Coating composition for forming hydrophilic coating film

Abstract

To provide a coating composition capable of forming a hydrophilic coating film which has high transparency and which is excellent in abrasion resistance (adhesion), hydrophilicity (anti-fogging, wettability and anti-fouling properties) and hydrophilic durability.A coating composition for forming a hydrophilic coating film, which comprises boehmite particles, silica particles, a binder and water, wherein the crystallite diameter of the boehmite particles, as calculated from the diffraction peak of the (120) plane, is from 20 to 50 nm, the average particle diameter of the silica particles is from 5 to 50 nm, the proportion of the boehmite particles is from 20 to 80 mass % based on the total amount of the boehmite particles and the silica particles, and the proportion of the binder is from 0.5 to 15 parts by mass per 100 parts by mass in total of the boehmite particles and the silica particles. The article having a hydrophilic coating film on a surface of a base material, has a hydrophilic coating film formed from the above coating composition.

Description

TECHNICAL FIELDThe present invention relates to a coating composition for forming a hydrophilic coating film.BACKGROUND ARTTransparent base materials made of glass, plastics, etc. are used in various applications to e.g. various lamp covers, lenses for eyeglasses, goggles, various instrument covers, transparent roof materials or transparent side wall materials in plant cultivation installations such as greenhouses. However, with these base materials, the hydrophilicity is not high, and they have a trouble such that dew condensation or fogging is likely to take place. For example, in the case of an instrument cover which is likely to be always exposed to outside air, dew condensation is likely to take place on the inner surface of the cover to form fogging, thus leading to a problem such that a sign or indication becomes invisible. Further, in the case of a plastic film to be used as a transparent roof material or a transparent side wall material of a plant cultivation installation, ...

AI Technical Summary

Benefits of technology

The present invention provides a coating composition for forming a hydrophilic coating film that has high transparency, abrasion resistance, hydrophilicity, anti-fogging property, wettability, and hydrophilic durability. The coating composition comprises boehmite particles, silica particles, a binder, and water. The composition has a crystallite diameter of the boehmite particles of 20 to 50 nm, an average particle diameter of the silica particles of 5 to 50 nm, and a ratio of boehmite particles to silica particles of 20 to 80 mass%. The binder is a water-soluble organic binder, preferably polyvinyl alcohol. The coating composition has a pH of 2.5 to 7. It also contains a water-soluble alcohol in a proportion of 10 to 70 mass%. The hydrophilic coating film has a film thickness of 100 to 700 nm and is formed on a resin material, preferably fluororesin.

Problems solved by technology

However, with these base materials, the hydrophilicity is not high, and they have a trouble such that dew condensation or fogging is likely to take place.

For example, in the case of an instrument cover which is likely to be always exposed to outside air, dew condensation is likely to take place on the inner surface of the cover to form fogging, thus leading to a problem such that a sign or indication becomes invisible.

Further, in the case of a plastic film to be used as a transparent roof material or a transparent side wall material of a plant cultivation installation, the transmittance of sunlight may be deteriorated by water drops or fogging, and the growth of plants may be thereby adversely affected.

However, in the hydrophilic coating films formed by the coating compositions (1) and (2), alumina particles and silica particles are merely attached by a surfactant on the surface of a base material film, and the adhesion between the coating film and the base material film is inadequate.

Accordingly, the abrasion resistance of the hydrophilic coating film is inadequate.

Further, the water resistance of the hydrophilic coating film is low, whereby the hydrophilicity cannot be maintained for a long period of time.

The hydrophilic coating film formed by the coating composition (3) contains a water-soluble resin (binder), whereby the adhesion is improved as compared with the hydrophilic coating films formed by the coating compositions (1) and (2), but the adhesion to the base material is still inadequate.

Accordingly, the abrasion resistance of the hydrophilic coating film is inadequate.

Further, the water resistance of the hydrophilic coating film is low, and the hydrophilicity cannot be maintained for a long period of time.

However, in a real outdoor exposure test, the hydrophilicity abruptly drops at some time.