JPH0458511B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating material that is transparent, electrically conductive, and capable of forming a coated film having antistatic properties, and particularly to a conductive transparent coating material that is stable against moisture. In recent years, there has been a rapid increase in the number of cases in which static electricity prevention is required for IC storage containers, other electronic and electrical equipment components, and architectural components such as carpets, flooring materials, and wall materials. Additionally, there is an increasing demand for conductive paints to prevent electromagnetic interference caused by microwaves. Conventionally, in response to such requests, paints made of conductive materials mixed with carbon powder, metal powder, or carbon fibers or metal fibers were applied, and organic materials with ion conductivity such as alkylamine halides were applied. was used to impart conductivity to the nonconductor and prevent it from being charged. However, in the former case, the color tone of the coated film becomes gray or black, so In the latter case, it is possible to form a transparent film with antistatic ability by applying it, but it will not become static unless the humidity is high. They have the disadvantage that they do not have a protective effect and are easy to peel off. Furthermore, if a solvent that does not dissolve water at all or hardly dissolves water is used in these paints, precipitation may occur due to moisture from the atmosphere during storage. There were flaws. From the above-mentioned viewpoints, the present inventors have discovered that the coating film itself has transparency that does not impair the color tone of the base, has excellent coating film adhesion, and has good electrical conductivity. When applied to a nonconductor, it imparts good conductivity and exhibits sufficient antistatic ability, and can be stored stably without being affected by moisture in the atmosphere. As a result of repeated research to obtain paints, we found that (a) Tin oxide (hereinafter referred to as SnO ₂ ) powder is white and conductive, but when antimony (Sb) is added to it, it becomes even more conductive. should be improved and thermally stable. (b) In order to prevent the transparency and color tone of the paint from being impaired even when the powder is mixed in, it is necessary that the powder to be mixed in does not absorb light, that is, it has a white color.
and its optical refractive index is close to the optical refractive index of the resin, which is the main component of the paint: 1.6 to 1.7, or the average particle size of the powder is 0.4 μm or less, that is, smaller than the wavelength of visible light, and the light scattering It is necessary that there be less (c) The above Sb-containing SnO ₂ powder has an optical refractive index of 2.0 to 2.1, so it can be used in paints for the purpose of imparting conductivity without impairing their color tone, especially transparency. When mixing, it is necessary to refine the average particle size to 0.4 μm or less. (d) In general, there are various synthetic resins including polyester resin as the main component for forming the coating film of paints, and various organic solvents such as tunnel are conventionally used as solvents, but there are also various types of solvents such as toluene. If a solvent that does not easily absorb water is used, the fine powder will separate and coagulate from the paint due to moisture entering the paint mixed with the fine powder during storage or during application. If you use a solvent that dissolves water, it will absorb water and this separation and coagulation will be less likely to occur. (e) In order to suppress the separation and coagulation of such fine powders, it is necessary to have a solvent that dissolves 3% or more of water in the paint solvent in an amount of 20% or more by weight. The findings shown in sections (a) to (e) above were obtained. This invention was made based on the above knowledge, and contains Sb: 0.1 to 20% by weight, with the remainder being substantially
A conductive fine powder with a composition of SnO ₂ and an average particle size of 0.4 μm or less, a resin that is the main element for forming a coating film, and a solvent in which at least 20% by weight dissolves at least 3% by weight of water. and a water-dissolving solvent consisting of one or more of MEK cyclohexane, THF, and acetone, and the blending ratio of the conductive fine powder is 5 to 5% of the total weight of the conductive fine powder and the resin. 95%, and the blending ratio of the solvent is 100 to 2000 parts per 100 parts of the total weight of the conductive fine powder and the resin.
