JPH0748117A - Porous silica sol and its production - Google Patents

Abstract

PURPOSE:To produce a porous silica sol which is a low refractive index filler for forming optical materials, especially reflection-preventing films having excellent effects for lenses and glass plates. CONSTITUTION:The porous silica sol having an average particle diameter of 0.3-100nm and a refractive index of 1.2-1.4 is produced by hydrolyzing a silicon alkoxide with ammonia and subsequently removing the residual ammonia. The obtained porous silica sol can be used as a low refractive filler for forming reflection-preventing films, and coating solutions for forming the highly excellent reflection-preventing films can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silica sol used as a low refractive index filler for forming an antireflection film in an optical material and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, light has been used as a medium in communication systems and measurement systems. However, the loss of optical power due to the reflection of light from the surface of a lens or the like, or the reflected light being output as an erroneous signal has caused various devices to malfunction. In addition, depending on the reflected light, image-related equipment such as a display surface of a display device, a surface cover material of the display device, a display surface of a TV Braun tube, a touch panel, a display surface of a liquid crystal display device, a front image surface of a cathode ray tube, and the like. However, the reflection on the front glass of the painting, the window glass, the glass of the showcase, the cover glass of the clock and the instrument occurred, which was a problem.

Therefore, the vacuum deposition method, the sputtering method,
By the ion plating method and the CVD method, a single-layer or multi-layer antireflection film is formed on the surface of the video equipment and various glasses to prevent reflected light. However, each of the above methods is a very expensive film forming method, and the size of the base material is limited due to the limitation of the device. Further, when the base material surface has irregularities, uniform film formation cannot be performed. There was such a problem. In particular, in the vacuum vapor deposition method, in order to make the film strength of the antireflection film strong enough to withstand long-term use, the base material must be 300 ° C. or higher, and in the sputtering method, the equipment cost is very high. There's a problem.

Therefore, as a countermeasure against the above-mentioned problem, if an antireflection film can be formed by a coating method instead of the above-mentioned processing method, a binder is selected for the problems of the size of the base material, the processing temperature and the expansion coefficient. It is very promising because it can be dealt with.

By the way, in optical materials, especially lenses and glass, unless the refractive index of the antireflection film is 1.45 or less, the antireflection effect is weak. Those having a value of 1.45 or less are only polytetrafluoroethylene. However, this material is not suitable as a binder for a coating liquid for forming an antireflection film because it has poor adhesion, is soft, requires high temperature treatment, and is very expensive.

Other binders have a refractive index of 1.4.
In order to obtain an antireflection film having a refractive index of 1.45 or less, a low refractive index filler having a refractive index of 1.45 or less needs to be dispersed in the binder. As the low refractive index filler having a refractive index of 1.45 or less, a refractive index of 1.
There are 35 cryolites, and it is speculated that this should be dispersed. By the way, it is known that the reflectance becomes 0% when the refractive index of the antireflection film is equal to the square root of the refractive index of the substrate. However, in the antireflection film for soda lime glass, which is a commonly used substrate, the reflectance is 0% when the refractive index of the antireflection film is 1.22. Therefore, as the low-refractive-index filler added to the binder, a low-refractive-index material is preferable to cryolite, but it is said that no material currently satisfies the above conditions.

Therefore, as a means for lowering the refractive index, it was found that by making the low refractive index material porous, this material exhibits a lower refractive index than the raw material.
It has been found that silica that has been made porous (porous silica) can be used. However, conventional porous silica is a polymer, or a high-boiling solvent is added, and after adjusting the silica gel, in order to measure the porosity by removing organic matter at high temperature,
The particle diameter was 0.5 μm or more, and there was a problem that a sufficiently transparent film could not be obtained even if it was made into a paint.

[0008]

The present invention has been made in view of these circumstances, and is used as a low refractive index filler for forming an antireflection film in an optical material,
It is intended to provide a porous silica sol and a method for producing the same.

[0009]

The object of the present invention is to provide a porous silica sol having an average particle size of 0.3 to 100 nm and a refractive index of 1.2 to 1.4 with a low refractive index filler. It is solved by using as. The porous silica sol can be produced by hydrolyzing the silicon alkoxide with ammonia and then removing the ammonia.

[0010]

By using a silicon alkoxide and mixing it with aqueous ammonia to hydrolyze the silicon alkoxide, a highly entangled and branched polymeric porous silica sol can be produced.

[0011]

EXAMPLES Next, the method for producing the porous silica sol of the present invention will be described in detail. As the silicon alkoxide used in the present invention, an alkylalkoxysilane or a carbon functional polyorganosiloxane is used. Specific examples of the alkylalkoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane,
Ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltripropoxysilane, propyltributoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyl Examples include dipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, methylethyldimethoxysilane, and methylpropyldiethoxysilane.

As the carbon functional polyorganosiloxane, 3,4-epoxycyclohexylalkyltrialkoxysilane, methacryloxyalkyltrialkoxysilane, vinyltrialkoxysilane, γ-glycidoxyalkylalkoxysilane and aminoalkyltrialkoxy are used. There is silane.

Any organic solvent may be used as long as it is water-soluble, and alcohols, ketones, esters and glycol ethers are used. In particular, methanol, ethanol, isopropyl alcohol, butyl alcohol,
Alcohols such as n-propyl alcohol are preferred.

