JPH0819257B2 - Synthetic resin composition for electromagnetic wave shielding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a novel synthetic resin composition for electromagnetic wave shielding, which comprises a low melting point alloy effective for shielding electromagnetic waves (in a broad sense), a fibrous filler and a thermoplastic resin. Regarding

[Conventional technology]

Electronic devices such as computers and various communication devices are sources of electromagnetic waves in a broad sense (hereinafter, electromagnetic waves refer to electromagnetic waves in a broad sense unless otherwise specified) and cause various problems, and at the same time, other electronic devices. There is a problem that the electromagnetic waves leaking from the device itself will cause damage. Therefore, in order to solve these problems relating to electromagnetic waves, measures such as sealing the source with a metal plate or the like have been taken.

However, in recent years, the trend toward lighter, thinner, shorter, and smaller electronic devices has forced a switch from a metal housing to a plastic housing that is ineffective in many cases from the standpoint of blocking electromagnetic waves.

This is the reason why the synthetic resin material must also be provided with the electromagnetic wave shielding ability.

However, the method conventionally used for this purpose is generally to use a mixture of plastics with metal particles such as lead or the like, or carbon powder, or to use it by applying it as a paint. There was (for example, Japanese Patent Publication Sho 57
-11440, JP-B-59-30240, JP-A-54-16558, etc.).

However, the current situation is that these methods have not yet obtained a sufficient shielding effect.

[Problems to be solved by the invention]

The present inventor has investigated the cause, and in the conventional method of simply kneading metal particles and the like into a synthetic resin, considerable voids are generated between the metal particles dispersed in the resin, which is one of the causes. He found that the electromagnetic wave was not completely shielded.

Therefore, as a result of research on a method for removing this cause, when the synthetic resin composition is thermoplasticized, if the mixed metal particles are melted and evenly dispersed, such voids disappear. Taking inspiration, I conducted further research to realize this.

However, in reality, even if a metal that melts at the plasticizing temperature of the synthetic resin is selected and mixed, even if it is plasticized and fluidity appears in both, the remarkable difference in specific gravity between the two causes There was an unexpected problem that the molten metal separated and aggregated, and as a result, the intended product was not obtained.

[Means for solving problems]

Therefore, the present inventor has further researched a method of uniformly dispersing a molten metal in a resin, and finally uses an alloy as a metal, and a target molten alloy by coexisting a fibrous filler such as glass fiber. Based on this finding, it was found that a synthetic resin molded product in which is uniformly dispersed is obtained, and the present invention has been completed.

That is, the present invention provides a synthetic resin composition effective for electromagnetic wave shielding, which is composed of an alloy that can be melted during thermoplasticization, a fibrous filler, and a synthetic resin.

 The present invention will be described in detail below.

The synthetic resin used in the present invention is not particularly limited, and those generally used conventionally in the field of electronic devices are widely used.

However, from the viewpoint of ease of molding and other required physical properties, the thermoplastic resin conventionally used for the housing of electronic equipment is preferable.

These resins include olefin resins, styrene resins, acrylate resins, vinyl chloride resins, polyamide resins, polyester resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, polyurethane resins. Examples include resins.

The alloy used in the present invention must be an alloy capable of melting when the synthetic resin composition containing the same is thermoplasticized.

Therefore, the thermoplastic temperature of the thermoplastic resin is usually 350 ° C.
Since it is below, an alloy having a melting point below this is preferable.

The shape of the alloy is not particularly limited, but granular or powdery ones are easy to handle.

Specific examples of the above alloys include zinc (Zn), lead (Pb),
Examples of the alloy include tin (Sn), bismuth (Bi), thallium (Tl), antimony (Sb), aluminum (Al), cadmium (Cd), and indium (In).

Examples of the alloy are Pb-Sn (solder), Pb-Sn-Zn, S
Low melting point alloys such as n-Zn, Zn-Cd, Zn-Al, Tl-Cd, Bi-Tl and In-Sn can be mentioned. Of these, Pb-Sn is particularly preferable.

It should be noted that in the case of an alloy, the metal is complicated because there are some that do not show a clear melting point depending on the composition of the alloy and the shape of the metal, and some show a so-called melting point drop when melting in synthetic resin. In order to determine the degree of melting point of a metal, the composition is once plasticized into a molded product, and the appearance, particularly the distribution state of metallic luster, is observed to determine the melting point of the metal.

