Acrylic adhesive composition, and pressure-sensitive adhesive sheet employing the same

An acrylic pressure-sensitive adhesive composition comprising:

• (A) a copolymer of butyl acrylate and acrylic acid;
• (B) an organophilic layered double hydroxide organically treated with an organic anion;
• and
• (C) a crosslinking agent,
• wherein the layered double hydroxide to be organically treated to provide the component (B) is a non-stoichiometric compound represented by one of the following general formula (1) and (2):
• [M2+1-xM3+x(OH)2]x+[An−x/n.mH2O]x− (1)
• [Li+1-xM3+x(OH)2](2x−1)+[An−(2x-1)/n.mH2O](2x−1)− (2)
• wherein M2+ is a metal ion of at least one divalent metal selected from the group consisting of Mg, Ca, Mn, Fe, Co, Ni, Cu and Zn;
• M3+ is a metal ion of at least one trivalent metal selected from the group consisting of Al, Fe, Cr, Mn, Co, Ni, La and Ga;
• An− is an n-valent inorganic anion selected from the group consisting of OH−, ClO3−, ClO4−, F−, Cl−, Br−, I−, CO32−, NO3− and SO42−;
• x is a positive number with 0<x<0.5;
• m is a positive number with 0<m;
• and n is a valence of the inorganic anion,
• wherein the component (B) is present in a proportion of from 3 parts by weight to 5 parts by weight based on 100 parts by weight of the component (A),
• wherein the component (C) is present in a proportion of from 0.1 to 3 parts by weight based on 100 parts by weight of the component (A), and
• wherein an adhesive strength of the acrylic pressure sensitive adhesive at 23° C. is from 3.5 to 6.8 N/20 mm.