JP2010076356A - Preform, and molding method for fiber-reinforced plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber-reinforced plastic capable of easily carrying out trimming work of an outer circumferential portion, that is a cost-increase factor in a conventional RTM molding, and capable of restraining the strength of a product outer peripheral part from getting low. <P>SOLUTION: A preform includes the first base material comprising at least only a reinforcement fiber, and the second base material impregnated preliminarily with a resin in the reinforcement fiber, wherein the second base material is arranged in at least one part of an outer peripheral part of the first base material, and a thickness of the second base material is thicker than that of the first base material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a preform for molding fiber reinforced plastic (FRP) and a method for molding fiber reinforced plastic. In particular, the present invention relates to RTM (Resin Transfer Molding) molding in which a liquid resin is injected after a preform is set in a mold cavity in advance.

Fiber reinforced plastics, especially carbon fiber reinforced plastics (CFRP) are used in various fields as composite materials having light weight and high mechanical properties. Particularly in the automobile field, the demand for weight reduction of the vehicle body is increasing from the viewpoint of improving fuel efficiency, and CFRP is being used. As one of FRP molding methods, there is known an RTM molding method in which a reinforcing fiber base material is placed in a mold cavity in advance, a liquid matrix resin is injected after mold clamping, and the reinforcing fiber base material is impregnated and heat-cured. ing. The RTM molding method effectively expresses the lightweight and high mechanical properties that are characteristic of CFRP, and the cavity is decompressed in advance before resin injection, so there are few defects such as pinholes on the molding surface. It can have a beautiful appearance. Therefore, it is one of the effective molding methods for automobile applications that require a high level of appearance quality.

  However, trim processing that cuts off unnecessary portions of the outer edge of the molded body obtained as post-processing after molding is required, and a method such as water jet processing or NC router processing is used, resulting in a significant increase in cost. In particular, CFRP is a large factor in cost increase because the reinforcing fiber is hard and the processing speed cannot be increased and the wear of the machining tool is extremely fast.

  In order to omit the trim processing that brings about such cost increase, there is a proposal on shaping of the reinforcing fiber base material in order to obtain the shape of the reinforcing fiber base material (near net shape) as close as possible to the product shape. There are various. However, if trim processing is to be omitted in the RTM molding method, it is necessary to prepare a preform shaped smaller than a predetermined product shape and arrange it so that the preform does not protrude from the mold cavity. . In such a molding method, a portion composed only of a matrix resin that does not include reinforcing fibers is generated in the outer peripheral portion of the product, so that a defect such as a lack of the outer peripheral portion occurs due to a difference in thermal expansion from the central portion.

  On the other hand, the proposal which arrange | positions the base material which is easy to trim in the outer peripheral part of a reinforced fiber base material is made | formed.

  For example, it has been proposed to comprise a main body part and a burr molding part extending outward from the outer periphery of the main body part. The burr molding part has a strength lower than that of the main body and a preform (precursor) is composed of a thin material ( Patent Document 1).

However, in the conventional method as described above, the outer peripheral portion of the product is not lost immediately after molding, but a low strength portion is generated on the outer periphery of the product. For example, when the automobile roof shown in FIG. 1 is manufactured by a conventional method, there is often a problem that the outer peripheral portion is missing when the mounting hole in the outer peripheral portion of the product is processed.
JP 2006-188050 A

  Therefore, the object of the present invention is to overcome the problems of the conventional preform and fiber strong plastic molding method described above, and to easily perform trim processing while ensuring a lightweight, high mechanical strength and good appearance. An object of the present invention is to provide a method for molding a preform and a fiber reinforced plastic in which the strength of the outer peripheral portion is equal to that of the product central portion.

To achieve the above object, the present invention adopts the following configuration. That is,
(1) It is composed of at least a first base material made of only reinforcing fibers and a second base material in which the reinforcing fibers are impregnated with a resin in advance, and the second base material is an outer peripheral portion of the first base material. A preform characterized in that the preform is arranged at least in part and the thickness of the second base material is thicker than the thickness of the first base material.
(2) The preform according to (1), wherein the thickness of the second base material is 1.5 times or less the thickness of the first base material.
(3) A preform in which a second base material in which a reinforcing fiber is impregnated with a resin in advance is arranged on at least a part of the outer peripheral portion of the first base material made only of reinforcing fibers, and the preform is made of gold A method for molding a fiber reinforced plastic, wherein the resin is injected and cured after being accommodated in a cavity of a mold.
(4) The method for molding fiber-reinforced plastic according to (3), wherein the height of the preform on which the second base material is disposed is higher than the height of the cavity of the mold.

