JP7473442B2 - Fiber Reinforced Sandwich Composites - Google Patents

Description

The present invention relates to a fiber-reinforced sandwich composite in which a fiber base material and a core material are laminated and bonded together by heating and compressing them together with a thermosetting resin.

2. Description of the Related Art In recent years, fiber-reinforced resin molded articles formed from composite materials of fiber base materials such as carbon fibers and glass fibers and thermosetting resins have been widely used in various fields and applications for the purpose of reducing weight and improving mechanical strength.
In particular, there is a high demand for lower fuel consumption in transportation equipment such as automobiles, trains, and aircraft, and since reducing the weight of vehicles and aircraft has a significant effect on improving fuel consumption, fiber-reinforced resin moldings, which have excellent light weight, are expected to serve as an alternative to metals.

As a method for producing a fiber-reinforced resin molded body, there is a method in which a fiber base material is impregnated with a thermosetting resin to form a prepreg, and then the prepreg is molded using an autoclave, a hot press, or the like.
When producing prepregs, the thermosetting resin with which the fiber substrate is impregnated is generally in liquid form. However, liquid resins have a limited pot life, and when a solvent is used, this can cause problems with the working environment and air pollution.
As a method for solving these problems, a prepreg made from a powdered resin has been proposed (Patent Document 1).

In addition, a lightweight fiber-reinforced sandwich composite has been proposed, which is obtained by laminating prepregs and a core material and hot pressing them (Patent Document 2).

JP 2006-232915 A JP 2020-44811 A

However, in molding methods using prepregs, whether a liquid resin or a powdered resin is used, problems arise in that the prepreg process requires large-scale equipment and the prepreg process management is complicated, resulting in high production costs for fiber-reinforced resin molded bodies and sandwich structures.
Furthermore, conventional prepregs have poor storage stability because the curing reaction proceeds gradually even at room temperature during storage before use, which can affect the quality of fiber-reinforced resin moldings and sandwich structures obtained by using the stored prepregs.

The present invention has been made in consideration of the above points, and aims to provide a fiber-reinforced sandwich composite integrated with a core material that can be produced easily, inexpensively, and safely without using prepregs or worrying about the storage stability of prepregs, and without risking environmental pollution.

The present invention is a fiber-reinforced sandwich composite in which a fiber base material and a core material are laminated and heated and compressed together with a thermosetting resin to bond and integrate them, and is characterized in that the core material has a 5% compressive stress of 0.15 MPa or more, the thermosetting resin is in a powder state before heating, has a viscosity of 1,500 Pa·s or less at a curing reaction start temperature Tb°C, and has a maximum viscosity of 1,000 Pa·s or more in the range of curing reaction start temperatures Tb°C to 190°C.

According to the present invention, a fiber-reinforced sandwich composite integrated with a core material can be obtained, which can be produced easily, inexpensively, and safely without using prepregs and without worrying about the storage stability of prepregs, and without risking environmental pollution.

FIG. 1 is a cross-sectional view of a fiber-reinforced sandwich composite according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing lamination and heat compression in one embodiment of the method for producing a fiber-reinforced sandwich composite of the present invention. 1 is a table showing the material, thickness, etc. of the core material used in each example and each comparative example. 1 is a table showing the melting initiation temperatures, curing reaction initiation temperatures, etc. of the thermosetting resins used in each of the examples and comparative examples. 1 is a table showing the configurations and physical properties of each of the examples and comparative examples. 1 is a graph showing the viscosity measurement results of thermosetting resins used in Examples 1, 6, and 7 and Comparative Examples 2 and 3.

An embodiment of the present invention will be described. In one embodiment of the fiber-reinforced sandwich composite 10 shown in FIG. 1, a fiber base material 11 and a core material 15 are heated and compressed together with a thermosetting resin 21, and are bonded together by hardening the thermosetting resin 21.

