Prepreg and diaphragm

Abstract

The present invention provides a prepreg and diaphragm that enable the fabrication of a laminated diaphragm without the use of adhesives. [Solution] A prepreg 2 in which a first impregnation resin is laminated on one side of a carbon fiber 20 and a second impregnation resin is laminated on the other side, wherein the first impregnation resin contains unmodified polypropylene and the second impregnation resin contains acid-modified polypropylene, and at least one of the first impregnation resin and the second impregnation resin contains an antioxidant.

Description

Technical Field

[0001] The present invention relates to prepregs and diaphragms.

Background Art

[0002] Speakers used in mobile devices, electronic devices, etc. are provided with diaphragms in order to convert electrical signals into sound waves. Patent Document 1 describes a diaphragm for a loudspeaker including a main body portion containing polyamide 6 or polyamide 66 and polypropylene, a sea structure made of polypropylene on the outer periphery of the main body portion, and an edge portion formed of an island structure made of crosslinked ethylene propylene diene rubber for improving heat resistance.

[0003] Patent Document 2 describes a diaphragm for a speaker containing carbon fiber fillers inside dicyclopentadiene resin for weight reduction and mass production. In this case, carbon fiber (carbon fiber) is a filler that can be injected into an injection mold and flow together with the resin.

[0004] Patent Document 3 describes a diaphragm for a speaker composed of a thermoplastic resin film layer and an inorganic fiber layer to which a thermosetting resin is attached. Examples of the inorganic fiber include carbon fiber, the thermoplastic resin includes polyamide, and the thermosetting resin includes epoxy resin.

[0005] Patent Document 4 describes a speaker diaphragm made of a polyamide resin reinforced with a fiber reinforcing material. Examples of the fiber reinforcing material include a carbon fiber cloth.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] With the miniaturization and weight reduction of diaphragms, composite structures in which foam is laminated onto an elastic material have been proposed. However, in conventional composite structures, an adhesive is required to bond the foam to the elastic material, and bonding can be difficult depending on the elastic material, leading to high adhesive selection and manufacturing costs. Furthermore, from an environmental perspective, the adhesives used must comply with VOC regulations and be outgassing-free.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a prepreg manufacturing film, a prepreg, and a diaphragm using the prepreg that can be manufactured without using an adhesive. [Means for solving the problem]

[0009] The present invention includes the following embodiments. The first embodiment is a film for manufacturing prepregs, characterized by containing polypropylene and an antioxidant. The second embodiment is characterized in that, in the first embodiment, the polypropylene is unmodified polypropylene. A third embodiment is characterized in that, in the first embodiment, the polypropylene is acid-modified polypropylene.

[0010] The fourth embodiment is characterized by further containing an ultraviolet absorber in any one of the first to third embodiments. The fifth embodiment is characterized by further containing a light stabilizer in any one of the first to third embodiments. The sixth aspect is characterized in that, in any one of the first to third aspects, it further contains an ultraviolet absorber and a light stabilizer.

[0011] The seventh aspect is a prepreg characterized in that an impregnated resin made of the film for producing a prepreg according to any one of the first to sixth aspects is laminated on at least one side of carbon fiber. The eighth aspect is a diaphragm characterized in that the prepreg according to the seventh aspect is laminated on at least one side of a foam.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a film for producing a prepreg, a prepreg, and a diaphragm using the prepreg, which can produce a laminated diaphragm without using an adhesive.

Brief Description of the Drawings

[0013] <​​​​​​​​​​​​​​​​​​​​​​​FIG. 1 shows an example of a diaphragm using the prepreg of the embodiment. In the diaphragm 3 shown in FIG. 1, prepregs 2 are laminated on both surfaces in the thickness direction of the foam 1, respectively.

[0018] For the diaphragm 3, four physical properties are important: (1) high flexural modulus, (2) high flexural rigidity, (3) low density, and (4) high internal loss.

[0019] When the flexural modulus (Pa) is E, the density (kg / m 3 ) is ρ, and the sound velocity (m / s) propagating in the medium is V, taking the square root as the 1 / 2 power, V = (E / ρ) 1 / 2 is expressed. For example, the sound velocity in air is about 340 m / s, but about 2400 m / s for polystyrene (PS), about 6000 m / s for iron, about 6400 m / s for aluminum, and about 6000 - 6500 m / s for carbon fiber reinforced plastic (CFRP).

