Method for manufacturing a plant fiber-containing resin board and plant fiber-containing resin board

Abstract

This invention provides a method for manufacturing a plant fiber-containing resin board that can be produced at low cost and has excellent moldability, as well as a plant fiber-containing resin board. [Solution] The following steps are performed in order: an unfolding step of spreading a bundle of plant fibers 20 into a planar shape; a fiber-containing resin sheet forming step of impregnating the spread-out plant fibers with thermoplastic resin and curing it to form a fiber-containing resin sheet 23; a fiber-containing resin piece forming step of cutting the fiber-containing resin sheet to form short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B; a laminate forming step of stacking the short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B in a distributed state to each region to form a laminate 11S; a heating step of heating the laminate 11S; and a press molding step of pressing the laminate 11S to form a plant fiber-containing resin board 10.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a method for manufacturing a plant fiber-containing resin board and a plant fiber-containing resin board.

Background Art

[0002] Conventionally, as a method for manufacturing a board member using plant fibers, for example, the method described in Patent Document 1 is known. Patent Document 1 describes a method for obtaining a fiber board for thermoforming by subjecting kenaf fibers defibrated from kenaf and cut short and short PP resin fibers to a mixer, forming them into a mat shape by a former, and then compression molding them to a predetermined thickness by a press and performing a cutting process.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the above-described conventional manufacturing method, a resin board having high rigidity even at a low basis weight and excellent handleability can be obtained. However, there is a demand for a plant fiber-containing resin board that can be manufactured at a lower cost and has excellent formability.

[0005] The technology disclosed in this specification has been completed based on the above circumstances, and an object thereof is to provide a method for manufacturing a plant fiber-containing resin board that can be manufactured at a low cost and has excellent formability, and a plant fiber-containing resin board.

Means for Solving the Problems

[0006] To solve the above problems, the method for manufacturing a plant fiber-containing resin board disclosed herein is completed and comprises the following steps in order: an unfolding step of spreading a bundle of plant fibers obtained from a plant in a planar manner such that the plant fibers are oriented in one direction; a fiber-containing resin sheet forming step of impregnating the planar plant fibers with a thermoplastic resin and curing it to form a fiber-containing resin sheet in which the plant fibers are bound by the thermoplastic resin; a fiber-containing resin piece forming step of cutting the fiber-containing resin sheet along the orientation direction of the plant fibers and cutting it in a direction intersecting the orientation direction of the plant fibers so that the lengths differ, thereby forming a plurality of short fiber-containing resin pieces containing relatively short plant fibers and a plurality of long fiber-containing resin pieces containing relatively long plant fibers; a laminate forming step of laminating the short fiber-containing resin pieces and the long fiber-containing resin pieces in a state where they are distributed to each region to form a laminate; a heating step of heating the laminate; and a press molding step of pressing the heated laminate to form a plant fiber-containing resin board in which the short fiber-containing resin pieces and the long fiber-containing resin pieces are integrated and molded into a predetermined shape.

[0007] According to the above manufacturing method, compared to the conventional method of producing plant fiber-containing resin boards from mats formed by mixing short-cut plant fibers and thermoplastic resin fibers, inexpensive pelletized or film-shaped thermoplastic resins can be used instead of fibrous thermoplastic resins. Furthermore, mixing equipment for mixing plant fibers and thermoplastic resin fibers, and equipment such as entanglement devices for forming mats are not required, thus reducing material and equipment costs compared to conventional methods. In addition, the generation of plant fiber dust can be suppressed compared to conventional manufacturing methods, thereby improving material yield.

[0008] Furthermore, because the fiber lengths of the plant fibers contained in each region differ, for example, by forming curved sections with short-fiber-containing resin pieces, the restraining force due to the fibers can be reduced compared to when long-fiber-containing resin pieces are used, thereby suppressing wrinkle formation during press molding and springback after molding. In other words, additional press molding to suppress springback becomes unnecessary. Also, by forming flat sections with long-fiber-containing resin pieces, the overall strength and rigidity of the plant fiber-containing resin board can be increased. In this way, a plant fiber-containing resin board with a high degree of freedom in molding, as well as high strength and rigidity, can be obtained using a simple manufacturing method.

