JPH0361708B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to a conductive resin composition used for shielding electromagnetic waves, and particularly to an electromagnetic wave shielding composition that has a better electromagnetic wave shielding effect than conventional electromagnetic wave shielding compositions. [Background of the Invention] In Western countries, electronic devices such as computers, word processors, etc. It is mandatory to use a housing such as a setter that has been treated to shield electromagnetic waves emitted by the electronic equipment. Electromagnetic wave shielding in electronic equipment as mentioned above is
There is a tendency for this to become mandatory sooner or later in Japan, and various methods of shielding electromagnetic waves are being considered. Shielding of electromagnetic waves as mentioned above can basically be achieved by imparting appropriate conductivity to the housing that encloses the electronic device. Conventionally, zinc was sprayed onto the inner wall of the housing to form a zinc coating. ,
There are well known methods for imparting conductivity to the housing, and methods for imparting conductivity to the housing by applying conductive paint to the inside of the housing. Furthermore, it is also known that a conductive material is introduced into the thermoplastic resin that forms the main body of the housing, thereby making the housing itself conductive. However, in the method of zinc spraying or applying conductive paint to the inner wall of the housing, the manufacturing time is reduced because zinc is sprayed or conductive paint is applied to the inner wall of the housing that has been formed in advance. In addition, especially in the case of conductive paints, the conductive paint itself is expensive, so there is a drawback that the cost is inevitably high. In addition, if a housing made by mixing conductive material with thermoplastic resin is intended to maintain a volume resistivity of 10 ^-1 to ^{10 -3} Ωcm, which has an electromagnetic shielding effect, the amount of conductive material mixed must be increased. On the other hand, if a housing with sufficient strength was to be manufactured, the electrical conductivity would not reach the above-mentioned value. Therefore, there is a need for an electromagnetic wave shielding composition that has a good electromagnetic wave shielding effect with a small amount of conductive material added. [Summary of the invention] The present invention has been made in view of the above points, and
An object of the present invention is to provide an electromagnetic shielding composition that can be used to manufacture electromagnetic shielding products having sufficient strength and conductivity. Therefore, in the electromagnetic wave shielding composition according to the present invention, metal fibers are added to a thermoplastic resin, and 1 to 52 parts by weight of tin oxide, which has not been subjected to conductive treatment, is added to 100 parts by weight of the thermoplastic resin. It is characterized by the fact that Furthermore, the second electromagnetic wave shielding composition according to the present invention includes metal fibers added to a thermoplastic resin, and 1 to 52 parts by weight of tin oxide that has not been subjected to conductive treatment per 100 parts by weight of the thermoplastic resin. It is characterized in that 0.1 to 2 parts by weight of one or more lubricants selected from the group consisting of fatty acid amides and metal soaps are added. According to the present invention, since an appropriate amount of tin oxide, which is a semiconductor, is added together with metal fibers, there is an advantage that the electromagnetic wave shielding effect can be improved without reducing the strength of the electromagnetic wave shielding molded product. . Further, according to the second composition for shielding electromagnetic waves according to the present invention, an appropriate amount of lubricant is added together with the above-mentioned tin oxide, and an even better electromagnetic wave shielding effect can be achieved. Since formation can be prevented, the metal fibers can be uniformly dispersed, and a large amount of metal fibers can be added at once. Therefore, there are advantages in that workability is significantly improved and reproducibility is improved. [Specific Description of the Invention] The present invention will be described in more detail. The electromagnetic wave shielding composition according to the present invention is basically a mixture of metal fibers in a thermoplastic resin, but such a thermoplastic resin is not fundamentally limited, and conventionally Resins used for housings of various types of electronic devices can be effectively used. For example, polypropylene resin,
