Alkali-resistant water repellent member, method for producing said water repellent member, and method for improving alkali resistance and wear resistance of water repellent member

An alkali-resistant water-repellent member, comprising:

• a substrate having surfaces;
• a silica layer disposed on at least one side surface of the substrate surfaces, containing at least 50% by weight of silica nanoparticles and at least 1% by weight of an organosilicon compound having a plurality of silanol groups in a molecule, and having a thickness of 1 nm to 5 μm;
• and
• a water/oil repellent layer disposed on an outer surface of the silica layer, composed mainly of a cured product of a hydrolyzable fluorine-containing organosilicon compound, and having a thickness of 0.5 to 30 nm;
• wherein the organosilicon compound having a plurality of silanol groups in a molecule, is a hydrolysis/partial condensate of tetraalkoxysilane, which has a silanol group amount of 0.001 to 0.5 mol in the molecule, and a mass average molecular weight of 5,000 to 50,000;
• and
• wherein the hydrolyzable fluorine-containing organosilicon compound is at least one selected from hydrolyzable fluorine-containing organosilicon compounds having the following general formulas (1) to (5):
• (A-Rf)α—ZWβ (1)
• Rf—(ZWβ)2 (2)
• Z′—(Rf—ZWβ)γ (3)
• wherein Rf is independently a divalent linear perfluorooxyalkylene polymer residue having —(CF2)d—O—(CF2O)p(CF2CF2O)q(CF2CF2CF2O)r(CF2CF2CF2CF2O)s(CF(CF3) CF2O)t—(CF2)d—,
• d is independently an integer of 0 to 8,
• p, q, r, s, and t are each independently an integer of 0 to 200 and the sum of p+q+r+s+t is an integer of 3 to 500,
• each repeating unit in parentheses to which p, q, r, s, and t are attached may be randomly combined,
• A is independently a fluorine atom, a hydrogen atom, or a monovalent fluorine-containing group whose terminal is a —CF3 group, a —CF2H group, or a —CH2F group,
• Z and Z′ are independently a single bond or a 2- to 8-valent organic group optionally including a nitrogen atom, an oxygen atom, a silicon atom, a phosphorus atom, or a sulfur atom and optionally substituted with fluorine,
• W is independently a monovalent organic group having a hydrolyzable silyl group at the terminal,
• α and β are each independently an integer of 1 to 7, and the sum of α+β is an integer of 2 to 8,
• γ is an integer of 2 to 8,
• A-Rf-Q-(Y)δ—B (4)
• Rf-(Q-(Y)δ—B)2 (5)
• wherein Rf and A are the same as described above,
• Q is independently a single bond or divalent organic group,
• δ is independently an integer of 1 to 10,
• Y is independently a divalent organic group having a hydrolyzable silyl group,
• and
• B is independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom.