Method for producing fiber-reinforced resin composite

Abstract

The present invention is a method for producing a fiber-reinforced resin composite (50) by vacuum-forming a resin-integrated reinforcing fiber sheet. The resin-integrated reinforcing fiber sheet is a semipreg sheet in which a thermoplastic powder resin applied to the surface of a reinforcing fiber sheet is fused, the reinforcing fiber sheet containing unidirectional continuous fibers obtained by opening a continuous fiber group and arranging the fibers in parallel in one direction. A thermoplastic resin material containing a thermoplastic resin that can be thermally bonded to the semipreg sheet is used as a bagging film (74). The bagging film (74) preferably includes two resin layers of different materials. Of the two resin layers (74a, 74b), the resin layer 74b serving as one surface layer (main surface) of the fiber-reinforced resin composite is a functional layer having any one function selected from decorativeness, blade resistance, and scratch resistance.

Description

Method for manufacturing fiber reinforced resin composite

[0001] The present invention relates to a method for manufacturing a fiber reinforced resin composite.

[0002] Fiber reinforced resins (FRP, FRTP) containing reinforcing fiber materials such as carbon fibers are used in general industrial fields. Fiber reinforced resins are characterized by excellent mechanical properties and are widely used in applications such as building members, laptop computer casings, IC trays, sports goods, wind turbines, automobiles, railways, ships, aviation, and space.

[0003] Carbon fibers are combined with various matrix resins, and the resulting fiber reinforced plastics are widely used in various fields and applications. In the aerospace and general industrial fields where high mechanical properties and heat resistance are required, composite materials of matrix resins and unidirectional continuous fibers are used. In particular, prepregs in which a thermoplastic resin is completely impregnated into a carbon fiber base material containing unidirectional continuous fibers are used.

[0004] However, when forming a molded body using a sheet-like prepreg in which a thermoplastic resin is completely impregnated into a carbon fiber base material, the laminate of the prepregs has a high hardness in its original state, so it is necessary to perform preheating for a certain period of time. Therefore, semi-prepregs in which the resin is not completely impregnated have attracted attention. In the semi-prepreg, the matrix resin is in a state of being fused on the fiber base material or in a semi-impregnated state with respect to the fiber base material. Therefore, the semi-prepreg is softer and has better formability than the prepreg. In addition, since a laminate of a plurality of semi-prepregs can be directly molded without preheating, the molding efficiency is also excellent. In particular, because of its good formability and the ability to mold large molded products, the vacuum molding method is used in the molding of semi-prepregs.

[0005] However, in the vacuum molding method, it is necessary to mold the base materials one by one, so improving productivity has been an issue from various viewpoints such as time, cost, and energy consumption.

[0006] Patent Document 1 discloses a substrate for molding fiber-reinforced plastics having a film layer as the outermost layer. Patent Document 2 discloses a method for manufacturing molded products that includes a step of attaching carbon fiber-reinforced thermoplastic (including so-called semipregs with reduced resin impregnation) to a mold using double-sided tape of a specific structure in order to improve the accuracy of the molded product. The technology disclosed in Patent Document 3 focuses on a substrate (resin-integrated reinforced fiber sheet) for improving moldability. Patent Document 3 uses a silicone resin film or fluororesin film with high heat resistance as a bagging film (a cover for creating a vacuum) used during vacuum forming.

[0007] Japanese Patent Publication No. 2014-50981 (Teijin Limited), Japanese Patent Publication No. 2017-109408 (Japan Steel Works, Ltd.), International Patent Document No. 2021 / 095626 (Kurabo Industries Ltd.)

[0008] However, the technology disclosed in Patent Document 1 requires a process of attaching the outermost layer in the preparation of the substrate, which is disadvantageous from the viewpoint of improving the molding efficiency of the molded product. Furthermore, since the substrate itself contains a resin film as the outermost layer, the three-dimensional shapeability of the substrate is poor, which is undesirable. In addition, the method for manufacturing molded products disclosed in Patent Document 2 includes a process of attaching carbon fiber reinforced thermoplastic (including so-called semipregs with reduced resin impregnation) to a mold using double-sided tape of a specific structure, which is disadvantageous from the viewpoint of improving the molding efficiency of the molded product. Moreover, the silicone resin film and fluororesin film bagging films disclosed in Patent Document 3 are relatively expensive. Although these bagging films can be reused, they deteriorate with use and are periodically discarded and replaced with new ones. In addition, thermoplastic resins with relatively high softening points are sometimes used as the resin contained in the resin-integrated reinforced fiber sheet, in which case the lifespan of the bagging film is even shorter. Therefore, the use of expensive bagging films is disadvantageous from the viewpoint of cost reduction and waste reduction, and consequently, disadvantageous from the viewpoint of improving the productivity of molded products.

[0009] Therefore, the present invention provides a method for producing fiber-reinforced resin composites with improved productivity and high strength in the vacuum forming method.

[0010] The present invention relates to a method for producing a fiber-reinforced resin composite by vacuum forming a resin-integrated reinforced fiber sheet, wherein the resin-integrated reinforced fiber sheet is a semipreg sheet in which a thermoplastic powder resin applied to the surface of a reinforced fiber sheet containing unidirectional continuous fibers in which a continuous fiber group is opened and arranged in parallel in one direction is fused, and the method includes: arranging one or more of the semipreg sheets and a bagging film in this order on a lower mold; reducing the pressure in the space between the bagging film and the lower mold; heating the semipreg sheet to a temperature above the softening point of the resin fused to the reinforced fiber sheet while maintaining the reduced pressure in the space, thereby shaping the semipreg sheet and the bagging film together; and demolding the obtained molded body from the mold after cooling, wherein the bagging film is a thermoplastic resin material containing a thermoplastic resin that can be heat-bonded to the semipreg sheet.

