KR102720727B1 - Sandwich composite and manufacturing method thereof - Google Patents

Abstract

According to one embodiment of the present invention, a sandwich composite includes a core layer made of a foam material and a skin layer made of a fiber aggregate formed by needle-punching two or more fibers and laminated on both sides of the core layer, wherein the core layer and the skin layer are impregnated with a matrix resin and then cured, and by laminating the fibers through a needle-punching process, the interfacial adhesive force between different materials is improved due to changes in the surface roughness of the fibers, and the composite has excellent rigidity and lightweight characteristics, and due to the physical bonding of the skin layer formed through the needle-punching process, it has the effect of improving process convenience in a sandwich structure lamination and resin injection process.

Description

{SANDWICH COMPOSITE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a sandwich composite used as a lightweight material, and more specifically, to a sandwich composite using a material applied with a needle punch process as a skin layer.

Conventionally, composites using reinforcing fibers such as carbon fibers or glass fibers are formed by impregnating and hardening reinforcing fibers in a matrix resin, and are used in various fields because they have excellent mechanical properties and are light in weight. Composites using reinforcing fibers such as carbon fibers or glass fibers are light in weight and have excellent strength, but they are usually low in rigidity because it is difficult to secure thickness.

To solve this problem, it is common to increase the number of fiber layers or insert structures, and among them, sandwich structures are used as one of the methods to increase rigidity by securing thickness without significantly increasing weight.

This sandwich structure is a structure in which different materials are laminated in the order of a skin layer on the outer surface, a core layer on the inner surface, and then a skin layer on the outer surface again, so that the individual properties of the materials constituting the skin layer and the core layer can be obtained. In addition, in the sandwich structure, the skin layer of the fiber composite material has the function of providing strength, and the core layer utilizes a foam material that is easy to secure thickness and has low density, so the sandwich structure has high strength and lightweight characteristics at the same time.

Due to the structural characteristics of these sandwich composites, sandwich composites are used in a variety of industrial fields, and the strength and weight of sandwich composites are designed in a variety of fields, such as internal combustion engine vehicles, electric and hydrogen vehicles, drones, and wind turbine blades, and are actively utilized in fields where increased energy efficiency due to weight reduction is required.

In addition, the skin layer composed of reinforcing fibers and the core layer composed of foam material are impregnated with a polymer resin such as epoxy resin as a matrix resin and hardened, thereby forming a bond between different materials. More specifically, the skin layer and the core layer are bonded using a resin infusion method, which is one of the methods of utilizing prepreg material in the skin layer or impregnating the resin.

However, sandwich composites using prepreg have poor adhesive strength between different materials due to insufficient resin content (RC), which causes problems in easy detachment by external force. To compensate for this, epoxy films are inserted between the skin and the core, but this method also has the problem of not securing sufficient resin content.

Korean Patent Publication No. 10-2174302

The present invention has been made to solve the above-described problems, and the problem to be solved by the present invention is to provide a sandwich composite and a method for manufacturing the same, which improves the mechanical strength by changing the roughness and density on the surface by applying a needle punching process to a plurality of fiber aggregates.

The above and other objects and advantages of the present invention will become apparent from the following description of preferred embodiments.

The above object is achieved by a sandwich composite including a core layer composed of a foam material and a skin layer formed of a fiber aggregate by needle-punching two or more fibers, which is laminated on both sides of the core layer, and the core layer and the skin layer are impregnated with a matrix resin and then cured.

Preferably, the thickness ratio of the fiber assembly before and after needle punching may satisfy the following mathematical expression 1.

(Mathematical formula 1)

1.25≤Fiber aggregate thickness after needle punching/Fiber aggregate thickness before needle punching≤6

Preferably, the area ratio of the hole formed by needle punching of the skin layer may be 0.007 to 3.5% per 1 cm ² of the skin layer.

Preferably, the X-axis and Y-axis spacing of the holes formed by needle punching of the skin layer can be 1.5 to 5 mm.

Preferably, the diameter of the hole formed by needle punching of the skin layer may be 65 to 300 μm.

Preferably, the density of the skin layer may be 1.2 to 1.6 g/cc, and the density of the core layer may be 0.08 to 0.2 g/cc.

Preferably, the fibers constituting the fiber assembly may be at least one selected from carbon fibers, glass fibers, aramid fibers, oxyfan fibers, and hybrid fibers.

Preferably, the form of the fibers constituting the fiber assembly may be at least one selected from a woven fabric, a nonwoven fabric, a knitted fabric, a UD fabric, and a multi-axial fabric.

Preferably, the adhesion between the skin layer and the core layer may be 95 to 120 gf/cm ² .

Preferably, the flexural modulus of the sandwich composite may be 3 GPa or greater.

In addition, the above object is achieved by a method for manufacturing a sandwich composite, which comprises a first step of laminating two or more fibers, a second step of manufacturing a fiber aggregate forming a skin layer by needle punching the laminated fibers, a third step of laminating skin layers on both sides of a core layer composed of a foam material, a fourth step of injecting and impregnating a matrix resin into the laminated core layer and skin layer, and a fifth step of manufacturing a sandwich composite by heat curing after the fourth step.

Preferably, the first step may be to laminate the fibers by arranging them in a predetermined angle.

According to a sandwich composite and a method for manufacturing the same according to one embodiment of the present invention, by laminating fibers through a needle punching process, the roughness and density of the fiber surface are changed, thereby improving the interfacial adhesiveness between different materials, preventing the fiber fabric arrangement that may occur during the manufacturing process of the sandwich composite, and having excellent rigidity and lightweight characteristics, etc.

In addition, it has the effect of improving the convenience of laminating sandwich structures and the process convenience in the resin injection process due to the strong physical bonding of the skin layer formed by the needle punching process.

However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

FIG. 1a is a configuration diagram of a sandwich composite according to one embodiment of the present invention.
FIG. 1b is a drawing illustrating a process of needle punching a fiber aggregate of a sandwich composite according to one embodiment of the present invention.
FIG. 2 is a drawing explaining a method for manufacturing a sandwich composite according to one embodiment of the present invention.
FIG. 3 is a photograph showing an actual product of a sandwich composite according to one embodiment of the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

In order to clearly express various layers and regions in the drawings, the thickness is enlarged and shown. Similar parts are designated by the same drawing reference numerals throughout the specification. When a part such as a layer, film, region, or plate is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, this specification, including its definitions, will control. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

FIG. 1a is a diagram illustrating a configuration of a sandwich composite according to one embodiment of the present invention, and FIG. 1b is a diagram explaining a process of needle punching a fiber aggregate of a sandwich composite according to one embodiment of the present invention.

Referring to FIGS. 1A and 1B, a sandwich composite according to one embodiment of the present invention includes a core layer (120) composed of a foam material and a skin layer (110) composed of a fiber aggregate formed by needle-punching two or more fibers and laminated on both sides of the core layer (120), and the core layer (120) and the skin layer (110) are impregnated with a matrix resin and then cured. Each component will be described separately in detail below.

1. Skin layer (110)

The fiber aggregate constituting the skin layer (110) has a structure in which two or more fibers are laminated, not just a single layer.

At this time, it is preferable that the fibers constituting the fiber assembly include at least one fiber selected from carbon fibers, glass fibers, aramid fibers, oxyfan fibers, and hybrid fibers, and it is more preferable to use carbon fibers. In addition, the form of the fibers may include various forms such as woven fabrics, nonwoven fabrics, knitted fabrics, UD fabrics, and multi-axial fabrics.

In one embodiment, the fiber assembly forming the skin layer (110) may be manufactured by needle-punching two or more fibers. As an example, the fiber assembly may be manufactured by needle-punching a laminate of plain-woven carbon fibers (12k), and a material whose properties are determined by the directionality of the fibers, such as a UD fabric, may be manufactured by differently stacking the fiber arrangements of each layer through a needle-punching process as needed.

As illustrated in FIG. 1b, the needle (211) used in the needle punching process in the present invention has a protrusion (212) formed at the bottom, so that when the needle (211) penetrates a fiber laminate (210) in which two or more fibers are laminated, a Z-axis physical network (221) is formed between the fibers. At this time, the Z-axis represents the thickness direction of the fiber laminate. For example, since a carbon fiber fabric penetrated by a needle (211) forms a network in the thickness direction by the protrusion (212) present in the needle, it not only strengthens the physical bonding between each fiber layer, but also can change the characteristics of the outermost surface of the fiber aggregate.

