JPH0757489B2 - Method for producing conductive fiber composite resin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a conductive fiber composite resin, and more particularly to a method for producing a conductive fiber composite resin for electromagnetic wave shielding.

[Conventional technology]

Plastic housings for electronic devices (Various methods are known for electromagnetic wave shielding methods for housing housings,
There are a plating method for providing a metal coating film, a thermal spraying method, a conductive coating method for providing a conductive coating, and a method in which a conductive material such as metal fibers or flakes is mixed in a plastic housing. As those related to these, for example, JP-A-59-22710,
JP-A-59-49918, JP-A-62-45659 and JP-B-62-440
There are 24 mag.

[Problems to be solved by the invention]

The above-mentioned conventional techniques are roughly classified into the following two types.
One is a method of attaching a conductive coating to a plastic molded case, and the other is a method of forming a case using a resin containing a conductive substance in advance.

As the problems of the former conductive coating film deposition method, there are many processing steps, labor is required, cost and labor are required for environment maintenance, and in addition, there is concern that the conductive coating film may have long-term adhesion and conductive performance. There are such things.

Regarding the latter conductive material, there is a problem that the performance is particularly deteriorated with respect to the composite resin. One of them is that, in the durability reliability test and the repeated thermal shock test (heat cycle test), as the number of repetitions increases, the conductive performance deteriorates and the shield effect decreases.

Yet another major problem is that when the conductive fibers are mixed with the resin to form pellets for molding, the conductive fibers are cut in the kneading step with the molten resin, so the shielding effect is reduced proportionally. That is. That is, there is a problem that the original performance of the conductive fiber is damaged by cutting.

Regarding the above problems, specific examples will be given. For example, in a resin composite material using copper fibers as conductive fibers,
When the test was conducted under the exposure condition that the thermal shock test condition was -20 ℃, 2 hours, and then left at 70 ℃, 2 hours for 1 cycle, the shielding effect was reduced to less than half of the initial value after 30 cycles. I'm confirming. Further, the cutting of the conductive fiber at the time of kneading with the resin is a problem that cannot be avoided by an ordinary method. Therefore, in order to maintain the level of the shield effect, a method of increasing the filling amount of the conductive fiber is taken, but a new problem that causes a decrease in mechanical strength and deterioration of molding processability is added. .

An object of the present invention is to solve the above-mentioned problems of the prior art and new problems relating to the shield technology, and to provide a method for producing a conductive fiber composite resin suitable for electromagnetic wave shielding of electronic devices. It is in.

[Means for solving problems]

The present invention relates to a method for producing pellets of a conductive fiber composite resin for molding electronic device casings, which relates to a novel composition and a method for producing the same, which are achieved by a combination of the following three elemental technologies. To be done.

(1) A pellet manufacturing method that does not cause cutting of conductive fibers, which greatly affects the reduction of the shield effect, and a bundle of fine strands is continuously supplied by using an extruder, and the pellets are placed in a thermoplastic resin matrix. A new construction method in which it is continuously covered and buried in the ground and cut to an appropriate length.

(2) Featuring an iron-based metal (stainless steel) fiber having excellent shielding properties as an essential component and a conductive fiber used in combination with another metal fiber (copper-based or aluminum) or a metal-coated fiber Novel composition.

(3) A material that is not easily stress-relieved and is not easily affected by a thermal shock load is used as the thermoplastic resin.
A novel conductive fiber composite resin composition characterized by using a resin of 80 to 210 ° C.

As a subordinate, a coloring pigment, a flame retardant, an internal mold release agent, an antioxidant and the like can be used in combination in the thermoplastic resin, if necessary.

Hereinafter, the above three elemental technologies will be specifically described in detail.

FIG. 1 shows a cross section of an extruder crosshead which is one of the components of the present invention.

As shown in FIG. 2 to FIG. 5 on the AA cross section, holes for penetrating 2 to 5 bundles of conductive fibers are provided. The reason for the difference in the hole diameter is that it corresponds to the difference in the cross-sectional diameter of the strand and the combination ratio depending on the material of the conductive fiber. The shape of the newly developed die is shown in FIG. 6 for the two-bundle wire die, and subsequently in FIG. 9 for the five-bundle wire die.

