JPH07188593A - Electrically-conductive coating material - Google Patents

Abstract

PURPOSE:To obtain a coating material suitable for forming a transparent electrically-conductive coating film and a transparent electrode for a liquid crystal display, comprising electrically-conductive tin-containing indium oxide fine powder prepared by adding an aqueous solution of an alkali to a solution of a tin salt and an indium salt and heat-treating the formed substance, a coating binder and a solvent. CONSTITUTION:An aqueous solution of an alkali such as ammonia water or an aqueous solution of an ammonium salt is added to a solution of a tin salt such as tin chloride and an indium salt such as indium sulfate while maintaining the solution at <=30 deg.C preferably 0-20 deg.C. The prepared tin oxide hydrate and indium oxide hydrate are heat-treated preferably at 509-1,000 deg.C to give the objective coating material comprising electrically-conductive tin-containing indium oxide fine powder, a coating binder and a solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paint suitable for forming a transparent conductive film such as an antistatic film and a transparent electrode such as a liquid crystal display by a coating method.

[0002]

2. Description of the Related Art Tin-containing indium oxide (ITO) films, which are widely used as transparent electrodes for solar cells, liquid crystal displays, etc., or transparent conductive films for electroluminescence displays, touch panels, etc., are generally prepared by the sputtering method.
It is formed by a vacuum vapor deposition method, a coating method, or the like. Among them, the coating method is capable of processing into a large area or a complicated shape, which is difficult by the spattering method or the vacuum vapor deposition method, and the pattern formation is easy, which is advantageous in cost. The organic sol-gel method is generally used as such a coating method, but with the recent development of fine particle manufacturing technology,
The method of applying this using fine powder has been attracting attention because the film forming temperature can be kept low, the degree of freedom in selecting the base material can be increased, and the cost can be reduced.

A conductive coating material using conductive fine powder for forming a transparent conductive coating is disclosed in Japanese Patent Publication No.
Nos. 1-9343, JP-B-63-13463, and JP-A-4-363366 have been proposed. In all of these, tin oxide or tin oxide doped with a different element such as antimony is used as the conductive fine powder. Therefore, its conductive function remains within the range of antistatic property, and it cannot be said that it is sufficient for the above-mentioned applications from the viewpoint of transparency. Also,
As a transparent conductive coating material using ITO fine powder, for example, Japanese Patent Publication No. 2-55461 is used to hydrolyze an aqueous solution of a tin compound or an indium compound under a pH of 8 to 12 to form a sol containing colloidal particles. It has been proposed to use conductive fine powder obtained by drying and firing a sol and then pulverizing it. However, in this method, when the colloidal particles are filtered off from the sol solution, the by-product salt is not easily removed and the conductivity is apt to be lowered, and the obtained coating film is not always satisfactory in transparency. , Haze value is also high, etc.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a transparent conductive paint capable of forming a tin-containing indium oxide (ITO) film having excellent transparency and conductivity. Especially.

[0005]

According to the present invention, a hydrate of tin oxide and indium oxide obtained by adding an alkaline aqueous solution to a solution of tin salt and indium salt while keeping the temperature at 30 ° C. or lower is heat-treated. The present invention relates to a conductive paint containing the conductive tin-containing indium oxide fine powder obtained by the above, a paint binder, and a solvent.

The ITO fine powder used in the present invention is obtained by heat treating a hydrate of tin oxide and indium oxide obtained by adding an alkaline aqueous solution to a solution of tin salt and indium salt while keeping the temperature at 30 ° C. or lower. It is obtained by doing. The tin salt and indium salt used may be water-soluble ones, such as tin chloride, tin sulfate, tin nitrate, indium chloride,
Examples thereof include indium sulfate and indium nitrate, and the tin salt may be either a stannous salt or a stannic salt. After dissolving such tin salt and indium salt in water and adding a water-soluble organic solvent such as alcohol or acetone and / or a mineral acid such as hydrochloric acid or nitric acid, if necessary, the temperature is 30 ° C. or lower, preferably Is 0
Add aqueous alkali solution while maintaining ~ 20 ° C. 30 ° C
If it exceeds, depending on other conditions, the particle size is generally coarse, and particles having a needle-like shape or particles having an aggregated form are produced. Even if the temperature is lower than 0 ° C., the effect is not particularly improved, and the cost of the cooling refrigerant or the like increases. Also,
In this case, the ratio of tin and indium is 1:99 to 20:80, preferably 4:96 to 15:85 in terms of SnO ₂ : In ₂ O ₃ weight ratio. If it is too small, the desired conductivity cannot be obtained.