In one embodiment, the needle punching interval is preferably 1.5 to 5 mm in the X-axis and 1.5 to 5 mm in the Y-axis. At this time, if the X-axis and Y-axis needle punching interval is less than 1.5 mm, a deterioration in physical properties occurs due to fiber damage, and if it exceeds 5 mm, there is a problem that it is difficult to form a physical network between fibers.

In addition, the diameter of the hole of the skin layer formed by needle punching is determined depending on the needle used, and is preferably 65 to 300 ㎛. At this time, if the diameter of the hole of the skin layer is less than 65 ㎛, it is difficult to form a physical network between fibers, and if it exceeds 300 ㎛, a rapid deterioration of the physical properties occurs.

In addition, it is preferable that the area ratio of the hole formed by the needle punching of the skin layer is 0.007 to 3.5% per 1 cm ² of the skin layer. At this time, if the area ratio of the hole is less than 0.007%, it is difficult to form a physical network between fibers, and if it exceeds 3.5%, there occurs a problem of rapid deterioration of the physical properties of the fiber aggregate due to fiber damage.

A sandwich composite according to one embodiment of the present invention has the above-described properties through a needle punching process to achieve the required physical bonding, thereby preventing the fiber aggregate from twisting during the process, thereby providing efficiency during the process.

In addition, the sandwich composite according to one embodiment of the present invention forms a fiber aggregate (220) through a needle punching process, thereby increasing the average roughness of the surface of the fiber aggregate. In this way, the increase in surface roughness of the fiber aggregate by needle punching affects the interface characteristics between the fiber aggregate (220) constituting the skin layer (110) and the foam material constituting the core layer (120).

In one embodiment, it is preferable that the thickness ratio before and after needle punching of the fiber assembly (220) satisfies the following mathematical expression 1.

(Mathematical formula 1)

1.25≤Fiber aggregate thickness after needle punching/Fiber aggregate thickness before needle punching ≤6

Additionally, in the present invention, it is preferable that the density of the skin layer (110) is 1.2 to 1.6 g/cc.

2. Core layer (120)

The core layer (120) is composed of foam material and has skin layers (110) positioned on both sides, and secures the thickness required by the sandwich composite within the sandwich composite.

It is preferable that the foam material constituting the core layer (120) includes at least one selected from polyethylene terephthalate (PET), polymethacrylamide (PMI), and urethane. In addition, the core layer (120) is positioned inside the skin layer (110) and is impregnated with a matrix resin together with the skin layer (110) and then cured.

The above-described skin layer (110) is laminated on both sides of the core layer (120) and then impregnated with matrix resin together with the core layer (120) and then cured to produce a sandwich composite. At this time, it is preferable that the matrix resin includes epoxy resin or phenol resin, and it is more preferable to use epoxy resin.

FIG. 2 is a drawing explaining a method for manufacturing a sandwich composite according to one embodiment of the present invention.

Referring to FIG. 2, a method for manufacturing a sandwich composite according to one embodiment of the present invention includes a first step (a) of laminating two or more fibers, a second step (b) of manufacturing a fiber aggregate forming a skin layer by needle punching the laminated fibers, a third step (c) of laminating skin layers on both sides of a core layer formed of a foam material, a fourth step (d) of injecting and impregnating a matrix resin into the laminated core layer and skin layer, and a fifth step (e) of heat-curing the fourth step to manufacture a sandwich composite. Each step is described below.

First, the first step (a) is a step of laminating at least one other fiber on one fiber. In Fig. 2, a fiber assembly in which five fibers are laminated is illustrated as an example, but the number of laminated fiber fabrics can be applied differently depending on the required properties. As the number of fiber fabrics increases, improved properties can be expected, but the material flexibility is low, which is disadvantageous for application to structures of various shapes such as curved surfaces, and the durability of the needle decreases, which causes a decrease in process efficiency. Therefore, it is desirable to control the number of fibers to be laminated in consideration of the required properties of the required use.

At this time, materials whose properties are affected by the direction of the fibers, such as UD, can be laminated by arranging the fiber arrangement direction to have a predetermined angle, such as a right angle or a 45 degree angle, as necessary. At this time, it is preferable that the type of fiber used includes at least one fiber selected from carbon fiber, glass fiber, aramid fiber, oxyphane fiber, and hybrid fiber, and it is more preferable to use carbon fiber. In addition, the form of the fiber can include various forms, such as woven fabric, nonwoven fabric, knitted fabric, UD fabric, and multi-axial fabric.