The conductive fibers used in the present invention are metal fibers or metal-coated fibers. That is, in more detail,
It is composed of at least two kinds selected from the following group A, group B, group C, and group D, and is characterized by comprising 2 to 5 kinds of fibers containing group A as an essential component.

Group A: Iron-based metal fiber (stainless steel) Section diameter 5 to 15 μm Group B: Copper-based metal fiber (brass, nickel silver) Section diameter 15 to 60 μm Group C: Aluminum-based metal fiber (A5052, A7075) Section diameter 15 to 60 μm D group: metal-coated fiber (nickel-plated carbon fiber, nickel-copper-plated glass fiber, nickel-copper-plated polymer fiber) Next, the thermoplastic resin which is the third component of the present invention will be described. A characteristic is that a thermoplastic resin having a heat distortion temperature of 80 to 210 ° C. is used. The reason for this is that in order to achieve the electromagnetic wave shielding function of the housing for electronic devices, which is the final purpose, and to maintain the electromagnetic wave shielding function for a long period of time, the conductive fibers are separated from each other by three.
Since the conductive circuit of so-called mesh structure is formed by having the entangled contact points in a dimension, it is specified from the necessity that the stress relaxation characteristic of the resin has a certain level or more in order to maintain the contact pressure of the contact. is there.

From this point of view, it is desirable that the heat distortion temperature is high, but if it exceeds 210 ° C., the formability is deteriorated, so that the upper limit temperature is restricted. Therefore, the more preferable heat distortion temperature range is 100 to 150.
C., particularly preferably 110 to 130.degree.

As the thermoplastic resin used in the present invention, any one selected from the following can be used.

These materials can be selected according to the strength level required for various electronic devices to be finally used.

Thermoplastic resin: polyphenylene ether, polyether sulfone, polybutylene terephthalate, ABS resin, high impact polystyrene, polycarbonate, nylon polypropylene and polymer alloy polyphenylene ether / polystyrene, polybutylene terephthalate / polycarbonate, ABS resin / polycarbonate, impact resistance Polystyrene / polycarbonate.

In the above thermoplastic resin, if necessary, a coloring pigment,
0.5-5wt% of additives such as flame retardant, internal mold release agent, antioxidant, etc.
It is desirable to include%.

Using the conductive fiber and the thermoplastic resin, the first
The crosshead shown in the figure is set in the extruder, and the cross-section of the pellet obtained by cutting the continuous conductor wire coated with the thermoplastic resin on the manufactured multifilamentary metal bundle into a fixed length of 5 to 10 mm
The two bundles in FIG. 10 to the five bundles shown in FIG. 13 are shown below.

In this case, the compounding ratio of the conductive fiber into the thermoplastic resin is determined by the level of the shielding ability of the final electronic device against unnecessary electromagnetic waves.
It is necessary to satisfy the regulations of the above and voluntary regulations of the Japanese electric industry (VCCI), etc. As a result of various examinations, the appropriate range is as follows.

Group A: Iron-based metal fiber 1 to 10 wt% Group B: Copper-based metal fiber 20 to 30 wt% Group C: Aluminum-based metal fiber 2 to 15 wt% Group D: Metal-coated fiber 5 to 15 wt% In the present invention, iron-based metal One feature is that fiber is an essential ingredient. Although it is possible to obtain a sufficient shielding effect with iron alone, it has the drawbacks that the conductivity is lower than that of other materials and that the economic efficiency is greatly disadvantageous compared with other materials. However, because it has the advantage of being remarkably excellent in thermal shock properties, it is possible to reduce the number of defects and to optimize the combination with other materials in order to utilize the advantages.

The combination of various conductive fibers is selected to meet the required level of the final product, but the total weight fraction is 7 ~.
40 wt% is preferred.

