JPH0222009B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical Field of the Invention The present invention is characterized in that it is extremely easily and stably dispersed in oil, and is applied to the surface of a glass substrate, ceramic substrate, metal material, etc. in the dispersed state, and then fired. The present invention relates to easily dispersible tin oxide-based fine powder necessary for forming conductive films, etc., and a method for producing the same. (b) Background of the technology Tin oxide-based transparent conductive films are used in the construction of electronic functional devices that involve light and electric fields, such as display elements (solid-state displays), photoelectric exchange elements (solar cells and image pickup tubes), and electrophotographic recording media. It is used as one of the elements. In addition, transparent conductive films are attracting attention as heat ray reflecting films that utilize infrared reflective ability, and are used in the energy saving field as cover glasses for solar heat collectors and heat radiation prevention films for solar heat collection tubes, etc., when formed on glass or metal tubes. It is applied in Furthermore, tin oxide-based fine powder is chemically stable, abundant in resources, and inexpensive, so it is widely used as a gas detection element in gas leak alarms for combustible gases such as city gas. ing. (c) Prior art and problems Conventionally, in order to form a tin oxide-based conductive film on the surface of a glass substrate, etc., a tin compound or a composition containing a tin compound and antimony, etc., was applied to the surface of the glass substrate, etc. Or it was fired after being sprayed. However, in this method, the surface tension of the composition liquid is large,
For this reason, the composition liquid was easily repelled by the surface of the glass substrate, etc., making it impossible to form a uniform tin oxide-based film. Alternatively, aqueous ammonia is added to an aqueous solution of a tetravalent tin salt (mostly Sncl ₄ ) to generate colloidal particles of α-stannic acid (white precipitate), and this colloidal dispersion is applied to the surface of a glass substrate, etc. A method of high temperature firing has been proposed. However, in this method, α−
Colloidal particles of stannic acid tend to separate or aggregate in the dispersion, making it impossible to obtain a uniform dispersion of α-stannic acid. Furthermore, as in the above case, the colloidal particle dispersion is easily repelled by the surface of the glass substrate, etc., and as a result, the surface of the glass substrate, etc. is coated with tin oxide. However, there were problems such as not being able to form a uniform film and increasing electrical resistance. (d) Purpose of the present invention The present invention is capable of dispersing in oil extremely easily and stably, and forming a uniform coating film without repelling when the dispersion is applied to the surface of a base material such as glass. It is an object of the present invention to provide a readily dispersible tin oxide-based fine powder that is used when forming a conductive film or the like by subsequent firing, and a method for producing the same, thereby eliminating the above-mentioned problems. (e) Structure of the invention That is, the first gist of the present invention relates to easily dispersible tin oxide-based fine particles, or tin oxide and at least antimony, indium, cadmium, gallium, and bismuth. The present invention is characterized in that a substantially monomolecular adsorption layer of a surfactant is formed on the surface of the fine particles made of a kind of oxide. The second aspect of the present invention relates to a method for producing the above-mentioned easily dispersible tin oxide-based fine powder, in which a tin salt solution alone or a tin salt and at least one of antimony, indium, cadmium, gallium, and bismuth is used. A solution containing a type of salt is hydrolyzed to produce colloidal particles, the colloidal particles are aged, washed with water, made acidic, oil is added thereto, and the range in which the colloidal particles migrate and disperse in the oil. The method is characterized in that a surfactant is added to the surface of the colloidal particles to form a substantially monomolecular adsorption layer of the surfactant on the surface of the colloidal particles, and this is separated by standing to recover an oil layer, which is then dried. . In the present invention, tin salts include inorganic tin compounds such as tin tetrachloride and tin tetraiodide, tin tetraethoxy, tin tetraisopropoxy, monobutyltin triisopropoxide, dibutyltin dichloride, dibutyltin oxide, triethoxytin, Dimethyltin dichloride, monobutyltin trichloride, dibutyltin oxide, monobutyltin tripropionate, trimethoxytin bromide, monobutyltin triacetate, diethoxytin chloride, dibutyltin diacetate, dibutyltin dimethoxide, bis(tributyltin) oxide, dioctyltin Dichloride, dioctyltin oxide, tetraoctyltin, monomethoxytin bromide, tributyltin chloride, tetramethyltin, tetrabutyltin, triethyltin acetate, tributyltin monomethoxide,
Examples include organic tin compounds such as triphenyltin chloride, triphenyltin hydroxide, tetraphenyltin, and tetrabutoxytin; however, the present invention is of course not limited to those exemplified here; Any material that produces tin oxide upon decomposition may be used. The concentration of this tin salt may be any concentration up to the concentration of a saturated solution, but if the concentration is too low (0.2wt%
(below) Productivity is poor and economically unfavorable. In addition, salts of antimony, indium, cadmium, gallium, and bismuth (hereinafter collectively referred to as M) refer to their inorganic salts and organic salts, such as their chlorides, bromides, iodides, sulfates, and acetates. Or oxalates, etc. At least one of these salts is added to tin oxide in order to improve the conductivity of tin oxide. The amount of M added to tin salt is M/(Sn+M) x 100, which is 1 to 15wt.
