Prepreg, sandwich panel, and method for manufacturing sandwich panel

Abstract

The prepreg of the present invention 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. (Procedure) The prepreg is cut into 10 cm squares to prepare test pieces, and then the mass x (g) is measured. Next, the test pieces are stirred with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours, and then removed. After that, they are dried under reduced pressure for 24 hours, and the mass y (g) is measured. Next, the test pieces are 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)} × 100 (1)

Description

[Technical Field]

[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. [Background technology]

[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 for housings or various components of transportation vehicles such as aircraft and automobiles, or for building structures and components thereof. 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 249672 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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, A prepreg having a component a identified by the following procedure of 72 mass % or less. (procedure) The prepreg is cut into 10 cm squares to prepare test pieces, and the mass x (g) is measured. Next, the test pieces are stirred with 400 ml of methanol in a 500 ml resin container at 20°C for 20 hours, and then removed. After that, they are dried under reduced pressure for 24 hours, and the mass y (g) is measured. Next, the test pieces are 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)}×100 (1) [2] The prepreg according to [1], A prepreg, wherein the solid content of the thermosetting resin composition in the prepreg is 30 to 50 mass %. [3] The prepreg according to [1] or [2], The prepreg, wherein the thermosetting resin composition contains one or more resins selected from the group consisting of phenolic resins, unsaturated polyester resins, epoxy resins, melamine resins and furan resins. [4] The prepreg according to any one of [1] to [3], The prepreg comprises one or more fibers selected from the group consisting of aramid fibers, polyester fibers, polyphenylene sulfide fibers, carbon fibers, graphite fibers, glass fibers, and silicon carbide fibers. [5] The prepreg according to any one of [1] to [4], The prepreg has a thickness of 0.05 to 10 mm. [6] A cured product of the prepreg described in any one of [1] to [5]. [7] A panel using a cured product of the prepreg described in any one of [1] to [5]. [8] A core layer having a honeycomb structure; The prepreg according to any one of [1] to [5] provided on both sides of the core layer, A sandwich panel comprising: [9] The sandwich panel according to [8], The core layer is made of aramid fibers.

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

[11] A method for producing the prepreg according to

[10] , The method for producing a prepreg, wherein the step of impregnating the fiber base material with the thermosetting resin composition is carried out in an atmosphere of 5°C to 40°C.

[12] A method for producing the prepreg according to

[10] or

[11] , A method for producing a prepreg, 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

[10] to

[12] , A method for producing a prepreg, wherein the thermosetting resin composition has a maximum exothermic peak of 80°C or higher and 150°C or lower 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.

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

[10] to

[13] , The method for producing a prepreg, wherein in the step of impregnating a fiber base material with the thermosetting resin composition, the thermosetting resin composition is a varnish.

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

[10] to

[14] , The method for producing a prepreg, wherein in the step of impregnating a fiber base material 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

[10] to

[15] , The method for producing a prepreg, wherein the glass transition temperature of the cured product of the thermosetting resin composition is 110 to 250°C.

[17] A placement step of placing the prepreg according to any one of [1] to [5] on both sides of a core layer having a honeycomb structure; an integration step of integrating the core layer and the prepreg by heat and pressure treatment; A method for manufacturing a sandwich panel, comprising: [Effects of the Invention]

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

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

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

[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 identified by the following procedure.

[0013] (procedure) The prepreg is cut into 10 cm squares to prepare test pieces, and then the mass x (g) is measured. Next, the test pieces are immersed in 400 ml of methanol in a 500 ml resin container, stirred at 20°C for 20 hours, and then removed. After that, they are dried under reduced pressure for 24 hours, and the mass y (g) is measured. Next, the test pieces are 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)}×100 (1)

[0014] This allows the prepreg to maintain good tack while improving its heat release properties. Here, component a is not extracted with methanol but is vaporized or incinerated by the baking treatment, and is considered to be a component in the thermosetting resin composition in which 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 in which the thermosetting reaction has progressed to a certain extent are not re-melted by the heat during the heat compression molding process 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 mass% or less, the heat release properties of the prepreg can be improved while effectively suppressing a decrease in tackiness. In addition, according to the prepreg of this embodiment, good tackiness ensures 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, and more preferably 65% ​​by mass or less. On the other hand, in order to maintain good moldability and productivity of the prepreg, the content of component a is preferably 10% by mass or more, and 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, phenol 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) derived from furfural or furfuryl alcohol obtained by reducing furfural as a starting material. 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. Examples of suitable epoxy resins include phenol aralkyl epoxy resins such as aryl epoxy resins (biphenyl aralkyl epoxy resins) and naphthol aralkyl epoxy resins having a biphenylene skeleton; naphthol epoxy resins such as dihydroxynaphthalene epoxy resins and epoxy resins obtained by glycidyl etherification of dihydroxynaphthalene dimers; triazine nucleus-containing epoxy resins such as triglycidyl isocyanurate and monoallyl diglycidyl isocyanurate; bridged cyclic hydrocarbon compound-modified phenol epoxy resins such as dicyclopentadiene-modified phenol epoxy resins; brominated epoxy resins such as brominated bisphenol A and brominated phenol novolac; and tris(hydroxyphenyl)methane epoxy resins. These epoxy resins may be used singly or 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 application. 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] (hardening 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, alicyclic acid anhydrides such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA), and acid anhydrides including 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, and more preferably 2 to 6 parts by mass, relative to 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 of suppressing repelling of the thermosetting resin composition and suppressing the occurrence of surface defects, for example, when producing a prepreg (when the thermosetting resin composition is impregnated into a fiber substrate). Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, silicon surfactants, and UV curable surfactants. Commercially available silicone surfactants include BYK302, BYK307, BYK333, BYK341, BYK345, BYK346, BYK347, BYK348, and BYK-361N (manufactured by BYK Japan).

