JP6155862B2 - Thermoplastic resin molded article and method for producing thermoplastic resin molded article - Google Patents

Description

  The present invention relates to a thermoplastic resin molded article and a method for producing a thermoplastic resin molded article, and particularly relates to a thermoplastic resin molded article containing carbon fibers and a method for producing a thermoplastic resin molded article containing carbon fibers.

  In recent years, with the rapid spread of electronic devices, for example, to prevent malfunction of electronic devices and prevent influence on the human body, a conductive function has been added to housings used for personal computers, mobile phones, automobile parts, etc. It is required to shield electromagnetic waves. In addition, molded products made of thermoplastic resin that are easy to mold are being used for IC trays that are used to transport ICs. To protect ICs from static electricity, IC trays made of thermoplastic resin are used. It is required to provide conductivity and provide an antistatic function.

  Alternatively, various technologies for sensing distances and speeds and sensing obstacles using electromagnetic waves have been realized, and in such cases, it is required to shield unnecessary electromagnetic waves for accurate sensing. .

  As a method for imparting a conductive function to a thermoplastic resin molded article for performing electromagnetic wave shielding, there is a method using a conductive resin, but since the conductive resin itself is expensive, it is not practical. For this reason, the method of giving a conductive function to a molded article is common, using the general thermoplastic resin marketed now. As a method for imparting a conductive function to a general thermoplastic resin molded article, there are roughly the following two methods. One is a method in which after forming with a thermoplastic resin, a conductive film is formed on the surface of the molded product by surface treatment such as plating or vapor deposition to obtain a conductive molded product. The other is blending a powdered conductive material such as carbon black or metal or a fibrous conductive material such as metal fiber or carbon fiber into a thermoplastic resin, and molding this to form a conductive molded product. Is the method.

  Of the two methods, the former method of forming a conductive film is a two-step process of molding with a thermoplastic resin and surface treatment by plating or vapor deposition, resulting in inferior manufacturing economics. There is. On the other hand, the latter method of blending a conductive material with a thermoplastic resin has an advantage that only one step of molding is required.

  When a conductive material is blended with a thermoplastic resin to provide a conductive function, a powdered conductive material or a fibrous conductive material is used, but with the same addition amount, a fibrous conductive material is used rather than a powdered conductive material. The material shows better conductivity. This is because the conductive function is expressed when the conductive materials dispersed in the thermoplastic resin are in contact with each other, but the fibrous conductive material is more mutually connected than the powdered conductive material. Based on easy contact. Therefore, it can be understood that even if the same fibrous conductive material is used, a longer conductive function can be provided with a higher conductive function. As the fibrous conductive material, metal fiber, carbon fiber, or the like can be used as described above. Among these, in order to impart an excellent conductive function, among these, carbon fiber having particularly good affinity with a resin, particularly long Fibrous carbon fibers are most preferred.

  For example, in Patent Document 1, in a thermoplastic resin molded article containing carbon fibers, the matrix thermoplastic resin is 70 to 99.5 wt%, and the total content of carbon fibers contained in the molded article is 0.5 to 30 wt%. (A) 0.1 to 4.7 wt% of carbon fiber having a length exceeding 1.5 mm (based on the total amount of thermoplastic resin and carbon fiber; the same applies hereinafter), (b) 0.5 to 0.5% Carbon fiber having a length of 1.5 mm of carbon fiber of 0.2 to 10.7 wt% and (c) carbon fiber of a length of less than 0.5 mm is 0.2 to 14.6 wt% It is disclosed that a molded product having excellent mechanical properties and electrical properties, particularly a surface appearance, can be obtained by using a thermoplastic resin molded product.

JP 2000-218711 A

  However, when the inventors performed the technique disclosed in Patent Document 1, a difference occurs in the shielding performance of electromagnetic waves depending on the direction of the vibration surface of the electromagnetic waves, and there is a large difference in shielding properties between horizontally polarized waves and vertically polarized waves. It was found to occur.