The multi-core pellets having a constant length obtained in the present invention can be used to easily mold an electronic device casing using an ordinary injection molding machine. This means that the glass fiber reinforced resin used for another purpose such as strength improvement (as a typical example, glass fiber weight ratio 30 wt%, volume ratio 15 vol
%), The volume fraction of the conductive fiber of the present invention is at most 7v
Since the volume ratio is about ol% and less than half, the moldability is easy. The possibility of cutting the conductive fibers during injection molding of the housing cannot be said to be zero, but it is much smaller than the degree of cutting that can occur during melt-kneading with the resin used to make pellets. .

The present invention has a great feature in devising this point, and in order to solve the problem of cutting at the time of melt-kneading, multi-core pellets having a constant length can be obtained.

Comparative Example Fig. 14 shows a copper fiber as a conventional conductive fiber system.
Polyphenylene ether resin 50 with a diameter of 50 μm and a length of 7 mm was melt-mixed with resin in an amount of 15 wt% by an extruder 50, a copper fiber (40 wt%) composite polyphenylene ether resin 51 obtained in the same manner and SUS304 as an iron-based metal fiber, Diameter 8μ
m, 7 mm long 15 wt% composite polyphenylene ether resin 52 pellets injection molded flat plate (200 mm mouth x 30 m
The volume resistivity of m) is shown.

When the compounding ratio of the conductive fiber is constant (15 wt%), the iron-based metal fiber (SUS304) composite material has a smaller volume resistivity than the copper-based fiber composite material and is excellent in conductivity. It is considered that this is because the diameter of the iron-based metal fiber is small and the number of contacts formed is much larger than that of the copper-based metal fiber, and the copper fiber is easily cut during kneading.

In order to lower the volume resistivity of the copper-based fiber, it is necessary to increase the compounding ratio as shown in FIG. 14 and Table 1. However, this is not a good idea because it causes an increase in specific gravity and a decrease in moldability and strength as a composite material.

Thermal shock test (-20 ℃ x 2h)
The change rate of the volume resistivity after + 70 ℃ × 2h) is much larger in the copper-based fiber than in the iron-based fiber. Therefore, the copper fiber composite material cannot be practically used in terms of durability.

It is considered that the reason why the rate of change in volume resistivity of the copper-based fiber composite material is large is that the thermal conductivity is large, the stress relaxation of the matrix resin is promoted, and the contact pressure of the contacts is lowered.

Therefore, as the matrix material, it is desirable that the stress is not easily relaxed, that is, that the heat deformation temperature is high.

On the other hand, the volume resistivity of the flat plate test piece 60 made of the copper-based fiber 15 wt% composite pellet produced by using the double bundle wire die of the present invention is about 1 as compared with that obtained from the pellet by the conventional method having the same mixing ratio. The value is as small as / 10, indicating that there is no influence of severing. In other words, in the conventional method, the inherent property of the conductive fiber as the starting material is that the performance is inevitably deteriorated because the conductive fiber is cut during the kneading process.

The iron-based metal fiber composite material has a small rate of change in the thermal shock test and is a very advantageous material in this respect, but it requires more steps in the process of obtaining ultrafine fiber, and has a volume resistivity higher than that of the copper-based fiber material. In addition to being inferior in the initial value, the price is several times more expensive, and it is a problem that it is used as a single system in terms of characteristics and economical efficiency.

Therefore, it was found that the combined use type metal fiber, which takes advantage of the fact that the initial value of the conductivity of the copper type fiber composite resin is excellent, and the advantage that the change of the iron type metal fiber with respect to thermal shock is small, is effective. The iron-based fiber is expensive because it increases the number of contacts because the wire system is thin. Nickel-double coated carbon fiber can be used instead of iron-based fiber, but there are some problems in manufacturing man-hours, volume resistivity, and price, and it cannot surpass iron-based fiber. In addition, instead of the copper-based fiber, an aluminum-based metal fiber, a nickel-copper-plated polymer fiber, or a nickel-copper-plated glass fiber can be used. Combinations with fibers or metallized fibers are effective.

The volume resistivity of the combined conductive fiber material 61 produced according to the present invention is also shown in FIG.

The material composition is as shown in Table 2.