[0032] (Inorganic filler) The resin composition of the present embodiment may contain an inorganic filler. The inorganic filler is used to increase the mechanical strength and 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, which can suppress aggregation of the inorganic filler and provide good flowability. As the coupling agent, known coupling agents such as various silane-based compounds such as epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, and vinylsilane, titanium-based compounds, aluminum chelates, and aluminum / zirconium-based compounds can be used.

[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 approximately 90 to 120°C using a heated kneader, heated roll, extruder, or the like. The resulting kneaded product is then cooled and pulverized to obtain a powdery or granular resin composition. If necessary, the resin composition may be crushed and then compressed into tablets, or crushed 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 base material] The prepreg of this embodiment has a fiber substrate made of 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 (completely cured). The degree of cure of the resin composition can be determined from the reaction rate measured by a differential scanning calorimeter.

[0039] The prepreg is then fully cured and can be suitably used for panels and the like used as wall materials and ceiling materials for buildings and transport equipment. Complete 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, and may be, for example, 0.05 to 10 mm.

[0041] <Prepreg manufacturing method> The method for producing the prepreg of this embodiment is as follows: a step of impregnating a fiber substrate with a thermosetting resin composition (impregnation step); a step of heating the fiber substrate impregnated with the thermosetting resin composition under any one of the following conditions i to iv to bring the fiber substrate into a B-stage (B-staging step); (Condition i) Allow to stand in an atmosphere of 70°C or higher and lower than 90°C for 20 minutes or longer and less than 50 minutes. (Condition ii) leaving the mixture in an atmosphere of 90°C or higher and lower than 100°C for 15 minutes or longer and shorter than 40 minutes; (Condition iii) leaving the container to stand in an atmosphere of 100°C or higher and lower than 110°C for 10 minutes or longer and less than 30 minutes; (Condition iv) Allowing the mixture to stand in an atmosphere of 110°C or higher and lower than 120°C for 5 minutes or longer and less than 20 minutes. Includes.

[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, resulting in a prepreg that can improve heat release properties while maintaining good tackiness.

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

[0044] [Impregnation process] First, the fiber substrate is impregnated with the thermosetting resin composition. The thermosetting resin composition may be in the form of a sheet or varnish. As the impregnation method, a conventionally known method can be used, such as a method of applying or coating a varnish-like thermosetting resin composition on the surface of a fiber substrate, or a method of immersing a 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, and more preferably 40% by mass or more and 70% by mass or less, thereby obtaining a resin composition with excellent workability and impregnation properties. 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. On the other hand, 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 a DSC curve obtained by heating the thermosetting resin composition 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 a DSC curve obtained by heating the thermosetting resin composition from 30°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter is preferably 150°C or less, more preferably 300°C or less, even more preferably 200°C or less, and particularly preferably 110°C or less. By controlling the maximum exothermic peak temperature in the DSC curve, it is possible to control the reaction temperature, suppress the reaction during storage of the prepreg, increase the reaction rate during curing of the prepreg, increase the mechanical strength of the cured product, and reduce warpage. As a result, it is possible to achieve both good tack and heat release properties of the prepreg at a higher level.

[0049] [B-stage process] The fiber base material impregnated with the thermosetting resin composition is heated under any one of the following conditions i to iv to bring it to a B-stage. (Condition i) Allow to stand in an atmosphere of 70°C or higher and lower than 90°C for 20 minutes or longer and less than 50 minutes. (Condition ii) leaving the mixture in an atmosphere of 90°C or higher and lower than 100°C for 15 minutes or longer and shorter than 40 minutes; (Condition iii) leaving the container to stand in an atmosphere of 100°C or higher and lower than 110°C for 10 minutes or longer and less than 30 minutes; (Condition iv) Allow to stand in an atmosphere of 110°C or higher and lower than 120°C for 5 minutes or longer and shorter than 20 minutes.