The concentration at this time is (SnO ₂
+ In ₂ O ₃ ) concentration of _{2 to} 50 g / l is suitable, and 2 g / l
If it is less than 1, the yield is low and it is uneconomical, and if it exceeds 50 g / l, the particle size becomes coarse.

As the alkaline aqueous solution, ammonia water,
Examples thereof include aqueous solutions of alkali hydroxide, alkali carbonate, ammonium carbonate and the like, but alkali metal salts containing a component that inhibits conductivity are not suitable, and aqueous ammonia and ammonium salt solutions are preferred. Then, a hydrate of tin oxide and indium oxide is produced by finally adding such an alkaline aqueous solution so that the pH becomes 5.0 to 9.0. If the pH is less than 5.0, the reaction is incomplete, and if the pH is
On the other hand, if it exceeds 9.0, deflocculation of some products occurs, and in any case, sintering is caused in the subsequent heat treatment step, and coarse particles are generated.

The addition time of the alkaline aqueous solution is not particularly limited, but is preferably about 30 minutes to 12 hours,
If the time is less than 30 minutes, the product becomes a gel, which makes filtration and washing difficult, and causes sintering in the subsequent heat treatment step. When the addition time is 12 hours or more, the productivity is lowered and the particle size becomes coarse.

Under the above conditions, the primary particle size is 0.01
A hydrate of tin oxide and indium oxide having a size of about 5 to 0.05 μm is formed. In the present invention, the hydrate is optionally dried after removing by-produced salts, and further heat-treated at 300 to 1200 ° C., preferably 500 to 1000 ° C. A fine powder of indium oxide can be obtained. In this case, if necessary, the conductivity is further improved by treating in an atmosphere of an inert gas such as N ₂ or Ar or a reducing atmosphere such as H ₂ or NH ₃ . The obtained ITO fine powder has colloidal particles in the conventional method when it is produced as a hydrate, but already has a skeleton as primary particles of about 0.015 to 0.05 μm, and is then dried and heat treated. Since it is crystallized without causing sintering in the process, it is a fine powder having a uniform particle size and not containing coarse particles.

The paint binder used in the present invention is
Any resin that can be used by ordinary coating technology may be used, and examples thereof include acrylic resins, vinyl resins, carbonate resins, polyester resins, urethane resins, epoxy resins, polypropylene resins, phenol resins, polyamide resins, and polyimide resins. It may also be a mixture or copolymer of these resins.

The content of the ITO fine powder is preferably mixed so as to be 40 to 95% by weight in the solid content of the conductive coating material. If the ITO fine powder is less than 40% by weight, the conductivity of the resulting coating film is not sufficient, and if it exceeds 95% by weight, the dispersion is poor and the transparency of the coating film and the adhesion to the substrate are impaired.

The conductive paint of the present invention can be obtained by dispersing or dissolving ITO fine powder and a paint binder in a solvent. As the solvent, any solvent that can dissolve the paint binder can be used, and alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, and cyclohexanol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, Examples thereof include ethers such as methyl cellosolve and ethyl cellosolve, esters such as ethyl acetate and methyl cellosolve acetate, hexane, cyclohexane, toluene and xylene. When a water-soluble resin is used, water can be used as the solvent. The use ratio of these solvents is not particularly limited and may be set according to the purpose of use, but the solid content in the coating material may be set in consideration of dispersion, viscosity and the like.
It is preferable that the amount is 10 to 90% by weight.

The conductive coating material of the present invention is prepared by the above-mentioned IT.
It is carried out by mixing O fine powder, a coating binder and a solvent with a ball mill, a sand mill, a paint shaker, a three roll, etc. which are usually used. At that time, a coupling agent such as a silane-based or titanate-based coupling agent or a surfactant may be added for the purpose of improving dispersibility.

The conductive coating material of the present invention prepared as described above is prepared by spraying, bar coating, dipping,
It is applied to a base material by a coating method such as a doctor blade method, and is put to practical use by being dried or optionally heat-treated.

[0016]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 5.9 g of stannous chloride (SnCl ₄ .5H ₂ O) and 75.9 g of indium chloride (InCl ₃ ) were dissolved in 4000 ml of water, and 2% aqueous ammonia was added thereto over 58 minutes to obtain a pH value. Was finally set to 7.85 to coprecipitate a hydrate of tin oxide and indium oxide. During this period, the liquid temperature was kept at 5 ° C. Then, the coprecipitate is washed, dried, and further calcined at 900 ° C. for 2 hours to obtain a tin-containing indium oxide (ITO) fine particle having a primary particle diameter of about 0.02 μm and a fine particle size not including coarse particles. A powder was obtained. 40 g of the ITO fine powder, 8 g of polyester resin, 50 g of (toluene-MEK-ethyl acetate) mixed solvent, and 1 g of a nonionic surfactant were mixed for 8 hours with a paint conditioner using zirconia beads as a dispersion medium to obtain a transparent conductive material. A paint was prepared.