By weight, it has good conductivity and antistatic ability, is transparent and can form a coating film without affecting the color tone of the base, and is stable against moisture intrusion. It is something. In the paint of this invention, synthetic resins used in general transparent paints such as acrylic, vinyl, carbonate, polyester, urethane, epoxy, and polyalkylene paints are used as the main component for forming the coating film. Can be done. In the paint of this invention, "a solvent that dissolves 3% by weight or more of water" means a solvent that has a water solubility of 3% by weight or more at the temperature normally encountered when the paint is stored or used, that is, at room temperature. , methyl ethyl ketone (MEK), cyclohexanone, tetrahydrofuran (THF), and acetone. In addition to the above-mentioned solvents that dissolve 3% by weight or more of water, the solvents of this invention include solvents that do not dissolve water at all or hardly, that is, solvents that dissolve less than 3% by weight of water, such as toluene,
It may contain less than 80% by weight of solvents commonly used in paints, such as xylene, cellosolves such as cellosolve acetate, petroleum spirits, solvent naphtha, methylene chloride, etc. The conductive fine powder and the main coating film-forming elements constituting the paint of this invention are designed to, on the one hand, provide the desired good conductivity and antistatic ability, and on the other hand, to ensure conductivity so as not to impair the transparency of the paint film. Fine powder: 5~
It is preferable to mix the ratio of 95% by weight to 95% to 10% by weight of the main elements forming the coating film, and the remaining component, the solvent, makes it easier to apply the paint and disperses the conductive fine powder appropriately and uniformly. For example, 100 to 2000 parts of the solvent may be added to 100 parts of the total weight of the conductive fine powder and the main coating film forming elements.
Parts by weight can be added. The paint of this invention is produced by mixing the main film-forming element such as polyester resin with a solvent, and then adding and mixing conductive fine powder thereto. To improve dispersibility, anionic surfactants such as sodium phosphate, sodium sulfonate, sodium oleate, sodium stearate, and sodium citrate, silane coupling agents such as alkylsilanes and alkoxysilanes, and alkyl titanates are used. A titanate coupling agent such as acrylic titanate or the like may be mixed and contained in the paint. Furthermore, the paint of this invention can be applied by any coating method used for general paints, but especially when spraying, bar coating, gravure coating, roll coating, and doctor blade methods are adopted. , good results are obtained. Next, in the coating material of the present invention, the reason why the Sb content and average particle size of the conductive fine powder and the water solubility and blending ratio of the solvent are limited as described above will be explained. (a) Sb content If the Sb content is less than 0.1% by weight, the electrical resistance will be high and the desired good conductivity cannot be secured, so the antistatic ability will not be sufficient. In this case, the fine powder loses its white color and becomes bluish, which impairs the color tone and transparency when mixed into paint. % by weight. (b) Average particle size If the average particle size exceeds 0.4μm, visible light will be scattered more and the transparency of the paint will be impaired when mixed into the paint. The average particle size must be as follows. The average particle size of the conductive fine powder in the conductive transparent paint of the present invention is determined by first placing 5 g of the fine powder and 40 cc of water in a polyethylene cylindrical container with an inner diameter of 45 mm and a capacity of 100 cc. After charging with 50 sintered alumina balls with a diameter of approximately 10 mm and rotating this container at a rotation speed of 400 rpm for 10 hours,
The contents, excluding the sintered alumina balls, are placed in a container of a centrifugal sedimentation device, and the powder is sedimented while changing the rotation speed and rotation time of the centrifugal sedimentation device, and the weight of each sedimented powder is measured. Based on this, a particle size distribution was created, and the average particle size was determined by taking the cumulative value of 50% of the particle size distribution. (c) Water solubility of the solvent and blending ratio of the solvent As the solvent for the conductive transparent paint containing the conductive fine powder and resin of this invention, a solvent that dissolves less than 3% by weight of water is used, or a solvent that dissolves less than 3% by weight of water is used. When less than 20% by weight of a solvent is used, when the paint is left in the atmosphere at a relative humidity of 70% and a temperature of 20°C, fine particles will be separated within 0.5 hours.
