JPH0619074B2 - Conductive paint - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a conductive coating material, and more particularly to a conductive coating material capable of forming a conductive coating film having excellent transparency.

TECHNICAL BACKGROUND OF THE INVENTION AND PROBLEMS THEREOF In recent years, it has been frequently attempted to prevent the base material from being charged by imparting conductivity to a transparent base material such as glass or plastics.

In order to impart conductivity to a base material, conventionally, a carbon powder, a metal powder, carbon fibers or a metal fiber is mixed on the surface of the base material and a coating material to which conductivity is imparted has been applied. However, this paint has a problem that the color tone of the base material is impaired because the paint film is gray or black. This is because carbon powder, metal powder, carbon fiber or metal fiber itself absorbs light.

Further, in order to impart conductivity to the base material, a method of forming a conductive coating film by applying a conductive coating material obtained by dispersing or dissolving conductive powder and a binder resin in an organic solvent to the surface of the base material is used. It has been widely practiced. In order to form a conductive coating film having excellent transparency, tin oxide, indium oxide and the like have been used as the conductive powder.

However, when trying to form a transparent conductive coating film using a conductive oxide such as tin oxide or indium oxide as the conductive powder, the transparency is not always satisfactory, and haze occurs on the surface of the base material. There was a problem that it would end up.

If a base is formed when a coating film is formed on the surface of a substrate, an image becomes unclear with a display material such as a display. The cause of such haze is considered to be light scattering due to irregularities on the surface of the coating film or light scattering due to conductive particles inside the coating film.

In order to prevent the unevenness of the surface of the coating film or the scattering of light by the conductive particles, the average particle diameter of the conductive particles contained in the coating film is made small, and 0.8 μm or more, preferably 0.
The proportion of coarse particles of 4 μm or larger must be reduced.

In order to solve the problems associated with the transparency of such a transparent conductive coating film, for example, Japanese Patent Publication No. 61-9343 discloses a tin oxide containing mantimon, the average particle size of which is visible light. A conductive paint using a conductive powder having a wavelength of 0.2 μm or less, which is smaller than the wavelength, is disclosed.

However, in the conductive paint disclosed in Japanese Examined Patent Publication No. 61-9343, an aqueous solution in which a specific amount of tin chloride and antimony chloride is dissolved is poured into heated water to hydrolyze the chloride to precipitate a precipitate. Since the electroconductive powder having a particle size of 0.2 μm or less is produced by performing the heat treatment after filtering and washing, the following problems occur. That is, as disclosed in the above publication, when a precursor of conductive fine powder is precipitated in a liquid by hydrolyzing a halide, the resulting precipitate is in a state in which extremely fine primary particles are aggregated. For this reason, the fine powder obtained by filtering and washing the precipitate and then heating the primary particles is sintered and the particle size distribution is generally broad.

Therefore, when the conductive fine powder is mixed and dispersed in the plastic or paint, it is necessary to grind the sintered fine powder in order to make the mixed dispersion uniform. However, the conductive fine powder before the heat treatment, which is manufactured through the above-described precipitation forming step, has a very small particle size and high surface activity, so that the binding force between the particles is strong and the powder is sintered during the heat treatment. However, the crushing is not always easy. In addition to this, even if it is pulverized by pulverization and its average particle size is reduced, it is not possible to obtain conductive fine particles with a sharp particle size distribution. There was a problem in that a relatively large amount of surfactant had to be used for the purpose of cleaning.

OBJECT OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and to form a coating film having excellent conductivity and transparency on a substrate such as glass or plastic. It is an object of the present invention to provide a method for producing a conductive paint that can be formed.

SUMMARY OF THE INVENTION The conductive coating material according to the present invention includes (a) tin oxide colloid in which tin oxide fine particles or tin oxide fine particles doped with a different element are dispersed in a dispersion medium, and (b) a binder resin dissolved in a solvent. Alternatively, it is dispersed.

The conductive paint according to the present invention comprises (a) tin oxide colloid and
(b) A binder resin is formed by being dissolved or dispersed in a solvent, and the average particle diameter of tin oxide, which is the conductive particle in the paint, is extremely fine at 0.1 μm or less, and is 0.8 μm or more. Since coarse particles having a particle size are scarcely included, a conductive coating film having excellent transparency can be formed.

DETAILED DESCRIPTION OF THE INVENTION The conductive coating material according to the present invention will be specifically described below.

Conductive paint according to the present invention, (a) tin oxide colloid,
(b) The binder resin is dissolved or dispersed in the solvent.

