Resin transfer molding method

Abstract

This invention provides a resin transfer molding method that enables high-speed resin impregnation of preforms and the molding of molded products with excellent strength. [Solution] A resin transfer molding method for forming a product by injecting resin into a mold in which a preform is placed and then curing it, comprising a preform molding step for pre-forming a preform 10 in the shape of the product, an injection step for injecting resin into a mold in which the preform 10 is placed, and a thermosetting step for heating the mold to cure the resin, wherein in the preform molding step, a prepreg P ​​formed by impregnating dry fiber F with thermoplastic resin R is laminated, and in the injection step, a liquid resin R' that reacts and solidifies upon heating is injected.

Description

Technical Field

[0001] The present invention relates to a resin transfer molding method.

Background Art

[0002] Fiber reinforced resin materials are widely used in various fields such as sports goods, medical materials, automotive materials, aerospace materials, and building materials because they are lightweight and have excellent strength. As a molding method for molded products made of fiber reinforced resin materials, a resin transfer molding (RTM) method is known. In the RTM molding method, first, a reinforcing fiber base material (dry fiber) such as a reinforcing fiber bundle or a reinforcing fiber fabric is cut into an appropriate shape, and then a necessary amount is arranged at a designed position / direction to create a preform in a state of being pre-shaped into a product shape. Next, after placing the preform in a pair of molds, while mixing a thermosetting resin and a curing agent, if it is necessary to shorten the resin injection time, it is injected into the mold under high pressure. The molded product is molded by heating the mold to thermally cure the thermosetting resin.

[0003] However, due to factors such as the narrow gaps between the fibers constituting the dry fiber and the insufficiently low viscosity of the thermosetting resin to be injected, the conventional RTM molding method has problems such as requiring a long time for injecting the thermosetting resin. Also, when injecting the thermosetting resin at high pressure to shorten the resin injection time, there is a problem that the fibers constituting the dry fiber are entangled or moved, and the designed strength is not achieved. Therefore, various improvements have been made from the perspective of molding a molded product with high speed and excellent strength.

[0004] The RTM molding method described in Patent Document 1 disposes an intermediate member that forms a resin flow path penetrating in the thickness direction between one mold and the other mold of the mold. By passing through this intermediate member, it is possible to inject resin into the dry fiber from a plurality of locations almost simultaneously and cause the resin to flow so as to spread over a wide area. Thereby, it is said that high-speed molding and improvement of the quality of the molded product are possible. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-246902 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, this requires preparing a mold with an intermediate component, which complicates the mold structure and increases equipment costs. Furthermore, because thermosetting resin must be injected evenly into the narrow gaps between the dry fibers, high pressure during injection is unavoidable even with an intermediate component. This tendency is particularly pronounced when molding molded products with a high fiber volume content (Vf).

[0007] This invention is based on the discovery of an RTM molding method that enables high-speed molding of molded products with superior strength by improving the reinforcing fiber substrate used when forming preforms. [Means for solving the problem]

[0008] This paper describes various aspects of a resin transfer molding method for solving the above problems. [Aspect 1] A resin transfer molding method for forming a product by injecting resin into a mold in which a preform is placed and then curing it, comprising a preform molding step of pre-forming a preform in the shape of a product, an injection step of injecting resin into a mold in which the preform is placed, and a thermosetting step of heating the mold to cure the resin, wherein in the preform molding step, a prepreg formed by impregnating dry fiber with thermoplastic resin is laminated, and in the injection step, the resin which is liquid at room temperature and hardens when heated is injected.

[0009] According to the above configuration, a prepreg, which is made by impregnating dry fibers with thermoplastic resin, is used as the reinforcing fiber base material when molding the preform. In a preform made by laminating prepregs, the thermoplastic resin is filled into the narrow gaps between the dry fibers that make up the prepreg. Therefore, when injecting liquid resin in the injection process, it is possible to evenly fill the unfilled areas of the thermoplastic resin inside the preform with resin, even without high pressure. Because the volume of the unfilled areas of thermoplastic resin is small, it is possible to shorten the time for injecting the resin into these areas. Resin impregnation in the injection process can be performed at high speed. Furthermore, since the occurrence of gaps that are not filled with resin in the injection process is suppressed, the occurrence of voids inside the molded product is suppressed. It is possible to mold a molded product with excellent strength in a short time.

[0010] [Aspect 2] The resin transfer molding method according to [Aspect 1], characterized in that the thermoplastic resin impregnated in the preform molding step is an in-situ polymerized thermoplastic resin.

[0011] In-situ polymerizable thermoplastic resins are supplied in the form of low molecular weight monomers and can be used as a low-viscosity liquid resin in the injection and impregnation processes. They then polymerize linearly to form a thermoplastic polymer. While the monomer state is a very low-viscosity liquid, the polymer state, formed by linear polymerization of monomers, exhibits thermoplasticity. Therefore, with in-situ polymerizable thermoplastic resins, it is possible to impregnate dry fibers with the low-viscosity liquid monomer state when forming prepregs. The thermoplastic resin has good impregnation properties into the narrow gaps between the fibers of the dry fibers that make up the prepreg. Furthermore, by using a prepreg with the thermoplastic resin already impregnated into the gaps between the dry fibers as a preform, resin injection in the subsequent injection process is facilitated. In the injection process, the resin can be injected into the gaps between the prepregs, achieving both high-speed injection and the development of strength in the molded product.

