JP5533320B2 - Sandwich structure - Google Patents

Description

  The present invention relates to a sandwich structure having a core material and a skin material provided on both surfaces of the core material, and more particularly to a sandwich structure in which the core material and the skin material are made of fiber reinforced resin.

  As a resin molded body reinforced with reinforcing fibers and having voids formed therein, a sandwich structure composed of a dense skin layer having almost no voids and a core layer having voids is known (for example, Patent Document 1: Special). (Kaihei 4-232047, Patent Document 2: JP-A-2002-18916, etc.). The voids in the core layer are formed by springback of reinforcing fibers.

  Patent Document 1 discloses that the amount of the fiber of the skin material (volume%) is less than that of the core material, thereby eliminating the expansion of the skin material, and increasing the melt viscosity to fiber reinforced molding of the core material. It suppresses the lifting of fibers on the body surface and improves the surface appearance. Patent Document 1 does not describe any elastic modulus of the skin material, and the strength and elastic modulus of the sandwich molded body described in the examples are also low.

  Patent Document 1 describes that glass fiber or rock wool is used as the reinforcing fiber for the skin material. However, glass fiber and rock wool have a sufficient bending elastic modulus for the skin material at a normal blending amount. Cannot be too high.

  Patent Document 2 relates to a molded body composed of a skin layer that hardly includes voids, and a core layer that has a high void ratio and has a beam structure in which reinforcing fibers are entangled with each other. In Patent Document 2, using a movable mold, a skin layer is first formed by injection molding one type of reinforcing fiber-containing resin composition, and then the mold is expanded and the core portion is expanded by a springback. Although the method is described, there is no description about how to specifically adjust the strength and elastic modulus of the skin layer. Further, although it is possible to provide a skin material on the surface of the skin layer, there is no description about the strength and elastic modulus of the skin material.

Japanese Laid-Open Patent Publication No. 4-232047 JP 2002-18916 A

  An object of the present invention is to provide a sandwich structure having a skin material with a high flexural modulus and a high rigidity and light weight.

The sandwich structure of the present invention is a sandwich structure having a core material and a skin material provided on both surfaces of the core material. The core material and the skin material have reinforcing fibers randomly in the matrix resin. In the sandwich structure made of dispersed fiber reinforced resin, the reinforcing fiber in the core material is PAN-based carbon fiber, the content is 20 to 80 wt%, and the reinforcing fiber in the skin material is pitch-based carbon fiber. And the content rate is 30 to 80 wt%, the bending elastic modulus of the skin material is 10 GPa or more, and the apparent density of the core material is 0.2 to 1.2 g / cm ³ or more. Is.

  It is preferable that the tensile elastic modulus in the fiber axis direction of the reinforcing fiber of the core material is less than 400 GPa, and the tensile elastic modulus in the fiber axis direction of the reinforcing fiber of the skin material is 400 GPa or more.

  The reinforcing fibers of the core material are preferably carbon fibers having a fiber length of 1 to 50 mm.

  The reinforcing fiber of the skin material is preferably liquid crystal pitch-based carbon fiber.

  It is preferable that the matrix resin of the core material and the skin material is the same thermoplastic resin.

  It is preferable that the skin material has a porosity of less than 10 vol%, and the core material has a porosity of 10 to 80 vol%.

  The sandwich structure of the present invention has a structure in which the properties of the core material and the skin material using the reinforcing fiber and the matrix resin are combined, that is, the skin material has a high bending elastic modulus, and the apparent density of the core material. By reducing the thickness of the sandwich structure, the allowable range of the thickness of the sandwich structure is widened compared to the conventional structure, and the sandwich structure is lightweight and highly rigid.

It is sectional drawing which shows an example of the manufacturing method of a sandwich structure. It is sectional drawing which shows the example of another manufacturing method of a sandwich structure.

  The sandwich structure of the present invention has a core material and a skin material each made of a fiber reinforced resin. First, the matrix resin and the reinforcing fiber constituting the core material will be described, and then the manufacturing method of the skin material and the sandwich structure will be described.

