Method for producing FRP product, core, and fusible composition
Patent Information
- Application Number
- JP2025521761
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2025-10-27
- Publication Date
- 2026-01-30
AI Technical Summary
The repeated reuse of wax in FRP product manufacturing leads to changes in physical properties such as melting temperature, coefficient of thermal expansion, and viscosity when left in a molten state, resulting in decreased manufacturing efficiency and process defects.
Incorporating an antioxidant into the wax fusible composition to suppress these physical property changes, allowing for the reuse of the wax while maintaining consistent manufacturing efficiency and preventing defects.
The use of antioxidants stabilizes the physical properties of the wax, preventing defects and maintaining efficiency in FRP product manufacturing by suppressing oxidation-induced changes, enabling the repeated use of wax without significant loss in production quality.
Abstract
Description
Method for manufacturing FRP products, cores, and fusible compositions
[0001] The present invention relates to a method for manufacturing an FRP product, a core, and a fusible composition.
[0002] Fiber-reinforced plastics (FRPs) are lightweight materials with excellent mechanical properties suitable for parts of automobiles, ships, railroad vehicles, manned aircraft, unmanned aircraft, and other transportation equipment, and their importance has been increasing in recent years. Patent Document 1 proposes a method for manufacturing FRP products with hollow sections or U-shaped cross sections, in which prepregs are placed in a molding die together with a core having a fusible portion made of wax and heated and cured in the molding die. Prepregs are intermediate materials used in molding FRP products, in which fiber reinforcement is impregnated with an uncured thermosetting matrix. Patent Document 2 describes a method for manufacturing FRP products with hollow sections, in which one or more metallocene polyolefin waxes and / or their derivatives are used as core materials, and an antioxidant may be present in the core material, selected from the group of alkanesulfonates.
[0003] International Publication No. 2018 / 079824 Japanese Patent Application Laid-Open No. 2006-116964
[0004] In a manufacturing method for FRP products in which a prepreg is placed in a mold together with a core having a fusible portion made of wax and then heated and cured in the mold, it is desirable to repeatedly reuse the wax. To reuse used wax to make a new core, it is necessary to heat and melt it. Furthermore, if the FRP product molded using this manufacturing method has a hollow portion, it is necessary to heat the wax to melt it and eject it from the hollow portion.
[0005] The inventors have found that leaving wax in a molten state can change its physical properties, such as melting temperature, thermal expansion coefficient, and viscosity at melting. This fact predicts that repeated reuse of wax in the production of FRP products using the above-mentioned method can lead to reduced manufacturing efficiency and process defects.
[0006] The present inventors have discovered that the above-mentioned changes in physical properties that occur when wax is left in a molten state can be effectively suppressed by adding an antioxidant to the wax, and have thus completed the present invention.
[0007] The present invention includes the following aspects: [1] A method for producing an FRP product, comprising: a first step of placing a prepreg together with a core having a fusible portion in a mold and heating and curing the prepreg in the mold to obtain a molded product; and a second step of melting the entire fusible portion after obtaining the molded product, wherein the fusible portion of the core has a first portion formed from a first fusible composition containing a first wax and an antioxidant, and optionally a second portion formed from a second fusible composition containing a second wax and no antioxidant. [2] The method for producing an FRP product according to [1], wherein the second step is performed to remove the fusible portion from the molded product or to produce a new core. [3] The method for producing an FRP product according to [1] or [2], wherein the molded product has a hollow portion, and further comprises discharging the melt of the fusible portion produced in the second step from the inside of the hollow portion through a discharge hole provided in the hollow portion. [4] The method for producing an FRP product according to any of [1] to [3], wherein the first fusible composition is reused to produce another core after the second step. [5] The manufacturing method of [3], wherein, after the second step, the first fusible composition is reused to produce another core, and at least a portion of the first fusible composition contained in the melt of the fusible portion is maintained in a molten state until the reuse. [6] The manufacturing method of any of [1] to [5], wherein the antioxidant contains at least one of a radical scavenger and a peroxide decomposer, preferably both. [7] The manufacturing method of any of [1] to [5], wherein the antioxidant contains at least one of a phenolic antioxidant and a phosphite antioxidant, preferably both. [8] The manufacturing method of any of [1] to [7], wherein the antioxidant contains a compound having a melting point of 50°C or higher or 100°C or higher. [9] The manufacturing method of any of [1] to [8], wherein the antioxidant contains a compound having a melting point higher than that of the first wax.
[10] The manufacturing method of any of [1] to [9], wherein the first wax is composed mainly of a hydrocarbon.
[11] The manufacturing method of any one of [1] to
[10] , wherein the first wax contains one or more waxes selected from the group consisting of paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.
[12] The manufacturing method of any one of [1] to
[11] , wherein at least a portion of the surface of the fusible portion melts in the first step.
[13] The manufacturing method of any one of [1] to
[11] , wherein the surface of the fusible portion does not melt in the first step.
[14] The manufacturing method of any one of [1] to
[13] , wherein the molding die is heated to a temperature of 100°C or higher in the first step.
[15] The manufacturing method of any one of [1] to
[14] , wherein a pressure of 0.1 MPa or higher is applied to the prepreg in the first step.
[16] The manufacturing method of any one of [1] to
[15] , wherein the content of the antioxidant in the first fusible composition is 0.1% by weight or more and 25% by weight or less.
[17] The manufacturing method according to any one of [1] to
[16] , wherein the fusible portion has the first portion and the second portion, and the first fusible composition and the second fusible composition are incompatible with each other and have different melting points.
[0008]
[18] A core placed in a mold together with a prepreg in a method for producing an FRP product, the method comprising heating and curing a prepreg in the mold, the core having a fusible portion, the fusible portion having a first portion formed of a first fusible composition containing a first wax and an antioxidant, and optionally a second portion formed of a second fusible composition containing a second wax but no antioxidant.
[19] The core of
[18] , wherein the antioxidant contains at least one of, preferably both, a radical scavenger and a peroxide decomposer.
[20] The core of
[18] or
[19] , wherein the antioxidant contains at least one of, preferably both, a phenolic antioxidant and a phosphite antioxidant.
