JP2016049646A - Carbon fiber-reinforced composite material molding and method for producing the same, and method for repairing carbon fiber-reinforced composite material molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving an interface adhesive strength between a carbon fiber and a resin in a CFRP molding in which a resin is used as a matrix; and a method for repairing lowering of a mechanical strength caused by deterioration, damage and the like due to use of the CFRP molding.SOLUTION: There is provided a CFRP molding in which a resin is used as a matrix. An area ratio of a gap portion between a carbon fiber and the peripheral resin to a cross-sectional area of the carbon fiber in a cross section in a thickness direction of the molding is in a range of 100:10 to 100:0.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a carbon fiber reinforced composite material molded body and a method for producing the same, and a simple method for repairing a deteriorated portion associated with the use of the molded body. Specifically, the carbon fiber in the molded body is directly heated. A molded body in which a gap between the carbon fiber and the resin generated by melting or softening the resin in the vicinity of the carbon fiber is melted or softened using the temperature increase of the resulting carbon fiber, and the resin is buried due to repeated stress, and the manufacturing method thereof, And a repair method.

  A composite material using carbon fiber is lightweight and excellent in mechanical properties such as strength and impact resistance, and thus is used in many fields such as aircraft members and automobile members. In particular, it is suitably used as an aircraft member application requiring light weight and high mechanical properties. As this forming method, a prepreg method is mainly employed.

  In the prepreg method, carbon fiber is impregnated with a thermosetting resin such as epoxy resin to create a sheet-like intermediate base material (hereinafter referred to as prepreg), and this prepreg is cut into a desired shape, laminated, and impregnated. This is a technique for obtaining a carbon fiber reinforced composite material (hereinafter referred to as CFRP) by curing a resin.

  As for the production method using the prepreg method, for example, a production method (Patent Document 1) using carbon fiber and a liquid epoxy resin whose glass transition temperature is 10 ° C. or more higher than the curing temperature, carbon fiber is bundled and substantially two-dimensionally oriented. In a molding material such as a carbon fiber sheet, a sizing agent containing a specific epoxy compound and a specific tertiary amine compound in a specific ratio is applied to the carbon fiber to improve the adhesion between the matrix resin and the carbon fiber. In addition to the method (Patent Document 2), there are numerous proposals.

  Although these methods have an advantage that high-performance CFRP can be reliably molded, a process of once heat-curing the prepreg is necessary, and there is room for improvement in productivity.

  On the other hand, in order to simplify the manufacturing process, a manufacturing method (Patent Document 3) in which a resin composition containing carbon fibers and a matrix resin is directly molded on a base material by an injection molding method or a compression molding method, or a predetermined method. Method for producing a resin composition (Patent Document 4) comprising a carbon fiber chopped strand having a volume resistivity in a range and a thermoplastic resin, a matrix comprising a pitch-resined carbon fiber having a specific thermal conductivity and shape and a synthetic resin CFRP (Patent Document 5), in which the carbon fiber filling rate is increased and the thermal conductivity in the thickness direction is improved, is proposed.

  A carbon fiber reinforced thermoplastic resin composite material (hereinafter referred to as CFRTP) using the thermoplastic resin matrix proposed above as a matrix. In this specification, “CFRP” includes “CFRTP” unless otherwise specified. ) Can be plasticized by heating and can be injection-molded, so that high-cycle molding is possible, productivity is high, and complex shapes can be molded with high accuracy. The carbon fiber used for this injection molding is a discontinuous fiber that is generally shorter than the carbon fiber used for the prepreg method. Therefore, the influence on the strength of the molded product is not only the addition of functions due to the entanglement of the carbon fibers. It is thought that a large part depends on the integration of the fiber and the resin.

  However, in the injection molding, the carbon fibers also move with the flow of the resin, so that the orientation and dispersion of the fibers may be uneven, and the actual molded body is lower than the strength obtained with a simple tensile test piece shape. Only strength can be achieved.

  Further, even when the thermoplastic resin is in a molten state, it is in a state of considerably higher viscosity than water, and the resin hardly penetrates between the carbon fibers, and the adhesiveness with the fibers is not always good. It is sufficient that the molded body is obtained in a state where the resin is sufficiently in contact with the periphery of the carbon fiber, but there is a gap between the carbon fiber and the surrounding resin due to the difference in thermal expansion and fluidity between them and the shrinkage of the resin. May occur, which may affect the mechanical properties of the molded body.