[Matrix resin for core material]
A thermoplastic resin is suitable as the matrix resin for the core material. Examples of the thermoplastic resin include polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate resins, polyethylene naphthalate resins, polybutylene terephthalate resins, and polyester resins, polystyrene resins, Vinyl resin, poly (meth) acrylate resin, polycarbonate resin, polyphenylene sulfide resin, polyamide resin, polyimide resin, polyacetal resin, polyether ether ketone (PEEK) resin, polyether sulfone (PES) resin, polyether imide (PEI) Resin, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, ABS resin, copolymer resin such as AS resin, or modified resins thereof, or EPM, And thermoplastic elastomers such as PDM, include the use alone or in combination of two or more. Moreover, you may use a well-known additive for a resin composition as needed.

  Among these, polyester resins, polyolefin resins, and polyamide resins are preferable from the viewpoints of cost, handleability, performance, and the like.

[Reinforcing fiber for core material]
As the reinforcing fiber of the core material, inorganic fibers such as carbon fiber, glass fiber, silicon carbide fiber, metal fiber and boron fiber, and short fibers of organic fiber such as aramid fiber and polyamide fiber are preferable. In the case of resin fibers, it is important that the melting point and softening point of the reinforcing fibers are higher than the melting point and softening point of the matrix resin.

  The reinforcing fiber of the core material has a tensile modulus of less than 400 GPa in the fiber axis direction, and it is easy to make the apparent density of the molded body randomly dispersed at a predetermined blending amount in the matrix resin within a predetermined range. Therefore, it is preferable that the pressure is 10 GPa or more for securing rigidity necessary for suppressing deformation due to compression or the like. The tensile elastic modulus of the reinforcing fiber of the core material is more preferably 50 to 300 GPa.

  The diameter of the reinforcing fiber is preferably 1 to 50 μm, and more preferably 3 to 30 μm from the viewpoint of strength, handleability, availability, and the like. The fiber length of the short fibers is preferably 1 mm to 50 mm, particularly preferably 5 to 30 mm in consideration of fiber entanglement, ease of handling, etc. in addition to the fiber material and required performance.

  The content of the reinforcing fiber in the core material is 20 to 80 wt%, preferably 40 to 70 wt%. When the reinforcing fiber content is less than 20 wt%, the strength is insufficient and the moldability is insufficient due to resin flow, and the springback is also weak. If the reinforcing fiber content is more than 80 wt%, the adhesiveness between the reinforcing fibers tends to be insufficient due to insufficient resin, and the moldability, strength, and elastic modulus are lowered.

[Matrix resin for skin material]
The matrix resin for the skin material may be a thermosetting resin, but is preferably a thermoplastic resin. As the thermoplastic resin, those described in the description of the matrix resin of the core material are used.

  If the same matrix resin is used for the core material and the skin material, or if they are highly compatible, or if they contain components (compatibility agents) that are compatible with each other's resin, Even if an adhesive layer is not provided between the core material and the skin material, the core material and the skin material are sufficiently bonded. The core material may be molded and the core and skin material may be laminated and integrated simultaneously by heating. In this case, the melting point or softening point of the matrix resin of the core material is the melting point of the matrix resin of the skin material. Or it is preferable that a softening point is the same or substantially the same. If the same resin is used for the core material and the skin material, it becomes easy to select the production conditions such as raw material preparation and molding temperature.

[Reinforcing fiber for skin material]
Examples of the reinforcing fiber for the skin material include carbon fibers, glass fibers, silicon carbide fibers, metal fibers, boron fibers and other inorganic fibers, aramid fibers, polyamide fibers and other organic fibers. Since the elastic modulus of the randomly dispersed molded body needs to be 10 GPa or more, the tensile elastic modulus in the fiber axis direction is preferably 400 GPa or more. Furthermore, in the present invention, when the skin material and the core material are integrally formed, the skin material is molded without a large spring back during the spring back molding of the core material. When the reinforcing fibers are broken, the springback function is reduced and a low porosity is required for forming a highly rigid sandwich structure. For these reasons, pitch-based or PAN-based carbon fibers having a tensile modulus of 400 GPa or more in the fiber axis direction are suitable as the reinforcing fibers of the skin material, and liquid crystal (mesophase) pitch-based carbon fibers are particularly suitable.