  This invention is made | formed in view of this point, The place made into the objective is to provide the thermoplastic resin molded product which does not have a big difference in shield performance, even if a polarization direction differs.

  In order to solve the above problems, the thermoplastic resin molded article of the present invention is a thermoplastic resin molded article containing carbon fibers, and the carbon fibers are contained in an amount of 0.4 mass% to 10 mass%, The average length of the carbon fiber is 0.5 mm or more and 15 mm or less, and the thermoplastic resin is polypropylene, and includes polypropylene having at least one of a carboxyl group and a carbonyl group, and further having a Cl group. The carbon fiber has a structure having at least one of a carboxyl group and a carbonyl group on the surface. There are generally three types of polypropylene: homopolymers, random copolymers of ethylene, and block copolymers of ethylene. Block copolymers with ethylene are called block polypropylene.

  With the above configuration, the compatibility between the surface of the carbon fiber and another resin having a Cl group is high, and the compatibility between another resin having a Cl group and polypropylene having at least one of a carboxyl group and a carbonyl group is also high. Therefore, the carbon fiber is uniformly dispersed in the polypropylene, and high shielding performance can be exhibited regardless of the polarization direction of the electromagnetic wave incident on the resin molded product.

  The another resin is preferably an epoxy resin or polypropylene.

  The polypropylene is preferably block polypropylene. With this configuration, the resin molded product has high impact resistance.

  The diameter of the carbon fiber is preferably 5 μm or more and 11 μm or less.

  The carbon fiber is preferably contained in an amount of 0.5% by mass or more and 5% by mass or less.

  The average length of the carbon fibers is preferably from 0.5 mm to 10 mm.

  The thermoplastic resin molded article is preferably formed by injection molding.

  The method for producing a thermoplastic resin molded article of the present invention comprises kneading a first resin material containing carbon fibers and a first thermoplastic resin and a second resin material containing a second thermoplastic resin. A method for producing a thermoplastic resin molded article comprising a step of forming a molten material and a step of injecting the molten material into a mold, wherein the carbon fibers contained in the first resin material have an average length Having a thickness of 0.5 mm or more and 15 mm or less and having a surface coated with a third resin having a Cl group, the first thermoplastic resin is a polypropylene having at least one of a carboxyl group and a carbonyl group, The molten material has a configuration in which the carbon fiber is contained in an amount of 0.4 mass% to 10 mass%.

  With the above configuration, the third resin having a Cl group covers the surface of the carbon fiber with good wettability, and the carbon fiber is uniformly dispersed in the polypropylene having at least one of a carboxyl group and a carbonyl group. A thermoplastic resin molded product in which carbon fibers are uniformly dispersed in the second resin material and can exhibit high shielding performance regardless of the polarization direction of electromagnetic waves incident on the resin molded product. Can be manufactured.

  The third resin is preferably an epoxy resin or polypropylene.

  The second thermoplastic resin may be a polypropylene different from the first thermoplastic resin.

  The second thermoplastic resin may be the same polypropylene as the first thermoplastic resin.

  The polypropylene is preferably block polypropylene.

  Since the thermoplastic resin molded product of the present invention has a high affinity between the surface of the carbon fiber in the molded product and polypropylene, the dispersion of the carbon fiber in the polypropylene is uniform in various directions, and the vibration surface of the electromagnetic wave is High electromagnetic shielding performance even in the direction.

It is a typical figure of the apparatus which evaluates the shielding performance of electromagnetic waves. It is a figure showing the relationship between the addition amount of carbon fiber, and electromagnetic wave attenuation. It is a figure showing the relationship between the average length of carbon fiber, and radio wave attenuation. It is the figure which compared the Example and the comparative example.

  Before describing the embodiments of the present invention, the background to the present invention will be described.

  When an object moves, it is always required to move safely and efficiently while avoiding collisions with other objects. Examples of the movement of an object include various types such as walking of a person, movement of parts and products in a factory on a production line, transportation between processes, and vehicle traffic. Avoiding collision accidents in traffic is an issue that has been studied for a long time.

