JP2019217651A - Method for forming composite material structure - Google Patents

Abstract

To provide the method for forming the composite material structure capable of suppressing occurrence of sink marks.SOLUTION: The composite material structure 1X comprising a core material 2, a first fiber reinforced resin layer 3A, and a second fiber reinforced resin layer 3B is formed. First, a spacer 4 is arranged along an outer edge 20a of a first main surface 21 of the core material 2. The spacer 4 has an elastic modulus smaller than that of the core material 2 and does not absorb a matrix resin of the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B. Thereafter, the first fiber-reinforced resin layer 3A and the second fiber-reinforced resin layer 3B are formed in molding dies 100, 101.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for forming a composite material structure in which an edge of a plate-shaped core material is sandwiched between a pair of fiber-reinforced resin layers.

  Patent Literature 1 below discloses a composite material structure in which an edge of a plate-shaped core material is sandwiched between a pair of fiber-reinforced resin layers. More specifically, the composite material structure has a plate-shaped core material, a first fiber-reinforced resin layer provided on a first main surface of the core material, and a first surface opposite to the first main surface of the core material. And a second fiber reinforced resin layer provided on the two main surfaces. An inclined side surface that is inclined at an acute angle with respect to the first main surface is formed between the first main surface and the second main surface. The first fiber reinforced resin layer extends along the first main surface of the core material and further extends outward from the outer edge of the inclined side surface. On the other hand, the second fiber reinforced resin layer extends along the second main surface and the inclined side surface, and extends along the first fiber reinforced resin layer outward from the outer edge described above. The first and second fiber reinforced resin layers are joined to each other outside the outer edge described above.

JP-A-2006-69320

  In such a composite material structure, since the second fiber reinforced resin layer is bent along the inclined side surface of the core material, the fiber layer in the second fiber reinforced resin layer is formed in the second fiber reinforced resin layer during molding. May be biased. As a result, the matrix resin is unevenly present at a portion where the first fiber reinforced resin layer and the second fiber reinforced resin layer are joined at the tip of the inclined side surface (formation of a resin pool). In the portion where the resin is biased, “sink” easily occurs on the surface of the first fiber reinforced resin layer.

  Accordingly, an object of the present invention is to provide a method for forming a composite material structure capable of suppressing the occurrence of sink marks in a composite material structure having the above-described structure.

  In the method for forming a composite material structure according to the present invention, a composite material structure including a plate-shaped core material, a first fiber-reinforced resin layer, and a second fiber-reinforced resin layer is formed. The core has a pair of first and second main surfaces and an inclined side surface inclined at an acute angle with respect to the first main surface. The first fiber reinforced resin layer extends along the first main surface, and further extends outward from the outer edge on the inclined side surface side. The second fiber reinforced resin layer extends along the second main surface and the inclined side surface, and further extends along the first fiber reinforced resin layer outside the outer edge described above. The first and second fiber reinforced resin layers are bonded to each other outside the outer edge described above. In the method for forming a composite material structure according to the present invention, first, a spacer having an elastic modulus smaller than the elastic modulus of the core material and not absorbing the matrix resin of the first and second fiber reinforced resin layers is formed on the first main surface. Place along the outer edge of After that, the first and second fiber reinforced resin layers are formed in a mold.

  According to the method of forming a composite material structure according to the present invention, it is possible to suppress the occurrence of sink marks on the surface of the first fiber reinforced resin layer.

FIG. 1 is a cross-sectional view (first stage) illustrating a method (PCM method) of forming a composite material structure according to the first embodiment. FIG. 2 is a cross-sectional view (second stage) illustrating the formation method according to the first embodiment. FIG. 3 is a cross-sectional view (third stage) illustrating the formation method according to the first embodiment. FIG. 4 is a cross-sectional view of the composite material structure formed by the forming method according to the first embodiment. FIG. 5 is a cross-sectional view (first stage) showing a method (RTM method) of forming a composite material structure according to the second embodiment. FIG. 6 is a cross-sectional view (second stage) illustrating the formation method according to the second embodiment. FIG. 7 is a cross-sectional view of a composite material structure formed by the forming method according to the second embodiment. FIG. 8 is a cross-sectional view (first stage) showing a method (PCM method) of forming a composite material structure according to a comparative example. FIG. 9 is a cross-sectional view (second stage) illustrating the formation method according to the comparative example. FIG. 10 is a cross-sectional view of a composite material structure formed by a forming method according to a comparative example.

