Intermediate sheet and method for producing composite material

Abstract

In order to provide an intermediate sheet by which a favorable composite material can be obtained with the intermediate sheet having a holding sheet affixed to a core material layer having a large number of divided portions, an intermediate sheet 10 used for producing a composite material 30 comprises: a core material layer 11 that is used in a core material 33 of the composite material 30, the core material layer 11 having a large number of divided portions 13 that are two-dimensionally arrayed in a plan view with the divided portions 13 being divided from each other by a gap 16 or a notch 16; and a holding sheet 14 that is affixed to the core material layer 11 and holds the array of the large number of divided portions 13. The holding sheet 14 is a sheet-like adhesive composed of a nonwoven fabric or a mesh sheet having a large number of voids 4 in a plan view.

Description

Intermediate sheet and method for manufacturing composite material

[0001] The present invention relates to an intermediate sheet or the like used in the production of a composite material.

[0002] A sandwich structure, in which a core material is sandwiched between skin materials, is known as a composite material structure. Sandwich-structured composite materials are characterized by their light weight and high rigidity, and are expected to be used in a variety of applications. A low-density, relatively high-rigidity material (e.g., rigid foam) is used as the core material. However, when a sheet of such a material is used as the core material in its original form, it is difficult to mold the sheet material to conform to a curved surface with a relatively large curvature, and it may be impossible to mold the composite material into a desired three-dimensional shape.

[0003] Patent Literature 1 describes a composite material having a core material composed of many plate-like pieces, which is excellent in formability into a three-dimensional shape. Patent Literature 1 describes a method for manufacturing such a composite material, in which an adhesive core sheet, in which many plate-like pieces are attached to a base sheet, is sandwiched between two skin sheets to obtain a laminate, and the composite material is then manufactured by heating the laminate, etc. Patent Literature 1 describes a second intermediate sheet, in which a sheet-like adhesive is attached to many plate-like pieces, as the adhesive core sheet.

[0004] Patent Document 2 describes a reinforcement structure made of a sheet-like base material, which has a material damping section that divides the base material into a number of material islands, which are separated by the material damping section but connected to each other by bridge sections.

[0005] Patent No. 7118481 U.S. Patent Application Publication No. 2019 / 0099964A1

[0006] The method for manufacturing the composite material described in Patent Document 1 makes it possible to easily arrange a large number of divisions on a skin sheet by simply laminating an intermediate sheet, which is made of a core material layer having a large number of divisions and a base sheet (retaining sheet) attached to the core material layer, onto a skin sheet such as a prepreg. However, the method does not take into consideration an intermediate sheet that can produce a good composite material.

[0007] The present invention was made in consideration of these circumstances, and aims to provide an intermediate sheet that can produce a good composite material, in which a retaining sheet is attached to a core material layer having a large number of divided portions.

[0008] In order to solve the above-mentioned problems, the first invention is an intermediate sheet used in the manufacture of a composite material, which comprises a core material layer that is a layer used for the core material of the composite material and in which a number of divided sections that are separated from each other are arranged two-dimensionally in a planar view, and a retaining sheet that is attached to the core material layer and maintains the arrangement of the many divided sections, and the retaining sheet uses a sheet-like adhesive made of a nonwoven fabric or mesh sheet that has a number of voids in a planar view.

[0009] A second aspect of the present invention is the optical fiber recording medium according to the first aspect of the present invention, further comprising a support sheet attached to the core material layer on the side opposite to the holding sheet.

[0010] In a third aspect of the present invention, in the second aspect, the support sheet is a sheet material having a bending resistance greater than that of the holding sheet.

[0011] A fourth aspect of the present invention is the first aspect of the present invention, further comprising a separator covering the surface of the supporting sheet opposite to the core material layer.

[0012] In a fifth aspect of the present invention, in the fourth aspect, the separator is a sheet material having a bending resistance greater than that of the holding sheet.

[0013] The sixth invention is a method for producing a composite material by carrying out a first lamination step of laminating an intermediate sheet of any one of the first to fifth inventions onto a first skin sheet so that the retaining sheet abuts against the first skin sheet; a second lamination step of laminating a second skin sheet onto the intermediate sheet to obtain a laminate in which the first skin sheet, the intermediate sheet, and the second skin sheet are laminated in this order; and a curing step of curing the first skin sheet and the second skin sheet in the laminate.

[0014] The seventh invention is the sixth invention, in which, after the first lamination step and before the second lamination step, a step of locally heating the retaining sheet to locally attach the core material layer to the first skin sheet is carried out.

[0015] In the present invention, a retaining sheet that maintains the arrangement of multiple segments is attached to a core material layer in which multiple segments are arranged two-dimensionally in a planar view. The inventors of the present application conducted extensive research into the manufacturing method of a composite material using an adhesive core material sheet described in Patent Document 1. As a result, they found that if a typical sheet-like adhesive without voids in a planar view is used as the retaining sheet attached to the core material layer having multiple segments, the amount of adhesive originating from the retaining sheet in the finished composite material may be greater than necessary, which may have a significant impact on the adhesive bonding the skin material (e.g., cured prepreg) and the core material (adhesives other than those originating from the retaining sheet, such as the prepreg matrix or resin injected in an RTM molding method). Furthermore, they found that when an intermediate sheet is laminated to a skin material sheet such as uncured prepreg, it is sufficient for the retaining sheet to have sufficient adhesiveness to temporarily attach the core material layer to the skin material sheet after lamination.

