Prepreg and method for producing prepreg

Abstract

This prepreg is obtained by impregnating a fiber base material with a thermosetting resin composition, and contains a component (a) specified by the following procedure in an amount of 72 mass% or less. (Procedure) The prepreg is cut into 10 cm squares to prepare a test piece, and then the mass x (g) is measured. Next, the test piece is stirred together with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours, and is subsequently taken out. Thereafter, the test piece is dried under reduced pressure for 24 hours, and then the mass y (g) is measured. Subsequently, the test piece is fired at 500°C for 4 hours, and then the mass z (g) is measured. The ratio (mass%) of the component a is calculated by formula (1) below.　(1): Component a = {(mass y - mass z) / (mass x - mass z)} × 100

Description

Prepreg and method for producing prepreg

[0001] The present invention relates to a prepreg and a method for producing a prepreg. More particularly, the present invention relates to a prepreg, a panel using a cured product of the prepreg, and a method for producing the prepreg.

[0002] Prepregs obtained by impregnating a fiber substrate with a thermosetting resin as a matrix resin are lightweight yet have excellent mechanical strength and heat resistance, and are therefore useful as housings or various components for transportation vehicles such as aircraft and automobiles, or as building structures and components. As such prepregs, for example, Patent Document 1 discloses a prepreg obtained by impregnating a fiber substrate with a resin composition containing a specified urethane (meth)acrylate (A), a polymerization initiator (B), and an amine catalyst (C) from the standpoint of workability and product stability.

[0003] International Publication No. 2022 / 249672

[0004] In recent years, there has been an increasing demand for improved performance of prepregs. In particular, when prepregs are used in aircraft and the like, they must satisfy various standards related to combustion behavior, such as combustion reaction, smoke emission, smoke toxicity, and heat release from the material during combustion. However, conventional technologies such as those disclosed in Patent Document 1 have room for improvement in terms of such combustion behavior.

[0005] Furthermore, a method of using a highly flame-retardant matrix resin is known, but if the degree of impregnation of the matrix resin is too high, the amount of matrix resin present on the surface of the prepreg becomes extremely small, which can result in insufficient tackiness of the prepreg.

[0006] The present inventors have focused on improving the heat release properties of prepreg while maintaining good tackiness, and as a result of extensive research, have found that components obtained when a prepreg is subjected to a predetermined procedure are involved in the heat release properties and tackiness. Further research has led to the development of a new index that uses the amount of components obtained by the predetermined procedure as an index, and the discovery that controlling this index is effective, leading to the completion of the present invention.

[0007] According to the present invention, the following prepreg and related techniques are provided.

[0008] [1] A prepreg in which a fiber substrate is impregnated with a thermosetting resin composition, wherein the component a, as specified by the following procedure, is 72% by mass or less. (Procedure) The prepreg is cut into a 10 cm square to prepare a test piece, and then the mass x (g) is measured. Next, the test piece is stirred with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours, and then removed. Thereafter, the test piece is dried under reduced pressure for 24 hours, and then the mass y (g) is measured. Subsequently, the test piece is baked at 500°C for 4 hours, and then the mass z (g) is measured. The proportion (mass %) of component a is calculated using the following formula (1): Component a = {(mass y - mass z) / (mass x - mass z)} x 100 (1) [2] The prepreg according to [1], wherein the solid content of the thermosetting resin composition in the prepreg is 30 to 50% by mass. [3] The prepreg according to [1] or [2], wherein the thermosetting resin composition comprises one or more types selected from the group consisting of phenolic resin, unsaturated polyester resin, epoxy resin, melamine resin, and furan resin. [4] The prepreg according to any one of [1] to [3], wherein the fiber base material comprises one or more types selected from the group consisting of aramid fiber, polyester fiber, polyphenylene sulfide fiber, carbon fiber, graphite fiber, glass fiber, and silicon carbide fiber. [5] The prepreg according to any one of [1] to [4], wherein the thickness of the prepreg is 0.05 to 10 mm. [6] A cured product of the prepreg according to any one of [1] to [5]. [7] A panel using the cured product of the prepreg according to any one of [1] to [5]. [8] A sandwich panel comprising: a core layer having a honeycomb structure; and the prepreg according to any one of [1] to [5] provided on each of both surfaces of the core layer. [9] The sandwich panel according to [8], wherein the core layer is made of aramid fiber.

[10] A method for producing a prepreg, comprising the steps of: impregnating a fiber substrate with a thermosetting resin composition; and heating the fiber substrate impregnated with the thermosetting resin composition under any of the following conditions i to iv to bring it to a B-stage; (Condition i) leaving it to stand for 20 to less than 50 minutes in an atmosphere of 70°C or higher and lower than 90°C, (Condition ii) leaving it to stand for 15 to less than 40 minutes in an atmosphere of 90°C or higher and lower than 100°C, (Condition iii) leaving it to stand for 10 to less than 30 minutes in an atmosphere of 100°C or higher and lower than 110°C, and (Condition iv) leaving it to stand for 5 to less than 20 minutes in an atmosphere of 110°C or higher and lower than 120°C.