[0012] Furthermore, on the surface of the prepreg, the monomers of the in-situ polymerized thermoplastic resin polymerize in a linear manner, resulting in a polymer state. Although it is thermoplastic, the resin composition is solidified and therefore lacks fluidity. Consequently, during prepreg lamination in the preform molding process, surface stickiness of the prepreg is suppressed, preventing the prepregs from sliding against each other and causing shape changes in the preform. This allows for the production of prepregs with good preform-forming ability.

[0013] On the other hand, in the thermosetting process, the resin injected into the mold and the in-situ polymerized thermoplastic resin molten inside the prepreg melt together. The in-situ polymerized thermoplastic resin inside the prepreg undergoes a crosslinking reaction upon heating and hardens in a compatible state with the resin from the injection process. As a result, high-strength molded products with suppressed void formation can be manufactured.

[0014] [Aspect 3] The resin transfer molding method according to [Aspect 1] or [Aspect 2], characterized in that the preform molding step involves laminating the prepreg to which thermoplastic resin particles are attached.

[0015] With the above configuration, the gaps between the laminated prepregs and the gaps between the dry fibers that make up the prepregs are widened by the attached thermoplastic resin particles. As a result, resin injection in the injection process is easier, and the effects of high-speed injection and improved strength of the molded product can be further enhanced.

[0016] [Aspect 4] The resin transfer molding method according to any one of [Aspect 1] to [Aspect 3], characterized in that the resin injected in the injection step is at least one of a site-polymerizable thermoplastic resin and a thermosetting resin.

[0017] According to the above configuration, since the resin injected in the injection step is liquid or has a low viscosity at room temperature or when heated, it can be filled evenly and at high speed into the unfilled portion of the thermoplastic resin inside the preform without high pressure. In addition, since the presence of gaps where the resin is not filled in the injection step is suppressed, the generation of voids is suppressed, and it is possible to mold a molded product with excellent strength.

[0018] [Aspect 5] The resin injected in the injection step is a resin having compatibility with the thermoplastic resin impregnating the dry fiber, according to any one of [Aspect 1] to [Aspect 4].

[0019] According to the above configuration, in the thermosetting step, the resin injected into the mold and the thermoplastic resin constituting the prepreg melt and combine at the interface between the prepreg and the injected resin. The thermoplastic resin constituting the prepreg cures in a compatible state with the resin in the injection step at the interface. Since it becomes seamless at the interface between the prepreg and the injected resin, it is possible to mold a molded product with excellent strength. [Advantages of the Invention]

[0020] According to the present invention, resin impregnation into the preform can be performed at high speed, and a molded product with excellent strength can be molded. [Brief Description of the Drawings]

[0021] [Figure 1] It is a diagram for explaining a resin transfer molding method. [Figure 2] It is a schematic diagram for explaining the state of the resin in the preform in the preform molding step and the injection step. (a) is a schematic diagram for explaining the state of the resin in the preform in the preform molding step and the injection step of the present embodiment, and (b) is a schematic diagram for explaining the state of the resin in the preform in the conventional preform molding step and the injection step. [Figure 3]This diagram illustrates the results of an investigation into the resin injection time during the injection process. [Figure 4] This figure illustrates the results of the study on the bending strength of the molded product in the example. [Figure 5] This figure illustrates the results of the study on the bending strength of the molded product in the example. [Figure 6] This figure illustrates the results of an investigation into the bending strength of the molded product in the comparative example. [Figure 7] This figure illustrates the results of an investigation into the bending strength of the molded product in the comparative example. [Modes for carrying out the invention]

[0022] The following describes a resin transfer molding method (RTM molding method) that embodies the present invention. As shown in Figure 1, the RTM molding method includes a preform molding step, an injection step, and a thermosetting step.

[0023] As shown in Figure 2(a), the RTM molding method of the present invention pre-forms a preform 10 by laminating a prepreg P, which is formed by impregnating dry fiber F with thermoplastic resin R, in the preform molding step. The steps of the RTM molding method will be described below.

[0024] <About the preform molding process> As shown in Figures 1 and 2(a), the preform molding process includes the steps of impregnating dry fiber F with thermoplastic resin R to form a prepreg P, attaching thermoplastic resin particles Pa to the prepreg P, and pre-molding a preform 10 by laminating the prepreg P ​​with the thermoplastic resin particles Pa attached.

