JP6777710B2 - Radar transmit / receive antenna protection - Google Patents

Description

The present invention relates to a thermoplastic resin composition for a molded product having millimeter wave shielding performance suitable for millimeter wave radar, and a molded product obtained from the thermoplastic resin composition.

Millimeter-wave radar is used for the purpose of automatic driving of vehicles and collision prevention.
The millimeter-wave radar device is mounted on the front of an automobile and has a high-frequency module incorporating an antenna that transmits and receives radio waves, a control circuit that controls the radio waves, a housing that houses the antenna and the control circuit, and transmits and receives radio waves from the antenna. It is provided with a radome to cover (background technique of Patent Document 1).
The millimeter-wave radar device configured in this way can transmit and receive millimeter waves from the antenna to detect the relative distance to the obstacle, the relative speed, and the like.

Since the antenna may also receive objects reflected on the road surface other than the target obstacle, the detection accuracy of the device may decrease.
In order to solve such a problem, the millimeter wave radar device of Patent Document 1 is provided with a shielding member that shields radio waves between the antenna and the control circuit.
It is described that the shielding member uses a radio wave absorber in which a conductor layer is laminated on either a dielectric loss layer or a magnetic loss layer having a larger dielectric loss than the radome.
The dielectric loss layer is described as being made of a carbon material selected from at least one of carbon nanotubes, carbon microcoils, shungite carbon, carbon black, expanded graphite, and carbon fibers (paragraph number 0023).
The magnetic loss layer is described as being made of hexagonal ferrite (paragraph number 0023).
Further, the dielectric loss layer or the magnetic loss layer preferably contains a substance (insulating polymer material or insulating inorganic material) having a higher electrical resistivity than the carbon material or the hexagonal ferrite. Is described (paragraph number 0024).

JP-A-2007-74662

KEC Information, No. 225, April 2013, pp. 36-41

An object of the present invention is to provide a thermoplastic resin composition for a molded product having millimeter wave shielding performance suitable for millimeter wave radar, and a molded product obtained from the thermoplastic resin composition.

The present invention has millimeter-wave shielding performance containing (A) a thermoplastic resin and (B) 0.5 to 5% by mass of carbon length fibers having a fiber length of 3 to 30 mm as a means for solving the problems. Provided is a thermoplastic resin composition for a molded product.

The present invention provides a means for solving other problems.
A molded product made of the thermoplastic resin composition according to any one of claims 1 to 4 and having millimeter wave shielding performance.
The weight average fiber length of the carbon fibers derived from the carbon length fibers of the component (B) remaining in the molded product is 1 mm or more.
Provided is a molded product having a millimeter-wave shielding performance in which the surface resistivity of the molded product is in the range of 1 × 10 ⁵ to 10 ⁹ Ω / □.

The molded product obtained from the thermoplastic resin composition of the present invention is particularly suitable as a protective member for a transmission / reception antenna of a millimeter wave radar because it has excellent millimeter wave shielding performance.

Explanatory drawing of measurement method of millimeter wave shielding performance (electromagnetic wave shielding property). The graph which shows the measurement result of the electromagnetic wave shielding property in an Example and a comparative example.

<Thermoplastic resin composition>
The thermoplastic resin of the component (A) is not particularly limited, and can be appropriately selected depending on the intended use.
As the component (A), one selected from polypropylene, aliphatic polyamide, aromatic polyamide, polybutylene terephthalate, polycarbonate, and a mixture thereof is preferable.

As the carbon filament of the component (B), a known polyacrylonitrile-based, pitch-based, rayon-based or the like can be used, but the polyacrylonitrile-based carbon filament is preferable.
The carbon filaments of the component (B) include those whose surface is coated with a metal. The surface coating method is not particularly limited, and is, for example, various known plating methods (for example, electrolytic plating, electroless plating, hot-dip plating, etc.), vacuum deposition method, ion plating method, CVD method (for example, thermal). (CVD, MOCVD, plasma CVD, etc.), PVD method, sputtering method and the like can be mentioned. Above all, the plating method is preferably used.
Examples of the metal for coating the surface include silver, copper, nickel, and aluminum, and nickel is preferable from the viewpoint of corrosion resistance of the metal layer. The thickness of the metal coating layer is preferably 0.1 to 1 μm, more preferably 0.2 to 0.5 μm.
The carbon length fiber of the component (B) has a fiber length of 3 to 30 mm, preferably a fiber length of 5 to 20 mm, and more preferably 6 to 15 mm in order to enhance the shielding performance of millimeter waves.

