JPH11329074A - Conductive resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition having excellent forming property and conductivity by using zinc-based metal powder carrying conductivity as a main component, and including a low melting point metal and synthetic resin in the zinc-based metal powder. SOLUTION: This conductive resin composition is composed of zinc group- based powder, a low melting point metal melted when molded, and a synthetic resin. As the zinc-based metal powder, metal zinc powder, brass powder and tin-zinc powder can be used. The zinc-based metal powder having 1-100 μm of grain size is desirably used, and the zinc-based metal powder is desirably blended at 10-60 vol.% in relation to the whole of the conductive resin composition at 100 vol.%. As the low melting point metal, tin or a tin alloy known as the solder can be used, and formed into fine powder so as to be blended with the resin. The low melting point metal is blended at 15 vol.% or less in relation to the whole of the composition. As the synthetic resin material, the thermoplastic resin can be used, and desirably blended at 30-80 vol.% in relation to the whole of the composition. As other component, metal fiber, metal powder except for the zinc-based, and the extender such as calcium carbonate and talc can be blended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive resin composition which can be used as a resin composition for electric wiring.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 7-49 discloses a conductive resin composition containing a low melting point metal which melts at the temperature during injection molding.
As disclosed in JP-A-491 and JP-A-5-325637, there is a conductive resin composition comprising a metal fiber, a low melting point metal and a synthetic resin. Such a conductive resin composition is formed into a predetermined shape by injection molding or the like, and the metal fibers and the low-melting-point metal, which are constituent components thereof, are buried in the resin in a state where they are in contact with each other. For this reason, the molded body has conductivity.

[0003]

Since the conventional conductive resin composition uses metal fibers as a main component for imparting conductivity, there is a problem that fluidity is poor and moldability is poor. If the compounding amount of the metal fiber is reduced to improve the formability and the compounding amount of the low melting point metal is increased by that amount, the low melting point metal is phase-separated during molding, and a molded body having uniform conductivity cannot be obtained. There is a problem. In addition, there is also a problem that metal fibers are expensive and are hardly used industrially.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an inexpensive conductive resin composition having excellent moldability and excellent conductivity.

[0005]

Means for Solving the Problems The present inventors have thought that the metal fibers used as the conductive material deteriorate the moldability, and have come to use metal powder instead of the metal fibers. The inventors have found that a combination of a zinc metal powder and a solder alloy containing tin as a main component has both excellent formability and resistance to phase separation, thereby completing the present invention. That is, the conductive resin composition of the present invention is characterized by containing a zinc-based metal powder, a low-melting-point metal that melts during molding, and a synthetic resin material.

It is considered that the large surface area of the zinc-based metal powder captures the molten low-melting metal and prevents the low-melting metal from phase-separating from the resin and the zinc-based metal powder. Further, since the powder is rounder than the fiber, the powder does not significantly impair the fluidity of the resin and has excellent moldability.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive resin composition of the present invention contains a zinc-based metal powder, a low melting point metal, and a synthetic resin material. Zinc-based metal powder is a basic component that ensures conductivity. Examples of the zinc-based metal powder include a metal zinc powder, a brass powder, and a tin-zinc powder. As a form of the powder, a spherical, elliptical, flaky or the like powder can be used. The surface of the powder preferably has a large specific surface area with many irregularities. By increasing the specific surface area, the trapping of the molten low melting point metal becomes stronger, and the phase separation of the molten low melting point metal can be more effectively prevented. In addition, zinc not only wets well with low melting point metals, especially tin, but also has a slow alloying with tin. For this reason, tin which wets and adheres to the surface of zinc has a low degree of being alloyed with zinc and absorbed by zinc, and exists as tin or a tin alloy that has long been melted on the zinc surface. This is convenient for joining zinc-based metal powders to each other.