[11] The method for producing a prepreg according to

[10] , wherein the step of impregnating a fiber substrate with the thermosetting resin composition is carried out in an atmosphere of 5°C to 40°C.

[12] The method for producing a prepreg according to

[10] or

[11] , wherein the gel time of the thermosetting resin composition at 90°C is 200 seconds or more.

[13] The method for producing a prepreg according to any one of

[10] to

[12] , wherein the maximum exothermic peak in a DSC curve obtained when the thermosetting resin composition is heated from 30°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter is 80°C or more and 150°C or less.

[14] The method for producing a prepreg according to any one of

[10] to

[13] , wherein in the step of impregnating a fiber substrate with the thermosetting resin composition, the thermosetting resin composition is a varnish.

[15] The method for producing a prepreg according to any one of

[10] to

[14] , wherein in the step of impregnating a fiber substrate with the thermosetting resin composition, the thermosetting resin composition is a film.

[16] A method for producing a prepreg according to any one of

[10] to

[15] , wherein the glass transition temperature of the cured product of the thermosetting resin composition is 110 to 250° C.

[17] A method for producing a sandwich panel, comprising: an arrangement step of arranging the prepregs according to any one of [1] to [5] on both sides of a core layer having a honeycomb structure, and an integration step of integrating the core layer and the prepregs by a heat and pressure treatment.

[0009] According to the present invention, a prepreg is provided that can improve heat release properties while maintaining good tackiness.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] In this specification, the expression "a to b" in the description of a numerical range means from a to b, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass or more and 5% by mass or less."

[0012] <Prepreg> The prepreg of this embodiment is a prepreg in which a fiber base material is impregnated with a thermosetting resin composition, and contains 72 mass % or less of component a, which is specified by the following procedure.

[0013] (Procedure) The prepreg is cut into a 10 cm square to prepare a test piece, and then the mass x (g) is measured. Next, the test piece is immersed in 400 ml of methanol in a 500 ml resin container, stirred at 20°C for 20 hours, and then removed. After that, it is dried under reduced pressure for 24 hours, and the mass y (g) is measured. Next, the test piece is baked at 500°C for 4 hours, and the mass z (g) is measured. The proportion (mass %) of component a is calculated using the following formula (1): Component a = {(mass y - mass z) / (mass x - mass z)} x 100 (1)

[0014] This improves the heat release properties while maintaining the good tackiness of the prepreg. Here, component a is not extracted with methanol but is vaporized or incinerated by the baking treatment. It is considered to be a component in the thermosetting resin composition where the thermosetting reaction has progressed to a certain extent or an impurity that does not contribute to thermosetting, and is therefore easily combustible. Furthermore, components where the thermosetting reaction has progressed to a certain extent are not re-melted by the heat during heat compression molding in the processing of the prepreg, and are therefore considered to be components that reduce adhesion. Therefore, it is presumed that by setting the content of component a to 72% by mass or less, it is possible to effectively suppress the reduction in tackiness while improving the heat release properties of the prepreg. In addition, according to the prepreg of this embodiment, the good tackiness allows high adhesion when the prepregs are laminated, making it easier to obtain flame retardancy in the laminate.

[0015] In order to achieve both good tackiness and high levels of heat release properties of the prepreg, the content of component a is preferably 70% by mass or less, more preferably 65% ​​by mass or less, whereas in order to maintain good moldability and productivity of the prepreg, the content of component a is preferably 10% by mass or more, more preferably 20% by mass or more.

[0016] A prepreg that satisfies the above conditions can be realized by adjusting the composition of the thermosetting resin composition or by devising a prepreg manufacturing method. For example, this can be achieved by adjusting the temperature and impregnation time when the thermosetting resin composition is impregnated into the fiber substrate. Details will be explained later in the prepreg manufacturing method.

[0017] In the above procedure, the stirring conditions can be 20 hours at 20°C and a rotation speed of 150 rpm. A reciprocating shaker (e.g., NR-30 manufactured by Taitec Co., Ltd.) can be used for stirring. The calcination treatment can be carried out using a muffle furnace.

[0018] The materials constituting the prepreg will be described below.

[0019] [Thermosetting Resin Composition] The content of the thermosetting resin composition in the prepreg is preferably 30 to 55 mass %, more preferably 32 to 52 mass %, even more preferably 35 to 50 mass %, and particularly preferably 40 to 50 mass %, in terms of solid content.

[0020] (Thermosetting Resin) The thermosetting resin composition contains a thermosetting resin. The thermosetting resin may be one or more selected from the group consisting of epoxy resin, phenolic resin, unsaturated polyester resin, melamine resin, and furan resin. Among these, furan resin is preferred.