[0011] In the present invention's method for producing fiber-reinforced resin composites, a thermoplastic resin material that can be integrated with the resin-integrated reinforced fiber sheet is used as the bagging film. This eliminates the problems of bagging film degradation and disposal, improving the productivity of the fiber-reinforced resin composite. Furthermore, since a semipreg sheet is used as the resin-integrated reinforced fiber sheet, which includes unidirectional continuous fibers in which continuous fiber groups are opened and arranged in parallel in one direction, and to which a thermoplastic powder resin applied to the surface is fused, a fiber-reinforced resin composite with high peel strength can be provided.

[0012] Figure 1 is a schematic perspective view of a resin-integrated reinforced fiber sheet (semipreg sheet) used in the method for manufacturing a fiber-reinforced resin composite according to the present invention. Figure 2 is a schematic cross-sectional view along the width direction of the semipreg sheet shown in Figure 1. Figure 3 is a schematic process diagram showing the method for manufacturing the semipreg sheet shown in Figure 1. Figure 4 is a schematic cross-sectional view of a vacuum pressure forming apparatus used in the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 5A is a schematic process diagram illustrating one step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 5B is a schematic process diagram illustrating one step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 6A is a schematic process diagram illustrating one step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 6B is a schematic process diagram illustrating one step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 6C is a schematic process diagram illustrating one step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 7 is a schematic cross-sectional view of a bagging film used in the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention. Figure 8 is a schematic process diagram illustrating one step in the manufacturing method of the fiber-reinforced resin composite of Example 1. Figure 9 is a schematic diagram illustrating the method for measuring peel strength. Figure 10 is a perspective photograph of the fiber-reinforced resin composite of Example 2 taken from the convex side. Figure 11 is a perspective photograph of the fiber-reinforced resin composite of Example 2 taken from the concave side.

[0013] The present invention relates to a method for producing a fiber-reinforced resin composite by vacuum forming a resin-integrated reinforced fiber sheet, and includes the following preparation steps, a depressurization step, a vacuum forming step, and a cooling / demolition step. The resin-integrated reinforced fiber sheet is a semipreg sheet containing a reinforced fiber sheet that includes unidirectional continuous fibers in which a continuous fiber group is opened and arranged in parallel in one direction, and a resin to which a thermoplastic powder resin applied to its surface is fused. In the method for producing a fiber-reinforced resin composite of the present invention, a semipreg sheet and a bagging film are used as molding materials. The bagging film is also called a bagging film or vacuum bag film. (Preparation Step) In the preparation step, one or more of the semipreg sheets and the bagging film are placed in this order on a lower mold having a vacuum line. The bagging film may be placed in contact with the semipreg sheet, or it may be placed above the semipreg sheet in a non-contact state. (Depressurization Step) In the depressurization step, the space between the bagging film and the lower mold is depressurized. The space refers to the space between the bagging film and the molding surface of the lower mold, and includes a passage through which air flows inside the semipreg sheet. Furthermore, if all or part of the lower mold side surface of the semipreg sheet placed on the lower mold in the preparation step is not in contact with the molding surface of the lower mold, the space includes the space between the semipreg sheet and the molding surface of the lower mold. (Vacuum forming step) In the vacuum forming step, while maintaining the reduced pressure in the space, the semipreg sheet, which has been heated to a temperature above the softening point of the thermoplastic powder resin, and the bagging film are integrated and formed. (Cooling and demolding step) The molded body obtained by integration and shaping is cooled and then demolded from the mold.

[0014] In the method for manufacturing fiber-reinforced resin composites of the present invention, the vacuum forming method is preferably a vacuum pressure forming method. The vacuum pressure forming method is a molding method in which, for example, air is sucked from the space between the lower mold and the bagging film from the vacuum line of the lower mold to create a vacuum in the space, the molding material is brought into close contact with the lower mold (vacuum forming), and the heated and softened molding material is pressed against the lower mold with compressed air supplied from the upper mold having a pressure line to the lower mold side (pressure pressing). Since the vacuum pressure forming method is a molding method in which uniform pressure is applied to the molding material by the bagging film from the upper mold side, it is possible to mold large molded bodies such as car bodies. Furthermore, the vacuum pressure forming method makes it possible to mold not only flat plates but also three-dimensional shapes. The vacuum pressure forming method can perform various shapes while integrating the molding material and is suitable as a molding method for thin-walled molded bodies. In the present invention, the bagging film is characterized in that it is a thermoplastic resin material containing a thermoplastic resin that can be heat-bonded to a semipreg sheet by the vacuum pressure forming method.

[0015] In this invention, the thermoplastic resin material functions as a bagging film during the manufacturing process of the fiber-reinforced resin composite, and in the resulting fiber-reinforced resin composite, it becomes one of the outermost layers. Therefore, there are no problems with deterioration due to repeated use of the bagging film or the disposal of the bagging film. Furthermore, in this invention, there is a high degree of freedom in selecting the material of the bagging film (thermoplastic resin material), which in turn increases the degree of freedom in selecting the material of the thermoplastic powder resin contained in the semipreg sheet, and also provides the advantage of a high degree of freedom in setting the temperature of the molding die.

