Phosphating process as cathode electrophoresis coating pretreatment

Abstract

The present invention discloses a phosphating process as a cathode electrophoresis coating pretreatment. The phosphating solution adopted by the process comprises: 33-37 g / L of zinc oxide, 123-127 g / L of 85% phosphoric acid, 12-14 g / L of nickel sulfate, 6-8 g / L of manganese carbonate, 5-7 g / L of potassium chlorate, 2-4 g / L of potassium fluoride, 9-11 g / L of hydroxylamine sulfate, 4-6 g / L of m-nitrobenzene sulfonic acid, 17-19 g / L of sodium citrate, 3-5 g / L of sodium polyphosphate, 0.5-1.5 g / L of triethanolamine, 1-2 g / L of phytic acid, 0.2-0.6 g / L of pentaerythritol phosphate, and the balance of water. The phosphating process comprises: carrying out acid washing, neutralization, deoiling degreasing, and water washing on a workpiece, immersing into a phosphating solution with temperature of 25-35 DEG C, a free acidity of 2-6 and the total acidity of 55-65, carrying out a reaction for 6-12 min, washing with water, and drying.

Description

technical field [0001] The invention relates to the technical field of surface treatment, in particular to a phosphating process used as a pretreatment for cathodic electrophoretic coating. Background technique [0002] As one of the core technologies of pre-painting treatment, phosphating has been widely used in the world for nearly a hundred years. At present, the most used phosphating technology is zinc-based phosphating technology, and the main component of the phosphating film formed is zinc phosphate, namely Zn 3 (PO 4 ) 2 4H 2 O, referred to as [H] film. However, as domestic large-scale coating production lines generally adopt the cathodic electrophoretic coating process, the traditional zinc-based phosphating technology can no longer meet the requirements of cathodic electrophoretic coating, because cathodic electrophoretic coating requires the phosphating film to have good alkali resistance and electrical conductivity. properties, corrosion resistance and adhes...

AI Technical Summary

Problems solved by technology

[0003] The main problems of zinc-nickel-manganese ternary phosphating solution currently used in cathodic electrophoretic coating are: high working temperature, many phosphating residues; complex composition ratio, narrow range of process parameters, and difficult to control; nickel, High manganese content, high cost, poor market competitiveness, and nickel and manganese are toxic heavy metals, which is not conducive to environmental protection; slow phosphating speed, not suitable for automatic painting assembly line operations

Chinese patent CN1221043A "Zinc-nickel-manganese ternary system medium-temperature phosphating solution" has simple composition, good film formation, and low requirements for accelerators, but the concentration of phosphating solution is high, the cost is high, and the working temperature is between 55°C and 65°C. °C, it is not suitable for low temperature phosphating, and the uniformity of the formed film is poor

Chinese patent CN1361309A "medium-temperature phosphating solution for automobile coating" is essentially a zinc-nickel-manganese ternary phosphating solution, the working temperature does not meet the requirements of low-temperature phosphating, the concentration of the phosphating solution is high, and the market competitiveness is poor

Although the Chinese patent CN1401820A "normal temperature phosphating solution" can realize normal temperature phosphating, it takes a long time to form a film and has a lot of phosphating residue, so it is not suitable for cathodic electrophoretic coating automation.