JPH0519241B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a conductive resin filler.

Dispersed conductive compositions such as conductive paints, conductive adhesives, conductive plastics, and conductive rubbers, which are made by blending conductive fillers with paints, adhesives, and other various resins or rubbers, are well known. Metal powders such as silver, copper, and nickel are well known as conductive fillers.

However, although these metal powders have excellent electrical conductivity, they have a large specific gravity and a large difference in specific gravity from the polymeric material that forms the matrix, making it difficult to form a uniformly dispersed state as a conductive composition. Particularly in the case of paints and adhesives, metal powder tends to settle and separate in a short period of time, which not only causes problems in workability when using them, but also causes problems with conductivity due to uneven distribution of metal powder in the composition. Inconveniences such as defects may occur.

Other conductive fillers such as carbon black and graphite are also known, but these have the drawbacks of having lower conductivity and poorer moisture resistance than metal powder.

Furthermore, silver-coated glass beads
92956) is also known, but this also has a problem with uniform dispersibility because it has a relatively high specific gravity (specific gravity of about 2.5). Furthermore, in order to obtain sufficient conductivity, a large amount of glass beads must be added, but there is a problem in that adding a large amount of glass beads impairs the inherent advantage of light weight of the polymeric material that is the matrix.

For this reason, the present inventors have conducted extensive studies to solve the problems of conventional conductive fillers, and have coated the surface of a specific spherical crosslinked polymer with a specific particle size with a conductive metal. The present inventors have discovered that resin beads exhibit excellent effects as conductive fillers, leading to the present invention.

That is, in the present invention, on the surface of a spherical crosslinked polymer mainly composed of styrene and having an average particle diameter of 1 to 50μ,
The present invention provides a conductive resin filler characterized by having a conductive metal coating layer having an average layer thickness of 200 Å or more.

The conductive resin filler of the present invention is based on a spherical cross-linked polymer mainly composed of styrene, but this spherical cross-linked polymer has a specific gravity of approximately 1, which is much higher than that of metal powder or glass beads. The conductive resin filler of the present invention, which is based on such a spherical crosslinked polymer, can be incorporated into paints, adhesives, etc. because its specific gravity is close to that of the polymeric substance that is the matrix of the dispersed conductive composition. It is possible to obtain a conductive composition with good dispersibility and a uniform composition. In addition, such spherical crosslinked polymers are infusible and have excellent solvent resistance and heat resistance, and the conductive resin filler of the present invention using this as a base material can be used under a wide range of temperature conditions. can.

In such spherical cross-linked polymers, the average particle size is an important factor; if the average particle size is smaller than 1μ, the particles tend to aggregate, and the surface area increases when coating metal, making it conductive. This is not preferable because it increases the amount of metal used, which is economically disadvantageous, and also impairs the advantage that the specific gravity of the particles is small.

Furthermore, if the average particle size exceeds 50μ, problems such as impaired surface smoothness and reduced mechanical strength of the resulting conductive composition tend to occur, especially in the case of paints and adhesives. This is undesirable because it reduces workability and reduces adhesion, making it easier for the coated surface to peel or fall off.

For this reason, in the present invention, a spherical crosslinked polymer having an average particle diameter of 1 to 50 microns, preferably 3 to 30 microns, more preferably 5 to 20 microns is used.

Here, the spherical crosslinked polymer mainly composed of styrene is a crosslinked polymer formed by copolymerizing styrene as a main component and a small amount of a polyfunctional monomer, and
At most 30% by weight of styrene may be copolymerized with other ethylenically unsaturated monomers such as acrylic esters (methyl acrylate, ethyl acrylate, etc.), methacrylic esters (methyl methacrylate, ethyl methacrylate, etc.), unsaturated It can be replaced with carboxylic acids (acrylic acid, methacrylic acid, etc.), nitriles (acrylonitrile, methacrylonitrile, etc.), dienes (butadiene, isoprene, etc.), etc.

Polyfunctional monomers are those that copolymerize with styrene to form crosslinked polymers, such as divinylbenzene, di- or tri(meth) of polyhydric alcohols, etc.
Examples include acrylic esters (ethylene glycol diacrylate, ethylene glycol dimethacrylate, etc.), and divinylbenzene is particularly preferred. The amount of polyfunctional monomer used is 0.5% by weight in the monomer mixture.
The above content is preferably 2 to 10% by weight. 0.5% by weight
If it is less than this, sufficient crosslinking will not be obtained and solvent resistance and heat resistance will be poor, which is not preferable.

