Removable water-based pressure-sensitive adhesive composition and removable pressure-sensitive adhesive sheet

A re-releasable aqueous pressure-sensitive adhesive composition comprising:

• as a main component, an emulsion [A] of a first (meth)acrylic acid-based ester copolymer, the emulsion [A] having a constituent unit that reacts with a crosslinker [C];
• an emulsion [B] of a second (meth)acrylic acid-based ester copolymer, in an amount of 0.6 parts by mass or more in terms of a solid content based on 100 parts by mass of a solid content of the emulsion [A], wherein the emulsion [B] functions as a crosslinking assistant;
• and further, the crosslinker [C] together with the emulsion [A] and the emulsion [B], wherein the crosslinker [C] comprises a hydrazide-based compound that is soluble or dispersible in water, the emulsion [A] of the first (meth)acrylic acid-based copolymer comprises:
• as a main component, a constituent unit (a1) derived from a first (meth)acrylate-based monomer;
• a constituent unit (a2) in an amount of 0.5 to 3.0% by mass, the constituent unit (a2) being derived from a first unsaturated monomer containing a functional group, wherein the first unsaturated monomer is at least one monomer selected from a group consisting of an unsaturated monomer having a carboxyl group and an unsaturated monomer having a hydroxy group;
• and a constituent unit (a3) in an amount of 0.1 to 1.0% by mass, wherein the constituent unit (a3) is derived from a first ethylenically unsaturated monomer and has reactivity with the hydrazide-based compound that is contained in the crosslinker [C] and that is soluble or dispersible in water, the emulsion [B] of the second (meth)acrylic acid-based ester copolymer comprises:
• a constituent unit (b1) derived from a second (meth)acrylate-based monomer in an amount of 15 to 60% by mass;
• a constituent unit (b2) derived from a second unsaturated monomer having a carboxy group in an amount of 20 to 50% by mass;
• and a constituent unit (b3) in an amount of 20 to 45% by mass, wherein the constituent unit (b3) is derived from a second ethylenically unsaturated monomer and has reactivity with the hydrazide-based compound that is contained in the crosslinker [C] and that is soluble or dispersible in water, the emulsion [B] is an emulsion that dissolves in water upon neutralization and is unmeasurable in a particle diameter analysis at a pH in a range from 6.5 to 7.5 and the crosslinker [C] is crosslinkable with at least the constituent unit (a3) of the emulsion [A] and the constituent unit (b3) of the emulsion [B].