[21] The core of any of
[18] to
[20] , wherein the antioxidant contains a compound having a melting point of 50°C or higher or 100°C or higher.
[22] The core of any of
[18] to
[21] , wherein the antioxidant contains a compound having a melting point higher than the melting point of the first wax.
[23] A core according to any one of
[18] to
[22] , wherein the first wax is composed primarily of a hydrocarbon.
[24] A core according to any one of
[18] to
[23] , wherein the first wax contains one or more waxes selected from the group consisting of paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.
[25] A core according to any one of
[18] to
[24] , wherein the weight-average molecular weight of the first wax after heating the first fusible composition under the following heating condition A is no more than three times that before heating the first fusible composition under the following heating condition A. (Heating condition A) A 1.5 kg specimen placed in a fluororesin-coated, 20 cm diameter, open-ended container is placed in a natural convection oven and maintained at 150°C for 600 hours.
[26] A core according to any one of
[18] to
[25] , wherein the difference in melting point of the first fusible composition after heating under the following heating condition A and the melting point before heating under the following heating condition A is within 2°C. (Heating Condition A) A 1.5 kg test object is placed in a fluororesin-coated container with a diameter of 20 cm and no lid, and the container is placed in a natural convection oven and maintained at 150° C. for 600 hours.
[27] The core of any of
[18] to
[26] , wherein the content of the antioxidant in the first fusible composition is 0.1% by weight or more and 25% by weight or less.
[28] The core of any of
[18] to
[27] , wherein the fusible portion has the first portion and the second portion, and the first fusible composition and the second fusible composition are incompatible with each other and have different melting points.
[0009]
[29] A fusible composition used in a core placed in a mold together with a prepreg in a manufacturing method for an FRP product, the method comprising heating and curing the prepreg in the mold, the fusible composition containing a wax and an antioxidant.
[30] The fusible composition of
[29] , wherein the antioxidant contains at least one of a radical scavenger and a peroxide decomposer, preferably both.
[31] The fusible composition of
[29] or
[30] , wherein the antioxidant contains at least one of a phenolic antioxidant and a phosphite antioxidant, preferably both.
[32] The fusible composition of any of
[29] to
[31] , wherein the antioxidant contains a compound having a melting point of 50°C or higher or 100°C or higher.
[33] The fusible composition of any of
[29] to
[32] , wherein the antioxidant contains a compound having a melting point higher than that of the wax.
[34] The fusible composition of any of
[29] to
[33] , wherein the wax is composed mainly of a hydrocarbon.
[35] The fusible composition of any of
[29] to
[34] , which contains one or more waxes selected from the group consisting of paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.
[36] The fusible composition of any of
[29] to
[35] , wherein the weight-average molecular weight of the wax after heating the fusible composition under heating condition A below is no more than three times that before heating under heating condition A below. (Heating condition A) A 1.5 kg test sample placed in a fluororesin-coated, 20 cm diameter, open-ended container is placed in a natural convection oven, and maintained at 150°C for 600 hours.
[37] The fusible composition of any of
[29] to
[36] , wherein the difference between the melting point after heating under heating condition A below and the melting point before heating under heating condition A below is within 2°C. (Heating Condition A) A 1.5 kg test sample placed in a fluororesin-coated container with a diameter of 20 cm and no lid is placed in a natural convection oven and maintained at 150° C. for 600 hours.
[38] The fusible composition according to any one of
[29] to
[37] , wherein the content of the antioxidant is 0.1% by weight or more and 25% by weight or less.
[0010] In a manufacturing method for FRP products in which a prepreg is placed in a mold together with a core having a fusible portion made of wax and then heated and cured in the mold, improvements are provided to prevent a decrease in manufacturing efficiency and the occurrence of process defects that accompany repeated reuse of wax.
[0011] Figure 1 shows a cross-sectional view of a core. Figure 2 shows a cross-sectional view of a preform having a near net shape placed around the core. Figure 3 shows a cross-sectional view of the preform together with the core placed in a mold. Figure 4 shows a cross-sectional view of the core. Figure 5 shows a cross-sectional view of the core.
[0012] 1. Method for Manufacturing an FRP Product A method for manufacturing an FRP product according to one embodiment of the present invention (hereinafter also referred to simply as "this manufacturing method") includes at least the following two steps: (i) a first step in which, to obtain a molded product, a prepreg is placed in a mold together with a core having a fusible portion, and is heated and cured in the mold; and (ii) a second step in which, after the molded product is obtained, the entire fusible portion is melted. The fusible portion of the core used in the first step has a first portion formed from a first fusible composition containing a first wax and an antioxidant. The fusible portion may consist of only the first portion, or may have, in addition to the first portion, a second portion formed from a second fusible composition containing a second wax but no antioxidant.
[0013] This manufacturing method is preferably used to manufacture FRP products having structures with bent or curved walls. Typical examples of structures with bent or curved walls include, but are not limited to, hollow structures, cylindrical structures, U-shaped cross-section structures, and L-shaped cross-section structures. Various undercuts also often have bent or curved walls within their structures. This manufacturing method can be used not only to manufacture structures made solely of FRP, but also to manufacture structures in which FRP is integrally molded with metal parts.
[0014] The first and second steps will be described below with reference to the drawings, using an example of molding an FRP hollow article having a rectangular cross section. (1) First Step: In the first step, prepreg is prepared as a raw material. Examples of prepreg include, but are not limited to, unidirectional prepreg (also called UD prepreg), woven fabric prepreg (also called cross prepreg), tow prepreg, SMC (sheet molding compound), nonwoven fabric prepreg, and NCF prepreg. Nonwoven fabric prepreg is a prepreg that uses nonwoven fabric as the fiber reinforcement material. NCF prepreg is a prepreg that uses NCF (non-crimp fabric) as the fiber reinforcement material.
[0015] In any prepreg, the type of fiber contained in the fiber reinforcement is not limited. Preferred examples of fibers are carbon fiber, glass fiber, and aramid fiber. These fibers are used depending on the application and required properties of the FRP product to be manufactured. Examples of base resins used in the thermosetting matrix of the prepreg include, but are not limited to, epoxy resin, urea resin, vinyl ester resin, unsaturated polyester resin, polyurethane resin, and phenolic resin. Two or more types of thermosetting resins may be used in combination as the base resin.
