Specifically, examples of the acryl-based resin include a polymer of acrylic acid, methacrylic acid, an acrylate such as methyl acrylate or ethyl acrylate, a methacrylate such as methyl methacrylate or ethyl methacrylate, acrylonitrile, acryl amide, or the like, a copolymer obtained by polymerizing such a monomer with another monomer, and the like.