Powder Corrosion and Chip-Resistant Coating

Abstract

A powder composition including a resin and from 5% to 70%, by weight based on powder composition weight, of a corrosion-inhibiting pigment, optionally including from 0% to 65%, by weight based on powder composition weight, zinc, the composition being substantially free from pigment providing a metallic effect is provided. The corrosion-inhibiting pigment may be present in amounts of up to 50%, by weight based on powder composition weight, for example, up to 35%. A method for coating a substrate with the powder composition and the coated substrate so formed are also provided.

Claims

1. A method of coating a high tensile steel substrate with a chip and corrosion resistant coating, the method comprising (a) applying to the substrate a powder composition comprising (i) an epoxy resin based on bisphenol A, (ii) a polyhydroxyl functional phenolic curing agent having a HEW of about 200 to about 500, and (iii) from 5% to 70% by weight based on powder composition weight of a corrosion-inhibiting pigment selected from the group consisting of molybdates, chromates, metal phosphides, silicates and phosphates, wherein the composition comprises zinc in an amount of 0% to 65% by weight based on the powder composition; and (b) heating the applied powder composition to fuse and cure the composition.

2. The method according to claim 1 wherein the powder composition further comprises at least one additive that toughens the powder composition, aids in foaming the powder composition, or reinforces the powder composition.

3. The method according to claim 1 wherein the epoxy resin is a thermoplastic resin or a thermoset resin.

4. The method according to claim 1 wherein the epoxy resin has an epoxy equivalent weight of less than 2300.

5. The method according to claim 1 wherein the epoxy resin is adducted to an elastomer.

6. The method according to claim 1 wherein the corrosion-inhibiting pigment is selected from the group consisting of simple molybdates, complex molybdates, simple chromates, complex chromates, metal phosphides, silicates, simple phosphates and complex phosphates.

7. The method according to claim 1 wherein said powder composition is substantially free from pigment providing a metallic effect.

8. The method according to claim 2 wherein the at least one additive is an additive that toughens the powder composition, wherein the additive is selected from the group consisting of elastomeric modifications, a random or block copolymer addition, addition of plasticizers, crosslinked or non-crosslinked core/shell resins, hollow spherical particles and discrete micro-domains thereof.

9. The method according to claim 8 wherein the additive is a random or block copolymer addition.

10. The method according to claim 1 wherein the at least one corrosion-inhibiting pigment is selected from the group consisting of zinc phosphate, strontium zinc phosphosilicate, calcium borosilicate, iron phosphide, strontium chromate, zinc molybdate and mixtures thereof.

Description

EXAMPLE 1

Formation of Powder Compositions and Application to Substrates

[0047]

TABLE-US-00001 TABLE 1.1A Powder compositions Zinc Phosphate-Containing Base Coat compositions Example No. 1-1 1-2 1-3 1-4 2-1    5%   10%   20%   30%   44% Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 Epoxy resin A 92 92 92 92 92 Imidazole 3 3 3 3 3 adduct B Carbon black 3 3 3 3 3 pigment Hydroxy 20.8 20.8 20.8 20.8 20.8 compound C Epoxy resin D 8 8 8 8 8 Zinc Dust 0 0 0 0 0 Zinc Phosphate 6.7 14.5 32 54 100 Fumed silica 0.30% 0.30% 0.30% 0.30% 0.30% Other Corrosion-Inhibiting Base Coat compositions 3-1 3-2 3-3 3-4 3-5 Epoxy resin A.sup.1 92 92 92 92 92 Imidazole adduct 3 3 3 3 3 B.sup.2 Carbon black 3 3 3 3 3 pigment Hydroxy 20.8 20.8 20.8 20.8 20.8 compound C.sup.3 Epoxy resin D.sup.4 8 8 8 8 8 Zinc Dust 237.5 225 200 175 150 Zinc Phosphate 0 0 0 0 0 FERROPHOS ™ 12.5 25 50 75 100 Strontium Zinc 0 0 0 0 0 Phosphosilicate Calcium 0 0 0 0 0 Borosilicate Fumed Silica 0.30% 0.30% 0.30% 0.30% 0.30% .sup.1Diglycidyl ether of bisphenol A epoxy resin with a weight per epoxide between 935 and 1175. .sup.2Imidazole adduct with a diglycidyl ether of bisphenol A epoxy resin. .sup.3Bisphenol A end capped diglycidyl ether of bisphenol A with a hydroxyl equivalent weight between 370 and 400. .sup.4Master Batch epoxy resin containing 90 wt % of a diglycidyl ether of bisphenol A epoxy resin with a weight per epoxide between 795 and 895 and 10 wt % of acrylic flow modifier.