In this case, if the molded piece is observed with a phase contrast microscope, it is possible to make a more quantitative and accurate judgment. By the way, according to the research by the present inventor, it has been observed that those exhibiting a good melt-dispersed state have dispersed metal particles having a particle diameter smaller by one digit or more than the metal particle diameter at the time of addition.

In the present invention, the amount of the alloy used is 5 to 80% by weight,
It is preferably 10 to 40% by weight. If the amount of the alloy used is too large, it correlates with the amount of the fibrous filler, but metal precipitation occurs in the molded product, and therefore it should be avoided.

The fibrous filler used in the present invention includes glass fibers, carbon fibers, metal fibers such as iron and stainless steel, asbestos, mica, inorganic whiskers, and other inorganic fibrous fillers, but it is easy to obtain those having suitable physical properties. In that respect, glass fiber is preferable.

The amount of the fibrous filler used is 5 to 30% by weight, and 10
-25% by weight is preferred.

Further, the composition of the present invention contains various pigments, dyes, flame retardants,
Antistatic agents, lubricants, plasticizers and the like may be appropriately blended according to the purpose.

Conventionally known compounding methods can be used for producing the synthetic resin composition of the present invention for electromagnetic wave shielding. For example, a melt-kneading method using a general kneader such as an open roll, an intensive mixer, an internal mixer, a cokneader, a continuous kneader with a twin-screw rotor, and a single-screw or twin-screw extruder is used.

Also, the order of mixing the respective components is not particularly limited, and may be simultaneous. Therefore, a method in which a resin containing glass fiber is first made of glass fiber and a synthetic resin and an alloy is added thereto may be used. It is also possible to use a method in which the glass fiber-containing resin is thermoplasticized and alloy particles are added thereto with a quantitative feeder.

[Work]

In the present invention, the molten alloy is uniformly dispersed in the plasticized synthetic resin, but the established conclusion has not yet been reached regarding the mechanism. However, as a hypothesis, in the kneading process, the alloy in which the fibrous filler such as glass fiber is melted is crushed, and at the same time, the alloy fine particles are interposed between the fibrous fillers to prevent the mutual aggregation of the alloys. The present inventor believes that the pieces may be lost.

〔Example〕

The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The injection molding machine used in each example was a 12 ounce machine manufactured by Toshiba Machine Co., Ltd., and the mold used was a flat plate mold of 5 mm × 200 mm × 200 mm.

Example 1 Styrene-acrylonitrile copolymer resin manufactured by Asahi Kasei Corporation
(Hereinafter abbreviated as SAN resin) contains 20% by weight of glass fiber
Glass fiber reinforced SAN resin (Styrac AS
-240A), 0.4 mm thick × 3 mm long × 3 mm wide Pb38 wt% −S
Pb-Sn alloy consisting of n 62 wt% is mixed to 30 wt%.
Mix at a co-operation.

This was thermoplasticized at 230 ° C. using a twin-screw extruder, and injection-molded using the injection molding machine and the mold. The obtained molded product (test piece) had no uniform metal separation and had a uniform surface.

Also, when the X-ray shielding degree was measured using this test piece (thickness 5 mm), the attenuation rate (I / I _O ) was 0.026 at a dose of 1500 μA and a voltage of 46 KV (I _O : before transmission) X-ray intensity, I: X-ray intensity after transmission).

It should be noted that, instead of the Pb-Sn alloy, when Pb powder that does not melt at the plasticizing temperature of this example (same particle size) was included in 30 wt% was measured, its attenuation rate (I / I _O ) was It was 0.06, and it was confirmed that the effect was considerably inferior to that of the product of the present invention.

Comparative Example 1 The same procedure as in Example 1 was carried out except that a glass fiber-free SAN resin was used in place of the glass fiber-reinforced SAN resin of Example 1. The appearance of the obtained molded product (test piece) had irregular and wide dents on the entire surface, and it was obvious after metal deposition.

Also, the X-ray attenuation was 0.38 under the same conditions as in Example 1, which was one digit inferior.

Example 2 The same glass fiber reinforced SAN resin as in Example 1 was used, and Pb containing 30% by weight of Pb and 70% by weight of Sn and having an average particle size of 100 μm was used.
The b-Sn alloy was mixed in a mixer so as to be 30% by weight.

This was thermoplasticized at 220 ° C. using a twin-screw extruder, and injection-molded using the above-mentioned injection molding machine and mold. As in Example 1, the obtained molded product (test piece) had no uniform metal separation and had a uniform surface.

Moreover, when the X-ray shielding degree was measured using this test piece (thickness: 5 mm) in the same manner as in Example 1, the attenuation rate (I / I _O ) was
It was 0.023.

