KR20230111011A - Cfrp foam-core sandwich structure and manufacturing method thereof - Google Patents

Abstract

The CFRP foam core sandwich structure according to the present invention has a structure in which a first prepreg, a mesh layer, and a second prepreg are sequentially stacked on the upper and lower surfaces of the foam core, and the area of the mesh layer is less than the area of the first prepreg and the second prepreg. Through this structure, the CFRP foam core sandwich structure according to the present invention can solve the problem of pinholes and surface non-uniformity, thereby improving the appearance and removing defects.

Description

CFRP foam core sandwich structure and its manufacturing method {CFRP FOAM-CORE SANDWICH STRUCTURE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a sandwich structure used as a material for construction, industry, and automobiles, and more particularly, to a CFRP foam core sandwich structure manufactured using a foam material and prepreg and a method for manufacturing the same.

Conventionally, sandwich structures are used in many industrial fields, and strength and weight of sandwich structures are designed in various fields as much as fields, and a structure in which a foam material is inserted into the sandwich structure is widely used to lighten the weight of the sandwich structure.

In the case of using such a foam material or core material, a method of achieving weight reduction and high strength at the same time is used by using a composite material having reinforcing performance as an outer covering material surrounding the foam material or core material.

On the other hand, in the composite material, a low-density foam material is used to dramatically increase stiffness by increasing the thickness of the laminate without increasing the weight. However, when forming the foam core sandwich structure, there is a fundamental problem in that resin is additionally consumed in pores existing on the surface of the foam material, which is the core material, and holes generated during the molding process. In addition, pinholes/holes are generated in the product during the CFRP manufacturing process due to pores existing on the surface of the foam material, which is the core material, and holes generated during the molding process. These pinholes generally appear on the surface or between structural layers of a product, which not only affects the appearance of the product but also acts as a defect that can have a certain effect on physical properties.

In addition, pinholes and voids must be filled to prevent moisture penetration into the product and potential degradation of physical properties, as well as to improve the appearance of composite materials. Composite materials can be vacuum treated during molding, or small surface defects such as pinholes can be filled by using hole fillers and coatings after molding. However, it requires additional processes such as vacuum, pretreatment, and sanding, and has a disadvantage in that it takes a lot of time. Moreover, pinholes less than 1 mm in diameter in the composite surface cannot be filled by spraying because the sprayed coating can bridge and outgas the pinhole, shrink back when the coating dries, or bridge through sanding. Therefore, a design that minimizes resin consumption is required in consideration of moldability and process technology in the layer design stage.

Korean Patent Publication No. 10-2011-0076269

The present invention has been made to solve the above-mentioned problems, and the problem to be solved by the present invention is to prevent pores from being trapped in the fabric and to prevent the resin from being consumed in the foam material by using a multi-layer assembly structure in which a mesh layer is inserted between the prepregs. It is to provide a CFRP foam core sandwich structure capable of suppressing the occurrence of pinholes and resolving surface imbalance, and a manufacturing method thereof.

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 CFRP foam core sandwich structure in which a first prepreg, a mesh layer, and a second prepreg are sequentially stacked on a foam core and upper and lower surfaces of the foam core, and the area of the mesh layer is less than or equal to the area of the first prepreg and the second prepreg.

Preferably, the weight per unit area of the mesh layer may be 20 to 40 g/m ² .

Preferably, 20 or less pinholes with a diameter of less than 1 mm per 1 m ² unit area may be present on the outer surface of the CFRP foam core sandwich structure.

Preferably, the mesh layer may include at least one of PET, glass fiber, and carbon fiber.

Preferably, the mesh layer may be in the form of a mesh or mat.

Preferably, the first prepreg is a woven prepreg, and the second prepreg may be a unidirectional (UD) prepreg.

Preferably, the flexural strength of the CFRP foam core sandwich structure may be 200 MPa or more.

Preferably, the surface roughness (Ra) of the CFRP foam core sandwich structure may be 2.0 μm or less.

Preferably, the first prepreg and the second prepreg may include at least one resin selected from an epoxy resin, a polyester resin, and a vinyl ester resin.

In addition, the above object is achieved by a method for manufacturing a CFRP foam core sandwich structure, which includes a first step of sequentially stacking a second prepreg, a mesh layer, and a first prepreg inside a lower mold, a second step of stacking a foam core on the first prepreg, a third step of sequentially stacking the first prepreg, a mesh layer, and a second prepreg on the foam core, a fourth step of press molding after meshing the upper mold, and a fifth step of demolding and processing.