The size of the zinc-based metal powder is 1 to 10 in terms of particle size.
0 μm, more preferably about 15 to 80 μm. The smaller the particle size, the more the oxide film increases and the lower the conductivity. Conversely, as the particle size increases, dispersibility decreases, and moldability and strength decrease. The amount of the zinc-based metal powder is 1 when the entire conductive resin composition is 100% by volume.
About 0 to 60% by volume is preferable. When good electric conductivity is required, the content is preferably 30% by volume or more, and more preferably 40% by volume or more. When the strength of the compact obtained by molding is required, the amount of the zinc-based metal powder is preferably 40% by volume or less.

It is preferable to treat the surface of the zinc-based metal powder with a silane-based or titanium-based coupling agent in order to strengthen the bond between the zinc-based metal powder and the resin.
As the low melting point metal, a tin alloy commonly known as solder can be used. Specifically, tin, tin-zinc, tin-copper, tin-
Indium, tin-silver and the like can be used. The low melting point metal is usually blended with the resin as a fine powder. The preferred particle size of the low melting point metal is about 6 to 50 μm.

The amount of the low melting point metal is about 3 to 30% by volume, more preferably 6 to 15% by volume, assuming that the whole conductive resin composition is 100% by volume. A thermoplastic resin can be used as the synthetic resin material. Specifically, 12 nylon, 6 nylon, 66 nylon, polyacetal, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene sulfide (P
PS), polystyrene, syndiotactic polystyrene (SPS), polypropylene (PP), polyethylene (PE), crystalline resin such as ethylene copolymer resin (EVA, EAA, ionomer), ABS, polyurethane, polycarbonate (PC), modified Amorphous resins such as polyphenylene oxide resins, liquid crystal polymers, and thermoplastic elastomers can be used. In addition, you may use as a polymer alloy which blended several types of thermoplastic resins. In a special case, a rubber material such as silicone rubber, fluorine rubber, or acrylic rubber, an epoxy resin, a phenol resin, or a thermosetting resin can be used.

The amount of the synthetic resin material is preferably about 30 to 80% by volume, more preferably 40 to 65% by volume, based on 100% by volume of the whole conductive resin composition. The relative mixing ratio between the zinc-based metal powder and the low-melting-point metal is preferably about 1 to 20, more preferably about 4 to 10 in terms of volume ratio. When the ratio is low, the low melting point metals are liable to aggregate with each other, and the moldability is reduced. Conversely, when the ratio increases, the electrical conductivity and electromagnetic shielding properties tend to decrease.

As other components, metal fibers, metal powders other than zinc-based metal powders, fillers such as calcium carbonate and talc, and other additives used in resin compositions can be blended. As the metal fiber, an aluminum-based metal fiber made of aluminum, an aluminum alloy, or the like is preferable. The diameter of the metal fiber is preferably about 50 to 100 μm, and the length is preferably about 2 to 5 mm from the viewpoint of moldability and conductivity. In addition, when aluminum-based metal fibers are used as metal fibers, zinc powder and aluminum-based metal fibers preferably occupy 20 to 50% by volume when the total composition is 100% by volume.

The ratio of the low-melting metal to the total volume of the zinc powder and the aluminum-based metal fiber, that is, (volume of zinc powder + volume of aluminum-based metal fiber) / volume of the low-melting metal is 2 to 17. preferable. As the ratio increases, the conductivity deteriorates, and when the ratio decreases, the low-melting point metal separates. The conductive resin composition can be prepared by melt-kneading the above-mentioned components using an extruder or the like to form pellets. Then, the conductive resin composition is injection-molded as a raw material to obtain a resin molded product having a desired conductivity. In particular, the conductive resin composition of the present invention is preferable as a circuit constituent material of an electric circuit. That is,
An excellent resin molded electric component is obtained by integrally molding an electric circuit molded product formed with the conductive resin composition of the present invention on a main body molded with a non-conductive resin composition by two-color molding. be able to.

