Adhesive composition, protective film and polarizing plate which comprise adhesive layer comprising same, and image display device comprising same

An adhesive composition comprising:

• a polyvinyl alcohol-based resin;
• a melamine-based crosslinking agent in 5 parts by weight to 100 parts by weight, with respect to 100 parts by weight of the polyvinyl alcohol-based resin;
• an acid catalyst in 1 part by weight to 20 parts by weight, with respect to 100 parts by weight of the polyvinyl alcohol-based resin, wherein the acid catalyst includes a sulfonic acid group, and a weight ratio of the melamine-based crosslinking agent and the acid catalyst is from 5:1 to 1:1;
• and
• a silane-based additive in 10 parts by weight to 100 parts by weight, with respect to 100 parts by weight of the polyvinyl alcohol-based resin,
• wherein the melamine-based crosslinking agent is represented by the following Chemical Formula 1:
• wherein, R1 to R6 are the same as or different from each other, and each is independently hydrogen, deuterium, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted imine group, a substituted or unsubstituted amine group, a substituted or unsubstituted heteroaryl group, or a substituted or unsubstituted aryl group.