[0016] Therefore, in the present invention, a sheet adhesive composed of a nonwoven fabric or mesh sheet having numerous voids in a planar view is used as a retaining sheet attached to a core material layer having numerous segments. Such a sheet adhesive has a lower density than a sheet adhesive without voids in a planar view. Therefore, compared to using a sheet adhesive without voids in a planar view, it is possible to reduce the amount of adhesive from the retaining sheet in the composite, thereby minimizing the impact on the adhesive bonding the skin material and the core material. According to the present invention, an intermediate sheet that can produce a good composite (a highly reliable composite) can be provided. The present invention is applicable to a core material layer of an intermediate sheet, including a core material layer in which numerous separate segments separated from each other by gaps or slits are arranged two-dimensionally, and a core material layer in which multiple segments are arranged two-dimensionally, with one side separated from each other by slits extending partway through the thickness direction.

[0017] Fig. 1(A) is a cross-sectional view of an intermediate sheet having a core material layer of a first type according to an embodiment, Fig. 1(B) is a cross-sectional view of an intermediate sheet obtained by providing a separator on the intermediate sheet of Fig. 1(A), Fig. 1(C) is a cross-sectional view of an intermediate sheet obtained by providing a support sheet on the intermediate sheet of Fig. 1(B), and Fig. 1(D) is a cross-sectional view of an intermediate sheet obtained by providing a second retaining sheet on the intermediate sheet of Fig. 1(A). Fig. 2(A) is a cross-sectional view of an intermediate sheet having a core material layer of a second type according to an embodiment, Fig. 2(B) is a cross-sectional view of an intermediate sheet obtained by providing a separator on the intermediate sheet of Fig. 2(A), Fig. 2(C) is a cross-sectional view of an intermediate sheet obtained by providing a support sheet on the intermediate sheet of Fig. 2(B), and Fig. 2(D) is a cross-sectional view of an intermediate sheet obtained by providing a second retaining sheet on the intermediate sheet of Fig. 2(A). Fig. 3(A) is a plan view of the core material layer of the intermediate sheet shown in Fig. 1(A) or 2(A), Fig. 3(B) is a partially enlarged plan view showing an example of a nonwoven fabric sheet used as a retaining sheet, and Fig. 3(C) is a partially enlarged plan view showing an example of a mesh sheet used as a retaining sheet. Figs. 4(A)-(D) are cross-sectional views illustrating a method for manufacturing an intermediate sheet having a first type of core material layer. Figs. 5(A)-(D) are cross-sectional views illustrating a method for manufacturing an intermediate sheet having a second type of core material layer. Figs. 6(A)-(B) are cross-sectional views illustrating a method for manufacturing a composite material. Fig. 6(C) is a cross-sectional view of a composite material manufactured using an intermediate sheet having a first type of core material layer, and Fig. 6(D) is a cross-sectional view of a composite material manufactured using an intermediate sheet having a second type of core material layer.

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are merely examples of the present invention and are not intended to limit the scope of the present invention, its applications, or its uses.

[0019] This embodiment relates to an intermediate sheet 10 used in the manufacture of a composite material 30 (see FIGS. 6C and 6D) in which fiber-reinforced plastics are used for the skin materials 31, 32, and a method for manufacturing the composite material 30 using the intermediate sheet 10. The intermediate sheet 10 is an intermediate material manufactured during the manufacturing process of the composite material 30. Below, two types of intermediate sheets 10 will be explained, followed by a method for manufacturing the composite material 30.

[0020] [Configuration of Intermediate Sheet] As shown in Fig. 1(A) (or Fig. 2(A)), the intermediate sheet 10 comprises a core material layer 11 in which a large number of mutually separated divisions 13 are arranged two-dimensionally in a plan view, and a retaining sheet 14 that is attached to the core material layer 11 and maintains the arrangement of the large number of divisions 13. In this specification, the term "large number" in "large number of divisions" means 10 or more. The number of divisions 13 in the intermediate sheet 10 is at least 10 or more, and may be 50 or more.

[0021] The intermediate sheet 10 shown in Fig. 1(A) and the intermediate sheet 10 shown in Fig. 2(A) differ in the shape of the core material layer 11. The core material layer 11 shown in Fig. 1(A) is obtained by fully cutting, in the thickness direction, a material sheet 1 made of a material that can be used for the core material 33 of the composite material 30, while the core material layer 11 shown in Fig. 2(A) is obtained by half-cutting the material sheet 1 in the thickness direction.

[0022] The core material layer 11 is entirely made of a material that can be used for the core material 33 of the composite material 30. For the core material layer 11, a material with a lower density than the skin materials 31 and 32 of the composite material 30 can be used. For the core material layer 11, a material with a density of 30 kg / m ３ More than 2000kg / m ３ Materials in the following ranges can be used, but from the viewpoint of reducing the weight of the composite material 30, ３ The following materials are preferred: The material of the core material layer 11 can be a resin (such as a hard resin foam), a wood material (such as balsa or plywood), or a metal foam (such as an aluminum alloy).

[0023] Examples of hard resin foams that can be used as the material for the core layer 11 include polystyrene foam, polyvinyl chloride foam, cellulose acetate foam, polyurethane foam, phenol foam, epoxy foam, acrylic foam, polymethacrylimide foam, polypropylene foam, polyethylene terephthalate foam, polycarbonate foam, polyamideimide foam, and polyphenylene sulfide foam.

[0024] In the core material layer 11, the planar shape (peripheral shape) of the divisions 13 is a regular polygon (a regular hexagon in this embodiment). When a large number of divisions 13 are uniformly arranged in the core material layer 11, the planar shape of the divisions 13 can be selected to be a triangle, a rectangle, a hexagon, or an equilateral pentagon. When the planar shape of the divisions 13 is a polygon, chamfers may be provided at each corner of the divisions 13 in a planar view. Note that the divisions 13 may be any shape as long as the periphery is a shape consisting of straight lines, curves, or a combination of straight lines and curves, and the planar shape of the divisions 13 can also be selected to be a circle, an ellipse, or the like.

