JPS6234931A - Electrically conductive composite material - Google Patents

Abstract

PURPOSE:To obtain a polymeric composite material having decreased filler content and improved electrical conductivity while preventing the breakage and deformation of filler during molding, by mixing a specific fibrous filler randomly in a polymeric material. CONSTITUTION:The filler for the above composite material is an electrically conductive fibrous material having a fiber diameter of 2-30mum and length of 1-10mm and obtained from a SUS 304 stainless steel fiber cold-worked at a working ratio of 60-98%, e.g. a collected strand of composite filaments produced by covering SUS 304 stainless steel filaments with a matrix composed of other metal, subjecting the strand to a prescribed cold-working optionally after heat-treatment to the final working ratio of 60-98% to attain the target fiber diameter, dissolving and removing the matrix material exclusively, and cutting to prescribed length. The objective electrically conductive composite material can be produced by mixing and kneading the filler to a polymeric material.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a polymer composite material having excellent electrical conductivity, for example, electromagnetic shielding effect.

<Prior Art> In recent years, with the spread of various electronic devices such as computers and communication devices, many attempts have been made to prevent interference caused by electromagnetic waves or the like from inside or outside the devices.

One way to achieve this is to uniformly disperse a conductive filler in the form of powder, flakes, fibers, etc. in a polymeric material such as plastic that is the material of the casing, in contact with each other. However, it is known that the amount of fibrous filler mixed in can be reduced by selectively using a material with a small diameter and a large aspect ratio (length/fiber diameter).

For example, according to the May 23, 1983 issue of Nikkei Mechanical, even if metal fibers with a large aspect ratio are mixed in at a low rate of about 1 to 2% by weight, the amount of metal fibers of 40 db or more (
It has been reported that a shielding effect can be obtained for I GHz), and it is attracting a lot of attention.

However, on the other hand, polymeric materials such as rubber and plastics in a molten state have extremely high viscosity. The filler is affected by kneading, fluidity during nozzle passage, and other processing conditions, and the filler has a considerable tensile force associated with it.

External forces such as bending force and shear force are applied. As a result, low-strength fillers that cannot withstand these conditions are subject to deformation such as bending or breakage, making it difficult to form good conductive circuits and making it difficult to obtain desired characteristics, which is an important problem.

In the past, as shown in Japanese Patent Application Laid-Open No. 57-150203, most of the efforts have been related to improvements in processing methods and working conditions, and it is said that the material properties of filler materials have not yet been sufficiently studied. It's tough.

(Objective of the Invention) The present invention was made as a result of active investigation into such problems, and by using a fibrous filler with predetermined characteristics, it is possible to prevent breakage and deformation of the filler during processing. The purpose of the present invention is to provide a polymer composite material that prevents the occurrence of oxidation and reduces the rate of contamination, and also improves conductivity.

(Disclosure of the Invention) The fibrous conductive filler used in the present invention comprises 2
The filler has a fiber diameter of ~30 μmm and a length of 1 to 10 nm, and has a processing rate of 60 to 9.
It uses 5US304 series stainless steel fiber material that has been cold worked within the range of 8%.

Such stainless steel fibers include, for example,
As disclosed in the specification of No. 11523, a filament material made of SUS 304 stainless steel rust is encapsulated with a matrix material made of another metal to form a bundled wire of a composite wire material, and subjected to a predetermined cold working process or a heat treatment process in between. A final processing rate of 60 to 98% is applied to obtain the desired fiber diameter for pressing.
Further, a continuous filament tow is manufactured by dissolving and removing only the matrix material.

Then its length is short wA in the range 1-10IIWl
The conductive filler can be obtained by cutting it into a fiber shape, for example, with a cutter.

Here, the reason why the fiber diameter of the filler is set to 2 to 30 μmm is that if it exceeds 30 μmm, wear with the mold etc. will be severe during kneading and extrusion in injection molding, etc.
In addition, the filler protrudes on the surface of the obtained product, making it difficult for W& to come out, resulting in an unfavorable appearance (3-3). Furthermore, in terms of conductivity, a large diameter inevitably means an increase in the mixing rate, which goes against the gist of the present invention.

In other words, when considering the constraint of a predetermined amount of mixed filler, in order to improve the conductivity even a little, the aspect ratio (length/fiber diameter) of the filler to be mixed needs to be thicker. It is effective to use a filler with a fiber diameter of 2 μmm or less. However, if it is less than 2 μmm, it becomes too thin, resulting in poor strength, which is not preferable. From the point of view (B), the $a fiber diameter is more preferably 2 to 30 μmm. shall be 2-20 μmm.

On the other hand, the length is set in the range of 1 to 10 mm, which facilitates uniform dispersion within the polymer material, but if it exceeds 10 I, there is a problem that the fillers tend to become entangled frequently during kneading. On the other hand, if it is less than 1 mm, the shape becomes powder-like, so although dispersibility improves, if the amount is small,
It becomes difficult to form a sufficient conductive circuit, resulting in poor conductivity.

Furthermore, in the present invention, in order to prevent breakage and deformation during the filler treatment, the filler material is 5US304 stainless steel fiber material with a processing rate of 60 to 98% in order to have a good balance of strength and toughness. Cold within range! It is characterized by having been subjected to R processing.

In general, polymer materials in a molten state are polymer-like and highly viscous, and during kneading and injection in injection molding, which is a type of strong processing, the filler is subject to extremely large tensile forces, shearing, bending, etc. external force is applied. Therefore, in order to withstand this and be dispersed in a substantially straight shape, the filler must have a certain level of strength.

