JP2013252981A - Method for producing conductive tin oxide sol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing conductive tin oxide aqueous sol having high transparency.SOLUTION: In a method for producing conductive tin oxide aqueous sol in which tertiary alkyl amine is mixed with tin oxide aqueous sol, and the mixture is subjected to hydrothermal treatment at 100-350°C, the tertiary alkyl amine to be mixed preferably has the molar ratio of 0.05-0.10 with respect to tin atoms in the tin oxide aqueous sol. The tin oxide aqueous sol is preferably tin oxide aqueous sol produced by reacting hydrogen peroxide with metal tin in an aqueous solution of an organic acid, while keeping the molar ratio of the hydrogen peroxide/metal tin in the range of 2-3.

Description

  The present invention relates to a method for producing a conductive tin oxide sol having high transparency and excellent conductive performance. The present invention also relates to a conductive tin oxide sol having excellent conductive performance.

  As tin oxide having conductivity, antimony-containing tin oxide, that is, antimony-doped conductive tin oxide (ATO) is known. ATO is excellent in terms of conductivity, but recently, toxicity of antimony has been a problem, and tin oxide containing no antimony is desired.

  In recent years, there has been a demand for a highly transparent antistatic coating that does not impair the transparency of the substrate in order to prevent the static plastic from being charged. Therefore, a highly transparent conductive material is desired.

  In order to obtain a highly transparent material, a wet manufacturing method is preferred. If a baking step is included in the manufacturing process, coarse particles are likely to be generated due to particle growth due to sintering at the time of baking, which causes a decrease in the transparency of the material.

  So far, a method for producing a conductive tin oxide sol by a wet method has been proposed. A method for producing a colorless and transparent tin oxide sol containing alkylamine as a dispersion stabilizer and using water or a mixed solution of water and a hydrophilic organic solvent as a medium is known (see Patent Document 1). The number of moles of alkylamine for peptizing the particles is as large as 0.15 to 0.50 times the number of moles of tin oxide. When the amount of alkylamine added is large, it acts as a resistance component, so there is a concern about deterioration of conductivity. Further, it is difficult to say that the film obtained using this tin oxide sol has a high haze and a high transparency.

  A method for producing a conductive tin oxide sol by hydrothermal treatment (see Patent Document 2) is known, but in this case, phosphorus is required as a dopant, and a coating made using the obtained conductive tin oxide sol is used. High surface resistance.

  A method for producing a tin oxide sol in which a divalent tin hydroxide is oxidized in an aqueous solution and a portion of the divalent tin is oxidized to a divalent or higher tetravalent tin (see Patent Document 3) is known. However, in this case, since a pulverization step with beads is included, impurities are mixed, and the volume resistance of the tin oxide sol powder is high.

  On the other hand, from the viewpoint of hydrothermally treating a tin oxide sol, a method for producing a modified stannic oxide sol (see Patent Document 4) is known, and an amine is added as an alkaline substance added to the hydrothermally treated tin oxide. Is not specified. In addition, since the obtained tin oxide is coated with antimony pentoxide or the like, conductivity is not exhibited.

Japanese Patent No. 4097925 JP 2008-50253 A JP 2011-26172 A JP 2006-176392 A

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method for producing a conductive tin oxide aqueous sol having high transparency and excellent conductive performance. An object of the present invention is to provide a conductive tin oxide sol having excellent conductive performance.

As a first aspect of the present invention, a method for producing a conductive tin oxide aqueous sol comprising mixing a tertiary alkylamine with a tin oxide aqueous sol and hydrothermally treating at 100 to 350 ° C.,
As a second aspect, the tertiary alkylamine is trimethylamine, triethylamine, tripropylamine, tributylamine, trisec-butylamine, tritert-butylamine, tripentylamine, triisopropylamine, triisobutylamine, triisopentylamine, N, N-dimethylethylamine, N, N-dimethylpropylamine, N, N-dimethylbutylamine, N, N-dimethylpentan-1-amine, N, N-dimethylhexylamine, N, N-diethylmethylamine, N , N-diethylpropylamine, N, N-diethylbutylamine, N, N-diethylhexylamine, N, N-diisopropylmethylamine, N, N-diisopropylethylamine, N, N-diisopropylisobutylamine, butyldi The conductive oxidation according to the first aspect, characterized in that it is at least one selected from the group consisting of sopropylamine, methyldibutylamine and dibutylethylamine, N, N-dibutylhexylamine, N, N-dihexylmethylamine Production method of tin sol,
As a third aspect, the tertiary alkylamine to be mixed is 0.05 to 0.10 as a molar ratio with respect to tin atoms in the tin oxide aqueous sol, as described in the first aspect or the second aspect. Method for producing conductive tin oxide aqueous sol,
As a fourth aspect, the tin oxide aqueous sol is produced by reacting hydrogen peroxide and metal tin in an aqueous solution of an organic acid while maintaining a molar ratio of hydrogen peroxide / metal tin in the range of 2-3. A method for producing a conductive tin oxide aqueous sol according to any one of the first to third aspects,
As a fifth aspect, during the reaction of hydrogen peroxide and tin metal in the aqueous solution of organic acid, the tin oxide concentration in the aqueous solution of organic acid is maintained at 40% by mass or less. A method for producing a conductive tin oxide aqueous sol according to the fourth aspect,
As a sixth aspect, the organic acid contains at least oxalic acid, and the method for producing a conductive tin oxide aqueous sol according to the fourth aspect or the fifth aspect,
As a seventh aspect, a conductive tin oxide aqueous sol having a volume resistance value of 100 to 10,000 Ω · cm of a green compact produced by applying a load of 100 kgf / cm ² after drying in air at 80 ° C.,
As an eighth aspect, there is provided a conductive tin oxide organic solvent sol having a volume resistance value of 100 to 10,000 Ω · cm of a green compact produced by drying at 80 ° C. in air and then applying a load of 100 kgf / cm ^2. .

