JPH02207902A - Production of metallic fiber for conductive resin - Google Patents

Abstract

PURPOSE:To obtain an excellent electromagnetic wave shield effect by assembling many pieces of metallic stock wires coated with a low melting metal on the surfaces to a bundle shape and rolling the bundles to a desired shape by means of grooved rolls without lubrication. CONSTITUTION:A prescribed number of bobbins 1 wound with phosphor bronze wires applied with solder plating are prepd. and are set to a supply stand. The solder plated phosphor bronze wires drawn out of the bobbins 1 are inserted by each prescribed number into the holes provided to a guide plate 2 to form a prescribed number of bundles of the metallic stock wire bundles b. The bundles are further passed through a guide die 3 consisting of cemented carbide dies of a prescribed diameter to form the bundles of prescribed number of wires. The front ends thereof are coated with aluminum foil. Such metallic stock wire bundles b are rolled by a tandem rolling mill arrayed with calibers having a nearly hexagonal shape in 36 steps vertically and horizontally. The stock wires condense to each other and constitute a piece of the wire at the time of emerging from the 5-th rolls. The solder plated phosphor fiber bundle of the prescribed diameter obtd. in such a manner is cut to a pellet shape and a prescribed amt. of the pellets are compounded with an ABS resin. The mixture is injection-molded as a conductive resin compsn.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a metal fiber for conductive resin, and in particular, it is blended into a thermoplastic resin in order to impart yAift properties to housings of electronic devices, etc. The present invention relates to a method for manufacturing metal fibers at low cost and efficiently.

[Conventional technology]

Housings for electronic devices such as computers, word processors, and facsimile machines are often made of injection molded thermoplastic resins such as ABS resin, polycarbonate resin, and polypropylene resin for the purpose of reducing weight and cost. However, the thermoplastic resin alone cannot block the electromagnetic waves emitted from electronic devices, nor can it prevent the intrusion of electromagnetic waves from the outside, so these electronic devices may interfere with each other. The problem of malfunctioning has been attracting attention.

One way to prevent leakage of electromagnetic waves is to change the design of the circuit itself so that it does not generate electromagnetic waves, but the most common method is to shield the electromagnetic waves by adding conductivity to the housing6. Methods such as spraying melting point metal onto the inner wall of the housing, applying conductive paint, and pasting metal foil are known. However, these methods require an additional process to be added after conventional injection molding, resulting in a significant cost increase due to changes in the production line.

In recent years, a method of injection molding conductive resin that can be used without modification using conventional manufacturing processes, that is, a method of adding metal fibers to thermoplastic resin and making it conductive by intertwining the metal fibers, has been considered promising. ing.

The metal fibers added to the thermoplastic resin include aluminum, copper alloys such as brass, stainless steel, tungsten, molybdenum, etc., and metal fiber bundles of 100 to 10,000 fibers with a diameter of 5 to 50 pmφ are bundled. is used. These metal fiber bundles are integrally coated with resin around them, cut into lengths of 3 to 30 mm, mixed in an appropriate amount into thermoplastic resin pellets that serve as a matrix, and then subjected to injection molding. There is.

The following methods are known as methods for producing the metal fiber bundles.

(1) Repeat wire drawing and heat treatment to produce ultra-fine wires with a diameter of 50 pm or less, and bundle them together in large numbers.

(2) A large number of plated metal wires are stored in metal tubes made of different materials, and each metal tube is extruded, rolled, and drawn to reduce the area of the many metal wires at the same time. Dissolve and remove the metal tube and plating layer.

(3) Instead of the above-mentioned plating, a large number of metal wires coated with a mold release agent are housed in a metal tube, the area is reduced all at once, and finally the metal tube is dissolved and removed to remove the mold release agent.

[Problem to be solved by the invention]

However, in the method (1) above, it is necessary to draw each metal wire separately. For example, in the case of copper wire, it is necessary to draw from a rough wire with a diameter of 8 mm to an ultra-fine wire with a diameter of 50 pm. It is necessary to use four to five continuous wire drawing machines until the wire is drawn, and the production amount per unit time is small (it is very expensive).

