JP2022146201A - Prepreg and diaphragm - Google Patents

Abstract

To provide a prepreg which enables manufacture of a laminated type diaphragm without using an adhesive, and a diaphragm using the prepreg.SOLUTION: A prepreg has a carbon fiber and an impregnation resin, where the impregnation resin is a thermoplastic resin containing acid-modified polypropylene. A diaphragm 3 can be manufactured by laminating a prepreg 2 on at least one surface of a foam 1.SELECTED DRAWING: Figure 1

Description

The present invention relates to prepregs and diaphragms.

2. Description of the Related Art A speaker used in a mobile device, an electronic device, or the like is provided with a diaphragm in order to convert an electric signal into a sound wave.
In Patent Document 1, in order to increase heat resistance, a main body containing polyamide 6 or polyamide 66 and polypropylene, and a sea structure of polypropylene and an island structure of crosslinked ethylene propylene diene rubber on the outer periphery of the main body are formed. A loudspeaker diaphragm with an edge is described.

Patent Literature 2 describes a speaker diaphragm containing a carbon fiber filler inside dicyclopentadiene resin with the intention of weight reduction and mass production. In this case, carbon fiber is used as a filler that can be injected into an injection mold and flow together with the resin.

Patent Document 3 describes a speaker diaphragm comprising a thermoplastic resin film layer and an inorganic fiber layer to which a thermosetting resin is adhered. Carbon fiber is exemplified as the inorganic fiber, polyamide is exemplified as the thermoplastic resin, and epoxy resin is exemplified as the thermosetting resin.

Patent Document 4 describes a speaker diaphragm made of a polyamide resin reinforced with a fiber reinforcing material. Carbon fiber cloth is exemplified as the fiber reinforcing material.

JP 2015-82744 A JP 2018-157285 A JP-A-62-109497 JP-A-1-229600

A composite structure in which a foam is laminated on an elastic material has been proposed as diaphragms have become smaller and lighter. However, conventional composite structures require an adhesive to adhere the foam to the elastic material, increasing manufacturing costs. In addition, from the viewpoint of environmental problems, the adhesives used are required to comply with VOC regulations and be free of outgassing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a prepreg and a diaphragm using the prepreg with which a laminated diaphragm can be produced without using an adhesive. and

In order to solve the above problems, the present invention provides a prepreg comprising carbon fibers and an impregnated resin, wherein the impregnated resin is a thermoplastic resin containing acid-modified polypropylene.

The thermoplastic resin may contain 40% by weight or more of acid-modified polypropylene.
The carbon fibers may have a diameter of 5-18 μm.
The carbon fibers may form a carbon fiber layer having a fiber weight of 40-250 g/m ² .
The carbon fibers may be continuous fibers.
The carbon fiber may be a UD (unidirectional) material or a cloth (woven) material.
A Vf value, which is a volume ratio of the carbon fibers in the prepreg, may be 35% or more.

The prepreg may be a diaphragm prepreg.

Further, the present invention provides a diaphragm comprising the prepreg laminated on at least one side of a foam.

According to the present invention, by using a prepreg obtained by impregnating carbon fibers with a thermoplastic resin containing acid-modified polypropylene, the prepreg can be laminated on a foam using the adhesiveness of the acid-modified polypropylene. . In addition, since the prepreg uses carbon fiber as the impregnated base material, the elastic modulus and rigidity are high. By combining the carbon fiber and the acid-modified polypropylene, it is possible to provide a diaphragm prepreg having a high propagation velocity of sound waves, a low density, and a large internal loss.

FIG. 2 is a cross-sectional view showing an example of a diaphragm using prepreg;

The present invention will be described below based on preferred embodiments.

A prepreg of an embodiment is a prepreg having carbon fibers and an impregnated resin, and the impregnated resin is a thermoplastic resin containing acid-modified polypropylene. Thereby, a prepreg suitable for a diaphragm prepreg is obtained.

FIG. 1 shows an example of a diaphragm using the prepreg of the embodiment. The diaphragm 3 shown in FIG. 1 has prepregs 2 laminated on both sides of the foam 1 in the thickness direction.

Four physical properties are important for the diaphragm 3: (1) high flexural modulus, (2) high flexural rigidity, (3) low density, and (4) large internal loss.

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

Therefore, the higher the modulus of elasticity and the lower the density, the faster the speed of sound and the more excellent vibration characteristics can be obtained. Also, if the diaphragm has insufficient strength and a low elastic modulus, there is a risk that the sound quality will deteriorate in the high range. When the internal loss (tan δ) is moderately large, the kinetic energy that deforms the diaphragm is released as thermal energy, and the vibration is easily damped and the amplitude can be suppressed.