  According to the production method of the present invention, a conductive tin oxide aqueous sol having high transparency can be obtained.

  The conductive tin oxide aqueous sol obtained by the present invention exhibits electron conductivity by mixing a tertiary alkylamine with the tin oxide aqueous sol and hydrothermally treating at 100 to 350 ° C.

The volume resistance value of the green compact of the conductive tin oxide aqueous sol or the conductive tin oxide organic solvent sol obtained by the present invention is 100 to 10,000 Ω · cm. The volume resistance value of the green compact is measured as follows. Conductive tin oxide aqueous sol or conductive tin oxide organic solvent sol 10.0 g was dried in air at 80 ° C. for 10 hours and then pulverized in an agate mortar, and then passed through nylon mesh sieves 120M and 250M in order, A classifying powder above 250M is prepared. About 50 mg of this classified powder is put into a cylindrical molding machine made of glass with a diameter of 5 mm, measurement terminals having the same area are brought into close contact with both sides of the classified powder, a load of 100 kgf / cm ² is applied for 30 seconds, and a green compact (diameter 5 mm) , Thickness resistance of 0.5 mm) is measured by the two-terminal method. The measurement is performed in a constant temperature and humidity chamber with an air temperature of 25 ° C. and a humidity of 50%.

  The tin oxide particles of the conductive tin oxide aqueous sol obtained by the present invention are very fine, and the primary particle diameter observed with a transmission electron microscope is 2 to 25 nm. The conductive tin oxide aqueous sol obtained by the present invention is highly transparent because it is produced by a wet method, and the total light transmittance measured using a haze meter NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) When the tin oxide concentration is 3.0 mass%, the optical path length is 10 to 70 to 90%.

  In addition, since the state of a well-dispersed aqueous sol is maintained after hydrothermal treatment, pulverization equipment such as dry pulverization, wet pulverization using media, ultrasonic homogenizer dispersion, pressure homogenizer, etc. are used for dispersion. There is no need to use it, and impurities from these devices do not occur.

The coating composition obtained by mixing the conductive tin oxide aqueous sol obtained by the production method of the present invention and a binder can form a highly transparent conductive film by applying it to a substrate. The conductive coating obtained using the conductive tin oxide aqueous sol obtained by the production method of the present invention has a total light transmittance of 80 to 100% at a thickness of 3.0 μm. The surface resistance value of the coating is 10 ⁵ to 10 ¹⁰ Ω / □, and has excellent antistatic performance.

  The tin oxide aqueous sol used as a raw material in the present invention is a tin oxide colloidal particle having a primary particle size of about 2 to 50 nm by a known method such as an ion exchange method, a peptization method, a hydrolysis method, or a reaction method. It can be produced in the form of a sol.

  Examples of the ion exchange method include a method of treating an aqueous solution of a stannate such as sodium stannate with a hydrogen cation exchange resin, or an aqueous solution of a stannic salt such as stannic chloride and stannic nitrate. The method of processing with a type | mold anion exchange resin is mentioned.

  As an example of the peptization method, stannic hydroxide gel obtained by neutralizing an aqueous solution of stannic salt with a base or neutralizing an aqueous solution of stannic acid with hydrochloric acid is washed with water, and then acidified. Or the method of peptizing with a base is mentioned.

  Examples of the hydrolysis method include a method of hydrolyzing tin alkoxide or a method of removing unnecessary acid after hydrolyzing a basic stannic chloride salt.

  Examples of the reaction method include a method of reacting metal tin powder with an acid.

  The tin oxide aqueous sol used as a raw material in the present invention is produced by reacting hydrogen peroxide and metal tin in an aqueous solution of an organic acid while keeping the molar ratio of hydrogen peroxide / metal tin in the range of 2-3. The tin oxide aqueous sol is preferable.

  Examples of the organic acid used include oxalic acid, citric acid, tartaric acid, lactic acid, malic acid, succinic acid, glycolic acid, acetic acid, formic acid and the like. In particular, in an aqueous oxalic acid solution, a hydrogen peroxide solution and metallic tin while maintaining the molar ratio of hydrogen peroxide / tin metal in the range of 2 to 3 so that the tin oxide concentration in the aqueous solution is 15 to 40% by mass. And an acidic tin oxide aqueous sol prepared by a method in which tin oxide colloidal particles are produced by adding and reacting with each other is more preferable.

  The aqueous organic acid solution preferably contains at least oxalic acid. In the organic acid aqueous solution, 80 to 100% by mass of the total organic acid is oxalic acid, and the balance can contain an organic acid other than oxalic acid such as formic acid and acetic acid.

  The organic acid aqueous solution can be used in an organic acid concentration range of 1 to 30% by mass, preferably 4 to 10% by mass. The tin oxide aqueous sol obtained by this method is acidic and has a pH of 3 or less. The tin oxide colloidal particles obtained by this method have a primary particle diameter of about 20 nm or less as observed with a transmission electron microscope.