The carbon filaments of the component (B) are the components of the component (A) obtained by melting the carbon fibers in a bundled state aligned in the length direction in order to enhance the dispersibility between the components (A) and the component (B). A product impregnated with a thermoplastic resin and integrated, cut into 3 to 30 mm (resin-impregnated carbon long fiber bundle) is preferable.
Such a resin-impregnated carbon filament bundle can be produced by a well-known production method using a die. For example, paragraph No. 0019 of JP2011-57811A and Reference Production Example 1 can be used in JP-A-6-. In addition to paragraph number 0007 of JP-A-313050 and paragraph number 0023 of JP-A-2007-176227, JP-A-6-2344 (method for producing and molding a resin-coated long fiber bundle), JP-A-6-114832. (Fiber-reinforced thermoplastic resin structure and its production method), JP-A-6-293023 (Method for producing long fiber-reinforced thermoplastic resin composition), JP-A-7-205317 (Method and length of fiber bundle extraction) (Method for manufacturing fiber reinforced resin structure), JP-A-7-216104 (Method for manufacturing long fiber reinforced resin structure), JP-A-7-251437 (Method for manufacturing long fiber reinforced thermoplastic composite material and manufacturing apparatus) ), JP-A-8-118490 (method for producing a crosshead die and a long fiber reinforced resin structure) and the like can be applied.
In addition, commercially available products such as Plastron (registered trademark; Daicel Polymer Co., Ltd.) can also be used.

When a resin-impregnated carbon long fiber bundle is used as the component (B), the content ratio of the carbon long fiber of the component (B) in the resin-impregnated carbon long fiber bundle is preferably 10 to 50% by mass, preferably 10 to 40% by mass. Is more preferable, and 10 to 30% by mass is further preferable.
In this case, the thermoplastic resin of the component (A) contained in the resin-impregnated carbon filament bundle is calculated as the content of the component (A).

The content ratio of the carbon filament of the component (B) in the composition is 0.5 to 5% by mass, preferably 0.5 to 3% by mass, and 0.8 to 0.8 to enhance the shielding performance of millimeter waves. 2% by mass is more preferable.

The thermoplastic resin composition of the present invention can contain a known resin additive as long as the problem can be solved.
Known resin additives include antioxidants, heat-resistant stabilizers, stabilizers such as ultraviolet absorbers, antistatic agents, flame retardants, flame retardant aids, colorants such as dyes and pigments, lubricants, and plasticizers. Examples thereof include a crystallization accelerator and a crystal nucleating agent.

<Molded body>
The molded product of the present invention is a molded product obtained by molding the above-mentioned thermoplastic resin composition, and the shape, size, and the like can be selected according to the intended use.

In the molded body of the present invention, in order to enhance the shielding performance of millimeter waves (electromagnetic waves in a predetermined frequency band), the weight average fiber length of the carbon fibers derived from the carbon length fibers of the remaining component (B) is 1 mm or more. Preferably, 2 mm or more is more preferable, and 3 mm or more is further preferable.
The weight average fiber length is measured by the method described in Examples.

Further, in the molded product of the present invention, the content ratio of the carbon fibers derived from the carbon filaments of the remaining component (B) having a fiber length of 1 mm or more is preferably 60% by mass or more, more preferably 70% by mass or more, and more preferably 80. It is more preferably by mass%.
Further, in the molded product of the present invention, the content ratio of the carbon fibers derived from the carbon filaments of the remaining component (B) having a fiber length of 2 mm or more is preferably 40% by mass or more, more preferably 50% by mass or more, and 60. It is more preferably mass% or more.

The molded body of the present invention has millimeter-wave shielding performance, and having millimeter-wave shielding performance means that millimeter waves (electromagnetic waves in a predetermined frequency band) obtained by the measurement method of Examples are used. ) Is evaluated by the electromagnetic wave shielding property (radiation wave transmission inhibitory property).
The electromagnetic wave shielding property of the molded product of the present invention is 30 dB or more, more preferably 40 dB or more, and further preferably 50 dB or more.
The frequency band of the millimeter wave in the present invention is in the range of 300 mm (1 GHz) to 1 mm (300 GHz), more preferably in the range of 20 mm (15 GHz) to 3 mm (100 GHz).
The millimeter wave shielding performance is measured by the method described in the examples.

Since the molded product of the present invention has a long average residual fiber length as described above, it exhibits conductivity in addition to millimeter-wave shielding performance even though the content of the component (B) is small.
The volume resistivity of the molded product of the present invention is in the range of 1 × 10 ² to 10 ⁹ Ω · m, preferably in the range of 1 × 10 ³ to 10 ⁸ Ω · m.
Similarly, the surface resistivity of the molded product of the present invention is in the range of 1 × 10 ⁵ to 10 ⁹ Ω / □, preferably in the range of 1 × 10 ⁶ to 10 ⁸ Ω / □.

The molded product of the present invention can be produced by applying a known resin molding method such as injection molding or press molding to the above-mentioned thermoplastic resin composition.
The molded product of the present invention is suitable for millimeter-wave radar, and is particularly suitable for a protective member for a transmission / reception antenna of a millimeter-wave radar.