[0009] In the laminate formation step, the short fiber-containing resin pieces may be laminated in the region that will become the edge of the laminate, and the long fiber-containing resin pieces may be laminated in the region other than the edge. With such a manufacturing method, the generation of burrs can be suppressed at the edge, where burrs are prone to occur during press molding.

[0010] In the laminate formation step, a frame with an internal section divided into a predetermined shape may be placed on the mold surface of the lower mold of a molding die having an upper mold and a lower mold, and the short fiber-containing resin pieces and the long fiber-containing resin pieces may be laminated in predetermined areas within the frame, after which the frame may be retracted. With such a manufacturing method, the short fiber-containing resin pieces and the long fiber-containing resin pieces can be easily laminated while distributed in predetermined areas.

[0011] In the heating step, only the portion of the laminate corresponding to the finished plant fiber-containing resin board may be heated. With this manufacturing method, the scraps generated during press molding are not made up of integrated fiber-containing resin pieces, and the fiber-containing resin pieces themselves remain as they were before lamination in the laminate formation step. Therefore, the scraps can be recycled as they are while maintaining their original properties, such as fiber length. Consequently, the material yield can be improved compared to conventional methods.

[0012] Furthermore, the plant fiber-containing resin board disclosed herein, which was completed to solve the above problems, is made up of multiple fiber groups formed by randomly laminating multiple plant fibers oriented in one direction and bound together with a thermoplastic resin, and the multiple fiber groups are integrated with each other, and the fiber groups include a short fiber group consisting of relatively short plant fibers and a long fiber group consisting of relatively long plant fibers, and the short fiber group and the long fiber group are distributed in each region.

[0013] The short fiber group may be arranged on the outer periphery. Alternatively, it may have an opening that penetrates the plate surface, and the short fiber group may be arranged around the opening. [Effects of the Invention]

[0014] The technology disclosed herein provides a method for manufacturing a plant fiber-containing resin board that can be manufactured at low cost and has excellent moldability, as well as a plant fiber-containing resin board. [Brief explanation of the drawing]

[0015] [Figure 1] Front view showing a trim board of one embodiment [Figure 2] Perspective view of a kenaf fiber bundle [Figure 3] Perspective view showing a kenaf fiber bundle spread out (unfolding process) [Figure 4] Perspective view showing a polypropylene film layered on spread-out kenaf fibers (fiber-containing resin sheet formation process) [Figure 5] Perspective view of a fiber-containing resin sheet [Figure 6] Diagram illustrating the fiber-containing resin piece formation process (during short fiber-containing resin piece formation) [Figure 7] Diagram illustrating the fiber-containing resin piece formation process (during long fiber-containing resin piece formation) [Figure 8] Side view showing the frame installed on the lower die of the press mold. [Figure 9] Side view showing the state of forming a laminate on the lower die of the press mold (laminated structure formation process) [Figure 10] Side view showing the state where the frame is retracted from the press mold (laminated body forming process) [Figure 11] Side view showing the state where a predetermined area of the laminated body is being heated (heating process) [Figure 12] Side view showing the state where the laminated body is being pressed by the press mold (pre-board forming process (press molding process)) [Figure 13] Side view showing the state where the press mold is opened [Figure 14] Side view showing the state where the pre-board is placed in the molding die [Figure 15] Side view showing the state where the pre-board is being formed into a predetermined shape by the molding die [Figure 16] Side view showing the trim board (cross-sectional view taken along line I-I in FIG. 1) [Figure 17] Front view showing the trim board of another embodiment

Mode for Carrying Out the Invention

[0016] One embodiment will be described with reference to FIGS. 1 to 16. In this embodiment, a trim board 10 for a vehicle as a plant fiber-containing resin board will be exemplified.