[0016] The content of the thermosetting matrix in the prepreg is not limited, but is, for example, 15 to 50% by weight. The thermosetting matrix may contain various additives as needed. Examples of additives include curing agents, thickeners, reactive diluents, low-shrinkage agents, flame retardants, antifoaming agents, defoaming agents, mold release agents, particulate fillers, colorants, and silane coupling agents.
[0017] Figure 1 shows a cross-sectional view of the core prepared in the first step. The core 3 comprises a fusible portion 1 formed from a fusible composition containing wax and an antioxidant, and an outer skin 2 covering the fusible portion 1. The outer skin 2 may be omitted if not necessary. The core 3 is manufactured to fit the shape of the preform 4 so that there is almost no gap between the core 3 and the preform 4 described below. The possible structures of the core 3, the materials of each portion of the core 3, and a manufacturing method for the core 3 will be described later.
[0018] After the core 3 is prepared, a preform 4 having a near net shape is fabricated from one or more prepregs and placed around the core 3 as shown in FIG. 2. In one example, the hollow preform 4 is fabricated by combining a plurality of prefabricated partial preforms. In another example, the hollow preform 4 is fabricated by winding prepreg around the core. The preform 4 may also be fabricated by winding prepreg tape around the core 3 using a winding machine. This method makes it possible to closely attach the preform and the core without any gaps.
[0019] When producing the preform 4, the prepreg may be heated, if necessary, to a temperature at which the curing reaction does not proceed. The preform 4 may contain a plurality of prepregs of the same type, or may contain two or more types of prepregs. In a preferred example, the preform 4 is produced from one or more prepregs selected from unidirectional prepregs, cross prepregs, tow prepregs, nonwoven fabric prepregs, and NCF prepregs, and SMC.
[0020] As shown in FIG. 3 , the preform 4 is placed together with the core 3 inside a molding die 10 consisting of a lower die 12 and an upper die 14. At this point, the molding die 10 is desirably maintained at the molding temperature. The molding temperature is defined as the temperature of the molding die when curing the prepreg (preform). After the core 3 and preform 4 are placed inside, the molding die 10 is clamped. The preform 4 is cured by being held inside the molding die 10 heated to the molding temperature. The molding temperature can be a temperature typically used for curing preforms, and may be, for example, 100° C. or higher, 100° C. or higher and 180° C. or lower, 120° C. or higher and 180° C. or lower, or 140° C. or higher and 160° C. or lower. The molding time may be, for example, 1 minute or higher and 30 minutes or lower, 3 minutes or higher and 20 minutes or lower, or 5 minutes or higher and 10 minutes or lower.
[0021] It is preferable that a pressure of 0.1 MPa or more is applied to the preform in the mold. After a predetermined molding time has elapsed, the mold 10 is opened and the molded product is removed. The molded product is a hollow article made of FRP, which is the cured product of the preform 4.
[0022] The first step includes a first mode in which the surface of the fusible portion 1 is not melted, and a second mode in which at least a portion of the surface of the fusible portion 1 is melted. When the first mode is employed, it is not necessary to provide the skin 2 on the core 3. When the first mode is employed, it is preferable, but not essential, that at least the surface of the fusible portion 1 be formed from a fusible composition having a melting temperature higher than the molding temperature. Even if the melting temperature of the fusible composition is equal to or lower than the molding temperature, the fusible portion 1 will not melt unless the surface of the fusible portion 1 reaches the melting temperature of the fusible composition within the molding time.
[0023] In the first embodiment, the core 3 may be preheated before being placed in the mold 10. In one example, preheating the core can be performed to control the amount of thermal expansion of the core in the mold. Since the thermal expansion coefficient of wax in a solid state tends to increase as it approaches the melting temperature, the higher the temperature immediately before being placed in the mold, the greater the amount of expansion of the core when heated in the mold. However, if the temperature before being placed in the mold is too close to the molding temperature, the temperature change of the core in the mold may be small, and the amount of expansion of the core in the mold may actually be reduced. In another example, preheating the core can be performed for the purpose of achieving uniform temperature throughout the core. Uniform temperature throughout the core can contribute to suppressing temperature variations in the preform during molding.
[0024] When the second embodiment is adopted, at least a portion of the surface of the fusible portion 1 is formed from a fusible composition having a melting temperature lower than the molding temperature. Because the fusible composition expands significantly when melted, when the fusible portion 1 begins to melt, the internal pressure of the molding die 10 rises rapidly, forcing the preform 4 firmly against the inner surface of the molding die 10. The internal pressure is generated because the fusible portion 1 attempts to expand against the clamping force of the molding die 10. When the second embodiment is adopted, an outer skin 2 may be provided on the core 3 to prevent the melt of the fusible composition from entering between the preform 4 and the molding die 10. The role of the outer skin is to seal gaps between the prepregs and between the prepregs and the inner surface of the molding die, preventing the melt of the fusible composition from entering these gaps.
[0025] Since prepreg contains a resin as a matrix, its thermal conductivity is not very high. Therefore, in the second embodiment, the core 3 may be preheated before being placed in the mold 10 so that the preform 4 does not harden before the core 3 melts due to the heat transferred from the mold 10 through the preform 4. Among prepregs, SMC is thicker than other prepregs, so preheating the core 3 can be particularly effective when the preform 4 contains SMC.
[0026] (2) Second Step In the second step, after obtaining a molded product (a hollow FRP article), the entire fusible portion 1 is melted. The molten core 3 inside the molded product (a hollow FRP article) is then discharged to the outside of the molded product through a discharge hole provided in the molded product. Specifically, a discharge hole is provided in a part of the molded product, and the molded product is heated, for example, in an oven, to melt the entire fusible portion of the core inside the molded product, and the molten material can be discharged through the discharge hole. A drill or a hole saw can be used, for example, to form the discharge hole. When melting the fusible portion, the molded product is heated so that its temperature does not reach its heat distortion temperature (deflection temperature under load). From the viewpoint of production efficiency, it is preferable to melt the fusible portion of the core after the first step, before the temperature of the molded product removed from the mold drops significantly. In another embodiment, when manufacturing an FRP product that is not a hollow article and does not have undercuts, it is not necessary to melt the entire fusible portion 1 in order to remove the core 3, but after removing the core 3, the entire fusible portion 1 is melted in order to create a new core with the fusible composition contained in the fusible portion 1.