Production Example 1 (Production of resin-impregnated carbon filament bundle)
A fiber bundle (bundle of about 24,000 fibers) composed of long carbon fibers (Trading Card T700SC, tensile strength 4.9 GPa) was passed through a crosshead die after being heated at 150 ° C. by a preheating device.
At that time, the crosshead die was supplied with polypropylene in a molten state (manufactured by SunAllomer Ltd., PMB60A) from a twin-screw extruder, cylinder temperature 280 ° C.), and the fiber bundle was impregnated with polypropylene.
Then, it was shaped with a shaping nozzle at the outlet of the crosshead die, shaped with a shaping roll, and then cut to a predetermined length with a pelletizer to obtain pellets (cylindrical molded body) having a length of 8 mm.
The carbon length fiber length is the same as the pellet length. In the pellets obtained in this way, the carbon filaments were substantially parallel in the length direction.

Example 1
Using 3% by mass of pellets (carbon length fiber content 40% by mass) obtained in Production Example 1 and 97% by mass of polypropylene resin (PMB60A manufactured by SunAllomer Ltd.), an injection molding machine (J-150EII; A molded product was obtained by molding at a molding temperature of 240 ° C. and a mold temperature of 60 ° C. by Japan Steel Works, Ltd.).
Each measurement shown in Table 1 was carried out using the obtained molded product.

Comparative Example 1
The pellets (carbon long fiber content 40% by mass) obtained in the production example were supplied to a twin-screw extruder (Japan Steel Works, Ltd .; twin-screw extruder TEX30α), and the pellets were molded again to contain short carbon fibers. Pellets (cylindrical molded product) were obtained.
Molded by an injection molding machine (J-150EII; Japan Steel Works, Ltd.) using 3% by mass of these carbon short fiber-containing pellets and 97% by mass of polypropylene resin (PMB60A manufactured by SunAllomer Ltd.). A molded product was obtained by molding at a temperature of 240 ° C. and a mold temperature of 60 ° C.
Each measurement shown in Table 1 was carried out using the obtained molded product.

Comparative Example 2
Using 25% by mass of pellets (carbon length fiber content 40% by mass) obtained in the production example and 75% by mass of polypropylene resin (PMB60A manufactured by SunAllomer Ltd.), an injection molding machine (J-150EII; ) Made by Japan Steel Works) to obtain a molded product by molding at a molding temperature of 240 ° C. and a mold temperature of 60 ° C.
Each measurement shown in Table 1 was carried out using the obtained molded product.

(1) Weight average fiber length About 3 g of a sample was cut out from the molded product, PP was dissolved and removed with sulfuric acid, and carbon fibers were taken out. The weight average fiber length was calculated from a part of the extracted fibers (500 fibers). As the calculation formula, [0044] and [0045] of JP-A-2006-274061 were used.

(2) Electromagnetic wave shielding property The measuring device shown in FIG. 1 was used.
A molded body 10 (length 150 mm, width 150 mm, thickness 2 mm) to be measured was held between a pair of antennas (broadband antenna; Schwarzbeck, BBHA9120A, 2-18 GHz) 11 and 12 facing in the vertical direction. .. The distance between the antenna 12 and the molded body 10 is 85 mm, and the distance between the molded body 10 and the antenna 11 is 10 mm.
In this state, an electromagnetic wave (1 to 18 GHz) is radiated from the lower antenna 12, the electromagnetic wave transmitted through the molded body 10 to be measured is received by the upper antenna 11, and the electromagnetic wave shielding property is obtained from the following equation 1. (Inhibition of radiation wave transmission) was determined.
S ₂₁ of Equation 1 is an S parameter (Equation 2) representing the ratio of the transmitted electromagnetic wave to the incident electromagnetic wave, and can be measured by a network analyzer.
In Equation 1, since the electromagnetic wave shielding property (dB) is represented by a positive value, the logarithm of the reciprocal of the S parameter is taken. With the measuring device of FIG. 1, the range of 0 to about 55 dB can be measured, and when the electromagnetic wave shielding property exceeds the measurement upper limit, it is described as “> 55 (dB)” in Table 1.
The measurement results are shown in Table 1, and the changes in the electromagnetic wave shielding property are shown in FIG.
Electromagnetic wave shielding property = 20log (1 / | S ₂₁ |) (Unit: dB) (Equation 1)
S ₂₁ = (transmitted electromagnetic wave) / (incident electromagnetic wave) (Equation 2)

(3) Tensile strength (MPa), tensile nominal strain (%)
Tensile strength and tensile nominal strain were measured according to JIS K7161.

(4) Density The density was measured according to ISO1183.