  For example, if the vehicle approaches from behind, the vehicle may be bumped by a steering wheel operation or a brake operation. For this reason, studies have been made to detect a vehicle behind the vehicle using a sensor using electromagnetic waves (so-called surveillance radar). In this case, if you do not selectively detect only the electromagnetic waves reflected from the vehicle behind you, you will receive an alarm due to noise electromagnetic waves, or the electromagnetic waves from the vehicles behind you will be buried in the noise and can not be detected. Situation.

  Since the transmitted electromagnetic wave is radiated with a certain degree of spread, it may be reflected by vehicle members around the transmitter and reach the receiving unit, which may become noise. It has been studied to arrange an electromagnetic shielding material around the receiving unit so as to block unnecessary radio waves other than electromagnetic waves traveling toward the rear vehicle.

  Since the installation location of the surveillance radar is limited, the electromagnetic shielding material generally has a complicated shape. Furthermore, the electromagnetic shielding material is required to have a condition that it has high electromagnetic shielding performance, is lightweight, has high mechanical strength, and can be manufactured at low cost. For example, although a metal plate has sufficient electromagnetic shielding performance, it is unsuitable for making it heavy and complicated, and measures against rust are also required. Accordingly, the inventors of the present application have made various studies with reference to Patent Document 1 so as to satisfy the above-mentioned requirements and to prevent the difference in electromagnetic wave shielding performance depending on the direction of the vibration surface of the electromagnetic wave. It was.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

(Embodiment 1)
In using a resin molded product containing carbon fiber as an electromagnetic shielding material, studies were made to make the electromagnetic shielding performance desired. Specifically, the shielding performance of a resin plate having a thickness of 3.0 mm was examined using a 24 GHz horizontally polarized electromagnetic wave as a monitoring radar. Even if the electromagnetic wave is vertically incident on the resin plate and the polarization plane of the electromagnetic wave is arbitrarily rotated around the traveling direction, the electromagnetic wave shielding performance equivalent to 11 dB or more is equivalent to that of the resin plate coated with the conductive material. We examined resin molded products that always had a damping amount. As the thermoplastic resin, polypropylene was used in consideration of cost and mechanical properties.

  The carbon fibers as conductors are dispersed in the resin molded product. When the resin molded product is irradiated with high-frequency electromagnetic waves such as a monitoring radar, a current flows through the carbon fiber due to an electromagnetic induction effect. When this current becomes an eddy current, the magnetic field lines generated by the eddy current in the direction opposite to the electromagnetic wave cancel the electromagnetic wave and exert a shielding function. In order to generate eddy currents, carbon fibers need to be brought into contact with each other, and this contact requires the formation of a conductor loop having a diameter equal to or less than half the wavelength of the electromagnetic wave. The wavelength of the electromagnetic wave of 24 GHz is about 1 cm.

  When the carbon fiber content is increased, adjacent carbon fibers in the resin molded product come into contact with each other. Here, if the carbon fiber is contained in a very large amount in the thermoplastic resin, the carbon fibers are sufficiently brought into contact with each other to form a conductor loop having a wavelength equal to or less than half of the wavelength of the electromagnetic wave. However, when the carbon fiber content is increased, the cost is increased, the flowability of the thermoplastic resin is deteriorated, and the wear of the cylinder and mold of the kneader is increased. Furthermore, when the length of the carbon fiber in the thermoplastic resin is shortened, contact between adjacent carbon fibers is not sufficiently generated unless the content is increased as compared with the case where the carbon fiber is long. The carbon fibers in the thermoplastic resin are shortened by the kneading step and the flow path during injection.

  The inventors of the present application have studied the above points, but have found a phenomenon in which the amount of attenuation varies depending on the vibration direction of the electromagnetic wave. This can be attributed to the fact that when injection molding is performed, carbon fibers are also likely to line up in the direction of resin flow. The amount of attenuation of the electromagnetic wave on the vibrating surface was the smallest. However, since it is necessary to set the minimum value of the attenuation amount to 11 dB or more, if the difference in the attenuation amount depending on the direction of the vibration surface is large, the carbon fiber content must be increased. As a result of various investigations, the combination of a certain type of carbon fiber surface treatment and a certain type of thermoplastic resin modification treatment can reduce the difference in attenuation depending on the direction of the vibration surface, and the carbon fiber content. It was found that can be reduced. Hereinafter, the thermoplastic resin molded article of the present embodiment will be described.

