-glycidoxypropyl; methyldimethoxysilane; and gamma-glycidoxypropylmethyldiethoxysilane.

19. The aqueous binder composition according to claim 18, wherein the R.sub.4(SiR.sub.1R.sub.2R.sub.3) of the organosilane oligomer with formula (I) is selected from a list (IIb): beta-(3,4-epoxycyclohexyl)-ethyl trimethoxysiloxane; beta-(3,4-epoxycyclohexyl)-ethyl methyl dimethoxysilane, beta-(3,4-epoxycyclohexyl)ethyl methyl diethoxysilane; and beta-(3,4-epoxycyclohexyl)-ethyltriethoxysilane.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) The present invention can be better understood from the following non-limiting exemplary embodiments.

IExamples of Formulations for a Binder Composition in Accordance with Embodiments of the Present Disclosure Comprising at Least One Metallic Phosphate

Example 1

Preparation of Part a of a Kit According to Embodiments of the Present Disclosure Starting from the Following Compounds

(2) an organosilane oligomer derived from gamma-glycidoxypropyltrimethoxysilane (C.sub.9H.sub.20O.sub.5Si): in the range 20 g to 40 g; demineralized water: in the range 60 milliliters (mL) to 80 mL.

(3) The pH of part A was adjusted to in the range 2 to 3 with the aid of p-TSA acid.

Preparation of Part B of the Kit According to Embodiments of the Present Disclosure Starting from the Following Compounds

(4) metal oxide powder based on aluminum with or without zinc: in the range 5 g to 65 g; zinc phosphate.

(5) In the range 25 g to 45 g of part A was mixed with part B to form an aqueous binder composition. The proportion by weight of particles of at least one metal oxide in the mixture of parts A and B was greater than or equal to 75% relative to the total dry weight of the aqueous composition. The proportion by weight of said zinc phosphate relative to the total dry weight of the aqueous composition was in the range 3% to 8%, limits included.

(6) After pigmentation of part A, the pH was again adjusted; in this particular example, the pH was in the range 2 to 3.

(7) Example 2 was strictly identical to Example 1, with the exception that the zinc phosphate was replaced by aluminum tripolyphosphate.

Example 3

Preparation of Part a of a Kit According to Embodiments of the Present Disclosure Starting from the Following Compounds

(8) an organosilane oligomer derived from trimethoxyvinylsilane (C.sub.5H.sub.12O.sub.3Si): in the range 10 g to 30 g; demineralized water: in the range 60 mL to 80 mL.

(9) The pH of part A was adjusted to between 2 and 3 with the aid of p-TSA acid.

Preparation of Part B of the Kit According to Embodiments of the Present Disclosure Starting from the Following Compounds

(10) metal oxide powder based on aluminum with or without zinc: 45-65 g; zinc phosphate.

(11) In the range 35 g to 55 g of part A was mixed with part B. The proportion by weight of particles of at least one metal oxide in the mixture of parts A and B was greater than or equal to 75% relative to the total dry weight of the aqueous composition. The proportion by weight of said zinc phosphate relative to the total dry weight of the aqueous composition was in the range 3% to 8%, limits included.

(12) After pigmentation of part A, the pH was again adjusted; in this precise example, the pH was in the range 2 to 3.

(13) Example 4 was strictly identical to Example 3, with the exception that the zinc phosphate was replaced by aluminum tripolyphosphate.

IIPreparation of a Control Support Using a Prior Art Method

(14) The surface of a steel support was coated with a sacrificial corrosion-protective coating by carrying out a prior art chromating method, in particular based on chromium VI. The support obtained was termed a prior art control.

(15) This support initially underwent a first step of preparing its surface; in particular, the surface was degreased with a basic degreaser such as that marketed by Henkel with reference TURCO 5948 DMP.

(16) The surface was then rinsed with demineralized water and dried with an air blower. The surface was thus ready for sanding, in particular using particles of white corundum with a grain size of the order of 80 m at a spray pressure for said particles of the order of 300 kPa in order to obtain a surface roughness of 2 m to 3 m thickness.

(17) The prior art aqueous binder composition was stirred for 24 h before use, then filtered through a stainless steel screen with openings of the order of 0.025 millimeters (mm). The composition was stirred again just before it was applied in two successive layers. The mean thickness of a compacted layer was thus 25 m. The support coated with a layer of binder composition was dried at a temperature of 80 C. for 15 min. The layer then changed from a green color to a gray color. The maximum time between this drying step and the annealing step was a maximum of 30 min. Thus, almost immediately after drying, the coated support was exposed to an intermediate annealing operation at 285 C. for a minimum of 3 h for each applied layer (intermediate annealing after application of each layer) or at 215 C. for a minimum of 20 h if the support had been cadmium-coated or 285 C. for 5 h for a final anneal. Each layer was compacted during an intermediate or final compacting step by blasting corundum with dimensions in the range 90-180 US mesh and applying a pressure of 1 kPa to 150 kPa.