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

[0051] The leaving is preferably carried out in air. The leaving method is not particularly limited and any known method can be used. For example, the leaving may be carried out in a hot air dryer set at a predetermined temperature, or in a reflow oven, in which the laminate 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 prepreg provided on each of 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 a sheet-like member obtained by impregnating a core layer substrate having a honeycomb structure with a binder resin, for example. The honeycomb structure allows the core layer to have high strength and light weight. The honeycomb structure is a known structure in which a plurality of substantially regular hexagonal through-holes are arranged, penetrating 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 is preferably in the form of a woven fiber cloth substrate, which allows for good 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] Furthermore, 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 forms the skin layer of the sandwich panel. The prepreg may be in a B-stage state, and when it is integrated with the core layer, it is fully cured and firmly bonded 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, as calculated from the results of DSC (differential scanning calorimetry), 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] <Sandwich panel manufacturing method> 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; (Step 2) an integration step of integrating the core layer and the prepreg by heat and pressure treatment. Each step will be described below.

[0066] (Process 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, and then the substrate is 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 obtained 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. The conditions for heat drying are not particularly limited, but are usually carried out at 100 to 220°C, preferably 120 to 190°C, for 2 to 10 minutes.

[0068] (Process 2) Next, the core layer and the prepreg are integrated by a 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 at 120 to 140°C and 0.3 to 1.0 MPa. By setting the temperature and pressure of the heating and pressurizing treatment to the above-mentioned lower limit values ​​or more, 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 the above upper limit values ​​or less, the prepregs can be properly integrated while preventing breakage.

[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 layers 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] Any known metal plate can be used, and examples thereof include SUS plates, tin plates, aluminum plates, magnesium plates, and the like. 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 product / cured product> The molded article of this embodiment uses a cured prepreg and is suitable for applications requiring flame retardancy. Specific examples include various structural components for transportation equipment such as automobiles, aircraft, railroad vehicles, and ships, buildings, office equipment, general-purpose machines, household electrical appliances, and electrical equipment. Furthermore, the molded article is suitable for use as a skin layer in the aforementioned 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. [Example]

[0077] The embodiments of 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 mass of furfuryl alcohol, 466 parts by mass of paraform, and 5 parts by mass of adipic acid were placed in a reaction vessel and heated to 117°C while stirring. After confirming that the paraform and adipic acid had dissolved in 1 hour and 40 minutes and that a homogeneous solution had been formed, the pH was measured and confirmed to be 3.1. When measuring the pH, the solution was mixed with pure water at a 1:1 ratio by weight. The reaction was carried out at a solution temperature of 117°C ± 3°C for 5 hours and 10 minutes. When the viscosity reached 312 mPa·s, cooling began. Once the temperature had dropped below 100°C, 11.3 parts by mass of a 25% aqueous potassium hydroxide solution was added to neutralize the mixture. 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 the mixture was allowed to react 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 Measurement The resulting varnish was subjected to the following measurements.

[0081] Gel Time The 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 heat peak temperature The varnish was heated from 30°C to 200°C at a heating rate of 10°C / min under 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) Prepreg fabrication 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. 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 rolled over the film to impregnate the glass fiber with the varnish. The resulting prepreg 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 with a thickness of 300 μm and the resin content shown in Table 1.

[0085] Next, the component a was measured for the obtained prepreg. Each prepreg obtained was cut into a 10 cm square to prepare a test piece, and 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 then removed. After that, it was dried under reduced pressure for 24 hours, and the mass y (g) was measured. A reciprocating shaker (e.g., NR-30 manufactured by Taitec Co., Ltd.) was used for stirring. Subsequently, the test piece was calcined 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)}×100 (1)

[0086] (4) Evaluation Rating -1: Tackiness The condition of the obtained prepreg surface when touched with a finger was evaluated by a professional technician according to the following criteria. The results are shown in Table 1. (standard) Strong: Varnish transfers to fingers Weak: Fingerprints remain but the varnish does not transfer to the finger None: No marks left on the prepreg and no varnish transfer to the fingers

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

[0088] [Table 1]

[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, the thermosetting resin composition contains a furan resin, A prepreg having a component a identified by the following procedure of 72% by mass or less. (procedure) The prepreg is cut into a 10 cm square to prepare a test piece, and then its 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 its mass y (g) is measured. Next, the test piece is baked at 500°C for 4 hours, and its 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, A prepreg, wherein the solid content of the thermosetting resin composition in the prepreg is 30 to 50 mass %.

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

4. The prepreg according to claim 1 or 2, The prepreg comprises one or more fibers selected from the group consisting of aramid fibers, polyester fibers, polyphenylene sulfide fibers, carbon fibers, graphite fibers, glass fibers, and silicon carbide fibers.

5. The prepreg according to claim 1 or 2, The prepreg has a thickness of 0.05 to 10 mm.

6. A cured product of the prepreg according to claim 1 or 2.

7. A panel using a cured product of the prepreg according to claim 1 or 2.

8. a core layer having a honeycomb structure; The prepreg according to claim 1 or 2, which is provided on both sides of the core layer; A sandwich panel comprising:

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

10. a placement step of placing the prepreg according to claim 1 or 2 on both sides of a core layer having a honeycomb structure; an integration step of integrating the core layer and the prepreg by heat and pressure treatment; A method for manufacturing a sandwich panel, comprising:

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