(5) Surface resistivity and volume resistivity For samples with a surface resistivity of 5 × 10 ⁷ Ω / □ or less and a volume resistivity of 2 × 10 ⁵ Ω · m or less, a low resistivity meter [Mitsubishi Chemical Co., Ltd. Lorester GP (MCP-T600)] was used, and the surface resistivity and volume resistivity were measured according to JIS K7194.
For samples with a surface resistivity of 1 x 10 ⁸ Ω / □ or more and a volume resistivity of 1 x 10 ⁴ Ω · m or more, use a high resistivity meter [Mitsubishi Chemical Co., Ltd., High Lester UP (MCP-HT450)]. The surface resistivity and volume resistivity were measured according to JIS K6911.
Incidentally, for example, in Table 1, denoted with "1.1 E + 07" in Example 1 indicates "1.1 × 10 ^7".
For "> 1.0E + 13 (Ω / □)" and "> 1.0E + 9 (Ω · m)" in Comparative Example 1 and Comparative Example 2, the upper limit of measurement of the high resistivity meter is set, and the surface resistivity is 1 × 10 ¹³ Since Ω / □ and the volume resistivity are 1 × 10 ⁹ Ω · m, it indicates that the resistivity is higher than these.
The description of "5 to 10E + 7 (Ω / □)" in Examples 1 to 3 indicates that the surface resistivity is higher than the measurement upper limit of the low resistivity meter and lower than the measurement lower limit of the high resistivity meter.

In the table, PP indicates polypropylene and CF indicates carbon fiber.
As for the electromagnetic wave shielding property, the larger the value, the better the millimeter wave shielding performance.
From the comparison between Example 1 and Comparative Example 1 and Example 3 and Comparative Example 2, it was confirmed that the electromagnetic wave shielding property can be enhanced by using long fibers if the amounts are the same.
In Comparative Example 3, it was confirmed that the electromagnetic wave shielding property was enhanced by increasing the content of the carbon fibers of the short fibers, but in Comparative Example 3, 16 times or more the amount of carbon fibers as in Example 1 was used. Despite this, Example 1 was superior in electromagnetic wave shielding property.
In Comparative Example 4, it was confirmed that when the content of the long carbon fibers was increased, an electromagnetic wave shielding property exceeding that of Examples 1 to 3 could be obtained, but in this case as well, the amount of carbon fibers was 16 times or more that of Example 1. It is economically disadvantageous, has a high density, and is also disadvantageous in reducing the weight of the molded product.

The frequency band shown in Table 1 and FIG. 2 is 1 to 18 GHz, but when the electromagnetic wave shielding property in the above range is in the state shown in Table 1 and FIG. 2, the skin depth is higher than the thickness even in the frequency band of 1 to 300 GHz. It is known that since the carbon fiber-blended resin behaves as a loss medium because it is sufficiently small, the attenuation constant increases as the frequency increases in the GHz region, and exhibits high electromagnetic wave shielding properties.
This fact can be confirmed, for example, from the description of Non-Patent Document 1, especially the description of "2.3 Electromagnetic shielding using a loss medium" and "Fig. 9 Shielding characteristics of the two-layer structure of the conductive material" from p39 to p40.

Claims (4)

(A) Thermoplastic resin,
(B) Carbon length fiber 0.5 to 5% by mass with fiber length 5 to 30 mm
The made of a thermoplastic resin composition containing, a protective member of the transmitting and receiving antennas of Relais over Da, such a molded body having a shielding performance electromagnetic wavelength in the range of 1～300GHz,
The carbon filaments of the component (B) are bundled with the carbon fibers aligned in the length direction, and the melted thermoplastic resin of the component (A) is impregnated and integrated. It was cut to 30 mm and
The weight average fiber length of the carbon fiber derived from the carbon length fiber of the component (B) in the molded product is 2.5 mm or more.
The content ratio of the carbon fibers derived from the carbon filaments of the component (B) in the molded product having a fiber length of 1 mm or more is 60% by mass or more.
The content ratio of the fiber length of the carbon fibers derived from long carbon fiber of the component (B) in the molded body is more than 2mm is 40 mass% or more, that Do a molded body having an electromagnetic wave shielding performance of the the protective member of the transmitting and receiving antennas of les over da. The thermoplastic resin of the component (A) is selected from polypropylene, aliphatic polyamide, aromatic polyamide, polybutylene terephthalate, and polycarbonate, and is a molded product having the electromagnetic wave shielding performance according to claim 1. Relais chromatography da protective member of the transmitting and receiving antennas. Electromagnetic wave is in a range of wavelengths. 1 to 100 GHz, according to claim 1 or 2 electromagnetic protection member Relais over da transmit and receive antennas, such a molded body having a shielding performance according. The ranges surface resistivity of ^{1 × 10 5 ~10 9 Ω /} □ of the molded article, such a molded article has a shielding performance of electromagnetic waves according to any one of claims 1 to 3 Relais Protective material for transmitting and receiving antennas of radar.

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