According to the CFRP foam core sandwich structure and method for manufacturing the same according to an embodiment of the present invention, a mesh reinforcing material is inserted as a means to solve the problems of pinholes and surface irregularities caused by foam core sandwich lamination, and these problems can be solved, and the appearance of the sandwich structure can be improved and defects can be eliminated.

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.

1 is a configuration diagram of a CFRP foam core sandwich structure according to an embodiment of the present invention.
2 is a flowchart showing a method of manufacturing a CFRP foam core sandwich structure according to an embodiment of the present invention.

With reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In the drawings, the thickness is shown enlarged to clearly express the various layers and regions. Like reference numerals have been assigned to like parts throughout the specification. When a part such as a layer, film, region, plate, etc. 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 defined otherwise, 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, the present specification, including definitions, will control. Also, although methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, suitable methods and materials are described herein.

1 is a configuration diagram of a CFRP foam core sandwich structure according to an embodiment of the present invention.

Referring to FIG. 1 , a CFRP foam core sandwich structure according to an embodiment of the present invention includes a foam core 110, a first prepreg 120, a mesh layer 130, and a second prepreg 140. At this time, the foam core 110 is located in the middle of the sandwich structure, and the first prepreg 120, the mesh layer 130, and the second prepreg 140 are sequentially laminated on the upper and lower surfaces of the foam core 110.

As such, the CFRP foam core sandwich structure according to an embodiment of the present invention is formed by forming a multi-layer assembly structure in which the first prepreg 120, the mesh layer 130, and the second prepreg 140 are sequentially stacked on and under the foam core 110. Hereinafter, each configuration will be described in detail.

First, the foam core 110 is a core layer of a CFRP foam core sandwich structure according to an embodiment of the present invention, and is a hard plate-like foam formed by compressing a foam material to a predetermined thickness in order to reduce the weight of the sandwich structure. In this specification, the foam material forming the core layer is referred to as 'foam material'.

The foam material forming the foam core 110 is a hard foam material containing at least one selected from PVC (Polyvinlychloride), PET (PolyEthyleneTerephthalete), PS (PolyStyrene), PU (Polyurethane), and PMI (PolyMethacryImide) It is preferable to use. However, the material of the foam core 110 is not limited to the above-described material, and any material capable of being foamed through a molding process may be used. As an example, the foam material forming the foam core 110 may be formed by mixing a foaming/curing agent with a foaming resin and molding at a predetermined temperature.

In addition, the foam material forming the foam core 110 preferably has heat resistance of 150° C. or higher in order to prevent deformation and deterioration of physical properties during a molding process.

Next, the reinforcing layer in which the first prepreg 120, the mesh layer 130, and the second prepreg 140 are sequentially stacked is formed by molding a composite material in which reinforcing fibers are impregnated with a resin to a predetermined thickness together with the mesh layer to secure the rigidity required in the sandwich structure.

At this time, it is preferable that the carbon fiber, which is a fiber reinforcing material constituting the first prepreg 120 and the second prepreg 140, has a woven material shape and a unidirectional shape. More specifically, the first prepreg 120 directly contacting the foam core 110 preferably includes a fabric prepreg, and the second prepreg 140 preferably includes a unidirectional (UD) prepreg. In general, since a unidirectional prepreg can exhibit higher stiffness at the same weight per unit area, it is preferable to use a unidirectional prepreg to ensure that the second prepreg 140 located outside has higher stiffness. In addition, by using a fabric prepreg as the first prepreg 120 and using a unidirectional prepreg as the second prepreg 140, the fiber arrangement directions of the two different prepregs are staggered, so that the external force applied in various directions can be secured.

In addition, the first prepreg 120 and the second prepreg 140 include a fiber reinforcement and a matrix resin.

At this time, the fiber reinforcing material preferably includes at least one fiber selected from carbon fiber, glass fiber, and Kevlar fiber, and more preferably includes carbon fiber. In addition, the first prepreg 120 and the second prepreg 140 may be formed by laminating one or more fiber reinforcements according to the design purpose and use and required mechanical strength.

In addition, various resins may be used as the matrix resin impregnated into the fiber reinforcement according to the size and shape of the sandwich panel. For example, as the matrix resin, one or more resins selected from epoxy resins, polyester resins, and vinyl ester resins, which are thermosetting resins used in general composite materials, may be used.