[0020] Therefore, the larger the elastic modulus and the lower the density, the faster the sound velocity and the better the vibration characteristics can be obtained. Also, if the diaphragm has insufficient strength and a low elastic modulus, the sound quality may deteriorate in the high - frequency range. When the internal loss (tanδ) is moderately large, the kinetic energy that deforms the diaphragm is released as heat energy, making the vibration easily attenuated and the amplitude can be suppressed.

[0021] In the prepreg of the embodiment, carbon fiber is used as the fiber base material impregnated with the thermoplastic resin. The carbon fiber may be a material obtained by carbonizing an organic fiber while keeping it fibrous by heating. The organic fiber as the raw material of the carbon fiber may be polyacrylonitrile (PAN) or a spun pitch obtained by spinning pitch. That is, the carbon fiber may be PAN - based carbon fiber with PAN as the main raw material or pitch - based carbon fiber with spun pitch as the main raw material.

[0022] The diameter of the carbon fibers is preferably smaller than the thickness of the prepreg, for example, it may be 3 to 20 μm in diameter. The average diameter of the carbon fibers may be in the range of 3 to 20 μm. As a method for calculating the average diameter, the number average of the diameters of the carbon fibers at a cross-section perpendicular to the length direction may be used. Having carbon fibers with an appropriate diameter facilitates impregnation with thermoplastic resin and allows for the production of a prepreg with high elasticity and high rigidity.

[0023] The carbon fibers are preferably continuous fibers. The longitudinal direction of the continuous fibers is preferably arranged substantially perpendicular to the thickness direction of the prepreg. The continuous fibers may be single fibers or filaments composed of multiple single fibers. The carbon fibers may be UD (unidirectional) material or cross (woven) material.

[0024] If the carbon fibers are UD (unidirectional) material, the carbon fibers may be arranged in parallel in the same direction throughout the entire thickness direction of the prepreg. Alternatively, a cross-ply structure may be used in which the carbon fibers are arranged in parallel in the same direction in each layer in the thickness direction, and the carbon fibers of different layers are laminated so that they intersect with each other.

[0025] When carbon fibers are used in a woven fabric, the carbon fibers, which intersect vertically and horizontally, are organized by reversing their orientation in a predetermined manner. The structure of the fabric is not particularly limited and includes plain weave, twill weave, satin weave, etc.

[0026] Open-fiber sheets, which are made by opening filaments composed of numerous single fibers to reduce the number of fibers in the thickness direction and increase the width, are suitable as impregnation substrates. Methods for opening fiber bundles include squeezing the fiber bundles using a round bar-shaped jig, dispersing the fiber bundles by applying a water flow or airflow, and dispersing the fiber bundles by irradiating them with ultrasound.

[0027] In the prepreg of the embodiment, the impregnation resin (matrix) impregnated into the carbon fibers is a thermoplastic resin. The thermoplastic resin used in the prepreg of the embodiment contains polypropylene and an antioxidant on at least one side of the prepreg.

[0028] The prepreg of this embodiment can be manufactured using carbon fibers and a resin film. For example, as shown in Figure 2, prepreg manufacturing films 21 and 22 are placed facing each other on both sides of a carbon fiber 20 and heat-pressed, causing the prepreg manufacturing films 21 and 22 to impregnate the carbon fiber 20, becoming the impregnating resin for the prepreg 2.

[0029] At least one of the prepreg manufacturing films 21 and 22 is a prepreg manufacturing film containing the above-mentioned polypropylene and antioxidant. Examples of polypropylene include unmodified polypropylene and acid-modified polypropylene. Unmodified polypropylene may also be homopolypropylene, random polypropylene, or block polypropylene other than acid-modified polypropylene.

[0030] The prepreg manufacturing films 21 and 22 used on each surface of the prepreg 2 are preferably formed from a resin selected from the following (1) to (6).

[0031] (1) A resin containing unmodified polypropylene and an antioxidant. (2) A resin containing acid-modified polypropylene and an antioxidant. (3) A resin containing unmodified polypropylene, acid-modified polypropylene, and an antioxidant. (4) A resin containing unmodified polypropylene and without added antioxidants. (5) A resin containing acid-modified polypropylene and without added antioxidants. (6) A resin containing unmodified polypropylene and acid-modified polypropylene, without the addition of antioxidants.

[0032] Preferably, at least one of the prepreg manufacturing films 21 and 22 is a thermoplastic resin with a weather-resistant formulation containing polypropylene and an antioxidant, for example, any resin selected from (1) to (3) above. This makes it possible to impart weather resistance to the prepreg and improve its long-term reliability.

[0033] Preferably, at least one of the prepreg manufacturing films 21 and 22 is an adhesive thermoplastic resin containing acid-modified polypropylene, for example, any resin selected from (2), (3), (5), and (6) above. This can improve the adhesion of the impregnation resin in the prepreg.

[0034] The proportion of polypropylene in the prepreg manufacturing films 21 and 22 is preferably 40% by weight or more, but may also be 70% by weight or more, 80% by weight or more, 100% by weight, etc. When using thermoplastic resins other than polypropylene in combination, thermoplastic resins compatible with polypropylene are preferred, such as polyolefins.

[0035] The proportion of unmodified polypropylene in the prepreg manufacturing films 21 and 22 is preferably 40% by weight or more, but may also be 70% by weight or more, 80% by weight or more, 100% by weight, etc. When using thermoplastic resins other than unmodified polypropylene in combination, thermoplastic resins compatible with unmodified polypropylene are preferred, such as acid-modified polypropylene.

[0036] The proportion of acid-modified polypropylene in the prepreg manufacturing films 21 and 22 is preferably 40% by weight or more, but may also be 70% by weight or more, 80% by weight or more, 100% by weight, etc. When using thermoplastic resins other than acid-modified polypropylene in combination, thermoplastic resins compatible with acid-modified polypropylene are preferred, such as unmodified polypropylene.

[0037] Unmodified polypropylene (PP) may be a homopolymer of propylene (homoPP), a propylene-ethylene copolymer (randomPP), or a block copolymer (blockPP), or a copolymer of propylene and other vinyl monomers. Other vinyl monomers may be selected from ethylene, 1-butene, isobutylene, 1-hexene, α-olefins, etc., and may be used individually or in combination of two or more. Preferably, 51% by weight or more of the monomers contained in polypropylene such as unmodified polypropylene and acid-modified polypropylene is propylene.

[0038] The melting points of polypropylene, such as unmodified polypropylene and acid-modified polypropylene, can be set as appropriate. Based on the characteristics of the flexural modulus of the prepreg, the melting point of polypropylene is preferably between 120°C and 200°C, more preferably between 135°C and 170°C, and even more preferably between 140°C and 150°C. Impregnation with polypropylene with a melting point below 120°C does not easily increase the flexural modulus of the prepreg. Impregnation of carbon fibers with polypropylene with a melting point above 200°C becomes difficult. Specific examples of melting points include the melting point of Admer® QF551 (135°C), QE060 (140°C), QF580 (145°C), and QF550 (165°C), all manufactured by Mitsui Chemicals, Inc.

[0039] The melt flow rate (MFR) of polypropylene, such as unmodified polypropylene and acid-modified polypropylene, can be set as appropriate. For example, it can be around 4 to 13 g / 10 minutes.

[0040] The method for producing unmodified polypropylene is not particularly limited, but a monomer mainly composed of propylene may be polymerized by an appropriate method.

[0041] The method for producing acid-modified polypropylene is not particularly limited, but it may be a graft copolymer obtained by grafting an acidic functional group-containing monomer onto unmodified polypropylene using a radical polymerization initiator. Acidic functional group-containing monomers may also be used as other vinyl monomers copolymerized with propylene. Examples of radical polymerization initiators include organic peroxides and aliphatic azo compounds.

[0042] Examples of monomers containing acidic functional groups include α,β-unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, maleic acid, nadic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, and tetrahydrophthalic acid, as well as unsaturated dicarboxylic acid anhydride monomers such as maleic anhydride, nadic anhydride, itaconic anhydride, and citraconic anhydride. In acid-modified polypropylene, one or more monomers containing acidic functional groups may be used. Maleic anhydride-modified polypropylene is particularly preferred.

[0043] The percentage of acidic functional group-containing monomers in acid-modified polypropylene (modification rate) is, for example, 0.01 to 10% by weight, with 0.05 to 2.5% by weight being more preferable. The modification rate can be calculated by quantifying the acidic functional groups contained in acid-modified polypropylene using methods such as infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, or titration, and then considering the molecular weight of the acidic functional group-containing monomers. In quantifying the acidic functional groups, the acidic functional groups may be detected directly, or other functional groups derived from the acidic functional groups may be detected.

[0044] Polypropylenes such as unmodified polypropylene and acid-modified polypropylene are preferably those that have physical properties suitable for impregnation and adhesion. For example, their molecular weights are not particularly limited, but examples include those of approximately 100,000 to 1,000,000.

[0045] The prepreg manufacturing film of this embodiment contains an antioxidant. This improves weather resistance to the outside air, sunlight, etc. The antioxidant is not particularly limited, but it is preferable that it has excellent compatibility with polypropylene.

[0046] Specific examples of antioxidants include one or more types of phenolic antioxidants such as hindered phenolic antioxidants, phosphorus-based antioxidants such as phosphite (phosphite ester) antioxidants and phosphonite antioxidants, and thioether antioxidants. Two or more of the phenolic antioxidants, phosphorus-based antioxidants, and thioether antioxidants may be used in combination, or one or more compounds belonging to any one of these groups may be used.

[0047] Examples of phenolic antioxidants include 2,6-di-tert-butyl-4-methylphenol, n-octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate, tetrakis(methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)methane, 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-isocyanurate, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenylmethyl)-2,4,6-trimethylbenzene.

[0048] Examples of phosphorus-based antioxidants include tris(2,4-di-tert-butylphenyl) phosphite, tetrakis(2,4-di-tert-butylphenyl)-4,4′-biphenylene phosphate, and tris(nonylphenyl) phosphite.

[0049] Examples of thioether-based antioxidants include dilauryl thiodipropionate, ditridecyl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, pentaerythritol-tetrakis(3-lauryl thiopropionate), pentaerythritol-tetrakis(3-dodecyl thiopropionate), pentaerythritol-tetrakis(3-octadecyl thiopropionate), pentaerythritol-tetrakis(3-myristyl thiopropionate), and pentaerythritol-tetrakis(3-stearyl thiopropionate).

[0050] The proportion of antioxidants in the film for prepreg manufacturing is not particularly limited, but it is preferable that the amount added is such that it does not affect the adhesive strength. Examples include approximately 0.01 to 5% by weight, approximately 0.01 to 1.0% by weight, and approximately 0.1 to 0.5% by weight.

[0051] The prepreg manufacturing film of the embodiment preferably contains an ultraviolet absorber. This improves weather resistance to the outside air, sunlight, etc. The ultraviolet absorber is not particularly limited, but it is preferably one that has excellent compatibility with polypropylene.

[0052] Specific examples of UV absorbers include one or more types of benzophenone-based UV absorbers and benzotriazole-based UV absorbers. Benzophenone-based UV absorbers and benzotriazole-based UV absorbers may be used in combination, or either one may be used.

[0053] Examples of benzophenone-based UV absorbers include 2,2′-dihydroxy-4,4′-di(hydroxymethyl)benzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 4-benzyloxy-2-hydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone, and 2,2′-dihydroxy-4,4′-dimethoxybenzophenone.

[0054] Benzotriazole-based UV absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazole, 2-(3,5-di-tert-pentyl-2-hydroxyphenyl)-2H-benzotriazole, 2-(2H-benzotriazole-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol, and 2-(2-hydro Examples include oxy-4-octyloxyphenyl)-2H-benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-2H-benzotriazole, 2,2′-methylenebis[6-(benzotriazol-2-yl)-4-tert-octylphenol], and the like.

[0055] The proportion of UV absorber in the film for prepreg manufacturing is not particularly limited, but it is preferably an amount that does not affect the adhesive strength. Examples include approximately 0.01 to 5% by weight, approximately 0.01 to 1.0% by weight, and approximately 0.1 to 0.5% by weight.

[0056] The prepreg manufacturing film of the embodiment preferably contains a light stabilizer. This improves weather resistance to outside air, sunlight, etc. The light stabilizer is not particularly limited, but it is preferably one that has good compatibility with polypropylene. Specific examples of light stabilizers include one or more types of hindered amine light stabilizers (HALS).

[0057] Examples of hindered amine light stabilizers (HALS) include bis(2,2,6,6-tetramethyl-1(octyloxy)-4-piperidinyl) decandioate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, and tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate.

[0058] The proportion of light stabilizers in the film for prepreg manufacturing is not particularly limited, but it is preferable that the amount added is such that it does not affect the adhesive strength. Examples include approximately 0.01 to 5% by weight, approximately 0.01 to 1.0% by weight, and approximately 0.1 to 0.5% by weight.

[0059] The prepreg manufacturing film of the embodiment contains at least an antioxidant for weather resistance, and may further contain an ultraviolet absorber and / or a light stabilizer. The weather-resistant prepreg manufacturing film may contain an antioxidant, an ultraviolet absorber, and a light stabilizer. This improves weather resistance to the outside air, sunlight, etc. From the viewpoint of suppressing the effect on adhesive strength, the total amount of the antioxidant, ultraviolet absorber, and light stabilizer may be 5% by weight or less of the prepreg manufacturing film.

[0060] The thermoplastic resin used for impregnation may contain desired additives other than the resin itself. Examples of additives include heat stabilizers, lubricants, mold release agents, colorants, flame retardants, plasticizers, silane coupling agents, antistatic agents, surfactants, nucleating agents, antiblocking agents, weathering agents, neutralizing agents, inorganic fillers, and rubber components. These additives may be used individually or in combination of two or more types.

[0061] The prepreg of the embodiment is impregnated with a thermoplastic resin containing polypropylene, such as unmodified polypropylene or acid-modified polypropylene, resulting in excellent adhesion and easy secondary processing. Preferably, the prepreg does not contain thermosetting resins such as epoxy resins. Since acid-modified polypropylene has adhesive properties, it is not necessary to use curing materials such as adhesives, but they may be used if they do not affect performance or subsequent processes. Since acid-modified polypropylene is a thermoplastic resin, when processing the prepreg, the acid-modified polypropylene can be softened or melted by heating, allowing it to repeatedly exhibit adhesive properties.

[0062] One method for impregnating a carbon fiber substrate with a thermoplastic resin involves laminating a film-shaped thermoplastic resin onto the substrate as a prepreg manufacturing film and then heat-pressing it. The thermoplastic resin, softened or melted by the heat-pressing, penetrates into the gaps between the carbon fibers, thereby impregnating the substrate.

[0063] When using opened fiber yarn, which consists of opened carbon fiber bundles, as the impregnation substrate, a desired number of opened fiber yarns may be formed into a sheet-like carbon fiber layer extending in the width direction, and a prepreg manufacturing film may be superimposed on at least one side thereof to produce a preform, which may then be heat-pressed. The fiber weight of the carbon fiber layer is, for example, 40 to 250 g / m². 2 That's fine.

[0064] The width of the opened yarn can range from approximately 1 to 30 mm. A desired number of opened yarns may be arranged in parallel in the width direction to match the width of the film used for prepreg manufacturing. The width of the film used for prepreg manufacturing is not particularly limited, but it can be 100 to 1000 mm or more.

[0065] During hot pressing, molds may be placed on both sides of the preform, which consists of the impregnated substrate and the prepreg manufacturing film stacked in the thickness direction, with a release film in between. This makes it less likely for the prepreg manufacturing film to adhere to the mold even if it melts.

[0066] The Vf value, which is the volume ratio of carbon fibers in the prepreg, is preferably 35% or more, and may be 50% or more. A Vf value of 75% or less is preferable. If the Vf value is 75% or more, the resin cannot sufficiently impregnate the material, making it prone to void formation, which reduces the flexural modulus.

[0067] The prepreg of the embodiment can be used to manufacture a diaphragm by laminating it on at least one side of a foam. The prepreg may also be laminated on both sides of the foam so that air bubbles in the foam do not appear on both sides in the thickness direction of the diaphragm.

[0068] Preferred materials for forming the foam include resins such as polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polystyrene (PS), polyimide (PI), polymethacrylimide (PMI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyurethane (PU), and polyamide (PA). Among these, PP, PS, PET, and PEI are preferred. The resin forming the foam may be one type or two or more types may be used in combination.

[0069] The method for foaming a resin to form a foam is not particularly limited, but examples include supersaturating the resin with gas, compounding a foaming agent into the resin, and stretching a molded body filled with a filler to create a gap around the filler. The foaming agent may be a pyrolysis-type foaming agent that releases gas by thermal decomposition, or a volatile foaming agent that is a low-boiling point liquid that gasifies when heated. Examples of volatile foaming agents include organic compounds such as hydrocarbons and halogenated hydrocarbons.

[0070] The diameter of the bubbles contained in the foam is not particularly limited, but can be appropriately set within the range of 0.1 to 100 μm, for example. The bubbles contained in the foam may be open-cell or closed-cell.

[0071] The thickness of the foam can be set as appropriate, but examples include approximately 0.05 to 4.0 mm. The thickness of the prepreg can also be set as appropriate, but examples include approximately 20 to 300 μm.

[0072] As a method for laminating the foam and prepreg, the thermoplastic resin contained in the prepreg may be softened or melted by heat sealing, heat pressing, etc., while the foam and prepreg are laminated. This makes it possible to produce a sheet-like laminate having foam and prepreg.

[0073] As described above, in the diaphragm 3 shown in Figure 2, prepreg 2 is laminated on both sides of the foam 1. Preferably, the prepreg of the embodiment is laminated on at least one side of the foam 1, and the prepreg 2 on both sides may be the prepreg of the embodiment. At least one side of the prepreg of the embodiment consists of a weather-resistant impregnated resin (polypropylene). At least an antioxidant is added to the weather-resistant impregnated resin, and at least one of an ultraviolet absorber and a light stabilizer is also added.

[0074] When the side of the prepreg 2 that is laminated onto the foam 1 is the inner surface 2a and the opposite side is the outer surface 2b, it is preferable that the weather-resistant impregnating resin is used on at least the outer surface 2b of the prepreg 2. One side of the outer surface 2b of the diaphragm 3 may be made with the weather-resistant resin, or both sides may be made with the weather-resistant resin. When the outer surface 2b of the prepreg 2 is made with the weather-resistant impregnating resin, the inner surface 2a may be made with an impregnating resin that is not weather-resistant.

[0075] For example, when molding a diaphragm 3 using a mold, it is preferable to use an impregnating resin with a weather-resistant formulation on the outer surface 2b of the prepreg 2 that comes into contact with the mold. This makes the impregnating resin on the mold side less likely to deteriorate, and the diaphragm material is less likely to stick to the mold. By suppressing the sticking of the diaphragm, the cooling efficiency of the diaphragm during molding is improved, and productivity can be improved.

[0076] Preferably, both the inner surface 2a and outer surface 2b of the prepreg 2 are made of a thermoplastic resin mainly composed of polypropylene. This results in a prepreg 2 with excellent adhesion between the impregnating resins. The impregnating resins on both sides penetrate the carbon fibers 20 and adhere well, so when the diaphragm 3 is formed by compression molding or the like, floating air bubbles and gaps in the carbon fibers 20 are suppressed, and voids can be reduced.

[0077] When forming a diaphragm by laminating foam and prepreg, a sheet-like laminate larger than the size of the diaphragm may be laminated first, and then molded to the size of the diaphragm. The diaphragm may be flat, or it may be molded into a three-dimensional shape such as a cone, dome, or horn.

[0078] When forming the diaphragm into a three-dimensional shape, the thermoplastic resin contained in the prepreg can be softened or melted to bond the laminate. Furthermore, a mounting portion for assembling the diaphragm into audio equipment such as a speaker may be integrally formed. The mounting portion may be shaped by bending or other methods in a direction different from that of the main body of the diaphragm.

[0079] The diaphragm of this embodiment can be used in audio equipment such as speakers and microphones. In a speaker, to convert an electrical signal into sound waves, a voice coil through which an electric current containing the electrical signal flows and a magnet (permanent magnet) may be combined with the diaphragm. By transmitting the vibration of the voice coil to the diaphragm, the sound represented by the electrical signal is reproduced in the air.

[0080] The diaphragm of this embodiment is suitable for audio equipment in electronic devices such as mobile phones, smartphones, personal computers, and portable terminal devices because it is easy to miniaturize. Because acid-modified polypropylene has high heat resistance, performance degradation can be suppressed even if the inside of the electronic device becomes hot. Because components of the electronic device can be arranged at high density, the electronic device can be miniaturized.

[0081] The audio equipment of this embodiment can be suitably used in transportation equipment such as automobiles, voice-operated devices, industrial equipment, household goods, and the like.

[0082] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0083] Acid-modified polypropylene exhibits excellent adhesion to various resins, metals such as aluminum, and other materials; therefore, the prepreg of this embodiment can be used for various adhesive applications. Since the matrix resin impregnated into the carbon fibers is a thermoplastic resin and does not have thermosetting properties, it offers excellent storage properties even in its prepreg state. Because it does not exhibit tack (adhesion) when cooled to room temperature, it also offers good handling characteristics.

[0084] Furthermore, since the prepreg of the embodiment is a thermoplastic prepreg in which carbon fibers are impregnated with a thermoplastic resin, the matrix resin does not heat-set and retains its thermoplastic properties, thus becoming a carbon fiber reinforced thermoplastic resin (CFRTP). Because the matrix resin retains its thermoformability even after molding, it is easy to perform thermoforming processes such as hot pressing two or more times.

[0085] Because the carbon fibers used as the impregnation base material for the prepreg are continuous fibers, it is possible to utilize the conductivity of the carbon fibers. Since carbon fibers have excellent mechanical strength, they can also be used in structural materials. [Examples]

[0086] The present invention will be specifically described below with reference to examples.

[0087] The manufacturing method for the prepreg is as follows: A thermoplastic resin film was layered with unidirectional (CFUD) carbon fiber (CF) material to create a preform. The preform was placed in a hot press machine and maintained at 170°C for 10 minutes, then heated and pressurized at a pressure of 1 MPa to produce the prepreg.

[0088] The method for manufacturing the diaphragm is as follows: A laminate, which will be the material for the diaphragm, was prepared by laminating prepreg on both sides of a foam. The diaphragm was then manufactured by pressure molding of this laminate.

[0089] The prepreg production film of Example 1 was manufactured by molding unmodified polypropylene with a weather-resistant formulation containing a mixture of phenolic, phosphite, and thioether antioxidants as the thermoplastic resin into a film.

[0090] In the prepreg of Example 1, the prepreg manufacturing film of Example 1 was used on one side of the carbon fiber, and the acid-modified polypropylene film was used on the other side. When a diaphragm was manufactured from this prepreg, the cooling time during pressure forming was 15 minutes, and a diaphragm with weather resistance and long-term reliability was obtained.

[0091] The prepreg production film of Example 2 was manufactured by forming a weather-resistant acid-modified polypropylene film containing a mixture of phenolic, phosphite, and thioether antioxidants as the thermoplastic resin.

[0092] In the prepreg of Example 2, the film for manufacturing the prepreg of Example 2 was used on one side of the carbon fiber, and the acid-modified polypropylene film was used on the other side. When manufacturing a diaphragm from this prepreg, the cooling time during pressure forming was 30 minutes, and a diaphragm with weather resistance and long-term reliability was obtained.

[0093] In Comparative Example 1, the prepreg used acid-modified polypropylene film on both sides of the carbon fiber. When manufacturing a diaphragm from this prepreg, the cooling time during pressure forming was 30 minutes, but the diaphragm did not exhibit weather resistance.

[0094] In Comparative Example 2, an unmodified polypropylene film was used on one side of the carbon fiber prepreg, and an acid-modified polypropylene film was used on the other side. When manufacturing a diaphragm from this prepreg, the cooling time during pressure forming was 15 minutes, but the diaphragm did not exhibit weather resistance. [Explanation of Symbols]

[0095] 1...Foam, 2...Prepreg, 2a...Inner surface of prepreg, 2b...Outer surface of prepreg, 3...Diaphragm, 20...Carbon fiber, 21,22...Film for manufacturing prepreg.

Claims

1. A prepreg in which a first impregnation resin is laminated on one side of a carbon fiber and a second impregnation resin is laminated on the other side, The first impregnating resin contains unmodified polypropylene, The second impregnation resin contains acid-modified polypropylene, A prepreg characterized in that at least one of the first impregnation resin and the second impregnation resin contains an antioxidant.

2. The prepreg according to claim 1, characterized in that the impregnation resin containing the antioxidant further contains at least one of an ultraviolet absorber and a light stabilizer.

3. The prepreg according to claim 1, wherein the antioxidant is a mixture comprising a phenolic antioxidant, a phosphite antioxidant, and a thioether antioxidant.

4. The prepreg according to claim 1, wherein the carbon fiber is a UD (unidirectional) material, a cross (woven) material, or an open fiber sheet.

5. A diaphragm having a prepreg according to any one of claims 1 to 4 laminated on at least one side of a foam, A diaphragm characterized in that the second impregnation resin in the prepreg is arranged on the foam side.

6. The prepreg is laminated on both sides of the foam in the thickness direction, The diaphragm according to claim 5, characterized in that the second impregnation resin in the prepreg on both sides is arranged on the foam side.

7. The diaphragm according to claim 5, characterized in that the first impregnation resin in the prepreg constitutes the outer surface of the diaphragm.

8. The diaphragm according to claim 5, characterized in that the foam and the prepreg are heat-sealed together with the second impregnation resin without the use of an adhesive.

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