  The fiber length of the reinforcing fiber of the skin material is preferably 1 to 50 mm, particularly preferably 5 to 30 mm. The content of the reinforcing fiber in the skin material is 30 to 80 wt%, preferably 40 to 70 wt% in order to ensure sufficient strength and rigidity, and to ensure moldability and good appearance.

  The porosity of the skin material is preferably less than 10% in order to exhibit sufficient mechanical properties in the sandwich structure. Moreover, it is preferable that the porosity of the skin material is less than 5% because the rigidity and strength of the skin material are further improved and the mechanical properties as a sandwich structure are further improved.

[Manufacturing method of core material, skin material and sandwich structure and apparent density of core material]
The sandwich structure of the present invention can be produced by separately producing a core material and a skin material and bonding them using an adhesive. It can also be produced by heat-sealing a separately produced skin material and core material. Usually, when an adhesive is used, since it is necessary to add an additional process and prepare an adhesive separately, in the present invention, it is preferable to manufacture by heat fusion.

First, as a method for producing a core material, a mat-like molded body containing reinforcing fibers for a core material and a matrix resin is heated and pressurized to a temperature above the softening point or melting point of the matrix resin, and then the pressure is released. A spring back method is preferred in which the porous fiber is expanded by a spring back that is intended to return to the original state when the residual stress of the reinforcing fiber is released. Reinforcing fibers are randomly dispersed in the core material. The apparent density of the core material is 0.2 to 1.2 g / cm ^3, preferably 0.4 to 1.0 g / cm ³ . When the apparent density of the core material is smaller than 0.2 g / cm ³ , the sandwich structure has insufficient strength, and when it is larger than 1.2 g / cm ³ , the apparent density of the sandwich structure becomes excessively large. The rigidity becomes small. Moreover, when said apparent density is considered, the porosity in a core material is about 10-80 vol%.

  When a mat mat-shaped molded body composed of reinforcing fibers and matrix resin fibers is used as the mat-shaped molded body for the core material, the matrix resin fibers are already mixed with the reinforcing fibers, and are easily reinforced when melted. This is preferable because it allows the impregnation process to be simplified. Further, in terms of adhesion in heat-sealing, the reinforcing fiber between the skin material and the core material is likely to be entangled, and the adhesive property between the skin material and the core material as a sandwich structure is excellent, which is preferable.

  In the present invention, a mat-like molded body containing a reinforcing fiber for a core material and a matrix resin for the core material or a product obtained by heat-pressing a mat-shaped molded body is used for reinforcing fibers for the skin material and for the skin material. A mat-like molded body containing a matrix resin or a sandwich-like laminated body sandwiched by using a hot-press molded mat-shaped molded body, and the laminated body is heated and made porous by a springback method similar to the above. A sandwich structure can be manufactured by simultaneously stacking and integrating the core material and the skin material. According to this method, the core material and the skin material can be firmly integrated without using an adhesive.

Further, in the present invention, a sandwich structure may be manufactured by sandwiching a porous core material manufactured in advance by a springback method with a skin material separately manufactured in advance and heating and pressing.
In any of these cases, as a method for producing the skin material, the reinforcing fiber for the skin material and the matrix resin are made into a mat-like molded body, and the mat-like molded body is heated and pressurized to reinforce the fiber. And a method of forming a fiber-reinforced molded body in which is randomly dispersed.

  As a papermaking method mentioned as a preferable manufacturing method of the reinforced fiber and matrix resin mat-shaped molded body for forming the core material and the skin material, the matrix resin fiber and the reinforced fiber are mixed and non-woven mat-shaped A method for obtaining a molded body is preferred. Examples of the blending method include a wet method and a dry method. As a method for producing a mat-like molded body for a core material, a sufficiently large basis weight can be obtained, and since many fibers in the thickness direction are contained and a high spring back function is provided, a card method, an airlaid type, etc. A dry method is preferred. As a method for producing a mat-like molded body for a skin material, a wet method or a dry method such as an airlaid method that can be easily molded with little fiber breakage is preferable. A fiber reinforced resin in which reinforcing fibers are randomly dispersed in a matrix resin is also produced from a nonwoven mat-like molded body obtained by any method.