  Hereinafter, embodiments will be described with reference to the drawings. Identical or equivalent components are denoted by the same reference numerals, and detailed description thereof will be omitted. The drawings are schematic and dimensions and ratios may differ from actual ones.

  A forming method according to the first embodiment will be described with reference to FIGS. In the present embodiment, the composite material structure 1X (see FIG. 4) is formed by a PCM (Prepreg Compression Molding) method. First, the formed composite material structure 1X will be described. The composite material structure 1X is used as an engine hood or a trunk lid of a vehicle. As shown in FIG. 4, the composite material structure 1 </ b> X includes a plate-shaped core material 2, a first fiber-reinforced resin layer 3 </ b> A provided on a first main surface 21 of the core material 2, and a The second fiber reinforced resin layer 3 </ b> B provided on the second main surface 22 is provided. The second main surface 22 is an opposite surface of the core 2 to the first main surface 21.

  The core material 2 is a high-performance foamed resin material having excellent strength and heat resistance. An inclined side surface 20 is formed between the first main surface 21 and the second main surface 22 of the core 2. The inclined side surface 20 is inclined at an acute angle with respect to the first main surface 21. More specifically, the surface of the inclined side surface 20 faces the second fiber reinforced resin layer 3B and is inclined so as to gradually approach the first fiber reinforced resin layer 3A. With such an inclination, the bent portion of the second fiber reinforced resin layer 3B is bent with a radius of curvature equal to or larger than the allowable minimum radius of curvature. If the radius of curvature of the fiber reinforced resin is small, the strength of the resin is reduced, and thus the allowable minimum radius of curvature is set in this manner. Further, a spacer 4 to be described in detail later is disposed along an outer edge (= a leading edge of the inclined side surface 20) 20a of the first main surface 21 on the inclined side surface 20 side.

  By adopting a structure in which the core material 2 is sandwiched between the fiber reinforced resin layers 3A and 3B, the strength and rigidity of the composite material structure 1X can be improved while suppressing an increase in the weight of the composite material structure 1X. The core material 2 is a foamed resin material and has an energy absorbing performance. Therefore, when the composite material structure 1X is used as an engine hood or a trunk lid, energy absorption performance can be imparted to the engine hood or the trunk lid. When the composite material structure 1X is used as an engine hood or a trunk lid, the core material 2 is disposed inside a bead formed on the back surface thereof. If sinks occur on the surface of the engine hood or the trunk lid, the appearance is greatly impaired. However, according to the present embodiment, the sinks can be suppressed by providing the spacer 4 as described later.

  The first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed of carbon fiber reinforced resin (CFRP). As will be clear from the following description of the forming method, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are joined to each other outside the outer edge 20a of the core member 2 on the side of the inclined side surface 20. It is integrated. Hereinafter, the mutually bonded portions are also referred to as a bonded fiber reinforced resin layer 3. In this embodiment, since the spacer 4 is arranged along the outer edge 20a, the bonding fiber reinforced resin layer 3 is formed outside the spacer 4. Further, in all the drawings, only one side surface (inclined side surface 20) of the core material 2 is shown, but the other side surfaces have the same configuration.

  Each of the fiber reinforced resin layers 3A and 3B includes a plurality of carbon fiber sheets 3X laminated therein. Each of the fiber reinforced resin layers 3A and 3B is formed by impregnating and curing the carbon fiber sheet 3X with the matrix resin. In addition, the carbon fiber sheet 3X in all the figures is schematically shown, and the number thereof is not accurately represented.

  Here, a bidirectional carbon fiber sheet 3X formed by weaving long carbon fibers into a sheet shape is laminated and used. However, a unidirectional carbon fiber sheet 3X may be used instead of a multidirectional carbon fiber sheet 3X such as a bidirectional carbon fiber sheet. Quasi-isotropic fiber reinforced resin layers 3A and 3B may be formed by using a plurality of anisotropic carbon fiber sheets 3X such as unidirectional or multidirectional.