In addition, the first prepreg 120 and the second prepreg 140 may further include a functional material as a measure of toughness reinforcement for shock absorption. The functional material is a thermoplastic resin particle having high toughness and may be used by being added to the matrix resin. Thermoplastic resin particles include polyacryl, polyester, polyvinyl, polyurethane, polyether, polyamide, polyimide, polyether amide, polyketone, polyether ketone, polyetheretherketone, polysulfone, At least one selected from the group of polyethersulfone, polyetherethersulfone, polyphenylsulfone, and polyphenylene oxide may be used.

In addition, the mesh layer 130 is positioned between the first prepreg 120 and the second prepreg 140 to solve problems of pinholes and surface irregularities. More specifically, the mesh layer 130 prevents pores from being trapped between the first prepreg 120 and the second prepreg 140 and prevents resin from being consumed in the foam material of the foam core 110, thereby suppressing the occurrence of pinholes and forming a uniform surface.

Preferably, the mesh layer 130 includes at least one material selected from PET, glass fiber, and carbon fiber.

At this time, the area of the mesh layer 130 is equal to or less than the area of the first prepreg 120 and the second prepreg 140 located on the upper and lower portions of the mesh layer 130, that is, the carbon fiber prepreg that is the reinforcing layer. When the area of the mesh layer 130 is larger than the areas of the first prepreg 120 and the second prepreg 140, impregnation of the matrix resin is reduced at the edges of the prepreg in the molding process. Therefore, in the present invention, by making the area of the mesh layer 130 smaller than the area of the first prepreg 120 and the second prepreg 140, it is possible to prevent impregnation degradation of the edge prepreg.

In addition, the weight per unit area of the mesh layer 130 is preferably 20 to 40 g/m ² . At this time, when the weight per unit area of the mesh layer 130 is less than 20 g/m ² , the effect of the mesh layer does not appear, and when it exceeds 40 g/m ² , surface defects and bending strength decrease.

In addition, the mesh layer 130 is preferably in the form of a mesh or mat.

Preferably, the CFRP foam core sandwich structure according to an embodiment of the present invention has 20 or less pinholes with a diameter of less than 1 mm per 1 m ² unit area on the outer surface. At this time, when the number of pinholes exceeds 20, unevenness occurs on the outer surface of the structure and mechanical properties are deteriorated.

In addition, the flexural strength of the CFRP foam core sandwich structure is preferably 200 MPa or more. At this time, when the flexural strength is less than 200 MPa, the reinforcing effect of the reinforcing fibers is reduced.

In addition, the surface roughness (Ra) of the outer surface of the CFRP foam core sandwich structure is preferably 2.0 μm or less. At this time, when the surface roughness (Ra) exceeds 2.0 μm, mechanical properties are deteriorated.

2 is a flowchart showing a method of manufacturing a CFRP foam core sandwich structure according to an embodiment of the present invention.

Referring to FIG. 2, a method of manufacturing a CFRP foam core sandwich structure according to an embodiment of the present invention includes a first step (S201) of sequentially stacking a second prepreg, a mesh layer, and a first prepreg inside a lower mold; A second step (S202) of laminating a foam core on the first prepreg; A third step (S203) of sequentially stacking the first prepreg, the mesh layer, and the second prepreg on the foam core, a fourth step (S204) of press molding after meshing the upper mold, and a fifth step (S205) of demolding and processing.

Before performing the first step (S201), a step of releasing the inside of the mold so that the prepreg can be easily separated from the inside of the mold may be additionally performed. Prior to laminating the first prepreg inside the mold, the inner surface of the mold is coated with a release agent. At this time, it is preferable to use a liquid release agent rather than a solid one to make the surface of the mold uniform and smooth. In addition, it is preferable to finish by wiping the surface to which the release agent is applied with a woven material such as wool. If the release agent is not uniformly and smoothly applied to the surface, stains of the release agent remain on the surface of the mold, which may be transferred to the surface of the molded product after molding, and the adhesive force with the mold surface may decrease when the prepreg is laminated due to the release agent remaining excessively on the mold surface.