[0025] A large number of divisions 13 are regularly and uniformly arranged in the core material layer 11. In this embodiment, the large number of divisions 13 are arranged in a staggered pattern, with the positions of the divisions 13 shifted by half a pitch between adjacent division row 13L (see FIG. 3(A)). In this embodiment, the planar shape of each division 13 is a regular hexagon, so the large number of divisions 13 present a honeycomb shape in plan view.

[0026] Regarding the planar dimensions of each dividing portion 13, in this embodiment where the dividing portion 13 is a regular hexagon, the length of one side can be set to a value of 1 mm or more and 100 mm or less. When the dividing portion 13 is a shape other than a regular hexagon, the planar dimensions can be set to a value of 1 mm or more and 100 mm or less, which is the average value of the distance from the center of gravity of the dividing portion 13 to the outer periphery (average value over 360 degrees; radius in the case of a circle). However, the dimensions of the dividing portion 13 may be set to a value outside the range described in this paragraph.

[0027] The holding sheet 14 is a sheet-like adhesive having numerous voids 4 (voids 4 penetrating in the thickness direction) in a plan view. Specifically, the holding sheet 14 is a nonwoven fabric or mesh sheet using fibers 5 made of a material that exhibits adhesiveness when heated or pressurized (see FIGS. 3(B)-(C)). The holding sheet 14 is primarily a sheet for maintaining the arrangement of the numerous division sections 13, but is also used to attach the core material layer 11 by heating or pressurization. In this regard, the holding sheet 14 is not used for adhesive lamination of the skin materials 31, 32 and the core material 33, but is also used for temporarily attaching the core material layer 11 to the skin material sheets 31A, 32A that are the materials for the skin materials 31, 32. The skin material sheets 31A, 32A are sheets in which reinforcing fibers are impregnated with a resin (matrix) (e.g., prepreg), or reinforced fiber materials that are not impregnated with resin (reinforced fiber materials used in RTM molding or infusion molding). The material of the retaining sheet 14 (the material of the fibers 5) can be a material that functions as an adhesive when heated, a material whose glass transition point is at or below room temperature, or a material that is adhesive at room temperature and allows the core material layer 11 to be attached by applying pressure alone without heating. The material of the retaining sheet 14 can be selected from, for example, a nonwoven fabric or mesh sheet made of a resin with a melting point of 130°C or less (preferably 100°C or less).

[0028] Furthermore, even when the resin used for the skin materials 31 and 32 functions to bond the interfaces between the skin materials 31 and 32 and the core material 33, the adhesive strength can be increased by the material of the holding sheet 14.

[0029] For example, the material of the retaining sheet 14 can be a thermoplastic resin such as polyurethane (PU), polyamide (PA), polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyimide (PI), polyether ether ketone (PEEK), or polyamideimide (PAI), or a thermosetting resin such as epoxy or phenol.

[0030] Numerical structural specifications of the holding sheet 14 are exemplified below. The holding sheet 14 has a porosity of 10% or more in a plan view. The thickness of the holding sheet 14 is 3 mm or less, preferably 1 mm or less. The density of the holding sheet 14 is 1000 g / m ２ less than 500 g / m ２ The following is preferable: The porosity of the holding sheet 14 in plan view is the area ratio of the voids 4 to the fibers 5 in plan view (that is, porosity = area of ​​voids 4 / (total area - area of ​​voids 4)).

[0031] <Intermediate sheet having a core material layer of the first type> As shown in Figure 1(A) , the core material layer 11 has a large number of separate segments 13 separated by gaps 6. Each segment 13 corresponds to the above-mentioned divided portion and is made of a material that can be used for the core material 33 of the composite material 30. Note that in Figure 1(A) , gaps 16 exist between adjacent segments 13, but adjacent segments 13 may also be in contact with each other through slits cut through the core material layer 11 in the thickness direction.

[0032] In the core material layer 11, a large number of divided bodies 13 having the same thickness are arranged two-dimensionally (arranged on a two-dimensional plane) along the surface of the retaining sheet 14. Each divided body 13 is made of the same material and has the same shape and size.

[0033] In the core material layer 11, all the divided bodies 13 are separated from one another. Each divided body 13 is separated from all the adjacent divided bodies 13 by a gap 16. Each divided body 13 has an island-like structure independent from the others.

[0034] Adjacent segments 13 face each other with one side thereof separated by a gap 16. The width of the gap 16 between adjacent segments 13 is constant around the entire periphery of each segment 13. The width of the gap 16 is designed appropriately depending on the size of the composite material 30, and can be set within the range of 0 mm or more and 10 mm or less, for example.

[0035] In this embodiment, each of the divided bodies 13 is thin and is a plate-like piece (a small, thin, flat piece). The thickness of each of the divided bodies 13 can be, for example, in the range of 0.05 mm to 10 mm (e.g., 0.05 mm to 2 mm).

[0036] As shown in FIG. 1(B), the intermediate sheet 10 may further include a separator 15 covering the side (back surface) of the holding sheet 14 opposite the core material layer 11. The separator 15 is removable from the holding sheet 14. By providing the separator 15, the holding sheet 14 and the core material layer 11 can be protected from foreign matter and the like. The separator 15 is made of a sheet material having a higher bending resistance (lower flexibility) than the holding sheet 14. The bending resistance is measured using a cantilever method. The separator 15 does not necessarily have to have a higher bending resistance than the holding sheet.

