JP5044916B2 - Method for producing carbon fiber reinforced plastic with integrated radio wave absorber - Google Patents

Description

  The present invention is applied to, for example, transportation equipment such as ships and airplanes, structures such as bridges and steel towers, anechoic chambers, devices and facilities for wireless communication, buildings such as buildings, and office supplies, and to prevent radio interference. The present invention relates to a radio wave absorber suitable for prevention and a method for manufacturing the same.

  The radio wave absorber includes an impedance matching layer that prevents reflection of incoming radio waves, a radio wave absorption layer that captures and attenuates incoming radio waves, and a radio wave reflection layer that reflects radio waves that have passed through the radio wave absorption layer to the radio wave absorption layer. Note that the impedance matching layer and the radio wave reflection layer may be omitted as long as the desired radio wave absorption performance is satisfied.

  The radio wave absorption layer is configured to absorb the captured radio waves using its own electrical loss and magnetic loss. The impedance matching layer has a normalized impedance viewed from the surface of 1 or as close to 1 as possible to prevent reflection of incoming radio waves, and acts so that more of the incoming radio waves are captured by the radio wave absorption layer. The radio wave reflection layer acts to reflect the radio wave that has passed through the radio wave absorption layer to the radio wave absorption layer, and to absorb again the radio wave that could not be absorbed in one pass.

  There are a wide variety of such radio wave absorbers and methods for manufacturing the same.

  For example, magnetic and conductive powders such as ferrite and metal pieces are mixed, and a method for obtaining a predetermined radio wave absorption by the mixing ratio (see Patent Documents 1 and 2), a two-layer effect of magnetic loss and electrical loss layer. What has (refer patent document 3) etc. are known. However, these conventional electromagnetic wave absorbers are expensive to manufacture because it is very difficult to mix an electrical loss material and a magnetic loss material in a base material so that they are uniform. There were drawbacks such as poor mechanical properties.

  In addition, a radio wave absorber (Patent Document 4) in which a conductor and a powder of an inorganic hollow body are bonded with an inorganic adhesive is known as a method that is superior in mechanical properties and light weight as compared with a conventional example. However, although the specific gravity of the radio wave absorber is light, the plate thickness is increased in order to obtain a desired radio wave absorption effect, so that the weight of the structure is increased. In addition, although the mechanical properties have been improved compared to the conventional examples, there is a problem that the mechanical properties are overwhelmingly lower than the mechanical properties of the materials used in the structure for use as a structure. .

  As a method for solving these problems, a radio wave absorber made of a radio wave absorption layer made of a composite material including carbon short fibers and non-conductive short fibers and a resin as shown in Patent Document 5 is known. . As a method for producing the radio wave absorber, a method of forming a prepreg of the mixed paper is mainly used. However, in the case of the method for producing the radio wave absorber, a prepreg process of mixed paper is necessary, and moreover, an expensive facility for heating and pressurizing when producing the radio wave absorber by forming a prepreg For example, a press or an autoclave was required. Also, because the prepreg of mixed paper is impregnated with resin, it does not have good shapeability. For example, when forming a shape such as a curved surface, there is a problem of wrinkles and it is difficult to apply it to complicated shapes. Met.

In the conventional technique, an impedance matching layer, a radio wave absorption layer, and a radio wave reflection layer are manufactured separately and then joined by mechanical or secondary bonding. The bonding of each layer has a problem of bonding material and cost required for the work, weight increase due to the bonding member, or bonding strength and durability.
JP-A 51-58046 JP 58-71698 A Japanese Patent Publication No. 50-4423 JP 2000-082892 A JP 2004-119450 A

Therefore object of the present invention has a conventional street excellent electromagnetic absorption performance, light weight, excellent in mechanical properties, yet the production of carbon fiber reinforced plastic with integrated wave absorber can be formed into complex shapes The method is to provide an inexpensive method .

In order to achieve the above object, the present invention takes the following means. That is, the present invention relates to a radio wave absorber having a radio wave absorption layer composed of a non-woven fabric containing at least conductive short fibers and non-conductive short fibers and a resin, and a radio wave reflection layer composed of a carbon fiber fabric and a resin. a method of manufacturing a carbon fiber reinforced plastic with an integrated, carbon fiber radio wave reflecting layer and the radio wave absorbing layer are integrated with wave absorber characterized in that it is constructed integrally with the resin of the same composition a reinforced plastic manufacturing method of.
The manufacturing method of a wave absorber of carbon fiber reinforced plastic with integrated is in a mold, and placed at least the nonwoven fabric, the carbon fiber fabric as provided in any of one side of the nonwoven fabric, Communicating with a resin container, creating a pressure difference between the mold and the container, and by injecting the resin into the mold by the differential pressure, the nonwoven fabric and the carbon fiber fabric are impregnated with the resin. By curing, the non-woven fabric and the carbon fiber fabric are integrated with a resin having the same composition.

