Package, and methods for producing and for using self-adhesive

A method for producing a self-adhesive to be arranged on a package comprising a space to store contents and an opening by which the space and an outside communicate, wherein the opening is repeatedly openable and sealable by the self-adhesive that consists of a cross-linking material of a resin composition containing a (meth)acrylic acid ester copolymer resin having a glass transition temperature of −22.8° C. or more, and a crosslinking agent, the resin composition being a resin composition foam, the method comprising:

• making the resin composition that contains the (meth)acrylic acid ester copolymer resin, and the crosslinking agent, the resin composition being either emulsion or dispersion;
• foaming the resin composition, to make the resin composition foam;
• and
• cross-linking the resin composition foam.