[0027] The fusible composition removed from the molding is collected, melted, and then used to produce a new core. If the molding has a hollow portion, it is preferable to keep the fusible composition melted to remove it from the hollow portion in a molten state until it is time to reuse it to produce a new core. This is because it takes time to re-melt a fusible composition that has solidified. If the time until reuse is sufficiently short, the energy required to keep the fusible composition in a molten state may be less than the energy required to re-melt the solidified fusible composition. If the time until reuse is long, the fusible composition can be solidified and stored, and the entire fusible portion 1 can be melted again when producing a core.
[0028] When the fusible composition is removed from a molded product or reused as a new core material, it comes into contact with air while heated to a temperature above its melting temperature, but the antioxidant contained in the composition prevents oxidation of the wax in the fusible composition, thereby preventing changes in the fusible composition's physical properties, such as its melting temperature, thermal expansion coefficient, and viscosity when molten.As a result, when the same FRP product is repeatedly molded under the same molding conditions while reusing the fusible composition, a decrease in production efficiency and molding defects caused by changes in the physical properties of the fusible composition are prevented.
[0029] The increase in viscosity of the fusible composition due to the oxidation of wax when the FRP product has a hollow portion can have a particularly large impact on the manufacturing efficiency of FRP products. It can take a significantly long time for the fusible composition with increased viscosity to be discharged through the discharge holes provided in the hollow portion. In extreme cases, it can become difficult to completely discharge the fusible composition from the hollow portion. Increasing the number of discharge holes or the diameter of the discharge holes is one way to solve this problem, but it is not always possible to do so.
[0030] Examples of process defects caused by changes in the physical properties of the fusible composition include the following: For example, if the thermal expansion coefficient of the fusible composition changes, when the fusible portion of the core is produced using a mold such as injection molding, the dimensions of the core become unstable.
[0031] If the thermal expansion coefficient of the fusible composition changes, the internal pressure applied to the prepreg in the first step of this production method will also change. If the internal pressure drops below the allowable range, the appearance and physical properties of the molded product will deteriorate, and conversely, if the internal pressure becomes too high, the fusible composition will leak out of the mold.
[0032] If the melting point of the fusible composition changes, the timing and amount of melting of the core surface in the first step of the production method may change, which may affect the quality of the molded product.
[0033] In this production method, the fusible composition contains an antioxidant, which suppresses changes in the physical properties of the fusible composition due to oxidation of the wax, making it possible to prevent the above-mentioned process defects over a long period of time, thereby increasing the number of times the wax can be reused and reducing costs.
[0034] 2. Core The structure that the core used in this manufacturing method may have, the materials of each part of the core, and the method for manufacturing the core will be described below.
[0035] (1) Core with Outer Skin As described above, in this production method, a core 3 can be used that is composed of a fusible portion 1 made of wax and an outer skin 2 that covers the fusible portion 1, as shown in Figure 1. The fusible portion 1 may be composed of one type of fusible composition, or may have two portions with different melting temperatures. Each portion may contain an antioxidant, or only the portion containing the wax that is more susceptible to oxidation may contain an antioxidant.
[0036] When the fusible portion 1 is made of one type of fusible composition, the fusible portion 1 may be made up of a single piece as a whole, or may be an assembly of multiple pieces made of the same fusible composition. When the fusible portion 1 is made of one type of fusible composition, the melting temperature of the fusible composition is higher than room temperature (25°C), preferably 50°C or higher, more preferably 60°C or higher, and lower than the molding temperature in the first step described above. There are no particular limitations on the type of wax contained in the fusible composition, and any of synthetic waxes, natural waxes, processed waxes, and blended waxes can be used.
[0037] In the core 3 shown in Fig. 4, the fusible portion 1 is composed of two incompatible portions having different melting temperatures: a first fusible portion 1a made of a first fusible composition and a second fusible portion 1b made of a second fusible composition. The first fusible portion 1a may be continuous as a whole, or may be an assembly of multiple pieces each made of the first fusible composition. Similarly, the second fusible portion 1b may be a single piece made entirely of the second fusible composition, or may be an assembly of multiple pieces each made of the second fusible composition.
[0038] The melting temperature of the first fusible composition is lower than the melting temperature of the second fusible composition, and in the first step, at least a part of the first fusible portion 1a melts in the mold, but the second fusible portion 1b does not melt at all or only a part of it melts. The melting temperature of the first fusible composition is higher than room temperature (25°C), preferably 50°C or higher, more preferably 60°C or higher, and lower than the molding temperature in the first step.
[0039] The melting temperature of the second fusible composition may be higher than the molding temperature in the first step described above, but is preferably equal to or lower than the molding temperature. Even if the melting temperature of the second fusible composition is lower than the molding temperature, the second fusible portion 1b will not melt completely in the first step unless the temperature of all parts of the second fusible portion 1b reaches the melting temperature of the second fusible composition within the molding time. The melting temperature of the second fusible composition is preferably 20°C or more lower than the heat distortion temperature of the molded product.
[0040] The first fusible composition and the second fusible composition are not compatible with each other. In other words, a melt of the first fusible composition will not dissolve the second fusible composition, and when a melt of the first fusible composition and a melt of the second fusible composition are placed in the same container, the two will separate into two phases. Because they are not compatible with each other, the first fusible composition and the second fusible composition can be easily separated after the second step described above.
[0041] For example, if the wax contained in one of the first and second fusible compositions is a wax whose main component is an organic compound having a polar group, and the wax contained in the other composition is a wax whose main component is a hydrocarbon, the second fusible composition and the second fusible composition are not compatible with each other. Examples of organic compounds having a polar group include hydroxy fatty acid amides, fatty acid amides, hydroxy fatty acid esters, and fatty acid esters. These organic compounds can be used alone or in combination with one or more other organic compounds having a polar group. Examples of waxes whose main component is a hydrocarbon include paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax. Any of these waxes can be used alone or in combination with one or more other waxes whose main component is a hydrocarbon.