[0016] Furthermore, in this invention, a semipreg sheet is used as the resin-integrated reinforced fiber sheet, which includes a resin formed by fusing a reinforcing fiber sheet with a thermoplastic powder resin (matrix resin) applied to its surface. Therefore, compared to, for example, a prepreg sheet in which the content of unidirectional continuous fibers and matrix resin are equal to those of the semipreg sheet, the surface of the semipreg sheet facing the thermoplastic resin material has a richer resin content, as well as many fine irregularities caused by the reinforcing fibers. As a result, the resin present on the surface of the reinforcing fiber sheet, which is not impregnated into the fiber sheet, effectively contributes to the adhesion between the semipreg sheet and the thermoplastic resin material, and the fine irregularities caused by the reinforcing fibers increase the bonding area between the semipreg sheet and the thermoplastic resin material. Consequently, it is presumed that the peel strength between the thermoplastic resin material and the semipreg sheet in a fully resin-impregnated state is increased. Thus, according to this invention, productivity in vacuum forming, preferably vacuum pressure forming, is improved, and a high-strength fiber-reinforced resin composite can be provided.

[0017] Next, an example of a resin-integrated reinforced fiber sheet (semipreg sheet) used in the method for producing the fiber-reinforced resin composite of the present invention will be described in more detail with reference to Figures 1 to 3.

[0018] [Semipreg Sheet] The semipreg sheet used in the method for producing the fiber-reinforced resin composite of the present invention comprises a reinforcing fiber sheet and a resin to which thermoplastic powder resin applied to the surface of the reinforcing fiber sheet is fused. It is a highly flexible, resin-integrated reinforcing fiber sheet that is unimpregnated and / or partially impregnated with resin. The reinforcing fiber sheet contains unidirectional continuous fibers (reinforcing fibers) in which continuous fiber groups are opened and arranged in parallel in one direction. By using this semipreg sheet, a fiber-reinforced resin composite with thinness, high strength, and excellent moldability can be obtained. In addition, direct molding is possible. That is, without preheating (preheating for softening before placement in the mold), shaping of the semipreg sheet or its laminate and filling (impregnation) of the entire reinforcing fiber sheet with resin can be performed almost simultaneously. Furthermore, because direct molding is possible, the thermal history of the thermoplastic powder resin fused to the surface of the reinforcing fiber sheet can be reduced, preventing deterioration of the resin.

[0019] The unidirectional continuous fibers (reinforcement fibers) are long fibers and preferably contain at least one type of reinforcement fiber selected from carbon fibers, glass fibers, and high modulus fibers with an elastic modulus of 380 cN / dtex or higher. Examples of the high modulus fibers include aramid fibers, para-aramid fibers (elastic modulus: 380-980 cN / dtex), polyarylate fibers (elastic modulus: 600-741 cN / dtex), heterocyclic polymer fibers (PBO, elastic modulus: 1060-2200 cN / dtex), high molecular weight polyethylene fibers (elastic modulus: 883-1413 cN / dtex), and polyvinyl alcohol fibers (PVA, strength: 14-18 cN / dtex). These fibers are useful as resin reinforcement fibers. Carbon fibers are particularly useful from the viewpoint of weight reduction.

[0020] Examples of the thermoplastic powder resin include, but are not limited to, polyamide resins, polycarbonate resins, polypropylene resins, polyester resins, polyethylene resins, acrylic resins, phenoxy resins, polystyrene resins, polyimide resins, polyetheretherketone resins, and polyphenylene sulfide resins.

[0021] In a semipreg sheet, the mixing ratio of resin (thermoplastic resin) and reinforcing fibers is preferably such that, when the total volume is 100%, the volume percentage (Vf) of reinforcing fibers is 20 to 70% and the volume percentage of thermoplastic resin is 30 to 80%. More preferably, the volume percentage (Vf) of reinforcing fibers is 20 to 65% and the volume percentage of thermoplastic resin is 35 to 80%. Even more preferably, the volume percentage (Vf) of reinforcing fibers is 25 to 60% and the volume percentage of thermoplastic resin is 40 to 75%. This allows the resin constituting the semipreg sheet and the resin constituting the bagging film to be used directly as the matrix resin component of the fiber-reinforced resin composite, eliminating the need to add new resin when molding the fiber-reinforced resin composite by vacuum forming, preferably by vacuum pressure forming.

[0022] The reinforcing fiber sheet preferably contains crosslinked fibers as a secondary component in a direction intersecting with unidirectional continuous fibers, and the thermoplastic resin to which the thermoplastic powder resin applied to the surface of the reinforcing fiber sheet is fused preferably integrates the unidirectional continuous fibers and the crosslinked fibers. The crosslinked fibers may originate from the unidirectional continuous fibers. Here, intersecting includes entanglement. For example, some or all of the crosslinked fibers are present in the reinforcing fiber sheet and intersect three-dimensionally with the unidirectional continuous fibers. The main component of the fibers constituting the reinforcing fiber sheet is unidirectional continuous fibers in which a group of continuous fibers is opened and arranged in parallel in one direction. The thermoplastic powder resin used to form the semipreg sheet preferably becomes a resin that is sprinkled on the surface of a reinforcing fiber sheet containing unidirectional continuous fibers and crosslinked fibers, and then heat-fused to them, thereby integrating the unidirectional continuous fibers and crosslinked fibers. In this semipreg sheet, unidirectional continuous fibers and crosslinked fibers are integrated by heat-fused thermoplastic powder resin (resin), resulting in good handling properties and a desirable feature from the viewpoint of improving the strength of the fiber-reinforced resin composite.

