JP2019023312A - Protective member of transmission/reception antenna of millimeter wave radar - Google Patents

Abstract

To provide a thermoplastic resin composition from which a formed body excellent in millimeter wave shielding performance is obtained.SOLUTION: A protective member of a transmission/reception antenna of a millimeter wave radar is a formed body which is formed of a thermoplastic resin composition that contains (A) a thermoplastic resin and (B) 0.5-5 mass% of a carbon long fiber with a fiber length of 3-30 mm and contains no glass fiber, in which the carbon long fiber of the component (B) is a substance obtained by cutting a substance obtained by impregnating a substance where carbon fibers are bundled while being aligned in a length direction with the thermoplastic resin of the melted component (A) and integrating the substances with each other into 3-30 mm., and has millimeter wave shielding performance, where a weight average fiber length of the carbon fiber derived from the carbon long fiber of the component (B) in the formed body is 1 mm or more, a content ratio of a substance with a fiber length of the carbon fiber derived from the carbon long fiber of the component (B) in the formed body of 1 mm or more is 60 mass% or more, a content ratio of a substance with a fiber length of the carbon fiber derived from the carbon long fiber of the component (B) in the formed body of 2 mm or more is 40 mass% or more, and the protective member is formed of a formed body having millimeter wave shielding performance.SELECTED DRAWING: None

Description

  The present invention relates to a thermoplastic resin composition for a molded article having a millimeter-wave shielding performance suitable for a millimeter wave radar, and a molded article obtained therefrom.

Millimeter wave radar is used for the purpose of automatic driving of vehicles and collision prevention.
The millimeter wave radar device is attached to the front of an automobile, and includes a high frequency module incorporating an antenna for transmitting and receiving radio waves, a control circuit for controlling the radio waves, a housing for housing the antenna and the control circuit, and transmission and reception of radio waves from the antennas. A covering radome is provided (background art of Patent Document 1).
The millimeter wave radar device configured as described above can detect a relative distance, a relative speed, and the like with an obstacle by transmitting and receiving millimeter waves from an antenna.

Since the antenna may receive the antenna reflected on the road surface other than the target obstacle, the detection accuracy of the apparatus may be lowered.
In order to solve such a problem, the millimeter wave radar device of Patent Document 1 includes 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 dielectric loss larger than that of the radome.
The dielectric loss layer is made of a carbon material selected from at least one of carbon nanotubes, carbon microcoils, sungite carbon, carbon black, expanded graphite, and carbon fibers (paragraph number 0023).
The magnetic loss layer is 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 electric resistivity than the carbon material or the hexagonal ferrite. (Paragraph number 0024).

JP 2007-74662 A

KEC Information, No. 225, April 2013, p36-41

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

  As a means for solving the problems, the present invention has a millimeter wave shielding performance containing (A) a thermoplastic resin and (B) 0.5 to 5% by mass of carbon fiber having a fiber length of 3 to 30 mm. A thermoplastic resin composition for a molded body is provided.

The present invention provides a solution to other problems.
A molded body having a millimeter-wave shielding performance comprising the thermoplastic resin composition according to any one of claims 1 to 4,
The weight average fiber length of the carbon fiber derived from the carbon long fiber of the component (B) remaining in the molded body is 1 mm or more,
Provided is a molded article having a millimeter wave shielding performance, wherein the molded article has a surface resistivity in the range of 1 × 10 ⁵ to 10 ⁹ Ω / □.

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

Explanatory drawing of the measuring 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 as the component (A) is not particularly limited and can be appropriately selected depending on the application.
The component (A) is preferably selected from polypropylene, aliphatic polyamide, aromatic polyamide, polybutylene terephthalate, polycarbonate, and mixtures thereof.

As the carbon long fiber of component (B), known polyacrylonitrile-based, pitch-based, rayon-based and the like can be used, but polyacrylonitrile-based carbon long fibers are preferable.
(B) The carbon long fiber of a component contains what the metal surface-coated. The surface coating method is not particularly limited. For example, various known plating methods (for example, electrolytic plating, electroless plating, hot-dip plating, etc.), vacuum deposition methods, ion plating methods, CVD methods (for example, thermal methods) CVD, MOCVD, plasma CVD, etc.), PVD method, sputtering method and the like. Of these, the plating method is preferably used.
Examples of the metal covering the surface include silver, copper, nickel, and aluminum. Nickel is preferable from the viewpoint of the 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 long fiber (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 improve millimeter wave shielding performance.