<Method for producing resin molded product>
The manufacturing method of the resin molded product is as follows.

  As a raw material, a master batch (first resin material) in which a large amount of carbon fiber is contained in the first thermoplastic resin, and a dilution pellet (second resin material) made of the second thermoplastic resin, Are mixed and put into a kneading extruder. The kneading extruder is, for example, a twin-screw extruder, and melts and kneads the master batch and the dilution pellet to uniformly disperse the carbon fibers in the thermoplastic resin.

  Next, the melted and kneaded molten material is injected into a mold and cooled to produce a resin molded product. The resin molded product is a member to which an electromagnetic wave transmission / reception device of a monitoring radar is attached, and includes a shielding portion on the lower side, the side, and the upper side.

<Evaluation of electromagnetic wave shielding performance of resin molded product>
The resin molded product was evaluated for electromagnetic wave shielding performance using the evaluation apparatus shown in FIG. The evaluation device uses a probe antenna for transmission and reception of radio waves. The transmitting antenna 20 and the receiving antenna 30 with the flange portion of the detector exposed are installed at a distance of 12 mm. Then, the resin molded product sample 10 is placed in front of the transmission antenna 20. The electromagnetic wave 40 to be transmitted / received is horizontally polarized with a frequency of 24.2 GHz, and the resin molded product sample 10 has two types, a case where the molten material flow direction is placed horizontally with the vibration surface of the electromagnetic wave, and a case where the molten material is placed vertically. Evaluation was performed with the installation form.

<Example>
As a masterbatch containing carbon fibers, the surface of carbon fibers having a diameter of 5 to 7 μm and a length of 8 mm in which carboxyl groups and carbonyl groups have been introduced by subjecting the surface to an oxidation treatment are treated with an epoxy resin having a Cl group (No. 1). 3) and a chip obtained by adding this carbon fiber to a block polypropylene modified with maleic anhydride. In this master batch, the mass ratio of the thermoplastic resin and the carbon fiber is 6: 4. The modified block polypropylene was confirmed to have a carbonyl group by measuring the wavelength absorption in the infrared region by FT-IR. Further, it was confirmed by XPS that a carboxyl group and a carbonyl group exist on the surface of the carbon fiber, and that a Cl group derived from the coated resin exists.

  Next, as a diluting material, an unmodified block polypropylene, an ethylene / α-olefin copolymer elastomer, and talc (average particle size 4 μm) mixed at a mass ratio of 60:15:25 were prepared. Then, the master batch and the above-mentioned dilution material are mixed and fed into a raw material hopper of an injection molding apparatus at a predetermined mass ratio, and injected into a one-point direct gate mold (360 mm × 250 mm × 3 mm) to form a resin. A product sample was prepared. The thickness of the resin molded product was 3.0 mm. The molding conditions were a resin temperature of 240 ° C., a mold temperature of 60 ° C., a screw rotation speed of 80 rpm (screw is a double flight screw), a back pressure of 10 MPa, an injection speed of 40 mm / s, and a holding pressure of 40 MPa × 4 sec.

  FIG. 2 shows the result of evaluating the shielding performance of electromagnetic waves by changing the amount of carbon fiber contained in the resin molded product sample. At this time, the carbon fiber was broken and shortened by injection molding, but as a result of measuring the carbon fiber length distribution by image analysis, the average length of the carbon fiber in the resin molded product sample was longer than 0.5 mm. . When the resin material sample is placed with the flow direction of the molten material horizontal to the vibration surface of the electromagnetic wave, the amount of radio wave attenuation is the largest, when it is placed vertically, the smallest is, and when placed at other angles, both The amount of attenuation was between.

