JPWO2006057119A1 - INORGANIC COATING COMPOSITION, LOW REFRACTIVE FILM COATING METHOD, AND METHOD FOR FORMING LOW REFRACTIVE FILM - Google Patents

Abstract

An inorganic coating composition that can form a low refractive index coating film having high transparency and excellent adhesion to an organic substrate. An inorganic coating composition having the following composition capable of forming a low refractive index coating film on an organic substrate, hollow silica particles having an average particle size of 5 to 3000 nm: 0.1 to 20% by mass, and an organic substrate can be swollen or dissolved In addition, an organic solvent miscible with water having a boiling point of 130 ° C. or higher at a pressure of 0.1 MPa: 1 to 20% by mass, a state in which the organic base material is not substantially swollen or dissolved, and a pressure of 0.1 MPa And a water-miscible organic solvent having a boiling point of 50 to 120 ° C. and water: 60 to 98.9% by mass.

Description

  The present invention relates to an inorganic coating composition capable of forming a highly transparent low refractive index coating film, a low refractive index coating film, and a method for forming a low refractive index coating film.

  Conventionally, various methods for forming low-refractive-index coatings for display panel cover materials and organic substrates such as optical lenses, optical filters, and polarizing films have been studied for the purpose of reducing reflectivity. Has been. As part of this study, vapor deposition methods such as sputtering and CVD can be mentioned. However, in the case of an organic base material, it cannot be heated to a high temperature, and an organic base material and a coating film with sufficient adhesion cannot be obtained. There is a problem. In addition, the above-described vapor deposition method generally requires a large amount of capital investment and increases the cost, and there is also a problem that it is difficult in terms of production technology for a large-area substrate. For this reason, since it can be produced inexpensively with a simple apparatus, for example, a wet method of forming a low refractive index coating film by applying a coating liquid containing porous silica fine particles and a binder is mentioned (Patent Document). 1). However, in this wet method, since a binder is indispensable, a coating film obtained by the influence of the binder that has a low reflectivity is not obtained. In addition, when forming inorganic particles such as silica on an organic substrate, a primer layer or a hard coat layer may be required as an intermediate layer in order to improve the adhesion between the organic substrate and the inorganic particles. There is a problem that becomes high.

  Also, as a method for forming a strong silica film on an organic substrate such as polycarbonate, a paint containing hydrophobically treated silica, water, and an organic solvent such as cellosolve acetate that is soluble in the organic substrate is disclosed. (Patent Document 2). However, this method has a problem that since the organic base material contains a large amount of an organic solvent that is soluble in the organic base material, the erosion of the organic base material is considerably advanced, and the obtained coating film product tends to become cloudy.

JP 7-48527 A US Pat. No. 4,413,088

  The present invention forms an inorganic coating composition, a low refractive index coating film and a low refractive index coating film that can form a low refractive index coating film having high transparency and excellent adhesion to an organic substrate. It aims to provide a way to do.