Furthermore, although it is well known that stainless steel has high strength and a high rate of work hardening due to processing, it has the property that it becomes brittle when processed in half and is easily broken due to bending or the like.

This tendency varies depending on the amount of various elements added in the filler material.In particular, stainless steel made of SUS 304 has the advantage of being able to easily obtain extremely high strength even with a small processing rate. When cold worked below 60%, the filler has a tensile strength of 140 Kg/
With a strength of more than mm2 and, for example, θ = 200 oersteds, it is possible to obtain a high magnetic permeability of μ = 10 breaths.
In the case of composite filling, they act and contribute to improving the shielding properties for both electric field waves and magnetic field waves.

Further, the upper limit of the processing rate is preferably 98% or less from the viewpoint of preventing the reduction in the toughness of the fiber material and preventing breakage during processing.

As explained above, conductive fillers that undergo severe processing in a highly viscous state have a certain level of strength (elasticity, tensile strength).
and toughness, and the processing rate is 60 to 9.
8% is considered the most balanced range.

Further, regarding the length of the filler cut in advance, it is thought that there is a relationship between the tensile strength and the aspect ratio (length/fiber diameter).

That is, fiber materials with low tensile strength have poor elasticity and are easily deformed and cut even by small forces, so the aspect ratio cannot be set too large, and the length must naturally be short.

Such a relationship can be expressed, for example, by the following formula, in which case the preferred value (A) ranges from about 2 to 25, and the larger the value (A), the less deformed it is. There is.

Based on this relationship, for example, for polymeric materials with high melt viscosity, by selecting a filler with a high value of (A) and using a filler with a larger aspect ratio, it is possible to prevent breakage and deformation. It is possible to prevent this and further improve conductivity.

Examples of polymeric materials used in the present invention include thermoplastic resins such as vinyl chloride resin, ABS@resin, polyethylene resin, polypropylene resin, and polyamide resin. Next, embodiments of the present invention will be described along with their effects.

<Example-1> SUS 304 obtained with a final cold drawing processing rate of 75%
Stainless steel fiber has tensile strength l g l Kg/
It consisted of 300 bundled tows having a diameter of m+++2 and a fiber diameter of 8 μllll11, which were continuously immersed in a styrene resin solution and dried with hot air at 125°C. The filling rate at this time was 50Vo1%.

After that, this composite bundle material is cut with a cutter to have a length of 5 mm to make composite pellets, and then mixed and kneaded with ABS@ fat pure pellets in a predetermined ratio using an injection molding machine (ζ injection molding machine). , filler filling rate is 5 wt,%, 10w
t,%, processed to 15wt%, size 10cm
Samples A-1 to A-3 having a square angle and a thickness of 31,111 mm were obtained.

In each sample obtained as a result, it was observed that the filler had little deformation or breakage, and was mostly straight and dispersed. In addition, the shielding properties of the sample were extremely good as shown in Table 1.

<Comparative example> 5US316L stainless steel fiber material subjected to focused wire drawing at a final processing rate of 50% has an average fiber diameter of 8 μml11 and 12
It has a tensile strength of 0 Kg/+w2, and after cutting it into length 5III11 using this, Example 1
By applying the same treatment as 5 wt%, 10 wt%
%, 15wt.

% comparative samples B-1 to B-3 were obtained.

The results are shown in Table 1.

Table 1 (Example 2) Next, sample A in which 10 wt% of the SUS 304.8μ stainless steel fiber filler obtained in Example 1 was mixed was prepared.
-2 and the same SUS 316L stainless steel as a comparison material ff! ! A heat cycle test was conducted using sample B-2 mixed with 10 wt% m-fiber filler,
We investigated changes in shielding effectiveness.

In addition, in the test method, each sample was heated at A1+80°C.
After being kept in the oven for 30 minutes, it was transferred to B, a -40°C oven, and kept in the same manner for 30 minutes.

A method was used in which processes A and B were treated as one cycle, and a total of three cycles were repeated.

The results are shown in Table 2. Table 2 (Effects) As detailed above, the present invention uses 60-98% cold-worked SUS 304 stainless steel fiber material as the filler material. This allows us to maintain a balance between strength and toughness, which prevents breakage and deformation during processing due to crosstalk, and as a result, we see a significant improvement in shielding performance. did it.

That is, as shown in Table 1, for example, 1.00 Ml
(When trying to obtain a shielding effect of 45 db electric field waves at z, conventional methods required a mixing rate of 10 wt%, but with the present invention, the mixing rate is only 5 wt%, which is about half the mixing rate. Similarly, it has become possible to reduce the mixing rate of magnetic field waves by half.

In addition, in Example 2, one of the severe tests for the composite amount
The results of a heat cycle test are shown,
As can be seen from this result, in the composite material of the present invention, the change in shielding properties due to thermal effects such as heating and cooling was only reduced by about 56, which was very good.

This is thought to be due to the fact that the internal filler can follow thermal deformation of the resin material base material well due to its strength and elasticity.

As described above, the composite material of the present invention is ideal because it is possible to reduce the percentage of filler mixed in, and the characteristics of the obtained material do not change much depending on the usage environment, and the industrial value of the present invention is extremely high. It is.

Claims (1)

[Claims] (1) A composite material formed by randomly mixing a conductive filler with a fiber diameter of 2 to 30 μmm and a length of 1 to 10 mm into a polymer material, wherein the conductive filler has a processing rate of 60 to 9.
A conductive composite material characterized in that it is made of SUS304 stainless steel fiber material that has been cold-worked within a range of 8%.