  When the amount of carbon fiber added is 0.5 mass%, the radio wave attenuation is 18 dB or more, and even if the flow direction of the molten material in the sample is changed with respect to the vibration surface of the electromagnetic wave, the fluctuation of the radio wave attenuation is 4 dB. It became a small value. This amount of radio wave attenuation and its fluctuation amount are sufficient electromagnetic wave shielding performance as a product. The amount of radio wave attenuation increased as the amount of carbon fiber added was increased to 1% by mass, but the variation in the amount of radio wave attenuation by changing the direction of the sample was as small as 3.5 to 4 dB. Assuming that the amount of radio wave attenuation when the amount of carbon fiber added is reduced below 0.5% by mass is extrapolated from the graph of FIG. Although it can be seen that the amount can be secured by setting the amount to 0.25% by mass or more, it is preferable to add 0.4% by mass or more from the viewpoint of data reliability. In consideration of variations in electromagnetic wave shielding performance of individual products due to variations in raw materials and manufacturing processes and variations due to locations in the products, the amount of radio wave attenuation is preferably 20 dB or more. This can be achieved if the amount is 0.55% by mass or more.

  Next, FIG. 3 shows how the electromagnetic wave shielding performance varies depending on the average length of the carbon fibers in the resin molded product sample. It is considered that the higher the degree of kneading in an injection molding machine, the higher the degree of breakage and the shorter the carbon fiber, so that the amount of carbon fiber added is 1% by mass, and the degree of kneading is changed to form a plurality of resin moldings. A product sample was prepared, and the average length of carbon fibers therein was measured.

  As shown in FIG. 3, when the average length of the carbon fiber is in the range of 0.54 mm to 1.03 mm, the average length is substantially proportional to the radio wave attenuation, and the radio wave attenuation by changing the direction of the sample. The variation was 2.3 to 5.5 dB. When the average length of the carbon fiber was 0.5 mm, the radio wave attenuation was 12.2 dB or more, and sufficient electromagnetic wave shielding performance as a product could be secured. The average length of the carbon fibers varies depending on the length of the carbon fibers contained in the master batch, the conditions of the kneading process, the mold shape, and the like, and the upper limit of the electromagnetic wave shielding performance is 15 mm.

<Comparative example>
The resin molded product sample of the comparative example was produced as follows. As a master batch containing carbon fibers, a chip was used in which unmodified block polypropylene was added with carbon fibers having a diameter of 5 to 7 μm and a length of 8 mm, the surface of which was oxidized to introduce a carbonyl group. The carbon fiber surface was not subjected to a coating treatment close to the resin. The same dilution material as in the example was used.

  In both Examples and Comparative Examples, the content of carbon fiber was 1% by mass, and a resin molded product sample having a thickness of 1.5 mm was produced under the same injection conditions. The average length of the carbon fibers in the sample was 1.03 mm in the example and 1.10 mm in the comparative example.

  FIG. 4A shows the electromagnetic wave shielding performance of the example, and FIG. 4B shows the electromagnetic wave shielding performance of the comparative example. In the comparative example, when the resin molded product sample was placed with the flow direction of the molten material horizontal with respect to the vibration surface of the electromagnetic wave, the radio wave attenuation was as good as 36 dB, but when it was kept vertical, it was 28 dB. The amount of radio wave attenuation changes greatly depending on the direction of the sample. On the other hand, in the embodiment, even if the direction of the sample is changed, the radio wave attenuation is within the range of 33 dB to 38 dB, the attenuation is very large, the fluctuation is small, and the electromagnetic wave shielding required in any direction. Has performance.

  In the case of the comparative example, since the thermoplastic resin is an unmodified block polypropylene, the wettability with the carbon fiber is inferior, and the dispersion of the carbon fiber becomes uneven in the thermoplastic resin molded product. For this reason, it is considered that the amount of radio wave attenuation varies greatly depending on the direction of the sample.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

  In the above-described embodiment, the resin molded product is manufactured by injection molding. However, the resin molded product may be manufactured by press molding. In the case of pressing, since the carbon fiber is not broken by injection molding, carbon fiber having an average length of up to 15 mm can be contained. The modified polypropylene used for the masterbatch may have both a carboxyl group and a carbonyl group, or may have either one. Further, only one of a carboxyl group and a carbonyl group may be present on the surface of the carbon fiber.