According to the method of producing a carbon fiber reinforced plastic with integrated radio wave absorber according to the present invention, on having an excellent electromagnetic absorption performance conventional street light weight, excellent mechanical properties, further, the complex shape method of producing a carbon fiber reinforced plastic with integrated possible the inexpensive wave absorber molding can be obtained in the.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a radio wave absorber 1 according to an embodiment of the present invention. As shown in FIG. 1, the present invention relates to a radio wave absorber 1 including a radio wave absorption layer 12 made of a composite material of a nonwoven fabric and a resin containing conductive short fibers and non-conductive short fibers , and a method for manufacturing the same. In the present embodiment, a configuration including a radio wave absorption layer 12, an impedance matching layer 11 provided on the first surface of the radio wave absorption layer 12, and a radio wave reflection layer 13 provided on the second surface of the radio wave absorption layer 12 is shown. However, the impedance matching layer 11 may be omitted. The material of the impedance matching layer 11 is not particularly limited as long as it is a material that hardly reflects incoming radio waves, but from the point of integration with the radio wave absorption layer 12, it is at least from a composite material composed of a non-conductive fiber fabric and resin. It is preferable to become. The material of the radio wave reflection layer 13 is not particularly limited, but is preferably made of a composite material composed of at least a conductive fiber fabric and a resin from the viewpoint of integration with the radio wave absorption layer 12.

  FIG. 2 shows a method for manufacturing the radio wave absorber 1 according to an embodiment of the present invention. FIG. 3 shows a cross-sectional view of the laminate 2 according to one embodiment of the present invention.

  As shown in FIG. 2, first, the laminated body 2 in which an arbitrary number of the nonwoven fabrics 22 are laminated is disposed on the lower mold 30. In the present embodiment, an arbitrary number of nonwoven fabrics are laminated to form the laminate 2, but the laminate 2 referred to in the present invention includes a case where the nonwoven fabric is a single layer (only one layer). From then on, the entire laminate 2 is covered with a bag film 34 as a bag base material. The bag film 34 is connected to a suction pipe 45 connected to the vacuum pump 43 and a resin feed pipe 41 connected to a resin tank 42 containing resin via a valve 40a. The connection position of the suction pipe 45 and the connection position of the resin feed pipe 41 are set to be opposite to each other with respect to the laminate 2. When the area of the laminated body 2 is large, it is preferable to dispose a resin diffusion medium 32 made of, for example, a net on the surface of the laminated body 2 because the resin can quickly diffuse in the in-plane direction of the laminated body 2.

  A double-sided tape 35 serving as a sealing member is interposed between the bag film 34 and the lower molding die 30, and the molding die is formed by sealing the whole from the periphery. In this state, the vacuum pump 43 is operated, and the inside (inside the mold) covered with the bag film 34 is brought into a vacuum state (reduced pressure state) by suction through the suction pipe 45. After that state, the valve 40 a is opened to inject the resin in the resin tank 42 into the bag film 34 through the resin feed pipe 41. Since the inside is in a vacuum state, the injected resin is quickly diffused along the resin diffusion medium 32 and impregnated into the laminate 2. If the method of this invention is used, resin will be efficiently and rapidly impregnated into the whole laminated body 2, and a cavity and a local unimpregnated part will not produce easily.

  Thereafter, the impregnated resin is cured, the bag film 34 and the resin diffusion medium 32 are removed, and the radio wave absorber 1 is obtained.

  In this embodiment, the laminated body 2 is covered with the bag film 34 and the inside is depressurized. However, there is no particular limitation as long as it is a manufacturing method in which a resin is injected into the laminated body 2 by a differential pressure from the resin pressure. For example, it includes a case where a cavity including a laminate is formed by using both molds of the lower mold and the upper mold as molds. In this case, the resin tank 42 is pressurized to atmospheric pressure or higher, and the differential pressure from the resin pressure is included. It is also possible to inject a resin using

  Substantially the laminated body is placed on the lower mold, covered with a bag base material, the inside is evacuated, and it is only necessary to inject the resin. Compared with the hand lay-up method in which the resin is impregnated with the resin, the equipment is very inexpensive and the manufacturing method is simple. Therefore, the manufacturing cost and the cost required for the entire production of the radio wave absorber are extremely low. Furthermore, since a resin diffusion medium can be used to quickly impregnate the resin in the in-plane direction, it is possible to manufacture a large wave absorber of, for example, 10 m or more, which was difficult with the conventional method. became.

