JPS6172060A - Electromagnetic wave-shielding plastic material - Google Patents

Abstract

PURPOSE:To facilitate the mixing of metal fibers, and to obtain the titled material exhibiting high electromagnetic wave-shielding property with only a small amount of added metal fibers, and suitable for the housing of electronic apparatus, etc., by compounding a plastic material with a specific amount of metal fibers having specific diameter and length. CONSTITUTION:Metal fibers (e.g. aluminum fiber, zinc fiber, etc.) having fiber diameter of 20-50mum and length of 5-15mm, preferably 5-10mm are added to a synthetic resin emulsion (e.g. emulsion of polystyrene) or solution (e.g. solution in an organic solvent such as toluene), and the mixture is dried and granulated. The obtained granules are added to a plastic material. The content of the metal fiber in the final product is 1-5vol%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of industrial application] The present invention relates to an electromagnetic shielding plastic material used for housings of electronic devices and the like.

[Conventional technology]

Housings for electronic devices and the like are desired to have electromagnetic shielding properties in order to prevent leakage of electromagnetic waves generated from inside and to prevent interference by electromagnetic waves from outside. Therefore, a conductive filler is mixed into the plastic housing material. A preferred filler is metal fiber. Since the metal fibers are intertwined with each other and form continuous particles in the plastic material, a high degree of electromagnetic shielding can be obtained with the addition of a small amount.

The entanglement of the metal fibers also improves the structural strength of the plastic. Conventionally, the shape of such metal fibers is considered to be good when the fiber diameter is 10 to 200 μm and the length is about 1.0 to 10 mm (Japanese Patent Application Laid-Open No. 78499-1999).
No.) 0 [Problems to be Solved by the Invention] However, the present inventors have found that the shape of the metal fibers to be mixed with plastics within the above range is not necessarily optimal.

[Means for solving problems]

The present invention, as a means to solve the above-mentioned conventional problems, involves incorporating metal fibers having a fiber diameter of 20 to 50 μm and a length of 5 to 15 M in an amount of 1 to 5 volumes per plastic.

[Structure and operation of the invention] The invention will be explained in detail below.

The metal fibers used in the present invention include metals or alloys such as aluminum, zinc, tin, brass, and stainless steel, or fibers such as glass fibers and ceramic fibers, coated with the above metals or alloys by vapor deposition or sputtering. Examples include metallized fibers.

The metal fiber has a fiber diameter of 20 to 50 μm and a length of 5 to 1
5. In order to give good electromagnetic shielding properties with a small amount of addition to plastic, the length of which is preferably between 5 and 10, the diameter of the metal fibers should be made as small as possible and the length should be made large to improve entanglement. On the other hand, if the metal fibers are made long and thin like this, they tend to curl into a light bulb and are difficult to handle. The above-mentioned limited range was set with the aim of obtaining good electromagnetic shielding properties with a small amount of addition and making it difficult to form a light bulb.

The plastics used in the present invention are mainly thermoplastics, such as polyethylene, polypropylene,
polystyrene, polymethacrylate, polyvinyl chloride,
Examples include acrylonitrile-butadiene-styrene copolymer, styrene-butadiene block copolymer, polyvinyl fluoride, polyvinylidene fluoride, polyphenylene oxide, polyphenylene/oxide modified product, and the like.

The metal fiber is mixed with the plastic in 1 to 5 volumes. When the metal fiber content is below the above range, sufficient electromagnetic shielding properties cannot be obtained, and when it is above the above range, the moldability of the plastic material deteriorates.

To mix the above metal fibers with the above plastics, the plastic is heated and softened, mixed with the metal fibers, and then pelletized, but the metal fibers break due to the shearing force during mixing or pelletizing, resulting in outside the above range. There is also a risk. To prevent such cutting of metal fibers and mix them into plastic, first mix metal fibers into a synthetic resin emulsion or solution, dry and granulate the mixture, and mix the metal fiber-containing base material into plastic during molding. The method to do so is recommended. In this method, the synthetic resin emulsion or solution has a much lower viscosity than the plastic softener, so the shearing force applied to the metal fibers during mixing is extremely small, and cutting of the metal fibers is reliably prevented. Ru. The synthetic resin emulsion or solution used in this method includes polystyrene, polymethacrylate,
Polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, styrene-butadiene block copolymer, polyvinyl fluoride, polyvinylidene fluoride.

Emulsions of synthetic resins such as polyethylene, polypropylene, polyacrylate, polyvinyl acetate, toluene, xylene, ethyl acetate, n-butyl acetate, acetate, methyl ethyl ketone, methyl isobutyl ketone,
Cellosolve acetate.

An example is an organic solvent solution such as ethylseronulp.

The mixing ratio of the emulsion or solution and the metal fibers is usually 5:1 to 1:2 by weight. The emulsion or solution in which the metal fibers are mixed is poured out onto a mold or mesh and heated and dried to create a synthetic resin film. In the case of an emulsion, if the film formation temperature is higher than room temperature, the synthetic resin film will crack during the drying process and will naturally become granular.

