Water/oil repellent composition, method for its production and article

A method for treating an article, which comprises steps 1 and 2:

• Step 1:
• a step of preparing a water/oil repellent composition comprising a copolymer (A) and an aqueous medium (B), wherein the aqueous medium (B) contains water and at least one film-forming assistant selected from a film-forming assistant (x) and a film-forming assistant (y) wherein (y) has a boiling point of at least 250° C., and
• Step 2:
• a step of treating an article with the water/oil repellent composition prepared in Step 1
• wherein the copolymer (A) has structural units based on the following monomer (a), structural units based on the following monomer (b), and at least one type of structural units selected from structural units based on the following monomer (c) and structural units based on the following monomer (d), wherein
• monomer (a) is a compound represented by the following formula (1):
• (Z—Y)nX (1)
• wherein Z is a C1-6 polyfluoroalkyl group or a group represented by the following formula (2), Y is a bivalent organic group having no fluorine atom, or a single bond, n is 1 or 2, and X is, when n is 1, any one of the groups represented by the following formulae (3-1) to (3-5) and, when n is 2, any one of the groups represented by the following formulae (4-1) to (4-4):
• CiF2i+1O(CFX1CF2O)jCFX2— (2)
• wherein i is an integer of from 1 to 6, j is an integer of from 0 to 10, and each of X1 and X2 is a fluorine atom or a trifluoromethyl group;
• —CR═CH2 (3-1)
• —C(O)OCR═CH2 (3-2)
• —OC(O)CR═CH2 (3-3)
• —OCH2-φ-CR═CH2 (3-4)
• —OCH═CH2 (3-5)
• wherein R is a hydrogen atom, a methyl group or a halogen atom, and φ is a phenylene group;
• —CH[—(CH2)mCR═CH2]— (4-1)
• —CH[—(CH2)mC(O)OCR═CH2]— (4-2)
• —CH[—(CH2)mOC(O)CR═CH2]— (4-3)
• —OC(O)CH═CHC(O)O— (4-4)
• where R is a hydrogen atom, a methyl group or a halogen atom, and m is an integer of from 0 to 4;
• monomer (b) is vinylidene chloride;
• monomer (c) is a monomer having no polyfluoroalkyl group nor crosslinkable functional group, the homopolymer of which has a glass transition temperature of at least 20° C.;
• and
• monomer (d) is a monomer having no polyfluoroalkyl group and having a crosslinkable functional group;
• wherein the film-forming assistant (x) is a compound represented by the following formula (5):
• R1O(CH2)r(CHR4)sC(O)NR2R3 (5)
• wherein r is an integer of from 0 to 3,
• s is 0 or 1,
• R1 is a C1-4 alkyl group,
• each of R2 and R3 which are independent of each other, is a C1-3 alkyl group (provided that it may contain an etheric oxygen atom), and
• R4 is a hydrogen atom or a methyl group;
• and wherein the film-forming assistant (y) is a compound represented by the following formula (6):
• R5—O—(CH2CH2O)t—R6 (6)
• wherein t is 3 or 4,
• each of R5 and R6 which are independent of each other, is a C1-4 alkyl group.