  Moreover, in the manufacturing method concerning this invention, the said resin can be selected freely and even when the density of the nonwoven fabric 22 is high, it can be made to impregnate uniformly by using resin with low viscosity. Furthermore, by reducing the pressure inside, it is possible to form a void with very few, and it is possible to easily manufacture a radio wave absorber that is excellent in quality, particularly mechanical characteristics. The resin is preferably a thermosetting resin such as an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a phenol resin, a polyimide resin, or a polybismaleimide resin. In particular, it is preferable to use an epoxy resin or a vinyl ester resin in terms of obtaining a radio wave absorber excellent in mechanical properties.

  Further, according to the manufacturing method of the present invention, pressure is evenly applied to the laminate by a mold or a bag film in terms of plate thickness and surface smoothness that affect radio wave absorption performance. Therefore, it is possible to obtain a radio wave absorber that is superior in thickness uniformity and surface smoothness, and thus excellent in radio wave absorption performance, as compared with the conventional example.

  Further, since the prepreg is a sheet impregnated with a resin, there is a problem that the formability is low, and there is a problem that wrinkles occur in a portion where deformation does not follow in a complicated shape such as a curved surface, but the laminate 2 is a fabric. For this reason, it is excellent in formability and can follow even a complicated shape such as a curved surface, so that it is possible to easily manufacture a radio wave absorber having a complicated shape.

In the present invention, the in the laminate 2, it includes a conductive fiber cloth 23 on either one side of the nonwoven fabric 22, the nonwoven fabric 22 and may you injecting and curing the integrally resins. By doing so, the composite material of the conductive fiber fabric 23 and the resin can form the radio wave reflection layer 13, and the radio wave absorption layer 12 and the radio wave reflection layer 13 can be integrated with a resin having the same composition. In the prior art, the radio wave absorption layer 12 and the radio wave reflection layer 13 are generally bonded by mechanical bonding such as bolts or secondary bonding using an adhesive after each layer is manufactured separately. If the manufacturing method concerning this invention is used, the formation and joining of the radio wave absorption layer 12 and the radio wave reflection layer 13 are performed in one process by laminating the nonwoven fabric 22 and the conductive fiber fabric 23 and injecting and curing the resin. can therefore, since it can Rukoto reduce such material-working time in the bonding, onto which can reduce the cost, it is possible to reduce the weight applied to the junction. In addition, the bonding in the conventional technique has a problem in the bonding strength between both layers, particularly in terms of durability. However, according to the manufacturing method of the present invention, the radio wave absorption layer 12 and the radio wave reflection layer 13 are resins having the same composition. Therefore, bonding strength does not become a problem.

In addition, it is necessary that the conductive fiber fabric 23 is a carbon fiber fabric and the radio wave absorption layer 12 is a carbon fiber reinforced plastic in terms of obtaining the effect of the present invention. For example, it goes without saying that the use ratio of carbon fiber reinforced plastic is increasing in transportation equipment such as aircraft, ships and automobiles, but according to the manufacturing method of the present invention, carbon fiber is used as a structural member of transportation equipment. When reinforced plastic is used, it is possible to manufacture a carbon fiber reinforced plastic member having a function of a radio wave absorber by simply laminating a carbon fiber fabric and the nonwoven fabric, and the waste of material can be saved at a very low cost. And a high intensity | strength electromagnetic wave absorber can be manufactured.

Moreover, in the said laminated body 2, a nonelectroconductive fiber fabric is contained in the 1st surface side of the nonwoven fabric 22, and it can also inject | pour and harden | cure with the said nonwoven fabric 22 integrally. The non-conductive fiber fabric 21 forms the impedance matching layer 11, and the radio wave absorption layer 12 and the impedance matching layer 11 can be integrated with a resin having the same composition. The non-conductive fiber fabric 21 preferably includes at least one fiber fabric selected from glass fiber, aromatic polyamide fiber, polyphenylene sulfide fiber, and polylactic acid fiber. In particular , it is preferable to use glass fiber or aromatic polyamide fiber because the radio wave absorption layer 12 and the radio wave reflection layer 13 can be made to have high strength and high rigidity by being formed of the same resin. The form of the fiber may be a short fiber or a long fiber, and may be a fabric form such as a woven fabric, a knitted fabric, or a non-woven fabric. Further, the conductive fiber fabric 23 may be included on the second surface side of the nonwoven fabric 22, and the resin is injected and cured simultaneously into the three layers of the radio wave absorption layer 12, the radio wave reflection layer 13, and the impedance matching layer 11. You can also.

