Method for forming thin MgF.sub.2 film and low-reflection film

Coating processes – Electrical product produced – Transparent base

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Details

427162, 427165, 4271262, 427226, 4274191, B05D 512

Patent

active

050858882

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a method for forming on a substrate a transparent thin MgF2 film having a low refractive index and also to a method for forming a low-reflection film on a substrate.


BACKGROUND ART

There have been proposed many methods for forming a low-reflection film on a substrate in the field of cathode-ray tube for TV and computer terminals, not to mention sheet glass, optical parts and optical instruments.
Conventional methods consist of coating the surface of a cathode-ray tube with an SiO.sub.2 layer having minute irregularities, thereby producing the anti-glare effect, or consist of etching the surface of a cathode-ray tube with hydrofluoric acid, thereby forming surface irregularities, as disclosed in Japanese Unexamined Patent Publication No. 118931/1986. The coating and etching by these conventional methods are called non-glare treatment because they merely form minute irregularities which reflect and scatter the incident light; they are not essentially designed to form a low-reflection film and hence they have a limit in decreasing the reflectivity of the substrate.
On the other hand, attempts have been made to coat the surface of lens or glass with a thin film of MgF.sub.2 (which is a stable substance having a low refractive index) by vacuum deposition. Unfortunately, vacuum deposition has a disadvantage of requiring an expensive apparatus and involving difficulties in handling large objects (such as finished cathode ray tube and sheet glass) and a large number of objects for mass production. All this leads vacuum deposition to high production cost.
The present invention was completed to eliminate the above-mentioned disadvantages involved in the conventional technology. Accordingly, it is an object of the present invention to provide a new method for forming on a substrate a stable, transparent thin film having a low refractive index in a simple chemical manner. It is another object of the present invention to provide a new method for forming on a substrate a thin film having the low-reflection characteristics.


DISCLOSURE OF THE INVENTION

The first aspect of the present invention resides in a method for forming a thin MgF.sub.2 film on a substrate which comprises coating a substrate with a liquid containing an Mg salt and a BF.sub.3 complex salt and subsequently heating the coating.
The second aspect of the present invention resides in a method for forming on a substrate a low-reflection film of monolayer or multilayer structure, with at least one layer being a thin MgF.sub.2 film, said process comprising coating a substrate with a liquid containing an Mg salt and a BF.sub.3 complex salt and subsequently heating the coating, thereby forming said thin MgF.sub.2 film.
The third aspect of the present invention resides in a method for forming on a substrate a thin MgF.sub.2 film and low-reflection film which comprises coating a substrate with a solution containing an MgF.sub.2 sol formed by the reaction between an Mg salt and a BF.sub.3 complex salt, and subsequently heating the coating.
The fourth aspect of the present invention resides in a method for forming on a substrate a thin MgF.sub.2 film and low-reflection film which comprises coating a substrate with a solution containing a silicon compound and an MgF.sub.2 sol formed by the reaction between an Mg salt and a BF.sub.3 complex salt, and subsequently heating the coat.
In the preferred embodiments of the present invention, the Mg salt is MgX.sub.2 (X=a halogen element other than fluorine), and is used in combination with a BF.sub.3 complex salt.
According to the method of the present invention, the thin MgF.sub.2 film is formed from an Mg salt (excluding a fluoride) and a BF.sub.3 complex salt which functions as a fluorinating agent. The reaction to form the thin MgF.sub.2 film is promoted if the Mg salt and BF.sub.3 complex salt as the starting materials are dispersed, mixed or dissolved in a solution, and the reaction rate is increased by heating.
The Mg salt as the starting material may be availab

REFERENCES:
patent: 4492721 (1985-01-01), Joosten et al.
patent: 4579638 (1986-04-01), Scherber
patent: 4681819 (1987-07-01), Gnyra
patent: 4874222 (1989-10-01), Vacha et al.

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