Patent ID: 7833404

Claim:
An electrolytic phosphate chemical treatment method of forming a film composed of a phosphate compound and a metal that is reduced and precipitated from an ionic state on the surface of a metal material article to be treated, comprising: performing the electrolytic phosphate chemical treatment on said metal material article in a phosphate chemical treatment bath by contacting said metal material article with said phosphate chemical treatment bath containing phosphate ions, phosphoric acid, nitrate ions, metal ions that form a complex with the phosphate ions and phosphoric acid in said phosphate chemical treatment bath, and metal ions, wherein a dissolution-precipitation equilibrium potential at which the metal ions in said phosphate chemical treatment bath are reduced and precipitate as the metal is equal to or greater than −830 mV, which is the cathodic reaction decomposition potential of water when indicated as a hydrogen standard electrode potential, wherein the electrolytic phosphate chemical treatment involves the application of voltage and current from an external power supply, and cathodic electrolysis is carried out using the metal material article for the cathode; the phosphate chemical treatment bath has a pH of 2.5 or lower and is substantially free of metal ions, other than those which are a component of the film, which will form sludge; Fe is present and an amount of Fe ions dissolved in the phosphate chemical treatment bath is controlled by changes in the amount of Fe ions dissolved into the phosphate chemical treatment bath from a Fe ion source, the Fe ion source being at least one of (1) an electrode when said electrode comprises Fe, (2) a replenishing liquid containing Fe ions and (3) the metal material article to be treated when the metal article to be treated comprises a steel material, so that the phosphate chemical treatment bath does not contain Fe 3+ ions in an amount of more than the solubility limit; NO 2 and/or N 2 O 4 gas generated and dissolved in the phosphate chemical treatment bath during a reduction reaction of the nitrate ions of the electrolytic treatment is removed from the treatment bath by separating a treatment tank into an electrolytic treatment tank where the electrolytic treatment is carried out and an auxiliary tank where no electrolytic treatment is carried out, circulating the treatment bath between the two tanks, and providing a mechanism that opens the treatment bath to the atmosphere at a reduced pressure either between the two tanks or within the two tanks, as a means of separating the NO 2 and/or N 2 O 4 gas from the treatment bath; and the oxidation-reduction potential (ORP) of said phosphate chemical treatment bath, indicated as the potential relative to the hydrogen standard electrode potential, is maintained at 770 mV to 960 mV, and is used to monitor the phosphate chemical treatment bath.