Prepreg manufacturing method

Abstract

To provide a prepreg capable of improving heat release properties while maintaining good tackiness. 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 prepregs and a method for producing prepregs. More specifically, the present invention relates to prepregs, panels using cured products of prepregs, and a method for producing prepregs.

Background Art

[0002] A prepreg obtained by impregnating a fiber base material with a thermosetting resin as a matrix resin is lightweight, has excellent mechanical strength, and has heat resistance. Therefore, it is useful as a housing or various members of a transport vehicle such as an aircraft or an automobile, or as a structure or its members of a building. As such a prepreg, for example, Patent Document 1 discloses a prepreg obtained by impregnating a fiber base material with a resin composition containing a predetermined urethane (meth) acrylate (A), a polymerization initiator (B), and an amine catalyst (C) from the viewpoints of workability and product stability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, the requirements for improving the performance of prepregs have been increasing. In particular, when used in aircraft or the like, various standards related to combustion behavior such as combustion reaction, smoke emission, smoke toxicity, and heat release properties released from materials during combustion must be satisfied. However, the conventional technology as disclosed in Patent Document 1 has room for improvement in such combustion behavior.

[0005] Furthermore, while methods using highly flame-retardant matrix resins are known, if the degree of matrix resin impregnation is too high, the amount of matrix resin present on the surface of the prepreg becomes extremely small, sometimes resulting in insufficient tackiness of the prepreg. [Means for solving the problem]

[0006] The inventors focused on improving the heat release properties of prepregs while maintaining good tackiness, and after diligent research, discovered that components obtained when a predetermined procedure is applied to the prepreg are involved in both heat release properties and tackiness. Therefore, further research was conducted, and a new index was devised using the amount of components obtained by this predetermined procedure as an indicator, and it was found that controlling this index is effective, thus completing the present invention.

[0007] According to the present invention, the following prepregs and related technologies are provided.

[0008] [1] A prepreg in which a thermosetting resin composition is impregnated into a fibrous substrate, A prepreg in which component a, identified by the following procedure, is 72% by mass or less. (procedure) The prepreg is cut into 10 cm squares to create a test specimen, and its mass x (g) is measured. Next, the test specimen 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. Subsequently, the test specimen is fired at 500°C for 4 hours, and its mass z (g) is measured. The proportion (mass%) of component a is calculated from the following formula (1). Component a={(mass y-mass z) / (mass x-mass z)}×100 (1) [2] [1] The prepreg described above, A prepreg in which the amount of solids in the thermosetting resin composition in the prepreg is 30 to 50% by mass. [3] A prepreg as described in [1] or [2], A prepreg comprising one or more thermosetting resin compositions selected from phenolic resins, unsaturated polyester resins, epoxy resins, melamine resins, and furan resins. [4] [1] to [3] A prepreg described in any one of the above, A prepreg in which the fibrous base material consists of one or more fibers selected from aramid fibers, polyester fibers, polyphenylene sulfide fibers, carbon fibers, graphite fibers, glass fibers, and silicon carbide fibers. [5] [1] to [4] A prepreg described in any one of the above, A prepreg having a thickness of 0.05 to 10 mm. [6] [1] to [5] A cured prepreg according to any one of the above. [7] A panel using a cured prepreg described in any one of [1] to [5]. [8] A core layer having a honeycomb structure, A prepreg according to any one of [1] to [5] provided on both sides of the core layer, A sandwich panel equipped with a sandwich panel. [9] [8] The sandwich panel described above, The core layer is a sandwich panel made of aramid fibers.

[10] A step of impregnating a fibrous substrate with a thermosetting resin composition, A step of heating the fibrous substrate impregnated with the thermosetting resin composition under any of the following conditions i to iv to stage B, (Condition i) Allow to stand for 20 minutes to less than 50 minutes in an atmosphere of 70°C to less than 90°C. (Condition ii) Leave to stand for 15 minutes to less than 40 minutes in an atmosphere of 90°C to less than 100°C. (Condition iii) Allow to stand for 10 minutes to less than 30 minutes in an atmosphere of 100°C to less than 110°C. (Condition iv) Allow to stand for 5 minutes to less than 20 minutes in an atmosphere of 110°C to less than 120°C. A method for producing prepregs, including the following: A method for producing a prepreg as described in