The fiber substrate 11 may be a single layer or multiple layers, and the number of layers is determined depending on the application of the fiber-reinforced sandwich composite 10. In the illustrated embodiment, the fiber substrate 11 is made of four layers. The fiber substrate 11 may be a woven fabric or nonwoven fabric made of glass fiber, aramid fiber, basalt fiber, carbon fiber, or the like, and is not particularly limited. However, a carbon fiber woven fabric is preferable because it is lightweight and has high rigidity. As the carbon fiber woven fabric, a woven fabric in which the fibers are woven in more than one direction is preferable. For example, a plain weave, twill weave, or satin weave made of warp and weft threads, and a triaxial weave made of threads in three directions are suitable. In addition, the carbon fiber woven fabric is preferably one having a fiber weight of 50 to 600 g/m ² in terms of impregnation of the thermosetting resin 21 and the rigidity of the fiber-reinforced sandwich composite 10.

The core material 15 has an effect of improving the strength of the fiber-reinforced sandwich composite 10, and preferably has a 5% compressive stress value of 0.15 MPa or more. A more preferable range of the 5% compressive stress is 0.15 to 1 MPa. The 5% compressive stress is the stress when a core material cut to a size of 50 x 50 mm is compressed by 5% of its thickness with a disk-shaped compressor of φ80 mm at a speed of 5 mm/min. An example of a stress measuring device is Shimadzu Corporation's Autograph AG-X.
The density (JIS Z8807) of the core material 15 is preferably 20 to 120 kg/ ^m3 .

The core material 15 is preferably a foam with a closed cell structure. In a foam with a closed cell structure, the cells (air bubbles) are closed and independent of each other. By using a foam with a closed cell structure as the core material 15, the molten thermosetting resin during the production of the fiber-reinforced sandwich composite 10 is less likely to penetrate the core material 15 with a closed cell structure, and the surface appearance of the fiber-reinforced sandwich composite 10 is excellent. If the core material 15 is made of a foam with an open cell structure in which the cells are open and connected to each other, the molten thermosetting resin during the production of the fiber-reinforced sandwich composite 10 is likely to penetrate the core material 15 with an open cell structure, and the amount of thermosetting resin on the surface of the fiber-reinforced sandwich composite 10 may be reduced, which may impair the appearance of the fiber-reinforced sandwich composite.

Examples of the closed-cell foam that constitutes the core material 15 include polyethylene terephthalate foam (PET foam), polymethacrylimide foam (PMI foam), polyvinyl chloride foam (PVC foam), and rigid polyurethane foam (rigid PU foam).

The thickness of the core material 15 is determined depending on the application of the fiber-reinforced sandwich composite 10, and may be, for example, about 3 to 20 mm.
In addition, the core material 15 is not limited to a single layer, and may be a multi-layered material. When the core material 15 is a single layer and the fiber base material 11 is a multi-layered material, the core material 15 is preferably positioned between the fiber base materials 11.

There is no particular limitation on the method for producing the core material 15. For example, the following method may be used.
A method in which resin foam particles are filled into a mold, heated and expanded using a heat transfer medium such as hot water or steam, and the expansion pressure of the resin foam particles causes the foam particles to fuse and integrate with each other to produce a foam having the desired shape (in-mold foam molding method).
A method in which a resin is supplied to an extruder together with a foam control agent, etc., and melt-kneaded in the presence of a foaming agent such as a chemical foaming agent or a physical foaming agent, and the molten mixture is extruded from the extruder to foam (extrusion foaming method).
A method of producing a foam by producing a block of expandable resin molding containing a chemical foaming agent and foaming this expandable resin molding in a mold.

The thermosetting resin 21 is used in the form of a solid powder when the fiber-reinforced sandwich composite 10 is manufactured. The shape of the powder may be spherical, needle-like, flake-like, or the like, and is not particularly limited. The powder of the thermosetting resin 21 is preferably arranged so as to be in contact with at least the fiber substrate 11 and the core material 15. For example, when the core material 15 is a single layer, the powder of the thermosetting resin 21 is arranged at least between the fiber substrate 11 and the core material 15, and when the fiber substrate 11 is a multiple layer, the powder of the thermosetting resin 21 may be arranged between the fiber substrate 11 in addition to between the fiber substrate 11 and the core material 15. In addition, when the core material 15 is laminated in multiple layers, it is preferable that the powder of the thermosetting resin 21 is arranged between the fiber substrate 11 and the core material 15 and between the core materials 15.
When the powder of thermosetting resin 21 is heated and compressed together with the fiber base material 11 and the core material 15 , it melts and impregnates the fiber base material 11 , and hardens in the state of contact with the core material 15 .