In addition, the methods (2) and (3) above are rational in that they reduce the area of a large number of metal wires at once, and are superior to the method (1) above. It is necessary to remove the layer or the mold release agent, which has the disadvantage of increasing costs.

By using conductive resin as the housing material,
Although electromagnetic shielding can be achieved efficiently, the metal wA fibers incorporated therein are relatively expensive due to the above-mentioned problems in the manufacturing method, which is an obstacle to practical application.

[Means to solve problems]

In view of these points, the inventors of the present invention have conducted intensive studies on a method to inexpensively and efficiently produce metal fibers to be incorporated into the conductive resin. After coating the surface of the metal strands, if a large number of them are bundled and rolled using grooved rolls without lubrication, the metal fiber bundles obtained in this way will have metal fibers that adhere to each other. Moreover, during injection molding, the low melting point metal melts and the individual metal fibers separate from each other, so it is necessary to melt the metal covering the metal fibers and remove the cracks after area reduction processing as in the conventional method. The present invention was completed after discovering that there is no such thing.

That is, the present invention provides a conductive material that is characterized in that a large number of metal wires whose surfaces are coated with a low melting point metal are assembled into a bundle, and this is rolled into a desired size using grooved rolls without lubrication. This is a method for producing metal fiber for resin.

Next, the implementation of the present invention tl@m will be specifically explained using the drawings.

In the present invention, a large number of pobbins l for feeding out metal wires a made of birch coated with a low-melting point metal as shown in FIG. The metal wires are bundled by a guide die 3 for focusing, thereby forming a bundle of metal wires. The metal wire bundle is rolled to a desired size ratio by a series of slotted rolling rolls 4, but since it tends to fall apart when being guided to the rolling rolls 4, the tip portion to be inserted is gathered in advance with aluminum foil or copper foil. In the present invention, since lubrication is omitted during the rolling process, the metal strands a stick together during the area reduction process using the rolling rolls 4. The metal wire bundle is integrated and can be handled as if it were a single wire.This adhesion becomes noticeable from around the fifth stage of the grooved rolling roll 4.

Metal fiber bundle C rolled and integrated in this way
is wound up on a winding pobbin 6 through a guide roll 5,
In a further step, it is cut to an appropriate length, blended into a thermoplastic resin, and used as a conductive resin composition.

The metal wire a has a diameter of 0.1 to 1. Ommφ is suitable; if the diameter is larger than this, the entire equipment will become larger and equipment costs will increase; if the diameter is less than 0.1 rrrmφ, the cost required for processing up to that point will already be high, and the merits of bulk rolling will be reduced. It becomes less. As for the material of the metal wire a, copper alloys such as pure copper, brass and phosphor bronze, and copper-based wires such as copper-coated steel wire are preferable from the viewpoint of conductivity and wettability with low melting point metals. As the material, a material having a melting point lower than the injection molding temperature of the conductive resin is appropriately selected from Sn, Pb, Cd, Bi, and alloys thereof.

Further, the groove shape of the grooved rolling roll 4 can be appropriately selected from a combination of nine-ellipse, Gouyer diamond, diamond square, and the like.

[Effect]

In the present invention, after coating the surface of a metal wire with a low melting point metal,
Since a large number of these are bundled together and rolled using grooved rolls without lubrication, the metal fiber bundles obtained in this way have metal fibers that adhere to each other and are integrated, unlike conventional methods. There is no need to extrude and coat the metal fiber bundle with resin to integrate it.

In addition, since a low melting point metal that melts at the temperature at which the conductive resin is injection molded is used as the coating metal to prevent metal wires from adhering, the low melting point metal melts during injection molding and separates the individual metals. The fibers are separated from each other, and there is no need to melt and remove the metal covering the metal fibers after area reduction processing as in the conventional method.Furthermore, according to the method of the present invention, a large number of metal wires can be processed at once. The steps of inserting the metal wire bundle into the metal tube and dissolving and removing the metal tube after the area reduction process, which are normally performed when performing the area reduction process, are no longer necessary, and the effect of reducing processing costs is extremely significant. .