[0023] When the total of unidirectional continuous fibers and crosslinked fibers in the reinforced fiber sheet is set to 100% by mass, the mass percentage of unidirectional continuous fibers is preferably 75 to 99% by mass, more preferably 80 to 97% by mass, and even more preferably 85 to 97% by mass. The mass percentage of crosslinked fibers is preferably 1 to 25% by mass, more preferably 3 to 20% by mass, and even more preferably 3 to 15% by mass. If the mass percentage of each fiber is within the above range, the semipreg sheet is preferable because it has high integrity and high tensile strength in the width direction. The average length of the crosslinked fibers is preferably 1 mm or more, more preferably 5 mm or more. The upper limit of the average length of the crosslinked fibers is preferably 1000 mm or less, and more preferably 500 mm or less. If the average length of the crosslinked fibers is within the above range, the semipreg sheet is preferable because it has high strength in the width direction and excellent handling properties.

[0024] Furthermore, the reinforcing fiber sheet may further include auxiliary threads arranged in a direction opposite to the longitudinal direction of the unidirectional continuous fibers. The auxiliary threads maintain a constant orientation of the reinforcing fiber sheet. Examples of auxiliary threads include glass fibers, aramid fibers, polyester fibers, nylon fibers, vinylon fibers, and the like.

[0025] The mass per unit area of ​​the aforementioned semipreg sheet is 10 to 500 g / m². 2 Preferably, and more preferably, 20 to 400 g / m² 2 More preferably 30 to 300 g / m² 2 More preferably, 30 to 200 g / m² 2 That is the case.

[0026] In the preparation step described above, the semipreg sheet placed on the lower mold may be one sheet or multiple sheets. From the viewpoint of increasing the isotropy of the strength of the molded product, it is preferable that the laminate, which is made up of multiple semipreg sheets, includes semipreg sheets in which the orientation direction of the unidirectional continuous fibers differs from that of the other semipreg sheets. Furthermore, the thickness of a single semipreg sheet is preferably 0.01 to 1.0 mm. Semipreg sheets with a thickness within this range are easy to vacuum form, preferably vacuum pressure forming. The preferred number of laminated semipreg sheets is 2 to 500 sheets, and more preferably 2 to 300 sheets.

[0027] Figure 1 is a schematic perspective view of a carbon fiber sheet 1, which is an example of the semipreg sheet, and Figure 2 is a schematic cross-sectional view of the carbon fiber sheet 1 shown in Figure 1. In Figure 1, crosslinked fibers 3 are arranged in various directions on the surface of unidirectional carbon fibers (unidirectional continuous fibers) 2, which are formed by opening up a continuous fiber group and arranging them in parallel in one direction. Thermoplastic powder resin sprinkled on the surface of the reinforcing fiber sheet containing the unidirectional carbon fibers 2 has melted and solidified to adhere to the surface and its vicinity as resin 4, and the resin 4 is either not impregnated into the interior of the reinforcing fiber sheet or is only partially impregnated.

[0028] As shown in Figure 2, cross-linked fibers 3a and 3b are present on the surface of the reinforcing fiber sheet containing unidirectional carbon fibers 2. All of the cross-linked fibers 3a are on the surface of the reinforcing fiber sheet containing unidirectional carbon fibers 2. Part of the cross-linked fibers 3b are on the surface of the reinforcing fiber sheet containing unidirectional carbon fibers 2, and part of them are inside and intertwined with the unidirectional carbon fibers 2. For example, part or all of the cross-linked fibers 3 are located inside the reinforcing fiber sheet containing unidirectional carbon fibers 2 and are three-dimensionally intertwined with the unidirectional carbon fibers 2. The resin 4 adheres and fixes the cross-linked fibers 3 to the surface of the reinforcing fiber sheet containing unidirectional carbon fibers 2. The carbon fiber sheet 1 also has parts to which the resin 4 is attached and parts 5 to which the resin is not attached. When the carbon fiber sheet 1 is heated and vacuum formed, preferably by vacuum pressure forming, the parts 5 to which the resin is not attached become passages through which air from inside the reinforcing fiber sheet escapes, making it easier for the resin 4 attached to the reinforcing fiber sheet to permeate the entire reinforcing fiber sheet. As a result, the resin 4 becomes the matrix resin of the fiber-reinforced resin composite.

[0029] Figure 3 is a schematic process diagram showing an example of the manufacturing method of the semipreg sheet described above. A group of carbon fiber filaments (tow) 8, which is an example of a continuous fiber group, is drawn out from a number of supply bobbins 7 (only one supply bobbin 7 is shown in Figure 3), passed between opening rolls 21a-21j, and tension is applied to the tow in the range of 2.5 to 30 N per 15,000 carbon fiber filaments (corresponding to a group of carbon fiber filaments supplied from one supply bobbin), thereby generating crosslinked fibers from the carbon fiber filaments when the tow is opened (roll opening process 23). Air opening may be used instead of roll opening. The opening rolls may be fixed or rotated, or may be vibrated in the width direction. Alternatively, the opened tow may be nipped between nip rolls 9a and 9b, passed between a plurality of bridge rolls 12a-12b installed in between, and tension applied to the tow in the range of 2.5 to 30 N per 15,000 carbon fiber filaments to generate crosslinked fibers from the carbon fiber filaments (crosslinked fiber generation step 24). The bridge rolls may rotate or vibrate in the width direction. The bridge rolls are, for example, a plurality of rolls with a textured, uneven, or mirrored surface, and crosslinked fibers are generated from the carbon fiber filaments by bending, fixing, rotating, vibrating, or a combination thereof of the carbon fiber filament group. If sufficient crosslinked fibers are generated by the roll opening step 23, the crosslinked fiber generation step 24 is unnecessary. 13a-13g are guide rolls.

