Antireflection film, process for forming the antireflection...

Details Antireflection film, process for forming the antireflection... Antireflection film, process for forming the antireflection...

2000-11-30

2002-10-29

Jones, Deborah (Department: 1775)

Coating processes

Electrical product produced

C428S447000, C428S451000, C428S429000, C427S168000, C427S169000, C427S387000, C106S287100, C106S287160, C106S287230, C106S287340

Reexamination Certificate

active

06472012

ABSTRACT:

The present invention relates to an antireflection film effective for improving the transparency of an image display device such as a liquid crystal display (LCD), a plasma display (PDP), CRT, EL or a touch panel, or an optical product made of glass, such as a lens for eye glasses, and an antireflection glass. Particularly, it relates to an antireflection glass excellent in mass productivity.
A transparent substrate such as a glass substrate provided with transparent electrodes, to be used for an image display device represented by LCD, PDP, CRT, EL or a touch panel, generates a reflected light of about 4% on one side thereof, which causes deterioration in the visibility or the transmittance. Therefore, for the purpose of improving the visibility or the transmittance by reducing the amount of light reflected from the substrate, a method of forming a so-called antireflection film such as a multi-layer film prepared by laminating thin films having low reflective indices or thin films having different refractive indices, on the substrate surface, has been employed.
In general, with an antireflection film of a multi-layer structure, effective antireflection can be realized within a wide wavelength region, but it is poor in mass productivity since a technique for controlling the film thickness of each layer with high precision is required. Therefore, some thin films having low refractive indices have been proposed which can be formed by a coating method as a method for forming an antireflection film simply and conveniently.
JP-A-6-157076 proposes to prepare an antireflection film having a low refractive index by forming fine irregularities on the surface of a coating film by using, as a coating liquid, a mixture of hydrolytic condensates of alkoxysilans having different molecular weights. However, there has been a problem such that control of the irregularities on the coating film surface by controlling the relative humidity at the time of forming the coating film is difficult, or the production of the condensates having different molecular weights is conversant.
JP-A-5-105424 discloses a method of employing a coating liquid containing fine particles of MgF
2
, but there has been a problem such that the formed coating film is poor in the mechanical strength and the adhesion to the substrate, and is further inferior in the antireflection performance.
The present inventors have previously found that by heat-treating a coating film obtained from a polysiloxane solution employing a fluoroalkylsilane, at a temperature of from 80 to 450° C., a coating film having a low refractive index and a large contact angle of water can be formed (U.S. Pat. No. 5,800,926; JP-A-9-208898). When such a coating film is formed on the surface of a display device, the large contact angle of water is a useful property as an additional function, but when it is used in the interior of the device as a highly transparent substrate, it will be essential to form another film on the surface of the coating film, and in such a case, the large contact angle of water is detrimental to the film forming on the coating film.
Therefore, a further study has been made, and as a result, it has been found that by optimizing the temperature of the heat treatment, it is possible to obtain a coating film having a small contact angle of water and a low refractive index.
Namely, it is an object of the present invention to provide an antireflection film which has a small contact angle of water and which is excellent in the antireflection performance, by a method which is capable of treating at a low cost, in a large amount and over a large area.
In a first aspect, the present invention provides a process for forming an antireflection film as adhered on a glass surface, which comprises preparing a reaction mixture comprising a silicon compound (A) of the following formula (1):
Si(OR)
4
  (1)
wherein R is a C
1-5
alkyl group, a silicon compound (B) of the following formula (2):
R
1
Si(OR
2
)
3
  (2)
wherein R
1
is a C
1-18
organic group, and R
2
is a C
1-5
alkyl group, an alcohol (C) of the following formula (3):
R
3
CH
2
OH   (3)
wherein R
3
is a hydrogen atom or an unsubstituted or substituted C
1-12
alkyl group, and oxalic acid (D), in a ratio of from 0.05 to 4.5 mol of the silicon compound (B) per mol of the silicon compound (A), in a ratio of from 0.5 to 100 mol of the alcohol (C) per mol of the total alkoxy groups contained in the silicon compounds (A) and (B), and in a ratio of from 0.2 to 2 mol of the oxalic acid per mol of the total alkoxy groups contained in the silicon compounds (A) and (B); heating the reaction mixture at a temperature of from 50 to 180° C. until the total amount of the silicon compounds (A) and (B) remaining in the reaction mixture becomes at most 5 mol %, while maintaining a SiO
2
concentration of from 0.5 to 10 wt % as calculated from silicon atoms in the reaction mixture and maintaining absence of water, to form a polysiloxane solution; coating the polysiloxane solution on a glass surface to form a coating film; and heat-curing the coating film at a temperature of from 480 to 520° C.
In a second aspect, the present invention provides the process for forming an antireflection film according to the first aspect, wherein in the formula (2) for the silicon compound (B), the organic group represented by R
1
contains fluorine atoms.
In a third aspect, the present invention provides the process for forming an antireflection film according to the first aspect, wherein the formula (2) represents a silicon compound (B) of the following formula (4):
CF
3
(CF
2
)
n
CH
2
CH
2
Si(OR
4
)
3
  (4)
wherein n is an integer of from 0 to 12, and R
4
is a C
1-5
alkyl group.
In a fourth aspect, the present invention provides an antireflection film having a refractive index of from 1.33 to 1.38 and a contact angle of water of at most 40°, which is formed as adhered on a glass surface, by preparing a reaction mixture comprising a silicon compound (A) of the following formula (1):
Si(OR)
4
  (1)
wherein R is a C
1-5
alkyl group, a silicon compound (B) of the following formula (2):
R
1
Si(OR
2
)
3
  (2)
wherein R
1
is a C
1-18
organic group, and R
2
is a C
1-5
alkyl group, an alcohol (C) of the following formula (3):
R
3
CH
2
OH  (3)
wherein R
3
is a hydrogen atom or an unsubstituted or substituted C
1-12
alkyl group, and oxalic acid (D), in a ratio of from 0.05 to 4.5 mol of the silicon compound (B) per mol of the silicon compound (A), in a ratio of from 0.5 to 100 mol of the alcohol (C) per mol of the total alkoxy groups contained in the silicon compounds (A) and (B), and in a ratio of from 0.2 to 2 mol of the oxalic acid per mol of the total alkoxy groups contained in the silicon compounds (A) and (B); heating the reaction mixture at a temperature of from 50 to 180° C. until the total amount of the silicon compounds (A) and (B) remaining in the reaction mixture becomes at most 5 mol %, while maintaining a SiO
2
concentration of from 0.5 to 10 wt % as calculated from silicon atoms in the reaction mixture and maintaining absence of water, to form a polysiloxane solution; coating the polysiloxane solution on a glass surface to form a coating film; and heat-curing the coating film at a temperature of from 480 to 520° C.
In a fifth aspect, the present invention provides the antireflection film according to the fourth aspect, wherein in the formula (2) for the silicon compound (B), the organic group represented by R
1
contains fluorine atoms.
In a sixth aspect, the present invention provides the antireflection film according to the fourth aspect, wherein the formula (2) represents a silicon compound (B) of the following formula (4):
CF
3
(CF
2
)
n
CH
2
CH
2
Si(OR
4
)
3
  (4)
wherein n is an integer of from 0 to 12, and R
4
is a C
1-5
alkyl group.
In a seventh aspect, the present invention provides an antireflection glass comprising a glass and the antireflection film as defined in the fourth aspect, formed on one side or both

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