[0021] The furan resin is a polymer or its precursor (oligomer) starting from furfural or furfuryl alcohol obtained by reducing furfural. Examples of furan resins include furfuryl alcohol, furfuryl alcohol-furfural co-condensation, furfuryl alcohol-aldehyde co-condensation, furfural-ketone co-condensation, furfural-phenol co-condensation, furfuryl alcohol-urea co-condensation, and furfuryl alcohol-phenol co-condensation. Modified furan resins include epoxy-modified, phenol-modified, aldehyde-modified, urea-modified, and melamine-modified resins.

[0022] Specific examples of epoxy resins include biphenyl-type epoxy resins; bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and tetramethylbisphenol F-type epoxy resins; stilbene-type epoxy resins; novolac-type epoxy resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins; polyfunctional epoxy resins such as triphenyl-type epoxy resins exemplified by triphenolmethane-type epoxy resins and alkyl-modified triphenolmethane-type epoxy resins; phenol aralkyl-type epoxy resins having a phenylene skeleton, naphthol aralkyl-type epoxy resins having a phenylene skeleton, and phenol aralkyl-type epoxy resins having a biphenylene skeleton. phenol aralkyl epoxy resins such as aryl-type epoxy resins (biphenyl aralkyl-type epoxy resins) and naphthol aralkyl-type epoxy resins having a biphenylene skeleton; naphthol-type epoxy resins such as dihydroxynaphthalene-type epoxy resins and epoxy resins obtained by glycidyl etherifying a dihydroxynaphthalene dimer; triazine nucleus-containing epoxy resins such as triglycidyl isocyanurate and monoallyl diglycidyl isocyanurate; bridged cyclic hydrocarbon compound-modified phenol-type epoxy resins such as dicyclopentadiene-modified phenol-type epoxy resins; brominated epoxy resins such as brominated bisphenol A and brominated phenol novolac; tris(hydroxyphenyl)methane-type epoxy resins. As the epoxy resin, one type from these may be used alone, or two or more different types may be used in combination.

[0023] Specific examples of the phenolic resin include novolac-type phenolic resins, resole-type phenolic resins, and aryl alkylene-type phenolic resins. As the phenolic resin, one of these may be used alone, or two or more types having different weight-average molecular weights may be used in combination, or one or more types may be used in combination with their prepolymers. Among these, it is preferable to use different types of phenolic resins in combination, and for example, it is more preferable to use a novolac-type phenolic resin and a resole-type phenolic resin in combination.

[0024] The content of the thermosetting resin is preferably 60 to 99 mass %, more preferably 70 to 98 mass %, and even more preferably 80 to 95 mass %, based on the solid content in the thermosetting resin composition.

[0025] Furthermore, the thermosetting resin composition may contain known compounds depending on the intended use. Examples of known compounds include additives such as curing agents, inorganic fillers, coupling agents, surfactants, curing accelerators, thermoplastic resins, elastomers, pigments, flame retardants, and adhesion promoters. Only one of these may be contained, or two or more may be contained.

[0026] (Curing Agent) The curing agent of the present embodiment is selected depending on the type of thermosetting resin, and is not particularly limited as long as it reacts with the thermosetting resin. Specific examples of the curing agent include polyaddition type curing agents, catalyst type curing agents, and condensation type curing agents.

[0027] Specific examples of the curing agent include phenolic curing agents, amines, polyoxystyrenes such as polyparaoxystyrene, acid anhydrides including alicyclic acid anhydrides such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA), and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA), polymercaptan compounds such as polysulfides, thioesters, and thioethers, isocyanate compounds such as isocyanate prepolymers and blocked isocyanates, and organic acids such as carboxylic acid-containing polyester resins. One or more of these may be used in combination.

[0028] Specific examples of the phenolic curing agent include one or more selected from novolac-type phenolic resins such as phenol novolac resin, cresol novolac resin, naphthol novolac resin, aminotriazine novolac resin, and trisphenylmethane-type phenol novolac resin; modified phenolic resins such as terpene-modified phenolic resin and dicyclopentadiene-modified phenolic resin; aralkyl-type resins such as phenol aralkyl resins having a phenylene skeleton and / or biphenylene skeleton and naphthol aralkyl resins having a phenylene skeleton and / or biphenylene skeleton; bisphenol compounds such as bisphenol A and bisphenol F; and resol-type phenolic resins. From the viewpoint of curability, the hydroxyl group equivalent of the phenolic resin-based curing agent is preferably, for example, 90 g / eq or more and 250 g / eq or less.

[0029] The content of the curing agent is preferably 0.5 to 10 parts by mass, more preferably 2 to 6 parts by mass, based on 100 parts by mass of the thermosetting resin.

[0030] The contents of the thermosetting resin and the curing agent are appropriately set depending on the thermosetting resin and the curing agent.

[0031] (Surfactant) The surfactant has the advantage that, for example, when producing a prepreg (when the thermosetting resin composition is impregnated into a fiber substrate), it can suppress repelling of the thermosetting resin composition and prevent the occurrence of surface defects. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, silicone surfactants, and UV curable surfactants. Examples of commercially available products include silicone surfactants such as BYK302, BYK307, BYK333, BYK341, BYK345, BYK346, BYK347, BYK348, and BYK-361N (manufactured by BYK Japan).

