Patent ID: 11692277

Abstract:
The present invention provides a high-concentration tin sulfonate aqueous solution, in which a divalent tin ion (Sn2+) concentration is 360 g/L to 420 g/L, a tetravalent tin ion (Sn4+) concentration is 10 g/L or less, a free methanesulfonic acid concentration is 40 g/L or less, a Hazen unit color number (APHA) is 240 or less, and a turbidity is 25 FTU or less. This aqueous solution is produced such that stannous oxide powder whose temperature is adjusted to a temperature of 10° C. or lower is added to an aqueous methanesulfonic acid solution having a concentration of 60% by mass to 90% by mass when the aqueous solution circulates in a state of being maintained at the temperature of 10° C. or lower, and the stannous oxide powder is dissolved.