  According to the present invention, a preform and a fiber reinforced that are lightweight and have high mechanical strength, can be easily trimmed while ensuring a good appearance, and the strength of the outer peripheral portion is equal to that of the product central portion. A plastic molding method can be provided.

  Specifically, when crushing the second base material during mold clamping, since the resin contained in the second base material is in a semi-cured state and has a high viscosity, the reinforcing base material and the resin are together. The outer peripheral portion having a high strength can be formed. At this time, since the resin is not impregnated on the inside of the product, a space remains, and the excess portion of the second base material flows to the inside of the product having a lower resistance than the mating surface of the upper and lower molds. There is almost no burrs. Since the liquid resin having a low viscosity is injected after the shape of the outer peripheral portion is formed in this way, most of the product can obtain a beautiful molded product with few pinholes.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  The preform in the present invention refers to a form in which reinforcing fiber base materials are laminated and integrated, and generally shaped into a shape to be molded. 2 and 3 show typical embodiments of the present invention.

  Examples of the reinforcing fibers include inorganic fibers such as carbon fibers and glass fibers, or organic fibers such as aramid fibers and polyethylene fibers. Carbon fibers are preferred because they are lightweight and have high mechanical strength. It can also be used in combination with other fibers for the purpose of improving impact resistance, improving impregnation during molding, and improving surface design.

  The first base material forms the main structure of the molded body, and is preferably formed of continuous fibers from the viewpoint of strength. For example, a woven fabric or the like can be selected. When a woven fabric is used, the woven structure is not particularly limited. Plain weave, satin weave, twill weave, as well as unidirectional weave and non-crimp cloth, etc. can be selected as appropriate. . In addition, satin weave and twill weave are good for drape, so they are preferably used when forming a three-dimensional shape with a deep depth. In addition to woven fabrics, it is also possible to use a substrate in which reinforcing fibers aligned in one direction are combined with a binder or stitch.

  Since the first base material is not impregnated with resin, it is preferable that the layers are integrated with a binder or stitches. As the binder, various materials such as a thermoplastic resin system, a thermosetting resin system, a material combining them, or a spray paste can be selected. The yarn for stitching is not particularly limited, but it is preferable to use a yarn as thin as possible in order to prevent strength reduction due to stress concentration. Exceptionally, when a simple shape such as a flat plate is formed, it can be formed even if it is not integrated.

  The laminated structure of the first base material is not particularly limited, and can be appropriately oriented according to the direction and magnitude of the force applied to the molded product.

  A 2nd base material is a material which comprises the outer peripheral part of a molded object, and intensity | strength may be low compared with a 1st base material. For example, a reinforcing fiber cut to a length of about 2.5 cm (1 inch) can be used. Of course, it is also possible to use continuous fibers in the same manner as the first substrate.

  Further, it is a material that has been previously impregnated with resin, and one-way prepreg, cross prepreg, SMC (sheet molding compound), and the like can be selected. The resin material to be impregnated is preferably an epoxy resin from the viewpoint of the physical properties of the molded product, but a thermosetting resin such as an unsaturated polyester resin, a vinyl ester resin, or a phenol resin can also be selected. Moreover, it is preferable to select the same type of resin as that injected into the first base material. The resin injected into the first base material and the resin previously impregnated into the second base material need not have the same composition, but it is important that they do not interfere with each other's reaction. When a different type of resin material is selected, it is necessary to inject the resin into the first base material after the curing reaction of the resin material impregnated in the second base material is completed, and the molding cycle becomes long. .

  Next, the positional relationship between the first base material and the second base material is such that the second base material is disposed on at least a part of the outer peripheral portion of the first base material as shown in FIGS. At this time, it is preferable that the first base material and the second base material are laminated so as to partially overlap each other because the strength of the joint between the two base materials is increased.

