JPH02129248A - Stainless fiber-filled conductive molding material - Google Patents

Abstract

PURPOSE:To obtain the title molding material having a good appearance, uniformly dispersed metal fibers and an excellent electromagnetic wave shielding effect by coating a stainless steel fiber bundle with a specified coating resin composition, cutting the coated bundle and mixing the cut bundle with a styrene resin. CONSTITUTION:A fiber bundle comprising a stainless steel fiber of a diameter of desirably 2-50mum is coated with a coating resin composition containing a low-MW thermoplastic resin (e.g., low-MW PE) of an MW <=1000 and desirably, a softening point >=150 deg.C and an styrene resin (e.g., styrene/acrylonitrile copolymer resin/ABS resin) desirably of an MW >=50000 in a mixing ratio of the former to the latter of desirably 0.1-30wt.% to 70-99.9wt.%. The coated bundle is cut to a predetermined length, and the cut bundle is mixed with a styrene resin (e.g., ABS resin) as a matrix resin.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention uses stainless steel fibers coated with a styrene resin containing a low molecular weight thermoplastic resin, so that the stainless steel fibers in the resin are uniformly coated. The present invention relates to a conductive molding material that is dispersed, has a good appearance, and has a large electromagnetic shielding effect.

[Prior Art] In recent years, electromagnetic shielding materials have been developed which are used to protect electronic circuits such as ICs and LSIs from external electromagnetic waves and to prevent harmful electromagnetic waves from leaking outside from various electronic devices. Various proposals have been made, and they can be broadly divided into methods that make only the surface conductive, such as vacuum evaporation, application of conductive paint, and zinc spraying, and methods that make only the surface conductive, such as methods that make only the surface conductive, and methods that mold a composition containing a conductive material in a resin. The method is known.

In the former, there is a concern about peeling during use, and in the case of complex shapes, there is great difficulty in implementing it, and in the latter, although it is a desirable method without the drawbacks of the former, It is difficult to uniformly disperse a conductive material and to produce a molded product with a good appearance.

Therefore, as a method to solve this problem, when incorporating a conductive material into a resin, continuous long metal fibers are used, and the resin is extruded and coated on top of the metal fibers, resulting in a resin-coated metal. A method has been proposed in which fibers are shredded into predetermined lengths, made into pellets, and mixed with a matrix resin to form a shielding material (Japanese Patent Application Laid-open No. 18/31/1989).
No. 5, JP-A-61-100.415, JP-A-62-9
7.806, etc.).

However, even with such a method, it may not always be possible to fully solve the above-mentioned problems, and further improvements in the layer have been desired.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to reduce the amount of stainless steel in the resin by using stainless steel fibers coated with a coating resin composition containing a low molecular weight thermoplastic resin and a styrene resin. An object of the present invention is to provide a conductive molding material in which fibers are uniformly dispersed, has a good appearance, and has a large electromagnetic shielding effect.

[Means for Solving the Problems] That is, the present invention covers a stainless steel fiber bundle with a coating resin composition containing a low molecular weight thermoplastic resin having a molecular weight of 10,000 or less and a styrene resin, and coats the stainless steel fiber bundle with a coating resin composition containing a styrene resin. This is a stainless steel fiber-containing conductive molding material mainly consisting of a stainless fiber-containing resin composition obtained by cutting into lengths and a styrene resin.

The stainless steel fiber used in the present invention has a diameter of the metal fiber or an equivalent diameter expressed by the following formula 2 x (cross-sectional area of fiber/pi) 1'' (hereinafter, both are simply referred to as diameter).
The amount is 2 to 501 U, preferably 8 to 25 p. If this diameter is smaller than 21Jx, it will be extremely difficult to impregnate the molten thermoplastic resin and the shielding effect will also be reduced.If it is larger than 50g, the shielding effect per unit amount added will be reduced and a large amount of fiber will be Both of these are not preferred.

Such stainless steel fibers are used as bundles of several hundred to tens of thousands of stainless steel fibers depending on the purpose, and a coating resin composition containing a styrene resin and a low molecular weight thermoplastic resin is coated on the surface of the stainless steel fibers. It is uniformly melted and coated integrally.

Examples of styrene resins used for this purpose include polystyrene resin, As resin (styrene-acrylonitrile copolymer resin), MS resin (styrene-methyl methacrylate copolymer resin), and styrene-anhydride arene polymer resin. , other copolymer resins containing one or more monomers copolymerizable with styrene or methylstyrene containing 50% by weight or more, high-impact polystyrene (HL
PS), ABS resin (styrene-butadiene-acrylonitrile copolymer resin), ASA resin, MS resin rubber-modified resin, styrene-maleic anhydride copolymer resin rubber-modified resin, and other vinyl aromatic ridges such as styrene and methylstyrene. Rubber-modified resins of styrenic copolymer resins obtained from styrene copolymer resins and styrene copolymer resins that can be copolymerized with these styrenes may be used, and only one type thereof may be used. They may be used as a mixture of two or more, or a combination of a rubber-unmodified resin and a rubber-modified resin may be used. The styrene resin used in the present invention preferably has a molecular weight of 50,000.
The above is preferable, and thereby the strength of the stainless fiber-containing resin composition is ensured.