  In the present invention, examples of the short fibers of the conductive fibers include carbon fibers and fibers such as metal fibers such as gold, silver, copper, nickel, aluminum, and iron. The conductive fiber is preferably a carbon fiber having excellent characteristics such that it has conductivity by itself without any special treatment and has high strength, high elasticity, and low specific gravity. The length of the short fiber is preferably 0.1 to 20 mm. If the fiber length is too short, the fibers are unlikely to overlap each other and the number of contacts decreases, and if the average fiber length is increased, the fibers are easily broken, so the number of contacts does not increase efficiently. The short carbon fibers are preferably contained in the radio wave absorption layer within a range of 0.02 to 5% by weight. That is, the amount of short carbon fiber affects the electrical loss of the radio wave absorption layer. If it is extremely small, the electric loss is lowered and the radio wave absorption performance is lowered. If it is extremely large, the electric loss is increased but the reflected radio wave is also increased.

  Non-conductive short fibers have a volume resistivity two or more orders of magnitude greater than that of carbon short fibers, such as polyester fibers, nylon fibers, glass fibers, aromatic polyamide fibers, polyphenylene sulfide fibers, polyether ether ketone fibers, There are polyparaphenylene benzobisoxazole fibers and polylactic acid fibers. Among these, glass fibers and aromatic polyamide fibers are preferable because they have high rigidity and good compatibility with carbon fibers having high strength and high elastic modulus. If such non-conductive short fibers are extremely few or extremely large, the number of non-conductive short fibers interposed between the short carbon fibers decreases, and it becomes difficult to control the overlapping of the short carbon fibers. It is preferable to be contained within the range of 30 to 99% by weight in the absorbent layer.

  By using the conductive short fibers and non-conductive short fibers, an extremely light wave absorber can be obtained. Furthermore, since the short fibers improve the strength of the resin, it is possible to obtain a radio wave absorber having excellent mechanical characteristics.

The form of the fiber sheet containing at least conductive short fibers and non-conductive short fibers is obtained by mixing both fibers into a non-woven fabric to form a sheet. The nonwoven fabric is not particularly limited as long as short fibers are uniformly dispersed in a sheet shape. The nonwoven fabric referred to here also includes a paper-like body. The paper-like body here includes a sheet obtained by a well-known paper making method. Examples of the paper material include vegetable fibers such as pulp, organic synthetic fibers such as polyester, nylon and aromatic polyamide fibers, fibers such as inorganic fibers such as glass fibers, and inorganic particles such as aluminum hydroxide. . The nonwoven fabric preferably has a basis weight of 50 to 200 g / m ² and a thickness of 50 μm to 300 μm. If the basis weight per sheet is too small, many sheets must be stacked in large amounts, and conversely, if the basis weight is too large, it becomes heavy and difficult to handle. Preferably there is.

  The radio wave absorber 1 according to the present invention preferably has a thickness in the range of 1 to 30 mm, and has a band exhibiting a reflection loss of 10 dB or more with a width of at least 1 GHz in a frequency band of 2 to 20 GHz. It is preferable in terms of absorption performance.

  The electromagnetic wave absorber of the present invention is attached to or attached to an anechoic chamber, a moving body such as a ship or an aircraft, a structure such as a bridge or a steel tower, a device or equipment for wireless communication, a building such as a building, or an office article. Can be used to prevent radio interference.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Example 1
In FIG. 2, first, a short carbon fiber (3% by weight), a glass chopped fiber (77% by weight), and an aromatic polyamide pulp (20% by weight) are formed on an aluminum molded lower mold 30 having a release agent coated on the surface. %) Was wet-made, and a laminate 2 (thickness 1.3 mm, 300 mm × 300 mm) obtained by laminating 6 ply of mixed paper for radio wave absorbing material (100 g / m ² per unit area) manufactured by Toray Industries, Inc. was disposed.

  Next, a peelable ply 31 (nylon taffeta) having a releasability and a # 400 mesh polyethylene net as a resin diffusion medium 32 were arranged on the laminate 2.

  Next, on the left side of the resin diffusion medium 32, a resin injection port 46 with an opening of an aluminum C-channel material positioned downward is disposed. The resin tank 42 was installed near the resin injection port and communicated with the resin feed pipe 41. On the other hand, an aluminum C-channel material is disposed as a vacuum suction port 47 on the right side. The vacuum suction port 47 is a suction pipe 45 using a tube and communicated with the vacuum trap 44 and the vacuum pump 43.