  The first fiber reinforced resin layer 3 </ b> A is provided on the first main surface 21 (the upper surface in FIG. 4) of the core 2. The first fiber reinforced resin layer 3A extends along the first main surface of the core material 2 and further extends outward from the outer edge 20a described above. On the other hand, the second fiber reinforced resin layer 3B is provided on the second main surface 22 (the lower surface in FIG. 4) of the core material 2. The second fiber reinforced resin layer 3B extends along the second main surface 22 and the inclined side surface 20 of the core material 2 and further extends along the first fiber reinforced resin layer 3A outward from the outer edge 20a described above. It has been extended. Therefore, the portion of the fiber reinforced resin layers 3A and 3B extending outward from the outer edge 20a (spacer 4) forms the above-described bonded fiber reinforced resin layer 3.

  In order to form the above-described composite material structure 1X by the PCM method, first, as shown in FIG. 1, the spacer 4 is arranged on the outer edge 20a of the inclined side surface 20 of the core 2. The spacer 4 has a trapezoidal cross-sectional shape in a cross section perpendicular to the outer edge 20 a (the cross-sectional views of FIGS. 1 to 4), and has an inclined front edge corresponding to the inclined side surface 20. The spacer 4 is attached to the core 2 along the outer edge 20a with an adhesive or the like. The spacers 4 are provided to prevent sinks from being formed on the surface of the composite material structure 1X (the first fiber-reinforced resin layer 3A). The spacer 4 has an elastic modulus smaller than the elastic modulus of the core material 2 and is formed of a material that does not absorb the matrix resin of the fiber reinforced resin layers 3A and 3B.

  Specifically, the spacer 4 is formed of closed-cell EPDM rubber (ethylene propylene diene monomer rubber). The spacer 4 is a foam made of closed cells, and the cells inside are formed independently. Therefore, since the air bubbles are not continuous, the spacer 4 does not absorb the matrix resin of the fiber reinforced resin layers 3A and 3B. Conversely, the matrix resin of the fiber reinforced resin layers 3A and 3B does not impregnate the interior of the spacer 4. Further, since the spacer 4 has a structure called a closed-cell foam and is formed of a material called EPDM rubber, it has elasticity.

  Subsequently, the core material 2 to which the spacers 4 are attached, the first prepreg 30A for forming the first fiber reinforced resin layer 3A, and the second prepreg 30B for forming the second fiber reinforced resin layer 3B, It is set in a pair of molds (molding dies) 100 and 101. The prepregs 30A and 30B are obtained by impregnating the above-described laminated carbon fiber sheet 3X with a matrix resin. The matrix resin is a thermosetting resin. The molds 100 and 101 are provided with a heating mechanism.

  In the molds 100 and 101, the spacer 4 is sandwiched and pressed by the prepregs 30A and 30B. The spacer 4 is deformed due to its elasticity, and forms an inclined surface corresponding to the inclined side surface 20. The spacer 4 has a volume of ４ to ４ due to the elastic deformation. At this time, the spacer 4 extends outside a region surrounded by an extension line (extension surface) of the first main surface 21 and an extension line (extension surface) of the inclined side surface 20. That is, the initial shape of the spacer 4 is set to a shape that exists outside this region even if it is elastically deformed during molding in the molds 100 and 101.

  Subsequently, as shown in FIG. 3, in the molds 100 and 101, the core material 2 to which the spacer 4 is attached, the first prepreg 30A for forming the first fiber-reinforced resin layer 3A, and the second The second prepreg 30B for forming the fiber reinforced resin layer 3B is heated and compressed. The interior of the molds 100 and 101 is preheated before being closed, and the matrix resin (thermosetting resin) of the prepregs 30A and 30B is heated by the molds 100 and 101 to be once softened or liquefied, and then subjected to a curing reaction. (Crosslinking reaction) proceeds and cures. When the matrix resin is cured, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed, and the composite material structure 1X shown in FIG. 4 is completed.