Such a spherical crosslinked polymer can be obtained by dispersing the above monomer mixture in water and subjecting it to suspension polymerization. The oil is added to the water containing the oil droplet and stirred and mixed using a stirrer with a large shearing force called a disperser or homogenizer until the oil droplets reach the desired size.
Next, it can be produced by heating and polymerizing under normal stirring conditions.

In the present invention, such spherical crosslinked polymers may be chlorinated, sulfonated, or nitrated as long as they do not decompose or deteriorate.

The spherical crosslinked polymer obtained in this way has a spherical shape close to a true sphere and has the smallest specific surface area, so that the amount used can be reduced when coating a metal.

The method for coating such a spherical crosslinked polymer with metal is not particularly limited, and can be effectively carried out by, for example, a chemical wet method, ie, electroless plating, or a vacuum evaporation method, which is a physical dry method.

Any metal is sufficient as long as it is conductive.
Gold, silver, copper, nickel, etc. are used in the electroless plating method, and gold, silver, copper, aluminum, etc. are used in the vacuum evaporation method.

As a coating method, for example, in the method using electroless plating, a metal salt aqueous solution, such as a silver-containing aqueous solution such as silver nitrate or silver cyanide, to which sodium salt or aqueous ammonia is added, is treated with an acid, if necessary.
If the spherical crosslinked polymer that has undergone pretreatment such as activation is sufficiently dispersed, then a reducing agent such as tartrate, formalin, glucose, etc. is added and mixed to precipitate and adhere silver to the surface of the polymer particles. good.

In the spherical crosslinked polymer coated with metal in the present invention, the metal coating layer preferably has an average layer thickness of 200 Å or more, and if it is smaller than 200 Å, sufficient conductivity cannot be obtained.

Thus, the conductive resin filler of the present invention can be used as a conductive filler in dispersed conductive compositions such as conductive paints, adhesives, plastics, and rubbers, and has a small difference in specific gravity from the polymeric substance that forms the matrix. Therefore, it has excellent dispersibility during blending, and can provide a conductive composition that is uniformly dispersed without causing problems such as sedimentation and separation, and can impart excellent conductivity.

Next, the present invention will be explained with examples.

However, "example middle part" indicates parts by weight.

Example 1 Cross-linked polystyrene [divinylbenzene:styrene = 4:96 (weight ratio)] particles with an average particle diameter of 5 μm were immersed in concentrated sulfuric acid at 80°C for 10 minutes, and after washing with water, 0.05% by weight palladium chloride acidic aqueous solution was added. dispersed into Add 0.2% by weight tin chloride acidic aqueous solution in a greenhouse,
A trace amount of palladium was attached to crosslinked polystyrene particles for activation.

10 g of preactivated crosslinked polystyrene was dispersed in 300 g of an aqueous solution containing 15.7 g of silver sulfate and 15 ml of a 28% ammonia aqueous solution. Next, 100 ml of a 7% by weight formalin aqueous solution was added to perform silver plating.
After repeating filtration and aqueous coating and drying, a conductive resin filler with an average silver thickness of about 900 Å and a specific gravity of 1.8 was obtained.

100 parts of the obtained conductive filler was mixed with 100 parts of solid content of acrylic lacquer (clear, solid content: 30% by weight) to obtain a conductive paint.

The dispersion stability of the filler was good, and only a slight amount of sediment was observed after standing for 24 hours. Further, the volume resistivity of the coating film obtained after coating and drying this coating material was 1×10 ^-2 Ωcm. Furthermore, the appearance of the coating film was smooth.

Example 2 Silver was vacuum-deposited onto crosslinked polystyrene [divinylbenzene:styrene=4:96 (weight ratio)] particles having an average particle diameter of 15 μm.

Using a resistance heating vapor deposition method, the silver placed in a heating furnace was vaporized in a high vacuum chamber (10 ^-4 Torr) while the sample was being cooled. After the deposition, microscopic observation of the particles revealed that they were coated almost uniformly, with approximately 24 parts of silver deposited per 100 parts of crosslinked polystyrene, and a specific gravity of 1.3. The thickness of the deposited silver was about 0.1 μm.

110 parts of the obtained conductive filler, 100 parts of unsaturated polyester resin (Japan U-Pica 4007A), 0.7 parts of curing aid (U-Pica PR-M), and 1 part of acetylacetone peroxide were mixed.

This mixture was cured at room temperature and then heated at 100°C for 2 hours.

When the volume resistivity of the cured product was measured, it was 1×
It was 10 ^-3 Ωcm.

Claims (1)

[Claims] 1. An average layer thickness of 200 Å is applied to the surface of a spherical crosslinked polymer mainly composed of styrene with an average particle diameter of 1 to 50 μ.
A conductive resin filler comprising the above conductive metal coating layer.