(B) The carbon long fiber of the component is a component of the component (A) in which the carbon fibers are melted in a bundle in the length direction in order to increase the dispersibility of the component (A) and the component (B). What is obtained by impregnating and integrating a thermoplastic resin into 3 to 30 mm (resin-impregnated carbon long fiber bundle) is preferable.
Such a resin-impregnated carbon long fiber bundle can be manufactured by a known manufacturing method using a die, such as paragraph number 0019 of Japanese Patent Application Laid-Open No. 2011-57811 and Reference Production Example 1, etc. In addition to paragraph number 0007 of Japanese Patent No. 313050, paragraph number 0023 of Japanese Patent Laid-Open No. 2007-176227, Japanese Patent Publication No. 6-2344 (manufacturing method and molding method of resin-coated long fiber bundle), Japanese Patent Laid-Open No. 6-114732. (Fiber-reinforced thermoplastic resin structure and method for producing the same), JP-A-6-293023 (method for producing a long fiber-reinforced thermoplastic resin composition), JP-A-7-205317 (method for taking out a fiber bundle and length thereof) Manufacturing method of fiber reinforced resin structure), JP-A-7-216104 (manufacturing method of long fiber reinforced resin structure), JP-A-7-25143 No. 8 (manufacturing method and manufacturing apparatus of long fiber reinforced thermoplastic composite material), JP-A-8-118490 (manufacturing method of crosshead die and long fiber reinforced resin structure), etc. Can do.
Commercial products such as Plastron (registered trademark; Daicel Polymer Co., Ltd.) can also be used.

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

  The content ratio of the carbon long fiber of the component (B) in the composition is 0.5 to 5% by mass, preferably 0.5 to 3% by mass, and is preferably 0.8 to 0.5% in order to improve the millimeter wave shielding performance. 2 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 stabilizers, stabilizers such as UV absorbers, antistatic agents, flame retardants, flame retardant aids, colorants such as dyes and pigments, lubricants, plasticizers, Examples thereof include crystallization accelerators and crystal nucleating agents.

<Molded body>
The molded body of the present invention is obtained by molding the thermoplastic resin composition described above, and the shape, size, and the like can be selected depending on the application.

The molded article of the present invention may have a weight average fiber length of 1 mm or more of carbon fibers derived from the remaining carbon fibers of the component (B) in order to improve the shielding performance of millimeter waves (electromagnetic waves in a predetermined frequency band). Preferably, it is 2 mm or more, more preferably 3 mm or more.
The weight average fiber length is measured by the method described in Examples.

In the molded product of the present invention, the content ratio of the carbon fiber derived from the remaining carbon fiber of 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 80 More preferably, it is mass%.
Further, in the molded article of the present invention, the content ratio of the carbon fiber having a fiber length of 2 mm or more derived from the remaining carbon fiber of the component (B) is preferably 40% by mass or more, more preferably 50% by mass or more. More preferably, it is at least mass%.

The molded body of the present invention has a millimeter wave shielding performance. The millimeter wave shielding performance means that a millimeter wave (electromagnetic wave in a predetermined frequency band) obtained by the measurement method of the example is used. ) In the electromagnetic wave shielding property (radiation wave transmission inhibition property).
The electromagnetic wave shielding property in the molded article of the present invention is 30 dB or more, more preferably 40 dB or more, and further preferably 50 dB or more.
The millimeter-wave frequency band in the present invention is in the range of 300 mm (1 GHz) to 1 mm (300 GHz), and 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 article of the present invention has a long average residual fiber length as described above, it exhibits conductivity in addition to the millimeter wave shielding performance even though the content of the component (B) is small.
The volume resistivity of the molded article 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 article of the present invention is in the range of 1 × 10 ⁵ to 10 ⁹ Ω / □, and preferably in the range of 1 × 10 ⁶ to 10 ⁸ Ω / □.