IIIPreparation of a Steel Support Using the Method Described Below, and Examples 1 to 4 of Pigmented Binder Compositions Described in Paragraph I

(18) A steel support was prepared by carrying out the same operations as for the control support: the only difference was that different sanding operation parameters were used in which the particles were blasted at a pressure of 300 kPa to 400 kPa and had larger dimensions, since they were less than or equal to 80 US mesh. Furthermore, no intermediate annealing step and no intermediate compacting steps were carried out.

(19) Activated part A from any one of Examples 1 to 4, i.e. with a pH in the range 2 to 3, was then mixed with a metallic paste (part B from any one of Examples 1 to 4) for 20 min to form an activated aqueous binder composition in accordance with any one of Examples 1 to 4, which was then filtered through a screen with openings of the order of 0.12 mm.

(20) The activated and pigmented binder composition of Examples 1 to 4 was stirred just before it was applied. The binder composition of any one of Examples 1 to 4 was applied in a single layer of moist film, for example 25 m to 200 m thick, depending on the low pressure pneumatic spray specifications, i.e., preferably at a pressure in the range 150 kPa to 200 kPa, in 2 to 6 crossed layers.

(21) For complex parts, it is possible to apply the binder composition in a plurality of layers.

(22) The coated support then underwent a drying step (ii) or stoving step during which it was exposed, for example, to a temperature of the order of 90 C. for at least 60 min in order to change the color of the layer from dark gray to pale gray.

(23) The coated support then underwent a final annealing step (vi) during which it was exposed to a temperature of 420 C. for 4 h or 285 C. for 20 h. The coating formed at the surface of the support was finally compacted during the final compacting step (vii) by spraying corundum with dimensions in the range 80 to 180 US mesh, limits included, at a pressure of approximately 200 kPa or more.

(24) Table I below summarizes the results of the tests carried out on the support obtained in accordance with the method described above in paragraph III; the results were the same for all of the aqueous binder compositions.

(25) TABLE-US-00001 TABLE 1 REQUIRE- TESTS STANDARDS MENTS RESULTS Application Continuous and Continuous and uniform visual uniform visual appearance appearance Final NF EN ISO 25 m to 90 m 25 m to 90 m thickness 2808 Corrosion, NF ISO 1000 h The red rust appeared appearance 9227-2012 in the damaged test of red rust coatings after more than 1200 h. With no damage, the red rust appeared after more than 2500 h Adhesion NF ISO 2409 Class 0 or 1 Class 0 Hardness NF ISO 1518 >2500 g before >2500 g before immersion immersion Behavior as NF ISO 2409 Specific to each Skydrol: regards NF ISO 1518 fluid Class 0 contaminants >2400 g after immersion Behavior - NF ISO 2409 10 cycles After 10 cycles moisture NF ISO 1518 Adhesion: class 0 Hardness: >2400 g Behavior- NF ISO 2409 100 cycles After 100 cycles temperature NF ISO 1518 Adhesion: class 0 variations Hardness: >2400 g Temperature NF ISO 20 (A) cycles No blisters were corrosion 9227-2012 25 (B) cycles formed on test 20 (C) cycles specimens, nor red rust, since the test coatings remained intact. Conductivity ASTM R <15 R <1 Ohm/square test Standard Ohms/square D 257-07 (2007): Standard Test Method for DC resistance or conductance of insulating materials. 20 (A) cycles, where each cycle (A) comprised, in succession: a first cycle of 6 h at 450 C., a second cycle of 1 h remaining in a vessel held at 35 C., a third cycle of 16 h under salt spray, a fourth cycle identical to the third cycle. 25 (B) cycles, where each cycle (B) was identical to cycle (A) with the exception that the temperature of the first cycle was 400 C. 20 (C) cycles, where each cycle (C) was identical to cycle (A) with the exception that the temperature of the first cycle was 550 C.

(26) Concerning corrosion to form red rust, the tests were carried out in salt spray on specimens with or without damage, the damage being a scratch in the form of a cross made in the coating to be tested, which coating had thickness in the range 40 m to 60 m.

(27) The salt spray and its conditions for application are defined in ISO standard 9227-2012.