The present invention has the gist characterized by the following.
(1) (a) 0.1 to 20% by mass of hollow silica particles having an average particle diameter of 5 to 3000 nm; (b) an organic base material can be swollen or dissolved, and at a pressure of 0.1 MPa. 1 to 20% by mass of water-miscible organic solvent A having a boiling point of 130 ° C. or higher; (c) a boiling point of 50 to 120 without substantially swelling or dissolving the organic base material and at a pressure of 0.1 MPa. Inorganic coating composition containing 60-98.9% by mass of organic solvent B and / or (d) water that is miscible with water and capable of forming a low refractive index coating film on an organic substrate. object.
(2) The inorganic coating composition according to the above (1), wherein the organic substrate is made of polycarbonate or acrylic resin.
(3) The organic solvent A is diglyme, N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetoacetate, N-methyl-2-pyrrolidinone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazo The inorganic coating composition according to the above (1) or (2), which is at least one selected from the group consisting of lysinone and dimethyl sulfoxide.
(4) An organic solvent miscible with water having a boiling point of 50 to 120 ° C. in a state of atmospheric pressure of 0.1 MPa without substantially swelling or dissolving the organic base material is methanol, ethanol, n-propanol, The inorganic coating composition according to any one of (1) to (3), which is at least one selected from the group consisting of isopropanol, n-butanol, isobutanol, sec-butanol, and t-butanol.
(5) A low refractive index coating film obtained by applying the inorganic coating composition according to any one of (1) to (4) to an organic substrate.
(6) The low refractive index coating film according to the above (5), wherein the low refractive index coating film has a haze of 1% or less in accordance with JIS K-7150 standards.
(7) The low refractive index coating film according to (5) or (6) above, wherein the low refractive index coating film has a refractive index of 1.1 to 1.4.
(8) (a) 0.1 to 20% by mass of hollow silica particles having an average particle diameter of 5 to 3000 nm; (b) the organic base material can be swollen or dissolved, and the atmospheric pressure is 0.1 MPa. 1 to 20% by mass of water-miscible organic solvent A having a boiling point of 130 ° C. or higher; (c) a boiling point of 50 to 120 without substantially swelling or dissolving the organic base material and at a pressure of 0.1 MPa. A step of preparing an inorganic coating composition containing an organic solvent B miscible with water and / or (d) 60 to 98.9% by mass of water, and the inorganic coating composition on an organic substrate A method for forming a low refractive index coating film, comprising: applying and drying to form a low refractive index coating film.

  According to the present invention, it is possible to obtain an inorganic coating composition and a low refractive index coating film which can form a low refractive index coating film having high transparency and excellent adhesion to an organic substrate. The present invention can also provide a simple and inexpensive method for forming a low refractive index coating film.

  The inorganic coating composition of the present invention contains (a) hollow silica particles, (b) an organic solvent A, and (c) an organic solvent B and / or (d) water.

  In the present invention, (a) the hollow silica particles are required to have an average particle diameter of 5 to 3000 nm. If the average particle size is less than 5 nm, the hollow silica particles become unstable in the inorganic coating composition, and it is not preferable because the particles may be aggregated and become too large, and the average particle size is more than 3000 nm. When a coating film is formed, it is difficult to embed it in an organic base material, and the adhesion may be lowered. The hollow silica particles preferably have an average particle size of 5 to 200 nm, and most preferably an average particle size of 5 to 100 nm, because the resulting coating film is excellent in transparency. In the present specification, the average particle diameter of the hollow silica particles is based on mass.

The hollow silica particles preferably have a refractive index of 1.2 to 1.5. This is preferable because a low refractive index coating film can be obtained. The refractive index of the hollow silica particles is preferably measured, for example, by the method described in JP-A No. 2001-233611. Specifically, with respect to various standard solutions with known refractive indexes, a few drops are dropped onto a glass plate, and hollow silica particles are mixed with this to refract the standard solution when the mixture becomes transparent. And a method in which the refractive index is the refractive index of the hollow silica particles. When the hollow silica particles are contained in the dispersion, it is preferable to evaporate the dispersion medium in the dispersion and then dry and use it as a powder. It is particularly preferable that the hollow silica particles have a refractive index of 1.3 to 1.4.
In the present specification, the hollow silica particles are silica particles having pores inside the particles, and the outer shell portion other than the pores may be porous or nonporous, and conventionally known ones. Can be used as needed. As a method for producing hollow silica particles, for example, porous inorganic particles are used as core particles, and the core particles are coated with silica using alkali silicate around the core particles, and then the core particles are dissolved with an acid. And a method of obtaining hollow particles. The hollow silica particles preferably have a pore diameter of 1/3 to 2/3 of the particle diameter.