The prepreg of the embodiment uses carbon fiber as a fiber base material to be impregnated with a thermoplastic resin. The carbon fiber may be a material obtained by carbonizing an organic fiber in a fibrous state by heating. Organic fibers that are raw materials for carbon fibers may be polyacrylonitrile (PAN) or spun pitch obtained by spinning pitch. That is, the carbon fiber may be a PAN-based carbon fiber using PAN as a main raw material, or may be a pitch-based carbon fiber using spun pitch as a main raw material.

The diameter of the carbon fibers is preferably smaller than the thickness of the prepreg, and may be, for example, 5-18 μm in diameter. The carbon fibers may have an average diameter in the range of 5-18 μm. As a method of calculating the average diameter, the number average of the diameters of the carbon fibers on a cross section perpendicular to the length direction may be used. When the carbon fibers have an appropriate diameter, impregnation with the thermoplastic resin is facilitated, and a prepreg with high elasticity and high rigidity can be obtained.

The carbon fibers are preferably continuous fibers. The length direction of the continuous fibers is preferably arranged substantially perpendicular to the thickness direction of the prepreg. A continuous fiber may be a single fiber or a filament composed of a plurality of single fibers. The carbon fiber may be a UD (unidirectional) material or a cloth (woven) material.

When the carbon fibers are UD (unidirectional) material, the carbon fibers may be arranged in the same direction over the entire thickness direction of the prepreg. Alternatively, a cross-ply structure may be employed in which carbon fibers are arranged in the same direction for each layer in the thickness direction, and carbon fibers in different layers are laminated so as to cross each other.

If the carbon fibers are a cloth material, crimped carbon fibers are organized by turning them upside down in a predetermined manner. The texture structure of the woven fabric is not particularly limited, and includes plain weave, twill weave, and satin weave.

A spread sheet obtained by spreading filaments composed of a large number of single fibers to reduce the number of fibers in the thickness direction and increase the width is suitable as an impregnation base material. As a method of opening the fiber bundle, a method of squeezing the fiber bundle using a round bar jig, a method of dispersing the fiber bundle by applying water flow or air flow, a method of irradiating ultrasonic waves to disperse the fiber bundle, etc. mentioned.

In the prepreg of the embodiment, the impregnating resin (matrix) with which the carbon fibers are impregnated is a thermoplastic resin. The thermoplastic resin used for the prepreg of the embodiment contains acid-modified polypropylene.

The proportion of the acid-modified polypropylene in the thermoplastic resin is preferably 40% by weight or more, and may be 70% by weight or more, 80% by weight or more, or 100% by weight. When a thermoplastic resin other than acid-modified polypropylene is used in combination, a thermoplastic resin compatible with acid-modified polypropylene is preferable, and examples thereof include polypropylene.

Polypropylene (PP) may be a propylene homopolymer (homo PP), a propylene-ethylene copolymer (random PP) or a block copolymer (block PP), and may be a copolymer of propylene and other vinyl monomers. It may be a coalescence. Other vinyl-based monomers include one selected from ethylene, 1-butene, isobutylene, 1-hexene, α-olefin and the like, or a combination of two or more. It is preferable that 51% by weight or more of the monomers contained in the acid-modified polypropylene is propylene.

The melting point of the acid-modified polypropylene is preferably from 120°C to 200°C, more preferably from 135°C to 170°C, still more preferably from 140°C to 150°C, from the viewpoint of the flexural modulus of the prepreg. Even if the prepreg is impregnated with an acid-modified polypropylene having a melting point of less than 120°C, the flexural modulus of the prepreg is unlikely to increase. Acid-modified polypropylene having a melting point of more than 200° C. is difficult to impregnate into carbon fibers. Specific examples of the melting point include the melting point of Admer (registered trademark) QF551 manufactured by Mitsui Chemicals, Inc. of 135°C, the melting point of QE060 of 140°C, the melting point of QF580 of 145°C, and the melting point of QF550 of 165°C.

The method for producing the 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. As another vinyl-based monomer to be copolymerized with propylene, an acidic functional group-containing monomer may be used. Examples of radical polymerization initiators include organic peroxides and aliphatic azo compounds.

Acid functional group-containing monomers 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, acid, tetrahydrophthalic acid, Unsaturated dicarboxylic anhydride monomers such as maleic anhydride, nadic anhydride, itaconic anhydride, and citraconic anhydride are included. In the acid-modified polypropylene, one kind of acidic functional group-containing monomer may be used, or two or more kinds thereof may be used in combination. In particular, maleic anhydride-modified polypropylene is preferred.