Next, the second step (b) is a step of manufacturing a fiber assembly forming a skin layer by needle punching the laminated fibers, and is a step of forming a physical network in a vertical direction to the laminated fibers through needle punching to create a fiber assembly and control the roughness and density of the fiber surface.

At this time, it is preferable to perform the needle punching process using a needle punching needle having a diameter of 65 to 300 μm so that the diameter of the hole formed is 65 to 300 μm. In addition, it is preferable to adjust the interval of the needle punching needles so that the interval between the X-axis and Y-axis of the hole formed by the needle punching is 1.5 to 5 mm.

Next, the third step (c) is a step of laminating skin layers on both sides of a core layer composed of a foam material, in which the skin layers formed in the form of a fiber aggregate by needle punching in the second step are positioned and laminated on both sides of the foam material forming the core layer. At this time, the type of foam material may include PET, PMI, urethane, etc.

Next, the fourth step (d) is a step of injecting and impregnating the matrix resin into the laminated core layer and skin layer. The laminated core layer and skin layer are positioned in the mold, and then the matrix resin is injected. It is preferable to use an epoxy-based resin as the matrix resin to be injected, and a resin for room temperature, low temperature, or high temperature curing can be used. Here, room temperature curing means a curing temperature of 25 to 30°C, low temperature curing means 40 to 70°C, and high temperature curing means 70 to 120°C.

At this time, it is preferable that the mold used is formed of one material selected from steel, aluminum, and glass. In addition, it is preferable that the core layer and skin layer are laminated after performing a release treatment using a release agent inside the mold. This release treatment is to ensure that the matrix resin is easily separated from the mold when injected and cured. As an example, it is more preferable to improve the release effect by repeating the process of applying a release agent and drying at 60°C three times.

More specifically, in the fourth step (d) of injecting matrix resin into the laminated core and skin layers, a peel ply and the laminate (core and skin layer laminate) formed in the third step (c) are laminated on the released lower mold, and then a peel ply and a breather are sequentially laminated, and then a bagging film is covered and then sealed with a sealant tape to prepare a resin injection system. If the bagging film is torn due to the thickness of the laminate when entering a vacuum state in the resin injection system, a bank should be arranged around the laminate to prevent the above phenomenon, and the type of bank can utilize a foam-type material.

Next, step 5 (e) is a step of manufacturing a sandwich composite by heat curing after step 4, in which a laminate impregnated with a matrix resin is cured by heat treatment by a pressure gradient to manufacture a sandwich composite (f).

According to one embodiment of the present invention, a sandwich composite manufactured through the above-described manufacturing method preferably has an adhesive strength between the skin layer (110) and the core layer (120) of 95 to 120 gf/cm ² .

In addition, it is preferable that the sandwich composite according to one embodiment of the present invention has a flexural modulus of 3 GPa or more.

FIG. 3 is a photograph showing an actual product of a sandwich composite according to one embodiment of the present invention.

Referring to FIG. 3, the sandwich composite according to one embodiment of the present invention described in FIG. 1A and FIG. 1B and FIG. 2 described above can improve surface roughness and change density through needle punching, thereby improving the loading ratio of the matrix resin and improving the interfacial adhesion between the skin layer and the core layer, thereby providing a sandwich composite having excellent strength (flexural elastic modulus).

More specifically, according to the present invention, by manufacturing a fiber assembly using needle punching and forming a skin layer in the form of a preform such as carbon fiber fabric, it is possible to prevent the phenomenon of fiber fabric arrangement disorder that may occur during the manufacturing process of a sandwich composite, and further, by increasing the surface roughness of the carbon fiber fabric through which the needle has passed, the contact area with the core layer is improved as the surface roughness of the skin layer increases, thereby improving the interfacial bonding force between the skin layer and the core layer, and further, due to the Z-axis physical network structure of the fiber assembly formed by needle punching, it is possible to prevent the interface from peeling off by providing a shear force between the layers of fibers under a bending load, and the strength of the sandwich composite can be improved by the skin layer that has become bulky due to physical interlocking.

Hereinafter, the present invention will be described more specifically through examples. These examples are intended to explain the present description more specifically, and the scope of the present invention is not limited to the examples.