Coagulation is observed, but if the total solvent contains 20% by weight or more of a solvent that dissolves 3% or more of water, the above separation and coagulation will not occur within 3 hours, and the paint will not dissolve for more than 3 hours. As the water solubility of the solvent and the blending ratio of the solvent increase, the stability of the paint against water increases. and 20% by weight or more. The conductive fine powder of the present invention is produced by dissolving tin chloride (hereinafter referred to as _SnCl4 ) and antimony chloride (hereinafter referred to as _SbCl3 ) in one or more mixed liquids of alcohol, hydrochloric acid aqueous solution, and acetone. It can be produced by a method in which a solution consisting of Sb-containing SnO ₂ is precipitated by adding it to heated water. Incidentally, Sb-containing SnO ₂ powder manufactured by a known method such as a method of firing SnO 2 powder and an Sb compound, or a method of mixing a Sn compound and _an Sb compound and then firing, both have a concentration of 0.4 The electrically conductive fine powder of the present invention having an average particle size of more than 0.4 μm cannot be produced by these known methods. Next, the conductive transparent paint of the present invention will be specifically explained with reference to Examples. Example While heating and maintaining 3000 cc of water at a temperature of 90°C and stirring vigorously, 173 g of SnCl ₄ and 20.9
Sb-containing SnO ₂ was obtained by slowly injecting a solution of 1 g of SbCl ₃ dissolved in 300 cc of alcohol over 4 hours.
Precipitate a powder, then separate this powder,
For the purpose of cleaning and subsequently improving crystallinity,
Heat treated in air at a temperature of 500°C for 2 hours to produce a Sb-containing product with an average particle size of 0.2 μm, containing 10% by weight of Sb and the remainder consisting of SnO _2
SnO2 fine powder was obtained. Then, a solvent having the composition shown in Table 1
24 g of the above Sb-containing SnO ₂ fine powder was added to a solution of 35 g of polyester resin (Toyobo Vylon 20) dissolved in 315 g, mixed and dispersed in a ball mill for 17 hours, and made into a paint to produce paints 1 to 4 of the present invention. Comparative paints 1 to 3 were produced in the same manner as above, except that a solvent outside the scope of the present invention was used, and these are shown in Table 1. The coating films formed by applying these paints immediately after manufacture have a coating thickness of 1 μm, a surface resistance of 10 ⁷ to 10 ⁸ Ω/mouth, a transparency of 80% in total transmission, and a haze of 20 to 30. It was %. In addition, 450 cc of each of these paint samples was placed in a cylindrical aluminum container with a diameter of 9 cm and a height of 7 cm, and mixed using a commercially available stirrer.
When the sample was stirred at a stirring speed of 62.5 rpm and left in an atmosphere at a temperature of 20°C and a relative humidity of 70%, conductive fine powder was removed from the paint after the time shown in Table 1.

[Table] Separated and coagulated. The fine powder was separated and coagulated at the time when the viscosity of the sample during stirring rose to five times the initial viscosity (usually 2 to 100 centipoise). From the results shown in Table 1, the present invention paints 1 to 4
are all extremely stable against moisture, whereas Comparative Paint 1 using a solvent outside the scope of the present invention
~3, conductive fine powder separates and coagulates in a short time,
It can be seen that it is unstable against the intrusion of moisture in the atmosphere. As mentioned above, the paint of the present invention has excellent conductivity and antistatic ability, and can form a transparent coating film that hardly impairs the color tone of the base, so it can be used for electronic and electrical parts. It exhibits outstanding performance when used to prevent static electricity and shield electromagnetic waves in construction materials, etc., and also exhibits excellent stability against moisture that enters from the atmosphere during storage and painting.

Claims (1)

[Claims] 1(a) Antimony: Contains 0.1 to 20% by weight, with the remainder consisting essentially of tin oxide, and
Conductive fine powder with an average particle size of 0.4 μm or less; (b) resin, which is the main element for forming the coating film; and (c) 20% by weight or more of the solvent contains 3% by weight of water.
MEK, cyclohexanone, which dissolves more than
A solvent that is a water-dissolving solvent consisting of one or more of THF and acetone, consisting of the above (a) to (c), (d) The blending ratio of the above conductive fine powder is the total weight of the above resin. (e) and the blending ratio of the solvent is 5 to 95% in terms of the total weight of the conductive fine powder and the resin: 100 parts;
100 to 2000 parts by weight of a conductive transparent paint that is stable against moisture.