[0042] The first and second fusible compositions may each contain optional additives other than wax and antioxidant, examples of which include pigments and dyes.
[0043] To prevent the outer skin 2 from breaking when the first fusible portion 1a expands and / or deforms in the first step, the material of the outer skin 2 is required to be capable of elongation and deformation at the molding temperature. This elongation and deformation may be elastic, plastic, or both. A preferred material for the outer skin 2 is an organic material, particularly a polymer. Specific examples include synthetic polymers such as polyolefin, polyamide, polyester, polyurethane, silicone, and fluororubber, as well as elastomers made from these synthetic polymers. The thickness of the outer skin 2 is not particularly limited as long as it serves the purpose of serving as a seal to prevent leakage of the molten fusible composition. For example, it may be 0.05 to 1 mm, 0.05 to 0.5 mm, or 0.05 to 0.1 mm.
[0044] (2) Core without a Skin When the first embodiment is adopted in the first step of this manufacturing method, a core consisting only of a fusible portion made of a fusible composition is used. Such a core is preferably made of one type of fusible composition having a melting temperature higher than the molding temperature, or, as shown in FIG. 5 , is preferably made of a third fusible portion 1c made of a third fusible composition having a melting temperature higher than the molding temperature, and a fourth fusible portion 1d made of a fourth fusible composition that is completely covered by the third fusible portion 1c and has a melting temperature lower than that of the third fusible composition. Here, the third fusible composition and the fourth fusible composition are incompatible with each other. The core temperature rises during heating and curing of the preform, but the melting temperature of the core may be lower than the molding temperature as long as it does not reach the melting temperature.
[0045] A core having only a fusible portion made of one type of fusible composition may be composed entirely of a single piece, or may be composed of a collection of multiple pieces made of the same fusible composition. The wax contained in the fusible composition is not particularly limited, and any of synthetic waxes, natural waxes, processed waxes, and compounded waxes can be used. The fusible composition may contain any additives other than wax and antioxidant. Examples of additives include pigments and dyes.
[0046] When the core 3 shown in FIG. 5 is used, the third fusible portion 1c does not melt in the mold in the first step, and the fourth fusible portion 1d may or may not melt. The melting temperature of the third fusible composition is preferably higher than the molding temperature in the first step. Thus, if the molding temperature is 120°C, the melting temperature of the third fusible composition is higher than 120°C, and if the molding temperature is 140°C, the melting temperature of the third fusible composition is higher than 140°C. The melting temperature of the third fusible composition is preferably the molding temperature in the first step + 30°C or lower. The melting temperature of the fourth fusible composition may be higher than the molding temperature in the first step, but is preferably equal to or lower than the molding temperature. The melting temperature of the fourth fusible composition is preferably at least 20°C lower than the heat distortion temperature of the molded product. As for the third fusible portion, the temperature of the core rises during heating and hardening of the preform, but the melting temperature of the third fusible portion may be lower than the molding temperature as long as it does not reach the melting temperature.
[0047] (3) Antioxidant The antioxidant to be blended in the fusible composition that forms the fusible portion can be appropriately selected from commercially available antioxidants that are used to prevent deterioration and discoloration due to oxidation of oils and fats, petroleum products, plastics, or synthetic rubbers. Antioxidants that have the above-mentioned uses are broadly divided into three types: radical scavengers, peroxide decomposers, and radical chain initiation inhibitors.
[0048] Typical examples of radical scavengers include, but are not limited to, phenolic antioxidants including hindered phenols such as 2,6-di-tert-butyl-p-cresol (also known as dibutylhydroxytoluene or BHT) and semi-hindered phenols such as 3,9-bis[2-{3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, and aromatic amine antioxidants such as di(4-octylphenyl)amine, N-phenyl-1-naphthylamine, phenylenediamine, and phenothiazine.
[0049] Typical examples of peroxide decomposers include, but are not limited to, sulfur compound-based antioxidants such as dibenzyl disulfide and dihexadecyl sulfide, sulfur-phosphorus-based peroxide decomposers such as zinc dialkyldithiophosphate (also known as ZnDTP) and zinc diallyldithiophosphate, phosphite-based antioxidants such as tris(2,4-di-t-butylphenyl)phosphite, phosphonite-based antioxidants, and thioether-based antioxidants. Typical examples of radical chain initiation inhibitors include, but are not limited to, N,N'-bis(salicylidene)-1,2-propanediamine and benzotriazole.
[0050] In a preferred embodiment, the antioxidant contains at least one of a radical scavenger and a peroxide decomposer, and may optionally contain other components. More preferably, the antioxidant contains both a radical scavenger and a peroxide decomposer. Phenol-based antioxidants, particularly hindered phenols, are preferred as radical scavengers. The melting point of the hindered phenols may be, for example, 50°C or higher and lower than 60°C, 60°C or higher and lower than 70°C, 70°C or higher and lower than 80°C, 80°C or higher and lower than 90°C, 90°C or higher and lower than 100°C, 100°C or higher and lower than 150°C, or 150°C or higher and lower than 250°C. A preferred example of the peroxide decomposer includes a phosphite-based antioxidant. In a preferred embodiment, the antioxidant contains at least one of a phenol-based antioxidant and a phosphite-based antioxidant, and may optionally contain other components. More preferably, the antioxidant contains both a phenol-based antioxidant and a phosphite-based antioxidant.
[0051] From the viewpoint of its own stability, the antioxidant preferably has a melting point of 50°C or higher, and more preferably a melting point of 100°C or higher. In addition, between the wax and antioxidant contained in the same fusible composition, it is preferable that the melting point of the antioxidant is higher than the melting point of the wax. If the melting point of the antioxidant is higher than the melting point of the wax, the antioxidant will not melt faster than the wax in the first step of this production method and exude onto the surface of the fusible part. Such exudation can affect the expansion behavior of the fusible part and the quality of the molded product, and also reduces the content of the antioxidant in the fusible composition.
