Fiber-reinforced plastic

Abstract

To provide a fiber-reinforced plastic capable of storing a matrix resin at a normal temperature, reducing management of a molding process while management of liquid preparation is unnecessary and further having an impact resistance.SOLUTION: A fiber base material in which a plurality of reinforcing fiber yarns are arranged in one direction and which has a high density of 50-65% fiber volume content calculated from thickness of a sheet at 0.1 Mpa pressure and is formed in a sheet shape is incorporated, and technical means is adopted in which the fiber base material or a laminate of the fiber base materials is impregnated with a one pack curable type thermoset acrylic resin and is incorporated by curing.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to improvements in fiber-reinforced plastics (FRP), and more specifically to fiber-reinforced plastics obtained by impregnating a reinforcing fiber substrate with a thermosetting acrylic resin that has a relatively low viscosity at room temperature and is one-component curing type as the matrix resin, followed by curing the resin, which allows the matrix resin to be stored at room temperature, eliminates the need for liquid preparation management, reduces the management of the molding process, and also provides impact-resistant fiber-reinforced plastics. [Background technology]

[0002] In recent years, fiber-reinforced plastics, which are obtained by combining reinforcing fiber materials such as carbon fiber, glass fiber, and aramid fiber with various matrix resins, have become widely used in various fields and applications because of their light weight and high strength.

[0003] The application of fiber-reinforced plastics to vehicles such as aircraft and ships, and to large structures in the energy sector such as rotor blades for wind power generation, not only has the effect of extending cruising range and saving fuel by reducing the weight of some parts, but also leads to the possibility of changing the design of surrounding parts and increases the degree of freedom in design changes such as dimensions and shape, so it is being actively applied.

[0004] When molding FRP parts like this, "RTM molding" is used as one of the relatively low-cost molding methods, and "VaRTM (Vacuum Assissted Resin Transfer Molding) molding" is sometimes used, especially for large structures (see, for example, Patent Document 1).

[0005] When such molding is carried out, the resin impregnation is carried out by adjusting the viscosity to a relatively low level by using a thermosetting resin so that the resin can be sufficiently impregnated into the reinforcing fiber substrate.

[0006] However, to achieve a viscosity that allows easy impregnation with thermosetting resin, the resin must be heated and maintained at around 50 to 80°C. Furthermore, thermosetting resins generally require the addition of two or more liquids, such as the base resin and curing agent, and depending on the resin, solid or powdered substances, which requires the time and effort of managing the weight and temperature of the raw materials used to prepare the resin, as well as the mixing conditions.

[0007] Furthermore, since thermosetting resins are generally prone to brittle fracture, measures are taken to prevent this in parts that require impact resistance, such as using special liquid preparations, changing the resin itself to a thermoplastic resin, or using metal materials.

[0008] However, preparing the special liquid is time-consuming, and changing to a thermoplastic resin poses the problem of the molding process itself being large-scale, while changing to a metal material poses the problem of not being able to achieve sufficient weight reduction. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-220609 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the above-mentioned conventional problems, and its object is to provide a fiber-reinforced plastic in which a reinforcing fiber substrate is impregnated with and cured using a thermosetting acrylic resin that has a relatively low viscosity at room temperature and is one-component curing type as the matrix resin, thereby enabling the matrix resin to be stored at room temperature, eliminating the need for liquid preparation management and reducing the management of the molding process, and also providing an impact-resistant fiber-reinforced plastic. [Means for solving the problem]

[0011] The means adopted by the present inventor to solve the above technical problems will be described below with reference to the accompanying drawings.

[0012] That is, the present invention provides a fiber substrate in the form of a sheet having a high density in which a plurality of reinforcing fiber threads are arranged in one direction and the fiber volume content calculated from the thickness of the sheet at a pressure of 0.1 MPa is 50 to 65%; A fiber-reinforced plastic was completed by adopting a technical means in which this fiber base material or a laminate of this fiber base material is impregnated with a one-component curing type thermosetting acrylic resin and cured.

[0013] Further, the fiber volume content is Vf=W / 10ρt Vf: Fiber volume content (%) W: Reinforced fiber weight (g / m 2 ) ρ: Density of reinforcing fiber (g / cm 3 ) t: Sheet thickness (mm) at 0.1 MPa pressure It is also possible to adopt a technical measure of calculating the value by the formula:

[0014] Furthermore, a technical means can be adopted in which the thermosetting acrylic resin is a one-component curing type thermosetting acrylic resin having a viscosity of 20 to 200 mPa·s at a resin temperature of 25°C.

[0015] Furthermore, it is also possible to employ a technical means in which the thermosetting acrylic resin contains a methacrylic acid ester as a main component and the tensile strain at maximum stress in the tensile test of JIS-K7161 is 10% or more.