[0032] (Inorganic Filler) The resin composition of this embodiment may contain an inorganic filler. The inorganic filler is used to increase the mechanical strength or to impart heat resistance, flame retardancy, etc. depending on the application of the prepreg. Specific examples of inorganic fillers include silicates such as talc, calcined clay, uncalcined clay, mica, and glass; oxides such as titanium oxide, alumina, boehmite, and silica; carbonates such as calcium carbonate, magnesium carbonate, and hydrotalcite; hydroxides such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide; sulfates or sulfites such as barium sulfate, calcium sulfate, and calcium sulfite; borates such as zinc borate, barium metaborate, aluminum borate, calcium borate, and sodium borate; nitrides such as aluminum nitride, boron nitride, silicon nitride, and carbon nitride; and titanates such as strontium titanate and barium titanate. These may be used alone or in combination of two or more.

[0033] (Coupling Agent) When the resin composition of the present embodiment contains an inorganic filler, it may contain a coupling agent. This can suppress aggregation of the inorganic filler and achieve good fluidity. As the coupling agent, known coupling agents can be used, such as various silane-based compounds such as epoxy silane, mercapto silane, amino silane, alkyl silane, ureido silane, and vinyl silane, titanium-based compounds, aluminum chelates, and aluminum / zirconium-based compounds.

[0034] Next, a method for producing the resin composition of this embodiment will be described. The method for producing the resin composition of this embodiment is not particularly limited. For example, when the thermosetting component and other optional components are liquid, they are mixed by stirring with a stirring spring using a Three-One Motor or the like. When the thermosetting component and other optional components are solid, they are mixed using a mixer or the like, and then melt-heated and kneaded at about 90 to 120°C using a heated kneader, heated roll, or extruder or the like. The resulting kneaded product is then cooled and pulverized to obtain a powdered or granular resin composition. If necessary, the resin composition may be pulverized and then compressed into tablets, or may be pulverized and then formed into a sheet by, for example, vacuum lamination or compression molding.

[0035] Alternatively, for example, the thermosetting component and other optional components may be dissolved, mixed, and stirred in a solvent using various mixers such as those employed in ultrasonic dispersion, high-pressure collision dispersion, high-speed rotation dispersion, bead mill dispersion, high-speed shear dispersion, or rotation-revolution dispersion, to prepare a varnish-like resin composition.

[0036] [Fiber substrate] In the prepreg of this embodiment, the fiber substrate is one or more fibers selected from aramid fiber, polyester fiber, polyphenylene sulfide fiber, carbon fiber, graphite fiber, glass fiber, and silicon carbide fiber. Glass fiber is preferred from the viewpoint of obtaining good heat resistance and flame retardancy.

[0037] Examples of the glass fiber include glass fibers formed from one or more types of glass selected from E glass, S glass, D glass, T glass, NE glass, UT glass, L glass, HP glass, and quartz glass.

[0038] [Physical Properties, Applications, etc.] The prepreg of this embodiment is in a B-stage state. The B-stage refers to a state in which 5 to 90% of the resin composition is cured (semi-cured), and the C-stage refers to a state in which more than 90% of the resin composition is cured (fully cured). The degree of cure of the resin composition can be determined from the reaction rate measured using a differential scanning calorimeter.

[0039] The prepreg is then fully cured and can be suitably used for panels used as wall materials or ceiling materials for buildings and transportation equipment. Full curing can be achieved, for example, by heating at 100 to 150°C for 60 to 240 minutes.

[0040] The thickness of the prepreg can be set appropriately depending on the application, but may be, for example, 0.05 to 10 mm.

[0041] <Method for manufacturing prepreg> The method for manufacturing prepreg of this embodiment includes: a step of impregnating a fiber base material with a thermosetting resin composition (impregnation step); and a step of heating the fiber base material impregnated with the thermosetting resin composition under any one of the following conditions i to iv to bring it to a B-stage (B-staging step); (Condition i) leaving it to stand for 20 minutes or more and less than 50 minutes in an atmosphere of 70°C or more and less than 90°C; (Condition ii) leaving it to stand for 15 minutes or more and less than 40 minutes in an atmosphere of 90°C or more and less than 100°C; (Condition iii) leaving it to stand for 10 minutes or more and less than 30 minutes in an atmosphere of 100°C or more and less than 110°C; and (Condition iv) leaving it to stand for 5 minutes or more and less than 20 minutes in an atmosphere of 110°C or more and less than 120°C.

[0042] That is, as shown by conditions i to iv, by precisely controlling the temperature and time in the B-staging step, the thermosetting resin composition can be appropriately impregnated into the fiber substrate and matured, and as a result, a prepreg can be obtained that has improved heat release properties while maintaining good tackiness.

[0043] Each step will be described in detail below.