  Once the matrix resin softens or liquefies in the molds 100 and 101 in the state shown in FIG. 3, the carbon fiber sheet 3X in the second prepreg 30B tends to be flat. When tension acts on the carbon fiber sheet 3X due to the shape of the composite material structure 1X (engine hood or trunk lid), the carbon fiber sheet 3X tends to be flatter. As a result, the position of the carbon fiber sheet 3X may be biased inside the second fiber reinforced resin layer 3B. In particular, in the vicinity of the spacer 4, the position of the carbon fiber sheet 3X is biased away from the spacer 4 due to the bending of the second fiber reinforced resin layer 3B.

  However, since the spacers 4 are arranged in advance, no resin pool is formed at the spacers 4. The resin pool is a place where the matrix resin is present unevenly, and is a place where the volume of the resin is partially larger than its surroundings. In general, it is known that when a resin pool is formed in resin molding, sink occurs on the surface due to shrinkage of the resin during cooling. In this embodiment, the resin pool is not formed by arranging the spacer 4 that does not absorb the matrix resin along the outer edge 20a. By preventing the formation of the resin pool, sink marks on the surface of the first fiber-reinforced resin layer 3A can be suppressed.

  Further, since the spacer 4 of the present embodiment does not absorb the matrix resin, the sink does not occur due to insufficient resin. Further, the spacer 4 of the present embodiment has elasticity as described above, and is appropriately deformed inside the molds 100 and 101 by receiving a pressing force from the softened or liquefied matrix resin. At the same time, the matrix resin is appropriately pushed back by the elastic restoring force. These forces are appropriately balanced, and the matrix resin is cured in a state where the balance is maintained to form the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B. It is considered that this balanced state also contributes to suppressing sink marks on the surface of the first fiber reinforced resin layer 3A.

  Further, since the spacer 4 receives heat when forming the fiber reinforced resin layers 3A and 3B, the spacer 4 is also required to have heat resistance. The present inventors have found that it is suitable to use closed-cell EPDM rubber as the spacer 4 in consideration of the above-mentioned plurality of required properties. There are not many that simultaneously satisfy a plurality of required properties, and closed-cell EPDM rubber is very excellent as the spacer 4. With respect to the elasticity, if the elastic modulus of the core material 2 is smaller than that of the spacer 4, the deformation of the core material 2 becomes larger than that of the spacer 4 during molding in the molds 100 and 101, and the composite material having an appropriate shape is formed. The material structure 1X is not formed. Therefore, the elastic modulus of the spacer 4 must be smaller than the elastic modulus of the core material 2.

  Here, a comparative example in which sink occurs due to not using the spacer 4 will be described with reference to FIGS. As shown in FIG. 8, in this comparative example, the spacer 4 is not provided along the outer edge 20a of the core material 2. For this reason, a minute gap is necessarily formed between the first prepreg 30A and the second prepreg 30B near the outer edge 20a. Other than that, it is the same as the first embodiment described above. In this state, similarly to the first embodiment, as shown in FIG. 9, the composite material structure 1Z is formed by the PCM method using the first prepreg 30A and the second prepreg 30B in the molds 100 and 101. I do.

  As shown in FIG. 9, the softened or liquefied matrix resin fills the gap near the outer edge 20a during molding, but the surrounding resin is consumed accordingly. Further, as described above, the position of the carbon fiber sheet 3X is biased inside the second fiber reinforced resin layer 3B, and the position of the carbon fiber sheet 3X is biased away from the spacer 4. As a result, a resin pool 10A is formed near the outer edge 20a. Due to the resin pool 10A, sink marks 10B as shown in FIG. 10 are formed on the surface of the first fiber reinforced resin layer 3A after the matrix resin is cooled.

  The post-sink composite material structure 1Z requires a post-process to hide sink marks. Specifically, the process of polishing after filling the fillet portion with the filler is repeated several times. After that, if the paint is applied, the sink mark will not be visible, but a post-process will be required. In addition, in order to use the appearance of the carbon fiber sheet as a design in CFRP, the coating may be a clear coating. In such a case, the sealant filled in the sink portion will be visible. If the sink is suppressed by providing the spacer 4, such a post-process is not required, and the appearance of the carbon fiber sheet when it is used as a design is improved.