[0025] First, a prepreg P ​​is formed by impregnating dry fiber F with thermoplastic resin. The reinforcing fiber used as dry fiber F can be appropriately selected from conventionally known reinforcing fibers. Specifically, examples include carbon fiber, glass fiber, aramid fiber, basalt fiber, boron fiber, silicon carbide fiber, steel fiber, alumina fiber, tyranno fiber, amorphous carbon fiber, etc. Among these, carbon fiber is preferred because it is lightweight and has excellent strength.

[0026] The reinforcing fibers may be a bundle of multiple reinforcing fibers, or a fabric made from multiple reinforcing fibers. In the case of a bundle of reinforcing fibers, the number of reinforcing fibers, fiber diameter, fineness, density, tensile strength, etc., that make up the bundle are not particularly limited. In the case of a fabric made from reinforcing fibers, the number of reinforcing fibers, fiber diameter, fineness, density, tensile strength, etc., as well as the type of fabric and the orientation of the reinforcing fibers are not particularly limited. Commercially available reinforcing fiber bundles and fabrics can be appropriately selected and used.

[0027] The thermoplastic resin R used in the preform molding process can be appropriately selected from conventionally known thermoplastic resins and in-situ polymerizable thermoplastic resins. Examples of thermoplastic resin R include thermoplastic epoxy resin, thermoplastic acrylic resin, thermoplastic urethane resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polystyrene resin, polyester resin, and the like.

[0028] The selected thermoplastic resin R is required to have excellent compatibility with the resin R' injected in the injection process. By selecting a thermoplastic resin R having such properties, it will melt well at the interface with the resin R' injected in the injection process, become seamless when solidified after heating, and a molded product with excellent strength can be obtained. For example, if the resin R' injected in the injection process is an epoxy resin, it is preferable that the thermoplastic resin R used in the preform forming process be a thermoplastic epoxy resin, which is a site-polymerized thermoplastic resin. Also, if the resin R' injected in the injection process is an acrylic resin, it is preferable that the thermoplastic resin R used in the preform forming process be a thermoplastic acrylic resin, which is a site-polymerized thermoplastic resin.

[0029] The amount of thermoplastic resin R impregnated into the prepreg P ​​is not particularly limited, but it is preferable to set it to 30% by volume or more. When the amount of thermoplastic resin impregnation is within this range, the strength of the molded product can be ensured to be good.

[0030] The method for impregnating the dry fiber F with the thermoplastic resin R is not particularly limited. Any method may be used, such as coating with a brush, injection using an injection device, or immersion in a storage tank containing the thermoplastic resin R.

[0031] In the step of attaching thermoplastic resin particles Pa to the prepreg P, the thermoplastic resin R is impregnated into the dry fiber F, and then the thermoplastic resin particles Pa are attached to the resulting prepreg P. Preferably, the thermoplastic resin constituting the particles Pa is the same as the thermoplastic resin R impregnated into the dry fiber F. For example, if the thermoplastic resin R impregnated into the dry fiber F is a thermoplastic acrylic resin, which is the thermoplastic resin of this embodiment described later, then it is preferable that the particles Pa attached to the prepreg P ​​are made of polymethyl methacrylate (PMMA) resin.

[0032] The amount of attached Pa particles and their particle size are not particularly limited. The amount of attached Pa particles is preferably about 2 to 20% by weight per unit weight of prepreg P, and more preferably about 5 to 15% by weight. The particle size is preferably about 20 to 200 μm, and more preferably about 50 to 100 μm.

[0033] As shown in Figure 2(a), by attaching the particles Pa, the particles can fill the gaps between the laminated prepregs P and the gaps remaining between the dry fibers F that make up the prepregs P, forming appropriate gaps. This makes it easier to inject the resin R' in the subsequent injection process. It also allows for lower resin pressure during the injection process and enables high-speed injection.

[0034] Next, multiple layers of prepreg P, to which thermoplastic resin particles Pa are attached, are laminated to pre-form a preform 10 in the shape of the product. Pre-forming of the preform 10 can be carried out by conventionally known methods.

[0035] As shown in Figure 2(a), in the pre-molded preform 10, the thermoplastic resin R fills the gaps between the laminated prepregs P and the gaps between the dry fibers F that make up the prepregs P, reducing the presence of voids V. In addition, the particles Pa attached to the prepregs P fill the voids V, maintaining the appropriate gaps formed by the prepregs P. In contrast, in Figure 2(b), which shows a conventional preform formed by laminating dry fibers F, all the spaces between the dry fibers F are voids V.

[0036] <About in-situ polymerized thermoplastic resins> An embodiment of a field-polymerized thermoplastic resin R used in the preform molding process will be described below. This will be referred to as the resin composition of this embodiment.

[0037] The resin composition of this embodiment is suitable for continuously forming tow prepregs by continuously supplying and conveying reinforcing fiber bundles and applying, impregnating, and curing the reinforcing fiber bundles. The method of impregnating dry fibers is not limited to this method; for example, it is also possible to form prepregs by applying and impregnating reinforcing fiber fabrics. In the following, the resin composition of this embodiment will be explained using an example where tow prepregs are formed by continuously supplying and conveying reinforcing fiber bundles and applying, impregnating, and curing the resin composition.