[0052] There is no particular lower limit to the content of the antioxidant in the fusible composition, as long as the antioxidant effect is exhibited. It is preferably 0.1 wt % or more, more preferably 0.2 wt % or more, and even more preferably 0.5 wt % or more. There is no particular upper limit to the content of the antioxidant in the fusible composition, but it is preferably 25 wt % or less, more preferably 15 wt % or less, even more preferably 5 wt % or less, and may be 2 wt % or less. The above upper and lower limits can be arbitrarily combined. Therefore, the content of the antioxidant in the fusible composition may be, for example, 0.1 wt % to 25 wt % or less, 0.1 wt % to 15 wt % or less, 0.2 wt % to 5 wt % or less, or 0.5 wt % to 2 wt % or less. When the antioxidant content is 0.1 wt % or more, changes in the physical properties of the fusible composition are easily suppressed for a long period of time. When the antioxidant content is 25 wt % or less, the addition of the antioxidant does not significantly change the physical properties of the fusible composition itself. In one example, adjusting the antioxidant content may allow for control of the expansion rate of the fusible composition, especially when using waxes with high expansion rates.
[0053] The following are examples of preferred embodiments of a fusible composition containing an antioxidant. In one embodiment, the weight-average molecular weight of the wax contained in the fusible composition, after the fusible composition is heated under the following heating condition A, is preferably three times or less than that before the composition is heated under heating condition A. (Heating Condition A) A 1.5 kg specimen is placed in a fluororesin-coated, open-lidded container with a diameter of approximately 20 cm, and the container is placed in a natural convection oven and maintained at 150°C for 600 hours.
[0054] Under the heating condition A, when the diameter of the container used is 20 cm, the area of the liquid surface formed by the molten fusible composition in the container is 314 cm ２ If the weight-average molecular weight of the wax contained is large, the viscosity of the fusible composition when molten increases, making it difficult to remove from the molded article having a hollow portion after the first step, or reducing usability when used to manufacture a new core after the second step. A fusible composition that shows a small increase in the weight-average molecular weight of the wax when heated under heating condition A is considered to show a small increase in the weight-average molecular weight of the wax even when repeatedly reused, and is therefore suitable for repeated reuse.
[0055] In one embodiment, the difference between the melting point of the fusible composition after heating under the heating condition A and the melting point before heating under the heating condition A is preferably within 2°C. As mentioned above, if the melting point of the fusible composition changes, the timing and amount at which the fusible portion of the core melts in the first step will change, which may affect the quality of the molded product. A fusible composition that shows a small change in melting point when heated under heating condition A is likely to show a small change in melting point when repeatedly reused, and is therefore suitable for repeated reuse.
[0056] (Method for manufacturing core) [Fusible portion] A fusible portion made of one type of fusible composition can be manufactured by, for example, a method of cutting out the solidified fusible composition by mechanical processing such as cutting or grinding, a method of melting and molding the fusible composition such as injection molding, or a method of forming a filament made of the fusible composition by 3D printing using a hot melt method. Molding or 3D printing may be combined with mechanical processing. A single fusible portion can also be made by assembling multiple pieces manufactured by the above methods. If necessary, the assembled pieces may be welded to each other.
[0057] A fusible portion consisting of a first fusible portion and a second fusible portion can be produced, for example, by producing the first fusible portion and the second fusible portion separately in the same manner as when producing a fusible portion consisting of one type of fusible composition, and then combining these. The same applies to a fusible portion consisting of a third fusible portion and a fourth fusible portion.
[0058] 4, when the first fusible portion 1a covers the surface of the second fusible portion 1b, a method can be used in which the second fusible portion 1b is produced in the same manner as in the production of a fusible portion made of one type of fusible composition, and then the surface of the second fusible portion 1b is coated with the first fusible composition to form the first fusible portion 1a. Coating can be performed, for example, by spraying the molten first fusible composition onto the surface of the second fusible portion 1b.
[0059] 5, when the third fusible portion 1c covers the surface of the fourth fusible portion 1d, a method can be used in which the third fusible portion 1a is produced in the same manner as in the case of producing a fusible portion made of one type of fusible composition, and then the fourth fusible portion 1d is formed by injecting the fourth fusible composition into the cavity inside the third fusible portion 1a. The injection port for the fourth fusible composition is blocked with the third fusible composition after injection.
[0060] Regardless of the type of fusible portion and the method used to make it, it is preferable that the antioxidant be incorporated into the fusible composition before the fusible portion is formed using the fusible composition.
[0061] [Outer Skin] The outer skin may be formed after the fusible portion is prepared. In one example, the outer skin may be formed by wrapping the fusible portion in a polymer film prepared for the outer skin. In another example, the outer skin may be formed by placing the fusible portion inside a shrink tube made of a polymer, heat-shrinking the shrink tube, and then heat-sealing both ends of the shrink tube. In this example, the shrink tube is the outer skin.
[0062] In yet another example, a low-temperature curing liquid rubber may be applied to the surface of the fusible portion, for example, by spraying, and then heated to a temperature at which the fusible portion does not melt to cure the rubber, thereby forming the outer skin. In yet another example, a raw material liquid of a UV-curable elastomer may be applied to the surface of the fusible portion, for example, by spraying, and then cured by UV irradiation to form the outer skin. The UV-curable elastomer is a UV-curable resin that forms a rubber-like elastic body when cured, and examples of such elastomers include UV-curable silicone rubber and UV-curable urethane acrylate.
[0063] 3. Experimental Results The results of the experiments conducted by the present inventors are described below.
[0064] The materials used in the experiment are as follows. Wax: Pyrolysis-type polypropylene wax with a melting point (melting temperature) of 123°C ("Viscol (registered trademark)" manufactured by Sanyo Chemical Industries, Ltd.). Hereinafter referred to as Wax A. Antioxidant A: A phenol-based antioxidant whose main component is the hindered phenol tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane ("ADK STAB (registered trademark) AO-60" manufactured by ADEKA Corporation). Antioxidant B: A phosphite-based antioxidant whose main component is tris(2,4-di-t-butylphenyl)phosphite ("ADK STAB (registered trademark) 2112" manufactured by ADEKA Corporation).
