JPS63297459A - Electrically conductive polymer blend - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive polymer, having excellent shielding characteristics and heat cycle resistance and suitable as thin-walled parts of precise parts, by blending a thermoplastic polymer with two kinds of electrically conductive fibers having a specific diameter in a specific proportion. CONSTITUTION:An electrically conductive polymer obtained by blending a thermoplastic polymer, (e.g. polystyrene or polyethylene) as a matrix polymer with (B) electrically conductive fibers having <=10mum diameter (e.g. stainless fiber) and (B) electrically conductive fibers (e.g. stainless steel or copper) having a diameter so as to provide >=50g strength (tensile strength X cross-sectional area) at 30:70-70:30 weight ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a conductive resin mixture whose main purpose is to shield electromagnetic waves.

(Prior art) In conductive resins in which conductive fibers are conventionally dispersed in resin, the conductive fibers to be mixed include short metal fibers, carbon fibers, metallized glass fibers, and There are metal fibers found in wire drawing.

The diameter of these fibers is 4 to 120μ in the crack vibration method, 5 to 10μ in the case of carbon fiber or metallized glass fiber, and 4 to 20μ in the case of metal fibers obtained by wire drawing. , copper fibers with a thickness of about 30 to 50 μm are generally used.

Therefore, when manufacturing a large, thick molded product such as a CRT casing using a conductive resin mixture, even fibers with a diameter of 50 μm, such as fibers obtained by the crack vibration method or copper fibers, must be uniformly dispersed. However, there is a drawback in that small precision parts, thin-walled products, or even large products with precision parts or thin-walled parts are difficult to fill with fibers sufficiently, resulting in leakage of electromagnetic waves. In addition, fibers produced using the Hipiri vibration method have a small aspect ratio, and carbon fibers have lower conductivity than metal fibers, so they cannot be produced in large quantities (
30-70! %), and a practical shielding effect cannot be obtained, resulting in increased weight, increased cost, and decreased moldability.

Therefore, resin mixtures containing stainless steel fibers with a diameter of 8 μm are currently being mainly studied and applied to cloth, but although this has a good initial shielding effect, it cannot be used practically after heat cycling. The shielding effect was reduced to the extent that it was. This is because fibers with a diameter of 8μ have a weak absolute strength, so they are easily cut during the production or molding of the resin mixture, and even if the aspect ratio is the same as that of a larger diameter fiber, the fiber length is as short as 1+ll or less. Thus, the number of contacts required to form conductive paths in the molded article is increased.

When heat cycles are applied to such molded products, they shrink.

It is presumed that the contact is broken due to expansion, resulting in more discontinuities than in a fiber with a larger diameter, and the shielding effect decreases as the volume resistivity increases.

(Problems to be Solved by the Invention) As a result of intensive research in view of the current situation, the present invention has a good shielding effect even in precision parts or thin-walled parts, and the shielding effect does not deteriorate even due to the influence of thermal cycles. We have developed a conductive resin mixture that does not cause

(Means for Solving the Problems) The present invention uses a thermoplastic resin as IJ Nox resin, and contains conductive fibers with a diameter of 10 μm or less and a strength (tensile strength x cross-sectional area) of 50? conductive fiber with a diameter of 30 to 70:30 by weight.
It is characterized by being mixed at a ratio of .

Stainless steel, copper, and copper alloys are used as the types of conductive fibers (A) and (B), but stainless steel fibers are particularly good as conductive fibers because they have low processing costs and high strength. fiber (g))
Examples include stainless steel, copper, and copper alloys.

Aluminum is better.

Also, in the present invention, the reason why the blending ratio of conductive fiber (A) and conductive fiber () is limited to 30:0 to 70:30 is that if the conductive fiber (■) is less than 30%, the filling amount in the details is There is insufficient electromagnetic shielding. If it exceeds 70%, although the amount of filling in the details is sufficient, the heat cycle resistance is poor.

In addition, if the content of the conductive fiber (B) is less than 30%, the heat cycle resistance of the shielding properties will be poor;
If it exceeds 0-, the amount of filling in the details will be slightly reduced and electromagnetic wave leakage will occur.

Further, as the thermoplastic resin serving as the matrix, polystyrene, 4-propylene, ABS, acrylic styrene copolymer, PBT, polycargonate, PA, etc. are used.