Comparative Example 2 The same procedure as in Example 2 was carried out except that the glass fiber-reinforced SAN resin in Example 2 was replaced by a SAN resin containing no glass fiber. There were irregular dents and metal precipitation was observed.

Example 3 Acrylonitrile-butadiene-styrene manufactured by Asahi Kasei Corporation
Glass fiber as a copolymer resin (abbreviated as ABS resin below)
Glass fiber reinforced ABS resin containing 20% by weight of
Iraq VGB-20), 0.4 mm thick × 3 mm long × 3 mm wide Pb
50 wt% -Sn 50 wt% Pb-Sn alloy made up of 50 wt%
Were mixed with a mixer so that

This was thermoplasticized at 220 ° C. using a twin-screw extruder, and injection-molded using the above-mentioned injection molding machine and mold. The obtained molded product (test piece) had no uniform metal separation and had a uniform surface.

100Hz from 300Hz to 2000Hz to check the sound shielding property
A tape recorder that was recorded for each of the cast iron BOX (200 ×
(200 × 200 mm), the lid made from the molded product of this example was put, and fixed with bolts. A condenser microphone was placed on it, and the sound was measured by inputting it to an impulse sound insulation meter. The volume at 400Hz showed a 61% attenuation compared to the case without the lid. At this time, if Pb-Su alloy is not added
There is only 68% attenuation. Also, in the volume measurement from 300Hz to 2000Hz, up to 1300Hz, the shielding property tends to increase as the amount of Pb-Sn alloy added increases, and in particular, the shielding property is particularly high at low frequencies from 300Hz to 800Hz. Was recognized.

Next, radio wave measurement (measurement of sound pressure level) was performed to examine the shielding property against radio wave noise.

For radio wave measurement, an AM radio (530 KHz) and a tape recorder were connected in a cast iron BOX, and the molded product of the present invention was attached in the same manner as in the case of sound volume measurement. A motorcycle plug was set at a position 120 cm from the one side of the test piece, and it was recorded by idling at 1200 rpm. The sound was input to an impulse sound level meter, subjected to frequency analysis with an FFT spectrum analyzer, and printed with a video frotter.

As a result, it was found that the sound pressure level was -17 dB in the case of the product of the present invention, which was -15 dB in the case without the lid, and a clear decrease was recognized, and the radio wave was blocked. It was also found that the sound pressure level tended to decrease as the amount of Pb-Sn alloy added increased.

Example 4 Styrene-modified polyphenylene ether tree manufactured by Asahi Kasei Corporation
20% by weight of glass fiber in fat (hereinafter abbreviated as PPE resin)
Glass fiber reinforced PPE resin (Zylon G702
2) Pb-Sn alloy consisting of 25 wt% Pb-75 wt% Sn.
Mixing was carried out with a mixer so as to be 0% by weight.

This was thermoplasticized at 220 ° C. using a twin-screw extruder, and injection-molded using the above-mentioned injection molding machine and mold. The obtained molded product (test piece) had no metal separation at all, had a uniform surface, and had excellent X-ray shielding properties.

〔The invention's effect〕

The synthetic resin composition of the present invention has the advantage that the electromagnetic wave shielding effect is excellent because the metal particles that are extremely finely dispersed are uniformly dispersed as compared with the conventional one.

Therefore, the composition of the present invention can contribute to solving the problem of malfunctions due to electromagnetic noise of information processing devices such as computers and electronic office machines, which have become more serious in recent years, or the problem of X-rays emitted from televisions and the like to the human body. It can be said to be a thing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-207947 (JP, A) JP-A-61-246252 (JP, A) JP-A-61-155454 (JP, A) JP-A-60- 243151 (JP, A)

Claims (3)

[Claims] 1. A lead-tin alloy, a lead-tin-zinc alloy, a tin-zinc alloy, a zinc-aluminum alloy, a zinc-cadmium alloy, a thallium-cadmium alloy, a bismuth-thallium alloy, and an indium-tin alloy. A synthetic resin composition for electromagnetic wave shielding, comprising one or more selected low-melting-point alloys that can be melted when thermoplastic, a fibrous filler, and a thermoplastic synthetic resin. 2. The electromagnetic wave shielding synthetic resin composition according to claim 1, wherein the low melting point alloy is a lead-tin alloy or a lead-tin-zinc alloy. 3. The synthetic resin composition for electromagnetic wave shielding according to claim 1, wherein the fibrous filler is glass fiber.