Corrosion resistant aqueous and solvent-based primer compositions containing synergistic blends of zinc borate and barium metaborate pigments

#This invention relates to coating compositions and in particular to corrosion resistant primer compositions.

#Primer compositions containing borates as corrosion inhibitive pigments are known in the art as shown by Orth, Jr., U.S. Pat. No. 2,809,949, issued Oct. 15, 1957; Russell Jr., U.S. Pat. No. 3,287,142, issued Nov. 22, 1966; Robinson, U.S. Pat. No. 3,380,836, issued Apr. 30, 1968 and Goodell, U.S. Pat. No. 3,829,395, issued Aug. 13, 1974. Thus, the primer compositions disclosed in the aforementioned patents employ borates such as sodium borates, barium borates including barium metaborates, calcium metaborate, and zinc borate as corrosion inhibitive pigments. Moreover, U.S. Pat. No. 3,287,142 to Russell, Jr. discloses a protective coating composition containing a mixture of a metal dust such as powdered zinc or lead and barium borate as corrosion inhibiting pigments. However, none of these prior art patents disclose or suggest that blends of zinc borate and barium metaborate would be particularly efficacious as corrosion inhibiting pigments and in fact in the present state of the art, zinc borate is regarded as the best corrosion inhibitive pigment with the other borates being noted as less effective. Accordingly, it was completely surprising and unexpected in accordance with this invention to find that when blends of zinc borate and barium metaborate are employed a corrosion inhibitive pigments 1n certain resinous film forming vehicle compositions corrosion resistance was markedly and synergistically enhanced when compared to the same compositions containing zinc borate or barium metaborate alone.

#The novel primer compositions of this invention may have a resin vehicle solids content of from about 20 to about 30 percent by weight but preferably 24 to 28 percent by weight of resin vehicle is employed. As indicated, the compositions contain blends of zinc borate-barium metaborate as corrosion inhibitive pigments. The compositions of the invention may have a zinc borate-barium metaborate pigment to resin vehicle solids ratio of from about 40 to 100 to about 90 to 100 with a preferred ratio being from 55 to 100. The ratio of zinc borate to barium metaborate in the corrosion inhibiting pigment blend may be from 10:90 to 95:5 with the preferred zinc borate to barium metaborate ratio being 63:37.

#The following examples are submitted to further illustrate the nature of the present invention and should not be considered as a limitation on the scope thereof. All parts and percentages in the examples and throughout the specification are by weight unless otherwise specified.

#These examples illustrate the synergistic effect achieved by utilizing a blend of zinc borate and barium metaborate as corrosion inhibitive pigments. In the examples, a control primer composition was prepared by admixing zinc borate pigment with a film-forming resin vehicle blend of an acrylic latex and an alkyd resin (Example 1). Test compositions were then prepared by admixing a blend of zinc borate and barium metaborate with the same resin vehicle blend (Example 2) and barium metaborate alone with the same resin vehicle blend (Example 3). In these compositions, the total pigment to resin vehicle solids ratio was maintained at the same level. The resultant primer compositions had the following formulations:

#______________________________________ Parts by Weight Ingredients Example No. 1 No. 2 No. 3 ______________________________________ Resin Vehicle (acrylic latex.sup.(1) 155.4 155.4 155.4 (soya alkyd resin.sup.(2) 89.4 89.4 89.4 Zinc borate pigment.sup.(3) 135.0 85.0 -- Barium metaborate -- 50.0 135.0 ______________________________________ .sup.(1) An acrylic polymer latex, having a solids content of 46 percent and a Brookfield viscosity range of 300-1500 centipoises prepared from a monomer mixture containing 33 percent by weight methyl methacrylate and 6 percent by weight ethyl acrylate, available commercially from the Monsant Corporation under the designation Rhoplex MV-1. .sup.(2) A long oil soya alkyd resin, having a solids content of 98.0 percent by weight, a Gardner-Holdt viscosity at 25.degree. C. of X-Z and an acid number of 5-9 on solution, prepared by esterification of a mixtur containing 78.0 percent soya oil, 17.0 percent isophthalic acid and 8.0 percent pentaerithrytol. .sup.(3) Zinc borate pigment having the formula: 2 ZnO . 3 B.sub.2 O.sub. . 3.5 H.sub.2 O.