  In the present invention, the organic solvent A is contained in the inorganic coating composition. Thereby, the adhesiveness of the coating film obtained can be improved. Although the mechanism by which the adhesion with the organic base material is improved by containing the organic solvent A has not been elucidated, the organic solvent A swells or dissolves the organic base material, so that the surface of the organic base material is microscopic. After creating a defect site and the hollow silica particles infiltrate into the micro defect site, the organic solvent A volatilizes, causing the resin to shrink at the surface of the organic substrate, and the hollow silica particles are embedded in the organic substrate. It is thought that it is fixed in the state.

  The organic solvent A can swell or dissolve the organic base material, and has a boiling point of 130 ° C. or higher under a pressure of 0.1 MPa. When preparing the inorganic coating composition, the organic solvent A needs to be mixed with water in the inorganic coating composition so that the inorganic coating composition does not cause phase separation. For this reason, it is preferable that the organic solvent A has a solubility in water of 2 or more. In the present invention, the solubility in water means the amount (g) of the organic solvent A dissolved in 100 g of water at a temperature of 20 ° C.

In addition, when the organic solvent A has a boiling point of 130 ° C. or higher in a state where the atmospheric pressure is 0.1 MPa, the organic solvent A can remain in the inorganic coating composition as compared with the organic solvent B and water. Can be shown. The organic solvent A particularly preferably has a boiling point of 160 to 300 ° C. under a pressure of 0.1 MPa. In the present invention, “atmospheric pressure” means absolute pressure.
Organic solvent A is diglyme, N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetoacetate, N-methyl-2-pyrrolidinone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone and dimethyl Any one selected from the group consisting of sulfoxides is preferred.

Moreover, the inorganic coating composition of this invention contains the organic solvent B and / or water. Similarly to the organic solvent A, the organic solvent B needs to be mixed with water in the inorganic coating composition so that the inorganic coating composition does not cause phase separation when preparing the inorganic coating composition. For this reason, it is preferable that the organic solvent B has a solubility in water of 2 or more. The organic solvent B and water can be used in an arbitrary ratio, and each may be used alone as described later.
The organic solvent B and water serve to stably disperse the hollow silica particles in the inorganic coating composition. Moreover, the organic solvent B is particularly preferable because it also serves to improve the coating property of the inorganic coating composition. By containing the organic solvent B and water, when the inorganic coating composition is applied and dried, the organic substrate A evaporates faster than the organic solvent A. This is preferable because it remains uniformly and the organic substrate can be uniformly swollen or dissolved. The organic solvent B needs to have a boiling point of 50 to 120 ° C. without substantially swelling or dissolving the organic base material and at a pressure of 0.1 MPa. If the boiling point of the organic solvent B is less than 50 ° C., it is not preferable because it tends to volatilize at room temperature and the handling of the inorganic coating composition becomes difficult. If the boiling point exceeds 120 ° C., the organic solvent B remains without volatilization. This is not preferable because the adhesion between the material and the hollow silica particles may be hindered. It is preferable to use an organic solvent B having a boiling point of about 50 to 80 ° C. lower than the boiling point of the organic solvent A at a pressure of 0.1 MPa.
As the organic solvent B, for example, any one selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol and t-butanol is preferable.

The inorganic coating composition of the present invention can contain a surfactant as necessary. As the surfactant, any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. It is preferable to contain a surfactant because it has excellent wettability with respect to the organic substrate. As the surfactant, —CH ₂ CH ₂ O—, —SO ₂ —, —NR— (R is a hydrogen atom or an organic group), —NH ₂ , —SO ₃ Y, or —COOY (Y is a hydrogen atom, Nonionic surfactants having a structural unit of sodium atom, potassium atom or ammonium ion are preferred. Among these, nonionic surfactants having a structural unit of —CH ₂ CH ₂ O— are particularly preferred because they do not impair the storage stability of the inorganic coating composition.
Nonionic surfactants include, for example, alkyl polyoxyethylene ether, alkyl polyoxyethylene-polypropylene ether, fatty acid polyoxyethylene ester, fatty acid polyoxyethylene sorbitan ester, fatty acid polyoxyethylene sorbitol ester, alkyl polyoxyethylene amine , Alkyl polyoxyethylene amide, polyether-modified silicone surfactants, and the like.