  Further, even with CFRP reinforced with continuous fibers, it is assumed that the carbon fibers and the resin are insufficiently adhered in the molded body due to bending by a press or the like. In addition, the internal structure may be deteriorated or damaged due to repeated loads or impacts when the molded body is used. If this can be repaired appropriately, cost reduction and continuous and long-term use are possible. Can be.

JP 2003-26820 A JP2013-117003A JP-A-10-278070 JP 2006-152023 A JP 2008-208490 A JP, 2014-139300, A JP 2002-13069 A

  The present invention has been made in view of the above-mentioned problems of the prior art, a method for improving the interfacial adhesive strength between carbon fiber and resin in a CFRP molded body using a resin as a matrix, and deterioration / damage caused by the use of a CFRP molded body. It is an object of the present invention to provide a method for repairing a decrease in mechanical strength accompanying the above.

  In order to solve the above-mentioned problems, the CFRP molded body of the present invention uses a resin as a matrix, and in the cross section in the thickness direction of the molded body, between the carbon fiber and the surrounding resin relative to the cross-sectional area of the carbon fiber. The area ratio of the voids is in the range of 100: 10 to 100: 0.

  In other words, the CFRP molded body is a state in which islands of carbon fibers are formed in the sea of the resin, and the resin is preferably in close contact with the carbon fibers. In particular, since carbon fibers used for injection molding in CFRTP molded products use discontinuous fibers (short chains) rather than continuous fibers, not only are they expected to have strength due to entanglement between fibers, but also carbon fibers and resins. It is desirable to improve the mechanical strength through cooperation. However, carbon fibers are dispersed at an appropriate density in the sea of resin fluidized in the injection molding process. If the resin wettability to the carbon fiber surface is poor or the resin shrinks significantly, the resin There is a possibility that voids that are not in close contact with the fibers are generated.

  As a conventional technique, a sizing agent such as a maleic anhydride compound or a urethane compound is attached to the surface of the fiber in order to improve the wettability of the resin (Patent Document 6). A method of adding a sizing agent such as an epoxy resin or a urethane resin excellent in compatibility (Patent Document 7) has also been adopted, but it is not always effective when using recycled carbon fiber or resin shrinkage. It's hard to say.

  Therefore, in the present invention, after CFRP is molded into a desired shape, a high frequency of 0.6 MHz to 2.2 MHz is irradiated for 10 minutes or less, and the carbon fiber in the CFRP molded body is heated by electromagnetic induction heating, The surrounding resin was selectively remelted or softened by heat generation of the fiber, thereby making the adhesion at the interface between the fiber and the resin more dense. By this treatment, in the cross section in the thickness direction of the molded body, the area ratio of the void portion between the carbon fiber and the surrounding resin with respect to the cross-sectional area of the carbon fiber is 100: 10 to 100: 0, preferably void. The area of the part is set to 0, and the mechanical strength of the molded body can be improved by the cooperation of the carbon fiber and the resin.

  In addition, the repair method of the present invention irradiates a CFRP molded body with a high frequency of 0.6 MHz to 2.2 MHz for 10 minutes or less to a portion that needs to be repaired such as deterioration within a period of use or a damaged portion, and electromagnetic induction heating. It is characterized by repairing a molded object by including the process to do.

  Conventionally, when the mechanical strength of a molded body is lowered or it becomes difficult to use due to damage or the like, it has been necessary to replace it with a new molded body. According to the repair method of the present invention, there is no need to newly replace the molded body, maintenance and management can be performed easily and at low cost, and if the high-frequency device is downsized, it may be repaired as it is at the site of use. it can.

  The CFRP molded body of the present invention has the same appearance, shape, and dimensions due to the close contact between the carbon fiber and the resin in the molded body, compared to the molded body obtained only by a normal molding process. Strength can be improved. In particular, regarding the CFRTP molded body, the volume content of the carbon fiber is also low, so that an improvement in function due to the cooperation between the fiber and the resin can be recognized.

  Moreover, in the manufacturing method of this invention, since an electromagnetic induction heating process is only added with respect to the existing equipment, introduction | transduction is easy. Furthermore, according to the repairing method of the present invention, it is possible to easily repair only the necessary damaged part, and it is economical because it is not necessary to discard the whole because of a defect of a part of the molded body.

FIG. 1 is a scanning electron microscope (SEM) observation photograph of a cross section of the molded article of the present invention. (A) shows before high-frequency processing, and (b) shows after high-frequency processing. FIG. 2 is a conceptual diagram illustrating an example of an electromagnetic induction heating device. FIG. 3 is a diagram showing the results of a three-point bending test of the molded body of the present invention. FIG. 4 is an SEM observation photograph of a cross section of the molded body for five samples before performing high-frequency treatment. FIG. 5 is an X-ray observation (3D) image of the molded body before performing high-frequency processing.