[0016] Furthermore, the bending properties in the fiber direction of a fiber reinforced plastic formed by impregnating and curing the thermosetting acrylic resin into a sheet-like fiber base material are Maximum load strain: ε max , The maximum load strain ε maxBending stress when strained by 1%: σ a , The maximum load strain ε max Maximum bending stress at: σ max , When The maximum bending stress σ max Residual stress rate: P (%) = 100 × σ a / σ max Technical measures can also be adopted to ensure that the ratio is at least 50%.

[0017] Furthermore, a technical measure can be adopted in which the reinforcing fibers are glass fibers or polyacrylonitrile carbon fibers having an elastic modulus of 70 GPa or more. [Effects of the Invention]

[0018] According to the fiber-reinforced plastic of the present invention, a thermosetting acrylic resin that has a relatively low viscosity at room temperature and is one-component curing type is used as the matrix resin, and the fiber-reinforced plastic is obtained by impregnating and curing the reinforcing fiber substrate with the resin. This allows the matrix resin to be stored at room temperature, eliminates the need for liquid preparation management, reduces the need for management of the molding process, and further imparts impact resistance. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a graph showing "Poisson's ratio" in a tensile test of a thermosetting resin according to an embodiment of the present invention. [Figure 2] 1 is a graph showing a "stress-strain curve" in a tensile test of a thermosetting resin according to an embodiment of the present invention. [Figure 3] 1 is a graph showing "bending characteristics" in a tensile test of a thermosetting resin according to an embodiment of the present invention. [Figure 4] 10 is a comparative photograph of a test piece after a drop weight impact test according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will be described below: First, a fiber substrate is formed in the form of a sheet by arranging a plurality of reinforcing fiber threads in one direction.

[0021] In this embodiment, the reinforcing fibers can be glass fibers or polyacrylonitrile (PAN)-based carbon fibers with an elastic modulus of 70 GPa or more. This allows for a high-strength, high-rigidity FRP product and contributes to reducing the weight of the structure. While glass fibers and carbon fibers are mentioned here from the perspective of high strength and high rigidity, they are not necessarily limited to these, and aramid fibers, polyester fibers, polyvinyl alcohol (PVA) fibers, etc. may also be used depending on the requirements of the FRP product.

[0022] The fiber base material has a high density of 50 to 65% fiber volume content calculated from the thickness of the sheet at a pressure of 0.1 MPa.

[0023] In this embodiment, the fiber volume content is Vf=W / 10ρt Vf: Fiber volume content (%) W: Reinforced fiber weight (g / m 2 ) ρ: Density of reinforcing fiber (g / cm 3 ) t: Sheet thickness (mm) at 0.1 MPa pressure The value calculated in is used.

[0024] To obtain the high strength and high rigidity characteristic of composite materials, a fiber volume fraction (Vf) of 50 to 65% is preferable. If Vf is less than 50%, the volume ratio of resin to reinforcing fibers in the composite material will be higher, resulting in a material with relatively low maximum stress and elastic modulus. On the other hand, if Vf is greater than 65%, it will be difficult to impregnate the gaps between the reinforcing fibers and the material surface with sufficient resin, resulting in the formation of voids and increasing defects within the composite material, resulting in reduced strength.

[0025] The fiber base material or a laminate of the fiber base material is impregnated with a one-component curing type thermosetting acrylic resin having a viscosity of 20 to 200 mPa·s at a resin temperature of 25°C and cured.

[0026] By using a one-component thermosetting acrylic resin instead of a two-component thermosetting resin, the process of preparing the liquid is eliminated, reducing labor. Furthermore, the viscosity within the above range is sufficient for impregnation at room temperature, eliminating the need for heating to control the temperature of the resin and mold during impregnation. This range is preferable because a viscosity below 20 mPa·s can lead to the problem of "racetracking," in which the resin preferentially flows into voids. On the other hand, a viscosity above 200 mPa·s can suppress racetracking compared to 20 mPa·s, but can make impregnation difficult in methods such as VaRTM, which uses reduced pressure inside the bag film to impregnate the film solely through the pressure difference between the inside and outside of the film.

[0027] Furthermore, in this embodiment, the thermosetting acrylic resin contains methacrylic acid ester as a main component, and the tensile strain at maximum stress in the tensile test of JIS-K7161 can be 10% or more.

