JPH03151038A - Composite sol of tungsten oxide/tin oxide and production therefor - Google Patents

Abstract

PURPOSE:To obtain composite sol of tungsten oxide/tin oxide which is made stable for a long period even in the high concn. by incorporating both the composite colloid particles consisting of tungsten oxide and tin oxide and cations such as alkali metal and ammonium. CONSTITUTION:The composite sol is obtained by incorporating both the composite colloid particles of tungsten oxide and tin oxide and cations such as alkali metal of Li and Na, etc., and ammonium or amine of ethyl amine, etc. The weight ratio of WO3 and SnO2 contained in this sol is regulated to (2-100) as WO3/SnO2. Further the amount of cation such as alkali metal, ammonium or amine is regulated to (0.02-0.7) molar ratio as M2O/(WO3+SnO2). The composite sol obtained in such a way is made stable for a long period even in the high concn., nearly colorless and transparent at about 1-9pH.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stable tungsten oxide-tin oxide composite sol and a method for producing the same. The tungsten oxide-tin oxide composite sol of the present invention is a treatment agent for fibers and metals; a surface treatment agent for metals, glass, plastics, etc.; a paint binder; a flame retardant aid for fibers, plastics, etc.; It is used as a binder for fibers, ceramics, etc.; as an antistatic agent for porcelain and plastics; and as a refractive index improver and hardness improver for hard coating agents.

(Prior art) Although a stable sol of tungsten oxide alone is not yet known, WOz obtained by adding silicate: Si
A sol in which the molar ratio of O□:MzO (M represents an alkali metal atom or an ammonium group) is 4 to 15:2 to 5:1 has been proposed in JP-A-54-52686.

Furthermore, in Japanese Patent Publication No. 50-40119, Si:
A silicic acid-stannic acid composite sol in which the molar ratio of Sn is 2 to 1000:1 has been proposed.

(Problems to be Solved by the Invention) The tungsten oxide sol described in JP-A-54-52686 has a tungsten acid aqueous solution obtained by deionizing a tungstate aqueous solution, and a silicate sol. However, it is stable only under strong acidity, and its usefulness is not widespread.

For example, even when used as a flame retardant aid, the effect of improving flame retardancy is small (also, when used as a hard coat agent, the effect of improving the refractive index of the coating film is small).

The silicic acid-tin M composite sol described in Japanese Patent Publication No. 50-40119 is obtained by decationizing a mixed aqueous solution of an alkali silicate and an alkali stannate, and as mentioned above, it has a wide range of applications. It is not suitable for

The present invention aims to provide a novel tungsten oxide-tin oxide composite sol suitable for various uses.

(Means for Solving the Problems) The stable tungsten oxide-tin oxide composite sol of the present invention is composed of tungsten oxide (WOa) and tin oxide (SnO□).
and an alkali metal, ammonium or amine cation, preferably the weight ratio of WO3 and Snug contained in this sol is 10, /SnO
□ is 2 to 100, and the amount of alkali metal, ammonium or amine cations contained in this sol is
M20/ WOs + SnO□ (However, M represents an alkali metal atom, ammonium group, or amine molecule.)
It is characterized by a molar ratio of 0.02 to 0.7.

The stable tungsten oxide-tin oxide composite sol of the present invention is preferably produced by combining a tungstic acid aqueous solution obtained by treating an aqueous tungstate solution with a hydrogen-type cation exchanger and a stannate aqueous solution using WO* /SnO□
M, o/ of the alkali metal hydroxide, ammonium hydroxide or amine in this mixed solution and the sum of these tungstic acid O1 and stannate SnO2. too3+ Snow
(However, M is the same as above.) The molar ratio is 0.02 to 0.
7.

Composite colloidal particles of WO3 and SnO2 contained in the tungsten oxide-tin oxide composite sol of the present invention are observed with an electron microscope, and are about 7 millimicrons or less, usually 5 to 2
It has a particle size of millimicrons.

The dispersion medium for colloidal particles in this sol may be either water or a hydrophilic organic solvent. Examples of this hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; linear amides such as dimethylformamide and N,N'-dimethylacetamide; and cyclic amides such as N-methyl-2-pyrrolidone. Examples include glycols such as ethyl cellosolve, phthyl cellosolve, and ethylene glycol.

Examples of alkali metals, ammonium or amines contained in the sol of the present invention include Li, Na, and K.

Rb, Cs, N114 + Alkylamines such as ethylamine, triethylamine, isopropylamine, n-propylamine; aralkylamines such as hensylamine; alicyclic amines such as piperidine; alkanolamines such as monoethanolamine and triethanolamine. . These may be contained as a mixture of two or more types.

A preferred sol of the present invention combines WO3 and SnO2 with WO:+
/SnO□ in a weight ratio of 2 to 100, and the above-mentioned alkali metals, ammonium, amines, etc. are contained in MzO/ WOz +
It is contained in a ratio of 0.02 to 0.7 as a Snow molar ratio.

The total concentration of ■03 and SnO□ contained in the sol of the present invention is usually 40% by weight or less, practically preferably 2% by weight or more, and preferably 10 to 30% by weight.

The sol of the present invention may contain any other components as long as the purpose of the present invention is achieved. In particular, about 30% by weight of oxycarboxylic acids based on the total amount of WO3 and Snug.
If the following components are contained, a further improved sol can be obtained. Examples of oxycarboxylic acids used include lactic acid, tartaric acid,
Examples include citric acid, gluconic acid, malic acid, and glycolic acid.

Preferred sols of the invention exhibit a pn of 1 to 9 and are colorless, clear or nearly clear liquids. The sol is stable for more than 3 months at room temperature and for more than 1 month at 60°C, and no precipitates are formed in this sol, and the sol does not thicken or gel. do not have.

Examples of the tungstates and stannates used in the production of the sol of the present invention include tungstates and stannates of the above-mentioned alkali metals, ammonium, amines, and the like. In particular, sodium tungstate Na2WO4.2
H20 and sodium stannate Na2SnO3 ・3H
20 is preferred. Also. It is also possible to use tungsten oxide, tungstic acid, stannic acid, etc. dissolved in an aqueous solution of an alkali metal hydroxide.

The hydrogen type cation exchanger used may be any conventional one, and hydrogen type cation exchange resins are conveniently available as commercial products. The alkali metal hydroxide, ammonium hydroxide, amine, etc. used may also be commercially available industrial products. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like.

Examples of amines include those exemplified above.

The aqueous solution of tungstic acid used in the production of the sol of the present invention can be easily prepared by treating the aqueous solution of the tungstate salt with the cation exchange resin at a temperature of 100°C or less, preferably from room temperature to 60°C. can get. Since this aqueous solution of tungstic acid has colloidal properties and therefore tends to gel, it is convenient to use it before gelation. The aqueous solution of the tungstate salt used to prepare the aqueous solution of tungstic acid preferably has a concentration of 0.1 to 15% by weight as WO3. About 15% by weight is preferable.

The aqueous solution of stannate used in the production of the sol of the present invention preferably has a SnO□ concentration of about 0.1 to 30% by weight, but it may be more concentrated than this. In some cases, solid stannate salts can also be used.

The sol according to the invention is produced by mixing the tungstic acid aqueous solution and the stannate aqueous solution. This mixing is carried out at room temperature to 100" C1 under sufficient stirring.
Preferably, it is carried out at room temperature to about 60°C. The amount of liquid to be mixed is a WOz/SnO2 weight ratio of 2 to 100.
degree is preferred. As a result of this mixing, M, 0 (M is the same as above) is present in the resulting mixed solution in a molar ratio of 0.015 to 0.44 with respect to the total of WO, and SnO□. A preferred sol according to the invention has MzO/
Since the W03+SnO□ molar ratio is 0.02 to 0.7, the M, 0/WO3+SnO2 molar ratio in the liquid obtained by the above mixing may be adjusted depending on the case.

The molar ratio in the liquid obtained by the above mixing can be increased by adding an alkali metal oxide, ammonium hydroxide, amine, etc. to the mixed liquid. This can be carried out by adding an alkali metal hydroxide, ammonium hydroxide, amine, etc. after treatment with a cation exchange resin so that the molar ratio of MzO/WOs + SnO□ becomes 0.02 to 0.7.

By the above mixture or with the above mixture M20/WO1+
By adjusting the SnO□ molar ratio, a stable tungsten oxide-tin oxide composite aqueous sol according to the present invention can be obtained.

When the concentration of the aqueous sol is low, the concentration of the aqueous sol can be increased, if desired, by a conventional concentration method such as an evaporation method or an ultrafiltration method. especially,
Ultrafiltration is preferred. Even in this concentration, the temperature of the sol is preferably maintained at about 100°C or less, particularly 60°C or less.

By replacing the water in the aqueous sol with the hydrophilic organic solvent, a hydrophilic organic solvent sol called an organosol can be obtained. The above-mentioned water and hydrophilic solvent can be easily replaced by a conventional method such as a distillation replacement method or an ultrafiltration method.

When the pH of the aqueous sol is high, it is preferable to add the oxycarboxylic acid to the aqueous sol before or at the same time as the above substitution.

Regardless of the presence or absence of this oxycarboxylic acid, it is preferable to maintain the temperature of the sol at a level below 100°C, particularly below 60°C, even during the replacement of the sol medium.

(Function) An aqueous solution of tungstic acid obtained by treating an aqueous solution of tungstate with a hydrogen-type cation exchange resin and an aqueous solution of stannate at a WO,/SnO2 weight ratio of 2 to
It has been found that a stable sol can be obtained by mixing at a concentration of 100%. The stability of this sol is determined by the alkali metal introduced by the stannate into the composite colloidal particles of tungsten oxide and tin oxide formed by the combination of colloidal particles of tin oxide and colloidal particles of tungsten oxide or polyanions produced by the above mixing. This is thought to be due to the formation of stable colloidal particles due to the combination of cations such as ammonium and amines.

However, if the weight ratio of WO3/5nOz in the obtained sol is less than 2, the sol is unstable when acidic, and
If this weight ratio exceeds 100, the sol still exhibits no stability. Silkworms containing cations such as alkali metals, ammonium, and amines contained in the sol are
Even when the molar ratio of 1+5 nOz is less than 0.02,
Such a sol has poor stability, and if the 20 molar ratio exceeds 0.7, the water resistance of a dried coating film obtained using such a sol will be low, which is not preferred in practice. high pH
The oxycarboxylic acid added when making the above organosol from the aqueous sol also contributes to stabilizing the sol, but the amount added is 30% relative to the total of kO3 and 5nu20 in the sol.
If the amount exceeds % by weight, the water resistance of the dried coating film obtained using such a sol will decrease. The pH of the sol changes depending on the amount of alkali metal, ammonium, amine, oxycarboxylic acid, etc. in the sol.

When the pH of the sol is 1 or less, the sol is unstable, and when the pH is 9 or more, composite colloidal particles of tungsten oxide and tin oxide are easily dissolved in the liquid. Oath in Sol 03 and 5nu2
When the total concentration of is as high as 40% by weight or more, the sol still has poor stability. If this concentration is too low, it is impractical, and the preferred concentration for industrial products is 10 to 30% by weight.

If instead of the production method of the present invention, an aqueous solution in which tungstate and stannate are dissolved is treated with a hydrogen-type cation exchange resin, the resulting colloid particles will be too small and precipitation of tin oxide will easily occur. A method for producing a sol by adding the above-mentioned alkali metal hydroxide, ammonium hydroxide, amine, etc. to the liquid obtained by treatment with a hydrogen-type cation exchange resin is not efficient.

Furthermore, if the concentration of the aqueous solution of tungstic acid used is less than 1% by weight of O, the concentration of the obtained sol decreases, and a large amount of water must be removed during concentration, which is not efficient. On the other hand, if the W (h concentration is 15% by weight) of this tungstic acid aqueous solution
If the concentration is higher than that, such aqueous solutions will have poor stability;
It can be difficult to handle.

When ultrafiltration is used as a concentration method, polyanions of tungsten oxide, ultrafine particles, etc. that coexist in the sol pass through the ultrafiltration membrane together with water, which causes instability of the sol. These polyanions, ultrafine particles, etc. can be removed from the sol.

At a temperature of 100°C or higher, the aqueous sol of the present invention
The composite colloidal particles of tungsten oxide and tin oxide in this sol are likely to undergo hydrolysis and dissolve, or these oxides may precipitate. kept below. A safe temperature that does not cause such changes is preferably 60°C or less.

(Example) Example 1 550 g of sodium tungstate Na2WO,.2H20 (reagent grade) was dissolved in 4850 g of water to obtain 5400 g of a water-soluble solution of sodium tungstate. This aqueous solution has a specific gravity of 1.086, a pH of 9.79,
WO, the content was 7.16 weight.

Next, the entire amount of the above aqueous solution was added to a hydrogen type cation exchange resin (
5,690 g of an aqueous solution of tungstic acid was passed through a column packed with 12 OB) (manufactured by Organo).
I got it. This aqueous solution has a specific gravity of 1,068, p)l 1.
60, viscosity 2. Ocp, WOz content 6.8% by weight
, Na, 0 content was 0.04% by weight, and it was a yellow transparent liquid. Moreover, when this aqueous solution was left at room temperature, it turned into a gel-like state after 1 hour.

Separately, by dissolving sodium stannate NazSnO3.3HzO (reagent grade) in water, the specific gravity is 1.244, p.
tl 12.8, including Snug! 15.0% by weight, Na
An aqueous sodium stannate solution having a NO content of 6.2% by weight was obtained.

Next, the aqueous solution 569 of tungstic acid immediately after the above production
A tungsten oxide-tin oxide composite aqueous sol of the present invention was obtained by adding 505 g of the above aqueous solution of sodium stannate to 0 g under strong stirring at room temperature. This sol had a slight colloidal color, but was completely colorless and transparent. And specific gravity 1.073, pH 5.03, viscosity 1.
5 cp, W (h content 6.25% by weight, SnO2 content 11.22% by weight, Na, 0 content 0.54% by weight, colloidal particle diameter of about 5 millimicrons by electron microscopy observation. The sol had stability for more than 3 months when left at room temperature under closed conditions. From the above values, the weight ratio of WO and SnO2 in this sol -〇z/SnO2 was 5.
．． 12. NazO/WO:++SnO□ molar ratio value is 0
．． 25 respectively.

Example 2 By passing 3100 g of the aqueous sol obtained in Example 1 through a column packed with hydrogen type cation exchange resin, the specific gravity was reduced to 1.0.
62, ptl 1.53, viscosity 1-5 cp 5WO3
Contains 15.69% by weight, 11.11% by weight contains 5nOz.
, an aqueous sol of the present invention containing 10.04% by weight of Na2O was obtained. From the above values, NazO/WOs + of this sol
The 5nOz molar ratio is calculated to be 0.02.

Next, 3400 g of this pH 1.53 sol and 3095 g of the pH 5.03 sol obtained in Example 1 were mixed at room temperature to obtain an aqueous sol of the present invention.

The sol obtained here had a slight colloidal color, but was almost colorless and transparent, with a specific gravity of 1.068 and a pH of 2.36.
, viscosity 1.5 cp, WO, content 5.96% by weight,
Sn0g content 1.17% by weight, Na2O content 28
% by weight, and the colloid particle diameter was approximately 5 millimicrons as determined by electron microscopy. It was stable for more than 3 months in a room temperature storage test. Furthermore, when calculated from the above values, W03/S
nO2 weight ratio 5.12, NazO/WO3+ Sno
□Molar ratio is 0.135.

Next, 6495 g of this pH 2.36 sol was concentrated by ultrafiltration to obtain 1840 g of highly concentrated sol. This sol also had a slight colloidal color, but was mostly colorless and transparent, with a specific gravity of 1.212 and a pH of 2.34.
, viscosity 2-5 C9% WO3 content 117.1% by weight, S
Contains nO2! 3.93% by weight, Na 20 content 0.88x4%, colloid particle size approximately 5 mm by electron microscopy, particle size 90 mm by dynamic light scattering method (N4 device manufactured by Coulter, USA). Met. Furthermore, the W O3/S n Ox weight ratio of this highly concentrated sol is 4.3.
5. The NazO/WOz+5nOz molar ratio is calculated to be 0.14. Furthermore, by the ultrafiltration described above, about 20% of WO3 in the sol before filtration was reduced. This decrease indicates that polyanions or microparticles of WO, which passed through the ultrafiltration membrane, were present in the sol before filtration.

Furthermore, when the above-mentioned high concentration sol was tested, it was found to have good dispersion in methanol and stability for more than 3 months at room temperature. Further, when the refractive index of light of this dried sol was measured, it was found to be 1.84.

Example 3 By passing 5400 g of a 17.16% by weight aqueous solution of sodium tungstate containing W03 through a column packed with a hydrogen type cation exchange resin, 613 g of an aqueous solution of tungstic acid was prepared.
5g was obtained. This aqueous solution has a specific gravity of 1.062, a pH of 1,
48, viscosity 2.5 cp, WO content 6.16% by weight, Na content 0.03% by weight.

Therefore, the NatO/W03 molar ratio is calculated to be 0.018.

Next, the aqueous solution 613 of tungstic acid immediately after the above production
5 g, an aqueous solution of sodium stannate (Snug II)
The aqueous sol 6 of the present invention
900g was obtained. This sol has a specific gravity of 1.073 and a pH of 6.
,72, viscosity 1.5 cp, WO3 content 5.60% by weight, SnO2 content 1.67% by weight, Na, 0 content 0
．． It was 71% by weight. By calculation, WOz/5nOz
Weight ratio 3.35, NazO/I40x + 5nOz
The molar ratio is 0.33.