[0030] Subsequently, dry powder resin 15 is sprinkled from the powder supply hopper 14 onto the surface of the open fiber sheet (reinforced fiber sheet), supplied into the heating device 16 in a pressure-free state and heated to melt the dry powder resin 15, and then cooled and solidified between the guide rolls 13e-13g. After that, dry powder resin (thermoplastic powder resin) 18 is also sprinkled from the powder supply hopper 17 onto the back surface of the open fiber sheet (reinforced fiber sheet), supplied into the heating device 19 in a pressure-free state and heated to melt the dry powder resin 18, cool, and then wound onto the winding roll 20 (powder resin application process 25). The dry powder resins 15 and 18 are, for example, polyamide resin (PA12, melting point: 175°C), the temperature inside the heating devices 16 and 19 is, for example, +5 to 60°C above the melting point or resin flow temperature of the resin, and the residence time inside the heating devices 16 and 19 is, for example, 4 seconds each. This increases the strength of the carbon fiber sheet in the width direction, preventing the constituent carbon fibers from falling apart and making the sheet easier to handle.

[0031] Thermoplastic powder resin can be applied to the open fiber sheet by methods such as powder coating, electrostatic coating, spraying, and fluid immersion. Among these, the powder coating method, in which the powder resin is dropped onto the surface of the open fiber sheet (reinforced fiber sheet), is preferred. For example, dry powder-type thermoplastic powder resin is sprinkled onto the open fiber sheet.

[0032] If the resin-integrated reinforced fiber sheet does not contain crosslinked fibers, for example, the crosslinked fiber generation step 24 in Figure 3 can be omitted. Furthermore, the resin-integrated reinforced fiber sheet can be manufactured by the method for manufacturing a resin-integrated reinforced fiber sheet disclosed in WO2021 / 095626.

[0033] [Bagging Film] The bagging film is a thermoplastic resin material containing a thermoplastic resin that can be heat-bonded to the semipreg sheet. The thermoplastic resin material may be composed of a single resin material, or, as shown in Figure 7, may be composed of two resin layers 74a and 74b made of different materials. The thickness of the thermoplastic resin material is preferably such that it can perform the same functions as conventionally known bagging films even when the thermoplastic resin material is preheated as described later, and is less prone to damage, thereby reducing the defect rate of the fiber-reinforced resin composite. The thickness of the thermoplastic resin material is preferably 0.01 mm or more and 5 mm or less. From the viewpoint of improving peel strength, it is preferable that the material of the thermoplastic resin material contains a resin that has good compatibility with the thermoplastic powder resin contained in the semipreg sheet. From the viewpoint of improving peel strength, it is preferable that the thermoplastic resin contained in the resin layer 74a (bonding layer) of the two resin layers that faces the semipreg sheet has good compatibility with the thermoplastic powder resin contained in the semipreg sheet. Furthermore, the resin layer 74b, which forms one of the two resin layers and becomes the surface layer (main surface) of the fiber-reinforced resin composite, may be a functional layer having one of the following functions selected from decorative properties, cut resistance, and scratch resistance. The thicknesses of the two resin layers may be different, and the bonding layer 74a may be thicker than the functional layer 74b.

[0034] Examples of thermoplastic resin materials include, but are not limited to, polyamide resins, polycarbonate resins, polypropylene resins, polyester resins, polyethylene resins, acrylic resins, phenoxy resins, polystyrene resins, polyimide resins, polyetheretherketone resins, and polyphenylene sulfide resins.

[0035] [Vacuum Pressure Forming] Next, an example of a method for manufacturing a fiber-reinforced resin composite according to the present invention will be described using Figures 4 to 6C. Figure 4 is a schematic cross-sectional view of a vacuum pressure forming apparatus used in a method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention, and Figures 5A to 6C are schematic process diagrams illustrating each step of the method for manufacturing a fiber-reinforced resin composite according to one embodiment of the present invention.

[0036] As shown in Figure 4, the vacuum pressure forming apparatus 60 includes a lower mold 63 having a vacuum line 64 and an upper mold 69 having a pressure line 70. The lower mold 63 is fixed on a base 61 and a mold base 62, and the vacuum line 64 extends to the forming surface 65. A vacuum pump (not shown) is connected to the vacuum line 64. The upper mold 69 includes an upper mold body 66 with a pressure line 70, and can supply compressed air downward (towards the lower mold 63) from air grooves 67 and air holes 71 in the faceplate 68. A compressor (not shown) is connected to the pressure line 70. The lower mold 63 can be heated and cooled by an electromagnetic induction heating type, resistance wire heating type, or infrared heating type heater 72 and a water cooling pipe 73 to control it to a predetermined temperature.

[0037] Figures 5A and 5B show the preparation process, Figure 6A shows the depressurization process, Figure 6B shows the vacuum pressure forming process, and Figure 6C shows the cooling and demolding process.

[0038] (Preparation Process) First, as shown in Figure 5A, a laminate 90, which consists of multiple semipreg sheets stacked together, is placed on the lower mold 63. If the shape of the fiber-reinforced resin composite is not flat but three-dimensional, it is preferable to place the laminate 90 on the lower mold 63 in a state where it has been preformed into the shape of the molded product before the depressurization process, as shown in Figure 5A, so that it is aligned with the molding surface 65 of the lower mold 63. Next, as shown in Figure 5B, a bagging film 74 is placed over the lower mold 63, and then the upper mold 69 is placed on top of the bagging film 74, so that the outer edge of the bagging film 74 is sandwiched between the upper mold 69 and the lower mold 63. Whether or not the outer edge of the laminate 90 is sandwiched between the upper mold 69 and the lower mold 63 in the same way as the bagging film 74 is determined according to the shape of the fiber-reinforced resin composite. In this way, a closed space 75 that can be maintained under a vacuum atmosphere is formed below the bagging film 74. It is preferable to preheat the bagging film 74 with a heater or the like before placing it on the laminate 90. This is preferable because it improves the conformability of the bagging film 74 to the laminate 90 during the reduced pressure process, especially when the shape of the fiber-reinforced resin composite is three-dimensional. Furthermore, in the vacuum forming process, preferably the vacuum pressure forming process, the preheated bagging film 74 adheres well to the laminate 90, improving the molding accuracy and increasing the bonding strength between the bagging film 74 and the adjacent semipreg sheet, which is also preferable.