First, in the first step of sequentially stacking the second prepreg, the mesh layer, and the first prepreg inside the lower mold (S201), the second prepreg is first laminated in the inner cavity of the lower mold, and then the mesh layer is laminated on the second prepreg. Next, the first prepreg is laminated to form a lower multi-layer assembly. At this time, one or more of the first prepreg and the second prepreg may be stacked to form a required thickness and strength.

At this time, it is preferable to laminate the laminated first prepreg and the mesh layer, the second prepreg and the mesh layer, and the interface between the second prepreg and the mold surface so that no air bubbles remain. In particular, air bubbles remaining at the interface between the second prepreg and the surface of the mold may cause appearance defects, so air bubble removal is more important.

Next, in the second step of laminating the foam core on the first prepreg (S202), the foam core is laminated on the first prepreg of the multilayer assembly formed in the first step (S201). At this time, the foam core may be formed to a required thickness in advance and laminated inside the mold, and may be molded to a thickness considering the compression of the foam core during the press molding process and laminated.

Next, in the third step of sequentially stacking the first prepreg, the mesh layer, and the second prepreg on the foam core (S203), the first prepreg is stacked on the foam core, the mesh layer is stacked on the first prepreg, and then the second prepreg is stacked to form an upper multi-layer assembly.

Next, before performing step S204 described later, a step of preheating the meshed mold at a temperature of 50 to 100° C. may be further performed. This is to improve the flowability by lowering the viscosity of the matrix resin impregnated in the prepreg, and through this preheating process, it is possible to improve the performance by improving the appearance of the sandwich structure. At this time, when the preheating temperature is less than 50 ° C, the effect of lowering the viscosity of the matrix resin is low, and the flowability of the resin is not improved.

Next, in a fourth step (S204) of press molding after meshing the upper mold, press molding is performed at a predetermined temperature and pressure after meshing the upper mold with the lower mold. At this time, the matrix resin of the first prepreg and the second prepreg is melted by the applied heat and pressure and compressed to a designed shape and thickness to form a CFRP foam core sandwich structure.

At this time, the temperature applied to the forming mold (press temperature) is preferably performed at a temperature of 100 to 180 ° C, and the pressing time is preferably 30 minutes to 2 hours. If the pressing temperature is less than 100 ° C, problems of molding defects and physical property degradation occur due to uncuring of the first prepreg and the second prepreg layer located inside the mold, and if the pressing temperature exceeds 180 ° C, the foam core inside the propeller mold, The problem of resin deterioration due to excessive temperature occurs in the first prepreg and the second prepreg.

Further, it is preferable that the pressing pressure applied to the molding die (pressing pressure of the press) is 0.5 to 5 MPa. At this time, when the pressurization pressure is less than 0.5 MPa, the prepreg placed inside the mold is not sufficiently pressurized due to the low pressure, and there is a problem that the surface is not impregnated or the interlayer adhesion between the first prepreg and the second prepreg and the mesh layer is lowered. If the pressurization pressure exceeds 5 MPa, the mold is deformed due to excessive pressure or the resulting cross-sectional shape of the sandwich structure is deformed.

Next, in the fifth step of demolding and processing (S205), it is preferable to demold after the mold is cooled below the glass transition temperature of the matrix resin. When demolding above the glass transition temperature, the cross-section of the sandwich structure swells due to the compressive repulsive force of the foam core, which may cause a problem in that performance deteriorates. In addition, in the fifth step (S205), a trimming step is performed, and a finishing operation is performed through processing such as removing burrs of the resin or carbon fiber protruding out of the sandwich structure shape.

Hereinafter, the present invention will be described in more detail through examples. This embodiment is intended to explain the present description in more detail, and the scope of the present invention is not limited to the embodiment.

[Example]

[Example 1]

A unidirectional prepreg (UD) impregnated with epoxy resin with a thickness of 0.15 mm, a carbon fiber mesh with a thickness of 0.1 mm, and a fabric prepreg impregnated with an epoxy resin with a thickness of 0.3 mm were sequentially laminated inside the lower mold. Next, a polyurethane foam material having a thickness of 5.5 mm was laminated on the fabric prepreg, and then the above-described fabric prepreg, carbon fiber mesh, and unidirectional prepreg (UD) were sequentially laminated on the foam material. At this time, the weight per unit area of the mesh layer was 20 g/m ² , and the same area as that of the prepreg was used.

Next, after aligning the upper mold, press molding was performed by pressurizing at a temperature of 120 ° C. at a pressure of 2 MPa for 2 hours, cooling the mold to 25 ° C., demolding the sandwich structure from the mold, and then performing post-processing through trimming to prepare a CFRP foam core sandwich structure.