61 is a case where a polyphenylene ether resin having a heat distortion temperature of 70 ° C. is used, and 62 is a case where a resin of 120 ° C. is also used. It can be seen that the 62 materials with small stress relaxation show small changes in the volume resistivity with respect to the thermal shock cycle.

[Action]

The present invention devises a new crosshead die structure for melting and kneading a conductive fiber composite thermoplastic resin to solve the problem of the fiber cutting of the conventional method, and to obtain an appropriate length of the multicore conductive fiber composite resin. By establishing a pellet manufacturing method with high quality, a large improvement in the conductive performance has been realized, which is a significant difference in action and effect compared to the conventional method.

In addition, the fact that the use of ultrafine wires of iron-based metal fibers (stainless steel) as an essential component makes it possible to improve the conductive performance by combining with other conductive fibers by utilizing the forming ability of many contacts. In addition to playing, the following excellent effects were added. That is, when used in combination with a copper-based fiber, the excellent conductivity of copper can be used to improve the conductive performance with a small blending ratio. It brought about the effect of comparing product casings. Further, other conductive fibers such as the metal-coated carbon fibers used in the present invention originally have a small specific gravity and have an unprecedented effect in terms of moldability and light weight.

Further, the thermoplastic resin as the matrix used in the present invention, by using a material with less stress relaxation, it is possible to suppress the rate of change in the thermal shock test to an extremely small level, and maintain the electromagnetic wave shielding performance of the housing of the final product for a long time. It has an effect that can be achieved.

The present invention will be described in more detail below with reference to examples.

〔Example〕

In describing the examples, typical materials, pellet manufacturing methods, and characteristic evaluation methods will be described.

The conductive fiber was a continuous arbitrary bundled wire. The diameter of the wire is as follows.

Ferrous metal fiber (abbreviated as stainless steel, SUS): 8μ
m Copper-based metal fiber (abbreviated as Cu): 50 μm Nickel plated carbon fiber (abbreviated as Ni-carbon): 12
μm Nickel-copper-plated acrylic fiber (abbreviated as Ni-acrylic): 15 μm Thermoplastic resin (typical example) Polycarbonate resin, heat distortion temperature 130 ℃ Polyphenylene ether resin, 〃120 ℃ Multi-core shape with the above conductive fiber and thermoplastic resin The pellet manufacturing method was carried out by using a crosshead (Fig. 1) equipped with the die of the present invention (described in Figs. 6 to 9) as a twin-screw extruder (screw diameter).
32mmφ, 3 thread, L / D = 28)
The bundle was continuously fed in 5 bundles, and the multifilamentary continuous body coated with the molten resin was cut to an appropriate length (7 mm) through a cooling step.

The pellets obtained here were used to mold test pieces (200 mm mouth x 3 t) and electronic equipment casings under the molding conditions of thermoplastic resin.
If necessary, it is also possible to mix and use a base thermoplastic resin for adjusting the conductive fiber concentration.

Regarding the electromagnetic wave shielding function of the electronic equipment housing, the shielding ability against unnecessary electromagnetic waves generated under the most severe operating condition of the electronic equipment was measured according to the contents of industry voluntary regulation (VCCI).

This time, the average value of the radiated electric field strength at a practical frequency of 30 to 100 MHz is shown.

The thermal shock test, which was conducted as one of the evaluation criteria for the durability of the conductive fiber composite resin, showed that
It was left for 30 hours in a 20 ° C constant temperature bath, and immediately left for 2 hours in the next 70 ° C constant temperature bath, which was repeated 30 times.

Example 1. Table 3 shows the volume resistivity and the radiated electric field strength of an electronic device housing of a test piece molded using pellets of a conductive fiber composite thermoplastic resin produced according to the present invention. Both values are at satisfactory levels. The characteristic values of the conventional method used for comparison are as already described in Table 1, and comparing the sample of Comparative Example No. 2 and the above-mentioned Example Sample No. 1 showed a small amount and equivalent effect. This proves the effectiveness of the present invention.

Example 2 The results of the thermal shock test are shown in Table 4 and FIGS. 14 and 15.