[0065] The melting point of the fusible composition was measured by DSC (differential scanning calorimetry). The measurement was performed using a TA Instruments DSC 250 according to the following procedure. A sample sealed in an aluminum sample pan was heated to 150°C at 5°C per minute, held at 150°C for 5 minutes, cooled to 40°C at 5°C per minute, held at 40°C for 5 minutes, and then heated again to 150°C at 5°C per minute. The melting peak temperature (peak top temperature) in the DSC curve during the second heating was used as the melting point.
[0066] The weight-average molecular weight of the wax was measured by GPC (gel permeation chromatography). For the measurement, Tosoh Corporation's HLC-8321GPC / HT was used, and the column temperature was set to 135°C. The solvent used was orthodichlorobenzene containing 0.5 g of dibutylhydroxytoluene per liter, and the sample concentration was adjusted to 0.1 wt%.
[0067] 3.1 Experiment 1 The changes in physical properties of fusible composition C1 consisting only of wax A when left in a molten state were investigated as follows. 1.5 kg of wax A was placed in a fluororesin-coated, approximately 20 cm diameter, open-top pan, heated to melt, and then degassed. Heating was performed so that the temperature did not exceed 150°C and the heating time did not exceed 1 hour. The pan was then placed in a natural convection oven and maintained at 150°C. Fusible composition C1 consisting only of wax A began to show an increase in viscosity after approximately 600 hours of holding time, and gelled after approximately 700 hours of holding time.
[0068] The melting point of the fusible composition C1 gradually decreased as the holding time increased, and was 120° C. when the holding time was about 600 hours. The weight average molecular weight of the fusible composition C1 when the holding time was about 600 hours was more than three times that of the unheated composition.
[0069] 3.2 Experiment 2 The changes in physical properties of fusible composition C2 (total antioxidant content: 0.20 wt%) containing wax A, antioxidant A, and antioxidant B when left in a molten state were investigated as follows. 1.5 kg of wax A, 1.5 g of antioxidant A, and 1.5 g of antioxidant B were placed in a fluororesin-coated, lidless pot with a diameter of approximately 20 cm. The mixture was heated to melt wax A, then stirred and degassed. The heating was performed so that the temperature did not exceed 150°C and the heating time did not exceed 1 hour. The pot was then placed in a natural convection oven and maintained at 150°C. Fusible composition C2 began to show an increase in viscosity after approximately 900 hours of storage, and gelled after approximately 1000 hours of storage.
[0070] The melting point of fusible composition C2 did not change substantially until the holding time reached about 300 hours, then began to decrease gradually once the holding time exceeded about 300 hours, and reached 120° C. when the holding time was about 1000 hours. The weight average molecular weight of wax A contained in fusible composition C2 was the same as that when the composition was not heated (less than three times) when the holding time was about 600 hours, but was more than three times that when the composition was not heated when the holding time was about 1000 hours.
[0071] 3.3 Experiment 3 The changes in physical properties of fusible composition C3 (total antioxidant content: 1.0 wt %) containing wax A, antioxidant A, and antioxidant B when left in a molten state were investigated as follows. 1.5 kg of wax A, 7.5 g of antioxidant A, and 7.5 g of antioxidant B were placed in a fluororesin-coated, open-top pot with a diameter of approximately 20 cm. The mixture was heated to melt wax A, then stirred and degassed. Heating was performed so that the temperature did not exceed 150°C and the heating time did not exceed 1 hour. The pot was then placed in a natural convection oven and maintained at 150°C. Fusible composition C3 showed no increase in viscosity even after a holding time of approximately 2,000 hours.
[0072] The melting point of fusible composition C3 decreased more slowly with increasing holding time than fusible composition C2, and even after a holding time of approximately 1,000 hours, the melting point was still 123° C. The weight-average molecular weight of wax A contained in fusible composition C3 was the same (less than three times) as when the composition was not heated, even after a holding time of approximately 1,500 hours.
[0073] 3.4 Experiment 4 Wax A was spread thinly to a thickness of about 1 mm in a fluorine-coated container with a diameter of 10 cm and no lid, and was then aged at 150°C for 45 hours. The specific volume (V) at 150°C was measured between Wax A after aging and Wax A before aging. １５０ ) and specific volume at 35°C (V ３５ ) ratio (V １５０ / V ３５ ) was compared, the former showed a decrease of about 10% compared to the latter. This result suggests that the wax expansion rate can change due to deterioration caused by heating in air.
[0074] The specific volume measurement was performed using a P-V-T test system manufactured by Toyo Seiki Seisaku-sho, Ltd., with the pressure fixed at 5 MPa, and the sample was heated from 35°C to 200°C and then cooled to 35°C. The specific volume was measured every 5°C. This measurement also revealed that the shape of the curve showing the temperature dependence of the specific volume of wax A after degradation was different from that before degradation.
[0075] While the present invention has been described above with reference to specific embodiments, these embodiments are presented as examples and do not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways within the scope of the effects of the invention, and can be combined with features described in other embodiments within the scope of feasibility.
[0076] The invention disclosed in this specification can be preferably used when manufacturing, from FRP, parts for automobiles, ships, railroad cars, aircraft, unmanned aerial vehicles, and other transportation equipment, as well as various sporting goods including tennis rackets and golf shafts, without limitation.
[0077] 1 Fusible part 1a 1st fusible part 1b 2nd fusible part 1c 3rd fusible part 1d 4th fusible part 2 Outer skin 3 Core 4 Press 10 Molding mold 12 Lower mold 14 Upper mold
Claims
1. a first step in which the prepreg is placed in a mold together with a core having a fusible portion and heated in the mold to harden the prepreg, in order to obtain a molded article; a second step of melting the entire fusible portion after obtaining the molded product, The fusible portion of the core has a first portion formed of a first fusible composition containing a first wax and an antioxidant, and may optionally have a second portion formed of a second fusible composition containing a second wax and no antioxidant.