[0038] The resin composition of this embodiment is a thermoplastic acrylic resin that is polymerized in situ. The resin composition of this embodiment contains (A) a monofunctional acrylate monomer that is liquid at room temperature, (B) non-crosslinked polymethyl methacrylate particles, (C) a photoradical initiator, (D) an organic peroxide, and (E) a reducing agent. Hereinafter, (A) the monofunctional acrylate monomer that is liquid at room temperature may simply be referred to as (A) monofunctional acrylate monomer.

[0039] The resin composition of this embodiment is a two-component mixture consisting of a first agent and a second agent. The first agent and the second agent are applied sequentially while conveying the reinforcing fiber bundle. The first agent contains (A) a monofunctional acrylate monomer, (B) non-crosslinked polymethyl methacrylate particles, (C) a photoradical initiator, and (D) an organic peroxide. The second agent contains (E) a reducing agent.

[0040] (A) Monofunctional acrylic monomers are the main components of the resin composition. (A) Monofunctional acrylic monomers undergo redox polymerization in the presence of (D) organic peroxides and (E) reducing agents. Redox polymerization forms polymers, causing the resin composition to lose its fluidity. In addition, (A) monofunctional acrylic monomers undergo photoradical polymerization with (G) photoradical initiators. (B) Non-crosslinked polymethyl methacrylate particles suppress the effect of oxygen inhibition during redox polymerization of (A) monofunctional acrylic monomers. (B) The inclusion of non-crosslinked polymethyl methacrylate particles allows the redox polymerization reaction in the presence of (D) organic peroxides and (E) reducing agents to proceed rapidly when the resin composition is applied while transporting reinforcing fiber bundles.

[0041] Next, we will describe each component that makes up the resin composition of this embodiment. ((A) Regarding monofunctional acrylate monomers) (A) The monofunctional acrylate monomer is a compound that undergoes redox polymerization to form a polymer in the presence of (D) an organic peroxide and (E) a reducing agent. It is also a compound that undergoes photoradical polymerization to form a polymer with (C) a photoradical initiator. Since component (A) is monofunctional, having one acryloyl group in one molecule, it becomes a linear polymer through redox polymerization. In the manufacturing method of this embodiment, the first agent is applied to the reinforcing fiber bundle while the reinforcing fiber bundle is being transported, so the (A) monofunctional acrylate monomer is liquid at room temperature.

[0042] (A) As monofunctional acrylate monomers, any of the following can be used: fatty acid acrylates, alicyclic acrylates, ether acrylates, cyclic ether acrylates, hydroxyl group-containing acrylates, aromatic acrylates, carboxyl-containing acrylates, etc. For example, methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate, isobutyl acrylate, lauryl acrylate, isodecyl acrylate, isobornyl acrylate, benzyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, tricyclodecanyl acrylate, ethyl carbitol acrylate, tetrahydrofurfuryl acrylate, lauryl acrylate, benzyl acrylate, cyclohexyl acrylate Examples of conventionally known monofunctional acrylates include rilate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-ethylhexyl carbitol acrylate, 2-phenoxyethyl acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, caprolactone-modified tetrahydrofurfuryl methacrylate, t-butylaminoethyl acrylate, t-butylaminoethyl methacrylate, polyester acrylate, tris(acryloyloxyethyl) isocyanurate, and urethane acrylate. Among these, acrylates with a structure in which one acryloyl group is bonded to a cyclic skeleton are preferred because they have an appropriate Tg. These may be used individually or in combination of two or more.

[0043] The content of component (A) in the resin composition is preferably 85% by mass or less of the total content of component (A) and component (B). Furthermore, the content of component (A) is preferably 60% by mass or more of the total content of component (A) and component (B).

[0044] ((B) Regarding non-crosslinked polymethyl methacrylate particles) (B) Non-crosslinked polymethyl methacrylate particles suppress the effects of oxygen inhibition during redox polymerization of (A) monofunctional acrylic monomers.

[0045] (B) The non-crosslinked polymethyl methacrylate particles preferably have an average particle size of 500 nm or less. The gaps between the reinforcing fibers that make up the fiber-reinforced substrate are about 500 nm. Therefore, if the average particle size of component (B) is 500 nm or less, it can easily penetrate into the fine gaps between reinforcing fibers such as carbon fibers and exhibit its function.

[0046] (B) Non-crosslinked polymethyl methacrylate particles can be appropriately selected from commercially available products. For example, bead-grade polymethyl methacrylate manufactured by Kuraray Co., Ltd. is an example.

[0047] The content of component (B) in the resin composition is preferably 15% by mass or more of the total content of components (A) and (B). Furthermore, the content of component (B) is preferably 40% by mass or less of the total content of components (A) and (B). When the content of component (B) is 15% by mass or more, the effect of oxygen inhibition in the redox polymerization reaction can be suitably suppressed. Furthermore, when the content of component (B) is 40% by mass or less, the increase in viscosity of the resin composition can be suppressed.