[0017] The trim board 10 forms a part of a door trim attached to the interior side of a door panel of a vehicle such as an automobile. It constitutes the wall surface of the passenger compartment and is an interior material for improving the appearance and habitability of the passenger compartment. The trim board 10 is mainly composed of a base material 11 containing plant fibers and a thermoplastic resin. As shown in FIGS. 1 and 16, it includes a substantially flat plate-shaped flat portion 12 and a standing wall 13 that rises from the edge of the flat portion 12 toward the outside of the vehicle compartment. An opening 14 penetrating the plate surface is provided in the flat portion 12, and the opening edge of the opening 14 also rises toward the outside of the vehicle compartment. The standing walls 13 and the opening edges of the opening 14 rise while curving from the flat portion 12. Note that the trim board 10 may be configured such that the interior surface of the base material 11 is covered with a skin.

[0018] Plant fibers are fibers derived from plants. Examples of plant fibers include fibers obtained from various plant bodies such as kenaf, flax, hemp, jute, Manila hemp, sisal, ganpi, mitsumata, kozo, banana, pineapple, coconut, corn, sugarcane, bagasse, palm, papyrus, reed, esparto, survivalgrass, wheat, rice, bamboo, various coniferous trees (such as cedar and cypress), broad-leaved trees, and cotton. The part of the plant body used as plant fiber is not particularly limited; as long as fibers can be extracted, any part of the plant body, including non-woody parts, stems, roots, leaves, and woody parts, may be used.

[0019] Plant fibers can be obtained by, for example, a letting process on the aforementioned plants. Specifically, the plant body is immersed in water, and the binding components contained within the plant (components such as pectin that bind plant fibers together within the plant) are broken down by microorganisms and enzymes in the water, removing parts other than the plant fibers, thereby obtaining plant fibers. This letting process does not result in the plant fibers being completely separated, but rather the bonds between the plant fibers are loosened, creating bundles that can be easily unraveled.

[0020] Furthermore, kenaf fiber is preferred as the plant fiber. Kenaf is an extremely fast-growing annual plant and has excellent carbon dioxide absorption capabilities, thus contributing to the reduction of carbon dioxide in the atmosphere and the effective use of forest resources. In addition, bast plant fibers such as kenaf are preferable in terms of weight reduction because the fibers themselves contain voids. In this embodiment, kenaf fiber with an average fiber diameter of 80 μm to 100 μm is used as the plant fiber.

[0021] On the other hand, the thermoplastic resin constituting the base material 11 of the trim board 10 in this embodiment mainly functions as a binder resin, and various thermoplastic resins can be used. Examples of thermoplastic resins include polyolefin resins, polyester resins, polystyrene, acrylic resins (resins obtained using methacrylate and / or acrylate, etc.), polyamide resins, polycarbonate resins, polyacetal resins, and ABS resins. Among these, polyolefin resins include polypropylene, polyethylene, ethylene-propylene copolymers (ethylene-propylene block copolymers, ethylene-propylene random copolymers), etc. Examples of polyester resins include aliphatic polyester resins such as polylactic acid, polycaprolactone, and polybutylene succinate, as well as aromatic polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. Only one of these thermoplastic resins may be used, or two or more may be used in combination. In this embodiment, polypropylene is used as the thermoplastic resin.

[0022] As shown in Figure 1, the trim board 10 of this embodiment contains multiple kenaf fiber groups 25 in a base material 11, each group of kenaf fibers 21 oriented in one direction and bound together by polypropylene 18. More specifically, each kenaf fiber group 25 consists of multiple kenaf fibers 21 oriented in one direction, arranged generally side-by-side (aligned in a direction intersecting the orientation direction) so as to spread out in the planar direction of the base material 11. Multiple such kenaf fiber groups 25 are arranged so as to spread out planarly, with the kenaf fibers 21 in each kenaf fiber group 25 having random orientations that do not coincide with the orientation direction of the kenaf fibers 21 in adjacent kenaf fiber groups 25, and are superimposed in the thickness direction of the base material 11. The orientation direction of the kenaf fibers 21 in a kenaf fiber group 25 is considered to be generally oriented in one direction, even if some of them are not oriented in the aforementioned one direction.