  Moreover, the inorganic coating composition of this invention can contain additives, such as coloring dye, a pigment, a ultraviolet absorber, antioxidant, as needed suitably.

  The content of the organic solvent A needs to be 1 to 20% by mass of the inorganic coating composition. As described above, the organic solvent A is considered to function to embed the hollow silica particles in the substrate by swelling or dissolving the organic substrate. Accordingly, the organic solvent A only needs to be present in an amount that covers the surface of the organic substrate, and depends on the overall concentration, not the solid content, in the inorganic coating composition. If the content of the organic solvent A is less than 1% by mass, the adhesion of the resulting coating film to the organic substrate may be reduced, such being undesirable. Further, when the content of the organic solvent A is more than 20% by mass, the influence of erosion on the organic base material is increased, the smoothness of the surface is impaired, and the transparency of the coating film may be reduced. Since the appearance of the coating film may be deteriorated, it is not preferable. The content of the organic solvent A is particularly preferably 3 to 10% by mass.

  The content of the organic solvent B and water needs to be 60 to 98.9% by mass of the inorganic coating composition. When the content of the organic solvent B and water is less than 60% by mass, the hollow silica particles or the organic solvent A is not preferable because it exceeds the predetermined range, and when it exceeds 98.9% by mass, the amount of the organic solvent A is Since it decreases, there is a possibility that the adhesion of the low refractive index coating film to the organic substrate may decrease, which is not preferable. In addition, the organic solvent B and water should just contain 60-98.9 mass% of the total amount, even when mix | blended in arbitrary ratios, or when used alone. That is, the inorganic coating composition of the present invention may not contain any of the organic solvent B or water. The content of the organic solvent B and water is particularly preferably 80 to 97% by mass.

  The solid content of the inorganic coating composition of the present invention is required to be 0.1 to 20% by mass. When the solid content is less than 0.1% by mass, unevenness is likely to occur when the inorganic coating composition is applied, and this is not preferable. When the solid content is more than 20% by mass, the solid content is more than 20% by mass. This is not preferable because the workability may be deteriorated. The solid content of the inorganic coating composition is particularly preferably 0.1 to 10% by mass.

  In the inorganic coating composition of the present invention, the surfactant is preferably 1 to 500 ppm. If the surfactant is less than 1 ppm, the wettability of the inorganic coating composition is lowered, so that the workability at the time of application may be deteriorated, which is not preferred, and if the surfactant is more than 500 ppm, the resulting coating is obtained. This is not preferable because the quality of the appearance of the film may be deteriorated. The surfactant is particularly preferably 10 to 400 ppm.

  The inorganic coating composition of the present invention preferably contains 1 to 50 parts by mass of silicic acid oligomer in terms of solid content with respect to 100 parts by mass of the hollow silica particles as necessary. Thereby, since the intensity | strength of the coating film obtained can be improved, it is preferable. When the content of the silicic acid oligomer is less than 1 part by mass, it is not preferable because there is almost no effect of improving the strength of the coating film, and when the content exceeds 50 parts by mass, the refractive index of the obtained coating film is It is not preferable because it may increase. The content of the silicic acid oligomer is particularly preferably 1 to 30 parts by mass.

Silicate oligomers include hydrolyzing alkoxides such as ethyl silicate, dialysis after alkali metal silicate decomposition with acid, peptizing alkali metal silicate, alkali metal silica What is obtained by the method etc. which contact an acid salt with an acid type cation exchange resin is preferable. Among them, a silicate oligomer obtained by a method in which an alkali metal silicate is brought into contact with an acid-type cation exchange resin has a high purity, and is particularly preferable since a binder force is strong when a coating film is formed.
As the alkali metal silicate, sodium silicate, potassium silicate, lithium silicate and the like are preferable. As the ion exchange resin, conventionally known ones can be used. For example, it is preferable to use a cation exchange resin having a —SO ₃ H group, a —COOH group or the like. The amount of alkali metal ions to be removed can be adjusted by controlling the amount of cation exchange resin used, the contact time, the contact method, and the like. In the present specification, the silicic acid oligomer refers to a polymer in which about ₂ to 20 SiO ₂ molecules are polymerized in a dispersion medium. In the silicic acid oligomer, 95% or more of the alkali metal is preferably removed. This is preferable because a low refractive index coated product having excellent weather resistance can be obtained.