It can be one or more of ABS resin, modified PPO resin, polyamide resin, polycarbonate resin, PPS resin, etc. The conductive substance used in the present invention is a metal fiber as described above, but the metal fiber used in the present invention is not fundamentally limited. For example, aluminum fibers, stainless steel fibers, copper fibers, lead fibers, tungsten fibers, molybdenum fibers manufactured by chatter vibration cutting method, pultrusion method, melt spinning method, etc., or Al alloys such as Al-Mg or Al-Ca. One or more types of fibers, copper alloy fibers such as brass, etc. can be effectively used. Furthermore, it is possible to use one or more types of metal fibers that are incompletely annealed at an annealing temperature of 85 to 95% of the complete annealing temperature (see Japanese Patent Application No. 183314/1983). The amount of metal fibers added to the thermoplastic resin according to the present invention is preferably 5 to 25% by volume, and the number of metal fibers per unit volume is preferably
500 lines/cm2 or ^more . This is because if the amount of metal fiber added is less than 5% by volume, there is a risk that sufficient conductivity cannot be imparted, and if it exceeds 25% by volume, there is a risk that it will be difficult to mold the electromagnetic wave shielding composition. . In addition, the number of existing pieces per unit volume is 500/
This is because if it is less than cm ² , sufficient conductivity may not be exhibited. Thermoplastic resin 100 tin oxide in such a composition
It is added in an amount of 1 to 52 parts by weight. It is not necessarily clear why the electromagnetic wave shielding effect is improved when such tin oxide is added to a thermoplastic resin, and various reasons can be considered. In other words, by adding tin oxide, the formation of an oxide coating on metal fibers can be suppressed, and since tin oxide has properties as a semiconductor, the conductive effect of tin oxide itself and the addition of tin oxide By doing so, it can be expected that the electromagnetic wave shielding effect will be improved due to the combined effect of improving the rigidity of the resin and preventing separation of the metal fibers. The tin oxide used in the present invention is basically not limited, and tin oxide produced by various methods can be used. For example, SnO,
SnO ₂ etc. can be used. In particular, SnO ₂ has a rutile structure and is an n-type semiconductor, making it a particularly desirable additive in the present invention. Such tin oxide is added in an amount of 1 to 52 parts by weight per 100 parts by weight of the thermoplastic resin. If the amount of tin oxide added is less than 1 part by weight, the effect of adding tin oxide will not be exhibited.On the other hand, if the amount added exceeds 52 parts by weight, no further improvement in the electromagnetic wave shielding effect can be expected, and the fluidity will be reduced. This is because it will get worse. Most preferably it is 2 to 20 parts by weight. The particle size of such tin oxide is preferably 1 to
50 μm, most preferably 5-20 μm.
If it is smaller than 1 μm, it will increase the melt viscosity when added to the resin, promoting cutting of metal fibers, making it difficult to recognize the effect of addition, and if it is larger than 50 μm, the resin strength will decrease even with a small amount added. This may cause drawbacks that impair practicality. In the second composition for shielding electromagnetic waves according to the present invention, such composition for shielding electromagnetic waves further includes:
One or more lubricants selected from the group consisting of fatty acid amides and metal soaps are added. Such a lubricant is added so that the metal fibers and tin oxide are uniformly dispersed in the resin by preventing the metal fibers from becoming fiber balls, that is, from curling up into a ball shape.
Therefore, a molded article manufactured using the electromagnetic wave shielding composition according to the present invention exhibits a stable electromagnetic wave shielding effect, and the electromagnetic wave shielding composition can be manufactured with good reproducibility. In addition, by adding this lubricant, it is possible to add a large amount of metal fibers at once, and it also prevents clogging of the extruder nozzle and cutting of the metal fibers.