% range, and even if the amount exceeds this range, at least the conductivity will deteriorate. If the above compound is difficult to dissolve in water, it may be used by promoting solubility with an acid such as nitric acid, hydrochloric acid or sulfuric acid, or by dissolving it in a solvent such as alcohol or ether. Alternatively, it may be dissolved in a mixture of water and alcohol. Further, during hydrolysis, if necessary, an alkali may be added. In this case, the alkali is preferably ammonia water or the like in addition to alkali metal hydroxides or oxides. Water is economically advantageous, impurities generated by the reaction (ammonium chloride, etc.) are relatively easy to remove (they evaporate during thermal decomposition), and the quality of tin oxide-based conductive films is stable. This is advantageous for the following reasons. The amount of alkali to be added may be any amount that can hydrolyze the tin salt, etc., and it is not necessarily necessary to add an equivalent amount of the alkali to the tin salt, etc. That is, the present invention is applied to fine particles of tin oxide, or fine particles consisting of fine particles of tin oxide and at least one oxide of M,
For example, it is applied to tin oxide mixed with antimony, indium, etc., or to stannate salts such as cadmium stannate, barium stannate, etc. Furthermore, ripening of colloidal particles is a process for growing and developing crystals to make them uniform and have an appropriate particle size. This step does not require particularly strict conditions, but preferably at a temperature of 70 to 100°C for 2 hours or more, 50 to 70°C for 6 hours or more, and room temperature for 60 hours or more. In addition, in order to quickly wash tin oxide-based colloidal particles produced by the wet method, it is important to quickly settle the colloidal particles after adding water and stirring. To achieve this purpose, washing is required before adding the surfactant, and washing after adding the surfactant is time-consuming, and moreover, there is a large loss of colloidal particles during washing. It is not suitable for mass production. Table 1 shows colloidal particles of tin oxide obtained under the same conditions.
When washing with warm water at 80℃, add a surfactant (45g per colloidal particle dispersion)
The time required for solid-liquid separation and the yield are shown for the cases in which the solid-liquid separation is performed after washing (adding sodium dodecylbenzenesulfonate) and before the addition of a surfactant.

[Table] Table 1 shows the time required for solid-liquid separation after one wash. The following may be the reason why such a result was obtained. In general, metal oxides and hydroxides (colloidal particles) are hydrophobic colloids that have a weak affinity for water, are unstable, and easily condense in a small amount of electrolyte. and chlorides (e.g., Sncl ₄ , Sncl ₄・
5H ₂ O) and an alkali metal hydroxide (for example, sodium hydroxide), sodium chloride (electrolyte) is produced as a byproduct. Therefore, solid-liquid separation of tin oxides and hydroxides is carried out quickly until sodium chloride as an impurity is almost completely eliminated.In other words, at the point where solid-liquid separation becomes poor, cleaning is almost completely completed. are doing. However, it is understood that when a surfactant is added, the colloidal particles become hydrophilic and are stably dispersed in the liquid, resulting in poor solid-liquid separation. Therefore,
It is important to wash the colloidal particles obtained by the wet method before adding the surfactant. In the present invention, it is necessary to acidify the solution after washing the precipitate, preferably to a pH range of 1.0 to 4.5, and the acid for this adjustment is as follows:
Hydrochloric acid or sulfuric acid of 2 to 8N is suitable. Colloidal particles obtained at a pH of 4.5 or higher have poor dispersion in oil, and too high acid concentrations (inorganic acids of 2N or higher) may lead to excessive dissolution of colloidal particles, and should be avoided. . In the present invention, oils include aliphatic hydrocarbon oils such as pentane, hexane, octane, decane, and heptane, aromatic oils such as benzene, toluene, and xylene, fatty acid esters, kerosene, etc., and toluene-acetone, etc. The surfactant refers to sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium caproate, sodium caprylate, sodium laurate, sodium oleate, sodium alkylnaphthalene sulfonate, sodium dialkyl sulfosuccinate, or is an anionic surfactant of phosphate ester salt type, for example, anionic surfactant such as higher alcohol phosphate monoester disodium salt, higher alcohol phosphate diester sodium salt, oleic acid, linoleic acid, linolenic acid, Refers to fatty acids such as stearic acid. In the present invention, when the generated colloid particles are separated from an aqueous solution, dehydrated, and dried, secondary aggregation occurs and the activity of the colloid particles decreases. A surfactant is added to the extent that the colloidal particles migrate and disperse, and the particles are dispersed in the state of primary particles, which are separated by standing to recover an oil layer, which is then dried. In the present invention, what is particularly important is to make it acidic, preferably to a pH of 1.0 to 4.5, and then add 5 to 50% of the colloidal particle dispersion to 100 parts by volume of the colloidal