[0037] By providing the separator 15, when the holding sheet 14 is attached to the core material layer 11, the holding sheet 14 can be heated through the separator 15 by a heater 40 (such as an iron or a heated roller), as described below. In addition, there are cases where the holding sheet 14 with the separator 15 attached can be more easily cut with a knife or plotter than the holding sheet 14 alone.

[0038] The separator 15 is a thin film material such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), cellophane, paper, etc. The separator 15 may be a type whose surface is treated with a release agent such as silicone, or a type that is not treated with a release agent.

[0039] 1(C), the intermediate sheet 10 may further include a support sheet 12 attached to the side of the core material layer 11 opposite the holding sheet 14. The support sheet 12 maintains the arrangement of the core material layer 11 (the arrangement of the multiple divided bodies 13) and protects the core material layer 11 from foreign matter. The support sheet 12 can maintain the arrangement of the core material layer 11 more stably than the holding sheet 14. The support sheet 12 is made of a sheet material that has a higher bending resistance (lower flexibility) and lower stretchability than the holding sheet 14. Note that the support sheet 12 does not necessarily have to have a higher bending resistance than the holding sheet 14.

[0040] By providing the support sheet 12, the bending resistance of the entire intermediate sheet 10 can be increased in cases where pre-cutting, as described below, is difficult with only the provision of the holding sheet 14 and separator 15, improving the ease of handling as a sheet and the ease of cutting with a knife or plotter. The provision of the support sheet 12 also serves to protect the entire sheet. The separator 15 may be omitted from the intermediate sheet 10 shown in FIG. 1(C).

[0041] The support sheet 12 can be a single-sided adhesive sheet. For example, the support sheet 12 is made of a thin film material such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), cellophane, or paper, with a pressure-sensitive adhesive such as acrylic or silicone applied to one side. The support sheet 12 is, for example, a sheet without voids 4 in a planar view. The support sheet 12 is made of a material that has a certain degree of elasticity and flexibility so that it can conform to any shape, and holds the core material layer 11. The support sheet 12 has an adhesive strength that allows it to be peeled off after being attached to the material sheet 1. Therefore, the support sheet 12 can be peeled off from the core material layer 11.

[0042] 1(D), the intermediate sheet 10 may be formed by attaching holding sheets 14 to both sides of the core material layer 11. In this case, a separator 15 may be provided on the outer surface of one of the holding sheets 14, or a separator 15 may be provided on the outer surface of each of the holding sheets 14.

[0043] <Intermediate sheet having a core material layer of a second embodiment> As shown in Figure 2(A) , the core material layer 11 is a sheet material in which a plurality of divided sections 13, separated from each other on the surface 11f side (one side) by half-cut slits 16 in the thickness direction, are arranged two-dimensionally in a plan view. This sheet material is made of a material that can be used for the core material 33. In the core material layer 11, adjacent divided sections 13 are connected to each other by a portion in the thickness range from the bottom of the slits 16 to the other surface of the core material layer 11 (the bottom of the slits 16). The half-cuts are made by, for example, press cutting or laser cutting.

[0044] In the core material layer 11, adjacent divisions 13 are divided by a common notch 16. The notch 16 constitutes a dividing point that divides adjacent divisions 13, and is provided around the entire periphery of each division 13. When viewed from above, adjacent divisions 13 face each other with one side thereof separated by the notch 16. In each division 13, the width of the notch 16 between adjacent divisions 13 is constant around the entire periphery.

[0045] In a cross-sectional view, the notches 16 have a V-shaped valley shape that widens from the valley bottom toward the surface 11f. The side surfaces of adjacent divisions 13 intersect at the valley bottom of the notches 16. Note that the cross-sectional shape of the notches 16 may be a shape other than a V-shaped valley shape.

[0046] The thickness D of the core material layer 11 can be, for example, less than 4 mm (e.g., 2 mm or less). However, the thickness D of the core material layer 11 may be 4 mm or more. The depth d of the notch 16 in the core material layer 11 can be 60% or more (preferably 70% or more, and more preferably 80% or more) of the thickness D of the core material layer 11. If the depth d of the notch 16 is shallower than 60% of the thickness D of the core material layer 11, it is difficult to obtain sufficient formability into a three-dimensional shape when a hard material is used for the core material layer 11. In this embodiment, the depth d of the notch 16 is approximately constant throughout the core material layer 11.

[0047] As shown in Fig. 2(B), the intermediate sheet 10 may further include a separator 15 covering the side (back surface) of the holding sheet 14 opposite the core material layer 11. The separator 15 is made of a sheet material having a higher bending resistance (lower flexibility) than the holding sheet. By providing the separator 15, the holding sheet 14 can be heated through the separator 15 by the heater 40, as with the intermediate sheet 10 shown in Fig. 2(A), improving cutting processability and also protecting the holding sheet 14.

[0048] As shown in FIG. 2(C), the intermediate sheet 10 may further include a support sheet 12 attached to the core material layer 11 on the side opposite the holding sheet 14. The support sheet 12 is made of a sheet material having a higher bending resistance (lower flexibility) and lower stretchability than the holding sheet 14. As with the intermediate sheet 10 shown in FIG. 2(A), the support sheet 12 improves sheet handling and processability when cutting with a knife or plotter, and also protects the entire sheet. The separator 15 may be omitted from the intermediate sheet 10 shown in FIG. 2(C). Alternatively, the intermediate sheet 10 may have holding sheets 14 attached to both sides of the core material layer 11, as shown in FIG. 2(D). In this case, a separator 15 may be provided on the outer surface of one of the holding sheets 14, or a separator 15 may be provided on the outer surface of each of the holding sheets 14.