First, the silicon alkoxide prepared as a silica raw material is used and mixed with the organic solvent. The silicon alkoxide may be used alone or as a mixture of two or more kinds. However, the concentration of the solid content of the silicon alkoxide is 0.
5 to 15% by weight is preferable. If it is less than 0.5% by weight, the economy is poor and the cost is high.
When the content is 5% by weight or more, the hydrolysis rate of the silicon alkoxide is too fast, and the particle size suddenly increases, and the stability of the generated porous silica sol is poor. The reason for this is that Rayleigh scattering occurs in the antireflection film obtained by using the above dispersion as a coating liquid for forming the antireflection film, and the transparency is lowered.

Then, ammonia water is gradually dropped while stirring the silicon alkoxide mixed with the organic solvent. Therefore, the alkoxide of silicon is hydrolyzed by ammonia, and unlike the hydrolysis under acidic conditions, a highly entangled and branched polymeric porous silica sol is produced. Further, the ammonia concentration can be arbitrarily set as long as the pH of the solution at the time of hydrolysis is in the range of 9 to 11.

Further, since ammonia is mixed as a water-soluble impurity in the porous silica sol, it is necessary to remove it. The ammonia is easily vaporized, and can be removed by refluxing at the boiling point of the organic solvent or by feeding air or nitrogen gas. Then,
By diluting the produced porous silica sol with an organic solvent, a porous silica sol having a concentration suitable for the application is produced. Further, the porous silica sol may be concentrated.

According to such a manufacturing method, the average particle size is 0.
From 3 to 100 nm, a porous silica sol free of impurities is obtained. Further, the porous silica sol has a low density due to the existence of voids in the particles, and the refractive index of the porous silica sol is 1.2 to 1 as compared with the refractive index of ordinary silica of 1.46. The refractive index significantly decreases to 1.4.

As described above, the porous silica sol of the present invention has an average particle size in the range of 0.3 to 100 nm by hydrolyzing a silicon alkoxide with ammonia and then removing the ammonia, and Since it has a refractive index of 1.2 to 1.4, it can be used as a low refractive index filler for forming an antireflection film, and when it is used, it has an excellent antireflection effect. A preventive film can be prepared.

(Embodiment 1) The effects of the present invention will be clarified by showing concrete examples below. First, tetraethoxysilane 1
730.8 parts by weight of ethanol was added to 00 parts by weight,
It was stirred. Then, a mixture of 29.2 parts by weight of 30% by weight aqueous ammonia and 100 parts by weight of ethanol was added dropwise thereto at room temperature and stirred for 48 hours to produce a porous silica sol.

Then, ethanol and ammonia were distilled off by an evaporator to obtain a porous silica sol having a solid content of 10% by weight. The average particle size of the porous silica sol thus produced was about 10 nm. The refractive index was determined as follows.

Using the porous silica sol thus obtained and a dispersible binder of this porous silica sol, for example, a hydrolyzate of tetramethoxysilane under acidic conditions, various porous silica / binder ratios are used. Was changed to prepare an antireflection film. Then, the relationship between the refractive index of the produced antireflection film and the concentration of porous silica was determined, and from this relationship, the concentration of 100% porous silica was extrapolated to determine the refractive index of the porous silica sol. As a result, the refractive index of the porous silica sol in this example was 1.25.

Example 2 Tetramethoxysilane 73.
To 7 parts by weight of methanol, 757.2 parts by weight of methanol was added and stirred, and 30% by weight of ammonia water 29.2 was added thereto.
A mixture of 100 parts by weight of methanol and 100 parts by weight of methanol was added dropwise at room temperature and stirred for 36 hours to produce a porous silica sol. Then, the mixture was refluxed for 8 hours to remove ammonia, and further concentrated by an evaporator to obtain a porous silica sol having a solid content of 10% by weight. The average particle size at this time was about 15 nm. The refractive index was determined as in Example 1. As a result, the refractive index of the porous silica sol in this example was 1.28.

(Example 3) 751.5 parts by weight of ethanol was added to 50 parts by weight of tetraethoxysilane and 29.3 parts by weight of methyltrimethoxysilane, and the mixture was stirred. A mixture of 0.6 parts by weight and 100 parts by weight of ethanol was added dropwise at room temperature and stirred for 48 hours to produce a porous silica sol. Then, ethanol and ammonia were distilled off by an evaporator, ethanol was further added, and ethanol was distilled off again to obtain a porous silica sol having a solid content of 10% by weight. The average particle size at this time was about 10 nm. The refractive index was determined as in Example 1. As a result, the refractive index of the porous silica sol in this example was 1.24.

[0024]

As explained above, the porous silica sol of the present invention has an average particle size in the range of 0.3 to 100 nm by hydrolyzing silicon alkoxide with ammonia and then removing ammonia. Moreover, since it has a refractive index of 1.2 to 1.4, it can be used as a low-refractive-index filler for a coating liquid for forming an antireflection film. It is possible to obtain the effect that the prevention film can be produced.

Claims (2)

[Claims] 1. A porous silica sol having an average particle diameter of 0.3 to 100 nm and a refractive index of 1.2 to 1.4. 2. A method for producing a porous silica sol, which comprises hydrolyzing a silicon alkoxide with ammonia and then removing the ammonia.