[0039] (Depressurization process) Next, as shown in Figure 6A, air is sucked from the vacuum line 64 into the lower mold 63 (closed space) to depressurize the closed space 75, drawing the laminate 90 and the bagging film 74 towards the lower mold 63 and making them tightly adhere to the lower mold 63. The degree of depressurization (vacuum) of the closed space of the lower mold 63 due to exhaust from the vacuum line 64 is preferably 0 to 0.1 MPa.

[0040] The lower mold 63 is heated by the heater 72. The heating of the lower mold 63 may start simultaneously with the start of decompression, or at any time before or after the start of decompression. It may also be before the placement of the laminate 90 on the lower mold 63. By heating the lower mold 63, the laminate 90 is heated to a temperature above the softening point of the thermoplastic resin fused to the reinforcing fiber sheet of the semi-prepeg sheet. The "temperature above the softening point" refers to the molding temperature T1, which is the temperature at which the resin softens or melts. From the perspective of improving the bonding strength between the backing film and the semi-prepeg sheet, the molding temperature is preferably higher than the softening point T3 (°C) of the thermoplastic resin contained in the surface of the backing film 74 facing the semi-prepeg sheet. Also, from the same perspective, the softening point (°C) of the thermoplastic resin contained in the surface of the backing film 74 facing the semi-prepeg sheet is preferably lower than the softening point T2 (°C) of the thermoplastic resin fused to the reinforcing fiber sheet of the semi-prepeg sheet. That is, it is preferable that the molding temperature T1 satisfies the following relationship. T1 > T2 > T3

[0041] (Vacuum Pressure Forming Process) Next, while maintaining the reduced pressure conditions in the closed space 75 during the reduced pressure process, as shown in Figure 6B, the semipreg sheet (laminated body 90), which has been heated to a temperature above the softening point of the thermoplastic resin fused to the reinforcing fiber sheet, and the bagging film 74 are pressed toward the lower mold 63 with compressed air, and formed while integrating them to obtain a molded body. Specifically, compressed air is supplied from the pressure line 70 of the upper mold 69 toward the lower mold 63, and the bagging film 74 and the laminate 90 are pressed against the lower mold 63 with the compressed air and pressurized. The air pressure of the compressed air supplied from the pressure line 70 of the upper mold 69 is preferably 0.1 to 2.0 MPa. In the vacuum pressure forming process, from the viewpoint of improving molding accuracy, it is preferable to maintain the temperature of the lower mold 63, the reduced pressure conditions in the closed space 75, and the air pressure from the compressed air for a predetermined time. In this way, the bagging film 74 and the laminate 90 are firmly bonded together, and the thermoplastic resin fused to the reinforcing fiber sheets of the semipreg sheet melts and fills the space within and between the reinforcing fiber sheets, becoming the matrix resin of the molded body. Filling, in this context, means that the thermoplastic resin fused to the reinforcing fiber sheets impregnates the reinforcing fiber sheets and fills the space between the reinforcing fiber sheets. The predetermined time is preferably 5 to 15 minutes. If the molding temperature is higher than the softening point (°C) of the thermoplastic resin contained in the surface of the bagging film 74 facing the semipreg sheet, the thermoplastic resin constituting the bagging film 74 may also be impregnated into the reinforcing fiber sheet at the interface with the semipreg sheet.

[0042] (Cooling and demolding process) Finally, preferably, the obtained molded body is cooled while maintaining the pressure conditions in the vacuum pressure molding process (degree of pressure reduction in the closed space 75 due to exhaust from the vacuum line 64 and air pressure due to compressed air), and after cooling, the pressure applied to the closed space 75 is released, and the fiber-reinforced resin composite 50 (vacuum pressure molded body) is demolded as shown in Figure 6C.

[0043] The present invention will be specifically described using the following examples. However, the present invention is not limited to the following examples.

[0044] 1. Preparation of Semi-Preg Sheet (1) Preparation of Carbon Fiber Unsized Tow The carbon fiber unsized tow used was made by Mitsubishi Chemical Corporation, product number: PYROFILE TR 50S15L (shape: regular tow filament 15K (15,000 filaments), single fiber diameter 7 μm). An epoxy-based compound was attached to the carbon fibers of this carbon fiber unsized tow as a sizing agent. (2) Opening of Unsized Tow It was opened using the opening device 6 shown in Fig. 3. In the opening process, the tension of the carbon fiber filament group (tow) was set to 15 N per 15,000 filaments. In this way, an opened sheet (reinforcing fiber sheet) with 15K carbon fiber filaments, an opening width of 500 mm, and a thickness of 0.22 mm was obtained. The crosslinked fibers were 3.3 mass%. (3) Preparation of Semi-Preg Sheet Polyamide resin powder (PA12, glass transition point: 50 °C, softening point: 180 °C) was used as the dry powder resin. The average particle diameter of the dry powder resin was 350 μm. This thermoplastic resin powder was applied at an average of 22.5 g / m² on one side and 45.0 g / m² on both sides to 80.3 g of carbon fiber sheet (reinforcing fiber sheet) per 1 m. The temperature in the heating devices 16 and 19 was 250 °C each, and the residence time was 5 seconds each. The mass per unit area of the obtained semi-preg sheet was 125.4 g / m², the fiber volume (Vf) was 50 volume%, and the volume ratio of the polyamide resin was 50 volume%. 2 per 1 m, an average of 22.5 g / m² on one side of the carbon fiber sheet (reinforcing fiber sheet), and 45.0 g / m² on both sides. 2 2 was applied. The temperature in the heating devices 16 and 19 was 250 °C each, and the residence time was 5 seconds each. The mass per unit area of the obtained semi-preg sheet was 125.4 g / m², the fiber volume (Vf) was 50 volume%, and the volume ratio of the polyamide resin was 50 volume%. 2