When only the electric circuit portion is formed of the conductive resin composition by two-color molding, the amount of the metal component such as the zinc-based metal powder and the low-melting metal is increased to increase the conductivity of the obtained electric circuit portion. It is also preferable to further enhance the properties. In the case of a molded article that requires electromagnetic shielding or heat conduction, the amount of the synthetic resin material can be increased and the amount of the metal component can be reduced to obtain the required strength. Further, for a gasket molded product of an electromagnetic shield, rubber or an elastomer can be used as a synthetic resin material.

[0015]

The conductive resin composition of the present invention contains zinc-based metal powder as a main component of the conductive material. Zinc-based metal is relatively soft and has a low melting point as a metal material. In addition, the zinc-based metal powder wets well with the tin alloy of the low melting point metal. Therefore, the molten low-melting-point metal adheres to and is captured by the surface of the zinc-based metal powder, and the molten low-melting-point metal rarely undergoes phase separation from the resin and the zinc-based metal powder. In addition, since the zinc-based metal powder is not in a fiber form but is relatively round as compared with the fiber, the flow of the molten resin is hardly hindered. Therefore, the conductive resin composition of the present invention has good moldability.

It is considered that the use of metal powder in place of metal fibers may deteriorate the conductivity of the molded body, but the degree of the decrease in conductivity is not so large that it does not pose a serious problem in practical use. It is necessary to increase the compounding amount of the resin component in order to cope with the deterioration of the moldability when a large amount of metal fibers are blended, but the use of the zinc-based metal powder enhances the moldability, and the zinc-based metal powder The mixing ratio can be increased and the mixing ratio of the resin component can be reduced. As a result, a decrease in conductivity due to the use of the zinc-based metal powder can be covered.

The conductive resin composition of the present invention comprises an electric circuit portion formed by two-color molding, a resin molded product having an electromagnetic shielding function,
Can be used for gaskets for electromagnetic shielding.

[0018]

EXAMPLES (Example 1) Eight kinds of conductive resin compositions shown in Table 1 were prepared. Lead-free solder having an average particle size of 50 μm (Sn—Cu—Ni, melting point 225)
° C) as zinc-based metal powder, zinc metal powder having a median particle size of 286 (tears) 65 (sphere) 22 (flakes) μm, and copper fiber (diameter 30 μm, length 2.5
mm) Aluminum fiber (diameter 90 μm, length 3 mm)
With ABS, PBT, polyphenylene sulfide (PPS), 12 nylon, modified polyphenylene oxide (modified PPE), thermoplastic elastomer (TP)
E) was used.

The conductive resin composition was prepared into a mixed raw material according to the composition shown in Table 1, and the mixed raw material was extruded into a rod shape by an extruder and then cut into pellets having a diameter of 5 mm and a length of 5 mm. Molding is performed using an injection molding machine under normal injection molding conditions, as shown in FIG. 1, with a thickness of 2 mm, a width of 15 mm, and a length of 74 mm.
The current-carrying material was bent into an S-shape of mm and had a through-hole with a diameter of 6 mm at the center in the width direction of 10 mm from both ends.

The moldability is described in Document No. Except for 8, there was no particular problem. Regarding the conductivity, a terminal having a diameter of 12 mm was screwed into two through holes of the current-carrying material, and the electric resistance between both terminals was measured with a milliohm high tester. The measurement results are shown in Table 1. Further, the temperature of the surface of the current-carrying material when a DC current of 20 A was passed between both terminals for 30 minutes was measured. In addition, room temperature was performed at 22 degreeC. The measurement results are shown in Table 1.

[0021]

[Table 1]

As shown in Table 1, the sample No. 1 to No.
The molded article obtained from the conductive resin composition of the present invention No. 5 had relatively low volume resistivity, generated little heat, and had good moldability. Sample No. 5, no. The conductive resin composition of No. 6 also has relatively low volume resistivity, low heat generation, and good moldability, but is expensive due to the use of expensive copper and aluminum fibers, and its value as a product is correspondingly low.