[0044] [Impregnation Step] First, the thermosetting resin composition is impregnated into the fiber substrate. A sheet-like or varnish-like thermosetting resin composition can be used. As the impregnation method, a conventionally known method can be used, such as a method of applying a varnish-like thermosetting resin composition to the surface of the fiber substrate or a method of immersing the fiber substrate in a varnish-like thermosetting resin composition. Furthermore, when the thermosetting resin composition is in the form of a sheet or film, it may be laminated on the surface of the fiber substrate and, if necessary, pressurized and heated to impregnate the fiber substrate with the thermosetting resin composition.

[0045] The impregnation step is preferably carried out in an atmosphere of 5° C. to 40° C. When a varnish-like thermosetting resin composition is used, the varnish-like thermosetting resin composition may be used at ambient temperature without being heated or cooled.

[0046] The solid content of the varnish-like thermosetting resin composition may be 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. This results in a resin composition with excellent workability and impregnation properties. Note that the varnish-like thermosetting resin composition may be used as is without dilution if the thermosetting resin is liquid, or may be diluted with a known solvent if the thermosetting resin is solid.

[0047] (Gel Time) The gel time of the thermosetting resin composition at 90° C. is preferably 200 seconds or more, more preferably 230 seconds or more, while the gel time of the thermosetting resin composition at 90° C. is preferably 1000 seconds or less, more preferably 600 seconds or less, and even more preferably 500 seconds or less.

[0048] The maximum exothermic peak in the DSC curve obtained when the thermosetting resin composition is heated from 30°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter is preferably 80°C or higher, more preferably 85°C or higher, and even more preferably 90°C or higher. The maximum exothermic peak in the DSC curve obtained when the thermosetting resin composition is heated from 30°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter is preferably 150°C or lower, more preferably 300°C or lower, even more preferably 200°C or lower, and especially preferably 110°C or lower. It is presumed that by controlling the maximum exothermic peak temperature in the DSC curve, the reaction proceeding temperature can be controlled, the reaction proceeding during storage of the prepreg can be suppressed, the reaction rate during curing of the prepreg can be increased, the mechanical strength of the cured product can be increased, and warping can be reduced. As a result, good tackiness and the heat release properties of the prepreg can be achieved at a higher level.

[0049] [B-Staging Step] The fiber substrate impregnated with the thermosetting resin composition is heated to B-stage by any one of the following conditions i to iv: (Condition i) leaving it to stand for 20 minutes or more and less than 50 minutes in an atmosphere of 70°C or more and less than 90°C, (Condition ii) leaving it to stand for 15 minutes or more and less than 40 minutes in an atmosphere of 90°C or more and less than 100°C, (Condition iii) leaving it to stand for 10 minutes or more and less than 30 minutes in an atmosphere of 100°C or more and less than 110°C, (Condition iv) leaving it to stand for 5 minutes or more and less than 20 minutes in an atmosphere of 110°C or more and less than 120°C.

[0050] The standing time under condition i is preferably 20 to 45 minutes, more preferably 20 to 40 minutes, and even more preferably 20 to 35 minutes. The standing time under condition ii is preferably 20 to 35 minutes. The standing time under condition iii is preferably 10 to 25 minutes, and more preferably 10 to 20 minutes. The standing time under condition iv is preferably 5 to 15 minutes, and more preferably 10 to 15 minutes.

[0051] The leaving is preferably carried out in air. The leaving method is not particularly limited, and known methods can be used. For example, the leaving method may be carried out in a hot air dryer set at a predetermined temperature, or in a reflow oven, in which the prepreg is placed on a moving bed and continuously passed through the oven. In this manner, the prepreg of this embodiment can be produced.

[0052] <Sandwich Panel> The sandwich panel of this embodiment includes a core layer having a honeycomb structure and the above-described prepregs provided on both sides of the core layer, thereby providing a sandwich panel with improved heat release properties.

[0053] Each component constituting the sandwich panel will be described below.

[0054] [Core Layer] The core layer may be, for example, a sheet-like member obtained by impregnating a core layer substrate having a honeycomb structure with a binder resin. The honeycomb structure allows the core layer to have high strength and light weight. The honeycomb structure is a well-known structure having a plurality of substantially regular hexagonal through-holes that penetrate from the upper surface to the lower surface.

[0055] Examples of the substrate having the honeycomb structure of the core layer include those formed into a honeycomb shape by a known method using aramid fibers, paper, balsa wood, plastic, aluminum, titanium, glass, and alloys thereof, etc. From the viewpoint of heat resistance, the substrate having the honeycomb structure of the core layer preferably contains aramid fibers.

[0056] The core layer preferably has a woven fiber cloth as the substrate shape. This improves processability into a honeycomb structure and reduces the weight of the sandwich panel. When the core layer contains a woven fiber cloth, the areas where the fibers cross are less likely to be pressurized during the manufacturing process, making it easier for voids to remain. However, in the sandwich panel of this embodiment, the manufacturing method described below effectively prevents voids from becoming apparent on the surface and becoming a cause of pinholes.