Furthermore, in the present invention, the low melting point metal that coats the metal wire is
It melts during injection molding, flows, and then solidifies to firmly bond the metal fibers together, which also has the secondary effect of improving the electromagnetic wave shielding properties of the molded product.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

We prepared 200 bobbins, each wrapped with two phosphor bronze wires (7P) each having a diameter of 0.5 mm and solder-plated (63Sn-37Pb) with a thickness of 10% m, as shown in Figure 1. The wire was set on a supply stand, and 20 solder-metal bronze 1 wires a pulled out from the pot 1 were inserted into the holes provided in the temporary guide 2 to make 20 bundles of metal wires.

This is further passed through a guide die 3 consisting of a carbide die with a diameter of 12 mm to form a bundle of 400 wires (metal wire bundle b),
I covered the tip with aluminum foil to prevent it from coming apart.

Next, the metal wire bundle thus prepared was rolled using a tandem rolling mill with approximately hexagonal holes as shown in FIG. 2 and arranged in 36 rows vertically and horizontally. Area reduction rate per roll is 12%
The cross section of the hole shape of the first stage roll has a cross-sectional area equivalent to a diameter of 10 mmφ, and the 36th stage has an approximately hexagonal hole shape equivalent to a diameter of 1.0 mmφ. The bundle of metal strands inserted through the groove rolling mill starts to become integrated after exiting the third groove rolling roll 4, and when it leaves the fifth roll, the strands stick together, making it look like one piece. It looks like the lines of a book. Once the wire has adhered in this manner, it becomes very easy to pass the wire through the rolling mill, and rolling up to 36 stages can be easily completed and the wire can be wound around the bobbin of the winding machine 6. Although the wire rolled in this manner does not have a circular cross section, it has sufficient characteristics to be usable as a metal fiber blended into a conductive resin.

The average cross-sectional area of the metal fibers is 0.002 mm, and the diameter is 5.
It corresponded to a round wire of 0IImφ.

The integrated soldered bronze fiber bundle with a diameter of 1.0 mm mφ obtained in this way was cut into a pellet shape with a length of 6 mm on a separate line, and 15 wt% was mixed into an ABS resin pellet. A conductive resin composition was prepared. The conductive resin composition thus produced was loaded into an injection molding machine and injection molded into a plate shape of 60 x 60 x 3 mm.

[Comparative example]

4 phosphor bronze wires with a diameter of 50 μm manufactured by wire drawing
00 pieces are bundled together and extrusion coated with ABS resin around the bundle, which is blended with ABS resin in the same manner as in the above example,
The examples were injection molded into the same shape.

Regarding the molded bodies obtained in the above Examples and Comparative Examples, heat cycle tests from -40°C to 80°C were repeated 100 times, and electromagnetic shielding properties before and after the heat cycle tests were measured. The obtained results are shown in Table 1 as a product according to the present invention and a comparative example product.

Table 1 (X) Shielding effect against 300 MHz electric field As is clear from Table 1, the product according to the present invention has a superior electromagnetic shielding effect compared to the comparative example product, and even when subjected to a short cycle (i.e., a long No deterioration of characteristics even after long periods of use
On the other hand, the comparative example product did not have very good electromagnetic shielding effect.
Moreover, its characteristics deteriorate significantly due to heat cycling.

〔Effect of the invention〕

According to the method of the present invention, metal fibers for conductive resin can be produced efficiently at low cost, and molded products obtained by injection molding a conductive resin composition in which the metal fibers are blended with a thermoplastic resin. It has excellent electromagnetic shielding effect,
Its properties do not deteriorate even after long-term use, and it has a remarkable industrial effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of the manufacturing process of the metal fiber for conductive resin according to the present invention, and FIG. 2 is an explanatory diagram showing an example of the groove shape of the grooved rolling roll used in the present invention. . 1--・Bobbin, 2--・Guide plate, 3--・-
・Guide die 4--groove rolling roll, 5--guide roll, 6--winding bobbin, a--metal wire, b--metal wire bundle, C--rolling process bundle of metal wires. Patent applicant Furukawa Electric Co., Ltd.

Claims (1)

[Claims] A metal fiber for conductive resin, which is characterized in that a large number of metal wires whose surfaces are coated with a low melting point metal are assembled into a bundle and rolled into desired dimensions using grooved rolls without lubrication. Production method.