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

Production Example 1 (Production of resin-impregnated carbon long fiber bundle)
A fiber bundle (a bundle of about 24,000 fibers) made of long carbon fibers (Torayca T700SC, tensile strength 4.9 GPa) was passed through a crosshead die through heating at 150 ° C. by a preheating device.
At that time, molten polypropylene (manufactured by Sun Allomer Co., Ltd., PMB60A) was supplied to the crosshead die from a twin screw extruder, cylinder temperature of 280 ° C., and the fiber bundle was impregnated with polypropylene.
Then, after shaping with a shaping nozzle at the exit of the crosshead die and shaping with a shaping roll, the pellet was cut into a predetermined length by a pelletizer to obtain a pellet (cylindrical shaped body) having a length of 8 mm.
The carbon long fiber length is the same as the pellet length. The pellets thus obtained had carbon long fibers substantially parallel to the length direction.

Example 1
Using 3% by mass of pellets (carbon long fiber content of 40% by mass) obtained in Production Example 1 and 97% by mass of pellets of polypropylene resin (manufactured by Sun Allomer Co., Ltd., PMB60A), an injection molding machine (J-150EII; The product was molded at a molding temperature of 240 ° C. and a mold temperature of 60 ° C. by Nippon Steel Works, Ltd.
Each measurement shown in Table 1 was implemented using the obtained molded object.

Comparative Example 1
The pellets obtained from the production example (carbon long fiber content: 40% by mass) were supplied to a twin screw extruder (Japan Steel Works, Ltd .; twin screw extruder TEX30α), and the pellets were molded again to contain carbon short fibers. A pellet (cylindrical shaped body) was obtained.
Using this carbon short fiber-containing pellet, 3% by mass, and 97% by mass of a polypropylene resin (PMB60A manufactured by Sun Allomer Co., Ltd.), molding is performed using an injection molding machine (J-150EII; manufactured by Nippon Steel Works Co., Ltd.). A molded body was obtained by molding at a temperature of 240 ° C. and a mold temperature of 60 ° C.
Each measurement shown in Table 1 was implemented using the obtained molded object.

Comparative Example 2
An injection molding machine (J-150EII; Co., Ltd.) was used by using 25% by mass of pellets (carbon long fiber content: 40% by mass) and 75% by mass of polypropylene resin (PMB60A manufactured by Sun Allomer Co., Ltd.). ) Manufactured by Nippon Steel Works) and molded at a molding temperature of 240 ° C. and a mold temperature of 60 ° C. to obtain a compact.
Each measurement shown in Table 1 was implemented using the obtained molded object.

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

(2) Electromagnetic wave shielding property The measuring apparatus shown in FIG. 1 was used.
Between a pair of antennas (broadband antennas; Schwartzbeck, BBHA9120A, 2-18 GHz) 11 and 12 that face each other in the vertical direction, a molded object 10 (length 150 mm, width 150 mm, thickness 2 mm) to be measured is held. . 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, and the electromagnetic wave transmitted through the molded body 10 to be measured is received by the upper antenna 11. (Radiation wave transmission inhibition) was determined.
S _{21 in} Equation 1 is an S parameter (Equation 2) that represents the ratio of transmitted electromagnetic wave and incident electromagnetic wave, and can be measured by a network analyzer.
In Equation 1, since the electromagnetic wave shielding property (dB) is expressed by a positive value, the logarithm of the reciprocal of the S parameter is taken. In the measuring apparatus of FIG. 1, a range of 0 to about 55 dB can be measured, and when the electromagnetic wave shielding property exceeds the upper limit of measurement, “> 55 (dB)” is shown in Table 1.
Table 1 shows the measurement results, and FIG. 2 shows the change in electromagnetic shielding properties.
Electromagnetic shielding property = 20 log (1 / | S ₂₁ |) (unit: dB) (Formula 1)
S ₂₁ = (transmitted electromagnetic wave) / (incident electromagnetic wave) (Formula 2)

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

(4) Density The density was measured according to ISO 1183.