In this case, since almost no shearing force is applied to the metal fibers during granulation, it can be said that there is virtually no cutting of the metal fibers due to granulation. When a synthetic resin film does not cause cracks, it is crushed using a crusher or the like, but since it is easy to crush a synthetic resin film and no large shearing force is applied to the metal fibers, the metal fibers are rarely cut. The matrix thus obtained is mixed with plastic. The base material and the plastic need not be mixed in advance and pelletized, but may be mixed during molding. This prevents the metal fibers from being cut during mixing of the base material and plastic and during pelletization.

The mixing ratio of the base material and the plastic is such that the metal fiber content in the final plastic material is from 1 to 5 volumes. The molding is mainly performed by injection molding.

〔Effect of the invention〕

Since the present invention has the above-mentioned structural action, the metal fiber does not become a light bulb and can be easily mixed with plastic, and a plastic material having high electromagnetic properties can be obtained by adding a small amount.

[Example 1] Emulsion of styrene-methyl methacrylate copolymer (solid content 50% by weight, viscosity 1500 cps/25°C
1 Film formation temperature 100″C) and fiber diameter 20 μm 1 Length 1
51rR aluminum fibers are mixed at a ratio of 1=2 squares. Mixing is done gently using a conventional stirrer. The mixture thus obtained is poured into a mold whose inside is coated with a mold release agent to form a two-layer thick layer. When the mold is placed in a heating furnace and dried at 150 DEG C. for 30 minutes to completely remove moisture and then cooled to room temperature, the mixture coating formed inside the mold cracks and becomes pellets. The obtained pellets are sieved to collect those with a diameter of 10 to 15 ff or less, and those larger than that are crushed to a diameter of 10 to 15 ff or less and mixed with the former.

A predetermined amount of the metal fiber-containing base material obtained in the above manner is mixed with a styrene-butadiene-styrene block copolymer to make a final aluminum fiber content of 3 vol. injection molded into the shape of.

[Example 2] Polyvinyl chloride emulsion (solid content 50% by weight, viscosity 500 cpr, / 25°C 1 film forming temperature 80'C
) and stainless steel fibers with a fiber diameter of 50 μm and a length of 5 mm are mixed in a 1:3 weight ratio in the same manner as in Example 1, and the resulting mixture is similarly poured into a cover, dried, and then cooled. The obtained mixture film cracks in the mold and becomes pellets, so it is sieved and those with a diameter of 5 m or more are crushed to a size of 5 m or less. A predetermined amount of the metal fiber-containing base material obtained as described above and polymethyl methacrylate are mixed to finally have a stainless steel fiber content of 3 volumes, and the mixture is injection molded into a predetermined shape. .

[Example 3] Polyvinyl acetate doluol solution (solid content 60% by weight, viscosity 5600 cps/25°C) and fiber diameter 35 μm 1 length 1
0 MM brass fibers were mixed at a weight ratio of 1:3 in the same manner as in Example 1, and the resulting mixture was similarly poured into a mold and dried by heating at 150° for 020 minutes. The resulting coating is peeled off from the mold and ground into pellets with a diameter of 10 or less. The metal fiber-containing base material obtained as above and the acrylonitrile-butadiene-styrene copolymer are mixed to finally have a brass fiber content of 1 volume ff1%, and the mixture is injected into a predetermined shape. Shape.

[Example 4] In Example 3, the content of brass fibers is 5 volumes.

[Comparative Example 1] Instead of the aluminum fibers used in Example 1, aluminum fibers with a fiber diameter of 20 μm and a length of 17M are used.

[Comparative Example 2] Instead of the stainless steel fibers used in Example 2, stainless steel fibers with a fiber diameter of 53 μm and a length of 5 mm were used.

[Comparative Example 3] Instead of the stainless steel fibers used in Example 2, stainless steel fibers with a fiber diameter of 50 μm and a length of 4 nm are used.

[Comparative Example 4] In Example 3, the content of brass fibers was set to 0.8 volume.

[Comparative Example 5] In Example 4, the content of brass fibers was set to 5.2 volume.

〔test〕

Molded product obtained in Example 1.2.3.4 and Comparative Example 1
．． For No. 2, 3.4.5, the volume resistivity, which is a guideline for electromagnetic shielding performance, was measured. The results are shown in Table 1.

Table 1 As shown in Table 1, in Comparative Example 1 in which the length of the metal fiber was longer than the limited range of the present invention, the metal fiber formed the light bulb and was difficult to mix uniformly with the plastic\Example Compared to IK, the volume resistivity actually decreases, and in Comparative Example 2, in which the metal fiber diameter exceeds the limited range of the present invention, the volume resistivity decreases significantly compared to Example 2, and the metal fiber Similarly, Comparative Example 3 using a material whose length is below the limited range of the present invention has a significantly lower volume resistivity compared to Example 2, and a comparative example whose metal content is below the limited range of the present invention. In Comparative Example 4, the volume resistivity is significantly lower than in Example 3, and the metal content is below the limited range of the present invention. Comparative Example 5 is a molding material for molding with good fluidity during injection molding. The throwing power was also poor and a molded product with a uniform thickness could not be obtained, and the volume resistivity was almost the same as in Example 4 or slightly decreased due to the non-uniformity of the thickness.

Claims (1)

[Claims] An electromagnetic shielding plastic material containing 1 to 5% by volume of metal fibers with a fiber diameter of 20 to 50 μm and a length of 5 to 15 mm based on the plastic.