[0028] The reason for this is that FRPs made with resins with a tensile strain of less than 10% at maximum stress are prone to brittle fracture when subjected to large strains, making them unsuitable for structures where complete fracture must be prevented. Until now, when such properties were required, thermoplastic resins were selected, or thermosetting resins were formulated with additives to give them toughness. However, thermoplastic resins have a high melt viscosity, making them difficult to impregnate, and even when thermosetting resins are toughened, their viscosity increases dramatically compared to their pre-toughened state, making them difficult to impregnate. Therefore, these problems can be solved by setting the tensile strain at maximum stress to 10% or more in tensile tests of one-component curing thermosetting resins.

[0029] Furthermore, in this embodiment, the bending properties in the fiber direction of the fiber reinforced plastic formed by impregnating and curing the thermosetting acrylic resin into one sheet-like fiber base material are as follows: Maximum load strain: ε max , Maximum load strain ε max Bending stress when strained by 1%: σ a , Maximum load strain ε max Maximum bending stress at: σ max , When Maximum bending stress σ max Residual stress rate: P (%) = 100 × σ a / σ max can be more than 50%.

[0030] That is, in the case of a general thermosetting resin such as epoxy resin, the bending characteristics of the fiber substrate cause it to break at the maximum load and become unable to withstand the load. In this case, if a similar phenomenon occurs in a structure, it may cause problems such as impairing safety and the role of the structure depending on the application. Therefore, in the FRP of this embodiment, the maximum load strain ε max Bending stress σ when strained by 1% a is the maximum load strain ε max Maximum bending stress σ max Stress residual rate P (P = 100 × σ a / σ max ) to 50% or more, the ultimate strength and load-bearing capacity can be improved, and the material can continue to withstand load even after fracture occurs at the maximum load.

[0031] Furthermore, in this embodiment, it is preferable to integrate the sheet-like fiber substrate or its laminate with a stitch thread. This can impart dimensional stability to the fiber substrate, making it easier to handle when shaping the fiber substrate in a mold to produce a preform. Furthermore, because the fibers are held by the stitch thread even when shaping involves in-plane shear deformation, shaping can be performed while maintaining the straightness of the fibers and the fiber orientation angle within the sheet in the same direction. Therefore, the FRP obtained by impregnating and curing the resin can fully retain the mechanical properties of the fiber substrate.

[0032] Furthermore, in this embodiment, the fiber orientation in the sheet-like fiber base material laminate can be stacked at different angles (for example, +45° / 90° / -45° / 0°, etc.). This allows the mechanical properties of the fibers to be imparted to the oriented direction, and by stacking at an appropriate orientation angle based on the design concept of the FRP product, it is possible to obtain an FRP product with the high strength and high rigidity required for that product. [Example]

[0033] The test results for the fiber-reinforced plastic of the present invention are shown below. First, tensile tests were carried out on the physical properties of the one-component thermosetting resin alone used in the product of the present invention, and on the physical properties of the two-component epoxy resin alone as a comparative example. The test conditions were as follows:

[0034] <Tensile test conditions for single-component thermosetting resin> Temperature: 23±2℃ Humidity: 50±10%RH Tensile test (strength, elastic modulus, Poisson's ratio) based on JIS K 7161-2 Test piece shape: 1B type Measuring device: INSTRON 5982 Grip: 30kN capacity chuck Orthogonal strain gauge attached on one side Using a non-contact video extensometer (AVE2) Load cell: 5kN Test speed: 1mm / min → 5mm / min (strain 0.3% switching) Chuck distance: 115mm

[0035] The physical properties of the test piece of this one-component thermosetting resin alone (product of the present invention) are as follows: [Table 1]

[0036] <Tensile test conditions for two-component epoxy resin alone> Temperature: 23±2℃ Humidity: 50±10%RH Tensile test (strength, elastic modulus, Poisson's ratio) based on JIS K 7161-2 Test piece shape: 1B type Measuring device: INSTRON 5982 Grip: 30kN capacity chuck Orthogonal strain gauge attached on one side Dynamic extensometer used Load cell: 5kN Test speed: 1mm / min → 5mm / min (strain 0.3% switching) Chuck distance: 115mm

[0037] The physical properties of the test piece of this two-component epoxy resin material alone (comparative example) are as follows: [Table 2]

[0038] A graph of the "Poisson's ratio" in a tensile test for each resin material alone is shown in Figure 1. A graph of the "stress-strain curve" is shown in Figure 2.

[0039] Furthermore, a graph of the "flexural properties" is shown in Figure 3. In Figure 3, five curves are drawn for the comparative epoxy resin and the one-component thermosetting resin (modified acrylic resin) used in the product of the present invention. Note that the comparative epoxy resin has small variations, so it appears to be one line on the graph. Furthermore, the bending stress of the modified acrylic resin of the present invention is very small compared to the comparative epoxy resin, but the bending strain is large, so the scales of the vertical and horizontal axes are changed to make the entire curve easier to see.