  The method for producing a conductive tin oxide aqueous sol of the present invention is obtained by mixing a tertiary alkylamine with the tin oxide aqueous sol to obtain an alkaline tin oxide aqueous sol, and then hydrothermally treating at 100 to 350 ° C.

The tertiary alkylamine used in the present invention is represented by the general formula (I).
NR ¹ R ² R ³ (I)
(In the formula (I), R ¹ , R ² and R ³ each represent an alkyl group having 1 to 6 carbon atoms.)
Specific examples of the tertiary alkylamine include trimethylamine, triethylamine, tripropylamine, tributylamine, trisec-butylamine, tritert-butylamine, tripentylamine, triisopropylamine, triisobutylamine, triisopentylamine, N , N-dimethylethylamine, N, N-dimethylpropylamine, N, N-dimethylbutylamine, N, N-dimethylpentan-1-amine, N, N-dimethylhexylamine, N, N-diethylmethylamine, N, N-diethylpropylamine, N, N-diethylbutylamine, N, N-diethylhexylamine, N, N-diisopropylmethylamine, N, N-diisopropylethylamine, N, N-diisopropylisobutylamine, butyldiyl Propylamine, methyl dibutyl amine and dibutyl ethylamine, N, N-jib hexyl amine, N, N-dihexyl-methyl amine.

  When the amine used is a primary alkyl amine or a secondary alkyl amine, even if the same hydrothermal treatment is performed, the obtained tin oxide aqueous sol cannot obtain sufficient conductivity.

  The amount of the tertiary alkylamine mixed in the tin oxide aqueous sol is 0.05 to 0.10 as a molar ratio with respect to tin atoms in the tin oxide aqueous sol. When the molar ratio is less than 0.05, the obtained tin oxide aqueous sol cannot obtain sufficient conductivity. Moreover, even if this molar ratio exceeds 0.10, the electroconductivity of the tin oxide aqueous sol obtained does not increase, and conversely, the compatibility between the tin oxide sol obtained and the binder resin is deteriorated.

  The hydrothermal treatment temperature in the present invention is 100 ° C. or higher, preferably 220 ° C. or higher, more preferably 240 or higher. Further, the hydrothermal treatment temperature in the present invention is 350 ° C. or lower, preferably 320 ° C. or lower. When the heat treatment is performed at a temperature lower than 100 ° C., the obtained tin oxide aqueous sol cannot obtain sufficient conductivity.

  The conductive tin oxide aqueous sol obtained by the present invention can be stabilized as a sol by adding an acid and / or a base as necessary. Examples of acids to be added include inorganic acids such as hydrochloric acid and nitric acid, oxalic acid, lactic acid, tartaric acid, malic acid, citric acid, glycolic acid, hydroacrylic acid, α-oxybutyric acid, glyceric acid, and tartronic acid. Can be used. Examples of bases to be added include ammonia, alkali metal hydroxides, alkylamines such as ethylamine, diethylamine, n-propylamine, isopropylamine, diisopropylamine, dipropylamine, n-butylamine, isobutylamine, diisobutylamine, triethylamine and benzylamine. , Alkanolamines such as monoethanolamine and triethanolamine, quaternary ammonium hydroxides such as guanidine hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide, carbonates such as ammonium carbonate and guanidine carbonate Organic bases can be used.

  The conductive tin oxide aqueous sol obtained by the present invention can be surface-modified with an acid group-containing surfactant, a hydrophobic amine compound or an organosilicon compound and then dispersed in an organic solvent by solvent substitution.

  In order to enhance the dispersibility in an organic solvent, an anionic, cationic or nonionic surfactant or an organosilicon compound can be used.

  As the surfactant having an acid group, a surfactant having at least one functional group selected from the group consisting of a carboxylic acid group, a sulfonic acid group and a phosphoric acid group is used.

  Examples of the surfactant having a carboxylic acid group include potassium laurate, potassium myristate, polyoxyethylene lauryl ether acetic acid, polyoxyethylene lauryl ether sodium acetate, polyoxyethyleneoxypropylene lauryl ether acetic acid, and polyoxypropylene lauryl ether. Examples include sodium acetate, polyoxyethylene tridecyl ether acetic acid, coconut oil fatty acid sarcosine triethanolamine, and lauroyl sarcosine ammonium.

  Examples of the surfactant having a sulfonic acid group include ammonium lauryl sulfate, polyoxyethylene lauryl ether ammonium sulfate, polyoxyethyleneoxypropylene lauryl ether ammonium sulfate, polyoxypropylene lauryl ether ammonium sulfate, polyoxyethylene nonylphenyl ether ammonium sulfate, and polyoxyethylene. Tristyryl phenyl ether ammonium sulfate, polyoxyethyleneoxypropylene tristyryl phenyl ether ammonium sulfate, polyoxypropylene tristyryl phenyl ether ammonium sulfate, polyoxyethylene coconut oil fatty acid monoethanolamide ammonium sulfate, polyoxyethyleneoxypropylene coconut oil fatty acid monoethanolamide ammonium sulfate Polyoxypropylene coconut oil fatty acid monoethanolamide ammonium sulfate, dioxyl sulfosuccinate polyoxyethylene sulfosuccinate lauryl diammonium, dioctyl sulfosuccinate polyoxyethylene oxypropylene sulfosuccinate lauryl diammonium, dioctyl sulfosuccinate polyoxypropylene sulfosuccinate lauryl diammonium Disodium oxyethylene lauryl sulfosuccinate, disodium polyoxyethylene tridecyl sulfosuccinate, disodium polyoxyethylene myristyl sulfosuccinate, diammonium lauryl polyoxyethylene oxypropylene sulfosuccinate, diammonium lauryl polyoxypropylene sulfosuccinate, coconut oil fatty acid Ammonium methyl taurate Ammonium monoisopropyl naphthalenesulfonic acid, ammonium diisopropylnaphthalene sulfonic acid, n- butyl naphthalene sulfonate, ammonium dodecyl diphenyl ether disulfonic acid, ammonium lignin sulfonate, and the like.