The thermosetting resin 21 preferably has a viscosity of 1,500 Pa·s or less at the curing reaction start temperature Tb°C. By setting the viscosity at the curing reaction start temperature Tb°C within this range, the molten thermosetting resin 21 can be sufficiently impregnated into the fiber base material 11, and a fiber-reinforced sandwich composite 10 with uniform physical properties can be obtained.

The thermosetting resin 21 preferably has a maximum viscosity of 1,000 Pa·s or more in the temperature range of the curing reaction start temperature Tb°C to 190°C. By setting the maximum viscosity in this range, the molten thermosetting resin 21 can be impregnated into the fiber base material 11 and cured sufficiently, and the fiber-reinforced sandwich composite 10 has good formability and can obtain sufficient strength in a short time.

The melting start temperature Ta°C of the thermosetting resin 21 and the curing reaction start temperature Tb°C are preferably in the relationship with the temperature Tc°C during heating and compression such that [Tb+(Tb-Ta)/3]-10≦Tc≦[Tb+(Tb-Ta)/3]+20. By having this relationship between the melting start temperature Ta°C of the thermosetting resin 21, the curing reaction start temperature Tb°C, and the temperature Tc°C during heating and compression, the powder of the thermosetting resin 21 melts well during heating and compression, and the thermosetting resin 21 is easily impregnated into the fiber base material 11, making it possible to obtain a fiber-reinforced sandwich composite 10 with uniform physical properties.

Thermosetting resin 21 preferably has a value of 40≦(Tb-Ta)≦70 (curing reaction start temperature Tb°C-melting start temperature Ta°C). By setting (Tb-Ta) in this range, the molten thermosetting resin 21 can be sufficiently impregnated into the fiber base material 11, and a fiber-reinforced sandwich composite 10 with uniform physical properties can be obtained.

It is preferable that the melting start temperature Ta°C of the thermosetting resin 21 is in the range of 60 to 100°C. By setting the melting start temperature Ta°C of the thermosetting resin 21 in this range, it is easy to control the temperature during heating and compression.

The thermosetting resin that can satisfy the above melting initiation temperature Ta°C, curing reaction initiation temperature Tb°C, (Tb-Ta) range, minimum viscosity, maximum viscosity, etc. is preferably selected from the group consisting of phenolic resin, mixed resin of phenolic resin and epoxy resin, mixed resin of phenolic resin and cyanate resin, and mixed resin of phenolic resin, cyanate resin, and epoxy resin. Phenolic resin has excellent flame retardancy and can impart excellent strength and flame retardancy to the fiber-reinforced sandwich composite 10.
The thermosetting resin 21 may contain various powder additives such as pigments, antibacterial agents, and ultraviolet absorbing agents, as long as they do not affect the viscosity and reactivity of the thermosetting resin.

The fiber-reinforced sandwich composite of the present invention can be manufactured by arranging powder of thermosetting resin 21 in contact with fiber substrate 11 and core material 15, and heating and compressing fiber substrate 11 and core material 15 together with powder of thermosetting resin 21 in a mold, thereby melting the powder of thermosetting resin 21 and impregnating it into fiber substrate 11 and curing it in contact with core material 15.

One embodiment of a manufacturing method for the fiber-reinforced sandwich composite 10 shown in FIG. 1 will be described with reference to FIG. 2. In the following description of the manufacturing method, the fiber substrates 11 at multiple positions are indicated by a combination of numbers and letters, such as "11A," to make it easier to understand their vertical positional relationship.