[11]

[10] , A method for producing a prepreg, wherein the step of impregnating a fibrous substrate with the thermosetting resin composition is carried out in an atmosphere of 5°C to 40°C. A method for producing a prepreg as described in

[12]

[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. A method for manufacturing a prepreg as described in any one of

[13]

[10] to

[12] , A method for producing a prepreg, wherein the maximum exothermic peak in the DSC curve obtained when the thermosetting resin composition is heated from 30°C to 200°C under a heating rate of 10°C / min using a differential scanning calorimeter is between 80°C and 150°C. A method for manufacturing a prepreg as described in any one of

[14]

[10] to

[13] , A method for producing a prepreg, wherein in the step of impregnating a fibrous substrate with the thermosetting resin composition, the thermosetting resin composition is a varnish. A method for manufacturing a prepreg as described in any one of

[15]

[10] to

[14] , A method for producing a prepreg, wherein in the step of impregnating a fibrous substrate with the thermosetting resin composition, the thermosetting resin composition is a film. A method for manufacturing a prepreg as described in any one of

[16]

[10] to

[15] , A 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] Arrangement step of placing one of the prepregs described in [1] to [5] on both sides of a core layer having a honeycomb structure, An integration step is performed to integrate the core layer and the prepreg by a heat and pressure treatment, A method for manufacturing sandwich panels, including the method described above. [Effects of the Invention]

[0009] The present invention provides a prepreg that can improve heat release properties while maintaining good tackiness.

Mode for Carrying Out the Invention

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

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

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

[0013] (Procedure) After cutting out a test piece by cutting the prepreg into a 10 cm square, the mass x (g) is measured. Next, the test piece is immersed in 400 ml of methanol in a resin container with a size of 500 ml, stirred at 20°C for 20 hours, and then taken out. After that, it is dried under reduced pressure for 二十四 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 component a is calculated from the following formula (1). Component a = {(mass y - mass z) / (mass x - mass z)} × 100 (1)

[0014] Thereby, while maintaining good tackiness of the prepreg, the heat release property can be improved. Here, component a is not extracted by methanol but is vaporized or ashed by firing treatment, and is a component in which the thermosetting reaction has proceeded to some extent in the thermosetting resin composition or an impurity that does not contribute to thermosetting, and is considered to be easily combustible. In addition, a component in which the thermosetting reaction has proceeded to some extent is considered to be a component that does not melt again by the heat during hot compression molding in the processing of the prepreg, and thus reduces the adhesion. Therefore, it is presumed that by setting the content of component a to 72% by mass or less, the heat release properties of the prepreg can be improved while effectively suppressing the decrease in tackiness. In addition, with the prepreg of this embodiment, good tackiness results in high adhesion when the prepreg is laminated, making it easier to obtain flame retardancy in the laminate.

[0015] Component a is preferably 70% by mass or less, and more preferably 65% ​​by mass or less, in order to achieve a higher level of both good tack and heat release properties of the prepreg. On the other hand, component a is preferably 10% by mass or more, and more preferably 20% by mass or more, from the viewpoint of maintaining good moldability and productivity of the prepreg.

[0016] A prepreg that meets the above conditions can be produced 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 impregnating the fibrous substrate with the thermosetting resin composition. Further details will be explained in the prepreg manufacturing method section below.

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

[0018] The following describes the materials that make up the prepreg.

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

[0020] (thermosetting resin) The thermosetting resin composition contains a thermosetting resin. The thermosetting resin can be one or more selected from epoxy resins, phenolic resins, unsaturated polyester resins, melamine resins, and furan resins. Among these, furan resin is preferred.

[0021] The above-mentioned furan resin is a polymer or precursor (oligomer) derived from furfural or furfuryl alcohol obtained by reducing furfural as a starting material. Examples of furan resins include furfuryl alcohol type, furfuryl alcohol-furfural cocondensation type, furfuryl alcohol-aldehyde cocondensation type, furfural-ketone cocondensation type, furfural-phenol cocondensation type, furfuryl alcohol-urea cocondensation type, and furfuryl alcohol-phenol cocondensation type. Examples of modified furan resins include epoxy-modified, phenol-modified, aldehyde-modified, urea-modified, and melamine-modified types.