  In the CFRP molded body using the resin of the present invention as a matrix, the area ratio of the void portion between the carbon fiber and the surrounding resin with respect to the cross-sectional area of the carbon fiber in the cross section in the thickness direction of the molded body, In the range of 100: 10 to 100: 0, more preferably, the void portion cannot be confirmed.

  The CFRP matrix resin of the present invention is not particularly limited, but it is preferable to use a thermoplastic resin suitable for an injection molded article. Therefore, it can be said that it is suitable for the CFRTP molded body. Examples of the thermoplastic resin include polycarbonate resin, polyester resin, polyamide resin, polyacetal resin, polyimide resin, polyolefin resin, and polystyrene resin. Any of these may be used alone or in combination of two or more.

  The “thickness direction of the molded body” means that observation is performed by cutting vertically from an appropriate portion of the molded body in the thickness direction of the molded body. However, depending on the arrangement of the carbon fibers located on the cut surface, the cross-sectional areas are different even if the carbon fibers have the same shape. For example, consider a cylindrical carbon fiber. The cross section perpendicular to the cylinder is a perfect circle, and the cross-sectional area is the same regardless of where the cut surface is viewed. However, when cut obliquely, it becomes an ellipse, so the cross-sectional area increases or decreases depending on the angle (angle). . Moreover, the vertical cross section from the height direction of a cylinder is a rectangle, the rectangle when cut | disconnected along the diameter of a circle has the largest cross-sectional area, and the area of a rectangle becomes small as it leaves | separates from there. In addition, when the cross section is viewed obliquely from the height direction of the cylinder, it can take a shape such as a semicircle or a semi-ellipse.

  Therefore, the “cross-sectional area of carbon fiber” of the present invention is defined as a vertical cross section in the thickness direction of a columnar or thread-like carbon fiber. That is, in the above example, if the carbon fiber has a columnar shape, it means a cross section (perfect circle) perpendicular to the column. As a result, even if the arrangement of the carbon fibers appearing on the cut surface of the molded body is different, the “cross-sectional area of the carbon fibers” to be compared is always a constant value.

  Further, the “area of the void portion” to be compared means the area of the void portion from the periphery of the fiber to the resin on the same plane as the cross section of the carbon fiber defined above. It is difficult to properly compare the void portion, which is a three-dimensional space, with respect to the cross-sectional area (two-dimensional) of the carbon fiber unless it is on the same plane. This is because it is easy to grasp the degree of interfacial adhesion with the resin.

  More specifically, it is shown in FIG. This figure is a scanning electron microscope (SEM) observation photograph of the cross section of the CFRTP molded product of the present invention. (A) The columnar carbon fiber in the figure is present with a gap between the resin and the surrounding resin, and (b) the gap has disappeared in the figure (thus, the carbon fiber It is understood that the cross-sectional area of the area: the area of the void portion = 100: 0).

  In the present invention, a suitable method for producing a CFRTP molded body is that after injection molding into a predetermined shape, a high frequency of 0.6 MHz to 2.2 MHz is irradiated to an arbitrary portion of the molded body for a time within 10 minutes. It is only necessary to add an electromagnetic induction heating process. Since an electromagnetic induction heating process is simply added to the conventional injection molding process, it can be easily introduced into the conventional manufacturing process. In the process, electromagnetic induction heating is used in which carbon fibers in the CFRTP molded body generate eddy currents by electromagnetic induction and heat is generated by resistance. Since the carbon fiber is dispersed using the thermoplastic resin as a matrix, only the carbon fiber that easily conducts electricity generates heat. Accordingly, it is considered that the amount, length, dispersion state, etc. of the carbon fiber directly influence the calorific value.

  It has been reported that electromagnetic induction heating is used during CFRTP press molding ("Journal of the Society of Materials, Japan", Vol. 58, No. 7, pp 642-648, July 2009). The CFRP of this document uses continuous fibers with many fiber crossings, and even if it is a frequency of ˜500 KHz, it is heated to some extent if time is taken. However, it is not used for post-processing after injection molding as in the present invention, and in an injection molded product in which discontinuous fibers with a short fiber length and few crossings are distributed, the frequency range of high-frequency induction heating is If it is not in the MHz band, it is difficult to heat the carbon fiber efficiently. In the present invention, it is desirable to use 0.6 MHz to 2.2 MHz, preferably 1.6 MHz to 2.2 MHz, which heats the carbon fiber most efficiently.