[0023] Furthermore, in this embodiment, the trim board 10 has kenaf fibers 21 that make up the kenaf fiber group 25 described above, with different fiber lengths for each region. Specifically, the kenaf fiber group 25 arranged around the outer periphery of the trim board 10 (the part that forms the edge) and around the opening 14 (the part that forms the edge) consists of relatively short fibers with a fiber length of 1 mm to 10 mm (hereinafter referred to as the short fiber group 25A), while the kenaf fiber group 25 arranged in the other parts, i.e., the flat part between the outer periphery and the opening 14, consists of relatively long fibers with a fiber length of 10 mm to 70 mm (hereinafter referred to as the long fiber group 25B) (see Figure 1).

[0024] Next, the manufacturing method of the trim board 10 of this embodiment will be described. The trim board 10 of this embodiment is manufactured using the long kenaf fiber bundles 20 obtained by the retting process described above. Due to this retting process, the kenaf fibers 21 are not completely separated, but rather the bonds between the kenaf fibers 21 are loosened, resulting in a bundle that can be easily untangled.

[0025] <Development process> In the unfolding process, a long, cylindrical bundle of kenaf fibers (an example of a bundle of plant fibers) 20, as shown in Figure 2, is opened up by loosening it in the transverse direction (Y direction) that intersects the extension direction (X direction) of the fiber bundle 20, as shown in Figure 3, and then spread out into a planar shape. The numerous kenaf fibers 21 that made up the kenaf fiber bundle 20 are kept in a state where they are generally oriented along the extension direction of the kenaf fiber bundle 20.

[0026] The term "planar" refers to a state in which numerous kenaf fibers 21 are arranged side by side in the transverse direction (a direction intersecting the direction in which the kenaf fibers 21 extend). Not all of the numerous kenaf fibers 21 are arranged side by side; in practice, multiple fibers are superimposed in the vertical direction (Z direction), forming a surface that is nearly flat overall.

[0027] Each kenaf fiber 21, spread out in a planar manner, is generally oriented in one direction (the X direction), but some of them form portions that extend laterally (in a direction intersecting the X direction), bridging the gap between adjacent kenaf fibers 21. In other words, the kenaf fibers 21 in a side-by-side arrangement are considered to have a state in which entanglement, snagging, and other bonds remain between them in directions intersecting their orientation.

[0028] In this embodiment, the length of the kenaf fiber bundle 20 before unfolding is approximately 2000 mm to 4000 mm, and the diameter is approximately 10 mm to 20 mm. The width (Y-direction dimension) of the multiple kenaf fibers 21 arranged side by side after unfolding is approximately 50 mm to 100 mm, and the thickness (Z-direction dimension) is approximately 0.5 mm. When spreading the kenaf fiber bundle 20 into a planar shape, it is preferable that the width of the kenaf fibers 21 arranged side by side after unfolding is 5 times or more the diameter of the kenaf fiber bundle 20, and more preferably 10 times or more.

[0029] <Process for forming fiber-containing resin sheets> Next, multiple kenaf fibers 21 spread out in a planar shape are impregnated with polypropylene 18, a thermoplastic resin. Specifically, as shown in Figure 4, a polypropylene film 28 stretched into a film shape is placed on top of multiple kenaf fibers 21 arranged side by side and heated, thereby melting the polypropylene 18 and impregnating the kenaf fibers 21. At this time, by applying pressure from the film 28 side toward the kenaf fibers 21 side, the polypropylene 18 can be distributed uniformly. After that, the polypropylene 18 is cooled and cured to form a fiber-containing resin sheet 23 in which the kenaf fibers 21 are bound by the polypropylene 18 (see Figure 5). In this embodiment, the thickness of the polypropylene film 28 used is 0.1 mm to 0.3 mm.