[Example 2]

A CFRP foam core sandwich structure was prepared in the same manner as in Example 1, except that the mesh layer having a weight per unit area of 40 g/m ² was used.

[Comparative Example]

[Comparative Example 1]

A CFRP foam core sandwich structure was prepared in the same manner as in Example 1, except that the mesh layer having a weight per unit area of 10 g/m ² was used.

[Comparative Example 2]

A CFRP foam core sandwich structure was prepared in the same manner as in Example 1, except that the mesh layer having a weight per unit area of 50 g/m ² was used.

For the CFRP foam core sandwich structures prepared in Examples 1 and 2 and Comparative Examples 1 and 2, physical properties were evaluated through the following experimental examples, and the results are shown in Table 1.

[Experimental example]

(1) Measurement of surface roughness (Ra)

The roughness (Ra) value of the surface of the sandwich structure was measured using a three-dimensional surface shape measuring instrument (KOSAKA, SE-600K).

(2) Measurement of flexural strength

Flexural strength was measured according to ASTM_D790.

(3) Measuring the number of pinholes

It was placed on a black-bottomed evaluation plate, and the number of pinholes having a diameter of less than 1 mm was visually confirmed (visual observation) on the surface of the sandwich structure under fluorescent light, and the number per 1 m ² unit area was recorded.

surface roughness
(μm) flexural strength
(MPa) number of pinholes Example 1 0.21 245 2 Example 2 0.30 230 3 Comparative Example 1 2.2 205 30 Comparative Example 2 1.8 192 25

As described in Table 1, it can be seen that Examples 1 and 2 according to the configuration of the present invention satisfy the configuration of the present invention in terms of surface roughness, flexural strength, and number of pinholes. As such, the CFRP foam core sandwich structure according to an embodiment of the present invention can solve the problem of pinholes and surface irregularities by satisfying all of the above physical properties, thereby improving the appearance of the structure and removing defects.

On the other hand, in Comparative Example 1, the surface roughness and the number of pinholes do not satisfy the physical properties required in the present invention, and it can be seen that the surface unevenness is severe and the number of pinholes is high.

In Comparative Example 2, the flexural strength and the number of pinholes do not satisfy the physical properties required in the present invention, and it can be seen that mechanical strength is lowered due to low flexural strength and many pinholes.

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 of those skilled in the art using the basic concepts of the present invention defined in the following claims are also within the scope of the present invention.

110: foam core
120: first prepreg
130: mesh layer
140: second prepreg

Claims (10)

foam core; and
A first prepreg, a mesh layer, and a second prepreg are sequentially stacked on the upper and lower surfaces of the foam core,
The area of the mesh layer is less than or equal to the area of the first prepreg and the second prepreg, CFRP foam core sandwich structure. According to claim 1,
The weight per unit area of the mesh layer is 20 to 40 g / m ² , CFRP foam core sandwich structure. According to claim 1,
A CFRP foam core sandwich structure in which there are 20 or less pinholes with a diameter of less than 1 mm on the outer surface of the CFRP foam core sandwich structure per 1 m ² unit area. According to claim 1,
The mesh layer comprises at least one of PET, glass fiber and carbon fiber, CFRP foam core sandwich structure. According to claim 1,
The mesh layer is a mesh or mat form, CFRP foam core sandwich structure. According to claim 1,
The first prepreg is a fabric prepreg,
The second prepreg is a unidirectional (UD) prepreg, a CFRP foam core sandwich structure. According to claim 1,
The CFRP foam core sandwich structure has a flexural strength of 200 MPa or more. According to claim 1,
The surface roughness (Ra) of the CFRP foam core sandwich structure is 2.0 μm or less, the CFRP foam core sandwich structure. According to claim 1,
The first prepreg and the second prepreg include at least one resin selected from an epoxy resin, a polyester resin, and a vinyl ester resin. A first step of sequentially stacking a second prepreg, a mesh layer, and a first prepreg inside a lower mold;
A second step of laminating a foam core on the first prepreg;
A third step of sequentially stacking a first prepreg, a mesh layer, and a second prepreg on the foam core;
A fourth step of press molding after meshing the upper mold; and
A fifth step of demolding and processing;
A method for manufacturing a CFRP foam core sandwich structure comprising a.