[0049] [Method for Manufacturing Intermediate Sheet] A method for manufacturing the intermediate sheet 10 will now be described. The method for manufacturing the intermediate sheet 10 involves performing, in this order, a first bonding step in which a support sheet 12 is bonded to a single-layer material sheet 1 made only of the material used for the core material 33 using a pressure-sensitive adhesive (a peelable adhesive), a cutting step in which the material sheet 1 is cut to form multiple divisions 13, and a second bonding step in which a holding sheet 14 is bonded to the multiple divisions 13. The material sheet 1 is the material for the core material layer 11.

[0050] <First Form of Method for Producing Intermediate Sheet Having Core Material Layer> In the first bonding step, a laminated sheet 19 (see FIG. 4(A)) is produced by bonding a support sheet 12 to a material sheet 1 with a pressure-sensitive adhesive.

[0051] In the cutting step, a full-cut cutting process is performed by press cutting or laser cutting, etc., to cut the material sheet 1 in the thickness direction, and as shown in Figure 4 (B), the material sheet 1 is divided into a number of divided bodies 13 on the support sheet 12 to form a core material layer 11.

[0052] If cuts are made in the support sheet 12 during the cutting step, the multiple divided bodies 13 attached to the support sheet 12 during the cutting step may be transferred to another support sheet 12. In this transfer, the other support sheet 12 is attached to the multiple divided bodies 13 with a pressure-sensitive adhesive, and then the original support sheet 12 is peeled off.

[0053] In the second attachment step, as shown in FIG. 4(C), a holding sheet 14 with separators 15 is laminated onto the multiple segments 13 on the support sheet 12, with the holding sheet 14 side facing the segments 13. The holding sheet 14, which is made of a nonwoven fabric or mesh sheet, is stretchable and flexible, so using a holding sheet 14 with separators 15 makes it easy to handle. Then, a heater 40 such as a heated roller or iron (heated soldering iron) is applied to the separators 15 to heat the holding sheet 14 via the separators 15, causing the adhesive of the holding sheet 14 to melt and exhibit adhesive properties, and the holding sheet 14 is attached to the multiple segments 13.

[0054] By using the holding sheet 14 with the separator 15, it is possible to perform heat and pressure bonding evenly without the adhesive of the holding sheet 14 sticking to the heater 40. However, if the heating surface of the heater 40 that is pressed against the object to be heated has been treated to be non-adhesive, the holding sheet 14 without the separator 15 may be used and the heater 40 may be pressed directly against the holding sheet 14.

[0055] By carrying out the second bonding step, the intermediate sheet 10 shown in Fig. 1(C) is obtained. Then, by peeling off the support sheet 12, a large number of divided bodies 13 are transferred from the support sheet 12 to the holding sheet 14, and the intermediate sheet 10 shown in Fig. 1(B) is obtained. Furthermore, by peeling off the separator 15, the intermediate sheet 10 shown in Fig. 1(A) is obtained.

[0056] Furthermore, a third bonding step may be performed in which a second holding sheet 14 is bonded to the intermediate sheet 10 shown in FIG. 1(C). In the third bonding step, after peeling off the support sheet 12, a second holding sheet 14 with a separator 15 is laminated on the opposite side of the multiple divided bodies 13 from the first holding sheet 14, with the second holding sheet 14 facing the divided bodies 13, as shown in FIG. 4(D). In this case, as in the second bonding step, a heater 40 is applied to the separator 15 to heat the holding sheet 14 through the separator 15, thereby bonding the holding sheet 14 to the multiple divided bodies 13. By performing the third bonding step and peeling off the two separators 15, the intermediate sheet 10 shown in FIG. 1(D) is obtained. Note that in FIG. 4(D), the second holding sheet 14 is shown on the bottom for convenience, but in reality, the sheet is flipped upside down so that the second holding sheet 14 is on the top.

[0057] <Second Form of Method for Producing Intermediate Sheet Having Core Material Layer> In the first bonding step, a laminated sheet 19 (see FIG. 5(A)) is produced by bonding a support sheet 12 to a material sheet 1 with a pressure-sensitive adhesive.

[0058] In the cutting step, a half-cut cutting process is performed by press cutting or laser cutting, etc., to cut the material sheet 1 halfway in the thickness direction, and as shown in Figure 5 (B), by forming slits 16 in the material sheet 1 on the support sheet 12, one side of the material sheet 1 is divided into a number of divisions 13 to form a core material layer 11.

[0059] In the second attachment step, a retaining sheet 14 with separators 15 is attached to a number of divided bodies 13, as shown in Figure 5 (C), using the same procedure as in the manufacturing method of the intermediate sheet 10 having the first form of core material layer 11.

[0060] By performing the second bonding step, the intermediate sheet 10 shown in Fig. 2(C) is obtained. Then, by peeling off the support sheet 12, the multiple divided bodies 13 are transferred from the support sheet 12 to the holding sheet 14, and the intermediate sheet 10 shown in Fig. 2(B) is obtained. Furthermore, by peeling off the separator 15, the intermediate sheet 10 shown in Fig. 2(A) is obtained.

[0061] 2(C), a third bonding step may be performed in which a second bonding sheet 14 is bonded to the intermediate sheet 10 in addition to the first bonding sheet 14. In the third bonding step, the second bonding sheet 14 is bonded to the opposite side of the multiple divided bodies 13 from the first bonding sheet 14, as shown in FIG. 5(D), using the same procedure as in the manufacturing method of the intermediate sheet 10 having the core material layer 11 of the first form. By performing the third bonding step and peeling off the two separators 15, the intermediate sheet 10 shown in FIG. 2(D) is obtained.