[0030] <Fiber-containing resin piece formation process> Next, the obtained fiber-containing resin sheet 23 is cut in a direction along the orientation direction of the kenaf fibers 21 (X direction in Figure 6) and in a direction perpendicular to the orientation direction (Y direction in Figure 6) to form multiple strip-shaped fiber-containing resin pieces 24. At this time, two types of fiber-containing resin pieces 24 with different lengths are formed. Specifically, two types of fiber-containing resin pieces 24 are cut out: short fiber-containing resin pieces 24A with dimensions of approximately 1 mm to 10 mm in the direction along the orientation direction of the kenaf fibers 21 (X direction), and long fiber-containing resin pieces 24B with dimensions of approximately 10 mm to 70 mm (see Figures 6 and 7). Note that the kenaf fibers 21 contained in one fiber-containing resin piece 24 are generally oriented in the longitudinal direction within that fiber-containing resin piece 24, but some kenaf fibers 21 extend in a direction intersecting the longitudinal direction. The width dimension of a single fiber-containing resin piece 24 (the dimension in the direction perpendicular to the orientation direction of the kenaf fibers 21) is approximately 1 mm to 10 mm for short fiber-containing resin piece 24A and approximately 10 mm to 70 mm for long fiber-containing resin piece 24B. The width dimension of a single fiber-containing resin piece 24 may be the same for both short fiber-containing resin piece 24A and long fiber-containing resin piece 24B.

[0031] Furthermore, the multiple kenaf fibers 21 contained in one short fiber-containing resin piece 24A constitute the short fiber group 25A described above. Also, the multiple kenaf fibers 21 contained in one long fiber-containing resin piece 24B constitute the long fiber group 25B described above.

[0032] <Laminate formation process> Next, on the mold surface 32A of the lower mold 32 of the press mold 30, which has an upper mold 31 and a lower mold 32, the two types of strip-shaped fiber-containing resin pieces 24A and 24B obtained are spread out in a planar manner, distributed to each region, and stacked in the thickness direction to form a laminate 11S (see Figure 10).

[0033] Specifically, in this embodiment, first, a frame 35 divided into regions is placed at a predetermined position on the flat mold surface 32A of the lower mold 32 (see Figure 8). This frame 35 is divided into a portion corresponding to the outer periphery (an example of an edge) of the finished trim board 10 (section 35A), a portion corresponding to the periphery of the opening 14 (an example of an edge) (section 35B), a portion located between sections 35A and 35B (section 35C), and a portion corresponding to the opening 14 (section 35D). Short fiber-containing resin pieces 24A are then laminated in sections 35A and 35B, and long fiber-containing resin pieces 24B are laminated in section 35C (see Figure 9). No fiber-containing resin pieces 24 are laminated in section 35D.

[0034] When laminating the fiber-containing resin pieces 24, the kenaf fibers 21 in one fiber-containing resin piece 24 are arranged and laminated in a random manner (without directionality) such that their orientation direction does not coincide with that of the kenaf fibers 21 in adjacent fiber-containing resin pieces 24.

[0035] After laminating the short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B in separate sections, the frame 35 is retracted (see Figure 10). This forms a laminate 11S in which the fiber-containing resin pieces 24 of different lengths, positioned at the boundary between the short fiber-containing resin pieces 24A and the long fiber-containing resin pieces 24B, are in contact with each other or partially mixed together. In this embodiment, the thickness of the laminate 11S is approximately 50 mm.

[0036] <Heating process> Next, a heating device 38 is inserted between the upper die 31 and the lower die 32 of the press die 30 (above the laminate 11S) to heat a portion of the laminate 11S (see Figure 11). Specifically, only the portion corresponding to the trim board 10 (base material 11) as the final product is heated, or only a slightly wider area than the portion corresponding to the trim board 10 is heated. Heating can be carried out, for example, by irradiating with far-infrared rays, applying hot air, or irradiating with microwaves while masking the portion other than the portion corresponding to the trim board 10. After heating, the heating device 38 is retracted from the press die 30.

