Patent ID: 8247475

Claim:
Hydrotalcite-based compound particles which are surface-treated with an organic compound having not less than 3 carbon atoms, and have a specific surface area of 5 to 150 m 2 /g, a conceptual value x of 0.06 to 0.59 and a conceptual value y of 0.225 to 0.260, wherein the conceptual value x corresponds to x represented by the following formula: x =( P /( V ×( P 0 −P )))/( P/P 0 ) (wherein V is a water vapor adsorption; P is a pressure at a measuring position; and P 0 is an atmospheric pressure), and the conceptual value y corresponds to y represented by the following formula: y=V m /S SET (wherein V m is a water vapor adsorption at P/P 0 =0.2; and S SET is a specific surface area of the sample), in which the values x and y are determined from a water vapor adsorption curve thereof in a range where P/P 0 is 0.045 to 0.355 when exposed to a temperature of 25° C. and a humidity of 50% for 250 hours.