In the embodiment shown in FIG. 2, of the four fiber base materials 11A to 11D, two fiber base materials 11A and 11B are layered, thermosetting resin powder 21A is placed on top of that, core material 15 is placed on top of that, thermosetting resin powder 21B is placed on top of that, and the remaining two fiber base materials 11C and 11D are layered on top of that to create a pre-molded laminate.

The particle size of the thermosetting resin powders 21A and 21B is preferably 10 to 500 μm in terms of ease of melting. The amount of the thermosetting resin powders 21A and 21B is preferably adjusted so that the VF value (%) of the molded body excluding the foamed portion of the core material is 40 to 70%. The VF value (%) is calculated by (total weight of fiber base material/density of fiber)/(volume of molded body excluding the foamed portion of the core material) x 100.

The pre-molded laminate thus produced is sandwiched between the lower die 31 and upper die 32 of a heated mold 30 and heat-compressed. A plastic film for release may be placed on the mold surface of the mold. The mold 30 is heated to a temperature Tc°C during the heat-compression process by a heating means such as an electric heater.

The pressure (compression) of the pre-molded laminate during heating and compression using the mold 30 is preferably 2 to 20 MPa so that the thermosetting resin powders 21A and 21B can be effectively impregnated into the fiber base materials 11A to 11D after melting.

The thermosetting resin powder 21A, 21B located on both sides (top and bottom) of the core material 15 melts as the laminate is heated by the mold 30, and the molten thermosetting resin impregnates the lower fiber base materials 11B, 11A and the upper fiber base materials 11C, 11D as a result of compression of the pre-molded laminate. The thermosetting resin that has impregnated the fiber base materials 11A-11D and is in contact with the core material 15 hardens, and the fiber base materials 11A-11D and the core material 15 between the fiber base materials 11B, 11C are bonded together in a compressed state, and the fiber-reinforced sandwich composite 10 shown in FIG. 1 is obtained, which is shaped to the mold surface shape of the lower mold 31 and the upper mold 32.

The fiber-reinforced sandwich composites of Examples 1 to 7 and Comparative Examples 1 to 3 shown in Figure 5 were produced using the core material shown in Figure 3 and the thermosetting resin powder shown in Figure 4.

The 5% compression stress of the core material was measured when the core material, cut to a size of 50 x 50 mm, was compressed by 5% of its thickness using a disk-shaped compression tool with a diameter of 80 mm at a speed of 5 mm/min. The stress measurement device used was a Shimadzu Autograph AG-X.

The viscosity of the thermosetting resin was measured using a rheometer Rheosol-G3000 manufactured by UBM Co., Ltd. under the following conditions.
1) 0.4 g of the sample is molded into a pellet (diameter φ18 mm, thickness approximately 0.4 mm), and the molded pellet is sandwiched between parallel plates with a diameter of φ18 mm.
2) The dynamic viscosity was measured at 2°C intervals over a temperature range of 40°C to 200°C under a constant temperature increase rate of 5°C/min, a frequency of 1 Hz, and a rotation angle (strain) of 0.1 deg.

For the fiber-reinforced sandwich composites of Examples 1 to 7 and Comparative Examples 1 to 3, the product appearance was judged, and the density, thickness, bending strength, and bending modulus were measured.
The appearance of the product was visually inspected for defects such as deformation or uneven resin impregnation on the surface of the fiber-reinforced sandwich composite. If there was no defect, it was marked as "O" and if there was a defect, it was marked as "X".
The density was measured based on JIS Z8807.
The bending strength and bending modulus were measured based on JIS K7074 Method A.

Example 1
As the fiber substrate, four sheets of carbon fiber fabric (manufactured by Teijin Limited, product name: W-3101, basis weight: 200 g/m ² , thickness 0.22 mm) cut to 210 x 297 mm were prepared. The weight of each fiber substrate after cutting was 12.5 g. Two sheets of the cut fiber substrate were laminated, and 25 g of the following resin A was roughly evenly placed on top of them as a thermosetting resin powder, and a polyethylene terephthalate foam with a closed cell structure (manufactured by 3A Composites Airex, AIREX (T10)) cut to 210 x 297 mm was placed on top of that as a core material, and 25 g of resin A was roughly evenly placed on top of that, and the remaining two fiber substrates were laminated on top of that to prepare a pre-molded laminate.
Resin A is a phenolic resin manufactured by Sumitomo Bakelite Co., Ltd., product name: PR-50252, average particle size: 30 μm.
The viscosity measurement results of Resin A (Examples 1, 6, and 7) are shown in the graph of FIG.