[0037] <Pre-board forming process (an example of a press molding process)> Next, by bringing the upper mold 31 and the lower mold 32 relatively close together, the laminate 11S, which has been heated only in the predetermined portion as described above, is pressed (see Figure 12). As a result, in the heated predetermined region, the molten polypropylene 18 contained in the laminate 11S (fiber-containing resin pieces 24) causes adjacent fiber-containing resin pieces 24 to become one, and consequently, the kenaf fiber groups 25 in each fiber-containing resin piece 24 are bonded together by the polypropylene 18, forming a pre-board 11P of a predetermined shape.

[0038] As shown in Figures 12 and 13, the scraps of pre-board 11P generated in this pre-board formation process (an example of a press molding process) (the parts that protrude from the mold surfaces of the upper mold 31 and lower mold 32, and the short fiber-containing resin pieces 24A) are kept in an unheated state, and the polypropylene 18 contained in the scraps is not in a molten state. Therefore, the short fiber-containing resin pieces 24A retain their original properties and are in the same state as when they were formed, and can be reused as the material for the trim board 10. In addition, since the edges of the pre-board 11P are made of short fiber-containing resin pieces 24A, the boundary between the pre-board 11P and the scraps separates easily, improving the recovery rate of the scraps.

[0039] <Base material molding process> The pre-formed board 11P is reheated and then set between the open upper mold 41 and lower mold 42 of the mold 40. The upper mold 41 and lower mold 42 are then closed to press-form the board into a predetermined shape (see Figures 14 and 15). After the polypropylene 18 has cooled, the mold is opened and the board is demolded to complete the trim board 10 (base material 11) (see Figure 16). At this time, the edges of the trim board 10 are made of short fiber-containing resin pieces 24A, so burrs are less likely to form.

[0040] Next, the effects will be explained. The manufacturing method of the trim board 10 of this embodiment includes a spreading step of spreading a kenaf fiber bundle 20 obtained from kenaf in a planar manner so that the kenaf fibers 21 are oriented in one direction; a fiber-containing resin sheet forming step of impregnating the spread-out kenaf fibers 21 with polypropylene 18 and curing it to form a fiber-containing resin sheet 23 in which the kenaf fibers 21 are bound by the polypropylene 18; and cutting the fiber-containing resin sheet 23 along the orientation direction of the kenaf fibers 21 and cutting it in a direction intersecting the orientation direction of the kenaf fibers 21 so that the lengths differ, thereby forming a plurality of short fiber-containing resin pieces 24A containing relatively short kenaf fibers 21, and The process involves sequentially performing the following steps: a fiber-containing resin piece forming step of forming a plurality of long fiber-containing resin pieces 24B containing symmetrically long kenaf fibers 21; a laminate forming step of forming a laminate 11S by laminating short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B in a distributed state for each region; a heating step of heating the laminate 11S; a pre-board forming step of pressing the heated laminate 11S to form a pre-board 11P in which the short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B are integrated and molded into a predetermined shape; and a base material forming step of heating and press-molding the pre-board 11P to form a base material 11 (trim board 10).

[0041] According to the above manufacturing method, compared to the conventional method of producing plant fiber-containing resin boards from mats formed by mixing short-cut plant fibers and thermoplastic resin fibers, inexpensive pelletized or film-shaped thermoplastic resins can be used instead of fibrous thermoplastic resins. Furthermore, mixing equipment for mixing plant fibers and thermoplastic resin fibers, and equipment such as entanglement devices for forming mats are not required, thus reducing material and equipment costs compared to conventional methods. In addition, the generation of plant fiber dust can be suppressed compared to conventional manufacturing methods, thereby improving material yield.

[0042] Furthermore, since the kenaf fibers 21 contained in each region have different fiber lengths, for example, by forming curved sections with short fiber-containing resin pieces 24A, the restraining force of the kenaf fibers 21 can be reduced compared to when they are formed with long fiber-containing resin pieces 24B, thereby suppressing the occurrence of wrinkles during press molding and springback after molding. In other words, additional press molding to suppress springback becomes unnecessary. Also, by forming flat sections with long fiber-containing resin pieces 24B, the overall strength and rigidity of the trim board 10 can be increased. In this way, a trim board 10 with a high degree of freedom in molding, as well as high strength and rigidity, can be obtained using a simple manufacturing method.