The proportion (modification rate) of the acid functional group-containing monomer contained in the acid-modified polypropylene is, for example, 0.01 to 10% by weight, more preferably 0.05 to 2.5% by weight. The modification rate is calculated by quantifying the acidic functional groups contained in the acid-modified polypropylene by infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, titration method, etc., and then considering the molecular weight of the monomer containing the acidic functional group. is possible. In quantifying the acidic functional group, the acidic functional group may be directly detected, or another functional group derived from the acidic functional group may be detected.

The acid-modified polypropylene preferably has physical properties suitable for impregnation and adhesion. Although the molecular weight of the acid-modified polypropylene is not particularly limited, it is, for example, about 100,000 to 1,000,000.

The thermoplastic resin that becomes the impregnating resin may contain desired additives as additives other than the resin. Additives include heat stabilizers, light stabilizers, antioxidants, lubricants, release improvers, colorants, flame retardants, plasticizers, silane coupling agents, antistatic agents, surfactants, nucleating agents, Examples include antiblocking agents, weathering agents, neutralizing agents, inorganic fillers, rubber components, and the like. These additives may be used alone or in combination of two or more.

Since the prepreg of the embodiment is impregnated with a thermoplastic resin containing acid-modified polypropylene, it has excellent adhesiveness and facilitates secondary processing. The prepreg preferably does not contain thermosetting resin such as epoxy resin. Since acid-modified polypropylene has adhesive properties, it is not necessary to use a curable material such as an adhesive, but it may be used as long as it does not affect performance and post-processes. Since the acid-modified polypropylene is a thermoplastic resin, the adhesion can be exhibited repeatedly by softening or melting the acid-modified polypropylene by heating when processing the prepreg.

As a method for impregnating the impregnating base material made of carbon fiber with the thermoplastic resin, a method of laminating the thermoplastic resin formed into a film on the impregnating base material and heat-pressing the same can be mentioned. The thermoplastic resin is impregnated by the penetration of the thermoplastic resin softened or melted by the hot press into the interstices of the carbon fibers.

In the case of using spread yarns made of spread carbon fiber bundles as the impregnated base material, a desired number of spread yarns are formed into a sheet-like carbon fiber layer that spreads in the width direction, and a thermoplastic resin film is formed on at least one side of the sheet-like carbon fiber layer. may be heat-pressed after a preform is produced by superimposing them on top of each other. The fiber weight of the carbon fiber layer may be, for example, 40-250 g/m ² .

The width of the spread yarn is about 1 to 30 mm. A desired number of spread yarns may be arranged in parallel in the width direction according to the width of the thermoplastic resin film.
Although the width of the thermoplastic resin film is not particularly limited, it can be 100 to 1000 mm or more.

At the time of hot pressing, molds may be placed on both sides of a preform in which the impregnated base material and the thermoplastic resin film, which are objects to be processed, are superimposed in the thickness direction, with a release film interposed therebetween. As a result, even if the thermoplastic resin film is melted, it is less likely to adhere to the mold.

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. The Vf value is preferably 75% or less. If the Vf value is 75% or more, voids are likely to occur due to insufficient resin impregnation, resulting in a decrease in bending elastic modulus.

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

Materials for forming the foam include polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polystyrene (PS), polyimide (PI), and polymethacrylimide (PMI). , polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyurethane (PU), and polyamide (PA). Among these, PS, PET and PEI are preferred. One type of resin may be used to form the foam, or two or more types may be used in combination.

The method of forming a foam by foaming a resin is not particularly limited, but a method of supersaturating the resin with a gas, a method of blending a foaming agent in the resin, a method of stretching a molded product in which a filler is filled in the resin, and a filler A method of forming a gap around the The foaming agent may be a thermally decomposing foaming agent that releases gas by thermal decomposition, or a volatile foaming agent that gasifies a liquid with a low boiling point when heated. Volatile blowing agents include organic compounds such as hydrocarbons and halogenated hydrocarbons.

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

The thickness of the foam can be set as appropriate, and is, for example, about 0.05 to 4.0 mm. The thickness of the prepreg can be set as appropriate, and is, for example, about 20 to 300 μm.

As a method for laminating the foam and the prepreg, the thermoplastic resin contained in the prepreg may be softened or melted by heat sealing, hot pressing, or the like while the foam and the prepreg are laminated. Thereby, a sheet-like laminate having the foam and the prepreg can be manufactured.