[0062] If the half-cut material sheet 1 is made of a material that is not easily broken, the first bonding step may be omitted and the cutting step may be performed on the material sheet 1 without the support sheet 12.

[0063] [Method for Manufacturing Composite Material] A method for manufacturing the composite material 30 (sandwich-structure panel) will be described.

[0064] The manufacturing method of the composite material 30 includes a first lamination step of laminating the intermediate sheet 10 onto the first skin sheet 31A, a second lamination step of laminating the second skin sheet 32A onto the intermediate sheet 10 on the first skin sheet 31A, and a curing step of curing the first skin sheet 31A and the second skin sheet 32A, in this order.

[0065] The manufacturing method of the composite material 30 using the intermediate sheet 10 shown in Fig. 1(A) and the manufacturing method of the composite material 30 using the intermediate sheet 10 shown in Fig. 2(A) have the same procedure for manufacturing the composite material 30, so the following description will be given using as an example the manufacturing method of the composite material 30 using the intermediate sheet 10 shown in Fig. 1(A). When using the intermediate sheet 10 shown in Figs. 1(B)-(D) or the intermediate sheet 10 shown in Figs. 2(B)-(D), the support sheet 12 and separator 15 are peeled off as appropriate before use in manufacturing the composite material 30.

[0066] In the first lamination step, as shown in FIG. 6A, the intermediate sheet 10 is laminated onto the first skin sheet 31A on the mold 25 so that the supporting sheet 14 abuts against it.

[0067] The first lamination step will be described in detail below when the upper surface of the mold 25 has a relatively large curve. In this case, by placing a plurality of first skin sheets 31A, which have been pre-cut to match the shape of the curved surface when developed into a plane, on the mold 25, the first skin sheets 31A can be made to conform neatly to the mold 25.

[0068] Next, the intermediate sheet 10 is placed on the first skin sheet 31A, and the intermediate sheet 10 is pre-cut with a blade such as a knife into a planar shape that easily follows the first skin sheet 31A. The intermediate sheet 10 shown in FIG. 1(C) is easy to handle and pre-cut because it has the support sheet 12 and separator 15. In this case, after peeling off the separator 15, the intermediate sheet 10 is placed on the first skin sheet 31A, and the pre-cutting is performed as described above with the support sheet 12 remaining. The intermediate sheet 10 is then attached to the skin sheet 31A either entirely or locally, as needed.

[0069] When the matrix of the prepreg used for each skin sheet 31A, 32A is a thermosetting resin, the intermediate sheet 10 can be placed on the first skin sheet 31A and bonded to the intermediate sheet 10 by the adhesiveness of the matrix of each skin sheet 31A, 32A, even if the holding sheet 14 of the intermediate sheet 10 itself does not exhibit adhesiveness. If this adhesiveness is weak and the first skin sheet 31A or the intermediate sheet 10 floats from the mold 25 or peels between the first skin sheet 31A and the intermediate sheet 10, for example, the first skin sheet 31A and the intermediate sheet 10 can be locally heated using a heating device 41 (such as a dryer) that emits heated air (see FIG. 6A) to increase the adhesive strength of the first skin sheet 31A. Furthermore, depending on the material of the holding sheet 14, this heating can also exhibit adhesiveness and increase the adhesive strength.

[0070] If the adhesive strength of the first skin sheet 31A or the holding sheet 14 is still insufficient for bonding even after heating using a heating device 41 such as a dryer, the adhesive strength can be supplemented by applying spray glue or the like.

[0071] If the support sheet 12 is stretchable, the holding sheet 14 is also stretchable, so that the intermediate sheet 10 can easily conform to the first skin sheet 31A, and the intermediate sheet 10 can be attached to the first skin sheet 31A while neatly conforming to it. The support sheet 12 is peeled off after the intermediate sheet 10 is attached.

[0072] On the other hand, when manufacturing the composite material 30 using a hand layup method, an infusion method, an RTM (resin transfer) method, a Vacuum Resin Transfer (VaRTM) method, or the like, the skin sheets 31A, 32A are raw reinforced fiber materials that are not impregnated with resin, and therefore are not adhesive. Furthermore, if the skin sheets 31A, 32A are metal plates or resin plates, they also do not have adhesive properties. In these cases, the intermediate sheet 10 can be laminated to each skin sheet 31A, 32A and attached by adhesive force by heating the holding sheet 14 with a heating device 41 such as a dryer to make it adhesive, or by applying spray glue.

[0073] In either case, the presence of the holding sheet 14 maintains the core arrangement to a certain extent, greatly improving workability compared to when the holding sheet 14 is not used. The presence of the holding sheet 14 also improves reworkability, allowing the intermediate sheet 10 to be peeled off and reapplied after it has been applied due to an operational error or a defective shape. Furthermore, the presence of the support sheet 12 further improves reworkability.

[0074] In the second lamination step, as shown in FIG. 6B , a second skin sheet 32A is laminated onto the core layer 11 on the first skin sheet 31A. In the second lamination step, a second skin sheet 32A cut in the same manner as the first skin sheet 31A is attached. In the second lamination step, an intermediate sheet 10 is also attached to the skin sheet 32A, either entirely or locally, as needed. The adhesive strength used for this attachment is the same as that used for the skin sheet 31A. However, when the skin sheets 31A and 32A are thermosetting prepregs, even if the support sheet 12 is on the skin sheet 31A side but not on the skin sheet 32A side, the skin sheet 32A side can often be attached by the adhesive strength of the matrix of the skin sheet 32A, and spray glue can be used as needed.