Basis weight of the core material for a mat-like molded product is preferably 1000~4000g / ^{m 2,} the basis weight for the skin material mat shaped body is preferably 100 to 2000 g / ^{m 2.}

[Specific examples of molding methods]
An example of the method for forming a sandwich structure of the present invention is shown in FIG. As shown in FIG. 1 (a), on both surfaces of the core mat-shaped molded body 1 manufactured by the papermaking method using the reinforcing fiber and the resin fiber, the skin manufactured by the papermaking method using the reinforcing fiber and the resin fiber. A fiber reinforced molded body 2 obtained by heat-press molding a mat-shaped molded body for a material is laminated, and this fiber reinforced molded body 2 / mat-shaped molded body 1 (three sheets in the figure) / fiber reinforced molded body. The plate-like bodies 3 are overlapped on both surfaces of the laminated body 2 and inserted between the hot press panels 4 and heated until the resin fibers (matrix resin) of the core-like mat-like molded body 1 are melted.
Here, the plate-like body 3 is used for ensuring the smoothness of the molding surface and assisting the uniformity of the molding pressure. As long as the deformation is small, it may be made of resin. In consideration of releasability from the molded body, the surface may be coated with a fluororesin or silicon resin, or may be treated with a release agent.

  After heating until the matrix resin is melted, the upper heating press panel 4 is pushed down or the lower heating press panel 4 to impregnate the molten matrix resin between the reinforcing fibers of the mat-shaped molded body for the skin material. And pressurizing at a pressure that does not cause damage to the reinforcing fiber for core material. As a result, as shown in FIG. 1 (b), the mat-like molded body 1 becomes the molten core material portion 5. Further, the core material portion 5 and the fiber reinforced molded body 2 are fused.

  Next, in the state where the matrix resin for core material is melted, the pressurization by the heating press panels 4 and 4 is released. As a result, the molten core material portion 5 is expanded by the springback of the reinforcing fiber to become the expanded core material 6. In general, the mat-like molded body 1 manufactured by the papermaking method has a strong spring back because the reinforcing fibers are randomly dispersed in a state close to a monofilament (single fiber), so that the molten core material part expands greatly. Thus, the expanded core member 6 having a gap is formed (FIG. 1 (c)).

  Next, the expanded core material 6, the fiber reinforced molded body 2 and the plate-shaped body 3 are overlapped and inserted between the cooling press panels 7 as shown in FIG. After pressurizing and cooling under the remaining conditions and shaping to a predetermined thickness, the plate-like body 3 is removed (FIG. 1 (e)). Thereby, the sandwich structure 8 which consists of the core material 8a and the skin material 8b is obtained. The core material 8a is derived from the expanded core material 6 and has a predetermined gap. The skin material 8b is derived from the fiber reinforced molded body 2, and is fixed to the core material 8a.

  When the matrix resin of the fiber reinforced molded body 2 and the core material are fused as shown in FIG. 1, the matrix resin of the fiber reinforced molded body 2 and the matrix resin of the mat-shaped molded body for the core material have the same composition. It is preferable to use this resin.

  In addition, although the fiber reinforced molded object 2 may be a single layer, in order to obtain predetermined | prescribed thickness, what laminated | stacked two or more may be sufficient. The thickness of the skin material 8b varies depending on the use of the sandwich structure, but is generally in the range of 0.03 to 1 mm.

  The matrix resin in the mat-like molded body for the core material is impregnated between the reinforcing fibers at the time of pressurization, but at the same time, the matrix resin oozes out to the interface with the fiber reinforced molded body 2 and is in the fiber reinforced molded body 2. Together with the melting of the two, both are firmly fused. Further, some of the reinforcing fibers in the core mat-shaped molded body also enter the fiber reinforced molded body 2, and the reinforcing fiber in the fiber reinforced molded body 2 is also formed from the mat-shaped molded body for the core material. By entering the core material portion 5, an anchor effect is produced, and the core material 8 a and the skin material 8 b are firmly bonded.

  Furthermore, the surface of the melted core material portion 5 expands while being constrained by the fiber reinforced molded body 2 for the skin material, and the fiber reinforced molded body 2 hardly expands. Does not occur, and the appearance of the molded product is improved.