  As the surfactant having a phosphoric acid group, for example, those having a polyoxyethylene group or a phenyl group are preferable. For example, polyoxyethylene alkylphenyl ether phosphate, polyoxyethylene alkyl ether phosphate, such as dipolyoxyethylene lauryl ether ammonium phosphate, dipolyoxyethylene oxypropylene lauryl ether ammonium phosphate, dipolyoxypropylene lauryl ether phosphate Ammonium, dipolyoxyethylene oleyl ether phosphate, dipolyoxyethyleneoxypropylene lauryl ether phosphate, dipolyoxypropylene oleyl ether phosphate, ammonium lauryl phosphate, octyl-ammonium terphosphate, ammonium cetyl ether phosphate, polyoxy Ethylene lauryl ether phosphate, polyoxyethyleneoxypropylene lauryl ether phosphate, polyoxypropylene lauric Examples include ruether phosphoric acid, polyoxyethylene tristyryl phenyl ether triethanolamine, polyoxyethyleneoxypropylene tristyryl phenyl ether triethanolamine, and polyoxypropylene tristyryl phenyl ether triethanolamine.

  As the surfactant having an acid group, a surfactant having a phosphate group is particularly preferably used. Examples of the surfactant having a phosphate group include Phosphanol (registered trademark) PE-510, PE-610, LB-400, EC-6103, RE-410, RS-410, RS-610, RS-710, and the like. (Both manufactured by Toho Chemical Industry Co., Ltd.), Disperbyk (registered trademark) -102, Disperbyk-110, Disperbyk-111, Disperbyk-116, Disperbyk-140, Disperbyk-161, Disperbyk-163, Disperbyk-164D, Commercially available products such as 180 etc. (all manufactured by Big Chemie Japan) can be used, but are not limited thereto.

  Examples of the hydrophobic amine compound include aliphatic amines, aromatic amines or aralkyl amines having a boiling point or decomposition temperature of 200 ° C. or higher, or amine surfactants having an average addition mole number of ethylene oxide of 1 to 60. Can be mentioned. Examples of the aliphatic amine or aromatic amine having a boiling point or decomposition temperature of 200 ° C. or higher include aliphatic amines having 9 or more carbon atoms such as dodecylamine, tetradecylamine, and octadecylamine, diphenylamine, and naphthylamine. Examples of the aralkylamine having a boiling point or decomposition temperature of 200 ° C. or higher include dibenzylamine, tribenzylamine, and phenylethylamine.

  Examples of the amine surfactant having an average addition mole number of ethylene oxide of 1 to 60 include oxyethylene dodecylamine, polyoxyethylene dodecylamine, polyoxyethylene octadecylamine, polyoxyethylene beef tallow alkylamine, polyoxyethylene tallow alkyl Examples include amines and alkylamine ethylene oxide derivatives such as polyoxyethylene beef tallow propylene diamine.

As said organosilicon compound, the silicon compound containing the following A component and / or B component is mentioned, for example.
Component A: General formula (II)
(R ⁴ ) _a (R ⁵ ) _b Si (OR ⁶ ) _{4- (a + b)} (II)
(In the formula (II), R ⁴ and R ⁵ are each an alkyl group, alkenyl group, aryl group, acyl group, halogen group, glycidoxy group, epoxy group, amino group, phenyl group, mercapto group having 1 to 9 carbon atoms. An organic group selected from the group consisting of a methacryloxy group and a cyano group, R ⁶ represents an organic group selected from the group consisting of an alkyl group having 1 to 8 carbon atoms, an alkoxy group, an acyl group and a phenyl group; a and b are integers of 0 or 1.) or a hydrolyzate thereof.
Component B: General formula (III)
_{{(OX) 3-a Si} (R 7)} 2 Y (III)
(In the formula (III), R ⁷ represents an organic group having 1 to 5 carbon atoms, X represents an alkyl group having 1 to 4 carbon atoms or an acyl group having 1 to 4 carbon atoms, and Y represents the number of carbon atoms. An organic silicon compound represented by the formula: a represents an organic group of 2 to 20, and a is an integer of 0 or 1.