  In the first embodiment described above, the provision of the spacers 4 prevents the resin pool 10A from being formed. As a result, formation of sink marks 10B can be suppressed. In this comparative example, the matrix resin is consumed to fill the gap near the outer edge 20a described above. However, in the above-described first embodiment, since the shape of the spacer 4 can be changed by its elasticity, it is considered that the volume of the gap can be offset in the above-described balanced state, and consumption of the matrix resin can be suppressed.

  In the first embodiment described above, the fiber reinforced resin layers 3A and 3B are formed by the PCM method. The formation of the fiber reinforced resin layers 3A and 3B is not limited to the PCM method, and may be formed by another method. In the second embodiment described below, the composite material structure 1Y (see FIG. 7) is formed by the RTM (Resin Transfer Molding) method. A forming method according to the second embodiment will be described with reference to FIGS.

  Since the core 2 to which the spacer 4 is attached is the same as that of the first embodiment described above, the description thereof is omitted. As shown in FIG. 5, the core 2 to which the spacer 4 is attached, the first preform 31A for forming the first fiber reinforced resin layer 3A, and the second preform 31A for forming the second fiber reinforced resin layer 3B. The second preform 31B is set in a pair of dies (molding dies) 200 and 201. The preforms 31A and 31B are carbon fiber sheets 3X that have been formed in advance by pressing using a die or the like into a shape that matches the shape of the composite material structure 1Y to be formed. The carbon fiber sheet 3X itself is the same as the carbon fiber sheet 3X of the first embodiment described above.

  Subsequently, as shown in FIG. 6, the matrix resin is filled into the molds 200 and 201 from the molds 200 and 201, respectively. The matrix resin of the present embodiment is a thermosetting resin. However, in the case of the RTM method, it is also possible to use a thermoplastic resin as the matrix resin. The molds 200 and 201 are provided with a heating mechanism (for curing the thermosetting resin) and a cooling mechanism (for early cooling of the thermoplastic resin) according to the type of the matrix resin. When the matrix resin is filled, the spacer 4 is deformed by the filling pressure of the matrix resin in the same manner as in the first embodiment. Since this modification has been described in the first embodiment, the description here is omitted.

  The filled matrix resin is impregnated into the preforms 31A and 31B, and is heated and compressed by the molds 200 and 201. The matrix resin (thermosetting resin) is heated by the molds 200 and 201 and once softened or liquefied, and then undergoes a curing reaction (crosslinking reaction) to be cured. When the matrix resin is cured, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed, and the composite material structure 1Y shown in FIG. 7 is completed.

  Also in the present embodiment, when the matrix resin is once softened or liquefied in the molds 200 and 201 in the state shown in FIG. 6, the carbon fiber sheet 3X of the second preform 31B tends to be flat. When tension acts on the carbon fiber sheet 3X due to the shape of the composite material structure 1Y, the carbon fiber sheet 3X tends to become flatter. As a result, the position of the carbon fiber sheet 3X may be biased inside the second fiber reinforced resin layer 3B. In particular, in the vicinity of the spacer 4, the position of the carbon fiber sheet 3X is biased away from the spacer 4 due to the bending of the second fiber reinforced resin layer 3B.

  However, since the spacers 4 are arranged in advance, no resin pool is formed at the spacers 4. In the present embodiment, by disposing the spacer 4 that does not absorb the matrix resin along the outer edge 20a so as not to form a resin pool, it is possible to suppress sink marks on the surface of the first fiber reinforced resin layer 3A. The balanced state of the spacers 4 described in the first embodiment is considered to occur in the present embodiment, and contributes to suppressing sink marks on the surface of the first fiber reinforced resin layer 3A. Seem. It should be noted that this balanced state is likely to occur when the matrix resin is a thermoplastic resin. Furthermore, even in the RTM method, the spacer 4 is required to have heat resistance. Therefore, in consideration of a plurality of required properties such as heat resistance, the use of closed-cell EPDM rubber as the spacer 4 is also suitable in the present embodiment.

  According to the forming method according to the first and second embodiments, the composite material structure 1X or 1Y including the core material 2, the first fiber reinforced resin layer 3A, and the second fiber reinforced resin layer 3B is formed. At this time, the spacer 4 is arranged along the outer edge 20 a of the first main surface 21 of the core 2. The spacer 4 has an elastic modulus smaller than the elastic modulus of the core material 2 and does not absorb the matrix resin of the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B. After that, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed in a mold (100 and 101 or 200 and 201).