[0048] ((C) Regarding photoradical initiators) (C) Photoradical initiators are compounds that decompose upon UV irradiation to generate radicals. (C) Photoradical initiators are formed by photoradical polymerization of (A) monofunctional acrylate monomers to form linear polymers.

[0049] (C) As a photoradical initiator, one can be appropriately selected from known photoradical generators used in the photopolymerization of (meth)acrylate monomers. Examples include benzophenone, benzyl, Michlar's ketone, thioxanthone derivatives, benzoin ethyl ether, diethoxyacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, acylphosphine oxide derivatives, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 4-benzoyl-4'-methyldiphenyl sulfide, etc. These may be used alone or in combination of two or more.

[0050] (C) The amount of photoradical initiator is preferably 0.5 parts by weight or more, and more preferably 1 part by weight or more, when the amount of components (A) to (E) in the resin composition is 100 parts by weight. Furthermore, the amount of photoradical initiator is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, when the amount of components (A) to (E) in the resin composition is 100 parts by weight or more.

[0051] ((D) Regarding organic peroxides) (D) Organic peroxides are compounds that decompose upon heating to generate radicals. (E) Together with a reducing agent, they initiate the redox polymerization reaction of (A) monofunctional acrylate monomers.

[0052] (D) Examples of organic peroxides include methyl ethyl ketone peroxide, t-butyl peroxybenzoate, cumene hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, diisopropylbenzene dihydroperoxide, methyl ethyl ketone peroxide, and benzoyl peroxide. These may be used individually or in combination of two or more.

[0053] (D) The amount of organic peroxide is preferably 0.5 parts by weight or more, and more preferably 1 part by weight or more, when the total amount of components (A) to (E) in the resin composition is 100 parts by weight or more. Also, (C) The amount of photoradical initiator is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, when the total amount of components (A) to (E) in the resin composition is 100 parts by weight or more.

[0054] (Regarding (E) reducing agents) (E) The reducing agent reduces and decomposes (D) the organic peroxide at relatively low temperatures, such as room temperature, forcibly releasing radicals. This redox polymerization reaction occurs simply by contact with (D) the organic peroxide, without mixing at the molecular level, and the radical polymerization reaction, once initiated, propagates over a certain distance without stirring.

[0055] (E) Examples of reducing agents include reaction condensates of various amines and aldehydes, N,N-dimethylparatoluidine, 2-mercaptobenzimidazole, methylthiourea, dibutylthiourea, tetramethylthiourea, ethylenethiourea, cobalt naphthenate, copper naphthenate, and vanadium compounds. These may be used individually or in combination of two or more.

[0056] (E) The amount of reducing agent is preferably 0.1 parts by weight or more, and more preferably 0.2 parts by weight or more, when the total amount of components (A) to (E) in the resin composition is 100 parts by weight. Furthermore, the amount of reducing agent (E) is preferably 1 part by weight or less, and more preferably 0.8 parts by weight or less, when the total amount of components (A) to (E) in the resin composition is 100 parts by weight.

[0057] (Regarding other additives) The resin composition of this embodiment may contain other additives as needed, provided that the function of the radical polymerization reaction is not impaired. Examples of other additives include reaction accelerators, curing modifiers, storage stabilizers, bulking agents, property modifiers, reinforcing agents, colorants, flame retardants, precipitation inhibitors, antioxidants, anti-aging agents, fragrances, pigments, dyes, and the like.

[0058] <Regarding the injection process> As shown in Figure 1, the injection process involves placing the preform 10 in molds 21 and 22 having product-shaped cavities C, and injecting resin R' into the molds 21 and 22 under reduced pressure conditions. The injection of resin R' can be carried out by conventionally known methods.

[0059] The resin R' used in the injection process is a liquid, low-viscosity resin at room temperature. Because it is liquid and low-viscosity, it is easy to impregnate the preform 10 with it. It may be a thermosetting resin or a field-polymerized thermoplastic resin. In the case of a field-polymerized thermoplastic resin, it may be the resin composition of this embodiment as described above. In any case, the resin R' is required to have excellent compatibility with the thermoplastic resin R impregnated in the preform molding process.

[0060] Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, polyvinyl ester resins, phenolic resins, guanamine resins, polyimide resins such as bismalade-triazine resins, furan resins, polyurethane resins, polydiallyl phthalate resins, melamine resins, urea resins, cyclopentadiene resins, and dicyclopentadiene resins.

[0061] The injection pressure, injection volume, and injection speed of the resin R' can be set as appropriate. The number and arrangement of resin injection ports 23 in the molds 21 and 22 can also be set as appropriate. <About the thermosetting process> As shown in Figure 1, the thermosetting process involves heating the molds 21 and 22 to thermoset the resin R' injected in the injection process. The heating temperature, heating time, etc., can be appropriately set according to the type of resin R', the shape, size, and thickness of the cavity C in the molds 21 and 22, etc.