[Example]

[Example 1]

(1) Manufacturing of fiber aggregate

After laminating five sheets of 12k carbon fiber fabric with a thickness of 0.45 mm, a needle punching process was performed using a needle mold using a CNC machining device. The number of needle penetrations was one, and the needle punching process was performed by penetrating all three protrusions existing at the bottom of the needle. At this time, the diameter of the hole formed by the needle punching process was 65 μm, and the interval between the X-axis and Y-axis of the hole was 2.5 mm. Two identical fiber assemblies were manufactured through this process.

(2) Manufacturing of sandwich composites

The manufactured fiber aggregate was positioned on both sides of polyester terephthalate (PET) foam material having a density of 0.171 g/cc and a thickness of 10 mm to form a laminate, and then the process of applying a release agent inside a steel mold and drying at 60°C was repeated three times to perform a release treatment, and then a peel ply and a laminate were laminated on the lower mold that had undergone the release treatment, and a peel ply and a breather were sequentially laminated again on the laminate, and a bagging film was covered and then treated with a sealant tape. Next, a low-temperature curing epoxy resin (resoltech, 1050 resin, 1056S hardener) was injected in a vacuum, and then heat-treated at 60°C for 2 hours to manufacture a sandwich composite.

[Example 2]

A sandwich composite was manufactured in the same manner as in Example 1, except that the hole diameter was 65 μm and the gap between the holes along the X-axis and Y-axis was 5 mm.

[Example 3]

A sandwich composite was manufactured in the same manner as in Example 1, except that the hole diameter was 300 μm and the gap between the holes along the X-axis and Y-axis was 1.5 mm.

[Example 4]

A sandwich composite was manufactured in the same manner as in Example 1, except that two plies of 0.45 mm thick 12K carbon fiber fabric were laminated and needle punched at 2.5 mm intervals along the X and Y axes.

[Comparative example]

[Comparative Example 1]

A sandwich composite was manufactured in the same manner as in Example 1, except that the needle punching process was not performed.

[Comparative Example 2]

A sandwich composite was manufactured in the same manner as in Example 1, except that the hole diameter was 64 μm and the gap between the holes along the X-axis and Y-axis was 6 mm.

[Comparative Example 3]

A sandwich composite was manufactured in the same manner as in Example 1, except that the hole diameter was 301 μm and the gap between the holes along the X-axis and Y-axis was 1.0 mm.

The physical properties of the sandwich composites manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated through the following experimental examples, and the results are shown in Table 1.

[Experimental example]

(1) Measurement of the area ratio of the hole

After polishing the surface of the cured product of the manufactured sandwich composite using a polisher, the surface is observed using an optical microscope to measure the diameter of the hole and the spacing between the X-axis and Y-axis to calculate the area ratio.

(2) Measurement of thickness ratio before and after needle punching

In the fiber assembly manufacturing step, the thickness of the laminated fiber assembly before the needle punching process is measured using a digital caliper (Mitutoyo, 500-500-10), the thickness of the fiber assembly after the needle punching process is measured, and the thickness ratio is calculated according to mathematical expression 1 (fiber assembly thickness after needle punching/fiber assembly thickness before needle punching).

(3) Surface roughness measurement

In the fiber assembly manufacturing step, the average roughness (Ra) of the center line of the surface of the fiber assembly is measured 10 times using a surface roughness measuring device (TOKYO SEMITSU, Surfcom 1500SD3), and then the average value is calculated.

(4) Measurement of interface adhesion

The manufactured sandwich composite is cut into a size of 25 X 100 mm (width X length) and the interfacial adhesion is measured using a peel force measuring device (Cheminstruments, AR-2000) at a test speed of 500 cm/min. At this time, after measuring 5 samples, the average value is used as the interfacial adhesion.

(5) Density measurement

In the fiber aggregate manufacturing step, the fiber aggregate manufactured is cured alone without foam material under the same curing conditions as in Example 1, and then the density is measured using an analytical balance (Sartorious, MSA Model).

(6) Flexural modulus

The manufactured sandwich composite is subjected to a four-point bending test according to the standard ASTM C393 under the following test conditions to measure the flexural modulus.