  Therefore, when the first fiber-reinforced resin layer 3A and the second fiber-reinforced resin layer 3B are formed in the molding die, the formation of the resin pool is suppressed by the spacer 4 that does not absorb the matrix. Further, when the first fiber-reinforced resin layer 3A and the second fiber-reinforced resin layer 3B are formed in the molding die, the spacer 4 is elastically deformed so as to reduce its volume, and the spacer 4 and the first fiber-reinforced resin layer 3A are formed. A state in which the second fiber reinforced resin layer 3B is balanced (a state in which they are adapted to each other) is formed. As a result, generation of sink marks on the surface of the first fiber reinforced resin layer 3A can be effectively suppressed.

  Here, in the first embodiment, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed by a PCM method using prepregs 30A and 30B impregnated with a thermosetting resin as a matrix resin. By doing so, the gap between the prepregs 30A and 30B that can be formed in the mold can be eliminated by the above-described balanced state of the spacer 4, and the occurrence of sinks can be effectively suppressed. On the other hand, in the second embodiment, the first fiber reinforced resin layer 3A and the second fiber reinforced resin layer 3B are formed by impregnating the preforms 31A and 31B with the matrix resin in the mold by the RTM method. By doing so, the above-mentioned balanced state of the spacer 4 can be formed by the charging pressure of the matrix resin of the first fiber reinforced resin layer 3A and the second fiber reinforced resin into the molding die, and the occurrence of sink marks can be effectively achieved. Can be suppressed.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a method of forming a composite material structure used as an engine hood or a trunk lid of a vehicle.

1X, 1Y Composite material structure 2 Core material 20 Inclined side surface 20a Outer edge 21 First main surface 22 Second main surface 3A First fiber reinforced resin layer 3B Second fiber reinforced resin layer 3X Carbon fiber sheet 30A First prepreg 30B Second Prepreg 31A First preform 31B Second preform 4 Spacer 100, 101, 200, 201 Mold (die)

Claims (4)

A first main surface, a second main surface opposite to the first main surface, and an inclined side surface between the first main surface and the second main surface inclined at an acute angle with respect to the first main surface. A plate-shaped core material, a first fiber-reinforced resin layer provided on the first main surface, and a second fiber-reinforced resin layer provided on the second main surface, wherein the first fiber-reinforced resin layer is provided. Is extended along the first main surface and further extended outward from the outer edge of the first main surface on the side of the inclined side surface, and the second fiber-reinforced resin layer is provided with the second main surface and the second main surface. The first fiber-reinforced resin layer and the second fiber-reinforced resin layer extend along the inclined side surface and further extend along the first fiber-reinforced resin layer outside the outer edge of the first fiber-reinforced resin layer. A method of forming a composite material structure, wherein the fiber-reinforced resin layers are bonded to each other outside the outer edge,
A spacer having an elastic modulus smaller than that of the core material and not absorbing the matrix resin of the first fiber reinforced resin layer and the second fiber reinforced resin layer is arranged along the outer edge of the first main surface. And then forming the first fiber-reinforced resin layer on the first main surface of the core material and forming the second fiber-reinforced resin layer on the second main surface in a molding die. Formation method. After placing the first prepreg of the first fiber-reinforced resin layer and the second prepreg of the second fiber-reinforced resin layer in the molding die,
The composite material according to claim 1, wherein the first prepreg and the second prepreg are cured in the mold by a PCM method to form the first fiber-reinforced resin layer and the second fiber-reinforced resin layer. The method of forming the structure. After placing the first preform of the first fiber-reinforced resin layer and the second preform of the second fiber-reinforced resin layer in the molding die,
The first preform and the second preform are impregnated with the matrix resin and then cured by filling the matrix resin into the mold by the RTM method. The method for forming a composite material structure according to claim 1, wherein the two-fiber-reinforced resin layer is formed.   The method for forming a composite material structure according to any one of claims 1 to 3, wherein the spacer is a closed-cell EPDM rubber.

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