In Comparative Examples 1 and 2 according to the related art, the volume resistivity suddenly increased, the electromagnetic wave shielding function was significantly reduced, and the level reached a level where it could not be put to practical use. Example 1
That is, 62 has a very small change in characteristics as shown in Table 4, Fig. 14 and Fig. 15, and its initial value (62) and after 30 cycles of thermal shock loading (62 ') are extremely excellent. I understand.

The same applies to the third embodiment.

〔The invention's effect〕

The present invention embodies the most effective method for imparting the function of shielding the unnecessary electromagnetic waves generated from the electronic equipment by the molded product of the thermoplastic resin composition in which the conductive fiber is composited, and the elemental technology is as follows. is there.

In the method of producing conductive fiber composite material pellets,
A multi-core pellet with a constant length without any severing can be obtained, and the conductive function can be fully exhibited.
The effect of being able to improve the conductive function with a small compounding ratio by using it in combination with other conductive fibers, and hence having good moldability and suppressing the increase in specific gravity to a small extent was produced. In addition, the effect of significantly improving the thermal shock resistance was produced by using a resin with less stress relaxation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a crosshead for manufacturing a multifilamentary wire used in a manufacturing method according to the present invention, and FIGS. 2 to 5 are cross-sectional views showing a cross section taken along the line AA ′ of FIG. 1, respectively. , Sixth
Fig. 9 is a perspective view showing a die mounted on the crosshead, Figs. 10 to 13 are perspective views showing pellets each having 2 to 5 cores and cut into a certain length, and Fig. 14 is a heat of volume resistivity. FIG. 15 is a graph showing the relationship with the impact cycle, and FIG. 15 is a graph showing the frequency characteristic of the radiated electric field strength of electronic equipment. 1 to 10 ... Conductive fiber introduction hole, 30 ... Thermoplastic resin, 62 ... SU
S / Cu / PPE-based conductive fiber composite resin housing, 70 ... Resin housing that does not contain conductive fiber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Makoto Iida Makoto Iida, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Hitachi, Ltd. Institute of Industrial Science (72) Inventor Akiichi Ota 1 Horiyamashita, Hadano-shi, Kanagawa Company Hiritsu Seisakusho Kanagawa Plant (72) Inventor Susumu Iwai 1 Horiyamashita, Hadano City, Kanagawa Prefecture Hiritsu Seisakusho Kanagawa Plant (56) Reference JP 61-100415 (JP, A) JP Sho 60 -162604 (JP, A) JP 59-22710 (JP, A) JP 53-138466 (JP, A)

Claims (3)

[Claims] 1. A bundle of two or more kinds of conductive fibers having different materials and cross-sectional shapes, which are individually arranged in a thermoplastic resin and extruded and coated in a multifilamentary wire. Group B, group C, group C, and at least two types selected from group D, and group A as an essential component, and the conductive fiber in the form of multifilamentary wire is continuously embedded in the longitudinal direction. A method for producing a conductive conductive fiber composite resin. Note Group A: Iron-based metal fiber, cross-section diameter 5 to 15 μm Group B: Copper-based metal fiber, cross-section diameter 15 to 60 μm Group C: Aluminum-based metal fiber, cross-section diameter 15 to 60 μm D group: Metal-coated fiber 2. A step of continuously feeding at least two kinds of continuous bundled wires of a conductive fiber to a crosshead portion of a plastic extruder and simultaneously coating them with a thermoplastic resin which is plasticized and melted into a multifilamentary wire, and a cooling step. In the step of cutting into a length of 3 to 10 mm and pelletizing, the weight fraction of the conductive fibers is set to 7 to 40 wt%. Manufacturing method of fiber composite resin. 3. The thermoplastic resin is polyphenylene ether, polyether sulfone, polybutylene terephthalate, ABS resin, impact-resistant polystyrene polycarbonate, nylon polypropylene and polymer alloy polyphenylene ether / polystyrene, polybutylene terephthalate / polycarbonate, ABS resin. The method for producing a conductive fiber composite resin according to claim 1, wherein the thermoplastic resin is any one kind of thermoplastic resin selected from the group consisting of / polycarbonate and high impact polystyrene / polycarbonate.