In the present specification, the tin oxide colloid means a colloid in which tin oxide fine particles, tin oxide fine particles doped with a different element, or both are dispersed in water or an organic solvent.

The average particle size of tin oxide particles in a tin oxide colloid or tin oxide particles doped with a different element is usually 0.1 μm.
m or less and 60% or more of all particles, preferably 70%
The above has a particle size of 0.1 μm or less, and contains almost no coarse particles of 0.8 μm or more, which significantly reduce the transparency of the coating film.

Such tin oxide colloid can be manufactured as follows.

First, tin oxide fine powder is prepared, and this tin oxide fine powder is heat-treated in an acid aqueous solution or an alkaline aqueous solution to produce a tin oxide colloid.

Here, the tin oxide fine powder refers to tin oxide itself fine powder or tin oxide with antimony, fluorine, phosphorus, tellurium,
It means a fine powder of tin oxide which is lightly doped with one or more elements such as bismuth and cadmium. A method for producing such tin oxide fine powder is conventionally known,
For example, an alcohol solution in which tin chloride and antimony chloride are dissolved, an aqueous solution of hydrochloric acid or an acetone solution is added to heated water for hydrolysis, and the resulting precipitate is dried and then calcined to obtain antimony-doped tin oxide fine powder. (Japanese Patent Application Laid-Open No. 56-156)
606). In addition, the tin compound solution is
By maintaining the condition of ~ 12 to gradually hydrolyze the compound in the liquid to generate a sol containing colloidal particles, and then drying and firing the sol,
It is also possible to produce fine powders of tin oxide.

The method for producing the tin oxide fine powder is described in detail in Japanese Patent Application No. 62-51008 filed by the applicant of the present invention. Any tin oxide fine powder produced by a known method can be used, including tin oxide obtained by the above-mentioned production method, but these fine powders are subjected to a baking treatment for the purpose of imparting conductivity. Therefore, the primary particles of tin oxide are in a sintered state, and the powder of this tin oxide tin oxide usually has a particle size in the range of several μ to several + μ.

When such tin oxide powder is heat-treated in an acid aqueous solution or an alkaline aqueous solution, a tin oxide colloid is obtained. The amount of tin oxide fine powder added to the aqueous acid solution or the aqueous alkali solution is preferably 40 parts by weight or less per 60 parts by weight of the aqueous solution. If too much tin oxide powder is added, it is difficult to make acid or alkali act on each tin oxide fine powder evenly, so it is difficult to make a sol. Because it cannot be held.

Mineral acids such as sulfuric acid and hydrochloric acid, oxycarboxylic acids such as tartaric acid and lactic acid, and carboxylic acids such as oxalic acid are used as acids, and alkalis such as sodium hydroxide and potassium hydroxide are used. Alkali metal hydroxides or quaternary ammonium salts are used. The amount of the acid or alkali used is at least 5% by weight of the powder to be treated, and if the amount is less than this amount, the tin oxide fine powder cannot be converted into a sol. On the other hand, increasing the amount of acid or alkali used
It does not cause any particular inconvenience, but is not highly recommended from an economic standpoint.

The temperature at the time of heat treatment can be arbitrarily selected within the range of 30 to 200 ° C. When a temperature higher than the boiling point of the acid aqueous solution or the alkaline aqueous solution is adopted, it is necessary to pressurize the solution so that it can maintain the liquid phase. In addition, usually, even if the treatment temperature is 200 ° C. or higher, no particularly advantageous result is brought about. The time required to make the tin oxide fine powder into a sol depends on the amount and particle size of the added fine powder, but is generally related to the processing temperature, and if the processing temperature is high, the fine powder will be solized in a short processing time. be able to.

In the heat treatment, an acid or alkali aqueous solution,
It is preferable to carry out stirring for the purpose of ensuring good contact with the fine powder. In this case, not only simple stirring but also an apparatus capable of pulverizing the powder to some extent, for example, an appropriate pulverizer such as an attritor, a sand mill and a ball mill can be used at the same time to further promote the sol formation of the fine powder. In addition, it is also effective to previously pulverize the tin oxide powder to be subjected to the heat treatment with the above pulverizer in order to promote the sol formation.

By treating the tin oxide powder as described above, an aqueous sol in which tin oxide is dispersed as colloidal particles using an acid aqueous solution or an alkaline aqueous solution as a dispersion medium is prepared. This aqueous sol can be deoxidized or dealkalized as necessary. For example, dealkalization may be performed by ion exchange treatment.