The conductive resin mixture of the present invention can be obtained by kneading the above-mentioned two types of fibers cut into an arbitrary length of 3 to 101 m with a matrix thermoplastic resin in a twin-screw extruder or the like; Alternatively, a large number of two types of fibers are bundled together, bundled with a molten highly fluid resin that is compatible with a thermoplastic resin, extrusion coated with a thermoplastic resin, and pelletized to an arbitrary length of 3 to 1 Qss. This method is based on a method in which fibers of different diameters are bundled using a resin dissolved in a solvent and pelletized into a desired length.

(Function) In the present invention, the conductive fiber (A) is limited to a diameter of 10μ or less because fibers with a diameter of 10μ or more cannot be filled into precision products or thin products, and the conductive fiber (B) is limited to 505L. The reason for limiting it to the above is 50 pages.
This is because the following fibers are easy to cut and impede heat cycle resistance.

Conductive fibers (A) with a diameter of less than 10 μm are expensive and are easy to break during molding or molding, but they are precision components.
It has the advantage of being evenly distributed even in thin-walled parts. Also lead''
50 in dL Note Fiber ■)? As mentioned above, fibers with a large diameter are low in cost, have high strength, and have good heat cycle resistance, but they cannot be filled into every corner and are difficult to process.

It has the disadvantage of causing a decline in physical properties. Note that if the diameter is 30μ or more, the appearance of the molded product will be impaired.

The present invention achieves low cost by mixing and molding two types of fibers to mutually compensate for their shortcomings. K is also filled with fibers and long fibers in every detail, which improves shielding properties and heat cycle resistance. It is possible to use an excellent conductive resin composition.

(Example) Example (1) A bundle of 5000 stainless steel fibers with a diameter of 8μ and 1if
A bundle of 500 stainless steel fibers of f130 μ (strength 1305') was put into a tandem extruder separately, and immediately after impregnation and convergence with IJA of low molecular weight (approximately 500 (B)),
The outer periphery was coated with ABS resin (JSR Co., Ltd.), and after cooling, it was pelletized into a length of 60 mm.The weight ratio of the stainless fiber core with a diameter of 8 μ and the stainless steel fiber CB with a diameter of 30 μ was 50. :50 and the total amount of stainless fibers was adjusted to be less than 10% by weight of the entire mixture to obtain a conductive resin mixture of the present invention.

Example (2) In Example (1), stainless steel fiber (A) with a diameter of 8μ and stainless fiber 4-(B) with a diameter of 30μ
All the examples were the same as those of Example (1) except that the weight ratio of
) A conductive resin mixture of the present invention was obtained.

Example (3) All procedures were carried out in the same manner as in Example (1) except that in Example (1), the stainless steel fiber (A) with a diameter of 8μ and the stainless steel fiber (6) with a diameter of 30μ were changed to a weight ratio of 70:30. A conductive resin composition of the present invention was obtained.

Example (A) The weight ratio of stainless steel fiber (A) with a diameter of 8 μm and copper fiber with a straight weight of 50 μm was adjusted to 50:50, and the total amount of these two types of fibers was 10% of the entire mixture.
All examples are Example (1) except that they were adjusted to be % by weight.
A conductive resin mixture of the present invention was obtained in the same manner as above.

Comparative Example (1) A comparative conductive resin mixture was obtained in the same manner as in Example (1) except that only stainless fiber particles having a diameter of 8 μm were mixed.

Comparative Example (2) A comparative conductive resin mixture was obtained in the same manner as in Example (1) except that only stainless fiber (B) having a diameter of 30 μm was mixed.

Thus obtained nine conductive resin mixtures of the present invention and comparative conductive resin mixtures were injection molded to produce precision parts (IC carriers).
The thick part (2~3 絽) and the thin part (0,5
m) volume resistivity (Ω-1) and heat cycle from -40°C to 80°C, i.e. -40°C for 2 hours, temperature rising for 1 hour, 80°C
The volume resistivity (Ω-1) was measured after repeating the test for 2 hours and the temperature was lowered for 1 hour 40 times.The results are shown in Table 1.

Table 1 (Effects) As detailed above, the conductive resin mixture of the present invention provides a good shielding effect even in thin-walled parts of precision parts, and does not affect the same shielding effect even when heat cycled. It is extremely useful industrially.

Claims (2)

[Claims] (1) A thermoplastic resin is used as a matrix resin, and conductive fibers (A) with a diameter of 10 μm or less and strength (
and a conductive fiber (B) having a diameter of 50 g or more (tensile strength x cross-sectional area) at a weight ratio of 30:70 to 70:3.
A conductive resin mixture characterized by being mixed at a ratio of 0. (2) The conductive resin mixture according to claim 1, characterized in that stainless steel fibers are used as the conductive fibers (A).