[0075] When using an intermediate sheet 10 (see FIG. 1(D)) provided with a second retaining sheet 14, it is possible to locally attach the second retaining sheet 14 to the second retaining sheet 14 of the intermediate sheet 10 by locally heating the outer surface of the second skin sheet 32A using a heating device 41 after placing the second skin sheet 32A without applying any adhesive or glue, thereby locally melting the second skin sheet 32A and the second retaining sheet 14.

[0076] As a result, a laminate 30B is obtained in which the intermediate sheet 10 is sandwiched between the pair of skin sheets 31A, 32A. Following the second laminating step, a curing step is performed in which the first skin sheet 31A and the second skin sheet 32A are cured in the laminate 30B.

[0077] When the matrix of the prepreg used for each skin sheet 31A, 32A is a thermosetting resin, the laminate 30B obtained in the second lamination step is sealed using a bagging film in the curing step. The laminate 30B sealed in the bagging film is then heated in an autoclave at a predetermined temperature and pressure (e.g., 130°C, 0.2 MPa) for a predetermined time (e.g., 2 hours). During this heating process, the semi-cured skin sheets 31A, 32A become fully cured skins 31, 32. As a result, a composite 30 (see FIG. 6C) is completed that has been cured into a predetermined shape.

[0078] On the other hand, when the matrix of the prepreg used for each of the skin sheets 31A, 32A is a thermoplastic resin (e.g., polyamide resin, polypropylene resin, or polyether ether ketone resin), in the curing step, after performing pressure-heat press molding or the like, the laminate 30B is cooled in an atmosphere at a temperature lower than the curing temperature of the matrix (e.g., room temperature), thereby curing each of the skin sheets 31A, 32A. As a result, a composite material 30 (see FIG. 6C) is completed that has been cured into a predetermined shape.

[0079] In the manufacturing method of the composite material 30 using the intermediate sheet 10 shown in FIG. 2(A), the composite material 30 shown in FIG. 6(D) is obtained.

[0080] The composite material 30 will now be described. The composite material 30 includes a core material 33, a first skin material 31 laminated on the core material 33, and a second skin material 32 laminated on the side of the core material 33 opposite the first skin material 31 and sandwiching the core material 33 together with the first skin material 31. Each of the skin materials 31, 32 is made of a different material from the core material 33, such as a skin material or a panel material. Fiber-reinforced plastic is used as the material for each of the skin materials 31, 32. As the fiber-reinforced plastic, fiber-reinforced plastic reinforced with carbon fiber can be used. Each of the skin materials 31, 32 may be made of a material such as metal, resin, paper, or wood.

[0081] The fibers of the fiber-reinforced plastic may be any of inorganic fibers, organic fibers, or metal fibers, such as glass fibers, carbon fibers, aramid fibers, polyethylene fibers, polyester fibers, tungsten fibers, steel fibers, boron fibers, hemp fibers, basalt fibers, etc. The matrix of the fiber-reinforced plastic may be any of thermosetting resins or thermoplastic resins, such as polyester resin, epoxy resin, phenolic resin, vinyl ester resin, polyimide resin, polypropylene resin, nylon resin, polyether ether ketone resin, polybutylene terephthalate resin, or bismaleimide resin.

[0082] The composite material 30 can be used as a structural material for transportation machinery such as aircraft, automobiles, bicycles, ships, air mobility, and drones, as well as electrical equipment, electronic equipment, office equipment, home appliances, medical equipment, building materials, and wind power generation structures.

[0083] [Effects of the Present Embodiment] In the present embodiment, a retaining sheet 14 that maintains the arrangement of the numerous segment portions 13 is attached to a core material layer 11 in which the numerous segment portions 13 are arranged two-dimensionally in a planar view. The retaining sheet 14 uses a sheet-like adhesive made of a nonwoven fabric or mesh sheet having numerous voids 4 in a planar view. Therefore, compared to using a sheet-like adhesive that does not have voids 4 in a planar view, it is possible to reduce the amount of adhesive derived from the retaining sheet 14 in the composite material 30, thereby minimizing the impact on the adhesive that bonds the skin materials 31, 32 and the core material 33. According to the present embodiment, an intermediate sheet 10 that allows a good composite material 30 (a highly reliable composite material 30) to be obtained can be provided.

[0084] Even if the density of the retaining sheet 14 is reduced and the amount of resin derived from the retaining sheet 14 is reduced, depending on the molded shape, the adhesive layer of the retaining sheet 14 may wrinkle during stacking, and the retaining sheet 14 may become a factor that leads to a deterioration in the performance of the molded composite material 30.

[0085] Furthermore, in the manufacturing method of the composite material 30, if a support sheet (single-sided adhesive sheet) 12 is provided on one side of the intermediate sheet 10, the adhesive strength of the support sheet 12 must be increased to maintain the alignment of the core material layer 11 when the intermediate sheet 10 is bonded to a shape with a large curvature. However, in this case, the support sheet 12 must be peeled off after bonding the intermediate sheet 10 to the first skin sheet 31A, creating a contradiction: to facilitate peeling, the adhesive strength of the support sheet 12 must be reduced. On the other hand, Patent Document 1 describes an intermediate sheet in which dot-shaped adhesive is applied to the surface of the core material layer 11 (division portion 13). However, dot-shaped adhesive has limited adhesive strength, making lamination workability difficult.