  The first substrate is preferably laminated so as to have a thickness substantially equal to the thickness of the mold cavity so as to match the dimensions of the molded product. When the thickness of the first base material is smaller than the thickness of the cavity of the mold, unevenness occurs in the thickness of the resin layer impregnated in the thickness direction, and there is a possibility that a locally weak portion may be generated. On the other hand, if it is too thick, wrinkles or the like may occur on the first base material, and the appearance may be uneven.

  Moreover, it is preferable that the part which laminated | stacked the 2nd base material is thicker than the cavity of a metal mold | die. In order to fit the preform in the cavity of the mold, it is necessary to make the preform smaller than the opening area of the cavity. In other words, a slight gap is formed between the outer peripheral portion of the cavity and the outer peripheral portion of the preform, and when the mold is closed, the second base material is crushed so that the outer peripheral portion of the cavity and the outer periphery of the preform are The part matches exactly. At this time, the thickness of the second substrate is preferably in the range of 110% to 150% with respect to the thickness of the cavity. If the thickness of the second substrate is too thick, the first substrate may meander due to the second substrate pushed inward.

  In addition, when the resin is injected from the end of the mold, a portion where the second base material is not disposed as shown in FIG. 4 may be provided. Since the end portion strength of the portion where the second base material is not disposed is low as in the prior art, it is necessary to select a portion that does not require strength.

  Hereinafter, it demonstrates still in detail based on an Example.

  In each example and comparative example, a flat plate was molded using a preform resin mold having the same cavity as a mold having a cavity dimension of 1000 mm in length and 1000 mm in width and 1.4 mm in thickness.

As the material, the first base material is a woven fabric in which a PAN-based carbon fiber having a tensile strength of 4.9 GPa is plain-woven at a basis weight of 200 g / m ² , and the second base material is the same carbon fiber as the first base material. A prepreg having a weight resin content of 33% impregnated with a general-purpose prepreg epoxy resin in a state of being spread in one direction at 200 g / m ^2. Epoxy resin was used. In addition, a binder having a melting point of 71 ° C. containing a thermoplastic resin as a main component was previously applied to the carbon fiber fabric used for the first base material.

  Using these materials, molding was performed by the following method.

Example 1
First, the prepreg used for the second substrate was cut into a width of 13 mm along the fiber direction and laminated along the outer periphery of the preform mold. Next, the same prepreg was cut into a width of 8 mm and laminated along the outer periphery of the preform mold as in the first layer. Next, the carbon fiber fabric used for the first substrate was cut into a 982 mm square size and laminated inside the second layer of the second substrate. Next, the third layer is cut and laminated in the same manner as the first layer of the second base material, and the carbon fiber fabric of the first base material is cut into a 969 mm square, and the inner side of the third layer of the second base material Laminated. At this time, it was crimped lightly with an iron so that the lower carbon fiber fabric and the binder were welded.

  Hereinafter, the 8 mm wide second base material and the 979 mm square first base material, the 13 mm wide second base material and the 969 mm square first base material, the 8 mm wide second base material and the 979 mm square base material Lamination was repeated in the order of the first substrate, and further, a second substrate having a width of 13 mm was laminated, and finally a carbon fiber woven fabric cut to a size of 995 mm × 1005 mm was laminated. The preforms laminated in this way are in the form shown in FIGS. 2 and 3. When the preform is removed from the preform mold and the thickness is measured with a micrometer, the outer peripheral portion on which the second substrate is disposed is 1.55 mm. Met. Moreover, it was 1.38 mm when the thickness of the part in which the 1st base material was laminated | stacked was measured with the U-shaped micrometer.

  This preform was set in a mold heated to 100 ° C. The set state is shown in FIG. At this time, the uppermost carbon fiber fabric was in a state of protruding into the film gate portion (0.5 mm thickness) of the mold, and the upper mold was closed as it was. Next, a hose was connected to the resin injection port and the resin suction port of the mold, and the air in the cavity was first sucked from the resin suction side. After leaving in this state for 3 minutes, a low viscosity epoxy resin for RTM was injected from a resin injection side with a commercially available resin injection device.

  Resin began to be discharged from the resin suction port in 1 minute after the start of resin injection. Close the discharge hose with a vise clip, hold the pressure for 20 seconds, repeat the operation to discharge the resin again 5 times, and finally discharge Both the injection side and the injection side were closed with vise clips. After leaving for 40 minutes in this state to cure the resin, the upper mold was opened and the molded body was taken out.