  The component A is represented by the aforementioned general formula (II), and specific examples of the organosilicon compound are as follows: methyl silicate, ethyl silicate, n-propyl silicate, iso-propyl silicate, n- Butyl silicate, tetraacetoxysilane, methyltrimethoxysilane, methyltripropoxysilane, methyltriacetoxysilane, methyltributoxysilane, methyltripropoxysilane, methyltriamyloxysilane, methyltriphenoxysilane, methyltribenzyloxysilane, Methyltriphenethyloxysilane, glycidoxymethyltrimethoxysilane, glycidoxymethyltrimethoxysilane, α-glycidoxyethyltrimethoxysilane, α-glycidoxytriethyoxysilane, β-glycidoxytrimethoxy Silane, β-glycidoxyethyltriethoxysilane, α-glycidoxypropyltrimethoxysilane, α-glycidoxypropyltriethoxysilane, β-glycidoxypropyltrimethoxysilane, β-glycidoxypropyltriethoxy Silane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltripropoxysilane, γ-glycidoxypropyltributoxysilane, γ-glycidoxypropyltriphenoxy Silane, α-glycidoxybutyltrimethoxysilane, α-glycidoxybutyltriethoxysilane, β-glycidoxybutyltriethoxysilane, γ-glycidoxybutyltrimethoxysilane, γ-glycidoxybutyltriethoxy Silane, δ-glycidoxy Butyltrimethoxysilane, δ-glycidoxybutyltriethoxysilane, (3,4-epoxycyclohexyl) methyltrimethoxysilane, (3,4-epoxycyclohexyl) methyltriethoxysilane, β- (3,4-epoxycyclohexyl) ) Ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltripropoxysilane, β- (3,4-epoxycyclohexyl) ethyltributoxysilane , Β- (3,4-epoxycyclohexyl) ethyltriphenoxysilane, γ- (3,4-epoxycyclohexyl) propyltrimethoxysilane, γ- (3,4-epoxycyclohexyl) propyltriethoxysilane, δ- (3 , 4-epoxycyclo Xyl) butyltrimethoxysilane, δ- (3,4-epoxycyclohexyl) butyltriethoxysilane, glycidoxymethylmethyldimethoxysilane, glycidoxymethylmethyldiethoxysilane, α-glycidoxyethylmethyldimethoxysilane, α -Glycidoxyethylmethyldiethoxysilane, β-glycidoxyethylmethyldimethoxysilane, β-glycidoxyethylethyldimethoxysilane, α-glycidoxypropylmethyldimethoxysilane, α-glycidoxypropylmethyldiethoxysilane , Β-glycidoxypropylmethyldimethoxysilane, β-glycidoxypropylethyldimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxyp Pyrmethyldipropoxysilane, γ-glycidoxypropylmethyldibutoxysilane, γ-glycidoxypropylmethyldiphenoxysilane, γ-glycidoxypropylethyldiethoxysilane, γ-glycidoxypropylethyldiethoxysilane, γ-glycidoxypropyl vinylmethoxysilane, γ-glycidoxypropyl vinylethoxysilane, γ-glycidoxypropylvinylphenylmethoxysilane, γ-glycidoxypropylvinylphenylethoxysilane, ethyltrimethoxysilane, ethyltriethoxy Silane, vinyltrimethoxysilane, vinyltriacetoxysilane, vinyltrimethoxyethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, γ-chloropropyltri Methoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropyltriacetoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ -Mercaptopropyltriethoxysilane, β-cyanoethyltriethoxysilane, chloromethyltrimethoxysilane, chloromethyltriethoxysilane, N- (β-aminoethyl) γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyltrimethoxysilane, N- (β-aminoethyl) γ-aminopropyltriethoxysilane, N- (β-aminoethyl) γ-aminopropylmethyldiethoxysilane, Methyldimethoxysilane, phenylmethyldimethoxysilane, dimethyldiethoxysilane, phenylmethyldiethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropylmethyldiethoxysilane, dimethyldiacetoxysilane, γ-methacryloxypropylmethyldimethoxysilane Γ-methacryloxypropylmethyldiethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptomethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, and the like.

  The component B is represented by the above general formula (III), and specific examples of the organosilicon compound are as follows: methylenebismethyldimethoxysilane, ethylenebisethyldimethoxysilane, propylenebisethyldiethoxysilane Butylene bismethyldiethoxysilane and the like.

  The A component and / or the B component organosilicon compound can be used alone or in combination with the A component or the B component. It is also possible to use two or more types of component A or two or more types of component B.

  Hydrolysis of the organosilicon compound of component A and / or component B is carried out by adding an acidic aqueous solution such as an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution or an aqueous acetic acid solution to the organosilicon compound of component A and / or B and stirring. Done.

  The conductive tin oxide aqueous sol obtained by the present invention can be made into an organic solvent sol by substituting water as a dispersion medium with an organic solvent. As a method for substitution with an organic solvent, known methods can be used, and examples thereof include a distillation substitution method and an ultrafiltration method.

  Examples of the organic solvent used as the dispersion medium include alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, and butyl alcohol, ethers such as methyl cellosolve and ethyl cellosolve, and ethers such as propylene glycol monomethyl ether. Alcohols, ketones such as methyl ethyl ketone, methyl isobutyl ketone, isobutyl acetate, isopropyl acetate, isopentyl acetate, esters such as ethyl acetate, butyl acetate, propyl acetate, pentyl acetate, ether esters such as propylene glycol monomethyl ether acetate, xylene , Hydrocarbons such as toluene and benzene.

(Production Example 1)
37.5 kg of oxalic acid ((COOH) ₂ .2H ₂ O) was dissolved in 383 kg of pure water, taken in a 500 L vessel, heated to 70 ° C. with stirring, 150 kg of 35% by mass hydrogen peroxide and metal tin ( 75 kg of Yamaishi Metal Co., Ltd. trade name: AT-SNNO200N) was added. Hydrogen peroxide solution and metallic tin were added alternately. First, 10 kg of 35 mass% hydrogen peroxide water was added, and then 5 kg of metallic tin. This operation was repeated after the reaction was completed (5-10 minutes during this time). After the total amount of hydrogen peroxide solution and metal tin was added, 10 kg of 35 mass% hydrogen peroxide solution was further added. The time required for the addition of the hydrogen peroxide solution and metal tin was 2.5 hours. After the addition was completed, the reaction was completed by further heating at 95 ° C. for 1 hour. The molar ratio of the hydrogen peroxide solution to metallic tin was 2.61 as H ₂ O ₂ / Sn. The obtained tin oxide aqueous sol had very good transparency. The yield of the tin oxide aqueous sol was 630 kg, the specific gravity was 1.154, the pH was 1.51, and the SnO ₂ content was 14.7% by mass. When the obtained sol was observed with a transmission electron microscope, it was a spherical, well-dispersed colloidal particle having a primary particle diameter of 10 to 15 nm. This sol showed a slight increase in viscosity when left standing, but was not stable when left at room temperature for 6 months. To the obtained sol (629 kg), 35 mass% hydrogen peroxide water (231 kg) and pure water (52 kg) were added, SnO ₂ was 10 mass%, and the molar ratio of H ₂ O ₂ / (COOH) ₂ to oxalic acid was 8 After adjusting to 0.0, the mixture was heated to 95 ° C. and aged for 5 hours. By this operation, the contained oxalic acid was decomposed into carbon dioxide gas and water by reaction with hydrogen peroxide. After the tin oxide slurry obtained by this operation is cooled to about 40 ° C., it is passed through a catalyst tower packed with about 15 L of a platinum-based catalyst (trade name: N-220, manufactured by Zude Chemie Catalysts Co., Ltd.). Hydrogen oxide was decomposed. The flow rate is about 30 L / min. And circulated for 5 hours. Further, the solution was passed through a column packed with an anion exchange resin (Amberlite (registered trademark) IRA-410: manufactured by Organo Corporation) to obtain 1545 kg of an acidic tin oxide aqueous sol. The obtained acidic tin oxide aqueous sol had a SnO ₂ concentration of 11.4% by mass, a pH of 3.97, and an electrical conductivity of 55 μS / cm.
Example 1
0.33 g of triethylamine (molar ratio of triethylamine to tin atom of 0.05) was added to 200 g of the sol prepared with pure water so that the SnO ₂ concentration was 5.0% by mass from the acidic tin oxide aqueous sol obtained in Production Example 1. The mixture was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 10.44 and an electric conductivity of 150 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 7.68, an electric conductivity of 715 μS / cm, and SnO _{2 of} 5.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle size (measured with a Zetasizer Nano ZS manufactured by Malvern) was 21 nm. Further, the SnO ₂ concentration of 3.0 mass%, (measured using a haze meter NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.)) total light transmittance due to optical path length of 10mm was 90.0%. Further, 10.0 g of this sol was dried in air at 80 ° C. for 10 hours, and then pulverized in an agate mortar, and then passed through nylon mesh sieves 120M and 250M in this order to prepare classified powder on 120M and 250M. About 50 mg of this classified powder is put into a cylindrical molding machine made of glass with a diameter of 5 mm, measurement terminals having the same area are brought into close contact with both sides of the classified powder, a load of 100 kgf / cm ² is applied for 30 seconds, and a green compact (diameter 5 mm) , Thickness 0.5 mm) was measured by the two-terminal method. The measurement was performed in a constant temperature and humidity chamber with an air temperature of 25 ° C. and a humidity of 50%. The volume resistance value of the green compact was 2900 Ω · cm. Further, X-ray diffraction analysis showed a peak of cassiterite.
(Example 2)
0.48 g of tripropylamine (molar ratio of tripropylamine to tin atom 0) was added to 200 g of the sol prepared by preparing the acidic tin oxide aqueous sol obtained in Production Example 1 with pure water so that the SnO ₂ concentration was 5.0% by mass. .05) was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 10.71 and an electric conductivity of 260 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 7.67, an electric conductivity of 675 μS / cm, and SnO _{2 of} 5.0% by mass. The primary scattered particle diameter observed by a transmission electron microscope is 2 to 25 nm, and dynamic light scattering. The average particle size according to the method was 27 nm. In addition, when the SnO ₂ concentration was 3.0% by mass, the total light transmittance at an optical path length of 10 mm was 89.0%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of the sol dried at 80 ° C. in air was 3600 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Example 3)
The acidic tin oxide aqueous sol obtained in Production Example 1 was adjusted to 0.61 g of tributylamine (molar ratio of tributylamine to tin atom of 0.05) with 200 g of sol prepared with pure water so that the SnO ₂ concentration was 5.0% by mass. ) Was gradually added with stirring, and stirring was continued for 30 minutes after the addition was completed to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 9.26 and an electric conductivity of 131 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 7.28, an electric conductivity of 498 μS / cm, and SnO ₂ of 5.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, dynamic light scattering. The average particle size according to the method was 29 nm. Further, the SnO ₂ concentration of 3.0 mass%, a total light transmittance due to optical path length of 10mm was 87.6%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of 80 ° C. dried product in the air of this sol was 3100 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
Example 4
The acid tin oxide aqueous sol obtained in Production Example 1 was adjusted with pure water so that the SnO ₂ concentration was 8.5% by mass to 10.0 kg of triethylamine 28.5 g (molar ratio of triethylamine to tin atom 0.05 ) Was gradually added with stirring, and stirring was continued for 30 minutes after the addition was completed to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 11.02 and an electric conductivity of 648 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated for 7 minutes at a processing temperature of 310 ° C. and a processing pressure of 20 MPa (megapascal) to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 10.35, an electrical conductivity of 454 μS / cm, and SnO _{2 of} 3.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle diameter was 13 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.2%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of 80 ° C. dried product in the air of this sol was 5000 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Example 5)
The acid tin oxide aqueous sol obtained in Production Example 1 was adjusted with pure water so that the SnO ₂ concentration was 8.5% by mass with 10.0 kg of sol, and 42.8 g of triethylamine (molar ratio of triethylamine to tin atoms was 0.075). ) Was gradually added with stirring, and stirring was continued for 30 minutes after the addition was completed to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 11.29 and an electric conductivity of 790 μS / cm. The tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at a treatment temperature of 310 ° C. and a treatment pressure of 20 MPa for 7 minutes to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 10.91, an electric conductivity of 681 μS / cm, and SnO _{2 of} 3.3% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle diameter was 14 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.3%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of 80 ° C. dried product in the air of this sol was 1500 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Example 6)