Next, the above sol was evaporated using a rotary evaporator.
When concentrated under reduced pressure, 1610 g of highly concentrated aqueous sol was obtained. This highly concentrated sol exhibited a slight colodral color, but was almost colorless and transparent, with a ratio of fi 1.385 and p) 1.
6.68, viscosity 2.6 cp, NO3 content 24.0
Weight %, SnO content 17.14 weight %, NagO content 3
．． 06% by weight, and the colloid particle diameter was approximately 5 mm by electron microscopy. It was also stable for more than 3 months in a room temperature storage test.

Example 4 22 g of n-propylamine was added to 3250 g of the aqueous sol obtained in Example 2 with a specific gravity of 1.068 and a pH of 2.36 while stirring.
and 19 g of tartaric acid to obtain an aqueous sol.

This sol has a specific gravity of 1.067, a pH of 3.82, and a viscosity of 1.067.
5cp, WO3 content 5.88% by weight, Snug content 1
1.16% by weight, Na20 content 0.28% by weight, amine content 0.67% by weight, tartaric acid content 0.58% by weight
Met. By calculation, NazO+ (amine)20/
WO: + + SnO2 molar ratio 0.31, tartaric acid/
WO3+ SnO29.52% by weight.

Next, this sol was concentrated under reduced pressure using a rotary evaporator to obtain 970 g of a highly concentrated aqueous sol. This sol had a slight colloidal color, but was almost colorless and transparent, with a specific gravity of 1.2 B2, pH of 3.68,
Viscosity 2.3 cp, WO3 content 11.99 wt., SnO content 3.93 wt%, Na2O content 0.95
Weight%, amine content 2.27% by weight, tartaric acid content 1
．． It was 97% by weight. This sol had good dispersibility in methanol and had stability when left at room temperature for 3 months or more.

Example 5 215 g of the aqueous sol with a specific gravity of 1.212 and a pH of 2.34 obtained in Example 2 was charged into a rotary evaporator.
While continuously adding methanol 31 little by little under reduced pressure, the sol medium was distilled off to obtain 376 g of methanol sol in which the water in the aqueous sol was replaced with methanol. This sol had a slight colloidal color, but was almost colorless and transparent, with a specific gravity of 0.932, pH of 3.46 (equal weight mixture of this sol and water), and a viscosity of 6.2 cp.
The WO content was 9.78% by weight, the SnO□ content was 2.25% by weight, and the water content was 7.5% by weight. Although this sol produced a very large amount of precipitate during standing, the amount did not increase even after the standing period was extended and remained stable.

Example 6 Regarding 300 g of the highly concentrated aqueous sol obtained in Example 4, 350 g of methanol sol was obtained by replacing the water in the medium with methanol in the same manner as in Example 5. Although this sol exhibited a slight colloidal color, it was completely colorless and transparent, with a specific gravity of 0.978, a pH of 5.28 (equal weight mixture of this sol and water), and a viscosity of 4. Ocp, WO, including 117
．． 1% by weight, SnO2 content of 13.37% by weight, NalO content of 0.81% by weight, n-propylamine content of 1.94% by weight, tartaric acid content of 1.69% by weight, water content of 3.5% by weight, and room temperature. After 3 months of standing, no sediment was formed and the product was stable.

Comparative Example 1 An aqueous solution of sodium tungstate having a WO3 content of 7.16% by weight was passed through a column packed with a hydrogen type cation exchange resin to obtain 1420 g of an aqueous solution of tungstic acid. This aqueous solution has a specific gravity of 1.068, a p) of 11.60, and a viscosity of 2. Ocp, WO, content 6.8% by weight, Na2
The O content was 0.04 weight.

Separately prepared SnO□ content 15.0% by weight, Na 2
An aqueous sol was obtained by adding 5 g of an aqueous solution of sodium stannate having a content of 6.2 wt. Immediately after production, this sol has a specific gravity of 1.0.
6 B, pH 1,62, -03 content 6.78% by weight, S
Contains nO2: 10.053% by weight, Na, 0: 10.06%
2% by weight, wo,,' 5nOz weight ratio is 128
, Na 10/WO3 +5nu2 molar ratio is 0.034
It is calculated as follows.