Example 2 40 g of ITO fine powder obtained in the same manner as in Example 1, 8 g of polyamide resin, 50 g of mixed solvent of (toluene-i-propanol), and 1 g of nonionic surfactant were used as a medium for dispersing zirconia beads. Was mixed for 8 hours with a paint painter to prepare a transparent conductive paint.

Example 3 3.9 g of stannous chloride (SnCl ₂ .2H ₂ O) and 121.6 g of indium nitrate [In (NO ₃ ) ₃ .3H ₂ O] were dissolved in 4000 ml of water, and 2% aqueous ammonia was added thereto. Was added over 73 minutes to bring the pH to 7.80 to coprecipitate the hydrates of tin oxide and indium oxide. During this time, the liquid temperature was kept at 20 ° C. The coprecipitate is then washed and dried, then 900
Firing at 2 ° C. for 2 hours gave an ITO fine powder having a primary particle size of about 0.035 μm and a fine particle size that was fine and did not contain coarse particles. 40 g of the ITO fine powder, 8 g of urethane resin, 50 g of (xylyl-butyl acetate) mixed solvent, and 1 g of nonionic surfactant were mixed for 8 hours with a paint conditioner using zirconia beads as a dispersion medium, and a transparent conductive paint was obtained. Was prepared.

Example 4 5.9 g of stannic chloride (SnCl ₄ .5H ₂ O) and 75.9 g of indium chloride (InCl ₃ ) were dissolved in 4000 ml of water, and 4.5% thereof was added.
The NH ₄ HCO ₃ aqueous solution was added over 360 minutes to finally adjust the pH.
By setting it to 5.8, a hydrate of tin oxide and indium oxide was coprecipitated. During this period, the liquid temperature was maintained at 25 ° C. Then, the coprecipitate is washed and dried, and further at 700 ° C. for 2
Firing was carried out for a period of time to obtain an ITO fine powder having a primary particle size of about 0.045 μm and having a fine particle size that was fine and did not contain coarse particles. Using the ITO fine powder, a transparent conductive paint was prepared in the same manner as in Example 1.

Comparative Example 1 IT was carried out in the same manner as in Example 1 except that the liquid temperature was maintained at 35 ° C.
O fine powder was obtained. The fine powder had a needle-like shape with a minor axis diameter of 0.05 to 0.07 μm and a major axis diameter of 0.30 to 0.35 μm. Using the fine powder, a conductive coating material was prepared in the same manner as in Example 1.

Comparative Example 2 I was prepared in the same manner as in Example 1 except that pH was finally set to 4.5.
TO fine powder was obtained. The fine powder contained a large amount of coarse particles. Using the fine powder, a conductive coating material was prepared in the same manner as in Example 1.

Comparative Example 3 I was prepared in the same manner as in Example 1 except that the final pH was 9.5.
TO fine powder was obtained. The fine powder contained a large amount of coarse particles as in Comparative Example 2. Using the fine powder, a conductive coating material was prepared in the same manner as in Example 1.

Comparative Example 4 IT was carried out in the same manner as in Example 1 except that the addition time was 20 minutes.
O fine powder was obtained. The fine powder contained a large amount of coarse particles as in Comparative Example 2. Using the fine powder, a conductive coating material was prepared in the same manner as in Example 1.

Test Example 1 Each coating material prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was applied onto a polyester sheet using a 1 mil doctor blade and dried at room temperature to obtain a coating film. Table 1 shows the results of measuring the surface resistance value of each coating film with Loresta FP (manufactured by Mitsubishi Yuka) and the total light transmittance and haze value with a haze meter (manufactured by Nippon Denshoku Co., Ltd.).

[0026]

[Table 1]

[0027]

EFFECT OF THE INVENTION Since the conductive coating material of the present invention uses ITO fine powder having a uniform particle size and not containing coarse particles as a conductive component, a coating film formed by using the ITO fine powder is transparent and conductive. It is excellent and useful as an antistatic coating, and also as a transparent electrode or a transparent conductive film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshijuro Kanazawa 1 at 96 Ikuno, Dojo Town, Kita Ward, Kobe City, Hyogo Prefecture Fuji Titanium Industry Co., Ltd. Kobe Research Laboratory

Claims (1)

[Claims] 1. A solution of tin salt and indium salt is heated to a temperature of 30.
A conductive tin-containing indium oxide fine powder obtained by heat treatment of a hydrate of tin oxide and indium oxide obtained by adding an alkaline aqueous solution while keeping the temperature below ℃, a coating binder and a solvent are contained. Characteristic conductive paint.