[0045] 2. Preparation of Prepreg Sheet The semi-preg sheet produced according to the above "1. Preparation of Semi-Preg Sheet" was made into a prepreg sheet. Specifically, the semi-preg sheet produced according to "1. Preparation of Semi-Preg Sheet" was thermally press-molded to impregnate the carbon fiber sheet with resin. In the thermal press molding, the press pressure was 3 MPa, and the semi-preg sheet was held in a mold at a temperature of 210 °C for 15 minutes. Then, while maintaining the press pressure, the mold was cooled to 30 °C and then taken out of the mold to obtain a prepreg sheet. The fiber volume (Vf) of the obtained prepreg sheet was 50 volume%, and the volume ratio of the polyamide resin was 50 volume%. Since transfer of the mold release agent applied to the mold surface was considered, the surface of the prepreg sheet was removed by polishing with #1000 sandpaper.

[0046] 3. Bagging Film As a bagging film, a commercially available thermoplastic resin material (manufactured by Mitsubishi Gas Chemical Company, product number: DF02U, length 300 mm x width 300 mm) with a two-layer structure including a polycarbonate layer (bonding layer, thickness 225 μm, melting point approximately 250°C, softening point approximately 150°C) and an acrylic resin layer (functional layer (scratch resistant), thickness 75 μm, melting point approximately 160°C, softening point approximately 100°C) was prepared.

[0047] 4. Preparation of Fiber-Reinforced Resin Composites (1) Lamination Conditions (Example 1) - Number of layers of semipreg sheets (resin-integrated reinforced fiber sheets, 220 mm in length x 120 mm in width): 4 - Fiber direction of continuous fibers constituting the semipreg sheet: Two directions (laminated in perpendicular directions, 0° / 90° / 90° / 0°) (Comparative Example 1) - Number of layers of prepreg sheets (150 mm in length x 55 mm in width): 4 - Fiber direction of continuous fibers constituting the prepreg sheet: Two directions (laminated in perpendicular directions, 0° / 90° / 90° / 0°)

[0048] (2) Vacuum pressure forming (Example 1) Using a vacuum pressure forming apparatus with the same configuration as the vacuum pressure forming apparatus shown in Figures 4 to 6C, except for the shape of the lower mold, a flat fiber-reinforced resin composite of Example 1 was produced by following the procedure below. Step 1: The bagging film is heated at 170°C for 16 seconds. Step 2: The semipreg sheet, release film, and bagging film are placed in this order on the nickel alloy lower mold, which has been preheated by the heater 72, according to the "(1) Lamination conditions" described above. Furthermore, the upper mold is placed on the bagging film 74, and the outer edges of these are sandwiched between the upper mold and the lower mold. In this way, a closed space is formed between the bagging film and the lower mold, which can be under a vacuum atmosphere by the reduced pressure in Step 3 below. However, in order to prevent the bagging film and the semipreg sheet from joining in the longitudinal half of the test piece described later, the release film 52 is placed on the right half of the semipreg sheet 10, as shown in Figure 8. Step 3: The closed space was depressurized so that the degree of depressurization from the vacuum line of the lower mold was 0.09 MPa. Step 4: After the lower mold temperature reached 210°C (molding temperature), the laminate consisting of the semipreg sheet 10, release film 52, and bagging film 74 was pressurized at 0.97 MPa with compressed air from above the bagging film, and the pressurized state was maintained for 10 minutes to perform vacuum pressure molding. Step 4 was carried out while maintaining the depressurization conditions of Step 3. Step 5: While maintaining the pressure conditions of Step 4 (degree of depressurization of the closed space due to exhaust from the vacuum line and air pressure due to compressed air), the lower mold was cooled to 40°C over 5 minutes, and then the vacuum line and pressurization line were shut off, and the obtained flat plate-shaped fiber-reinforced resin composite was demolded. In this way, two fiber-reinforced resin composites of Example 1 were produced.

[0049] (Comparative Example 1) A flat fiber-reinforced resin composite was prepared in the same manner as in Example 1, except that a prepreg sheet was used instead of a semipreg sheet. Two fiber-reinforced resin composites of Comparative Example 1 were prepared.

[0050] [Peel Test] 1. Preparation of Test Specimens The fiber-reinforced resin composites obtained from Example 1 and Comparative Example 1 were cut, and the release sheets were removed to prepare test specimens measuring 150 mm in length and 15 mm in width. In each test specimen, the bagging sheet and semipreg sheet were bonded in the longitudinal half, and the bagging sheet and semipreg sheet were not bonded in the other half. Ten test specimens were prepared, five from each of the two fiber-reinforced resin composites of Example 1, and six test specimens were prepared, three from each of the two fiber-reinforced resin composites of Comparative Example 1.