Furthermore, the low molecular weight thermoplastic resin that constitutes the coating resin composition for stainless steel fibers together with the styrene resin needs to have a molecular weight of 10,000 or less, preferably 7,000 or less. If the molecular weight of the low molecular weight thermoplastic resin exceeds 10,000, a problem arises in that the stainless steel fibers are not sufficiently dispersed. As such a low molecular weight thermoplastic resin, it is particularly preferable that the melting point (softening point) is 150'C or less, more preferably 130'C or less.
'C or below. Specific examples of such low molecular weight thermoplastic resins include low molecular weight polyethylene, low molecular weight polyethylene-propylene copolymer, low molecular weight polyethylene-styrene copolymer, low molecular weight polypropylene, low molecular weight polystyrene, or maleic anhydride thereof. Examples include modified products. These can be used alone or in combination of two or more.

The molecular weights of the above-mentioned styrene resins and low molecular weight thermoplastic resins can be measured using GPC (Gepermeat), which is a method of fractional measurement that utilizes the difference in adsorption ability of polymers to appropriate substances.
ion chromatography) method.

This low molecular weight thermoplastic resin is essential in order to improve its dispersibility in the molded article containing stainless steel fibers, and the amount used is within the range of 0.1 to 30% by weight in the coating resin composition. , preferably within the range of 0.1 to 10% by weight. If the amount used is less than 0.1% by weight, the effect of improving the dispersibility of stainless steel fibers cannot be expected, and if it is more than 30% by weight, it may be difficult to knead the resin, especially if the molecular weight of the low molecular weight thermoplastic resin is low. Sexuality becomes worse.

The above-mentioned styrene resin and low molecular weight thermoplastic resin are uniformly kneaded in advance to form a coating resin composition,
This coating resin composition is used to coat the stainless steel fibers. The amount of coating resin composition used for this stainless steel fiber is 10 to 100 parts by weight per 100 parts by weight of stainless steel fiber.
The amount is 400 parts by weight, preferably 40 to 200 parts by weight.

If the amount used is less than 10 parts by weight, the coating on the stainless steel fibers may be insufficient;
If the amount is more than the Iffi part, a large amount of the stainless fiber-containing resin composition will be required in the production of the conductive molded body, which is not practical.

In order to prepare a stainless fiber-containing resin composition consisting of resin-coated stainless fibers using the above-mentioned stainless steel fibers and coated resin composition, for example, while passing the above-mentioned stainless steel fiber bundle through a die of a normal resin extruder, The surface of the stainless steel fiber bundle is coated and integrated with a coating resin composition melted in a router, and cut into a predetermined length, for example, 3 to 8 IrI!, by ordinary cutting means. Conventionally known methods such as cutting into lengths of r1, preferably 4 to 6 lengths to form pellets can be employed.

The resin pellets prepared in this way are blended and serve as a matrix in the conductive molded product, for example, polystyrene resin, As resin (
Styrene-7crylonitrile copolymer resin), MS resin (styrene-methyl methacrylate copolymer resin), styrene-maleic anhydride copolymer resin, others 50% by weight
Copolymer resins of the above styrene or methylstyrene and one or more monomers copolymerizable with these, high impact polystyrene (HIPS), ABS resins (
Styrene-butadiene-acrylonitrile copolymer resin), ASA resin (acrylonitrile-styrene-acrylonitrile copolymer resin), Zarani, the above MS resin, styrene-maleic anhydride copolymer resin, or other 5
Examples include rubber-modified resins of styrene resins, such as copolymer resins of 0% by weight or more of styrene or methylstyrene and one or more monomers copolymerizable with these. Only one type of these can be used, and two
It can also be used as a mixture of more than one species. This matrix resin is also usually formed into pellets for use.

In order to mold a conductive molded article using the stainless fiber-containing resin composition and matrix resin obtained in this way, the two are tri-blend mixed by a conventional method and molded into a desired shape by injection molding or the like. Just mold it. Also,
The content of stainless steel fibers in the conductive molded body formed in this way varies depending on the desired shielding effect, especially the type of radio wave or magnetic wave, the frequency, the required dB value, etc., but is usually 0.5 to 3. Volume %, preferably 0.7-1.
Generally, the amount is about 5% by volume, and when mixing the stainless fiber-containing resin composition and the matrix resin, the blending ratio is determined taking these points into consideration.