[0057] In this embodiment, the binder resin used in the core layer may be a thermosetting resin composition, and may be the same as or different from the thermosetting resin composition of the prepreg. From the viewpoint of effectively improving adhesion and enhancing flame resistance, it is preferable that the binder resin used in the core layer and the thermosetting resin composition of the prepreg are the same.

[0058] The thickness of the core layer is not particularly limited, but may be, for example, 1 mm or more and 50 mm or less, 3 mm or more and 40 mm or less, or 5 mm or more and 30 mm or less.

[0059] The size of each core cell in the core layer is not particularly limited, but may be, for example, 1 mm or more and 10 mm or less on a side.

[0060] The surface area (upper and lower surfaces) of the core layer is not limited, but may have the surface area of ​​one sandwich panel, or may have the total surface area of ​​multiple sandwich panels. This makes it possible to cut one sandwich panel into individual pieces and obtain multiple panels, thereby improving productivity. For example, the surface area (upper and lower surfaces) of the core layer can be large, for example, 1 m ２ It may be more than that.

[0061] The core layer may be subjected to various surface treatments on the inside and / or outside in order to improve corrosion resistance and heat resistance.

[0062] [Prepreg] The prepreg becomes the skin layer of the sandwich panel. The prepreg may be in a B-stage state, and is fully cured when integrated with the core layer, thereby being firmly fixed to the core layer.

[0063] The B-stage state means that the reactivity of the binder resin (thermosetting resin composition) impregnated into the prepreg substrate, calculated from the results of measurement using a DSC (differential scanning calorimeter), is preferably greater than 0% and not greater than 60%, more preferably 0.5% to 55%, and even more preferably 1% to 50%.

[0064] In the sandwich panel, the thickness of each prepreg may be adjusted as appropriate, but is preferably 0.05 to 10 mm, and more preferably 0.1 to 5 mm.

[0065] <Method for manufacturing sandwich panel> Next, a method for manufacturing the sandwich panel of this embodiment will be described. The method for manufacturing the sandwich panel of this embodiment includes the following steps: (Step 1) a step of arranging prepregs on both sides of a sheet-like core layer having a honeycomb structure, and (Step 2) an integration step of integrating the core layer and the prepregs by a heat and pressure treatment. Each step will be described below.

[0066] (Step 1) First, a core layer substrate is prepared. The core layer substrate has a honeycomb structure and is preferably made of aramid fibers. A substrate having a honeycomb structure is prepared, and the substrate is impregnated with a binder resin. The substrate is then dried to obtain a core layer.

[0067] In the core layer, examples of the method for impregnating the binder resin include a method of dissolving the binder resin in a solvent and spraying the resulting binder solution onto the binder substrate using an injector such as a spray nozzle; a method of immersing the binder substrate in the binder solution; a method of applying the binder solution to the binder substrate using various coaters such as a knife coater or a comma coater; and a method of transferring the binder solution to the binder substrate using a transfer roll. Among these, the method of immersing the binder substrate in the binder solution is preferred. Furthermore, the conditions for heat drying are not particularly limited, but are typically carried out at 100 to 220°C, preferably 120 to 190°C, for 2 to 10 minutes.

[0068] (Step 2) Next, the core layer and the prepreg are integrated by heat and pressure treatment.

[0069] The heating and pressurizing treatment is preferably carried out at 110 to 150°C and 0.1 to 3.0 MPa, more preferably 120 to 140°C and 0.3 to 1.0 MPa. By setting the temperature and pressure of the heating and pressurizing treatment to at least the lower limit values, the prepreg and the core layer can be firmly integrated. On the other hand, by setting the temperature and pressure of the heating and pressurizing treatment to at most the upper limit values, appropriate integration can be achieved while suppressing damage to the prepreg.

[0070] Alternatively, the heat and pressure treatment may be performed by placing a release film between a laminate in which prepregs prepared on both sides of a core layer are laminated and a metal plate used for the heat and pressure treatment. That is, the heat and pressure treatment is performed on the above-mentioned laminate together with the release film using a metal plate, whereby the prepregs are cured and integrated with the core layer.

[0071] In the laminate, one or more prepregs may be laminated on one surface of the core layer. The number of laminated prepregs is not particularly limited, and may be 1 to 5 on one surface of the core layer.

[0072] Any known release film can be used, and examples thereof include films made of one or more resins selected from polyester resin, poly 4-methyl 1-pentene resin, polyamide resin, and polypropylene resin.

[0073] Known metal plates can be used, including, for example, SUS plates, tin plates, aluminum plates, and magnesium plates. The thickness of the metal plate is not particularly limited, but may be, for example, 0.5 mm to 10 mm, 0.8 mm to 5 mm, or 1.0 mm to 2.0 mm. By keeping the thickness within these ranges, a balance between rigidity and thermal conductivity can be achieved.