[0062] After cooling the molds 21 and 22, the molded product 30 is obtained by demolding. <Regarding the operation and effects of the RTM molding method of this embodiment> Next, the effects of the RTM molding method of the above embodiment will be explained along with its operation.

[0063] (1) The diameter of the dry fibers that make up reinforcing fiber bundles and reinforcing fiber fabrics is about a few micrometers. For example, in the case of carbon fibers, the diameter of the dry fiber (monofilament) is about 5 to 7 micrometers, and reinforcing fiber bundles are formed by bundling together thousands to tens of thousands of such dry fibers. Therefore, the gaps formed between the dry fibers are fine, less than 1 micrometer.

[0064] As shown in Figure 2(b), when resin is injected into a preform molded with conventional dry fibers F, all spaces between the dry fibers F are voids V. Therefore, very high pressure is required when injecting the resin R' during the injection process. In addition, the injection process requires a long time.

[0065] In contrast, in the RTM molding method of this embodiment, as shown in Figure 2(a), a preform 10 is pre-molded by laminating a prepreg P ​​formed by impregnating dry fibers F with thermoplastic resin R. In the pre-molded preform 10, the thermoplastic resin R fills the gaps between the dry fibers F that make up the prepreg P. The volume of the voids V in the preform 10 is reduced by the thermoplastic resin R that has filled the gaps. In the injection process, resin R' is injected into the voids V remaining in the preform 10. Because the volume of the voids V is reduced, it is possible to use a low resin pressure for the resin R' in the injection process and to inject it at high speed. This eliminates the need to use large and expensive equipment to apply high pressure, which can contribute to reducing the manufacturing cost of molded products.

[0066] (2) In the RTM molding method of this embodiment, a prepreg P ​​is formed by impregnating a dry fiber F with a thermoplastic resin R, and then thermoplastic resin particles Pa are attached to the prepreg P. As shown in Figure 2(a), the particles Pa attached to the prepreg P ​​enter into voids V, maintaining an appropriate gap. Because the voids V maintain their shape, it is possible to lower the resin pressure of the resin R' during the injection process and to inject at a higher speed.

[0067] (3) In the RTM molding method of this embodiment, resin R' is injected into the small volume of voids V in the preform 10 during the injection process. Therefore, the generation of voids in the molded product originating from the voids V is suppressed during the thermosetting process. As a result, a molded product with excellent strength can be formed.

[0068] (4) The resin R' injected in the injection process is at least one of a site-polymerizable thermoplastic resin or a thermosetting resin, which is liquid at room temperature and has low viscosity. Therefore, even without high pressure, it is possible to fill the unfilled portions (voids V) of the thermoplastic resin R inside the preform 10 evenly at high speed.

[0069] (5) The resin R' injected into the preform 10 in the injection process is a resin with excellent compatibility with the thermoplastic resin R. Therefore, in the thermosetting process, the thermoplastic resin R and the resin R' melt well together at the interface, and the formation of an interface when cooled and solidified is suppressed. This also improves the strength of the molded product.

[0070] (6) The thermoplastic resin R impregnated into the dry fiber F in the preform molding process is, for example, the in-situ polymerized thermoplastic resin exemplified as the resin composition of this embodiment. The in-situ polymerized thermoplastic resin is a very low-viscosity liquid in its monomer state, but becomes a thermoplastic solid in its polymer state when monomers are polymerized in a linear chain.

[0071] Therefore, when forming the prepreg P, it is possible to impregnate the dry fibers F in a low-viscosity liquid monomer state. The thermoplastic resin R has good impregnation properties into the narrow gaps between the fibers of the dry fibers F that make up the prepreg P. This makes it easier to inject the resin R' in the subsequent injection process, and further improves the effect of high-speed injection. In addition, it is possible to reduce the volume of the voids V, which further improves the effect of increasing the strength of the molded product.

[0072] (7) On the surface of the prepreg P ​​impregnated with the resin composition of this embodiment, the monomers of the in-situ polymerized thermoplastic resin polymerize in a linear manner, and the resin composition is solidified and therefore has no fluidity. As a result, when the prepreg P ​​is laminated in the preform molding process, the stickiness of the surface of the prepreg P ​​is suppressed, and the slippage of the prepreg Ps and the resulting shape change of the preform 10 are suppressed. A prepreg P ​​with good preform forming ability can be manufactured.

[0073] The above embodiment can be modified as follows. Note that the above embodiment and the following modifications can be combined and applied to the extent that they do not contradict each other technically. • While it was explained that the amount of thermoplastic resin R impregnating the dry fiber F should be set to 30% by volume or more, it is not limited to this range. It may be less than 30% by volume.

[0074] The resin composition of this embodiment was described as a thermoplastic resin R suitable for use in the continuous production of tow prepregs. However, it can also be used in the production of sheet prepregs and prepreg tapes, not just tow prepregs. Furthermore, it is not limited to continuous production. [Examples]

[0075] The RTM molding method embodying the present invention will be described based on examples. <Test 1: Test on resin injection into preforms> We investigated the advantages of the injection process when forming a preform using a thermoplastic resin prepreg. Specifically, we measured the time required for resin injection for both thermoplastic resin prepregs and dry fibers.

