Surface treatment agent

A surface-treating agent comprising at least one perfluoro(poly)ether group containing silane compound of any of the formulae (A1), (A2), (B1), (B2), (C1) and (C2):

• wherein:
• PFPE is each independently at each occurrence a group of the formula:
• —(OC4F8)a—(OC3F6)b—(OC2F4)c—(OCF2)d—
• wherein a, b, c and d are each independently an integer of 0-200, the sum of a, b, c and d is 1 or more, and the occurrence order of the respective repeating units in parentheses with the subscript a, b, c or d is not limited in the formula;
• Rf is each independently at each occurrence an alkyl group having 1-16 carbon atoms which may be substituted by one or more fluorine atoms;
• R1 is each independently at each occurrence a hydrogen atom or an alkyl group having 1-22 carbon atoms;
• R2 is each independently at each occurrence a hydroxyl group or a hydrolyzable group;
• R11 is each independently at each occurrence a hydrogen atom or a halogen atom;
• R12 is each independently at each occurrence a hydrogen atom or a lower alkyl group;
• n is, independently per a unit (—SiR1nR23-n), an integer of 0-3;
• there is at least one R2 in the formulae (A1), (A2), (B1) and (B2);
• X1 is each independently a single bond or a 2-10 valent organic group;
• X2 is each independently at each occurrence a single bond or a divalent organic group;
• t is each independently at each occurrence an integer of 1-10;
• α is each independently an integer of 1-9;
• α′ is each independently an integer of 1-9;
• X5 is each independently a single bond or a 2-10 valent organic group;
• β is each independently an integer of 1-9;
• β′ is each independently an integer of 1-9;
• X7 is each independently a single bond or a 2-10 valent organic group;
• γ is each independently an integer of 1-9;
• γ′ is each independently an integer of 1-9;
• Ra is each independently at each occurrence —Z—SiR71pR72qR73r;
• Z is each independently at each occurrence an oxygen atom or a divalent organic group;
• R71 is each independently at each occurrence Ra′;
• Ra′ has the same definition as that of Ra;
• in Ra, the number of Si atoms which are straightly linked via the Z group is up to five;
• R72 is each independently at each occurrence a hydroxyl group or a hydrolyzable group;
• R73 is each independently at each occurrence a hydrogen atom or a lower alkyl group;
• p is each independently at each occurrence an integer of 0-3;
• q is each independently at each occurrence an integer of 0-3;
• r is each independently at each occurrence an integer of 0-3;
• in one Ra, the sum of p, q and r is 3, and there is at least one R72 in the formula (C1) and C2);
• Rb is each independently at each occurrence a hydroxyl group or a hydrolyzable group;
• Rc is each independently at each occurrence a hydrogen atom or a lower alkyl group;
• k is each independently at each occurrence an integer of 1-3;
• l is each independently at each occurrence an integer of 0-2;
• m is each independently at each occurrence an integer of 0-2;
• the sum of k, l and m is 3 in each unit in parentheses with the subscript γ,
• wherein a proportion of the perfluoro(poly)ether group containing silane compound having a molecular weight of 3,000 or less in the perfluoro(poly)ether group containing silane compounds of any of the above general formulae is 9 mol % or less;
• and
• wherein the number average molecular weight of the perfluoro(poly)ether group containing silane compound of any of formulae (A1), (A2), (B1), (B2), (C1) and (C2) is 10,000 or less.