JPS6317865B2 - - 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 is 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, the electromagnetic wave shielding composition according to the present invention includes metal fibers added to a thermoplastic resin, as well as one or more of the following general formula oxide powder and TiO ₂ powder (however, TiO ₂ powder alone). (excluding cases)
It is characterized in that 1 to 80 parts by weight of is added to 100 parts by weight of the thermoplastic resin. M ₁ M ₂ O ₃ (M ₁ represents Ba, Sr, Ca, M ₂ represents Ti, Sn
In addition, the second electromagnetic wave shielding composition according to the present invention includes metal fibers added to a thermoplastic resin, and one or more of the following general formula oxide powder and TiO ₂ powder (however, TiO ₂ (Excluding the case of powder alone)
1 to 80 parts by weight per 100 parts by weight of 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. M ₁ M ₂ O ₃ (M ₁ represents Ba, Sr, Ca, M ₂ represents Ti, Sn
According to the present invention, the dielectric constant is 30 along with the metal fiber.
Since an appropriate amount of the above powder is added, there is an advantage that the electromagnetic wave shielding effect can be improved without reducing the strength of the electromagnetic wave shielding molded product. Furthermore, according to the second composition for shielding electromagnetic waves according to the present invention, an appropriate amount of lubricant is added together with the powder, thereby achieving an even better electromagnetic wave shielding effect and preventing the formation of fiber balls of metal fibers. Therefore, the metal fibers can be uniformly dispersed,
It becomes possible to input a large amount of metal fiber 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-Cu. 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/ ^cm3 or more. If the amount of metal fiber added is less than 5% by volume, sufficient conductivity may not be imparted, and if it exceeds 25% by volume, it may be difficult to mold the electromagnetic shielding composition. . In addition, the number of existing pieces per unit volume is 500/
This is because if it is less than cm ³ , sufficient conductivity may not be exhibited. In the present invention, such a composition has the general formula: M ₁ M ₂ O ₃ ... (where M ₁ represents Ba, Sr, Ca, M ₂ represents Ti, Sn
). Such metal oxides exhibit high dielectric constants. For example, SrTiO ₃ is 332 (25℃,
1KHz), _BaTiO3 exhibits a high dielectric constant of 1000-2000 (25℃, 1KHz). Also used with the metal oxides
TiO ₂ also exhibits a relatively high dielectric constant of 30 to 90. It is not necessarily clear why the electromagnetic wave shielding effect is improved when such a powder with a high dielectric constant is added, and various reasons can be considered. If an electromagnetic wave shielding material can be considered as a single space, the fundamental laws that give the material's unique electrical properties (electrical conductivity, permittivity, and magnetic permeability) should hold within this space. In an actual system, resin, metal fibers, and high-permittivity powder are mixed together in a complex spatial configuration, but in order to attempt a theoretical interpretation, this space is made up of resin, metal fibers,
If we simply divide the space into the space within each powder substance and the space at the interface between the substances, we can see the formation of an electrical equivalent circuit. In other words, the surface resistance (Rs), volume resistance (Rb), resistance at the mutual interface (Rgb) of the resin, metal fiber, and powder, and the capacitance (Cb) of the resin, metal fiber, and powder at the mutual interface. This is a schematic equivalent circuit consisting of capacitance (Cgb). The actual circuit is the circuit shown in Figure 1 (R: Rb, Rgb C: Cb, Cgb)
Although it is composed of many combinations of parallel and series combinations, C is still large. Cb and Cgb are large, such as TiO ₂ and BaTiO ₃ , but Rb is smaller than semiconductor behavior, and Cb
However, it is not hard to imagine that by filling electromagnetic shielding materials with materials that are much smaller than CGB, these materials can act as a capacitive capacitor. The effect on electromagnetic wave shielding is thought to be that because this compound system acts as a capacitor in this way, the phase of the electromagnetic waves shifts, and electromagnetic wave shielding occurs. Apart from this, these high dielectric constant powders help absorb electromagnetic waves reflected between the metal fibers in the system. It can be determined that the above two effects act synergistically to improve the electromagnetic wave shielding effect. One or more types of oxides selected from the metal oxides and TiO ₂ shown in this general formula (however,
(Except for _TiO2 alone) powder is thermoplastic resin
Add 1 to 80 parts by weight per 100 parts by weight. If the amount of the powder added is less than 1 part by weight, the effect of adding the powder will not be apparent, while if it is added in excess of 80 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 2
~35 parts by weight. The particle size of such powder is preferably 0.1 to 10 μm
and most preferably 0.2 to 5 μm. 0.1μ
If it is smaller than m, it will increase the melt viscosity when added to wood, promoting cutting of metal fibers, etc.