  In the electromagnetic induction heating process of the present invention, unlike the case where the resin in the mold at the time of injection molding is molded in the process of cooling from melting, only the resin around the carbon fiber is selectively heated. That is, the entire resin can flow during injection molding, whereas the resin located at a certain distance from the carbon fiber maintains a solid state during electromagnetic induction heating, and only the limited resin around the fiber melts. In addition, although the volume of the resin is increased by melting, there is no increased place for the resin except for the void portion. Therefore, the molten resin and the fiber are forcibly brought into close contact with each other. Moreover, because of partial heating, the molten resin is cooled faster by the surrounding non-heated resin than the cooling rate at the time of injection molding.

  In this way, even if the relationship between the carbon fiber and the resin is poor due to factors such as partially molten resin, rapid heating, rapid cooling, and limited space due to electromagnetic induction heating, the interface between the two The adhesive strength can be further strengthened. This effect can improve the mechanical strength of the CFRP molded body.

  Moreover, even if the heat treatment is performed on the entire molded body, the resin to be melted can be limited only to the resin located in the vicinity of the carbon fiber, so that the size and shape of the entire molded body are not affected. That is, since it is not necessary to make a new injection mold, the net additional investment is limited to the electromagnetic induction device, and it is easy to introduce this manufacturing process into the conventional equipment.

  The electromagnetic induction heating step can be performed not only on a CFRP molded body before shipment but also on a molded body in use. When cracks (including voids and unbonded states even if there are no voids) occur between the carbon fiber and the resin in the molded body due to the load and impact received during use, the electromagnetic Induction heating is performed. In a composite material composed of different combinations, deterioration and damage are likely to occur at the interface between the carbon fiber and the resin, and this is a starting point for destruction of the entire CFRP molded body. If such a starting point can be appropriately repaired, the molded body can be used over a long period of time. Therefore, the repair method of the present invention irradiates a CFRP molded body with a high frequency of 0.6 MHz to 2.2 MHz, preferably 1.6 MHz to 2.2 MHz for a time within 10 minutes to a portion that requires repair of the molded body. And a step of electromagnetic induction heating.

  The part requiring repair is not always clear in appearance. In such a case, use the repair method of the present invention as a guide for locations where the CFRP molded body has been damaged in the past as a guide, or for locations that have been impacted or repeatedly subjected to load during use. By doing so, it is possible to take preventive measures before destruction of the entire compact occurs.

  The apparatus used for the electromagnetic induction heating process of this invention is demonstrated. The electromagnetic induction heating device has holding means for fixing the CFRP molded body so as to be rotatable, and means for heating the CFRP molded body at high frequency electromagnetic induction. FIG. 2 shows an outline of this apparatus. The CFRTP molded body 1 is held at a relative position with respect to the magnetic field 3 by the holding means 2 of the apparatus, and can apply a magnetic field from a predetermined direction. The holding means only needs to be able to fix the CFRTP molded body during processing or to orient it in a predetermined direction, and does not need to have a special structure. As long as the material does not generate heat even when a magnetic field is applied, a material such as a glass table on which a molded body can be placed may be used.

  The predetermined part of the molded body can be selectively heated by rotating or moving the holding means back and forth and right and left. For example, a portion where joining marks appear (referred to as welds) in the joined portion of the melted CFRTP in injection molding is intensively heated, a thin-walled portion and a thick-walled portion, a surface having a flat surface and a step, etc. By processing this, the electromagnetic induction heating process is completed in a shorter time with the aim of a portion estimated to be weak in strength. Thus, a low-priced and high-quality CFRP molded product can be supplied by improving both the function of the product and manufacturing efficiency.

  The electromagnetic induction heating means for causing the magnetic field 3 to act on the CFRTP molded body includes a supply unit (not shown) that supplies a high-frequency current and an induction heating coil 4 that generates a magnetic field. As a specific example of such high-frequency electromagnetic induction heating, an electromagnetic induction device (power supply unit IH-052W, transmission unit IH-052M-FC) manufactured by Wyeth Electronics Industry Co., Ltd. is suitable. In this apparatus, low noise is achieved with a high-frequency inverter for dielectric heating using a field effect transistor, and an ultra-high frequency band of 2 MHz can be used with this inverter. This makes it possible to rapidly heat non-magnetic metals, carbon fibers, and the like by electromagnetic induction heating, which conventionally has been mainly heating magnetic metals. In FIG. 2, the magnetic field 3 is conceptually indicated by a thick dotted downward arrow, but this is merely an image diagram.