Sample No. 2 containing only zinc metal powder and no low melting point metal was blended. Sample No. 7 and copper fiber alone, and no low melting point metal was blended. All of the molded products of No. 8 had high volume resistivity. In particular, the sample No. The molded product of No. 8 suffered from poor electrical conduction due to a rise in temperature and could not be used as an electrically conductive material, and had a problem in moldability. (Example 2) Three kinds of conductive resin compositions shown in Table 2 were prepared. Spherical material with low melting point and average particle size of 5
0 μm Sn—Cu—Ni solder (melting point: 225 ° C.) and spherical Sn solder having an average particle size of 40 μm (melting point: 232 ° C.)
Was used as the zinc-based metal powder, spherical zinc metal powder having a median particle size of 3 μm and spherical median particle size of 70 μm. As the resin, a polymer alloy of polyphenylene oxide (PPE) and polypropylene (PP) and syndiotactic polystyrene (SPS) were used.

As for the conductive resin composition, a mixed raw material was prepared according to the composition shown in Table 2, and the mixed raw material was extruded into a rod shape by an extruder and cut as in Example 1 to obtain pellets having a diameter of 5 mm and a length of 5 mm. Thereafter, the current-carrying material shown in FIG. 1 was molded under the usual injection molding conditions using an injection molding machine in the same manner as in Example 1. There was no particular problem with the moldability of all the compositions. Table 2 shows the melting index (MI) and the volume resistivity for reference. NO. It is not clear that the volume resistivity of the current-carrying material obtained from the 12 materials is high.

[0025]

[Table 2]

Example 3 6% by volume of Sn solder (melting point: 232 ° C.) having a spherical average particle diameter of 40 μm as a low melting point metal, and 50% by volume of zinc metal powder having a spherical and median particle diameter of 70 μm as a zinc-based metal powder. A mixed raw material was prepared with a composition of 44% by volume of a polymer alloy of polyphenylene oxide (PPE) and polypropylene (PP) as a resin, and the mixed raw material was formed into pellets and a current-carrying material in the same manner as in Example 1.

The volume resistivity of the obtained conductive material is 1.5 ×
10 ^-4 Ω · cm, thermal conductivity of 14.4 W / mk, tensile strength of 18.9 MPa, tensile elongation of 6%, specific gravity of 4.4
3. Deflection temperature under load The test load was 0.451 MPa at 142 ° C. in accordance with ASTM D-648. Furthermore, using this conductive material, the shielding effect of a magnetic field and the shielding effect of electrolysis were examined using a commercially available shield evaluation machine. FIG. 2 shows an outline of the shield test method. In addition, as the test piece, the conductive material in which silver-copper-based metal powder was mixed into a metal plate (iron) having a thickness of 4 mm and a resin plate having a thickness of 4 mm together with the conducting material of Example 3 was used. The sample was tested. The test results are shown in FIGS.

As is clear from FIG. 3, the magnetic field shielding effect of the current-carrying material of this embodiment is measured at a measurement frequency of 10 to 1000M.
It showed a high shielding effect comparable to a metal plate at Hz. Further, as shown in FIG. 4, the shielding effect of electrolysis was substantially the same as that of the metal plate. (Example 4) Spherical low-melting point metal having an average particle size of 40 µm
Of Sn solder (melting point 232 ° C.), teardrop-shaped zinc metal powder having a median particle size of 18 μm as zinc-based metal powder, aluminum fiber having a diameter of 90 μm and a length of 3 mm, and polyphenylene oxide (PPE) as a synthetic resin
And a polypropylene (PP) polymer alloy.
Then, zinc metal powder and aluminum fiber are each
The combination of volume% and 25% by volume (combination of the symbol “◆” in FIG. 5 described later) and the combination of zinc metal powder and aluminum fiber in 10% and 25% by volume (FIG.
, A combination of 15% by volume and 20% by volume of zinc metal powder and aluminum fiber (a combination of ▲ in FIG. 5 described later) and a combination of 15% by volume of zinc metal powder and aluminum fiber, respectively. Four types of combinations of 25% by volume (combinations indicated by ● in FIG. 5 described later) were used. Further, 12 types of conductive resin compositions were prepared in the same manner as in Example 1 by adding the Sn solder at 3% by volume, 4% by volume and 5% by volume, respectively, and using the remainder as the synthetic resin.