IVComparative Examples of Aqueous Binder Compositions without Metallic Phosphate

(28) Two binder compositions with references 5 and 6, respectively corresponding to the binder composition examples 1 and 2, were prepared, each time without metallic phosphate.

(29) Concerning the corrosion test until red rust appeared, red rust was observed to appear in the damage at approximately 500 h. Without damage, red rust only appeared at approximately 1000 h. These results were obtained for the two binder compositions 5 and 6.

(30) Concerning the temperature corrosion test, the formation of blisters was observed after 5 cycles in the three cases (A), (B) and (C) for both binder compositions 5 and 6.

(31) In conclusion, adding at least one metallic phosphate, in particular zinc phosphate or aluminum tripolyphosphate, can double the salt spray resistance of the coating according to embodiments of the present disclosure including damage in comparison with coatings that are free of metallic phosphate.

(32) With no scratching of the specimens, after 2500 h of exposure to salt spray, the test specimens exhibited neither pitting linked to corrosion, nor blisters. Adding at least one metallic phosphate, in particular zinc phosphate or aluminum tripolyphosphate, thus doubled the salt spray resistance of the undamaged sacrificial protective coatings according to embodiments of the present disclosure.

(33) Adding at least one metallic phosphate, in particular zinc phosphate or aluminum tripolyphosphate, can thus very significantly improve the electrochemical activity of the sacrificial corrosion-protective coating as well as the salt spray and temperature corrosion resistance.

(34) Prepared samples as described in paragraph III and comprising binder composition 5 exemplified above were tested at various stages of the method of the present disclosure:

(35) 1) sample 1, heat treatment 1 h at 90 C., corresponding to the evaporation step (v);

(36) 2) sample 2, 1 h at 90 C. then 4 h at 420 C., corresponding to steps (v) and (vi);

(37) 3) sample 3, 1 h at 90 C. then 4 h at 420 C., corresponding to steps (v) and (vi) followed by compacting at a pressure of 4 (metric) tonnes (t) for 1 min.

(38) Analysis of samples 1-3 was carried out with a MagiX wavelength dispersion X-ray fluorescence spectrometer from Philips.

(39) In order to carry out X-ray fluorescence analysis, the samples need to be compacted, either pure or with a binder, and the total mass of the pellet must be 200 milligrams (mg) for 13 mm diameter pellets. The three samples were thus each prepared by mixing 100 mg of the example binder composition to be analyzed with 100 mg of boric acid. Each mixture was then compacted under a pressure of 4 t for 1 min in order to obtain 13 mm diameter pellets. Analysis of these pellets was carried out under vacuum (5 Pascals).

(40) The results of the semi-quantitative analyses are indicated in Table 2 below. They are expressed as the percentages by weight. The method can be used to detect elements from boron to uranium. However, given that the presence of boric acid means that oxygen cannot be assayed and in the light of the nature of the samples (metallic appearance), the results are presented without the oxygen values. Carbon was detected in sample 1, but no signal was observed in the other two samples 2 and 3.

(41) Conversion of the pigmented binder composition was close to 100% since no carbon was detected using X-ray fluorescence in the films after curing (step (v)).

(42) If one of the binder compositions 1 to 4 had been tested, Table 2 would have shown the phosphorus and the metal obtained from said at least one metallic phosphate, in particular zinc or aluminum, which would have been added to the metallic particles.

(43) TABLE-US-00002 TABLE 2 Sample 1 C Al Si Zn Concentrations 15.5 81.9 2.33 0.02 Sample 2 Al Si Zn Concentrations 97.2 2.43 0.02 Sample 3 Al Si Zn Concentrations 97.4 2.14 0.07

(44) Advantageously, the combination of the method of the present disclosure and the binder composition according to embodiments of the present disclosure means that a sacrificial corrosion-protective coating can be formed in which the matrix is essentially formed by silica, metallic particles, and at least one metallic phosphate having high-temperature corrosion resistance properties (at 400 C. or higher) and salt spray corrosion resistance properties as defined in ISO standard 9227 with or without damage being present, which properties are doubled compared with a sacrificial protective coating that is free of at least one metallic phosphate.

(45) Where any standards of national, international, or other standards body are referenced (e.g., ISO, NF, etc.), such references are intended to refer to the standard as defined by the national or international standards body as of the priority date of the present specification. Any subsequent substantive changes to such standards are not intended to modify the scope and/or definitions of the present disclosure and/or claims.

(46) Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. The true scope of the disclosure is indicated by the following claims.