Comparative Example 2 Specific gravity obtained in Example 2: 1.062, pll: 1.53
Contains 2100g of aqueous sol and SnO2! An aqueous sol was obtained by mixing with 300 g of an aqueous sodium stannate solution containing 15.0% by weight and a NazO content of 6.2% by weight with strong stirring. This sol exhibits a slight colloidal color, is colorless and transparent, has a specific gravity of 1.079, a pH of 8.02, a viscosity of 1.5 cpSW (h content 4.98 wt., Sn0g content 2.85 wt.%, Na , 0 content was 0.81% by weight.

Next, this sol was concentrated under reduced pressure in a rotary evaporator, and as the concentration progressed, it became cloudy.

Separately, when the pH was lowered by adding a hydrogen-type cation exchange resin to the above sol while stirring, the pll was approximately 5.
When this was reached, the sol increased in viscosity and a stable sol could not be obtained.

According to the above contents of -Ol, 5nOz, Na, and 0, this sol has a Woe/Snow weight ratio of 1.75 and a NazO/Snow weight ratio of 1.75.
The WO3+SnO□ molar ratio is 0.32.

(Effects of the Invention) The novel tungsten oxide-tin oxide composite sol of the present invention is stable for a long period of time even at high concentrations and has many useful properties. The colloidal particles of this sol are composite colloidal particles produced by the combination of colloidal particles of tungsten oxide and colloidal particles of tin oxide, and are stabilized by cations such as alkali metals, ammonium, and amines, and have a particle size of approximately 7 mm. It is smaller than a micron and is negatively charged. This sol is stable in the range of pl+ of about 1 to 9, and is almost colorless and transparent.

Since the colloidal particles in this sol are negatively charged, it has good miscibility with sols made of other negatively charged colloidal particles, such as silica sol, antimony pentoxide sol,
It can be stably mixed with dispersions such as anionic or nonionic surfactants, aqueous solutions of polyvinyl alcohol, anionic or nonionic resin emulsions, water glass, aqueous solutions of aluminum phosphate, etc.

The dry coating of this sol is transparent and about 1.8 to 1.
It exhibits a high refractive index of 9, has high bond strength and hardness, and has high water resistance and adhesion.

Furthermore, antistatic properties, heat resistance, abrasion resistance, etc. are also good.

This sol is therefore used in numerous applications. For example, flame retardant or non-combustibility imparting agent, coating refractive index improver,
Hard coat agents, antistatic agents, anti-slip agents, dyeability improvers, wettability improvers, corrosion resistance improvers, various paints, adhesives,
It can be used as a molding binder, an anti-dusting agent for inorganic fibers, a surface treatment agent for glass, ceramics, plastics, metals, etc., a catalyst, etc.

Such a sol of the present invention can be easily prepared by the method of the present invention from an aqueous solution of tungstate and an aqueous solution of stannate.
Moreover, it can be efficiently manufactured as an industrial product.

Sender: Nissan Chemical Industries, Ltd.

Claims (4)

[Claims] (1) Tungsten oxide (WO_3) and tin oxide (Sn
A stable tungsten oxide-tin oxide composite sol characterized by containing composite colloidal particles of O_2) and an alkali metal, ammonium or amine cation. (2) Stable tungsten oxide according to claim (1)
The tin oxide composite sol contains WO_3 and S
The weight ratio of nO_2 is 2 to 1 as WO_3/SnO_2
00, and the amount of alkali metal, ammonium or amine cations contained in this sol with respect to the total amount of these WO_3 and SnO_2 is M_2O/WO_3+S
nO_2 (However, M represents an alkali metal atom, ammonium group, or amine molecule.) 0.02 to 0 as a molar ratio
．． Stable tungsten oxide characterized by a
Tin oxide composite sol. (3) Mixing an aqueous solution of tungstic acid obtained by treating an aqueous solution of tungstate with a hydrogen-type cation exchanger and an aqueous solution of stannate at a ratio of 2 to 100 as a WO_3/SnO_2 weight ratio. A method for producing a tungsten oxide-tin oxide composite sol, characterized by: (4) The mixed liquid obtained by the mixing according to claim (3) is mixed with M_2O (where M represents an alkali metal atom, an ammonium group, or an amine molecule) based on the total number of moles of WO_3 and SnO_2 in this mixed liquid. .) A method for producing a tungsten oxide-tin oxide composite sol, which comprises adjusting the molar ratio so that the molar ratio M_2O/WO_3+SnO_2 becomes 0.02 to 0.7.