When laminating a foam and a prepreg to form a diaphragm, a sheet-like laminate larger than the size of the diaphragm may be laminated and then molded to the size of the diaphragm. The diaphragm may be planar, or may be formed into a three-dimensional shape such as a cone shape, a dome shape, or a horn shape.

When molding the diaphragm into a three-dimensional shape, the laminate can be bonded by softening or melting the thermoplastic resin contained in the prepreg. Also, a mounting portion for mounting the diaphragm to an acoustic device such as a speaker may be integrally formed. The mounting portion may be formed by bending or the like in a direction different from that of the main body portion of the diaphragm.

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

Since the diaphragm of the embodiment can be easily miniaturized, it is suitable for acoustic equipment for electronic devices such as mobile phones, smart phones, personal computers, and portable terminal devices. Since the acid-modified polypropylene has high heat resistance, deterioration of performance can be suppressed even if the inside of the electronic device becomes hot. Since the components of the electronic device can be arranged with high density, the electronic device can be miniaturized.

The acoustic equipment of the embodiments can be suitably used for transportation equipment such as automobiles, voice-operated equipment, industrial equipment, household goods, and the like.

Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

Since acid-modified polypropylene has excellent adhesion to various resins, metals such as aluminum, etc., the prepreg of the embodiment can be used for various adhesion purposes. Since the matrix resin with which the carbon fibers are impregnated is a thermoplastic resin and does not have thermosetting properties, it is excellent in storage stability even in the state of prepreg. Since it does not have tackiness (adhesiveness) when cooled to room temperature, it is easy to handle.

In addition, since the prepreg of the embodiment is a thermoplastic prepreg in which carbon fibers are impregnated with a thermoplastic resin, the carbon fiber reinforced plastic (CFRP) obtained by molding the prepreg is not heat-cured, and the matrix resin is not heat-cured. To retain plasticity, it becomes a carbon fiber reinforced thermoplastic (CFRTP). Since the matrix resin has thermoformability even after molding, it is easy to perform a thermoforming process such as hot pressing two or more times.

It is also possible to utilize the conductivity of the carbon fiber by using the continuous fiber as the carbon fiber that is the impregnated base material of the prepreg. Since carbon fiber has excellent mechanical strength, it can be used as a structural material.

EXAMPLES The present invention will be specifically described below with reference to Examples.

An acid-modified polypropylene (melting point: 140° C.) as a thermoplastic resin was formed into a film and laminated with a carbon fiber (CF) UD (unidirectional) material (CFUD) to prepare a preform. The preform was placed in a hot press, held at 170° C. for 10 minutes, and heated and pressurized at a pressure of 1 MPa. Thus, a prepreg of Example was obtained.

The flexural strength and flexural modulus of the prepreg of Example were measured according to JIS K7074 (bending test method for carbon fiber reinforced plastics).

The carbon fiber volume content Vf value of the prepreg of Example was measured according to JIS K7075 (testing method for fiber content and void content of carbon fiber reinforced plastics) and found to be 48.5%.

When the flexural modulus of carbon fiber (425 GPa) is Ef, the flexural modulus of prepreg of the example (152.7 GPa) is Ep, and the Vf value of the example is 0.485, the formula (Ep/Ef)× (100/Vf) (%) was used to obtain the expression rate of the elastic modulus. The prepreg of Example had an elastic modulus expression rate of 74%.

DESCRIPTION OF SYMBOLS 1... Foam, 2... Prepreg, 3... Diaphragm.

Claims (9)

A prepreg comprising carbon fibers and an impregnated resin,
A prepreg, wherein the impregnated resin is a thermoplastic resin containing acid-modified polypropylene. The prepreg according to claim 1, wherein the thermoplastic resin contains 40% by weight or more of acid-modified polypropylene. The prepreg according to claim 1 or 2, wherein the carbon fibers have a diameter of 5 to 18 µm. The prepreg according to any one of claims 1 to 3, wherein the carbon fibers form a carbon fiber layer having a fiber weight of 40 to 250 g/ ^m2 . The prepreg according to any one of claims 1 to 4, wherein the carbon fibers are continuous fibers. The prepreg according to any one of claims 1 to 5, wherein the carbon fiber is a UD (unidirectional) material or a cloth (fabric) material. The prepreg according to any one of claims 1 to 6, wherein a Vf value, which is the volume ratio of the carbon fibers in the prepreg, is 35% or more. The prepreg according to any one of claims 1 to 7, wherein the prepreg is a diaphragm prepreg. A diaphragm comprising the prepreg according to any one of claims 1 to 8 laminated on at least one side of a foam.

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