The pre-molded laminate was placed on the molding surface (mold surface) of the lower die of a mold heated to 150°C, the upper die of the mold was placed over the pre-molded laminate, the mold was closed, and the laminate was heated and compressed at a pressure of 5 MPa for 10 minutes. The thermosetting resin powder melted when heated, and impregnated the fiber base material of each layer as the pre-molded laminate was compressed, and curing was completed when the pre-molded laminate was in contact with the core material, producing the fiber-reinforced sandwich composite of Example 1 in which the fiber base material and core material were laminated together as the thermosetting resin cured.

The fiber-reinforced sandwich composite of Example 1 had a product appearance of "good," a density of 0.24 g/cm ³ , a flexural strength of 23 MPa, and a flexural modulus of 6.2 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Example 2
A fiber-reinforced sandwich composite of Example 2 was produced in the same manner as in Example 1, except that Resin B below was used as the thermosetting resin powder.
Resin B is a phenolic resin manufactured by Sumitomo Bakelite Co., Ltd., product name: PR-310, average particle size: 30 μm.

The fiber-reinforced sandwich composite of Example 2 had a product appearance of "good", a density of 0.26 g/cm ³ , a flexural strength of 19 MPa, and a flexural modulus of 4.3 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Example 3
A fiber-reinforced sandwich composite of Example 3 was produced in the same manner as in Example 1, except that a resin (25 g) obtained by uniformly mixing 12.5 g of Resin A and 12.5 g of Resin C described below was used as the thermosetting resin powder, and the mold temperature was set to 170°C.
Resin C was an epoxy resin (product name: jER-1001, manufactured by Mitsubishi Chemical Corporation) that was crushed in a mortar and used. The average particle size was 100 μm.

The fiber-reinforced sandwich composite of Example 3 had a product appearance of "good," a density of 0.23 g/cm ³ , a flexural strength of 24 MPa, and a flexural modulus of 6.8 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Example 4
A fiber-reinforced sandwich composite of Example 4 was produced in the same manner as in Example 1, except that a resin (25 g) obtained by uniformly mixing 12.5 g of Resin D and 12.5 g of Resin E was used as the thermosetting resin powder and the mold temperature was set to 160°C.
Resin D was a phenolic resin manufactured by Sumitomo Bakelite Co., Ltd., product name: PR-50235D, which was ground in a mortar and used. The average particle size was 90 μm.
Resin E was a cyanate resin (manufactured by Mitsubishi Gas Chemical Company, Inc., product name: CYTESTER TA) that was ground in a mortar and used. The average particle size was 100 μm.

The fiber-reinforced sandwich composite of Example 4 had a product appearance of "good", a density of 0.26 g/cm ³ , a flexural strength of 30 MPa, and a flexural modulus of 7.5 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Preparation of Example 5 A fiber-reinforced sandwich composite of Example 5 was prepared in the same manner as in Example 1, except that a resin (24.9 g) obtained by uniformly mixing 8.3 g of Resin D, 8.3 g of Resin E, and 8.3 g of Resin C was used as the thermosetting resin powder, and the mold temperature was set to 170°C.

The fiber-reinforced sandwich composite of Example 5 had a product appearance of "good," a density of 0.28 g/cm ³ , a flexural strength of 28 MPa, and a flexural modulus of 7.2 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Example 6
A fiber-reinforced sandwich composite of Example 6 was produced in the same manner as in Example 1, except that a polymethacrylimide foam having a closed-cell structure (manufactured by Evonik Industries, product name: Rohacell (IG-31)) was used as the core material.