[0043] Furthermore, in the laminate formation process, short fiber-containing resin pieces 24A are laminated around the outer periphery and the opening 14 that will form the edge of the laminate 11S, and long fiber-containing resin pieces 24B are laminated in areas other than the edge (part of the flat portion 12). With this manufacturing method, it is possible to suppress the generation of burrs at the edge, where burrs are prone to occur during press molding.

[0044] Furthermore, in the laminate formation process, a frame 35, whose interior is divided into predetermined shapes, is placed on the mold surface 32A of the lower mold 32 of a press mold 30 having an upper mold 31 and a lower mold 32. Short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B are laminated into predetermined areas within the frame 35, and then the frame 35 is retracted. With this manufacturing method, short fiber-containing resin pieces 24A and long fiber-containing resin pieces 24B can be easily laminated while distributed into predetermined areas.

[0045] Furthermore, in the heating process, only the portion of the laminate 11S corresponding to the finished trim board 10 is heated. With this manufacturing method, the scrap material generated during press molding is not formed by integrating the short fiber-containing resin pieces 24A with each other, and the short fiber-containing resin pieces 24A themselves remain as they were before lamination in the laminate formation process. Therefore, the scrap material can be recycled as is while maintaining its original properties, such as fiber length. Consequently, the material yield can be improved compared to conventional methods.

[0046] Furthermore, the trim board 10 of this embodiment is formed by randomly stacking multiple fiber groups 25, each consisting of multiple kenaf fibers 21 oriented in one direction and bound together by polypropylene 18, and the multiple fiber groups 25 are integrated with each other. The fiber groups 25 include short fiber groups 25A consisting of relatively short kenaf fibers 21 and long fiber groups 25B consisting of relatively long kenaf fibers 21, with the short fiber groups 25A and long fiber groups 25B distributed according to region.

[0047] Furthermore, the trim board 10 has a group of short fibers 25A arranged around its outer periphery. The trim board 10 also has an opening 14 that penetrates the board surface, and the group of short fibers 25A is arranged around the opening 14.

[0048] <Other Embodiments> The technologies disclosed herein are not limited to the embodiments described above in the description and drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.

[0049] (1) In the above embodiment, a configuration was shown in which short fiber-containing resin pieces 24A were arranged around the outer periphery of the trim board 10 and around the opening 14, but the areas in which the short fiber-containing resin pieces and long fiber-containing resin pieces are arranged are not limited to the above embodiment.

[0050] (2) In the above embodiment, the polypropylene 18 is impregnated into the kenaf fibers 21 by heating the polypropylene film 28 while it is superimposed on a plurality of kenaf fibers 21 arranged side by side during the fiber-containing resin sheet formation process. However, the impregnation method is not limited to the above embodiment. For example, molten polypropylene may be directly placed onto the kenaf fibers using an extruder to impregnate them.

[0051] (3) In the above embodiment, a configuration in which the frame 35 is used in the laminate formation process is shown, but configurations in which the frame is not used are also included in the technical scope.

[0052] (4) In the heating process, the entire laminate may be heated.

[0053] (5) The pre-board formation step can be omitted. In such cases, similar to the pre-board formation step in the above embodiment, only the portion of the laminated body stacked on the mold surface of the lower mold that corresponds to the finished pre-board (base material) can be heated (an example of a heating step), and the material can be directly press-molded into the shape of the base material (an example of a press molding step).

[0054] (6) In the above embodiment, the laminate formation process is shown to be carried out on the mold surface of the lower mold of the molding die. However, the laminate may be formed in a flat plate shape other than the mold, heated, and then moved to a press mold for pressing.