The electromagnetic wave shielding effect can also be improved. Examples of such fatty acid amides include ethylene bisstearamide, oxystearamide, stearamide, and palmitic acid amide, and examples of metal soaps include cadmium stearate,
Cadmium laurate, cadmium ricinoleate, cadmium naphthenate, cadmium 2-ethylhexoate, barium stearate, barium laurate, barium ricinoleate, barium naphthenate, barium 2-ethylhexoate,
Calcium stearate, calcium laurate, calcium ricinoleate, strontium stearate, zinc stearate, zinc laurate, zinc ricinoleate, zinc 2-ethylhexoate, lead stearate, dibasic lead stearate, lead naphthenate, tin stearate. , aluminum stearate, magnesium stearate, and the like. One or more lubricants selected from the group consisting of fatty acid amides and metal soaps are added in an amount of 0.1 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of the thermoplastic resin. The amount of lubricant added is 0.1
If the amount is less than 2 parts by weight, there is no effect of adding the lubricant, while if it exceeds 2 parts by weight, there is a risk that the resin molded product will lack mechanical strength. Next, examples of the present invention will be described. Example 1 100 parts by weight of ABS resin, diameter 30μm, length 2
mm, 18% by volume (56 parts by weight) of Al fiber with an aspect ratio of 67, 0.8 parts by weight of ethylene bisstearamide as a lubricant, and SnO ₂ added in varying amounts to achieve electromagnetic shielding effect. was measured. Measurements were made using Takeda Riken's near-field electromagnetic wave shielding material evaluator (TR-17301) and spectrum analyzer (TR-4172), and magnetic field waves (SEH) [shown as the average value of 100MHz to 600MHz] were performed. The results are shown in Figure 1. Circles in the figure indicate the electromagnetic wave shielding effect when the amount of SnO ₂ added is changed. Also,
The data when the amount of SnO ₂ added is 0 indicates the electromagnetic wave shielding effect of the conventional electromagnetic wave shielding composition. As is clear from FIG. 1, when SnO ₂ was not added, the electromagnetic wave shielding effect was 36 dB for magnetic field waves. On the other hand, the electromagnetic wave shielding composition according to the present invention can reach 64 dB or more even in the case of magnetic field waves, and for electric field waves that are relatively easy to shield, the measurement range of this measuring device is 75 bB. It was found that the electromagnetic wave shielding effect was significantly improved. Next, 20℃/50%RH→50℃/85%RH→20
℃/50%RH→-20℃→20℃/50%RH→50℃/
The rate of decline in the electromagnetic shielding effect was measured when a moist heat cycle of 30% RH → 20°C/85% RH → 20°C was performed for 10 cycles, each step having 2 hours and a total of 16 hours. The results are shown in Figure 1. ● in the figure shows SnO ₂ resin 100%
This is the electromagnetic wave shielding composition according to the present invention in which a variable amount (parts by weight ₎ was added to the electromagnetic wave shielding composition according to the present invention. The amount of Al fiber added in both compositions was 56 parts by weight, the same as above. As is clear from this figure, the electromagnetic wave shielding effect of the conventional electromagnetic wave shielding composition in magnetic field waves decreased from 36 dB to 20 dB (reduced to 55%) after the moist heat cycle, but the electromagnetic wave shielding effect of the electromagnetic wave shielding composition according to the present invention In terms of materials, when the amount of SnO ₂ added is 4.3 parts by weight, it is 58 dB.
It was found that the rate of decrease was small at 47 dB (reduced to 81%). Example 2 100 parts by weight of ABS resin, diameter 30μm, length 2
An electromagnetic wave shielding composition was prepared by adding 22% by volume (72 parts by weight) of Al fibers with an aspect ratio of 67 mm and an aspect ratio of 67, and 4.3 parts by weight of SnO ₂ . At this time, the kneading speed of ABS resin and Al fiber is per 1 kg.
It took 17 minutes. (shown as Example 2A in Table 1 below). For comparison, when 1.4 parts by weight of ethylene bisstearic acid amide was added as in Example 1 (shown as Example 2B in Table 1 below), it was possible to knead well in 8 to 9 minutes per 1 kg. It has become clear that the kneading time can be reduced by about half by adding . A test piece was manufactured from such an electromagnetic wave shielding composition, and the electromagnetic wave shielding effect was measured. The results are shown in Table 1 below.

〔Effect of the invention〕

As explained above, the electromagnetic wave shielding composition according to the present invention can produce an electromagnetic wave shielding product having a good electromagnetic wave shielding effect, and
The combined use of a lubricant has the advantage of making it possible to manufacture electromagnetic shielding compositions with good workability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the measurement of the electromagnetic wave shielding effect of the electromagnetic wave shielding composition according to the present invention, and a graph showing the decrease in the electromagnetic wave shielding effect due to moist heat cycles.

Claims (1)

[Scope of Claims] 1. An electromagnetic wave characterized by adding metal fibers to a thermoplastic resin and adding 1 to 52 parts by weight of tin oxide which has not been subjected to conductive treatment based on 100 parts by weight of the thermoplastic resin. Composition for shielding. 2. A lubricant prepared by adding metal fibers to a thermoplastic resin, and adding 1 to 52 parts by weight of tin oxide that has not been subjected to conductive treatment to 100 parts by weight of the thermoplastic resin, a fatty acid amide, and a metal soap. An electromagnetic wave shielding composition characterized in that 0.1 to 2 parts by weight of one or more of the following are added.