[0076] (Example 1-1) The tests were conducted assuming the formation of a preform using a prepreg. The prepreg used was TAFTEX® CF / PP (manufactured by Mitsui Chemicals, Inc., 200 g / m²), a unidirectional tape made of carbon fiber compounded with polypropylene (thermoplastic resin). 2 (0.2mm thick) was used. The prepreg tape was approximately 3cm long. 2 The material was cut to a suitable size and used as chopped prepreg. The chopped prepreg was laminated in a mold, and thermosetting epoxy resin (manufactured by Nagase ChemteX Corporation) was injected at a pressure of 1 bar using the Va-RTM method. During the filling of the chopped prepreg into the mold, the prepreg layers were bonded together at 165°C and 1 bar.

[0077] (Examples 1-2) The procedure is the same as in Example 1-1, except that the chopped prepreg was bonded between the prepregs at 100°C and 1 bar during lamination in the mold.

[0078] (Comparative Example 1-1) The tests were conducted assuming the formation of a preform using dry fiber. The dry fiber used was Toray® CO6347B (manufactured by Toray Industries, Inc., fabric weight 200g / m²), a carbon fiber fabric. 2 A material with a thickness of approximately 0.2 mm was used. The procedure was the same as in Example 1-1, except that dry fiber was used.

[0079] (Comparative Example 1-2) The test was conducted assuming the formation of a preform using dry fiber. The dry fiber used was Torayca® T700SC-24000 (manufactured by Toray Industries, Inc., with 24,000 fibers), a carbon fiber tape, approximately 3 cm long. 2It was used as chopped prepreg cut to a suitable size. The procedure was the same as in Example 1-1, except that dry fiber was used.

[0080] The results for Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2 are shown in Figure 3. As shown in Figure 3, resin injection was completed in approximately 1 minute in Examples 1-1 to 1-2. In contrast, Comparative Examples 1-1 to 1-2 required several tens of minutes.

[0081] <Test 2; Strength test of molded product> The bending strength of molded products (CFRP sheets) formed by the RTM molding method was investigated. (Example 2-1) As the prepreg used to form the preform, a prepreg tape was used, which was formed by impregnating PYROFIL® TR50S15L (manufactured by Mitsubishi Chemical Corporation), a carbon fiber tow tape, with thermoplastic epoxy resin (manufactured by Nagase ChemteX Corporation). Multiple prepreg tapes were laminated to pre-form the preform so that the orientation direction of the carbon fibers was 0°. The preform was placed in a mold and thermosetting epoxy resin (manufactured by Nagase ChemteX Corporation) was injected. The injection conditions were as follows: The mold, which was at room temperature (approximately 20°C), was heated to 80°C to heat-cur the thermosetting epoxy resin and obtain a test specimen as a plate-shaped molded product. The size of the test specimen was 250 mm x 250 mm.

[0082] Mold temperature during resin injection: 20℃ Injection time: 1.3 minutes Injection pressure; vacuum pressure 0.1 MPa Curing; 80℃ / 1 hour (Examples 2-2, 2-3) Test specimens for Examples 2-2 and 2-3 were obtained in the same manner as in Example 2-1.

[0083] (Examples 2-4) As the prepreg used to form the preform, a prepreg tape was used that was formed by impregnating PYROFIL® TR50S15L (manufactured by Mitsubishi Chemical Corporation), a carbon fiber tow tape, with the above-mentioned in-situ polymerization resin composition as the resin composition of this embodiment. Multiple prepreg tapes were laminated so that the orientation directions of the carbon fibers were 0° and 90° to pre-form the preform. The preform was placed in a mold, and with the mold heated to 60°C, the REDOX curable resin was injected. The REDOX curable resin used here was prepared by adding 0.5 parts by weight of cumene hydroperoxide and 0.5 parts by weight of cobalt naphthenate to 100 parts by weight of low viscosity liquid polyfunctional methacrylate resin. The injection conditions were as follows. The REDOX curable resin was heat-cured approximately 7 minutes after the start of resin injection to obtain a test piece as a plate-shaped molded product.

[0084] Mold temperature during resin injection: 60℃ Injection time: 3 minutes Injection pressure; vacuum pressure 0.1 MPa (+ pressurized to 0.3 MPa after injection) Curing; 60℃ / 7 minutes (Examples 2-5 to 2-8) Test specimens for Examples 2-5 to 2-8 were obtained in the same manner as in Example 2-4.

[0085] (Comparative Example 2-1) To compare the bending strength with that of Examples 2-1 to 2-8, a molded product of Comparative Example 2-1 was formed.