  On the other hand, the sandwich structure of the present invention can also be manufactured by the double belt conveyor type continuous press device 18 that continuously performs the heating, pressurizing, pressure releasing, and cooling steps shown in FIG. In the double belt conveyor type continuous press 18, a pair of endless belts 19 are stretched between rotating drums 20 and 21. The roller chains 23, 24, 25 are installed so as to be in contact with the back side of the endless belts 19, 19 at the clamping portion. Each of the roller chains 23 to 25 can press the endless belt 19 by a hydraulic ram 22. By controlling the hydraulic ram 22, the distance between the endless belts 19, 19 and the clamping pressure between them are controlled. A heating panel 26 is installed inside the roller chains 23 and 24, and a cooling panel 27 is installed inside the roller chain 25.

  The interval between the endless belts 19, 19 is gradually narrowed until reaching the roller chain 24, and then gradually increased until reaching the rotating drum 21. The mat-shaped molded body 28 for the skin material is laminated along the rotary drums 20 and 20 on both surfaces of the mat-shaped molded body 1 for the core material manufactured by the papermaking method using the reinforcing fibers and the resin fibers. This laminate is heated by the roller chain 23 until the matrix resin of the mat-like molded body 1 is melted. Thereafter, the molten matrix resin is impregnated between the reinforcing fibers of the mat-like molded body 1 by being pressurized by the roller chain 24. Thereafter, the interval between the endless belts 19 and 19 gradually increases until the endless belt 19 reaches the rotating drum 21 from the roller chain 24. Therefore, the molten core material portion derived from the mat-shaped molded body 1 expands immediately after passing through the roller chain 24. Thereafter, the laminated body is cooled by the roller chain 25, passes through the rotating drum 21, leaves the endless belts 19, 19, and the sandwich structure 8 is continuously formed. Reference numeral 9 denotes a core material having a gap.

  When a double belt conveyor type continuous press is used, the pair of endless belts 19 and 19 serve as plate-like bodies. As the endless belt 19, a metal belt such as a steel belt is usually used, but it may be made of resin as long as it can withstand the heating temperature. In consideration of releasability with the sandwich structure, coating using a fluororesin, silicon resin, or the like, or a release agent treatment may be performed.

  Also in the method of FIG. 2, the matrix resin in the mat-shaped molded body 1 is melted when the roller chain 24 is pressurized, and the core material 9 and the skin are combined with the molten matrix resin of the mat-shaped molded body 28 for the skin material. A sandwich structure 8 in which the material (fiber-reinforced molded body 2) is firmly fused is obtained. In addition, since the molten core material part is uniformly expanded between the roller chains 24 and 25 while being constrained by the endless belts 19 and 19, the sandwich structure 8 having good mechanical properties and appearance can be obtained. . (In FIG. 2, the mat-shaped molded body 28 for the skin material is in a state before being heated and pressurized, and the resin fibers that are the matrix resin are in an unmelted state.)

According to the present invention, improvement in mechanical properties and light weight benefits utilizing the specific stiffness 20GPa / (g / cm ³⁾ or more, for example 20~100GPa / (g / cm ³⁾ about the sandwich structure is obtained.

  Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples. In the following Examples and Comparative Examples, the physical property measurement method and the thickness accuracy evaluation method are as follows.

(1) Flexural properties The flexural strength and flexural modulus of the skin material and sandwich structure were measured using a universal material testing machine (UH-10 manufactured by Shimadzu Corporation). The skin material was measured by preparing a sample having a thickness of 2 mm. The prepared sample was cut into a predetermined size based on JIS-K7074, and then measured by a four-point bending test with a load cell of 100 kN and 500 kN at a crosshead speed of 5 mm / min.

(2) Apparent density and specific rigidity The apparent density of the sandwich structure was determined by cutting the prepared sandwich structure into a size of 10 cm x 10 cm, and then measuring the weight, thickness, length and width by digital calipers to 0.1 mm. The accuracy was measured and calculated. The specific rigidity was determined by dividing the value of the flexural modulus (GPa) in the sandwich structure bending test by the apparent density calculated by the previous method.

(3) Porosity The porosity of the fiber reinforced molded product was calculated by the following formula.

