Coating solution for forming insulating film with excellent corrosion resistance property and film close adhesion property and film intensity without chrome and a method for making the insulation film on non-oriented electrical steel sheet by using it
There is provided a chromium-free coating composition for forming an insulation film, the composition having excellent corrosion resistance and excellent film adhesion and film strength after stress relief annealing (SRA), including, based on a 100 g phosphate solution having a solid content of 60% by weight, in which monoaluminum phosphate and monozinc phosphate are mixed at a 1:1 ratio: 0.5˜5 g of a solid in which cobalt hydroxide and strontium hydroxide are mixed at a 1:1 ratio: 100˜300 g of an emulsified polyester resin or an emulsified epoxy resin having a solid content of 20% by weight; 3˜10 g of aluminum silicate having a solid content of 20% by weight; and 0.1˜6 g of a titanium chelate.
1. A chromium-free coating composition for forming an insulation film, the composition having excellent corrosion resistance, film adhesion and film strength after stress relief annealing (SRA), comprising, based on a 100 g phosphate solution having a solid content of 60% by weight, in which monoaluminum phosphate and monozinc phosphate are mixed at a 1:1 ratio:
0.5˜5 g of a solid, in which cobalt hydroxide and strontium hydroxide are mixed at a 1:1 ratio;
100˜300 g of an emulsified polyester resin or an emulsified epoxy resin having a solid content of 20% by weight;
3˜10 g of aluminum silicate having a solid content of 20% by weight; and
0.1˜6 g of a titanium chelate.
2. The chromium-free coating composition for forming an insulation film according to claim 1 , wherein:
the monozinc phosphate has a solid content of 2.75M or 52.5%;
the mixed solution of the monoaluminum phosphate and the monozinc phosphate has a solid content of 60% by weight and a viscosity of 30˜70 cp; and
the emulsified polyester resin has a molecular weight of 40000˜50000, a glass transition temperature (Tg) of 40˜50° C. and a solid content of 20% by weight.
3. The chromium-free coating composition for forming an insulation film according to claim 1 , wherein:
the monozinc phosphate has a solid content of 2.75M or 52.5%,
the mixed solution of the monoaluminum phosphate and the monozinc phosphate has a solid content of 60% by weight and a viscosity of 30˜70 cp, and
the emulsified epoxy resin has a molecular weight of 10000˜20000, a glass transition temperature (Tg) of 50˜60° C. and a solid content of 20% by weight.
4. The chromium-free coating composition for forming an insulation film according to claim 1 , wherein the titanium chelate is any one selected from among triethanolamine titanate, titanium 2,2,2-nitrilotrisethanolate, and an organic-inorganic porous titanate compound.
5. The chromium-free coating composition for forming an insulation film according to claim 1 , wherein the emulsified epoxy resin has a structure in which bisphenol is combined with epoxide, one part of the structure being substituted with an acrylic group, and is thus maintained in an emulsion state.
6. A method of forming an insulation film on a non-oriented electrical steel sheet using the chromium-free coating composition according to any one of claims 1 to 5 , comprising:
applying the chromium-free coating composition on the non-oriented electrical steel sheet such that an application amount thereof is in a range of 0.5˜6.0 g/m 2 on each surface of the steel sheet; and
heat-treating the applied coating composition at a temperature of 350˜700° C. for 10˜50 seconds.