[0040] Next, a test was carried out using a test piece of the fiber reinforced plastic (GFRP) of the present invention. The base material of the test piece was made by laminating eight sheets of NCF (Non-Crimp-Fabric) (U600G manufactured by SHINDO Co., Ltd.) in the same direction, impregnating them with resin using the VaRTM method, and then heating the material to harden the resin and form it. The material composition of the base material of this test piece (NCF = U600G) is a unidirectionally oriented glass fiber base material, but strictly speaking, a small amount of glass fiber is also present in the 90° direction. The basis weight in the 0° direction is 630 g / m 2 , 90° direction = 36g / m 2 is.

[0041] Two types of resins were used for the test pieces: the modified acrylic resin used in the product of the present invention and the epoxy resin used in the comparative example. The epoxy resin was prepared by measuring and mixing the specified amounts of EPICRON EXA-8372 manufactured by DIC Corporation and the curing agent LUCKAMIDE EXC-1030. The modified acrylic resin is a one-component curing type, so it was used as is without any preparation work.

[0042] The results of elastic modulus measurements conducted on these fiber-reinforced plastic test pieces are shown below. The elastic modulus of the resin alone described above is about one-tenth that of the one-component thermosetting resin used in the product of the present invention compared to that of epoxy resin, but the fiber-reinforced plastic only shows a decrease of about 10%, demonstrating the performance of fiber-reinforced plastic. [Table 3]

[0043] Next, a drop weight impact test was performed under the following conditions on an FRP test piece (comparative example) made with a conventional two-component epoxy resin and an FRP test piece (invention product) made with the acrylic thermosetting resin of the present invention. The drop weight impact test board was made by laminating eight sheets of the NCF (U600G) so that the 0°-oriented fibers were in an orientation of [0 / 90 / +45 / -45]s, impregnating them with resin using the VaRTM method, and then heating the resin to harden and mold it.

[0044] <Drop weight impact test conditions> Drop height: 0.623 (m) Impact speed (estimated): 3.494 (m / s) Impact energy (assumed to be potential energy): E = mgh = 30.6 (J) Falling weight: 5.014kg Striker shape: Striker with a hemispherical tip (diameter 16±0.2mm) The operation was carried out with reference to the impact test section described in the JIS standard "JIS K7089" for CFRP compression after impact testing methods.

[0045] Figure 4 shows a comparison photograph of the test pieces after the drop weight impact test. The area circled on the surface of the test piece is the area that was destroyed by the impact. Compared to the conventional product, the area of ​​destruction on the surface of the test piece of the present invention was smaller, demonstrating its superior impact resistance.

Claims

1. A fiber substrate is configured in a sheet shape with a high density, in which a plurality of reinforcing fiber yarns are arranged in one direction and the fiber volume content calculated from the thickness of the sheet at a pressure of 0.1 MPa is 50 to 65%; The fiber-reinforced plastic is characterized in that it is constructed by impregnating and curing this fiber base material or a laminate of this fiber base material with a one-component curing type thermosetting acrylic resin.

2. The fiber volume content is Vf = W / 10ρt Vf: fiber volume content (%) W: Reinforced fiber basis weight (g / m ２ ) ρ: Density of reinforcing fiber (g / cm ３ ) t: Sheet thickness (mm) at 0.1 MPa pressure 2. The fiber reinforced plastic according to claim 1, wherein the value is calculated by the following formula:

3. 2. The fiber reinforced plastic according to claim 1, wherein the thermosetting acrylic resin is a one-component curing type thermosetting acrylic resin having a viscosity of 20 to 200 mPa·s at a resin temperature of 25°C.

4. The fiber reinforced plastic according to claim 1, characterized in that the thermosetting acrylic resin is mainly composed of methacrylic acid ester and has a tensile strain of 10% or more at maximum stress in a tensile test according to JIS-K7161.

5. The bending properties in the fiber direction of the fiber reinforced plastic formed by impregnating and curing the thermosetting acrylic resin into a sheet-like fiber base material are as follows: Maximum load strain: ε ｍａｘ , The maximum load strain ε ｍａｘ Bending stress when strained by 1%: σ ａ , The maximum load strain ε ｍａｘ Maximum bending stress at: σ ｍａｘ , When The maximum bending stress σ ｍａｘ Stress remaining rate: P (%) = 100 × σ ａ / σ ｍａｘ 2. The fiber-reinforced plastic according to claim 1, wherein the ratio of the cross-sectional area to the cross-sectional area is 50% or more.

6. 2. The fiber-reinforced plastic according to claim 1, wherein the reinforcing fibers are glass fibers or polyacrylonitrile-based carbon fibers having an elastic modulus of 70 GPa or more.

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