The fiber-reinforced sandwich composite of Example 6 had a product appearance of "good", a density of 0.38 g/cm ³ , a flexural strength of 41 MPa, and a flexural modulus of 14.3 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Example 7
A fiber-reinforced sandwich composite of Example 7 was produced in the same manner as in Example 1, except that a polyvinyl chloride foam with a closed-cell structure (manufactured by GURIT, product name CoreCell (HT-80)) was used as the core material.

The fiber-reinforced sandwich composite of Example 7 had a product appearance of "good," a density of 0.25 g/cm ³ , a flexural strength of 26 MPa, and a flexural modulus of 5.7 GPa, and was therefore excellent in appearance, had high strength and rigidity, and was lightweight.

Comparative Example 1
A fiber-reinforced sandwich composite of Comparative Example 1 was produced in the same manner as in Example 1, except that a rigid polyurethane foam (manufactured by Inoac Corporation, product name: THERMAX (SII-25)) was used as the core material.

The fiber-reinforced sandwich composite of Comparative Example 1 had a product appearance of “good”, a density of 0.21 g/cm ³ , a bending strength of 5 MPa, and a bending modulus of elasticity of 0.6 GPa. The strength of the fiber-reinforced sandwich composite was insufficient due to the low 5% compressive strength of the core material used.

Comparative Example 2
A fiber-reinforced sandwich composite of Comparative Example 2 was produced in the same manner as in Example 1, except that the following resin F was used as the thermosetting resin powder and the mold temperature was set to 100°C.
Resin F is a phenolic resin manufactured by Sumitomo Bakelite Co., Ltd., product name: PR-50699, average particle size: 30 μm.
The results of viscosity measurement of Resin F (Comparative Example 2) are shown in the graph of FIG.

In Comparative Example 2, the thermosetting resin had a high viscosity (fast reaction) and poor impregnation into the fiber substrate, so a uniform fiber-reinforced sandwich composite was not obtained, and the density, thickness, bending strength, and bending modulus could not be measured.

Comparative Example 3
A fiber-reinforced sandwich composite of Comparative Example 3 was produced in the same manner as in Example 1, except that a resin (24.9 g) obtained by uniformly mixing 8.3 g of Resin A and 16.6 g of Resin D was used as the thermosetting resin powder and the mold temperature was set to 160°C.
The results of viscosity measurement for resin A/resin D=1/2 (Comparative Example 3) are shown in the graph of FIG.

In Comparative Example 3, the thermosetting resin was not cured sufficiently, and the fiber-reinforced sandwich composite was deformed when demolded, making it impossible to measure the density, thickness, bending strength, and bending modulus.

As described above, according to the present invention, a fiber-reinforced sandwich composite can be obtained that can be produced easily, inexpensively, and safely without the risk of environmental pollution, since no prepreg is used, no solvent is required for the liquid thermosetting resin, and there is no risk of environmental pollution, and the thermosetting resin has no pot life.
The present invention is not limited to the embodiments, and can be modified without departing from the spirit of the invention.

REFERENCE SIGNS LIST 10 Fiber-reinforced sandwich composite 11, 11A to 11D Fiber base material 15 Core material 21 Thermosetting resin 21A, 21B Thermosetting resin powder 30 Mold 31 Lower mold 32 Upper mold

Claims (3)

A fiber-reinforced sandwich composite in which a fiber base material and a core material are laminated and heated and compressed together with a thermosetting resin to bond and integrate the fiber base material and the core material,
The core material has a 5% compressive stress of 0.15 MPa or more,
The thermosetting resin is in a powder state before heating, has a viscosity of 1,500 Pa·s or less at a curing reaction initiation temperature Tb°C, and has a maximum viscosity of 1,000 Pa·s or more in the curing reaction initiation temperature range of Tb°C to 190°C. A fiber-reinforced sandwich composite. 2. The fiber-reinforced sandwich composite of claim 1, wherein the core material is a closed-cell foam. 3. The fiber-reinforced sandwich composite according to claim 1, wherein the core material has a 5% compressive stress of 0.15 MPa or more and 1 MPa or less.

Images