Further, the tin oxide organonozzle can be obtained by substituting the dispersion medium water with a hydrophilic organic solvent as it is or after deoxidizing or dealkalizing the aqueous sol. Then, in order to replace such water with an organic solvent, a known method can be adopted, and as the hydrophilic organic solvent,
Alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol, ethylene glycol, trimethylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, tetrahydrofuran, etc. Ethers, methanolamine, ethanolamine,
Amines such as morpholine, acid amides such as dimethylformamide and N-methyl-2-pyrrolidone are used.

A tin oxide colloid is obtained in this way, but when the raw material tin oxide powder is viewed microscopically, this powder is regarded as a set of sintered bodies in which some of the fine primary particles are sintered in the firing process. However, if this powder is heat-treated in an aqueous acid or alkaline solution, the acid or alkali acts on the sintered parts of the individual sintered bodies to loosen their bonds or significantly reduce their bonding strength. Therefore, it is considered that the tin oxide fine powder is made into a colloidal size by an operation of stirring the tin oxide dispersion liquid.

The method for producing the above tin oxide fine powder is described in detail in Japanese Patent Application No. 61-75283 filed by the present applicant.

As the (b) binder resin used in the present invention, those conventionally used as a binder resin in conductive paints are widely used. Specifically, for example, vinyl chloride resin, vinyl acetate resin, polyester resin, acrylic resin, urethane resin, epoxy resin, polycarbonate resin, melamine resin, butyral resin, polyimide resin, polysulfone resin. , A polyether sulfone resin or an ultraviolet curable resin is used. Also, a mixture of the above resins or a copolymer of the above resins can be used.

The mixing ratio of the (a) tin oxide colloid and the (b) binder resin is 40 to 95% by weight based on the total weight of the tin oxide fine particles or the tin oxide fine particles doped with a different element, and the binder resin. Preferably 60-9
It is preferably used in an amount of 0% by weight. (a) If the tin oxide colloid is less than 40% by weight, the conductivity of the coating film obtained will be poor, while if it exceeds 95% by weight, the adhesion between the coating film and the substrate and the transparency of the coating film obtained will be poor. It is not preferable because it gets worse.

In the conductive paint according to the present invention, the above components are dissolved or dispersed in a solvent, as the solvent,
(b) It can be used as long as it can dissolve the binder resin, and specifically, for example, methyl ethyl ketone,
Methyl isobutyl ketone, toluene, cyclohexane,
Isopropanol, n-butanol and the like are used alone or in combination. Such an organic solvent is used in an amount such that the conductive paint has a viscosity such that it can be applied onto the substrate. When a water-soluble binder resin is used, water can be used as the solvent.

In the conductive coating material according to the present invention, in addition to the above (a) tin oxide colloid and (b) binder resin, in order to prevent the reaggregation of particles by improving the dispersibility of the tin oxide colloid, a surfactant is added. A wide variety of surfactants such as anionic, nonionic and cationic surfactants can be used. Further, a coupling agent may be added to the conductive coating material in order to improve the dispersibility of the tin oxide colloid and prevent reaggregation of particles.
As such a coupling agent, a silane-based, titanium-based, aluminum-based, zirconium-based, or magnesium-based coupling agent is used.

The method for producing a conductive coating material according to the present invention will be described below. (A) Tin oxide colloid and (b)
It is obtained by adding a binder resin and the like to a solvent and then uniformly dispersing it in the binder resin.

The base according to the present invention is a conductive coating such as the above glass,
A conventionally known coating method such as a bar coating method, a spraying method, a roll coating method, a spinner method, a dip method, a mail bar method, an air knife method, a gracia printing method or a screen printing method on a transparent substrate such as plastic. When applied and then dried, a conductive coating film is obtained.

EFFECTS OF THE INVENTION The conductive paint according to the present invention comprises (a) tin oxide colloid and
(b) A binder resin is formed by being dissolved or dispersed in a solvent, and the average particle diameter of tin oxide, which is the conductive particle in the paint, is extremely fine at 0.1 μm or less, and is 0.8 μm or more. Since coarse particles having a particle size are scarcely included, a conductive coating film having excellent transparency can be formed.

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

Example 1 310.0 g of potassium stannate and 38.4 g of tartar were dissolved in 686 g of water to prepare a raw material liquid. The above-mentioned raw material liquid was added together with nitric acid to 1000 g of water heated to 50 ° C. under stirring over 12 hours, and the pH in the system was kept at 8.5 to cause hydrolysis to obtain a sol. . After colloidal particles are filtered out from this sol and washed to remove by-product salts, the particles are dried, calcined in air at 350 ° C. for 3 hours, and further calcined in air at 650 ° C. for 2 hours to obtain a fine powder. Obtained (fine powder A).