[0055] (7) In the above embodiment, two types of resin pieces containing short fibers 24A and long fibers 24B, which have different lengths of kenaf fibers 21, were used as the material for the trim board 10. However, the fiber-containing resin pieces are not limited to two types, and three or more types of resin pieces with different lengths of plant fibers may be used, as shown in the trim board 50 in Figure 17. Alternatively, fiber-containing resin powder may be used. In such a configuration, properties that are superior in both moldability and rigidity can be obtained according to the shape of the plant fiber-containing resin board.

[0056] (8) The technologies disclosed herein are not limited to the trim board 10 for vehicle door trims, but are applicable to various plant fiber-containing resin boards. [Explanation of Symbols]

[0057] 10, 50…Trim board (plant fiber-containing resin board) 11…Base material (plant fiber-containing resin board) 11P…Pre-board 11S…Laminate 12…Flat section 13…Vertical wall 14…Opening 18…Polypropylene (thermoplastic resin) 20…Kenaf fiber bundle (bundle of plant fibers) 21…Kenaf fiber (plant fiber) 23…Fiber-containing resin sheet 24…Fiber-containing resin piece 24A…Short fiber-containing resin piece 24B…Long fiber-containing resin piece 25…Kenaf fiber group (fiber group) 25A…Short fiber group 25B…Long fiber group 30…Press mold (molding mold) 31…Upper mold 32…Lower mold 32A…Mold surface 35…Frame 35A…Compartment 35B…Compartment 35C…Compartment 35D…Compartment 38…Heating device 40…Molding mold 41…Upper mold 42…Lower mold

Claims

1. A development step in which a bundle of plant fibers obtained from a plant is spread out in a planar manner so that the plant fibers are oriented in one direction, A fiber-containing resin sheet forming step involves impregnating the plant fibers, which are spread out in a planar shape, with a thermoplastic resin and curing it to form a fiber-containing resin sheet in which the plant fibers are bound together by the thermoplastic resin, A fiber-containing resin piece forming step involves cutting the fiber-containing resin sheet along the orientation direction of the plant fibers and cutting it in a direction intersecting the orientation direction of the plant fibers so that the lengths differ, thereby forming a plurality of short fiber-containing resin pieces containing relatively short plant fibers and a plurality of long fiber-containing resin pieces containing relatively long plant fibers. A laminate formation step is to form a laminate by laminating the short fiber-containing resin pieces and the long fiber-containing resin pieces in a state where they are distributed to each region, A heating step for heating the laminated body, A method for manufacturing a plant fiber-containing resin board, comprising the steps of: pressing the heated laminate to form a press molding step in which the short fiber-containing resin pieces and the long fiber-containing resin pieces are integrated and molded into a predetermined shape to form a plant fiber-containing resin board.

2. A method for manufacturing a plant fiber-containing resin board according to claim 1, wherein in the laminate formation step, the short fiber-containing resin pieces are laminated in the region that will become the edge of the laminate, and the long fiber-containing resin pieces are laminated in the region other than the edge.

3. A method for manufacturing a plant fiber-containing resin board according to claim 1 or 2, wherein in the laminate formation step, a frame having a predetermined shape on the inside is placed on the mold surface of the lower mold of a mold having an upper mold and a lower mold, the short fiber-containing resin pieces and the long fiber-containing resin pieces are laminated in predetermined areas within the frame, and then the frame is retracted.

4. A method for manufacturing a plant fiber-containing resin board according to claim 1 or 2, wherein in the heating step, only the portion of the laminate corresponding to the finished form of the plant fiber-containing resin board is heated.

5. Multiple plant fibers oriented in one direction are bonded together with a thermoplastic resin, and these fiber groups are randomly layered, with the multiple fiber groups being integrated with each other. The fiber group includes a short fiber group consisting of relatively short plant fibers and a long fiber group consisting of relatively long plant fibers. The aforementioned short fiber group and the aforementioned long fiber group are plant fiber-containing resin boards distributed according to region.

6. The plant fiber-containing resin board according to claim 5, wherein the group of short fibers is arranged on the outer periphery.

7. A plant fiber-containing resin board according to claim 5 or claim 6, having an opening that penetrates the board surface, with the short fiber group arranged around the opening.

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