It becomes difficult to recognize the effect of addition, and if the diameter is larger than 10 μm, the strength of the resin decreases even with the addition of a small amount, which may cause a drawback that impairs 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 powder 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, which improves the electromagnetic wave shielding effect. can. Examples of such fatty acid amides include ethylene bisstearamide, oxystearamide, stearamide, and palmitic acid amide, and examples of metal soaps include cadmium stearate and lauric acid amide. cadmium acid, 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, Mention may be made, to name a few, of zinc laurate, zinc ricinoleate, zinc 2-ethylhexoate, lead stearate, dibasic lead stearate, lead naphthenate, tin stearate, aluminum stearate, and magnesium stearate. 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, the addition of the lubricant will have no effect, while if it exceeds 2 parts by weight, the resin molded product may 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, 22% by volume (72 parts by weight) of Al fibers with an aspect ratio of 67, 1.2 parts by weight of ethylene bisstearamide as a lubricant, and TiO 2 with a relative dielectric constant of 114 as a high dielectric constant powder and TiO ₂ with a dielectric constant of about 1500. _BaTiO3
were added in varying amounts, and the electromagnetic wave shielding effect was measured. Measurement was performed using Takeda Genken's near-field electromagnetic wave shielding shielding material evaluator (TR-17301)
and a spectrum analyzer (TR-4172) to analyze electric field waves and magnetic field waves (SEH) [respectively.
100MHz to 600MHz]. The results are shown in Figure 2. In the figure, 〇 is BaTiO ₃ , □ is
This shows the electromagnetic shielding effect of TiO ₂ . Also, BaTiO ₃ ,
The data in which the amount of TiO ₂ added is 0 indicates the electromagnetic wave shielding effect of the conventional electromagnetic wave shielding composition. As is clear from Figure 2, if high dielectric constant powder is not added, the electromagnetic wave shielding effect is due to magnetic field waves.
It was 42dB. On the other hand, the electromagnetic wave shielding composition according to the present invention can reach 70 dB or more even in the case of magnetic field waves, and for electric field waves that are relatively easy to block, the measurement limit of this measuring device is 75 dB. It was found that the electromagnetic wave shielding effect was significantly improved. Next, 20℃/50%RH→50℃/85%RH→20
℃/50%→-20℃→20℃/50%RH→50℃/30%
The rate of decrease in the electromagnetic shielding effect was measured when a moist heat cycle of RH→20°C/50%RH→−20°C was performed for 10 cycles of 2 hours per step for a total of 16 hours. The results are shown in Figure 3. 〇 in the figure is BaTiO ₃ resin
This is an electromagnetic wave shielding composition according to the present invention in which 17.2 parts by weight was added to 100 parts by weight, and x indicates the results of a conventional electromagnetic wave shielding composition to which BaTiO ₃ was not added. The amount of Al fiber added in both compositions was 72 parts by weight, the same as above. As is clear from Figure 3, the electromagnetic shielding effect of the conventional electromagnetic shielding composition on magnetic field waves decreased from 42 dB to 13 dB (31%) after the moist heat cycle.
However, in the electromagnetic wave shielding composition according to the present invention, from 70 dB to 69 dB (reduced to 98%).
It was found that the rate of decline was small. Example 2 100 parts by weight of ABS resin, diameter 30μm, length 2
An electromagnetic wave shielding composition containing 22% by volume (72 parts by weight) of Al fibers with an aspect ratio of 67 and 17.2 parts by weight of BaTiO ₃ powder with a relative dielectric constant of about 1500 as a high dielectric constant powder was added. Manufactured. At this time, the kneading speed of ABS resin and Al fiber is per 1 kg.
It took 25 minutes. As a comparison, when 1.2 parts by weight of ethylene bisstearic acid amide was added as in Example 1, it was possible to knead well in 12 to 13 minutes per 1 kg, so it is clear that the kneading time can be reduced to about half by adding a lubricant. It became. A test piece was manufactured from such an electromagnetic shielding composition, and the electromagnetic shielding effect was measured. The results are shown in Table 1 below along with Example 1.

〔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 the drawing]

Fig. 1 is a diagram showing an equivalent circuit, Fig. 2 is a graph when measuring the electromagnetic wave shielding effect of the electromagnetic wave shielding composition according to the present invention, and Fig. 3 is a graph showing the decrease in the electromagnetic wave shielding effect due to moist heat cycle. .

Claims (1)

[Claims] 1. Metal fibers are added to a thermoplastic resin, and one or more of the following general formula oxide powder and TiO ₂ powder (excluding the case of TiO ₂ powder alone)
An electromagnetic wave shielding composition characterized in that 1 to 80 parts by weight of is added to 100 parts by weight of a thermoplastic resin. M ₁ M ₂ O ₃ (M ₁ represents Ba, Sr, Ca, M ₂ represents Ti, Sn
2 Adding metal fibers to a thermoplastic resin, as well as one or more of the following general formula oxide powder and TiO ₂ powder (however, excluding the case of TiO ₂ powder alone)
1 to 80 parts by weight per 100 parts by weight of thermoplastic resin,
1. An electromagnetic wave shielding composition 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. M ₁ M ₂ O ₃ (M ₁ represents Ba, Sr, Ca, M ₂ represents Ti, Sn
)