[0074] The release film and the metal plate are then separated to obtain a sandwich panel. The release film has good releasability, which prevents the sandwich panel from sticking to the metal plate, making it easy to remove the sandwich panel.

[0075] <Molded Article / Cured Product> The molded article of this embodiment is made using a cured product of the prepreg and is suitable for applications requiring flame retardancy. Specific examples include various structural components for transportation equipment such as automobiles, aircraft, railway vehicles, and ships, buildings, office equipment, general-purpose machines, household electrical appliances, and electrical equipment. Furthermore, as a structure, it is suitable for use as a skin layer of the above-mentioned side switch panel.

[0076] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0077] The present invention will be described in detail based on examples and comparative examples, but the present invention is not limited to these examples.

[0078] (1) Preparation of Thermosetting Resin Composition (Varnish) The following raw materials were mixed in the blending ratios shown in Tables 1 and 2 to prepare thermosetting resin compositions (varnishes).

[0079] [Raw Materials] Thermosetting Resin 1: At room temperature and pressure, 1,000 parts by weight of furfuryl alcohol, 466 parts by weight of paraform, and 5 parts by weight of adipic acid were added to a reaction vessel and heated to 117°C while stirring. After confirming that the paraform and adipic acid had dissolved and formed a homogeneous solution in 1 hour and 40 minutes, the pH was measured and confirmed to be 3.1. The solution used for pH measurement was a 1:1 mixture of solution and pure water by weight. The reaction was carried out at a temperature of 117°C ± 3°C for 5 hours and 10 minutes. When the viscosity reached 312 mPa·s, cooling began. Once the solution reached 100°C or below, 11.3 parts by weight of a 25% aqueous potassium hydroxide solution was added for neutralization. The pH at this point was 5.6. The pressure inside the reaction vessel was reduced to 80 torr while the temperature was raised, and the mixture was heated and distilled at 140°C and 80 torr for 1 hour. After cooling to 100°C, water was added. Urea was added by weight and reacted at 55°C. Water was added to adjust the viscosity to 653 mPa·s, resulting in thermosetting resin 1. Coupling agent 1: N-2-(aminoethyl)-3-aminopropyltrimethoxysilane 30% aqueous solution Surfactant 1: "BYK-361N" manufactured by BYK Japan

[0080] (2) Characteristics and Measurements The varnish obtained was subjected to the following measurements.

[0081] Gel Time A drop of varnish was dropped onto a hot plate set at 90°C, and the time until gelation was measured was taken as the gel time (seconds).

[0082] Maximum exothermic peak temperature The varnish was heated from 30°C to 200°C at a heating rate of 10°C / min in a nitrogen stream using a differential scanning calorimeter (DSC7020, manufactured by SII) to obtain a DSC curve. The maximum exothermic peak temperature (°C) in the DSC curve was determined.

[0083] Viscosity The viscosity of the varnish was measured using an E-type viscometer (for example, RE85U manufactured by Toki Sangyo Co., Ltd.) at 25° C., a rotation speed of 50 rpm or 20 rpm, and a cone plate type of “3°×R12”.

[0084] (3) Preparation of prepregs Each varnish obtained in (1) above was applied to a release film (product name: TV212, manufactured by Toyobo Co., Ltd.) using a squeegee to a thickness of 80 μm to 150 μm, and a 20 cm square glass fiber (#7781, manufactured by HEXCEL) was placed on the applied varnish, and a release film was then placed over it. A rubber roller was then lightly applied over the film to impregnate the glass fiber with the varnish. The resulting mixture was then B-staged using a hot air dryer under the conditions shown in Tables 1 and 2, and the release film was removed to obtain a prepreg having a thickness of 300 μm and the resin content shown in Table 1.

[0085] Subsequently, the component a was measured for the obtained prepregs. Each obtained prepreg was cut into a 10 cm square to prepare a test piece, and then the mass x (g) of each was measured. Next, the test piece was stirred with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours at a rotation speed of 150 rpm and removed. Thereafter, it was dried under reduced pressure for 24 hours, and then the mass y (g) was measured. A reciprocating shaker (e.g., NR-30 manufactured by Taitec Co., Ltd.) was used for stirring. Next, the test piece was baked in a muffle furnace at 500°C for 4 hours, and then the mass z (g) was measured. Using these measured values, the proportion (mass %) of component a was calculated according to the following formula (1). Component a = {(mass y - mass z) / (mass x - mass z)} x 100 (1)

[0086] (4) Evaluation - Evaluation 1: Tackiness When a finger was placed in contact with the surface of the obtained prepreg, a professional technician evaluated the state of the surface according to the following criteria. The results are shown in Table 1. (Criteria) Strong: Varnish was transferred to the finger Weak: Fingerprints were left behind, but the varnish was not transferred to the finger None: No marks were left on the prepreg, and the varnish was not transferred to the finger