  The thermoplastic resin molded product of the present application is not limited to a vehicle member, and may be any member as long as it is a member that needs to shield electromagnetic waves, such as a casing of an electronic device or a body of a robot.

  The thermoplastic resin molded article of the present application may contain fillers, additives, elastomers and the like in addition to carbon fibers. The polypropylene contained in the carbon fiber-containing pellet may be one type or a blend of a plurality of types, and in the case of a plurality of types, at least one of them has at least one of a carboxyl group and a carbonyl group. It only has to be. One type of polypropylene for dilution may be used, or a plurality of types of blends may be used. The dilution polypropylene (second thermoplastic resin) may be the same polypropylene as the masterbatch polypropylene (first thermoplastic resin).

  The polypropylene contained in the thermoplastic resin molded product of the present application is not limited to block polypropylene, and may be a homopolymer or a random copolymer with ethylene.

  The resin coated on the surface of the carbon fiber may be a resin other than an epoxy resin, such as a phenol resin or polypropylene.

  As described above, the thermoplastic resin molded article according to the present invention is excellent in electromagnetic wave shielding performance and is useful as an electromagnetic wave shielding member.

10 resin molded product sample 20 transmitting antenna 30 receiving antenna 40 electromagnetic wave

Claims (12)

A thermoplastic resin molded article containing carbon fiber,
The carbon fiber is contained in an amount of 0.4 mass% to 10 mass%,
The average length of the carbon fiber is 0.5 mm or more and 15 mm or less,
The thermoplastic resin is polypropylene, and includes polypropylene having at least one of a carboxyl group and a carbonyl group, and further includes another resin having a Cl group,
The carbon fiber is a thermoplastic resin molded product having at least one of a carboxyl group and a carbonyl group on the surface.   The thermoplastic resin molded product according to claim 1, wherein the another resin is an epoxy resin or polypropylene. The thermoplastic resin molded article according to claim 1 or 2 , wherein the polypropylene is a block polypropylene which is a block copolymer of propylene and ethylene .   The thermoplastic resin molded article according to any one of claims 1 to 3, wherein the carbon fiber has a diameter of 5 µm or more and 11 µm or less.   The thermoplastic resin molded article according to any one of claims 1 to 4, wherein the carbon fiber is contained in an amount of 0.5 mass% to 5 mass%.   The thermoplastic resin molded product according to any one of claims 1 to 5, wherein an average length of the carbon fibers is 0.5 mm or more and 10 mm or less.   The thermoplastic resin molded article according to any one of claims 1 to 6, which is formed by injection molding. A step of kneading a first resin material containing carbon fiber and a first thermoplastic resin and a second resin material containing a second thermoplastic resin into a molten material;
A method for producing a thermoplastic resin molded article comprising the step of injecting the molten material into a mold,
The carbon fiber contained in the first resin material has an average length of 0.5 mm or more and 15 mm or less, and the surface thereof is coated with a third resin having a Cl group,
The first thermoplastic resin is polypropylene having at least one of a carboxyl group and a carbonyl group;
The method for producing a thermoplastic resin molded article, wherein the molten material contains 0.4% by mass or more and 10% by mass or less of the carbon fiber.   The method for producing a thermoplastic resin molded article according to claim 8, wherein the second thermoplastic resin is a polypropylene different from the first thermoplastic resin.   The method for producing a thermoplastic resin molded article according to claim 8, wherein the second thermoplastic resin is the same polypropylene as the first thermoplastic resin.   The method for producing a thermoplastic resin molded article according to claim 8, wherein the third resin is an epoxy resin or polypropylene. The method for producing a thermoplastic resin molded article according to any one of claims 8 to 11, wherein the polypropylene is a block polypropylene which is a block copolymer of propylene and ethylene .

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