  When the molded product was observed, the film gate contained one piece of carbon fiber fabric, but the side without the gate had only a thin resin burr. In addition, the appearance of the fiber was not significantly disturbed, and the end of the product had a black color indicating that the carbon fiber was contained, and it was finished finely.

  The film gate could be removed in 30 seconds using a rod-shaped metal file, and the thin resin burr could be removed in 10 seconds. Furthermore, although a hole with a diameter of 7 mm was opened with a hand drill at a position 5 mm from the end of the molded body, it could be processed neatly.

(Example 2)
Molding was performed in the same manner as in Example 1. However, when the second substrate having a width of 13 mm was first laminated, four pieces were laminated at a time, and the thickness of the outer peripheral portion after the lamination was 2.15 mm.
When this molded body was observed, the fibers in the vicinity of the boundary between the first base material and the second base material meandered, and the surface was undulated.

(Comparative Example 1)
Molding was performed in the same manner as in Example 1. However, the first 13 mm-width second base material was omitted and laminated, and the thickness of the outer peripheral portion after lamination was 1.35 mm.

  When this molded product was observed, bubbles were generated at the end of the molded product.

(Comparative Example 2)
Five carbon fiber fabrics used for the first substrate were cut to a size of 995 mm square and laminated in a preform mold. At this time, the lower carbon fiber fabric and the binder were lightly ironed for each layer so that the binder was welded. Next, carbon fiber woven fabrics cut to a size of 995 mm × 1005 mm were laminated and similarly crimped with an iron. The preform thus laminated was removed from the preform mold, and the thickness measured with a U-shaped micrometer was 1.36 mm.

  When this preform was molded in the same manner as in Example 1, the molded product was observed. As a result, a portion exhibiting only the color of the resin at the end of the product was observed. Moreover, when the operation | work which removes the resin burr | flash with the rod-shaped metal file similarly to Example 1 was performed, the part which has shown the color only of resin was missing.

(Comparative Example 3)
After laminating five carbon fiber fabrics in the same manner as in Comparative Example 2, a glass surface mat with a basis weight of 30 g / m ² was laminated so as to protrude outward from the gaps of the preform mold. Thereafter, molding was performed in the same manner as in Comparative Example 2, and the finished molded product was observed. As a result, a portion exhibiting the same color as the resin layer was seen at the end of the product. When a hole drilling operation was performed with a hand drill in the same manner as in Example 1, the gap between the hole and the outer peripheral portion was missing.

  The present invention can be applied to a method for producing an FRP structure in which the arrangement of reinforcing fibers is desired to every corner and a preform used for molding the FRP structure. In particular, the present invention can be applied to an FRP thin plate structure that requires strength of an end portion for automobile parts, aircraft parts, and other general work applications, but the application range is not limited thereto.

The perspective view of an example suitable for application of the present invention. The longitudinal cross-sectional view of an example of the preform of this invention. The top view of an example of the preform of the present invention. The top view of an example of the preform of the present invention. The longitudinal cross-sectional view which shows the state which set the preform of this invention to the metal mold | die.

Explanation of symbols

1: First base material 2: Second base material 3: Lower mold 3a: Cavity 3b: Film gate 3c: Resin injection port 3d: Resin suction port 4: Upper mold 10: Roof for automobile 11: Mounting hole

Claims (4)

It is composed of at least a first base material made of only reinforcing fibers and a second base material in which the reinforcing fibers are impregnated with a resin in advance, and the second base material is at least a part of the outer peripheral portion of the first base material. The preform is characterized in that the second base material is thicker than the first base material. The preform according to claim 1, wherein the thickness of the second base material is 1.5 times or less the thickness of the first base material. A preform in which a second base material in which a reinforcing fiber is impregnated with a resin in advance is arranged on at least a part of the outer peripheral portion of the first base material made of only reinforcing fibers, and the preform is formed into a cavity of a mold. A method for molding a fiber reinforced plastic, wherein the resin is injected and cured after being stored in the container. The method for molding a fiber-reinforced plastic according to claim 3, wherein the height of the preform on which the second base material is disposed is higher than the height of the cavity of the mold.

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