parts by volume of oil, preferably 8 to 30 parts by volume of oil are added, to which a solution of 0.01 to 3 mol/surfactant,
Preferably, a solution of 0.3 to 2 moles of surfactant is gradually added while stirring until the colloidal particles are transferred to and dispersed in the oil. In the present invention, adding a surfactant to the extent that colloidal particles migrate and disperse into oil means adding oil to a dispersion of colloidal particles and gradually adding the surfactant while stirring the colloidal particles. When the surfactant is adsorbed to the particle surface and forms a monomolecular adsorption layer, the colloidal particles become hydrophobic and easily migrate and disperse into oil, but from this point on, further surfactant is gradually added. It gradually forms a bimolecular adsorption layer and gradually becomes hydrophilic, and as a result, it becomes difficult to disperse in oil, in other words,
This refers to the range in which approximately single molecules of surfactant are adsorbed on the surface of colloidal particles. In other words, this refers to the range from the point where colloidal particles are once dispersed in oil to the point where they begin to be dispersed again in water by adding a surfactant. If the amount of surfactant adsorbed on the colloidal particles is small, the migration and dispersibility into oil will be poor, while if the amount is excessive, the colloidal particles will become hydrophilic and the migration into oil and dispersibility will be poor. becomes worse. Then, BET the surface area of the above colloidal particles
When the adsorption state of the anionic surfactant was calculated from the relationship between this surface area and the adsorption cross-section area of the anionic surfactant, it was found to be a substantially monomolecular adsorption layer. Incidentally, the easily dispersible tin oxide-based fine powder of the present invention is dispersed in oil, and this is applied to a glass substrate, etc., and baked, thereby forming a tin oxide-based conductive film on the surface of the glass substrate, etc. In this case, the ratio of the tin oxide-based fine powder to the oil can be arbitrarily selected depending on the thickness of the conductive film to be formed on the glass substrate, etc. (the thicker the film, the higher the concentration of the dispersion liquid. From the viewpoint of ease of handling, it is preferable to use 2 to 50 parts by weight of tin oxide-based fine powder per 100 parts by weight of oil, and the firing temperature of the coating solution for glass substrates, etc. should be set in an oxygen-containing atmosphere such as air. In this case, the temperature is above the decomposition temperature of the surfactant used and up to 1200°C, and if it is above 1200°C, the electric resistance of the tin oxide-based fine powder increases, so it is not preferable. (f) Effects of the Invention In short, the present invention forms a substantially monomolecular adsorption layer of surfactant on the surface of the tin oxide-based fine powder, which allows for good dispersion in oil. The liquid can be easily prepared, and since the prepared dispersion liquid does not separate even after a long period of time, it is extremely convenient to prepare the dispersion liquid in advance. Since a substantially monomolecular adsorption layer of surfactant is formed on the surface of the glass substrate, a uniform coating film is formed without repelling when the dispersion is applied to the surface of a glass substrate, etc., and as a result, a conductive film with a uniform thickness can be formed. can be formed. Furthermore, since the easily dispersible tin oxide-based fine powder of the present invention is in powder form, a dispersion liquid of any concentration can be prepared. It is extremely convenient because the thickness can be easily changed. Furthermore, since the easily dispersible tin oxide fine powder of the present invention is a fine particle and has extremely high surface activity, it has excellent performance as a gas detection element. The tin oxide-based fine powder may be used as a conductive paint depending on the purpose, or it can be used in a powdered state for a variety of purposes such as pigments. In other words, since the easily dispersible tin oxide fine powder of the present invention is in powder form, it can be used for a variety of purposes. Further, the method of the present invention is extremely advantageous because easily dispersible tin oxide-based fine powder on which substantially monomolecular surfactant is adsorbed can be produced easily and efficiently on an industrial scale at low cost. Next, the present invention will be explained in detail based on examples. (g) Examples of the invention Example 1 130g of Sncl _{4.5H 2} O was dissolved in a mixed solution of water and ethanol (1:1 by volume), and in this solution,
5N-NH ₄ OH is added at a constant rate until the pH reaches 1.0 to generate tin oxide colloidal particles. This reaction is carried out with good stirring. After the reaction, the colloidal particles are aged at 80° C. for 3 hours and then washed until ammonium ions are no longer detected. After washing with water,
Bring the total volume to 3, add 4N-HCl to it and adjust the pH.
After adjusting the amount to 2 to 3, add 0.4 of toluene-acetone mixed oil (volume ratio 1:1). Next, a 1 mol/mol sodium laurate solution is added to this solution until the colloidal particles are transferred and dispersed in the toluene-acetone mixed oil. Next, this solution is separated by standing to recover an oil layer, and the colloidal particles of tin oxide are dried to obtain easily dispersible tin oxide fine powder. The yield was 95.5%. 30g of easily dispersible tin oxide fine powder obtained in this way
, toluene-acetone mixed oil (volume ratio 1:1)
A homogeneous dispersion can be obtained by adding 150g of the solution to the solution and stirring vigorously for 10 minutes using a stirrer. The obtained dispersion did not change even after 10 days had passed after being stored in the container, and no precipitate or supernatant was formed. A glass substrate was immersed in this dispersion and pulled up (pulling speed: 15 cm/min), and then baked in air at 800° C. for 1 hour to create a transparent conductive film.
The thickness of the obtained transparent conductive film was 650 Å, the sheet resistance was 3×10 ⁴ Ω/sq, and the transparency was also sufficiently satisfactory. Example 2 130 g of Sncl ₄・5H ₂ O and 6 g of Sbcl ₃ were dissolved in a mixed solution of water and ethanol (volume ratio 1:1) 4, and a 15% by weight NaOH aqueous solution was added at a constant rate until the pH of this solution reached 3.0. In addition, colloidal particles of tin oxide and antimony oxide are co-precipitated. This reaction is carried out with good stirring. After the reaction, the colloidal particles are aged at 90° C. for 2 hours and then washed until chlorine ions are removed. After washing with water, adjust the total amount to 3 and add 3N-Hcl to it to make the pH 1-2.
After adjusting to 0.4 n-hexane. To this solution, 0.5 mol/sodium dodecyl sulfate solution is added until the colloidal particles are transferred to n-hexane and dispersed. This solution is separated by standing to collect an oil layer, which is dried to obtain easily dispersible tin oxide-antimony oxide fine particles. The yield was 91.5%. 40 g of easily dispersible tin oxide-antimony oxide fine particles thus obtained were added to 150 g of n-hexane and vigorously stirred for 10 minutes using a stirrer to obtain a uniform dispersion. After storing the obtained dispersion in a container,
There was no change even after 10 days had passed, and it was stable and no precipitate or supernatant was formed. After immersing the glass substrate in this dispersion and pulling it up (pulling speed 15 cm/min), in air,
A transparent conductive film was created by baking at 750°C for 1 hour. The thickness of the obtained transparent conductive film was 750 Å, the sheet resistance was 2×10 ³ Ω/sq, and the light transmittance was also sufficiently satisfactory. Example 3 85 g of dimethyltin dichloride was dissolved in a mixed solution of water and ethanol (1:1 by volume), and a 20% by weight NaOH aqueous solution was added to this solution at a constant rate until the pH reached 3.5 to dissolve tin oxide. Adjust colloidal particles. Xylene as oil and as surfactant
Easily dispersible tin oxide was obtained in the same manner as in Example 2 except that a 1.5 mol/mol oleic acid solution was used.
