Treatment agent for chromium-free insulating coating formation, insulation-coated grain-oriented electrical steel sheet, and method for manufacturing the same

A treatment agent for chromium-free insulating coating formation suitable for forming an insulating coating on a surface of a grain-oriented electrical steel sheet, the treatment agent comprising:

• a component (A):
• at least one selected from the group consisting of phosphates of Mg, Ca, Ba, Sr, Zn, Al, and Mn;
• a component (B):
• colloidal silica;
• a component (C):
• at least one selected from the group consisting of organic acid salts of Mg, Ca, Ba, Sr, Zn, Al, Mn, Fe, Ni, Cu, and Co;
• and
• a component (D):
• phosphoric acid,
• wherein the component (B) is contained in an amount in a range of 50 to 150 parts by mass on a SiO2 solid basis, and the component (C) is contained in an amount of 5.0 parts by mass or more on an elemental metal basis, the amounts being based on 100 parts by mass, on a solid basis, of the component (A),
• the component (D) is contained in excess of a molar ratio of phosphoric acid and metal of the phosphate derived from the component (A), and in an amount that a molar ratio of M2+ and M3+, each being a metal element in the treatment agent for chromium-free insulating coating formation, to a phosphorus element P satisfies:
• 0.50<(M2++1.5×M3+)/P≤1.20
• where M2+ is at least one selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Mn, Ni, Cu, and Co, and M3+ is at least one selected from the group consisting of Al and Fe,
• the treatment agent for chromium-free insulating coating formation has a pH of less than 4.5.