[0086] In contrast, because the intermediate sheet 10 includes the support sheet 12 and separator 15, the intermediate sheet 10 can be easily processed, and the adhesive layer serving as the holding sheet 14 is less likely to wrinkle. Furthermore, because the holding sheet 14 is attached to the core material layer 11 on the side opposite the support sheet 12 (and separator 15 may be provided in some cases), increasing the adhesive strength of the support sheet 12 can be avoided or minimized in order to maintain the alignment of the core material layer 11, thereby minimizing the reduction in ease of peeling of the support sheet 12. The nonwoven fabric used for the holding sheet 14 can be manufactured using methods such as spunbonding, meltblown, and airlaid, allowing for the production of low-basis-weight nonwoven fabrics at low cost. Furthermore, the resin material for the nonwoven fabric can be selected from a variety of thermoplastic resins, and hot-melt nonwoven adhesive sheets can be manufactured using the various manufacturing methods described above. By selecting the resin for the retaining sheet 14, the adhesive strength at the interface between the skin materials 31, 32 and the core material 33 can be improved without impeding the matrix resin of the composite material 30 such as prepreg as the skin material, or it can contribute to the adhesive strength at the interface.

[0087] Furthermore, in this embodiment, when a manufacturing method (such as an infusion molding method or an RTM molding method) is used as the molding method (FRP molding method) for the skin materials 31, 32 of the composite material 30, in which the skin material sheets 31A, 32A and the core material 33 are set in a molding die and then resin is poured into the molding die, the low density of the retaining sheet 14 present at the interface between the skin materials 31, 32 and the core material 33 makes it easy to fill with resin.

[0088] In this embodiment, in the intermediate sheet 10 (intermediate sheet 10 having a half-cut core material layer 11) shown in Figures 2(A)-(D), a retaining sheet 14 is attached to the core material layer 11. The intermediate sheet 10 is placed on the skin sheet 31A without removing the retaining sheet 14. Here, if the retaining sheet 14 is not provided, if the incisions 16 in the core material layer 11 are made deep and the bottoms of the incisions 16 are made extremely thin (i.e., if the ratio of the depth d of the incisions 16 to the thickness D of the core material layer 11 is increased), some of the divisions 13 may become detached, making it difficult to form multiple divisions 13 with such deep incisions 16. Furthermore, even if a thin core material layer 11 is used to form multiple divisions 13 with the incisions 16, it is difficult to use a thin core material layer 11 because some of the divisions 13 may become detached.

[0089] In contrast, in this embodiment, even if the slits 16 are made deeper or a thin core material layer 11 is used in the intermediate sheet 10 shown in Figures 2(A)-(D), the divisions 13 do not separate, and the intermediate sheet 10 can be easily placed on the skin sheet 31A. Furthermore, even if the core material layer 11 breaks at the bottom of the slits 16, the retaining sheet 14 maintains the arrangement of the multiple divisions 13. Therefore, it is possible to perform half cuts with slits 16 deep enough that they easily break at their bottoms, thereby improving the ability of the intermediate sheet 10 to conform to a three-dimensional shape. It is also possible to form multiple divisions 13 using the slits 16 in the thin core material layer 11.

[0090] In this embodiment, the intermediate sheet 10 shown in Figures 1(B)-(C) and the intermediate sheet 10 shown in Figures 2(B)-(C) each have a support sheet 12 and / or a separator 15. If the intermediate sheet 10 were made up of only the core material layer 11 and the holding sheet 14, the high flexibility of the holding sheet 14 would make the intermediate sheet 10 difficult to handle and would also make pre-cutting and other processing on the first skin sheet 31A difficult. In contrast, if the intermediate sheet 10 has a support sheet 12 and / or a separator 15, the intermediate sheet 10 is easier to handle and can easily be pre-cut and other processing on the first skin sheet 31A.

[0091] The present invention is applicable to intermediate sheets and the like used in the manufacture of composite materials.

[0092] 4 gap 10 intermediate sheet 11 core material layer 12 support sheet 13 division portion, division body 14 holding sheet 15 separator 16 gap, notch 30 composite material 31, 32 skin material 33 core material

Claims

1. An intermediate sheet used in the manufacture of a composite material, comprising: a core material layer, which is a layer used for the core material of the composite material, and in which a large number of segments separated from one another are arranged two-dimensionally in a planar view; and a retaining sheet, which is attached to the core material layer and maintains the arrangement of the large number of segments, and the retaining sheet uses a sheet-like adhesive made of a nonwoven fabric or mesh sheet having a large number of voids in a planar view.

2. The intermediate sheet according to claim 1, further comprising a support sheet attached to the core material layer on the side opposite to the holding sheet.

3. The intermediate sheet according to claim 2, wherein the support sheet is a sheet material having a greater bending resistance than the holding sheet.

4. The intermediate sheet according to claim 1, further comprising a separator covering the surface of said holding sheet opposite said core material layer.

5. The intermediate sheet according to claim 4, wherein the separator is a sheet material having a bending resistance greater than that of the holding sheet.

6. A method for manufacturing a composite material by carrying out a first laminating step of laminating an intermediate sheet according to any one of claims 1 to 5 onto a first skin sheet so that the retaining sheet abuts against the first skin sheet; a second laminating step of laminating a second skin sheet onto the intermediate sheet to obtain a laminate in which the first skin sheet, the intermediate sheet, and the second skin sheet are laminated in this order; and a curing step of curing the first skin sheet and the second skin sheet in the laminate.

7. A method for producing a composite material according to claim 6, wherein after the first lamination step and before the second lamination step, a step of locally heating the retaining sheet is carried out to locally attach the core material layer to the first skin sheet.

Images