[0087] Evaluation 2: Flame retardancy of sandwich panel Two prepregs were placed on each side of a honeycomb core layer (aramid fiber, thickness 12.7 mm, HRH-10-1 / 8-3.0 (manufactured by HEXCEL), area 1 m × 3 m), and polypropylene films (thickness 30 μm) were placed on the top and bottom surfaces. Next, SUS plates (thickness 1.5 mm, Rz 1.0 μm) were pressed against the top and bottom surfaces, and a mechanical press was used to heat and press the prepreg at 0.7 MPa, 130 ° C., and 60 minutes to harden the prepreg into a skin layer, integrating the core layer and the skin layer. Thereafter, the SUS plates and polypropylene films on the top and bottom surfaces were separated, and a sandwich panel was obtained in which the skin layers (cured prepregs) were laminated above and below the core layer. Next, when the sandwich panel was burned in accordance with the heat release test specified in ASTM E906, the maximum heat release rate measured within 5 minutes of ignition was determined as the maximum heat release rate (HRR: kW / m ２ ), total heat release rate for 2 minutes from ignition (THR: kW x min / m ２ The results are shown in Table 1.

[0088]

[0089] This application claims priority based on Japanese Patent Application No. 2024-026700, filed February 26, 2024, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A prepreg in which a fiber substrate is impregnated with a thermosetting resin composition, wherein the component a specified by the following procedure is 72% by mass or less. (Procedure) The prepreg is cut into a 10 cm square to prepare a test piece, and then the mass x (g) is measured. Next, the test piece is stirred with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours, and then removed. After that, it is dried under reduced pressure for 24 hours, and then the mass y (g) is measured. Next, the test piece is baked at 500°C for 4 hours, and then the mass z (g) is measured. The proportion (mass %) of component a is calculated using the following formula (1): Component a = {(mass y - mass z) / (mass x - mass z)} x 100 (1) 2. The prepreg according to claim 1, wherein the solid content of the thermosetting resin composition in the prepreg is 30 to 50 mass %.

3. A prepreg according to claim 1 or 2, wherein the thermosetting resin composition comprises one or more resins selected from the group consisting of phenolic resin, unsaturated polyester resin, epoxy resin, melamine resin and furan resin.

4. A prepreg according to any one of claims 1 to 3, wherein the fiber substrate is made of one or more fibers selected from the group consisting of aramid fiber, polyester fiber, polyphenylene sulfide fiber, carbon fiber, graphite fiber, glass fiber, and silicon carbide fiber.

5. A prepreg according to any one of claims 1 to 4, wherein the thickness of the prepreg is 0.05 to 10 mm.

6. A cured product of the prepreg according to any one of claims 1 to 5.

7. A panel using a cured product of the prepreg according to any one of claims 1 to 5.

8. A sandwich panel comprising: a core layer having a honeycomb structure; and a prepreg according to any one of claims 1 to 5 provided on each of both sides of said core layer.

9. A sandwich panel according to claim 8, wherein the core layer is made of aramid fibers.

10. A method for producing a prepreg, comprising: a step of impregnating a fiber substrate with a thermosetting resin composition; and a step of heating the fiber substrate impregnated with the thermosetting resin composition under any of the following conditions i to iv to bring it to a B-stage; (Condition i) leaving it to stand for 20 minutes or more and less than 50 minutes in an atmosphere of 70°C or more and less than 90°C; (Condition ii) leaving it to stand for 15 minutes or more and less than 40 minutes in an atmosphere of 90°C or more and less than 100°C; (Condition iii) leaving it to stand for 10 minutes or more and less than 30 minutes in an atmosphere of 100°C or more and less than 110°C; (Condition iv) leaving it to stand for 5 minutes or more and less than 20 minutes in an atmosphere of 110°C or more and less than 120°C.

11. A method for producing a prepreg according to claim 10, wherein the step of impregnating the fiber substrate with the thermosetting resin composition is carried out in an atmosphere of 5°C to 40°C.

12. A method for producing a prepreg according to claim 10 or 11, wherein the gel time of the thermosetting resin composition at 90°C is 200 seconds or more.

13. A method for producing a prepreg according to any one of claims 10 to 12, wherein the maximum exothermic peak in a DSC curve obtained when the thermosetting resin composition is heated from 30°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter is 80°C or higher and 150°C or lower.

14. A method for producing a prepreg according to any one of claims 10 to 13, wherein in the step of impregnating a fiber substrate with the thermosetting resin composition, the thermosetting resin composition is a varnish.

15. A method for producing a prepreg according to any one of claims 10 to 14, wherein in the step of impregnating a fiber substrate with the thermosetting resin composition, the thermosetting resin composition is in the form of a film.

16. A method for producing a prepreg according to any one of claims 10 to 15, wherein the glass transition temperature of the cured product of the thermosetting resin composition is 110 to 250°C.

17. A method for manufacturing a sandwich panel, comprising: a placement step of placing a prepreg according to any one of claims 1 to 5 on each side of a core layer having a honeycomb structure; and an integration step of integrating the core layer and the prepreg by heat and pressure treatment.

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