Disclosed is a polyester synthetic fiber treatment agent that contains a silicone (A), a silicone (B), a nonionic surfactant, an anionic ingredient, and optionally a silicone (C). The amount of the silicone (C) contained in the polyester synthetic fiber treatment agent is less than 10% by mass. The silicone (A) is a silanol-modified silicone with a number average molecular weight of not less than 50,000 but less than 200,000. The silicone (B) is a silane coupling agent having at least one functional group selected from the group consisting of a methoxy group, an ethoxy group, an amino group, and an isocyanate group but not including an epoxy group in the molecule. The silicone (C) is at least one selected from the group consisting of silicone resins, dimethyl silicones, and alkyl-modified silicones but excluding those corresponding to being the silicone (A).

Disclosed is a polyester synthetic fiber treatment agent that contains a silicone (A), a silicone (B), a nonionic surfactant, an anionic ingredient, and optionally a silicone (C). The amount of the silicone (C) contained in the polyester synthetic fiber treatment agent is less than 10% by mass. The silicone (A) is a silanol-modified silicone with a number average molecular weight of not less than 50,000 but less than 200,000. The silicone (B) is a silane coupling agent having at least one functional group selected from the group consisting of a methoxy group, an ethoxy group, an amino group, and an isocyanate group but not including an epoxy group in the molecule. The silicone (C) is at least one selected from the group consisting of silicone resins, dimethyl silicones, and alkyl-modified silicones but excluding those corresponding to being the silicone (A).

Disclosed is a polyester synthetic fiber treatment agent that contains a silicone (A), a silicone (B), a nonionic surfactant, an anionic ingredient, and optionally a silicone (C). The amount of the silicone (C) contained in the polyester synthetic fiber treatment agent is less than 10% by mass. The silicone (A) is a silanol-modified silicone with a number average molecular weight of not less than 50,000 but less than 200,000. The silicone (B) is a silane coupling agent having at least one functional group selected from the group consisting of a methoxy group, an ethoxy group, an amino group, and an isocyanate group but not including an epoxy group in the molecule. The silicone (C) is at least one selected from the group consisting of silicone resins, dimethyl silicones, and alkyl-modified silicones but excluding those corresponding to being the silicone (A).

Disclosed is a polyester synthetic fiber treatment agent that contains a silicone (A), a silicone (B), a nonionic surfactant, an anionic ingredient, and optionally a silicone (C). The amount of the silicone (C) contained in the polyester synthetic fiber treatment agent is less than 10% by mass. The silicone (A) is a silanol-modified silicone with a number average molecular weight of not less than 50,000 but less than 200,000. The silicone (B) is a silane coupling agent having at least one functional group selected from the group consisting of a methoxy group, an ethoxy group, an amino group, and an isocyanate group but not including an epoxy group in the molecule. The silicone (C) is at least one selected from the group consisting of silicone resins, dimethyl silicones, and alkyl-modified silicones but excluding those corresponding to being the silicone (A).