300 g of the fine powder A thus obtained was added to 700 g of an aqueous potassium hydroxide solution (containing 30 g of KOH), and a tin oxide colloid was obtained while stirring the mixed solution at 30 ° C. for 3 hours with a sand mill. Then, the tin oxide colloid was treated with an ion exchange resin to obtain a dealkalized tin oxide colloid. The dealkalized tin oxide colloid contained no precipitate, the solid content concentration was 30% by weight, and the average particle diameter of the colloid particles was 0.07 μm. The amount of particles having a size of 0.1 μm or less was 86% of all particles.

Tin oxide colloid 10 dealkalized in this way
0 g and 20 g of acrylic emulsion resin were added to 380 g of a water / methanol (weight ratio 1/1) mixed solvent and sufficiently stirred to obtain a paint. This coating material was applied to a glass plate with a bar coater # 6 and dried at 110 ° C for 10 minutes to obtain a coating film.

Example 2 To 200 g of the dealkalized tin oxide colloid obtained in Example 1, 800 g of n-butanol was added, and then water and a part of n-butanol were distilled off with a rotary evaporator to disperse n-butanol as a dispersion medium. An organotin oxide colloid was obtained. This organotin oxide colloid contained no precipitate, the solid content concentration was 30% by weight, and the average particle diameter of the colloid particles was 0.07 μm. 0.1 μm
The amount of particles below was 86% of all particles.

Organo tin oxide colloid 10 thus obtained
0 g and 15 g of butyral resin were added to 100 g of a mixed solvent of i-propanol / n-butanol (weight ratio 1/1) and sufficiently stirred to obtain a paint. Apply this paint to a bar coater # 6
Was coated on a PET film by the above method and dried at 110 ° C. for 10 minutes to obtain a coating film.

Comparative Example 1 30 g of the tin oxide fine powder A obtained in Example 1 and 15 g of butyral resin were added to 100 g of iso-propanol / n-butanol (weight ratio 1/1) mixed solvent and sufficiently stirred to obtain a paint. . The average particle size of the conductive tin oxide in this paint is 0.3 μm, and the amount of particles of 0.1 μm or less is
It was 7% of all particles. This coating material was applied onto a PET film with a bar coater # 6 and dried at 110 ° C for 10 minutes to obtain a coating film.

Comparative Example 2 A solution was prepared by dissolving 173 g of tin chloride and 20.9 g of antimony chloride in 300 cc of methanol. The solution obtained as described above was added to 3000 g of water heated to 90 ° C. and under stirring for 4 hours to cause hydrolysis, and the formed precipitate was separated by filtration, washed, dried and dried. Medium 50
It was baked at 0 ° C. for 2 hours to obtain a tin oxide fine powder.

150 g of the tin oxide fine powder thus obtained and 64 g of butyral resin were added to and mixed with 500 g of a mixed solvent of iso-propanol / n-butanol (weight ratio 1/1), and this was mixed with a sand mill 2 It was crushed for an hour to obtain a conductive paint.

A coating film was obtained in the same manner as in Example 1 using this conductive paint.

The average particle diameter of the conductive fine particles in the conductive coating material thus obtained was 0.32 μm, and in this conductive coating material, particles having a particle diameter of 0.8 μm or more were contained in an amount of about 20% by weight. Existed.

The average particle of the conductive fine particles contained in the paints obtained in the above-mentioned Examples and Comparative Examples was measured by using an ultracentrifugal particle size measuring device (manufactured by Horiba, Ltd.) and the solid content concentration of the measurement sample liquid was 0.5.
It was adjusted to the weight% and measured at 5000 rpm. The total light transmittance (Tt) and haze (H) of the obtained coating film were measured by a haze computer (manufactured by Suga Test Instruments Co., Ltd.), and the surface resistance (Rs) was measured by an electrode cell (manufactured by YHP).

The results are shown in Table-1.

From Table 1, it can be seen that the conductive paint according to the present invention is a conductive paint having excellent conductivity and transparency.

Claims (1)

[Claims] 1. A tin oxide colloid having (a) tin oxide fine particles or tin oxide fine particles doped with a different element dispersed in a dispersion medium, and (b) a binder resin dissolved or dispersed in a solvent. Characteristic conductive paint.