  Next, the double-sided tape 35 was arrange | positioned around the laminated body 2, and the whole was covered with the bag film 34 as a bag material. The valve 40b on the suction side was opened, and the pressure in the bag was reduced to 1 torr from the vacuum suction port 47.

  Next, the valve 40 a on the injection side was opened, and the resin in the resin tank 42 was injected from the resin injection port 46. As the resin, vinyl ester resin R-806 made by Showa High Polymer was used. The resin was instantaneously filled into the resin injection port 46 and diffused in the resin diffusion medium 32 in about 1 minute, and then impregnated into the laminate 2.

  Since the resin completed the impregnation of the entire laminate 2, the injection side valve 40a was closed. Next, the resin in the laminate 2 was cured. After confirming the curing of the resin, the molded product was demolded to obtain a radio wave absorber 1 (thickness 1.2 mm) consisting only of the radio wave absorption layer 12.

On the other hand, the laminate ² of the aromatic polyamide fiber woven fabric 5ply having a basis weight of 460 g / m ² was injected and cured by the same method as described above to obtain the impedance matching layer 11 (thickness 2.8 mm).

  Next, FIG. 4 shows a result of measuring the reflection loss at 2 to 18 GHz for the radio wave absorber 1 on an aluminum plate having a thickness of 1 mm to be the radio wave reflection layer 13.

  The reflection loss refers to the reflection level (unit: dB) when a radio wave is vertically applied to an aluminum plate having a length of 30 cm, a width of 30 cm, and a thickness of 1 mm, and the reflection level when a radio wave is similarly applied to a flat plate wave absorber. It calculated | required from the difference with (unit: dB). For the measurement, a network analyzer manufactured by Agilent Technologies was used.

  In this embodiment, an aluminum plate is used as the radio wave reflection layer 13, but in the laminate 2, the laminate 2 in which the aromatic polyamide fiber fabric 5ply, the mixed paper 6ply, and the carbon fiber fabric are sequentially laminated is used. By arranging and injecting and curing the resin by the same method as described above, the radio wave absorber 1 having equivalent performance can be obtained.

  The present invention is more applicable when applied to structures requiring electromagnetic wave absorption effects and mechanical properties, such as transportation equipment such as ships and airplanes, structures such as bridges and steel towers, and buildings such as buildings. Although it is preferable from the point which can be performed, it can apply also to uses, such as an anechoic chamber, the apparatus and equipment for radio | wireless communication, and office supplies.

1 is a schematic side view of a radio wave absorber according to an embodiment of the present invention. It is a cross-sectional view of one embodiment of a method for producing a radio wave absorber according to the present invention. It is a schematic side view of the laminated body which concerns on one Embodiment of this invention. 3 is a graph showing the reflection loss of the radio wave absorber according to Example 1.

Explanation of symbols

1: Radio wave absorber 2: Laminate body 11: Impedance matching layer 12: Radio wave absorption layer 13: Radio wave reflection layer 21: Non-conductive fiber fabric 22: Non-woven fabric 23: Conductive fiber fabric 30: Lower mold 31: Peel ply 32: Resin diffusion medium 33: Breather 34: Bag film 35: Double-sided tape 40a, b: Valve 41: Resin feed pipe 42: Resin tank 43: Vacuum pump 44: Vacuum trap 45: Suction pipe 46: Resin injection port 47: Suction port

Claims (3)

In a method for producing a carbon fiber reinforced plastic in which a radio wave absorber made of a composite material composed of a resin and a nonwoven fabric containing at least conductive short fibers and non-conductive short fibers is integrated, in the mold, at least the nonwoven fabric and The carbon fiber fabric is disposed so as to be provided on one side of the nonwoven fabric, communicated with the resin container, and a pressure difference is generated between the mold and the container. Radio wave absorption characterized in that the nonwoven fabric and the carbon fiber fabric are integrated with a resin having the same composition by injecting the resin into the mold and simultaneously impregnating and curing the nonwoven fabric and the carbon fiber fabric. Manufacturing method of carbon fiber reinforced plastic with integrated body. Within the mold, the non-conductive fiber fabric is disposed on the first surface side of the non-woven fabric, the carbon fiber fabric is disposed on the second surface side, and a resin is injected and cured, whereby the non-woven fabric and the non-conductive fiber are disposed. The manufacturing method of the carbon fiber reinforced plastic which integrated the electromagnetic wave absorber of Claim 1 which integrates a property fiber fabric and the said carbon fiber fabric. The radio wave absorption according to claim 1 or 2, wherein a differential pressure is generated between the lower mold and a bag material, and a pressure difference between the lower mold and the resin container is generated by reducing the pressure inside the mold. Manufacturing method of carbon fiber reinforced plastic with integrated body.

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