  The silicic acid oligomer is preferably used as a dispersion by dispersing it in water or an organic solvent such as methanol, ethanol or isopropanol as needed. The content of the silicic acid oligomer in the dispersion is preferably 1 to 10% by mass.

  The inorganic coating composition of the present invention can form a low refractive index coating film by applying it to an organic substrate. The resulting coating film preferably has a refractive index of 1.1 to 1.4. As the organic base material, various materials can be used as appropriate, but it is preferable to use a substrate made of polycarbonate or acrylic resin. Further, the shape of the substrate is not limited to a flat plate, and may have a curvature on the entire surface or a part thereof.

  The coating film obtained by the present invention preferably has a minimum reflectance of 1% or less in a wavelength range of 380 to 780 nm. The reflectance is preferably measured with a spectrophotometer. If the minimum value of the reflectance is more than 1%, the function as a low refractive index coating film may be insufficient, which is not preferable. The thickness of the coating film obtained by the present invention is preferably adjusted so that the reflectance at a wavelength of 550 nm takes a minimum value. The film thickness can be adjusted by the formula λ / 4n = 138 / n (where λ is the wavelength of light and n is the refractive index of the film).

  Moreover, since the low refractive index coating film obtained by applying the inorganic coating composition of the present invention is excellent in transparency, it is particularly suitable for use when the organic substrate is transparent. . About transparency, it is preferable to evaluate by a haze value according to the specification of JIS K7150. The obtained low refractive index coating film preferably has a haze value of 1% or less. When the haze value is more than 1%, the transparency of the coating film is deteriorated and the transmittance is lowered, which is not preferable. The haze value of the obtained coating film is particularly preferably 0.5% or less.

  In the present invention, a step of adjusting an inorganic coating composition containing 0.1 to 20% by mass of hollow silica particles, 1 to 20% by mass of organic solvent A, 60 to 98.9% by mass of organic solvent B and water, And since a low-refractive-index coating film can be formed by passing through the process of forming a low-refractive-index coating film by apply | coating and drying an inorganic coating composition on an organic base material, it is preferable.

  The inorganic coating composition of the present invention can be applied by a known method. Examples include brush coating, roller coating, hand coating, spin coating, dip coating, coating by various printing methods, curtain flow, die coating, gravure coating, reverse coating, roll coating, flow coating, spray coating, dip coating, and the like. . Moreover, you may perform irradiation by a heating, an ultraviolet-ray, an electron beam, etc. as needed in order to raise the mechanical strength of a coating film. The heating may be determined in consideration of the heat resistance of the organic base material, but is preferably 60 to 100 ° C. When applying the inorganic coating composition of the present invention, no pretreatment is required for the organic substrate, but for the purpose of further improving the adhesion of the coating film, plasma treatment, corona treatment, UV treatment, ozone treatment, etc. Discharge treatment, chemical treatment such as water, acid or alkali, or physical treatment using an abrasive.

  In this invention, it is preferable that the thickness of the coating film obtained is 30-3000 nm. If the coating film thickness is less than 30 nm, the function as a low refractive index coating film may be insufficient, which is not preferable. If the coating film thickness exceeds 3000 nm, cracks tend to occur. Or interference fringes may occur or scratches may be noticeable. It is particularly preferable that the coating film has a film thickness of 50 to 1000 nm.