[0086] As the prepreg used to form the preform, the same carbon fiber toe tape as in Example 2-1, PYROFIL® TR50S15L (manufactured by Mitsubishi Chemical Corporation), was used. Multiple toe tapes were stacked in the mold so that the orientation direction of the carbon fibers was 0°, and thermosetting epoxy resin (manufactured by Nagase ChemteX Corporation) was injected by the Va-RTM method under vacuum pressure at a mold temperature of 100°C. The molding conditions were as follows. Subsequently, the mold was heated to 140°C to heat-cur the thermosetting epoxy resin and obtain a test piece as a plate-shaped molded product.

[0087] Mold temperature during resin injection: 100℃ Injection time: 30 minutes Injection pressure; vacuum pressure 0.1 MPa Curing; 140℃ / 120 minutes (Comparative Examples 2-2, 2-3) Test specimens for Comparative Examples 2-2 and 2-3 were obtained in the same manner as for Comparative Example 2-1.

[0088] (Comparative Example 2-4) As a prepreg used to form the preform, carbon fiber fabric (plain weave 440g / m²) is used. 2 TenCate® CetexTC0415 (manufactured by Tencate Advance Composites Holding BV), a sheet prepreg impregnated with a thermoplastic resin (polyamide 66), was used. Multiple carbon fiber fabrics were laminated in a mold with the carbon fiber orientations at 0° and 90°, and a test specimen was obtained as a plate-shaped molded product by a heat and seal molding method, in which heating and cooling were applied under pressure using a press machine. The molding conditions were as follows.

[0089] Molding pressure: 5 MPa Heating temperature: 250°C (Heating time: 30 minutes) Cooling time: 30 minutes (Comparative Example 2-5) A test specimen for Comparative Example 2-5 was obtained in the same manner as for Comparative Example 2-4. (Comparative Examples 2-6, 2-7) As a prepreg used to form the preform, carbon fiber fabric (twill weave 200g / m 2 Tepex Dynalite201-C200 (manufactured by Bond Laminates), a sheet prepreg impregnated with a thermoplastic resin (polyamide 66), was used. Except for the use of a sheet prepreg, test specimens for Comparative Examples 2-6 and 2-7 were obtained in the same manner as for Comparative Example 2-1.

[0090] (Bending test) Each test specimen from Examples 2-1 to 2-8 and Comparative Examples 2-1 to 2-7 was cut to obtain strip-shaped test specimens for bending tests. The fiber volume ratio and dimensions of each bending test specimen are shown in Table 1. The bending tests were performed using a 5kN Autograph testing machine (manufactured by Shimadzu Corporation) in accordance with JIS K 7074.

[0091] [Table 1] The conditions for the bending tests on each test specimen used in Examples 2-1 to 2-8 are as follows:

[0092] Test speed: 2 mm / min Distance between fulcrums: 120mm The conditions for the bending tests on each test specimen for Comparative Examples 2-1 to 2-5 are as follows:

[0093] Test speed: 5.3 mm / min Distance between fulcrums: 80mm The conditions for the bending tests on the test specimens used in Comparative Examples 2-6 to 2-7 are as follows:

[0094] Test speed: 0.9 mm / min Distance between fulcrums: 32mm The stress-strain curves for each bending test specimen in Examples 2-1 to 2-3 are shown in Figure 4. The stress-strain curves for each bending test specimen in Examples 2-4 to 2-8 are shown in Figure 5. The stress-strain curves for each bending test specimen in Comparative Examples 2-1 to 2-3 are shown in Figure 6. The stress-strain curves for each bending test specimen in Comparative Examples 2-3 to 2-7 are shown in Figure 7.

[0095] Furthermore, Table 2 shows the bending strength and bending modulus of each test specimen obtained from the bending tests.

[0096] [Table 2] The results in Table 2 show that the RTM molding method of the present invention yields molded products with bending strength and bending modulus comparable to those produced by conventional molding methods. Furthermore, it was found that when the compatibility between the resin impregnated in the prepreg and the resin injected in the injection process is low, the strength variation is large and the strength is unstable.

Claims

1. A resin transfer molding method in which a resin is injected into a mold containing a preform and then cured to form a product, A preform molding process for pre-forming the preform in the shape of the product, An injection step in which resin is injected into a mold in which the preform is placed, A heat curing step in which the mold is heated to harden the resin. Equipped with, In the aforementioned preform molding process, prepregs formed by impregnating dry fibers with thermoplastic resin are laminated. The resin transfer molding method is characterized in that the injection step involves injecting the resin, which is liquid at room temperature and hardens upon heating.

2. The resin transfer molding method according to claim 1, characterized in that the thermoplastic resin impregnated in the preform molding step is an in-situ polymerized thermoplastic resin.

3. The resin transfer molding method according to claim 1, characterized in that the preform molding step involves laminating the prepreg to which thermoplastic resin particles are attached.

4. The resin transfer molding method according to claim 1, characterized in that the resin injected in the injection step is at least one of a site-polymerizable thermoplastic resin and a thermosetting resin.

5. The resin transfer molding method according to any one of claims 1 to 4, characterized in that the resin injected in the injection step is a resin compatible with the thermoplastic resin impregnated into the dry fiber.

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