Theoretical density = reinforcing fiber weight / 100 × density of reinforcing fiber
+ (1−reinforcing fiber weight / 100) × density of matrix resin Porosity (%) = (1−apparent density / theoretical density) × 100

(4) Thickness accuracy evaluation method A sandwich structure was manufactured with a target thickness of 4.0 mm, and the difference between the actual thickness of the molded body and the target thickness of 4.0 mm was within ± 0.3 mm. What was larger than 0.3 mm was evaluated as x.

[Example 1]
PAN-based carbon fiber (trade name “Pyrofil TR50S”, manufactured by Mitsubishi Rayon, tensile elastic modulus 230 GPa, 6 mm cut fiber, density 1.9 g / cm ³ ) is used for the core material, and copolymer polyester fiber is used as the matrix resin. (Trade name “N701Y”, manufactured by Kuraray Co., Ltd., 5 mm cut fiber, melting point 130 ° C., density 1.38 g / cm ³ ) was used. After blending 60% by weight of the reinforcing fibers and 40% by weight of the matrix resin fibers, using a airlaid nonwoven fabric production apparatus (manufactured by Oji Kinocross Co., Ltd.), a mixed mat-like molded body (hereinafter abbreviated as “mat A”) having a basis weight of 600 g / m ² did.

For the skin material, pitch-based carbon fiber (trade name “DIALEAD 6371T”, manufactured by Mitsubishi Plastics, tensile elastic modulus 640 GPa, 6 mm cut fiber, density 2.1 g / cm ³ ) is used as the reinforcing fiber, and the matrix resin is shared. Polymerized polyester fiber (trade name “N701Y”, manufactured by Kuraray Co., Ltd., 5 mm cut fiber, melting point 130 ° C., density 1.38 g / cm ³ ) was used. After blending 60% by weight of the reinforcing fibers and 40% by weight of the matrix resin fibers, a mixed mat-shaped molded body (hereinafter abbreviated as Mat B) having a basis weight of 1000 g / m ² using an airlaid nonwoven fabric production apparatus (manufactured by Oji Kinocross). It was.

  Thickness 3 by stacking four mats A, forming a melt press at a temperature of 200 ° C. and a clearance of 3.4 mm with a pressurization holding time of 5 minutes, then moving to a cooling press and cooling under a pressurization condition with a clearance of 3.0 mm. A core material of 0.0 mm (carbon fiber length 3 to 50 mm: 50% by weight or more) was produced. Further, the mat B is melt press-molded at a temperature of 280 ° C. and a clearance of 0.5 mm with a pressurization holding time of 5 minutes, and then cooled under a pressurizing condition to thereby form a skin material having a thickness of 0.5 mm (carbon fiber length: 3-50 mm: 50% by weight or more). The evaluation results of these materials are shown in Table 1. Furthermore, the skin material is superposed on both surfaces of the core material, and a pair of upper and lower heating presses are used to perform melt press molding at a temperature of 200 ° C. and a clearance of 3.0 mm with a pressurization holding time of 5 minutes, and then spread to a clearance of 4.0 mm. A sandwich structure having a thickness of 4.0 mm was produced by cooling. The evaluation results of this structure are shown in Table 1.

[Example 2]
In Example 1, the resin fiber of the matrix resin used for the core material is a melt-spun fiber of polypropylene resin (trade name “NOVATEC PP FL6H”, manufactured by Nippon Polypro Co., Ltd., melting point 150 to 165 ° C., density 0.9 g / cm ³ ) A core material, a skin material, and a sandwich structure were produced under the same conditions as described above. These evaluation results are shown in Table 1.

[Example 3]
In Example 1, a core material, a skin material, and a sandwich structure were produced under the same conditions except that the number of mats A used for the core material was three, and the evaluation results are shown in Table 1.

[Example 4]
In Example 1, the resin fiber of the matrix resin used for the skin material is a polypropylene resin (trade name “NOVATEC PP FL6H”, manufactured by Nippon Polypro, melting point 150 to 165 ° C., density 0.9 g / cm ³ ), and the mat B A core material, a skin material, and a sandwich structure were produced under the same conditions except that the basis weight was 800 g / m ² . These evaluation results are shown in Table 1.