  The carbon fiber 5 is dispersed inside the CFRTP molded body 1, but the carbon fiber 5 ′ in the region where the magnetic field 3 acts (indicated by a dotted circle 6 in FIG. 2) is guided. The temperature rises due to heating. This is because Joule heat is generated by eddy current and electric resistance flowing in the carbon fiber by the magnetic field.

  The result of the electromagnetic induction heat treatment of the CFRTP molded body using the apparatus configured as shown in FIG. 2 is shown below.

(Example 1)
Using a pellet made of polypropylene as a matrix, carbon fiber length of about 3.5 mm, and carbon fiber content of about 30% by weight (PYROFIL PP-C-30A manufactured by Mitsubishi Rayon), an injection molding machine (Nissei Plastic Industry Co., Ltd.) NEX110-12E) was used to form a CFRTP molded body.

  1. Using the electromagnetic induction device (power supply unit IH-052W, oscillation unit IH-052M-FC, coil has an inner diameter of 30 mm and the number of windings is 2) of Wyeth Electronics Industry Co., Ltd. for the molded body. Irradiation was performed at a frequency of 0 MHz for 5 minutes. FIG. 3 shows the results of testing with a span of 60 mm in accordance with a three-point bending test (JISK7074) with and without electromagnetic induction heat treatment (invention). In addition, (a) of the SEM observation photograph shown in FIG. 1 is a thing only by injection molding, (b) is what performed the electromagnetic induction heating process.

  From FIG. 3, it was confirmed that the molded body that had undergone the treatment process of the present invention had an improvement in bending elastic modulus of about 10% compared to that of injection molding alone. Therefore, it can be seen that the mechanical strength can be improved by bringing the resin into close contact with the periphery of the carbon fiber by electromagnetic induction heating.

(Experimental example 1)
FIG. 4 shows SEM observation photographs of five samples (I to V) that have been cut before the high-frequency treatment of the same CFRTP molded body used in Example 1. In addition, the square part enclosed with the dotted line of each photograph shows the location which used the area of the space | gap part of carbon fiber and the resin of the circumference | surroundings for calculation. The ratio with the cross-sectional area of this carbon fiber is shown in Table 1 below.

  As shown in the table, depending on the conditions such as injection molding, if the cross-sectional area of the carbon fiber is 100, the area of the void portion with the resin is larger than 10 in a considerable proportion, It can be seen that there is a problem in the adhesion between the carbon fiber and the resin.

(Experimental example 2)
FIG. 5 shows a sample (X-ray) of the same CFRTP molded body used in Example 1 before being processed by high frequency using a microfocus X-ray CT apparatus (inspeXio SMX-100CT) manufactured by Shimadzu Corporation. 3D image when the tube voltage is 80 kV and the voxel equivalent length is 0.004 mm / voxel). In the figure, the cube indicates the molded body, and the whiter portion indicates the void portion. Although depending on the conditions of injection molding, it was estimated that considerable voids were generated inside the molded body.

  As described above, the CFRP molded body of the present invention can contribute to the improvement of the function of the molded body by simple and short-time processing just by adding the electromagnetic induction heating processing step to the normal injection molding manufacturing process. it can.

  Since the manufacturing method of the present invention can be used in an injection molding manufacturing process using CFRP and can be easily introduced, it can be applied to CFRP molded bodies used for various purposes.

  In addition, the electromagnetic induction heating device as a whole can be miniaturized and can be introduced at a small manufacturing site regardless of the installation location. Take it to the site where the CFRP molded product is actually used, It can also be used for strength recovery and repair.

DESCRIPTION OF SYMBOLS 1 CFRTP molded article 2 Holding means 3 Magnetic field 4 Coil 5, 5 'Carbon fiber 6 Field where magnetic field acts

Claims (3)

A molded body of a carbon fiber reinforced composite material having a resin as a matrix,
In the cross section in the thickness direction of the molded body,
The carbon fiber-reinforced composite material molded article, wherein an area ratio of a void portion between the carbon fiber and the surrounding resin to a cross-sectional area of the carbon fiber is within a range of 100: 10 to 100: 0. . After molding the carbon fiber reinforced composite material,
A step of irradiating a high frequency of 0.6 MHz to 2.2 MHz with respect to an arbitrary portion of the molded body for a period of time within 10 minutes, and electromagnetic induction heating;
The manufacturing method of the molded object of Claim 1 characterized by the above-mentioned. For the carbon fiber reinforced composite material molded body,
A step of irradiating a portion requiring repair of the molded body with a high frequency of 0.6 MHz to 2.2 MHz for a period of 10 minutes or less and electromagnetic induction heating,
A method for repairing a molded article of carbon fiber reinforced composite material, comprising: