JPH0512917A - Conductive coating - Google Patents

Abstract

PURPOSE:To provide silver conductive coating having excellent conductivity even if its metal powder content is little. CONSTITUTION:In conductive coating being mixed with metal powder, the metal powder, being conductive material, is silver foil pulverized powder, having a mean particle diameter of 100mum or less, a mean thickness of particles of 0.5mum or less, and an apparent density of 0.01-0.1g/cm3, and moreover the amount of the silver foil pulverized powder is less than the amount of resin, being adhesive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paint for mixing a conductive material such as metal powder to obtain a conductive coating film. More specifically, a good conductive coating film can be obtained even if the amount of the conductive material added is small. The present invention relates to the conductive paint obtained. The fields of application are electromagnetic shielding, antistatic, surface heating, parabolic antenna reflection, and conductive coatings for various plating substrates.

[0002]

2. Description of the Related Art Conventionally, conductive paints using metal powder as a conductive material have been used more often for electromagnetic wave shielding because they have better conductivity than paints using carbon as a conductive material.
However, the conductive paint mixed with metal powder had the drawbacks that conductivity could not be obtained unless a large amount of metal powder was added, sedimentation was fast, and redispersibility was poor. Silver powder used as a metal powder maintains stable conductive performance in various environmental reliability tests, but conductive paint highly filled with silver powder is very expensive and unsuitable for use in coating a large area. Therefore, although a conductive paint in which a conductive material coated with silver is mixed with various inorganic materials has been developed, it is also a paint in which a large amount of conductive material is mixed.

[0003]

In the conventional conductive paint mixed with metal powder, the suitable amount of resin used as an adhesive is 100 to 40 parts by weight of metal powder, and 20 to 40 parts by weight is suitable. When it increases, the conductivity disappears.
That is, unless the amount of metal powder is larger than the amount of resin, the conductive paint cannot be obtained. Ordinary conductive paint adds a solvent to this,
Adjust the viscosity to suit the application such as brush coating, dip coating, and spray coating. In particular, the viscosity of a paint to be spray-painted such as an electromagnetic wave shield paint is low, and the metal powder is settled, and thus the conductivity of the paint film varies and the redispersibility is poor. A conductive paint having a small amount of metal powder mixed therein, slow sedimentation in the paint and good conductivity is required, but such a paint has not been developed yet.

The inventors of the present invention have conducted an earnest study on a conductive coating material containing silver powder, focusing on the shape of the silver powder, showing the electrically conductive silver powder. The present invention has found that a coating material that has excellent properties and that has excellent conductivity even with an amount of silver powder that is 1/10 or less of the conventional amount can be obtained.

[0005]

According to the present invention, in a conductive paint mixed with metal powder, the metal powder as a conductive material has an average particle diameter of 100 μm or less, an average particle thickness of 0.5 μm or less, and an apparent density of 0.01. The conductive paint is characterized by mixing ˜0.1 g / cm ³ of pulverized silver foil powder in an amount less than the amount of resin.

The pulverized powder of silver foil which is a conductive material of the present invention is obtained by mechanically pulverizing silver foil, and the foil thickness of the pulverized silver foil needs to be 0.5 μm or less on average. If it is thicker than 0.5 μm, the apparent density of the pulverized powder becomes a low bulk silver powder of 0.1 g / cm ³ or more, and it becomes impossible to obtain excellent conductivity with a small amount as in the present invention. The optimum thickness of the silver foil is about 0.2 μm considering the manufacturing method of the silver foil. It is also important that the apparent density of the crushed silver foil powder is within the range of 0.01 to 0.1 g / cm ³ .
When the apparent density is 0.1 g / cm ³ or more, it is necessary to mix a large amount with the paint in order to obtain conductivity, which makes the paint expensive. The smaller the apparent density is, the smaller the amount of the mixture that can be obtained is the conductivity, but if it is 0.01 g / cm ³ or less, the wettability between the resin and the silver powder becomes very poor, and the fluidity and adhesion of the paint may deteriorate. Yes, it is not preferable. Optimal apparent density is 0.03
It is about 0.07 g / cm ³ .

The average particle size of the crushed silver foil powder is preferably 100 μm or less. When it is 100 μm or more, the smoothness of the coating film is poor, and there are drawbacks such as difficulty in spray coating.

In the conductive paint of the present invention, since the conductive material is silver, the resin that can be used as the adhesive is acrylic resin, phenol resin, polyvinyl chloride resin, epoxy resin, urethane resin, polyester resin, cellulose resin, etc. From organic synthetic resin, acrylic emulsion,
Aqueous organic or inorganic adhesives such as sodium silicate can be used.

The solvent used for adjusting the viscosity may be optionally used by adapting it to an organic solvent such as toluene, xylene or alcohol, or an adhesive using water or the like.

The ratio between the crushed silver foil powder and the amount of resin must be smaller than the amount of resin used as an adhesive. When crushed silver foil powder with an apparent density of 0.01 to 0.1 g / cm ³ is used, if the amount of resin is small, the adhesive strength as a paint cannot be obtained and the conductivity will also deteriorate. The optimum compounding ratio is preferably 400 to 1000 parts by weight of resin with respect to 100 parts by weight of crushed silver foil.

With conventional conductive paints, the conductivity is lost when the resin amount is 20 to 40 parts by weight or more with respect to 100 parts by weight of silver powder. That is, even if the amount of resin is 10 to 20 times that of the conventional one, excellent conductivity can be obtained. That is, when the metal powder is added to the paint obtained by mixing the resin and the solvent in order to impart the conductivity, the conductivity can be obtained with the addition amount of 1/10 to 1/20 of the conventional amount. Very little conductive paint. The solvent evaporates and the coating film is formed of metal powder and resin, but if the amount of metal powder is less than the amount of resin as in the present invention, the strength and elasticity of the coating film will be improved, and a cheap coating film Can be provided.

[0012]

The following is considered as the reason why an excellent conductive coating film can be obtained in a much smaller amount than the conventional silver powder.
Conventional flaky silver powder is made into flakes while being spread by mechanical crushing. It is coarse and has an average thickness of 0.5 μm, average grain size of 25 μm (grain size / thickness ratio is 50), and fine grain. Average thickness 0.2 μm, average particle size 5 μm (particle size / thickness ratio is 2
In 5), the apparent density is generally 1.5 to 2.5 g / cm ³ . The crushed silver foil powder used in the present invention has a uniform thickness of 0.2 μm and the average particle size can be the maximum usable particle size. For example, when the average particle diameter is 25 μm, the particle diameter / thickness ratio is 125, which is a metal powder shape having a high aspect ratio and easy to obtain conductivity. Further, the crushed powder of silver foil is not formed into pieces while spreading and is not only uniform in thickness, but also contains almost no fine powder, and the end portions of the silver powder also have a sharp rupture shape in which the silver powder easily contacts each other. Since it has, the conductivity may be obtained with a smaller addition amount.

The optimum apparent density of the crushed silver foil powder used in the present invention is 0.03 to 0.07 g / cm ^3, which is 20 times more bulky than the conventional silver powder, and when mixed in a paint, even a very small amount of metal The chances that the powders come into contact with each other increase, and the conductivity becomes easier.

Since the pulverized silver foil powder is thin and uniform, the pulverized powder has a low settling time even in the coating material and has good workability such as redispersibility. Therefore, the conductive coating material of the present invention containing the crushed silver foil powder is a novel coating material in which the amount of metal powder mixed is small, the sedimentation in the coating material is slow, and good conductivity is obtained.

[0015]

The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

Example (1) Dispersion of 100 parts by weight of crushed silver foil having an average particle size of 50 μm and an apparent density of 0.03 g / cm ³ obtained by crushing a silver foil having an average thickness of 0.2 μm, 1000 parts by weight of acrylic resin, and 3000 parts by weight of toluene. And stirred for 10 minutes to obtain a conductive paint.

The conductivity of the conductive paint thus obtained is
The BS resin plate was spray coated to a coating thickness of 30 μm and the specific resistance value was measured. As a result, a very excellent conductivity of 7 × 10 ⁻⁴ Ω · cm was shown. A cellophane tape peel test was conducted to check the strength of the coating film, but no peeling was observed.

Example (2) Dispersion of 100 parts by weight of crushed silver foil having an average particle diameter of 25 μm and apparent density of 0.07 g / cm ³ obtained by pulverizing an average 0.2 μm thick silver foil, 800 parts by weight of acrylic resin, and 2500 parts by weight of toluene. And stirred for 10 minutes to obtain a conductive paint.

As a result of measuring the conductivity by the same method as in Example (1), the conductivity was 6 × 10 ⁻⁴ Ω · cm, which was very excellent.

Example (3) Dispersion of 100 parts by weight of crushed silver foil having an average particle diameter of 25 μm and an apparent density of 0.1 g / cm ³ of crushed silver foil having an average thickness of 0.5 μm, 400 parts by weight of acrylic resin, and 1250 parts by weight of toluene. And stirred for 10 minutes to obtain a conductive paint.

The conductivity was measured by the same method as in Example (1). As a result, the thickness of the silver foil was thick and the apparent density was high, so twice the amount of silver powder as in Example (2) had to be mixed. , 6 ×
It showed a very excellent conductivity of 10 ⁻⁴ Ω · cm.

Example (4) 100 parts by weight of crushed silver foil having an average particle size of 50 μm and an apparent density of 0.03 g / cm ³ obtained by crushing a silver foil having an average thickness of 0.2 μm, 1000 parts by weight of phenol resin, 1500 parts by weight of butyl carbitol. Was stirred with a disper for 10 minutes to obtain a conductive paint.

The conductivity of the conductive paint thus obtained was brush coated on a phenol resin plate so that the coating film thickness was 50 μm, and the specific resistance value was measured. The result was 9 × 10 ⁻⁴ Ω · cm. It showed excellent conductivity.

Example (5) 100 parts by weight of crushed silver foil having an average particle size of 50 μm and an apparent density of 0.03 g / cm ³ obtained by crushing a silver foil having an average thickness of 0.2 μm, and 2000 parts by weight of an acrylic emulsion resin containing 50% solid content. ,
1000 parts by weight of water was stirred with a disper for 10 minutes to obtain a conductive paint.

As a result of measuring the conductivity by the same method as in Example (1), a very excellent conductivity of 5 × 10 ⁻³ Ω · cm was shown.

Example (6) 100 parts by weight of crushed silver foil having an average particle diameter of 50 μm and an apparent density of 0.03 g / cm ³ were crushed from an average 0.2 μm thick silver foil. The conductive paint was obtained by stirring for 1 minute.

The conductivity of the conductive coating material thus obtained was spray-coated on an asbestos board to a coating thickness of 50 μm, and the specific resistance value was measured. As a result, it was 5 × 10 ⁻³ Ω · cm, which was extremely excellent. It showed conductivity.

Example (7) Dispersed with 100 parts by weight of crushed silver foil having an average particle size of 50 μm and an apparent density of 0.03 g / cm ³ , silver foil having an average thickness of 0.2 μm, 1000 parts by weight of polyurethane resin and 3000 parts by weight of toluene. And stirred for 10 minutes to obtain a conductive paint.

The conductivity of the conductive coating material thus obtained was spray coated on a polyester resin plate so that the coating film thickness was 50 μm, and the specific resistance value was measured to be 8 × 10 ⁻⁴ Ω · cm. It showed excellent conductivity.

Example (8) An average particle size of 100 μm obtained by crushing a silver foil having an average thickness of 0.15 μm,
100 parts by weight of crushed silver foil powder having an apparent density of 0.01 g / cm ³ , 1250 parts by weight of acrylic resin, and 3000 parts by weight of toluene were stirred with a disper for 10 minutes to obtain a conductive paint.

As a result of measuring the conductivity by the same method as in Example (1), it was 5 × 10 ⁻³ Ω · cm, and it could be used for electromagnetic wave shielding. Further, as a result of performing a cellophane tape peeling test to check the strength of the coating film, peeling was not recognized.

Comparative Example (1) Average thickness 0.5 μm, average particle size 25 μm, apparent density 2.0 g / c
100 parts by weight of conventional flaky silver powder of m ³ , acrylic resin 400
By weight, 1250 parts by weight of toluene was stirred with a disper for 10 minutes to prepare a paint.

As a result of measuring the conductivity of this paint by the same method as in Example (1), there was no conductivity at all.

As a result of increasing the amount of silver powder until a specific resistance value of 6 × 10 ⁻⁴ Ω · cm was obtained, 1500 parts by weight of silver powder, which is 15 times or more that of the present invention, 400 parts by weight of acrylic resin, 1250 parts by weight of toluene. It was necessary to increase the amount of silver powder up to the composition of parts. In this way, the paint containing 3.7 times the amount of resin mixed with silver powder has a poor redispersibility and is a very expensive paint.

Comparative Example (2) A silver foil having an average thickness of 0.15 μm was crushed to have an average particle size of 100 μm,
A crushed powder of silver foil having an apparent density of 0.008 g / cm ³ was obtained. An attempt was made to prepare a paint by mixing 100 parts by weight of this pulverized silver foil powder with 1250 parts by weight of an acrylic resin and 3000 parts by weight of toluene in the same manner as in Example (8), but it was not fluid and could not be formed into a paint. Therefore, from 3000 parts by weight of toluene,
Conductive paint was prepared by increasing the amount to 00 parts by weight, and Example (1)
As a result of measuring the conductivity by the same method as the above, it was as bad as 10 Ω · cm, and a great amount of silver powder fell off in the cellotape peeling test.

On the other hand, when the amount of toluene was the same and the amount of acrylic resin was increased from 1250 parts by weight to 1500 parts by weight, a paint was obtained although the viscosity was high. However, when the conductivity was measured by the same method as in Example (1), the result was 1000 Ω · cm, which was poor.

Comparative Example (3) A silver foil having an average thickness of 0.5 μm was crushed to obtain an average particle size of 25 μm.
A crushed powder of silver foil having an apparent density of 0.5 g / cm ³ was obtained. 100 parts by weight of this pulverized powder of silver foil was mixed with acrylic resin in the same manner as in Example (3).
A coating material was prepared by mixing with 400 parts by weight and 1250 parts by weight of toluene.

As a result of measuring the conductivity by the same method as in Example (1), there was no conductivity at all. As a result of increasing the amount of silver powder, a conductivity of 6 × 10 ⁻⁴ Ω · cm was obtained with a blending composition of 1000 parts by weight which is 10 times or more the amount of silver powder, 400 parts by weight of acrylic resin, and 1250 parts by weight of toluene. .. However, since it is a paint that contains 2.5 times the amount of silver powder as the amount of resin, the redispersibility is also poor and the paint is expensive.

[0039]

As described in detail above, the conductive coating material of the present invention has excellent conductivity by selecting the metal powder as the conductive material with the mixed amount of metal powder less than 1/10 of the conventional amount. It is a conductive paint.

The fact that the amount of metal powder is small not only improves the workability as a paint, but also makes it a very inexpensive conductive paint, making it the most suitable conductive paint for electromagnetic wave shielding and electrostatic prevention for coating a large area. became.

Claims (1)

Claim: What is claimed is: 1. In a conductive coating material containing a mixture of metal powder, the metal powder as a conductive material has an average particle diameter of 100 μm or less, an average particle thickness of 0.5 μm or less, and an apparent density of 0.01 to 0.1. A conductive paint characterized in that it is g / cm ³ of pulverized silver foil and that the amount of pulverized silver foil is less than the amount of resin as an adhesive.