Each of these 12 types of conductive resin compositions was heated to a size of 120 mm × 120 mm × 1 mm.
Two types of plate materials were formed. The resistance at 120 mm intervals was measured on the surface of these plate materials using a milliohm high tester (four-point type). The results obtained are shown in FIG. As shown in FIG. 5, when the total amount of the zinc metal powder and the aluminum fiber is small, the resistance value of the sheet material greatly changes due to the difference of 1% by volume of the composition of the low melting point alloy.

[0030]

The conductive resin composition of the present invention has good moldability and excellent electrical conductivity and thermal conductivity. Further, since inexpensive zinc metal powder is used, it is inexpensive and has high value as a conductive material and a heat conductive material.

[Brief description of the drawings]

FIG. 1 is a plan view of a molded product used for a test of a conductive material.

FIG. 2 is a diagram showing an outline of a shield evaluation test method for a conductive material.

FIG. 3 is a diagram showing a magnetic field shielding effect of a current-carrying material molded with the composition of Example 3.

FIG. 4 is a diagram showing an electrolytic shielding effect of a current-carrying material molded with the composition of Example 3.

FIG. 5 is a graph showing the relationship between the composition ratio of a low-melting metal, a zinc metal powder, and an aluminum fiber of a current-carrying material formed from the composition of Example 4 and the resistance value of a conductive material obtained. It is a top view of the molded article used for the test of the conductive material.

Continued on the front page. (72) Inventor Masatoshi Harada 1 Toki-cho, Haruki, Togo-cho, Aichi-gun, Aichi Prefecture Inside Togo Seisakusho Co., Ltd.

Claims (13)

[Claims] 1. A conductive resin composition comprising a zinc-based metal powder, a low-melting metal which melts during molding, and a synthetic resin material. 2. The zinc-based metal powder having a particle size of 1 to 10
The conductive resin composition according to claim 1, which has a thickness of 0 µm. 3. The conductive resin composition according to claim 1, wherein the low melting point metal is tin or an alloy containing tin. 4. The low melting point metal comprises 15% by volume of the total composition.
The conductive resin composition according to claim 1, which is as follows. 5. The synthetic resin material is nylon, PBT,
Liquid crystal polymer, ABS, PPS, thermoplastic elastomer, SPS, PC, PP, PE, ethylene copolymer resin,
The conductive resin composition according to claim 1, which is at least one of polyphenylene resin, silicone rubber, fluorine rubber, acrylic rubber, and epoxy resin. 6. The conductive resin composition according to claim 1, wherein the zinc-based metal powder accounts for 40% by volume or more of the total composition. 7. The conductive resin composition according to claim 1, wherein the total volume of the zinc-based metal powder is 4 to 10 times the total volume of the low melting point metal. 8. The conductive resin composition according to claim 1, comprising a metal fiber. 9. The conductive resin composition according to claim 8, wherein the content of the zinc-based metal powder and the metal fibers is 50% by volume or less of the whole composition. 10. The conductive resin composition according to claim 8, wherein the total volume of the zinc-based metal powder and the metal fibers is 4 to 10 times the total volume of the low melting point metal. 11. The metal fiber has a diameter of 50-10.
The conductive resin composition according to claim 8, which has a thickness of 0 µm. 12. The metal fiber has a length of 2 to 5 mm.
The conductive resin composition according to claim 8, which is: 13. The conductive resin composition according to claim 8, wherein said metal fiber is an aluminum-based metal fiber.