2. The manufacturing method according to claim 1 , wherein the second step is performed to remove the fusible portion from the molding, or the second step is performed to create a new core.
3. The manufacturing method according to claim 1, wherein the molded product has a hollow portion, and further comprises discharging the melt of the fusible portion produced in the second step from the inside of the hollow portion through a discharge hole provided in the hollow portion.
4. 10. Any manufacturing method according to claim 1, wherein after the second step, the first fusible composition is reused to make another core.
5. 4. The manufacturing method according to claim 3, wherein after the second step, the first fusible composition is reused to produce another core, and at least a portion of the first fusible composition contained in the melt of the fusible portion is kept in a molten state until the time of reuse.
6. The method according to claim 1, wherein the antioxidant contains at least one of a radical scavenger and a peroxide decomposer, and preferably both.
7. The method according to claim 1, wherein the antioxidant contains at least one of a phenol-based antioxidant and a phosphite-based antioxidant, and preferably both.
8. The method according to claim 1 , wherein the antioxidant contains a compound having a melting point of 50° C. or higher or 100° C. or higher.
9. The method of claim 1 , wherein the antioxidant comprises a compound having a melting point higher than the melting point of the first wax.
10. The process of claim 1 wherein the first wax is predominantly hydrocarbon.
11. 2. The method according to claim 1, wherein the first wax comprises at least one wax selected from the group consisting of paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.
12. The manufacturing method according to claim 1 , wherein in the first step, at least a portion of the surface of the fusible portion is melted.
13. The manufacturing method according to claim 1 , wherein the surface of the fusible portion does not melt in the first step.
14. The method according to claim 1 , wherein the mold is heated to a temperature of 100° C. or higher in the first step.
15. The manufacturing method according to claim 1, wherein a pressure of 0.1 MPa or more is applied to the prepreg in the first step.
16. The method according to claim 1 , wherein the content of the antioxidant in the first fusible composition is 0.1% by weight or more and 25% by weight or less.
17. The manufacturing method according to any one of claims 1 to 16, wherein the fusible portion has the first portion and the second portion, and the first fusible composition and the second fusible composition are incompatible with each other and have different melting points.
18. In a method for manufacturing an FRP product, the method includes heating and curing a prepreg in a molding die, and a core is placed in the molding die together with the prepreg, It has a fusible portion, The fusible portion has a first portion formed of a first fusible composition containing a first wax and an antioxidant, and optionally has a second portion formed of a second fusible composition containing a second wax and no antioxidant. core.
19. 19. The core of claim 18, wherein the antioxidant comprises at least one of, and preferably both, a radical scavenger and a peroxide decomposer.
20. 19. The core according to claim 18, wherein the antioxidant comprises at least one of, and preferably both of, a phenolic antioxidant and a phosphite antioxidant.
21. 20. The core of claim 18, wherein the antioxidant comprises a compound having a melting point of 50°C or higher or 100°C or higher.
22. 20. The core of claim 18, wherein the antioxidant comprises a compound having a melting point higher than the melting point of the first wax.
23. 20. The core of claim 18, wherein the first wax is predominantly hydrocarbon.
24. 20. The core of claim 18, wherein the first wax comprises one or more selected from the group consisting of paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.
25. 19. The core of claim 18, wherein the weight average molecular weight of the first wax after heating the first fusible composition under heating condition A is no more than three times that before heating the first fusible composition under heating condition A. (Heating condition A) A 1.5 kg test object is placed in a fluororesin-coated container with a diameter of 20 cm and no lid, and the container is placed in a natural convection oven and maintained at 150° C. for 600 hours.
26. 19. The core of claim 18, wherein the difference between the melting point of the first fusible composition after heating under heating condition A below and the melting point before heating under heating condition A below is within 2°C. (Heating condition A) A 1.5 kg test object is placed in a fluororesin-coated container with a diameter of 20 cm and no lid, and the container is placed in a natural convection oven and maintained at 150° C. for 600 hours.
27. 20. The core of claim 18, wherein the content of the antioxidant in the first fusible composition is 0.1% by weight or more and 25% by weight or less.
28. The core according to any one of claims 18 to 27, wherein the fusible portion has the first portion and the second portion, and the first fusible composition and the second fusible composition are incompatible with each other and have different melting points.
29. In a manufacturing method of an FRP product, which includes heating and curing a prepreg in a molding die, the present invention is used for a core that is placed in the molding die together with the prepreg, Contains wax and antioxidants, Fusible composition.
30. 30. The fusible composition of claim 29, wherein the antioxidant comprises at least one of, and preferably both, a radical scavenger and a peroxide decomposer.
31. 30. The fusible composition of claim 29, wherein the antioxidant comprises at least one of, and preferably both of, a phenolic antioxidant and a phosphite antioxidant.
32. 30. The fusible composition of claim 29, wherein the antioxidant comprises a compound having a melting point of 50°C or higher or 100°C or higher.
33. 30. The fusible composition of claim 29, wherein the antioxidant comprises a compound having a melting point higher than the melting point of the wax.
34. 30. The fusible composition of claim 29, wherein the wax is predominantly hydrocarbon.
35. 30. The fusible composition of claim 29, comprising one or more waxes selected from the group consisting of paraffin waxes, microcrystalline waxes, Fischer-Tropsch waxes, polyethylene waxes, and polypropylene waxes.
36. 30. The fusible composition according to claim 29, wherein the weight average molecular weight of the wax after heating the fusible composition under heating condition A below is no more than three times that before heating under heating condition A below. (Heating condition A) A 1.5 kg test object is placed in a fluororesin-coated container with a diameter of 20 cm and no lid, and the container is placed in a natural convection oven and maintained at 150° C. for 600 hours.
37. 30. The fusible composition according to claim 29, wherein the difference between the melting point after heating under the heating condition A below and the melting point before heating under the heating condition A below is within 2°C. (Heating condition A) A 1.5 kg test object is placed in a fluororesin-coated container with a diameter of 20 cm and no lid, and the container is placed in a natural convection oven and maintained at 150° C. for 600 hours.
38. 38. The fusible composition according to claim 29, wherein the content of the antioxidant is 0.1% by weight or more and 25% by weight or less.