In addition, in the conductive molded body formed in this way,
If necessary, additives such as fillers, stabilizers, flame retardants, mold release agents, dyes and pigments, and plasticizers can be added. It may be added at the stage of manufacturing the containing resin composition, or it may be added at the stage of mixing the stainless fiber-containing resin and the matrix resin to form a molded body.

[Function] In order to disperse the stainless steel fibers in the styrene resin of the matrix resin, it is preferable to coat the stainless steel fibers with the styrene resin. However, when covering stainless steel fibers with styrene resin and dispersing the stainless steel fibers in the styrene resin matrix, it is difficult to uniformly disperse the stainless fibers. Therefore, in the present invention, a resin composition of a styrene resin containing a low molecular weight thermoplastic resin is used as a coating resin to coat the stainless steel fibers, and the stainless fibers are coated with the styrene resin as uniformly as possible.
Additionally, during molding and melting, the low molecular weight thermoplastic resin melts first, which makes the coating resin brittle and facilitates the dispersion of the stainless steel fibers. It is thought that this will ensure good dispersibility.

[Examples] The present invention will be specifically described below based on Examples and Comparative Examples.

Examples 1 to 4 Using 8 parts by weight of a continuous stainless steel fiber bundle obtained by bundling 1500 stainless steel fibers with a diameter of 15 μs and 8 parts by weight of the coating resin composition shown in Table 1, an extruder was used. Cylinder temperature 180-240℃, die temperature 240'
The above stainless steel fiber bundle was uniformly coated with the coating resin composition under the conditions of C and screw rotation speed of 3 orpm to form a resin coating layer integrally, and this was cut into a length of 6 # and coated with the resin. Stainless steel fiber-containing pellets were prepared.

16 parts by weight of the stainless steel fiber-containing pellets and 84 parts by weight of matrix resin pellets shown in Table 1 prepared in pellet form were mixed, and an injection molding machine was used to produce 160#
A flat molded product with a size of 160m x 0.5m is molded,
Dispersion state of stainless steel fibers in the obtained molded product and 1
The electromagnetic shielding effect at 00MH2 was investigated. The results are shown in Table 1.

The dispersion state of the stainless steel fibers was obtained by tri-blending stainless steel fiber-containing pellets and matrix resin pellets so that the stainless steel fiber content in the molded product was 6% by weight, and then injection molding the pellets into 150 #X 150 #X 3.
100 test pieces of M were molded, and those with no undefinated stainless fibers were considered good products, and the percentage of non-defective products among the 100 molded products was determined. Regarding the electromagnetic shielding effect,
Using Atopan Test Model Ding R4172 measuring machine,
Measurement was performed on a test piece of 150a++X 150#X 3 mm at a frequency of 100) IHz.

Comparative Examples 1 to 2 Stainless steel fiber-containing pellets were prepared in the same manner as in each example using only the styrene resin used in preparing the coating resin composition in each of the above examples, and the matrix shown in Table 1 was prepared. A flat molded product similar to that of each of the above Examples was molded using a resin. Regarding these molded products, the state of dispersion of stainless steel fibers and the electromagnetic shielding effect were investigated in the same manner as in each example. The results are shown in Table 1.

Comparative Example 3 Using the same stainless steel fibers as in each of the above examples, the stainless steel fiber bundles were sufficiently loosened and heated to 150°C, and then impregnated with the low molecular weight polyethylene shown in Table 1, without convergence. Adjust the amount of impregnation from the stainless steel fiber 8
Convergent fibers containing 0% by weight and 20% by weight of low molecular weight polyethylene were obtained.

Next, the surface of the convergent fibers was coated with AS/ABS resin as an outer layer so that the ratio with low molecular weight polyethylene was the value shown in Table 1, and the following treatments were carried out in the same manner as in each example.
A layered stainless steel fiber-containing pellet was prepared.

Using this stainless steel fiber-containing pellet, a plate-shaped molded product was molded in the same manner as in each of the above Examples, and the state of dispersion of the stainless fibers and the electromagnetic shielding effect were examined. The results are shown in Table 1.

[Effects of the Invention] According to the present invention, it is possible to obtain a molded product that has a good appearance, has metal fibers uniformly dispersed, and has a large electromagnetic shielding effect, and has extremely high industrial effects. Remarkable.

Patent applicant: Nippon Steel Chemical Co., Ltd.

Claims (2)

[Claims] (1) Contains stainless steel fibers obtained by coating a stainless steel fiber bundle with a coating resin composition containing a low molecular weight thermoplastic resin with a molecular weight of 10,000 or less and a styrene resin, and cutting the bundle into a predetermined length. A conductive molding material containing stainless steel fibers, mainly consisting of a resin composition and a styrene resin. (2) The coating resin composition is a low molecular weight thermoplastic resin of 0.1 to
The conductive molding material containing stainless steel fibers according to claim 1, comprising 30% by weight of the styrene resin and 70 to 99.9% by weight of the styrene resin.