[0022] Specific examples of epoxy resins include, for example, biphenyl-type epoxy resins; bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol AD-type epoxy resin, and tetramethylbisphenol F-type epoxy resin; stilbene-type epoxy resins; novolac-type epoxy resins such as phenol novolac-type epoxy resin and cresol novolac-type epoxy resin; polyfunctional epoxy resins such as triphenyl-type epoxy resins, including 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 include phenol aralkyl epoxy resins such as 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 a dimer of dihydroxynaphthalene; triazine core-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-type epoxy resins. One of these epoxy resins may be used alone, or two or more different types may be used in combination.

[0023] Examples of the phenolic resins mentioned above include novolac-type phenolic resins, resol-type phenolic resins, and arylalkylene-type phenolic resins. One of these phenolic resins may be used alone, or two or more with different weight-average molecular weights may be used in combination, or one or more types may be used in combination with their prepolymers. In particular, it is preferable to use different types of phenolic resins in combination, and for example, it is more preferable to use novolac-type phenolic resin and resol-type phenolic resin in combination.

[0024] The thermosetting resin content is preferably 60 to 99% by mass, more preferably 70 to 98% by mass, and even more preferably 80 to 95% by mass, relative to the solid content of 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 enhancers. The compound may contain only one of these, or two or more.

[0026] (Hardening agent) The curing agent in this embodiment is selected according to the type of thermosetting resin and is not particularly limited as long as it reacts with it. Specific examples of curing agents include polyaddition curing agents, catalytic curing agents, and condensation curing agents.

[0027] Specifically, the curing agents 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] Phenolic curing agents specifically include one or more selected from the following: novolac-type phenolic resins such as phenol novolac resins, cresol novolac resins, naphthol novolac resins, aminotriazine novolac resins, and trisphenylmethane-type phenol novolac resins; modified phenolic resins such as terpene-modified phenolic resins and dicyclopentadiene-modified phenolic resins; 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. Furthermore, from the viewpoint of curability, the hydroxyl group equivalent of the phenolic resin 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, per 100 parts by mass of the thermosetting resin.

[0030] Furthermore, the amounts of thermosetting resin and hardener are set appropriately according to the thermosetting resin and hardener.

[0031] (Surfactants) The surfactant has the advantage of suppressing the repulsion of the thermosetting resin composition and reducing the occurrence of surface defects, for example, during the manufacturing of prepregs (when impregnating a fiber substrate with a thermosetting resin composition). Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, silicone surfactants, and UV-curing surfactants. Examples of commercially available silicone-based surfactants include BYK302, BYK307, BYK333, BYK341, BYK345, BYK346, BYK347, BYK348, and BYK-361N (manufactured by Bic Chemie Japan).

[0032] (Inorganic filler) The resin composition of this embodiment may also contain an inorganic filler. Inorganic fillers are used to enhance the mechanical strength of prepregs, or to impart properties such as heat resistance and flame retardancy, depending on the application of the prepreg. Examples of inorganic fillers include silicates such as talc, calcined clay, uncalcined clay, mica, and glass; oxides such as titanium dioxide, 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 individually or in combination of two or more.

[0033] (Coupling agent) The resin composition of this embodiment may also contain a coupling agent if it contains an inorganic filler. This suppresses the aggregation of the inorganic filler and allows for good fluidity. As coupling agents, known coupling agents such as various silane compounds including epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, and vinylsilane, as well as titanium compounds, aluminum chelates, and aluminum / zirconium 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, but for example, if the thermosetting component and other arbitrary components are liquid, they are mixed by stirring with a stirring spring using a three-way motor or the like. If the thermosetting component and other arbitrary components are solid, they are mixed using a mixer or the like, and then kneaded by melting and heating at about 90 to 120°C using a heated kneader, heated roll, or extruder or the like. Next, the resulting kneaded material is cooled and pulverized to obtain a powdered or granular resin composition. The resin composition may be compressed into tablets after pulverization as needed, or it may be made into a sheet by, for example, vacuum lamination or compression molding after pulverization.

[0035] Alternatively, for example, a varnish-like resin composition may be prepared by dissolving, mixing, and stirring thermosetting components and other arbitrary components in a solvent using various mixers such as ultrasonic dispersion, high-pressure impact dispersion, high-speed rotation dispersion, bead mill, high-speed shear dispersion, or rotation-orbit dispersion.

[0036] [Fiber-based material] The prepreg of this embodiment may be one or more fiber base materials selected from aramid fibers, polyester fibers, polyphenylene sulfide fibers, carbon fibers, graphite fibers, glass fibers, and silicon carbide fibers. Glass fibers are preferred in terms of obtaining good heat resistance and flame retardancy.

[0037] Examples of the above-mentioned glass fibers 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 in this embodiment is in the B-stage state. Stage B represents a state where 5-90% of the resin composition has hardened (partially hardened), while Stage C represents a state where more than 90% of the resin composition has hardened (fully hardened). The degree of hardening of the resin composition can be determined by the reaction rate measured by a differential scanning calorimeter.

[0039] The prepreg is then fully cured and can be suitably used as panels for walls, ceilings, and other materials in buildings and transportation equipment. Complete curing can be achieved, for example, by heating at 100-150°C for 60-240 minutes.

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

[0041] <Prepreg manufacturing method> The method for manufacturing the prepreg according to this embodiment is: A process of impregnating a fibrous substrate with a thermosetting resin composition (impregnation process), The process involves heating the fibrous substrate impregnated with the thermosetting resin composition under any one of the following conditions i to iv to stage B (B-stage stage), (Condition i) Allow to stand for 20 minutes to less than 50 minutes in an atmosphere of 70°C to less than 90°C. (Condition ii) Leave to stand for 15 minutes to less than 40 minutes in an atmosphere of 90°C to less than 100°C. (Condition iii) Allow to stand for 10 minutes to less than 30 minutes in an atmosphere of 100°C to less than 110°C. (Condition iv) Allow to stand for 5 minutes to less than 20 minutes in an atmosphere of 110°C to less than 120°C. Includes.

[0042] In other words, as shown in conditions i to iv, by precisely controlling the temperature and time in the B-stage process, the thermosetting resin composition can be appropriately impregnated into the fiber substrate and matured, resulting in a prepreg that maintains good tackiness while improving heat release properties.

[0043] The following explains the details of each step.

[0044] [Impregnation process] First, the thermosetting resin composition is impregnated into the fibrous substrate. A sheet-like or varnish-like thermosetting resin composition can be used. Conventional methods such as applying a varnish-like thermosetting resin composition to the surface of a fiber substrate, or immersing the fiber substrate in a varnish-like thermosetting resin composition, can be used for impregnation. Furthermore, if the thermosetting resin composition is in the form of a sheet or film, it may be laminated onto the surface of a fibrous substrate and then impregnated into the fibrous substrate by applying pressure and heating as needed.

[0045] Furthermore, the impregnation process is preferably carried out in an atmosphere of 5°C to 40°C. Also, when using a varnish-like thermosetting resin composition, the varnish-like thermosetting resin composition may be used at ambient temperature without heating or cooling.

[0046] In a varnish-like thermosetting resin composition, the solid content 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. This results in a resin composition with excellent workability and impregnation properties. Furthermore, if the thermosetting resin composition is in the form of a varnish, it may be used as is without dilution if the thermosetting resin is in liquid form, or it may be diluted with a known solvent if the thermosetting resin is in solid form.

[0047] (Geltime) The gel time of the thermosetting resin composition at 90°C is preferably 200 seconds or more, and 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] When a thermosetting resin composition is heated from 30°C to 200°C using a differential scanning calorimeter under a heating rate of 10°C / min, the maximum exothermic peak in the DSC curve obtained is preferably 80°C or higher, more preferably 85°C or higher, and even more preferably 90°C or higher. When a thermosetting resin composition is heated from 30°C to 200°C using a differential scanning calorimeter under a heating rate of 10°C / min, the maximum exothermic peak in the DSC curve obtained is preferably 150°C or lower, more preferably 300°C or lower, even more preferably 200°C or lower, and most preferably 110°C or lower. By controlling the maximum exothermic peak temperature in the DSC curve, the reaction temperature can be controlled, suppressing the progression of the reaction during prepreg storage, while increasing the reaction rate during prepreg curing. This is expected to enhance the mechanical strength of the cured product and reduce warping. As a result, a higher level of both good tack and heat release properties of the prepreg can be achieved.

[0049] [B-stage process] The fibrous substrate impregnated with the thermosetting resin composition is heated by one of the following conditions i to iv to bring it to stage B. (Condition i) Allow to stand for 20 minutes to less than 50 minutes in an atmosphere of 70°C to less than 90°C. (Condition ii) Leave to stand for 15 minutes to less than 40 minutes in an atmosphere of 90°C to less than 100°C. (Condition iii) Allow to stand for 10 minutes to less than 30 minutes in an atmosphere of 100°C to less than 110°C. (Condition iv) Allow to stand for 5 minutes to less than 20 minutes in an atmosphere of 110°C to less than 120°C.

[0050] The standing time for 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 for condition ii is preferably 20 minutes or more and 35 minutes or less. The standing time for 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 for 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] In all cases, the settling process is preferably carried out under air. The settling method is not particularly limited, and known methods can be used. For example, it may be carried out in a hot air dryer set to a predetermined temperature, or in a reflow oven, where the material is placed on a moving bed and continuously passed through the oven. As described above, the prepreg of this embodiment can be manufactured.

[0052] <Sandwich Panel> The sandwich panel of this embodiment comprises a core layer having a honeycomb structure and the above-mentioned prepreg provided on both sides of the core layer. This provides a sandwich panel with improved heat release properties.

[0053] The following describes each component that makes up the sandwich panel.

[0054] [Core Layer] The core layer can be, for example, a sheet-like member made by impregnating a core layer substrate with 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, and refers to a structure in which multiple roughly hexagonal through-holes are arranged, penetrating from the top surface to the bottom surface.

[0055] Examples of substrates having a honeycomb structure in the core layer include those formed into a honeycomb shape by known methods using aramid fibers, paper, balsa wood, plastics, aluminum, titanium, glass, and their alloys. From the viewpoint of heat resistance, it is preferable that the substrate having a honeycomb structure in the core layer contains aramid fibers.

[0056] The core layer is preferably made of woven fiber cloth as the base material. This improves the processability into a honeycomb structure and allows for a lighter sandwich panel. When the core layer includes a woven fiber cloth, the areas where the fibers intersect 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 later effectively suppresses the manifestation of voids on the surface, which can cause 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 described above. 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 for example, it may be 1 mm to 50 mm, 3 mm to 40 mm, or 5 mm to 30 mm.

[0059] The size of each core cell in the core layer is not particularly limited, but for example, it can be between 1 mm and 10 mm on each side.

[0060] The surface area (top and bottom) of the core layer is not limited; for example, it may have the surface area of ​​one sandwich panel, or it may have the surface area of ​​multiple sandwich panels combined. This makes it possible to cut out multiple panels from a single sandwich panel, thereby improving productivity. For example, the surface area (top and bottom) of the core layer can be large, for example, 1 m². 2 That's fine too.

[0061] Furthermore, the core layer may be subjected to various surface treatments on its interior and / or exterior 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 fully hardens when it integrates with the core layer, resulting in a strong bond with the core layer.

[0063] The B-stage state refers to a state in which the reaction rate calculated from the measurement results of a DSC (Differential Scanning Calorimeter) for the binder resin (thermosetting resin composition) impregnated into the prepreg substrate is preferably greater than 0% and 60% or less, more preferably between 0.5% and 55%, and even more preferably between 1% and 50%.

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

[0065] <Manufacturing method for sandwich panels> Next, the manufacturing method for the sandwich panel of this embodiment will be described. The manufacturing method of the sandwich panel according to this embodiment includes the following steps. (Step 1) A step of placing prepregs on both sides of a sheet-like core layer having a honeycomb structure, (Step 2) Includes an integration step of integrating the core layer and the prepreg by heating and pressurizing. The following describes each step.

[0066] (Process 1) First, prepare the substrate for the core layer. The substrate for the core layer has a honeycomb structure and is preferably made from aramid fibers. A substrate with a honeycomb structure is prepared, and a binder resin is impregnated into the substrate. Then, the substrate is dried to obtain a core layer.

[0067] In the core layer, methods for impregnating with binder resin include, for example, dissolving the binder resin in a solvent and spraying the resulting binder solution onto the binder substrate using a spraying device such as a spray nozzle; immersing the binder substrate in the binder solution; coating the binder solution onto the binder substrate using various coaters such as a knife coater or comma coater; and transferring the binder solution onto the binder substrate using a transfer roll. Among these, the method of immersing the binder substrate in the binder solution is preferred. Furthermore, while there are no particular limitations on the conditions for heating and drying, it is 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 performed at 110-150°C and 0.1-3.0 MPa, and more preferably at 120-140°C and 0.3-1.0 MPa. By setting the temperature and pressure of the heating and pressurizing process to above the above lower limits, the prepreg and the core layer can be firmly integrated. On the other hand, by keeping the temperature and pressure of the heating and pressurizing process below the above upper limits, the prepreg can be properly integrated while suppressing damage.

[0070] Alternatively, a release film may be placed between a laminate, which is formed by laminating prepregs prepared on both sides of the core layer, and a metal plate used for the heat and pressure treatment, before performing the heat and pressure treatment. That is, the laminate is subjected to heat and pressure treatment with the metal plate together with the release film, thereby hardening the prepreg and integrating it with the core layer.

[0071] In the laminate, the prepreg may be a single layer or multiple layers on one side of the core layer. The number of layers is not particularly limited and may be 1 to 5 layers on one side of the core layer.

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

[0073] Any known metal sheet can be used, including, for example, SUS sheets, tin sheets, aluminum sheets, and magnesium sheets. Furthermore, the film 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 it within these ranges, a balance between rigidity and thermal conductivity can be achieved.

[0074] Subsequently, the release film and metal plate are separated to obtain the sandwich panel. Furthermore, because the release film has good release properties, it prevents the sandwich panel from sticking to the metal plate, allowing the sandwich panel to be easily removed.

[0075] <Molded product / cured product> The molded product of this embodiment uses a cured prepreg and is suitable for applications requiring flame retardancy. Specifically, examples include various structural components for transportation equipment such as automobiles, aircraft, railway vehicles, and ships, as well as buildings, office equipment, general-purpose machinery, household electrical appliances, and electrical equipment. Furthermore, structurally, it is suitably used as a skin layer for the aforementioned switch panel.

[0076] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

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

[0078] (1) Preparation of thermosetting resin composition (varnish) A thermosetting resin composition (varnish) was prepared by mixing the following raw materials in the proportions shown in Tables 1 and 2.

[0079] [Raw materials] • Thermosetting resin 1: At room temperature and pressure, 1000 parts by mass of furfuryl alcohol, 466 parts by mass of paraform, and 5 parts by mass of adipic acid were added to a reaction vessel and heated to 117°C while stirring. Paraform was added after 1 hour and 40 minutes. aldehyde After confirming that the adipic acid had dissolved and a homogeneous solution had been obtained, the pH was measured and confirmed to be 3.1. For the pH measurement, a mixture of the solution and pure water in a 1:1 weight ratio was used. 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, and when the temperature dropped below 100°C, potassium hydroxide was added. 25% 11.3 parts by mass of aqueous solution were added to neutralize the solution. The pH at this point was 5.6. The temperature in the reaction vessel was raised under reduced pressure to 80 torr, 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 add The mixture was reacted at 55°C. Water was added to adjust the viscosity to 653 mPa·s, which was then designated as thermosetting resin 1. • Coupling agent 1: 30% aqueous solution of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane • Surfactant 1: "BYK-361N" manufactured by Big Chemie Japan Co., Ltd.

[0080] (2) Characteristics and Measurement The following measurements were performed on the obtained varnish.

[0081] Geltime Varnish was dropped onto a heating plate set to 90°C, and the time it took for it to gel was measured and defined as the gel time (seconds).

[0082] • Maximum peak heat temperature For the varnish, a differential scanning calorimeter (SII, DSC7020) was used to heat it from 30°C to 200°C under a nitrogen atmosphere and a heating rate of 10°C / min, and a DSC curve was obtained. 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, the 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. A 20 cm square glass fiber (#7781, manufactured by HEXCEL Co., Ltd.) was placed on top of the applied varnish, and another release film was placed over it. The glass fiber was then impregnated with varnish by lightly rolling a rubber roller over the film. Subsequently, the glass fiber was subjected to B-stage drying in a hot air drying apparatus 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 obtained prepreg was subjected to measurement of component a. Each obtained prepreg was cut into 10 cm squares to create test specimens, and the mass x (g) of each was measured. Next, the test specimens were 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 drying under reduced pressure for 24 hours, the mass y (g) was measured. A reciprocating shaker (e.g., NR-30 manufactured by Taitec) was used for stirring. Next, the test specimen was fired in a muffle furnace at 500°C for 4 hours, and its mass z (g) was measured. Using these measurements, the proportion (mass%) of component a was calculated using 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 a finger was touched to it was evaluated by a specialist according to the following criteria. The results are shown in Table 1. (standard) Strong: Varnish transfers to the finger. Weak: Fingerprints remain, but the varnish does not transfer to the finger. None: No traces are left on the prepreg, and the varnish does not transfer to the fingers.

[0087] • Rating - 2: Flame retardancy of sandwich panels Two prepreg sheets were placed on each surface of a honeycomb core layer (aramid fiber, 12.7 mm thick, HRH-10-1 / 8-3.0 (manufactured by HEXCEL), area 1 m x 3 m), and polypropylene film (30 μm thick) was 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 the prepreg was heated and pressurized using a mechanical press at 0.7 MPa, 130°C, and 60 minutes to cure it into a skin layer, integrating the core layer and the skin layer. After that, the SUS plates and polypropylene film on the top and bottom surfaces were separated to obtain a sandwich panel in which the skin layer (cured prepreg) was laminated on the top and bottom of the core layer. Next, in accordance with the heat release test specified in ASTM E906, the maximum heat release rate (HRR: kW / m²) measured within 5 minutes of ignition when the sandwich panel was burned was defined as the maximum heat release rate (HRR: kW / m²). 2 ), total heat output (THR: kW × min / m²) for 2 minutes from ignition 2 The following was measured. The results are shown in Table 1.

[0088] [Table 1]

[0089] This application claims priority based on Japanese Patent Application No. 2024-026700, filed on 26 February 2024, and incorporates all of its disclosures herein.

Claims

1. A step of impregnating a fibrous substrate with a thermosetting resin composition, The process involves heating the fibrous substrate impregnated with the thermosetting resin composition under non-pressurized conditions i to iv to bring it to the B stage, (Condition i) Allow to stand for 20 minutes to 40 minutes in an atmosphere of 70°C to less than 90°C. (Condition ii) Allow to stand for 15 to 35 minutes in an atmosphere of 90°C or higher but less than 100°C. (Condition iii) Allow to stand for 10 to 20 minutes in an atmosphere of 100°C or higher but less than 110°C. (Condition iv) Allow to stand for 5 to 15 minutes in an atmosphere of 110°C to less than 120°C. Includes, The thermosetting resin composition is It contains only furan resin as the thermosetting resin, The gel time at 90°C is more than 360 seconds and less than or equal to 1000 seconds. A method for manufacturing a prepreg, wherein the maximum exothermic peak in the DSC curve obtained when heating from 30°C to 200°C under a heating rate of 10°C / min using a differential scanning calorimeter is between 90°C and 110°C.

2. A method for manufacturing a prepreg according to claim 1, A method for producing a prepreg, 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.

3. A method for manufacturing a prepreg according to claim 1 or 2, A method for producing a prepreg, wherein in the step of impregnating a fibrous substrate with the thermosetting resin composition, the thermosetting resin composition is a varnish.

4. A method for manufacturing a prepreg according to claim 1 or 2, A method for producing a prepreg, wherein in the step of impregnating a fibrous substrate with the thermosetting resin composition, the thermosetting resin composition is a film.

5. A method for manufacturing a prepreg according to claim 1 or 2, A method for producing a prepreg, wherein the glass transition temperature of the cured product of the thermosetting resin composition is 110 to 250°C.

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