1. Field of the Invention
The present invention relates to a coating composition that contains calcium phosphite as one of the anti-corrosive agents which composition protects a surface from corrosion and to a process of using the composition.
2. Description of the Prior Art
It is known in the art to provide materials in coating compositions which impart corrosion resistance to surfaces coated by the compositions. For example, in U.S. Pat. No. 3,846,148, there is disclosed composite pigments which are stated as having excellent corrosion inhibition and tannin absorptive properties. The composite pigments comprise inert silicate mineral base pigments having adhered to the particles thereof and in intimate association therewith at least one additive compound which may be a basic or hydrated metal phosphate, phosphite, borate or chromate wherein the metal is preferably calcium or magnesium.
U.S. Pat. No. 4,294,621 describes an anti-corrosive pigment having a phosphate basis. The pigment is prepared by reacting one or more calcium or magnesium compounds with phosphoric acid or acid alkali metal or ammonium phosphate by intimately mixing an aqueous suspension or solution of the reactants using a dispersing means rotating at high speed. After reaction and drying, an anti-corrosive pigment is obtained which is comprised of a homogenous mixture and/or mixed crystals of which 10 to 95 mole % is calcium hydrogen phosphate dihydrate with the balance being magnesium hydrogen phosphate trihydrate.
U.S. Pat. No. 3,395,027 discloses a coating composition, particularly for magnesium surfaces, consisting essentially of a slurry of finely divided inorganic solid particulate material in an aqueous solution containing substantial amounts of phosphate, nitrate, and dissolved metal. Typical phosphates which can be used are monobasic, dibasic and tribasic orthophosphates of magnesium, zinc, ferrous or ferric iron, calcium or alkali metals.
U.S. Pat. No. 2,120,212 relates to phosphated metal coatings wherein the phosphate is an acid phosphate of barium, strontium, calcium, magnesium, aluminum, zinc, manganese, nickel, cadmium, lead, copper, arsenic or silver.
U.S. Pat. No. 4,294,808 sets forth a process for making phosphorous-containing anti-corrosive pigments by reacting one or more compounds of magnesium, calcium, strontium, barium, zinc, aluminum, iron, chromium or manganese with an oxygen acid of phosphorous or its alkali metal or ammonium salt.
U.S. Pat. No. 4,083,860 describes metal compounds of monoesters of phosphoric acid which are useful as corrosion inhibitors, corrosion protecting films, thickeners, fungicides or biocides. The compounds may be prepared in a two-step process wherein the first step involves reacting a dialkyl phosphite with a low-molecular weight alkyl residue in a non-aqueous medium and in the absence of solvents with metal or organometallic compounds and wherein the second step involves transesterifying the metal monoalkyl esters produced in the first step to introduce a defined substituent.