(5) Surface resistivity and volume resistivity For samples having 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 Corporation Manufactured, Lorester GP (MCP-T600)], and surface resistivity and volume resistivity were measured according to JIS K7194.
For samples with a surface resistivity of 1 × 10 ⁸ Ω / □ or more and a volume resistivity of 1 × 10 ⁴ Ω · m or more, use a high resistivity meter [manufactured by Mitsubishi Chemical Corporation, High Lester UP (MCP-HT450)]. The surface resistivity and volume resistivity were measured according to JIS K6911.
For example, in Table 1, the notation “1.1E + 07” in Example 1 indicates “1.1 × 10 ⁷ ”.
In Comparative Examples 1 and 2, “> 1.0E + 13 (Ω / □)” and “> 1.0E + 9 (Ω · m)” are the upper limit of measurement of the high resistivity meter, and the surface resistivity is 1 × 10 ^13. Since Ω / □ and volume resistivity are 1 × 10 ⁹ Ω · m, the resistivity is higher than these.
The description of “5-10E + 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 represents polypropylene and CF represents carbon fiber.
The electromagnetic wave shielding property indicates that the higher the numerical 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 shielding properties could be improved by using long fibers if the amount was the same.
In Comparative Example 3, it was confirmed that the electromagnetic wave shielding property was improved by increasing the content of the short-fiber carbon fiber, but in Comparative Example 3, carbon fiber that is 16 times the amount of Example 1 or more was used. Nevertheless, Example 1 was superior in electromagnetic wave shielding properties.
In Comparative Example 4, it was confirmed that when the content of the carbon long fiber was increased, electromagnetic wave shielding properties exceeding Examples 1 to 3 could be obtained. This is economically disadvantageous and has a large density, which is also disadvantageous for reducing the weight of the molded body.

The frequency band shown in Table 1 and FIG. 2 is 1 to 18 GHz. 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 more than the thickness even in the frequency band of 1 to 300 GHz. Since the carbon fiber compounded resin behaves as a loss medium because it is sufficiently small, it is known that the attenuation constant increases as the frequency increases in the GHz region and exhibits high electromagnetic shielding properties.
This fact can be confirmed from, for example, the description of Non-Patent Document 1, particularly “2.3 Electromagnetic Shielding Using Loss Medium” from p39 to p40 and “FIG. 9 Shielding Characteristics of Two-Layer Structure of Conductive Material”.

Claims (4)

(A) thermoplastic resin,
(B) Carbon long fiber having a fiber length of 3 to 30 mm 0.5 to 5% by mass
Contains no glass fiber,
(B) The carbon long fibers of component (3) are obtained by impregnating the melted thermoplastic resin of component (A) with a bundle of carbon fibers bundled in the length direction. A protective member for a transmission / reception antenna of a millimeter wave radar comprising a molded article having a millimeter wave shielding performance, comprising a thermoplastic resin composition cut to 30 mm,
The weight average fiber length of the carbon fibers derived from the carbon long fibers of the component (B) in the molded body is 1 mm or more,
The content ratio of the carbon fiber having a fiber length of 1 mm or more derived from the carbon long fiber of the component (B) in the molded body is 60% by mass or more,
The carbon fiber derived from the carbon long fiber of the component (B) in the molded body is a molded body having a millimeter-wave shielding performance in which the content ratio of the fiber length of 2 mm or more is 40% by mass or more. Protective member for millimeter wave radar transmission / reception antenna.   The thermoplastic resin as the component (A) is selected from polypropylene, aliphatic polyamide, aromatic polyamide, polybutylene terephthalate, and polycarbonate. This is a protection member for a transmitting / receiving antenna of a millimeter wave radar.   The protective member for a transmission / reception antenna of a millimeter wave radar comprising a molded body having a millimeter wave shielding performance according to claim 1 or 2, wherein the millimeter wave has a wavelength in the range of 1 to 300 GHz. The millimeter made of a molded article having a millimeter wave shielding performance according to any one of claims 1 to 3, wherein the molded article has a surface resistivity in a range of 1 x 10 ⁵ to 10 ⁹ Ω / □. Protective member for transmission / reception antenna of wave radar.

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