Surface treatment agent for substrate, comprising perfluoropolyether group-containing phosphate compound

1. A surface treatment agent, comprising a perfluoropolyether group-containing phosphate compound, wherein the perfluoropolyether group-containing phosphate compound is a compound represented by formula (1):

B 1 —(C m F 2m O) n1 -A 1   (1)

wherein A 1 is a monovalent organic group having at least one phosphoric acid group at its terminal, B 1 is R F1 —O— or D 1 -Q 1 -O—CH 2 — and a compound represented by the formula (1) wherein A 1 is a monovalent organic group having at least one phosphoric acid group at its terminal, B 1 is A 2 -O—, wherein a content of the compound represented by the formula (1) wherein B 1 is A 2 -O— is from 10 to 60 parts by mass, per 100 parts by mass in total of the compound represented by the formula (1) wherein B 1 is R F1 —O— or D 1 -O 1 —O—CH 2 —,

wherein R F1 is a C 1-6 perfluoroalkyl group, D 1 is CF 3 — or CF 3 —O—, O 1 is a C 1-20 fluoroalkylene group comprising a hydrogen atom, a C 2-20 fluoroalkylene group comprising a hydrogen atom and having an etheric oxygen atom between carbon-carbon atoms, a C 1-20 alkylene group, or a C 2-20 alkylene group having an etheric oxygen atom between carbon-carbon atoms, and A 2 is a monovalent organic group having at least one phosphoric acid group at its terminal,

m is an integer of from 1 to 6, and

n1 is an integer of from 1 to 200, provided that when n1 is at least 2, (C m F 2m O) n1 may be one composed of at least two types of (C m F 2m O) different in m.

2. The surface treatment agent according to claim 1 , wherein (C m F 2m O) n1 is a group represented by formula (2-1):

(C r F 2r O) n2 (C s F 2s O) n3   (2-1)

wherein r is an integer of from 1 to 3, s is an integer of from 3 to 6, provided that r and s are not both 3, n2 is an integer of at least 1, n3 is an integer of at least 1, provided that n2+n3 is an integer of from 2 to 200, and a bonding order of (C r F 2r O) and (C s F 2s O) is not limited.

3. The surface treatment agent according to claim 1 , wherein (C m F 2m O) n1 is a group represented by formula (2-2):

(CF 2 O) n7 (CF 2 CF 2 O) n8   (2-2)

wherein n7 is an integer of at least 1, n8 is an integer of at least 1, provided that n7+n8 is an integer of from 2 to 200, and a bonding order of (CF 2 O) and (CF 2 CF 2 O) is not limited.

4. The surface treatment agent according to claim 1 , wherein A 1 is a group represented by formula (3):

-Q F1 (CX 2 ) w1 -E 1 -Y 1 —O—P(═O)(OH) 2   (3)

wherein Q F1 is a C 1-20 perfluoroalkylene group, CX 2 is CH 2 or CHF, w1 is 0 or 1, E 1 is a single bond, —C(═O)NH— (provided that Y 1 is bonded to N), —OC(═O)NH— (provided that Y 1 is bonded to N), —O—, —C(═O)O— (provided that Y 1 is bonded to O), —OC(═O)O—, —NHC(═O)NH— or —NHC(═O)O— (provided that Y 1 is bonded to O),

wherein Y 1 is an alkylene group, a poly(oxyalkylene)-alkylene group, a cycloalkylene group, an arylene group, or an alkylene group in which at least one of hydrogen atoms is substituted by a hydroxy group, provided that E 1 is not —O—, —OC(═O)NH— or —OC(═O)O— when w1 is 0, and Y 1 is not an alkylene group when w1 is 1, CX 2 is CH 2 and E 1 is a single bond.

5. The surface treatment agent according to claim 1 , wherein Q 1 is a group represented by formula (4-1), (4-2) or (4-3):

-Q F2 -O—CHFCF 2 —  (4-1)

-Q F2 -CHFCF 2 —  (4-2)

-Q F2 -C z H 2z —  (4-3)

wherein Q F2 is a single bond, a C 1-15 perfluoroalkylene group, or a C 2-15 perfluoroalkylene group having an etheric oxygen atom between carbon-carbon atoms, Q F2 is bonded to D 1 , and z is an integer of from 1 to 4, provided that Q F2 is not a single bond in the formula (4-1) and (4-2) when D 1 is CF 3 —O—.

6. The surface treatment agent according to claim 1 , wherein a number average molecular weight (Mn) of the compound represented by the formula (1) is 2,000 to 10,000.

7. The surface treatment agent according to claim 1 , wherein in the compound represented by the formula (1), B 1 is R F1 —O— or D 1 -Q 1 -O—CH 2 —.

8. The surface treatment agent according to claim 1 , which is suitable for treating a surface of a sapphire substrate.

9. A coating agent comprising the surface treatment agent of claim 1 and a liquid medium.

10. A substrate having a surface layer formed from the surface treatment agent of claim 1 .