JPH0418976B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing metal fibers suitable for making plastic conductive and imparting electromagnetic shielding properties.

(Prior art) and (Problems to be solved by the invention) The use of metals for making plastics conductive and for electromagnetic shielding has been expanding in recent years in the electrical equipment industry and related industries, and there is a large market. Be expected.

However, conventional conductive metal powders and fibers are still expensive, and inexpensive conductive materials are desired.

Conventionally, methods for manufacturing such metal powders and metal fibers include the water foil method, atomizer method, electric method, thermal spray method, chatter vibration method, and rolling method, but all of them are carried out using special machines and production is difficult. It also has the disadvantage of being low in sex.

The present inventors have arrived at the present invention as a result of conducting various studies in order to make it possible to produce inexpensive, high-quality metal fibers suitable for plastic conductive applications without using special machinery.

(Means for Solving the Problems) That is, the present invention provides a conductive metal for plastics, which is characterized in that a metal is ground with an unbalanced metal grinding wheel and metal fibers are obtained by utilizing vibrations caused by the unbalance. It relates to a method for producing fibers.

The machine used in the present invention is not a special machine like that used in the chatter vibration cutting method, but is a conventionally used grinding machine with an appropriate unbalance, so the equipment cost is low. Also,
With conventional metal fiber manufacturing methods, it is often difficult to turn difficult-to-cut metals into fibers, and fine fibers with large aspect ratios are very expensive, but the present invention can easily turn difficult-to-cut metals into fibers. obtain.

That is, the metal that is the object of the present invention may be any metal that can be ground, and since a cutting tool is not used as in the chatter vibration method, even difficult-to-cut materials such as stainless steel can be made into fibers.

For example, aluminum or its alloys, copper or its alloys, nickel, zinc, tin, gold, silver, magnesium, carbon steel and alloys for machine structures according to JIS standards,
There are also special purpose steels.

Examples of grinding configurations that can be used in the present invention are shown in FIGS. 1-3.

FIG. 1 shows a centerless grinding mechanism in which a metal material c1 is ground between a grinding wheel a1 and a feed roller b1.
Place it on the blade d1 between the feed rollers b1
Move it while rotating it with w ₁ , and grind it by applying it to the whetstone a1 which is rotating with w ₂ .

Fig. 2 shows a cylindrical grinding mechanism, in which a metal material c2 is supported by both centers b2 and rotated at _w1 , and is moved back and forth and left and right to grind against grindstone a2 which is rotating at _w2 . do.

FIG. 3 shows a surface grinding mechanism, in which a metal material c3 is fixed to a moving table d3, moved back and forth and left and right, and is ground by applying it to a whetstone rotating at w.

Grinding grains of the metal grinding wheel used in the present invention in such a grinding machine include TiC, WC, Al ₂ O ₃ ,
Clay, SiC, SiO ₂ , TiB, CN ₂ , BN, etc.
A molded whetstone made of binder such as feldspar, china stone, sodium silicate, Bakelite, phenolic resin, natural rubber, synthetic rubber, etc. The size of the abrasive grains and the type of binder can be adjusted depending on the type of metal material and aspect ratio. It can be changed.

In addition, the surface of the whetstone is constantly dressed with diamond to maintain constant conditions, thereby controlling the grinding conditions.

During grinding, a grinding oil containing a surfactant as a main component is used as the grinding oil, and the grinding wheel and the surface of the metal material are constantly wetted and cooled.

The method of the present invention differs from conventional general grinding in that grinding is performed by creating an unbalanced grinding wheel to generate minute vibrations. For this purpose, a residual unbalance is intentionally provided in the shaft or grindstone mounting flange of the grinding mechanism as shown in FIGS. 1 to 3. That is, by adjusting the balance weight on the radius of the correction surface, an appropriate amount of unbalance is created and the grindstone is caused to vibrate minutely.

An example of this is shown in Fig. 4. In Fig. 4, a grindstone b, a mounting flange d, and a retaining ring e are attached to a shaft a, and balance weights c are placed at 3 to 5 locations around the outer circumference of the flange d. It is installed on the machine, and first balance it. Thereafter, by moving the balance weight c onto the outer periphery of the flange d by a distance calculated from the desired unbalance amount, the necessary unbalance amount can be applied to the grindstone.

The amount of unbalance imparted in this manner can be expressed in terms of the balance quality grade (G) mm/s according to JIS standard B0905 (1978).

According to the method of the present invention, the shape of the obtained metal fiber can be made complex without changing the aspect ratio or fiber diameter. When such metal fibers are mixed with plastics, the metal fibers are appropriately intertwined, so when used as a filler for conductive plastics, there is an advantage that the filling amount can be small.