The yield of tin oxide was 90.5%. 30 g of easily dispersible tin oxide thus obtained was added to 150 g of xylene and stirred vigorously for 10 minutes using a stirrer to obtain a uniform dispersion. No change was observed in the obtained dispersion even after 10 days had passed after storage in the container. After dipping the glass substrate into this dispersion and pulling it up (pulling speed 15cm/
min) in air at 750° C. for 1 hour to create a transparent conductive film. The thickness of the obtained transparent conductive film was 650 Å, the sheet resistance was 1.5 × 10 ³ Ω/sq,
Translucency was also sufficiently satisfactory. Example 4 130 g of Sncl ₄・5H ₂ O and 6 g of Incl ₃ were dissolved in a mixture of water and ethanol (volume ratio 1:1), and 5N-NH ₄ OH was added to this solution at a constant rate until the pH reached 1.5. is added to co-precipitate tin oxide and indium oxide. After aging at 95℃ for 2 hours, 2N−Hcl
Easily dispersible tin oxide-indium oxide fine particles were obtained in the same manner as in Example 1, except that the pH was adjusted to 1.5 to 2.5 and cyclohexane was used as the oil. The yield was 96.5%. 30 g of easily dispersible tin oxide-indium oxide thus obtained was added to 150 g of cyclohexane and stirred vigorously for 10 minutes using a stirrer to obtain a uniform dispersion. No change was observed in the resulting dispersion even after 10 days had passed since it had been stored in a container. After immersing the glass substrate in this dispersion and pulling it up (pulling speed 15cm/min), it was placed in the air.
A transparent conductive film was created by baking at 750°C for 1 hour. The thickness of the obtained transparent conductive film was 650 Å, the sheet resistance was 1.5×10 ³ Ω/sq, and the light transmittance was also sufficiently satisfactory. (h) Application examples of easily dispersible tin oxide-based fine powder produced according to the present invention Application examples (1) Catalyst CO oxidation using the tin oxide-antimony oxide fine powder (hereinafter referred to as catalyst) obtained in Example 2 I tested the activity. Reaction temperature: 70°C Reaction gas: CO6 volume % + air 94 volume % Flow rate: 95 cm ³ /min Catalyst amount: 13 g The conversion rate of CO was 72%, showing high activity even at a relatively low temperature. (2) Gas detection element The tin oxide-based fine powder obtained in Example 1 was kneaded with water, the resulting paste-like substance was applied to a detection substrate, and after drying, it was baked at 680°C for 2.5 hours in an N ₂ gas atmosphere. A gas sensing element was obtained. When a hydrogen gas detection test was conducted using the obtained gas detection element, the results shown in curve A in the figure were obtained. On the other hand, a gas detection element was manufactured in the same manner as above using commercially available tin oxide powder and tested in the same manner as above, and the results are as shown by curve 2 in the figure. From this result, it was recognized that the tin oxide of the present invention is promising as a material for a detection element for combustible gases. The results shown in the figure are obtained by measuring the resistance change of the element due to contact with the detection gas in the gas detection measurement electric circuit as the voltage change across the load resistance. (3) Conductive paint The tin oxide-antimony oxide fine powder produced in Example 2 was fired at 800°C for 2 hours in the air, and the electrical resistance of the sintered body made by doping the tin oxide with antimony was 9.5× It showed high conductivity of 10 ^-4 Ωcm. From this result, it can be used as a conductive pigment alone, or in combination with conductive fine powder such as silver, in conductive paints depending on the purpose. Conductive paints are used in printed wiring for radios, television radars, hearing aids, etc.

[Brief explanation of drawings]

The figure shows the results of a detection test of a gas detection element using fine tin oxide powder. B... Shows the test results of a gas sensing element made by sintering the tin oxide fine powder of the present invention. B...The results of a test on a gas detection element made from commercially available tin oxide fine powder are shown.

Claims (1)

[Claims] 1. Fine particles of tin oxide or tin oxide and antimony,
A readily dispersible tin oxide-based fine powder comprising fine particles comprising an oxide of at least one of indium, cadmium, gallium, and bismuth, characterized in that a substantially monomolecular adsorption layer of a surfactant is formed on the surface of the fine particles. . 2 Hydrolyze a tin salt solution alone or a solution containing a tin salt and at least one salt of antimony, indium, cadmium, gallium and bismuth to produce colloidal particles, age the colloidal particles and wash with water, then acidify it, add oil to it, add a surfactant to the oil to the extent that the colloidal particles migrate and disperse, and form a substantially monomolecular adsorption layer of the surfactant on the surface of the colloidal particles. A method for producing easily dispersible tin oxide-based fine powder, which comprises separating the oil layer by standing still and recovering an oil layer, followed by drying.