  Examples 1, 2, 5, and 6 are shown below as examples. Examples 3 and 4 are shown as comparative examples. Hereinafter, the mass% is simply indicated by%. In addition, about the refractive index of a hollow silica particle, it carries out with the following method. That is, the dispersion medium is evaporated from the hollow silica fine particle-dispersed sol by an evaporator and then dried at 120 ° C. to obtain a powder. A standard refraction liquid having a known refractive index is dropped on a glass plate of a few drops, and the above powder is mixed therewith. This operation is performed with various standard refracting liquids, and the refractive index of the standard refracting liquid when the mixed liquid becomes transparent is used as the refractive index of the fine particles.

[Example 1]
In a glass reaction vessel having a capacity of 200 ml, a dispersion sol of hollow silica fine particles (a dispersion in which isopropanol having an average particle size of 60 nm, a pore size of 30 nm, a refractive index of 1.3, and a solid content of 20% is used as a solvent, Has a boiling point of 82.3 ° C. at a pressure of 0.1 MPa), 85 g of isopropanol, N, N-dimethylacetamide (boiling point of 166 ° C. at a pressure of 0.1 MPa, solubility in water: soluble at an arbitrary ratio) ) After adding 10 g and mixing, the mixture is stirred at 20 ° C. for 1 hour to obtain an inorganic coating composition having a solid content of 1%. The content of N, N-dimethylacetamide is 10%, and the content of isopropanol is 89%.

[Evaluation test]
Using the resulting inorganic coating composition, it was applied onto a polycarbonate plate (length 100 mm × width 100 mm, thickness 3.5 mm, refractive index: 1.584) wiped with ethanol and spun at 150 rpm for 70 seconds. After coating, it is dried at 100 ° C. for 20 seconds to form a coating film having a thickness of 100 nm.

  Hereinafter, the sample on which the coating film is formed is evaluated by the following method. The evaluation results are shown in Table 1. In Examples 2 to 6, the obtained inorganic coating composition is used for the same operation as in Example 1 for evaluation. The evaluation results are also shown in Table 1.

  As appearance evaluation, the coating unevenness of the coating film obtained is judged visually. The case where there is no coating unevenness and the appearance is good is evaluated as ◯, and the case where there is coating unevenness and impractical is evaluated as ×.

  As the transparency evaluation, evaluation is performed based on the haze value. The haze measurement is evaluated according to JIS K7150. The haze value of the coating film on the substrate is measured with a haze computer (manufactured by Suga Test Instruments Co., Ltd., model name: HGM-3DP). Those having a haze value of 1% or less are accepted, and those exceeding 1% are rejected.

  As reflectance evaluation, the reflectance of the coating film obtained is measured using a spectrophotometer (Hitachi Ltd. make, model: U-4100). A reflectance of less than 1% at a wavelength of 550 nm is regarded as acceptable.

  As refractive index evaluation, the refractive index of the obtained coating film is measured using an ellipsometer (manufactured by ULVAC, model: ESM-1AT). Those having a refractive index in the range of 1.1 to 1.4 are considered acceptable.

  For adhesion evaluation, a cellophane tape is adhered to the coating film in the sample, and the peeling state of the coating film when the cellophane tape is peeled off is observed with the naked eye. The case where the coating film is not peeled off at all is indicated by ○, the case where a part of the coating film is peeled off is left as Δ, and the case where more than half is peeled off is indicated as ×.

  As the abrasion resistance evaluation, the surface of the coating film of the sample is worn back and forth 100 times with a cotton cloth, and the peeling state of the coating film is observed with the naked eye. The case where the coating film is not peeled off at all is indicated by ○, the case where more than half of the part of the coating film is left is Δ, and the case where more than half is peeled is indicated by ×.

[Example 2]
In Example 1, 85 g of isopropanol was added to 85 g of water and a nonionic surfactant having a content of 0.1% (manufactured by Nihon Unicar Co., Ltd., trade name: L-77) in an ethanol solution (note that ethanol has a boiling point at a pressure of 0.1 MPa. Is 78.2 ° C.) The same operation is carried out except that the content is changed to 0.1 g to obtain an inorganic coating composition having a solid content of 1%. The content of N, N-dimethylacetamide is 10%, and the total content of isopropanol, water and ethanol is 89%.