TABLE-US-00002 TABLE 1.1B Powder compositions Zinc Phosphate-Containing Base Coat compositions Example No. 2-2 44% Zn3(PO4)2 2-3 2-4 2-5 2-6 Control Epoxy 92 92 92 92 92 92 resin A Imidazole 3 3 3 3 3 3 adduct B Carbon 3 3 3 3 3 3 black pigment Hydroxy 20.8 20.8 20.8 20.8 20.8 20.8 compound C Epoxy 8 8 8 8 8 8 resin D Zinc Dust 150 175 200 225 237 250 Zinc 100 75 50 25 12.5 0 Phosphate Fumed 0.30% 0.30% 0.30% 0.30% 0.30% 0.30% silica Other Corrosion-Inhibiting Base Coat compositions 4-1 4-2 4-3 4-4 Epoxy resin A.sup.1 92 92 92 92 Imidazole adduct B.sup.2 3 3 3 3 Carbon black 3 3 3 3 pigment Hydroxy 20.8 20.8 20.8 20.8 compound C.sup.3 Epoxy resin D.sup.4 8 8 8 8 Zinc Dust 0 0 0 0 Zinc Phosphate 0 0 0 0 FERROPHOS ™ 0 0 0 0 Strontium Zinc 3.2 14 0 0 Phosphosilicate Calcium Borosilicate 0 0 6.7 22.4 Fumed Silica 0.30% 0.30% 0.30% 0.30% .sup.1Diglycidyl ether of bisphenol A epoxy resin with a weight per epoxide between 935 and 1175. .sup.2Imidazole adduct with a diglycidyl ether of bisphenol A epoxy resin. .sup.3Bisphenol A end capped diglycidyl ether of bisphenol A with a hydroxyl equivalent weight between 370 and 400. .sup.4Master Batch epoxy resin containing 90 wt % of a diglycidyl ether of bisphenol A epoxy resin with a weight per epoxide between 795 and 895 and 10 wt % of acrylic flow modifier.

[0048] Powder samples were electrostatically applied onto 7.68cm×12.8cm×0.082 cm (3 inch×5 inch×0.032 inch) steel panels. Panels were supplied by ACT Laboratories, Inc., B-958, P-60 (Zinc Phosphate/Non Chrome Rinse). Powder coated panels were placed into an electric air circulating oven maintained at 160° C. (320° F.) for 20 minutes. Cured film thickness was 50 to 101 μm (2.0-4.0 mils).

EXAMPLE 2

Evaluation of Powder Coated Panels

[0049] Each of the coated panels exhibited a direct/reverse impact rating of 1.84 kg-m (160 in-lb)/1.84 kg-m (160 in-lb).

[0050] The coated panels of Example 1 were scribed with an ‘X’ and placed in a Salt Fog Cabinet According to ASTM Method B 117. At intervals panels were removed from the cabinet and scraped with a dull knife, perpendicularly to scribed lines. Maximum undercutting (corrosion) was measured in inches outwardly from the scribe line. Panels were typically exposed for 3000 to 4000 hours.

[0051] As shown in Table 2.1, below, the powder composition-coated panels of the present invention, Examples 1-1, 1-2, 1-3, 1-4, and 2-1, exhibited a useful level of impact resistance and salt spray corrosion resistance.

TABLE-US-00003 TABLE 2.1 Creepback from X-scribe during ASTM B 117 Salt Spray Exposure Example No. Comparative 1-1 1-2 1-3 1-4 2-1 HOURS 66% Zn 5% 10% 20% 30% 44% EXPOSED Dust Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 Zn3(PO4)2 192 NC NC NC NC NC NC 384 NC NC NC NC NC NC 552 NC NC NC NC NC NC 672 NC NC NC NC NC NC 840 NC NC NC NC NC NC 1008 NC <1/32″ <1/32″ <1/32″ <1/32′ <1/32″ 1176 NC NC <1/32″ <1/32″ <1/32′ NC 1344 NC <1/32″ <1/32″ <1/32″ <1/32′ <1/32″ 1512 NC <1/32″ <1/32″ <1/32″ <1/32′ <1/32″ 1680 <1/32″ <1/32″ <1/32″ <1/32″ <1/32′ <1/32″ 1848 <1/32″ <1/32″ 1/32″ 1/32″ <1/32′ <1/32″ 2016 <1/32″ 1/32″ 1/32″ 1/32″ 1/32″ 1/32″ 2184 <1/32″ 1/32″ 1/32″ 1/32″ <1/32″ <1/32″ 2352 <1/32″ 1/32″ 1/32″ 1/32″ 1/32′ <1/32″ 2520 <1/32″ >1/32″ 1/16″ 1/32″ >1/32″ <1/32″ 2688 <1/32″ 1/16″ 1/16″ 1/16″ 1/16′ 1/32″ 2856 <1/32″ 1/16″ >1/16″ 1/16″ 1/16′ 1/16″ 3024 <1/32″ 1/16″ 3/32″ 3/32″ 3/32″ 1/16″ 3192 <1/32″ 1/16″ 3/32″ 3/32″ 3/32″ 1/16″ 3360 1/32″ 3/32″ ⅛″ >3/32″ 3/32″ 1/16″ 3528 1/32″ 3/32″ ⅛″ ⅛″ 3/32″ 1/16″ 3696 1/32″ 3/32″ ⅛″ ⅛″ 3/32″ 1/16″ 3864 1/32″ ⅛″ 3/16″ ⅛″ ⅛″ 1/16″ 4056 1/16″ ⅛″ >1/4″ 3/16″ 3/16″ 3/32″