The acid tin oxide aqueous sol obtained in Production Example 1 was adjusted with pure water so that the SnO ₂ concentration was 8.5% by mass, and 10.0 kg of triethylamine (molar ratio of triethylamine to tin atoms was 0.10). ) Was gradually added with stirring, and stirring was continued for 30 minutes after the addition was completed to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 11.46 and an electric conductivity of 1009 μS / cm. The tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at a treatment temperature of 310 ° C. and a treatment pressure of 20 MPa for 7 minutes to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 11.10, an electric conductivity of 774 μS / cm, SnO _{2 of} 3.3% by mass, a primary particle diameter observed by a transmission electron microscope of 2 to 25 nm, and an average by a dynamic light scattering method. When the particle diameter was 13 nm and the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.3%. Further, the volume resistance value (measured in the same manner as in Example 1) of the green compact of the sol dried at 80 ° C. in air was 1700 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Example 7)
The acid tin oxide aqueous sol obtained in Production Example 1 was adjusted with pure water so that the SnO ₂ concentration was 8.5% by mass, and 10.0 kg of diisopropylethylamine (molar ratio of diisopropylethylamine to tin atom was 0). 10) was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 11.52 and an electric conductivity of 1140 μS / cm. The tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at a treatment temperature of 310 ° C. and a treatment pressure of 20 MPa for 7 minutes to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 10.63, an electric conductivity of 672 μS / cm, SnO _{2 of} 3.7% by mass, a primary particle diameter observed by a transmission electron microscope of 2 to 25 nm, and an average by a dynamic light scattering method. When the particle diameter was 30 nm and the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 87.5%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of the sol dried at 80 ° C. in air was 6800 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Example 8)
225 g of conductive tin oxide methanol sol was obtained by substituting water in 1891.9 g of SnO ₂ 3.7 mass% conductive tin oxide aqueous sol obtained in Example 7 with methanol using a rotary evaporator under reduced pressure. Obtained. This conductive tin oxide methanol sol has a pH of 8.28 (measured at a 1: 1 mass ratio of methanol sol and water), conductivity 42 μS / cm, SnO ₂ 31.2 mass%, dynamic light The average particle diameter by a scattering method was 34 nm, the SnO ₂ concentration was 3.0% by mass, and the total light transmittance at an optical path length of 10 mm was 87.3%. The volume resistance value (measured in the same manner as in Example 1) of the green compact of the sol dried at 80 ° C. in air was 6800 Ω · cm.
Example 9
A thermosetting resin WB-650-25 (manufactured by Sensho Kasei Co., Ltd.) was added to 6.6 g of sol obtained by concentrating the conductive tin oxide aqueous sol obtained in Example 5 to 30.5% by mass of SnO ₂ using an evaporator. ) 8.0 g and water 1.4 g were mixed to obtain a thermosetting resin composition containing conductive tin oxide. The dispersion state of the obtained resin composition was good. On the upper surface of the PET film (125 μm), No. After applying using a 12 (27.4 μm) wire bar, it was dried on a hot plate to obtain a PET film having a conductive coating. The film thickness of this conductive film was 3.0 μm. The total light transmittance (Tt) of the PET film with a conductive film measured using a haze meter NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) was 98.3%, and the haze value was 0.0. Moreover, the surface resistance value of this film measured using a surface resistivity measuring apparatus Hiresta UP (manufactured by Mitsubishi Chemical Corporation) was 6 × 10 ⁷ Ω / □ under the conditions of a temperature of 25 ° C. and a humidity of 50%.
(Comparative Example 1)
0.24 g of butylamine (molar ratio of butylamine to tin atom of 0.05) was added to 200 g of the sol prepared by preparing the acidic tin oxide aqueous sol obtained in Production Example 1 with pure water so that the SnO ₂ concentration was 5.0% by mass. The mixture was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a primary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 7.77 and an electric conductivity of 149 μS / cm. This primary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 8.00, an electrical conductivity of 356 μS / cm, and SnO _{2 of} 5.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle size by was 24 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.3%. The volume resistance value (measured in the same manner as in Example 1) of the compact of 80 ° C. dried product in the air of this sol was 240000 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Comparative Example 2)
Dibutylamine 0.43 g (molar ratio of dibutylamine to tin atom 0.05) was added to 200 g of the sol prepared by preparing the acidic tin oxide aqueous sol obtained in Production Example 1 with pure water so that the SnO ₂ concentration was 5.0% by mass. ) Was gradually added with stirring, and stirring was continued for 30 minutes after the addition was completed to prepare a secondary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 10.68 and an electric conductivity of 266 μS / cm. This secondary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 9.76, an electrical conductivity of 578 μS / cm, and SnO _{2 of} 5.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle size by was 24 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.2%. Further, the volume resistance value (measured in the same manner as in Example 1) of the green compact of 80 ° C. dried product in the air of this sol was 49000 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Comparative Example 3)
0.27 g of triethylamine (0.04 mole ratio of triethylamine to tin atom) was added to 200 g of the sol prepared by preparing the acidic tin oxide aqueous sol obtained in Production Example 1 with pure water so that the SnO ₂ concentration was 5.0% by mass. The mixture was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 10.64 and an electric conductivity of 214 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was hydrothermally treated at 240 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 7.38, an electric conductivity of 597 μS / cm, and SnO _{2 of} 5.0% by mass. The primary particle diameter observed with a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle diameter was 22 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.3%. Further, the volume resistance value (measured in the same manner as in Example 1) of the green compact of 80 ° C. dried product in the air of this sol was 36000 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.
(Comparative Example 4)
0.33 g of triethylamine (molar ratio of triethylamine to tin atom of 0.05) was added to 200 g of the sol prepared with pure water so that the SnO ₂ concentration was 5.0% by mass from the acidic tin oxide aqueous sol obtained in Production Example 1. The mixture was gradually added under stirring, and stirring was continued for 30 minutes after completion of the addition to prepare a tertiary alkylamine mixed alkaline tin oxide aqueous sol. The aqueous sol had a pH of 10.44 and an electric conductivity of 150 μS / cm. This tertiary alkylamine mixed alkaline tin oxide aqueous sol was heated at 90 ° C. for 5 hours using an autoclave to obtain a conductive tin oxide aqueous sol. This conductive tin oxide aqueous sol has a pH of 10.52, an electric conductivity of 328 μS / cm, and SnO _{2 of} 5.0% by mass. The primary particle diameter observed by a transmission electron microscope is 2 to 25 nm, and the dynamic light scattering method. The average particle diameter was 19 nm. When the SnO ₂ concentration was 3.0% by mass, the total light transmittance with an optical path length of 10 mm was 90.2%. Further, the volume resistance value (measured in the same manner as in Example 1) of the compact of 80 ° C. dry product in the air of this sol was 3600000 Ω · cm. In the X-ray diffraction analysis, a peak of cassiterite was shown.