[Example 3]
The same operation as in Example 1 was conducted except that 65 g of isopropanol and 30 g of N, N-dimethylacetamide were used in Example 1, to obtain an inorganic coating composition having a solid content of 1%. In addition, the content of N, N-dimethylacetamide is 30%, and the content of isopropanol is 69%.

[Example 4]
In Example 1, the same operation as in Example 1 was carried out except that N, N-dimethylacetamide was not used and 95 g of isopropanol was used to obtain an inorganic coating composition having a solid content of 1%. The content of isopropanol is 99%.

[Example 5]
Example 1 except that in Example 1, 93 g of isopropanol was used, and 2-pyrrolidinone (boiling point 245 ° C. at a pressure of 0.1 MPa, solubility in water: dissolved in an arbitrary ratio) was 2 g instead of N, N-dimethylacetamide. In the same manner as in No. 1, an inorganic coating composition having a solid content of 1% can be obtained. The 2-pyrrolidinone content is 2% and the isopropanol content is 97%.

[Example 6]
In Example 1, except that the base material is changed to polymethyl methacrylate (refractive index: 1.521), the same operation as in Example 1 is performed to form a coating film.

By using the inorganic coating composition of the present invention, a low refractive index coating film can be applied to various articles having an organic substrate such as a display panel cover material, an optical lens, an optical filter, and a polarizing film. it can.

The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2004-342184 filed on November 26, 2004 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (8)

  (A) 0.1 to 20% by mass of hollow silica particles having an average particle diameter of 5 to 3000 nm; (b) an organic base material can be swollen or dissolved and has a boiling point of 130 ° C. at a pressure of 0.1 MPa. 1-20 mass% of the above organic solvent A miscible with water; (c) without boiling or dissolving the organic base material, and having a boiling point of 50-120 ° C. at a pressure of 0.1 MPa, An inorganic coating composition which contains an organic solvent B miscible with water and / or (d) 60 to 98.9% by mass of water and can form a low refractive index coating film on an organic substrate.   The inorganic coating composition according to claim 1, wherein the organic substrate is made of polycarbonate or acrylic resin.   The organic solvent A is diglyme, N, N-dimethylformamide, N, N-dimethylacetamide, ethyl acetoacetate, N-methyl-2-pyrrolidinone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone and The inorganic coating composition according to claim 1 or 2, which is at least one selected from the group consisting of dimethyl sulfoxide.   An organic solvent miscible with water having a boiling point of 50 to 120 ° C. in a state of atmospheric pressure of 0.1 MPa without substantially swelling or dissolving the organic base material is methanol, ethanol, n-propanol, isopropanol, n The inorganic coating composition according to any one of claims 1 to 3, which is at least one selected from the group consisting of butanol, isobutanol, sec-butanol, and t-butanol.   The low-refractive-index coating film obtained by apply | coating the inorganic coating composition in any one of Claims 1-4 to an organic base material.   The low-refractive-index coating film according to claim 5, wherein the low-refractive-index coating film has a haze according to JIS K-7150 standards of 1% or less.   The low refractive index coating film according to claim 5 or 6, wherein the low refractive index coating film has a refractive index of 1.1 to 1.4.   (A) 0.1 to 20% by mass of hollow silica particles having an average particle diameter of 5 to 3000 nm; (b) an organic base material can be swollen or dissolved and has a boiling point of 130 ° C. at a pressure of 0.1 MPa. 1-20 mass% of the above organic solvent A miscible with water; (c) without boiling or dissolving the organic base material, and having a boiling point of 50-120 ° C. at a pressure of 0.1 MPa, A step of preparing an inorganic coating composition containing an organic solvent B miscible with water and / or (d) 60 to 98.9% by mass of water; and applying the inorganic coating composition on an organic substrate; A method for forming a low refractive index coating film, which comprises a step of forming a low refractive index coating film by drying.