In carrying out the present invention, in order to prevent oxidation of metal fibers during grinding and improve grindability, unlike in the case of general grinding, a cooling mechanism is provided in the grinding oil circulation section to keep the grinding oil at a low temperature. By cooling the grinding oil to a temperature of -20°C to +40°C, good metal fibers can be ground with good productivity.

Furthermore, in carrying out the present invention, it is important to efficiently distribute the grinding oil between the grindstone and the surface of the metal material to be ground and to prevent the outside air from coming into contact with the grinding oil in order to prevent heat generation during grinding. Therefore, depending on the type of metal material, it is possible to inject liquid N ₂ or liquid CO ₂ into the grinding oil injection area, which is effective for preventing oxidation.

Further, the grinding oil should be selected according to the metal material used, and it is particularly desirable to select it according to its hardness. For example, KLEKAT TC-59, TC-360, Noritake Cool S-100N are preferably used for nickel and stainless steel, and KLEKAT NET500L, NET500B-1, etc. are preferably used for aluminum steel and copper alloy.

By using these grinding oils and adopting appropriate grinding temperature conditions that are conditioned by the grinding wheel's grain size, bond strength, porosity, abrasive grain rate, peripheral speed of the grinding wheel, unbalance amount, and depth of cut, Target wire diameter,
Metal fibers having different lengths and aspect ratios can be obtained.

In a preferred embodiment of the present invention, the grinding grain size is 14
~No. 24, bonding degree L ~ M, porosity 2 ~ 4%, abrasive grain rate
Using 42~50 alumina grinding wheel, circumferential speed 2000 ~
Metal grinding is performed at 3000 m/min, balance G1.0-2.5 mm/s, depth of cut 2-15 μm, and grinding oil temperature 0-15°C. The resulting metal fibers have a wire diameter of 5 to 25 μm, a strip or rod shape, a length of 100 to 550 μm, and an aspect ratio of 5 to 110.
On the other hand, the wire diameter obtained by general grinding is 2 to 2 when the unbalance amount is corrected.
It was 3 μm in length and 50 to 200 μm in length, and was mostly debris.

Example 1 A stainless steel round bar of SUS-306 was ground with an alumina grindstone with a balance of 1.0 to 1.2 using Krecuttu TC360 grinding oil at 5℃ and a circumferential speed of 2500 m/min to obtain wire diameter of 4 to 10 μm and length of 180 to A stainless steel fiber with a diameter of 320 μm and an aspect ratio of 31 was obtained.

75 parts of this stainless steel fiber was mixed with 100 parts of urethane resin and cured to obtain a sheet with a thickness of 1 mm. A resistor element which became conductive at a pressure of 50 g/cm ² was obtained from this sheet.

On the other hand, the fibers obtained by correcting the imbalance and performing the grinding have a wire diameter of 2 to 3 μm and a length of
It was 50 to 200 μm, and most of it was debris. When this fiber was mixed with urethane resin at the same blending ratio as above, the resulting sheet became electrically conductive by 79
A pressure of g/cm ² was required.

Example 2 For comparison with conventional fibers, a comparison was made with fibers obtained by the chatter vibration method, and it was found that the metal fibers obtained by the method of the present invention had a fiber diameter of 3 to 12 mm compared to that obtained by the chatter vibration method. It was about 1/2 of the amount. Moreover, the length is about 1/4 to 1/50, and it is much easier to mix with the base resin as a filler for plastics.

Fibers made from brass using the chatter vibration method (wire diameter 20-50μm, length 1-3mm, aspect ratio 20-
150) was mixed with 100 parts of urethane resin and cured to make a sheet with a thickness of 2 mm. The electrical resistance of this sheet was 10 ^-2 Ωcm. On the other hand, the same brass was ground with an alumina grindstone with an unbalance of 2.3, using the grinding oil KREKATSU TC59, at a cooling temperature of -3℃ and a cylindrical grinder at a circumferential speed of 3000m/min. The electrical resistance of the sheet obtained by mixing the same number of fibers (wire diameter 2 to 8 μm, length 80 to 290 μm, aspect ratio 10 to 145) with the urethane resin was 10 ⁻⁴ Ωcm.

[Brief explanation of drawings]

Figure 1 is a centerless grinding mechanism, Figure 2 is a cylindrical grinding mechanism, Figures 3a and b are front views schematically showing a surface grinding mechanism, Figure 4a is a side view of an example of a balance adjustment device, and b is a front view. a...shaft, b...grindstone, c...balance weight, d...flange, e...retaining ring.

Claims (1)

[Claims] 1. A method for producing metal fibers for conductive plastics, which comprises grinding metal with an unbalanced metal grinding wheel and obtaining metal fibers by utilizing vibrations caused by the unbalance.