  The tin oxide sol produced by the production method of the present invention has high transparency and conductivity, and a coating composition obtained by mixing a binder can form a highly transparent conductive film by applying it to a substrate. it can. When the substrate is a transparent substrate, a member having a conductive or antistatic coating can be produced without impairing the transparency of the substrate.

Claims (8)

  A method for producing a conductive tin oxide aqueous sol, wherein a tertiary alkylamine is mixed in an aqueous tin oxide sol and hydrothermally treated at 100 to 350 ° C.   The tertiary alkylamine is trimethylamine, triethylamine, tripropylamine, tributylamine, trisec-butylamine, tritert-butylamine, tripentylamine, triisopropylamine, triisobutylamine, triisopentylamine, N, N-dimethyl. Ethylamine, N, N-dimethylpropylamine, N, N-dimethylbutylamine, N, N-dimethylpentan-1-amine, N, N-dimethylhexylamine, N, N-diethylmethylamine, N, N-diethylpropyl Amine, N, N-diethylbutylamine, N, N-diethylhexylamine, N, N-diisopropylmethylamine, N, N-diisopropylethylamine, N, N-diisopropylisobutylamine, butyldiisopropylamino 2. The production of a conductive tin oxide sol according to claim 1, wherein the conductive tin oxide sol is at least one member selected from the group consisting of methyldibutylamine and dibutylethylamine, N, N-dibutylhexylamine, and N, N-dihexylmethylamine. Method.   The electrically conductive tin oxide aqueous sol according to claim 1 or 2, wherein the tertiary alkylamine to be mixed is 0.05 to 0.10 as a molar ratio with respect to tin atoms in the tin oxide aqueous sol. Production method.   The tin oxide aqueous sol is produced by reacting hydrogen peroxide and metal tin in an aqueous solution of an organic acid while maintaining a hydrogen peroxide / metal tin molar ratio in the range of 2 to 3. The method for producing a conductive tin oxide aqueous sol according to any one of claims 1 to 3, wherein:   5. The tin oxide concentration in the organic acid aqueous solution is maintained at 40% by mass or less during the reaction of hydrogen peroxide and tin metal in the organic acid aqueous solution. The manufacturing method of electroconductive tin oxide aqueous sol of description.   The method for producing a conductive tin oxide aqueous sol according to claim 4 or 5, wherein the organic acid contains at least oxalic acid. A conductive tin oxide aqueous sol having a volume resistance of 100 to 10000 Ω · cm of a green compact produced by applying a load of 100 kgf / cm ² after drying at 80 ° C. in air. A conductive tin oxide organic solvent sol having a volume resistance value of 100 to 10,000 Ω · cm of a green compact produced by applying a load of 100 kgf / cm ² after drying at 80 ° C. in air.