[0051] 2. Test Method A peel test in the 90° direction was performed using a peel test apparatus (Autograph AG-10kNIS) manufactured by Shimadzu Corporation, in accordance with JIS K6854-1. Specifically, the procedure was as follows. The test speed was set to 50 mm / min. The average value of the peel strength (N) of the portion excluding the first and last 5 mm of the 60 mm stroke length is shown in Table 1 below. (1) As shown in Figure 9, the unjointed portion (grip portion 74a) of the bagging film is exposed between the two rollers 61a and 61b, and the grip portion 74a is gripped by the film gripping part 62 of the peel test apparatus. (2) The sample piece is lifted until it is touching the rollers. (3) With tension applied to the sample piece, the measurement of the peel strength was started, and the measurement was stopped when the stroke length exceeded 60 mm (data length 50 mm).

[0052]

[0053] As shown in Table 1, using semipreg sheets instead of prepreg sheets yields a fiber-reinforced resin composite with higher peel strength. However, one of the test specimens No. 2 in Comparative Example 1 fractured midway through the gripping portion.

[0054] (Example 2) A fiber-reinforced resin composite was prepared in the same manner as in Example 1, except that a vacuum pressure forming apparatus shown in Figures 4 to 6C was used. Photographs of the obtained fiber-reinforced resin composite are shown in Figures 10 and 11. As shown in Figures 10 and 11, no damage such as tearing of the bagging film was observed, and no unimpregnated areas were found.

[0055] The fiber-reinforced resin composite obtained by the method for producing fiber-reinforced resin composites of the present invention can be widely applied in applications such as aerospace, automotive, sports, 3D printers, industrial applications, building materials, wind turbines, bicycles, railways, ships, and more.

[0056] 1 Carbon fiber sheet 2 Unidirectional carbon fiber 3, 3a, 3b Crosslinked fiber 4 Resin 5 Area without resin adhesion 6 Fiber opening device 7 Supply bobbin 8 Carbon fiber filament group (unopened carbon fiber tow) 9a, 9b Nip roll 12a-12b Bridge roll 13a-13g Guide roll 14, 17 Powder supply hopper 15, 18 Dry powder resin 16, 19 Heating device 20 Winding roll 21a-21j Fiber opening roll 23 Roll fiber opening process 24 Crosslinked fiber generation process 25 Powder resin application process 50 Fiber-reinforced resin composite 52 Release film 10 Resin-integrated reinforced fiber sheet (semipreg sheet) 60 Vacuum pressure forming device 64 Vacuum line 63 Lower mold 69 Upper mold 70 Pressure line 90 Laminate

Claims

1. A method for producing a fiber-reinforced resin composite by vacuum forming a resin-integrated reinforced fiber sheet, wherein the resin-integrated reinforced fiber sheet is a semipreg sheet in which a thermoplastic powder resin applied to the surface of a reinforced fiber sheet containing unidirectional continuous fibers in which a continuous fiber group is opened and arranged in parallel in one direction is fused; the method includes: arranging one or more of the semipreg sheets and a bagging film in this order on a lower mold; reducing the pressure in the space between the bagging film and the lower mold; heating the semipreg sheet to a temperature above the softening point of the resin fused to the reinforced fiber sheet while maintaining the reduced pressure in the space, thereby shaping the semipreg sheet and the bagging film together; and demolding the obtained molded body from the mold after cooling, wherein the bagging film is a thermoplastic resin material containing a thermoplastic resin that can be heat-bonded to the semipreg sheet.

2. The method for producing a fiber-reinforced resin composite according to claim 1, wherein the vacuum forming is vacuum pressure forming.

3. The method for producing a fiber-reinforced resin composite according to claim 2, wherein, in the step of shaping the semipreg sheet and the bagging film while integrating them, after the resin fused to the reinforcing fiber sheet reaches a temperature above its softening point, the semipreg sheet and the bagging film are pressurized from above the bagging film with compressed air.

4. The method for producing a fiber-reinforced resin composite according to any one of claims 1 to 3, wherein the thermoplastic resin constituting the surface of the bagging film that is in contact with the semipreg sheet and the thermoplastic powder resin are mutually compatible resins.

5. The method for producing a fiber-reinforced resin composite according to any one of claims 1 to 4, wherein the softening point of the thermoplastic resin constituting the surface of the bagging film in contact with the semipreg sheet is lower than the softening point of the resin fused to the reinforcing fiber sheet of the semipreg sheet.

6. The method for producing a fiber-reinforced resin composite according to any one of claims 1 to 5, wherein the bagging film comprises two resin layers made of different materials.

7. The method for manufacturing a fiber-reinforced resin composite according to claim 6, wherein one of the two resin layers, which forms the surface layer of the fiber-reinforced resin composite, is a functional layer having one of the functions selected from decorative properties, cut-resistant properties, and scratch-resistant properties.

8. The method for producing a fiber-reinforced resin composite according to any one of claims 1 to 7, wherein the reinforcing fiber sheet further comprises crosslinked fibers derived from the unidirectional continuous fibers, and the crosslinked fibers are intertwined with the unidirectional continuous fibers.

9. A method for producing a fiber-reinforced resin composite according to any one of claims 1 to 8, wherein the fiber volume (Vf) of the resin-integrated reinforced fiber sheet is 30 to 70% by volume, and the volume percentage of the resin fused to the reinforced fiber sheet is 30 to 70% by volume.

10. A method for producing a fiber-reinforced resin composite according to any one of claims 1 to 9, wherein the bagging film is placed on a laminate formed by laminating two or more semipreg sheets, and the laminate includes semipreg sheets in which the orientation direction of the unidirectional continuous fibers is different from that of the other semipreg sheets.

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