<Test Conditions>

- Dimensions of the specimen (thickness x width x length): 13.47 x 30 x 200mm

- Support span length: 150mm

- Load span length: 50mm

- Test speed: 6.0mm/min

Hole area ratio
(%) Needle punching
order
Thickness ratio winding
Elasticity
(GPa) Ra
(㎛) Interface
Adhesion
(gf/cm ² ) Core layer
density
(g/cc) Skin layer
density
(g/cc) Example 1 0.05306 5.95 3.74 0.34 100.53 0.12 1.339 Example 2 0.01326 5.94 3.12 0.29 95.28 0.12 1.355 Example 3 3.4618 5.94 4.07 0.41 118.22 0.12 1.303 Example 4 0.05306 1.25 3.02 0.31 97.44 0.12 1.333 Comparative Example 1 - - 2.97 0.09 91.02 0.12 1.505 Comparative Example 2 0.01286 5.95 2.75 0.28 91.38 0.12 1.352 Comparative Example 3 7.1121 5.94 2.69 0.55 124.26 0.12 1.285

As described in Table 1, Examples 1 to 3 satisfying the composition of the present invention can be seen to have excellent interfacial adhesion and containment ratio by securing the required surface roughness and density through the needle punching process.

On the other hand, it can be seen that Comparative Example 1, which did not perform the needle punching process, has a small surface roughness, low interfacial adhesion, and a high density, which is disadvantageous for weight reduction, compared to Example 1, which performed the needle punching process.

In addition, in Comparative Example 2, where the hole diameter is small and the gap between the holes is wide, the interfacial adhesive strength hardly increases compared to Comparative Example 1, where needle punching was not performed. Rather, it can be seen that the material properties, such as the flexural modulus, deteriorate because the hole diameter is too small and the gap is excessive.

In addition, in Comparative Example 3, where the hole diameter is large and the hole spacing is narrow, the interfacial adhesive strength increases, but the material properties deteriorate due to relatively excessive needle punching, resulting in a lower flexural modulus.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

110: Skin layer
120: Core layer
210: Fiber laminate in which two or more fibers are laminated
211: Needles used in needle punching process
212: Needle tip
220: Fiber aggregate
221: Z-axis physical network

Claims (12)

a core layer composed of foam material; and
A skin layer formed of a fiber assembly in which a Z-axis physical network is formed between fibers by needle-punching two or more fibers, and which is laminated on both sides of the core layer;
Including,
The above core layer and skin layer are impregnated with matrix resin and then cured.
A sandwich composite material, wherein the X-axis and Y-axis spacing of the holes formed by needle punching of the above skin layer is 1.5 to 5 mm, and the diameter of the holes is 65 to 300 μm. In the first paragraph,
A sandwich composite material in which the thickness ratio of the fiber assembly before and after needle punching satisfies the following mathematical expression 1.
(Mathematical formula 1)
1.25≤Fiber aggregate thickness after needle punching/Fiber aggregate thickness before needle punching≤6 In the first paragraph,
A sandwich composite material, wherein the area ratio of holes formed by needle punching of the above skin layer is 0.007 to 3.5% ^per 1 cm2 of the skin layer. delete delete In the first paragraph,
The density of the above skin layer is 1.2 to 1.6 g/cc,
A sandwich composite having a density of the core layer of 0.08 to 0.2 g/cc. In the first paragraph,
A sandwich composite, wherein the fibers constituting the above fiber assembly are at least one selected from carbon fibers, glass fibers, aramid fibers, oxyphane fibers, and hybrid fibers. In the first paragraph,
A sandwich composite, wherein the form of the fibers constituting the above fiber assembly is at least one selected from a woven fabric, a nonwoven fabric, a knitted fabric, a UD fabric, and a multi-axial fabric. In the first paragraph,
A sandwich composite having an adhesive strength between the skin layer and the core layer of 95 to 120 gf/cm ² . In the first paragraph,
A sandwich composite having a flexural modulus of 3 GPa or more. In the method for manufacturing a sandwich composite according to Article 1,
A first step of laminating two or more fibers;
A second step of manufacturing a fiber assembly forming a skin layer by needle punching laminated fibers;
A third step of laminating skin layers on both sides of a core layer made of foam material;
A fourth step of impregnating the laminated core layer and skin layer with matrix resin;
Step 5: heat curing after Step 4 to produce a sandwich composite;
A method for manufacturing a sandwich composite, comprising: In Article 11,
The above first step is a method for manufacturing a sandwich composite by arranging the fiber arrangement direction at a predetermined angle and laminating it.