[Comparative Example 1]
In Example 1, a core material, a skin material, and a sandwich structure were produced under the same conditions except that the amount of the reinforcing fiber used for the core material was 90% by weight. The evaluation results are shown in Table 1. In Comparative Example 1, the core material and the sandwich structure expand without being able to suppress the spring back due to insufficient resin when taken out from the press apparatus, and the thickness of the sandwich structure greatly exceeds the target 4.0 mm. As a result.

[Comparative Example 2]
In Example 1, a core material, a skin material, and a sandwich structure were produced under the same conditions except that the amount of the reinforcing fiber used for the core material was 10% by weight. These evaluation results are shown in Table 1. In Comparative Example 2, a flow caused by excessive resin occurs during the press molding of the sandwich structure, and the spring back becomes insufficient due to insufficient reinforcing fibers, resulting in a thickness of less than 4.0 mm. It was.

[Comparative Example 3]
In Example 1, the core material, the skin material, and the sandwich structure were manufactured under the same conditions except that the basis weight of the mat A used for the core material was 400 g / m ² and the number of laminated layers at the time of press molding was one. . The evaluation results are shown in Table 1.

[Comparative Example 4]
In Example 1, a core material, a skin material, and a sandwich structure were produced under the same conditions except that the amount of the reinforcing fiber used in the skin material was 20% by weight. The evaluation results are shown in Table 1.

[Comparative Example 5]
Except that the reinforcing fiber used for the skin material in Example 1 was a PAN-based carbon fiber (trade name “Pyrofil TR50S”, manufactured by Mitsubishi Rayon, tensile elastic modulus 230 GPa, 6 mm cut fiber, density 1.9 g / cm ³ ). A core material, a skin material, and a sandwich structure were produced under the same conditions. The evaluation results are shown in Table 1.

As shown in Table 1, all of Examples 1 to 4 have high flexural modulus and specific rigidity, and good thickness accuracy. On the other hand, Comparative Examples 1-5 have low bending elastic modulus and specific rigidity. In Comparative Examples 1 and 2, the thickness accuracy of the sandwich structure is low. In Comparative Example 3, the apparent density of the core material is as low as 0.1 g / cm ³ and the specific rigidity is remarkably low.

DESCRIPTION OF SYMBOLS 1 Mat-shaped molded object for core materials 2 Fiber-reinforced molded object for skin materials 3 Plate-shaped body 4 Heating press board 5 Core material part in a molten state 6 Expanded core material 7 Cooling press board 8 Sandwich structure 8a, 9 Core material 8b Skin Material 19 Endless belt 23, 24, 25 Roller chain 26 Heating board 27 Cooling board 28 Mat-shaped molded body for skin material

Claims (6)

A sandwich structure having a core material and a skin material provided on both surfaces of the core material,
The core material and the skin material are sandwich structures made of fiber reinforced resin in which reinforcing fibers are randomly dispersed in a matrix resin.
The reinforcing fiber in the core material is PAN-based carbon fiber, the content is 20 to 80 wt%, the reinforcing fiber in the skin material is pitch-based carbon fiber, and the content is 30 to 80 wt%. Yes,
The flexural modulus of the skin material is 10 GPa or more,
A sandwich structure having an apparent density of the core material of 0.2 to 1.2 g / cm ³ or more.   The sandwich according to claim 1, wherein the tensile elastic modulus in the fiber axis direction of the reinforcing fiber of the core material is less than 400 GPa, and the tensile elastic modulus in the fiber axis direction of the reinforcing fiber of the skin material is 400 GPa or more. Structure.   3. The sandwich structure according to claim 1, wherein the reinforcing fiber of the core material is a carbon fiber having a fiber length of 1 to 50 mm.   The sandwich structure according to any one of claims 1 to 3, wherein the reinforcing fiber of the skin material is a liquid crystal pitch-based carbon fiber.   The sandwich structure according to any one of claims 1 to 4, wherein the core resin and the matrix resin of the skin material are the same thermoplastic resin.   The sandwich structure according to any one of claims 1 to 5, wherein the skin material has a porosity of less than 10 vol%, and the core material has a porosity of 10 to 80 vol%.

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