JP7533040B2 - Method for manufacturing fiber-reinforced plastic molded body - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced plastic molding.

Fiber-reinforced plastic molded bodies made from nonwoven fabrics (also called substrates for fiber-reinforced plastic molded bodies) containing reinforcing fibers such as carbon fiber and glass fiber are already being used in a variety of fields, including sports and leisure goods, aircraft materials, and electronic equipment components. Conventionally, thermosetting resins such as epoxy resins, unsaturated polyester resins, and phenolic resins have been used as the matrix resins in fiber-reinforced plastic molded bodies. However, when using thermosetting resins, the nonwoven fabrics mixed with thermosetting resins and reinforcing fibers must be stored in a refrigerator, which is problematic in that they cannot be stored for long periods of time.

For this reason, in recent years, there has been progress in the development of fiber-reinforced plastic moldings that use thermoplastic resins as the matrix resin. Such nonwoven fabrics that mix thermoplastic resins with reinforcing fibers have the advantage that they are easy to store and can be stored for long periods of time. In addition, nonwoven fabrics containing thermoplastic resins are easier to mold than nonwoven fabrics that contain thermosetting resins, and molded products can be formed by applying heat and pressure.

For example, Patent Document 1 discloses a method for producing a fiber-reinforced composite material, which includes a step (a) of placing a nonwoven fabric in a mold, the fiber amount of which is in the range of 40 to 500 g/ ^m2 per unit area of the reinforcing fibers, and a step (b) of injecting a thermoplastic resin into the mold to obtain a molded product composed of the nonwoven fabric and the thermoplastic resin. Patent Document 2 discloses a composite material layer containing a thermoplastic resin as a binding resin. Patent Document 2 discloses a method for producing a product of any shape by heating the composite material layer before and/or during a pressurizing operation.

International Publication No. 2011/118226 Japanese Unexamined Patent Publication No. 2-196625

However, in conventional manufacturing methods for molded bodies, there are cases where a molded body with sufficient density cannot be obtained, and there is room for improvement in moldability. In particular, in Patent Document 1, the operation is complicated and moldability is insufficient because resin is injected into a set nonwoven fabric. In Patent Document 2, the nonwoven fabric is not wrapped in an insulator, so there are safety issues because current flows through the press body immediately after electricity is applied, causing a short circuit. Also, insufficient electricity application causes insufficient heating, which prevents sufficient density from being obtained and affects moldability.

Therefore, in order to solve these problems with the conventional technology, the inventors have carried out research with the aim of providing a manufacturing method for molded bodies with excellent moldability.

As a result of intensive research to solve the above problems, the present inventors have found that in a method for producing a fiber-reinforced plastic molded body, which includes the steps of electrically heating a nonwoven fabric containing carbon fiber and a thermoplastic resin, and press-molding the nonwoven fabric, a fiber-reinforced plastic molded body with excellent moldability can be obtained by sandwiching the nonwoven fabric between insulators.
Specifically, the present invention has the following configuration.

[1] A nonwoven fabric containing carbon fiber and a thermoplastic resin is sandwiched between insulators,
A method for producing a fiber-reinforced plastic molded product, comprising the steps of electrically heating a nonwoven fabric and press-molding the nonwoven fabric.
[2] The method for producing a fiber-reinforced plastic molded body according to [1], wherein the electrically heating step and the press molding step are performed simultaneously.
[3] The method for producing a fiber-reinforced plastic molded body according to [1], wherein a press molding step is provided after the electric heating step.
[4] The method for producing a fiber-reinforced plastic molding according to any one of [1] to [3], wherein the density of the nonwoven fabric is 0.05 g/ ^cm3 or more.
[5] The method for producing a fiber-reinforced plastic molding according to any one of [1] to [4], wherein the number average fiber length of the carbon fibers is 3 to 50 mm.
[6] The method for producing a fiber-reinforced plastic molding according to any one of [1] to [5], wherein the content of carbon fibers in the nonwoven fabric is 20 to 80 mass% based on the total mass of the nonwoven fabric.
[7] The method for producing a fiber-reinforced plastic molded body according to any one of [1] to [6], wherein the heating temperature in the electrically heating step is equal to or higher than the softening temperature of the thermoplastic resin.
[8] The method for producing a fiber-reinforced plastic molded body according to any one of [1] to [7], wherein the insulator comprises at least one selected from the group consisting of ceramic, glass, and resin.

The manufacturing method of the present invention makes it possible to obtain fiber-reinforced plastic molded products with excellent moldability.

FIG. 1 is a schematic diagram illustrating the configuration of an apparatus in a process of electrically heating. FIG. 2 is a schematic diagram illustrating the configuration of an apparatus in a press molding process.

The present invention will be described in detail below. The following explanation of the constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

(Method for manufacturing fiber-reinforced plastic molded body)
The present invention relates to a method for producing a fiber-reinforced plastic molded body, comprising the steps of sandwiching a nonwoven fabric containing carbon fiber and a thermoplastic resin between insulators, electrically heating the nonwoven fabric, and press-molding the nonwoven fabric. The method for producing a fiber-reinforced plastic molded body of the present invention includes the steps of electrically heating the nonwoven fabric containing carbon fiber and a thermoplastic resin while sandwiching the nonwoven fabric between insulators, and press-molding the nonwoven fabric, so that a fiber-reinforced plastic molded body having a high density can be obtained. That is, in the present invention, a fiber-reinforced plastic molded body having excellent moldability can be obtained. Furthermore, since the fiber-reinforced plastic molded body obtained by the production method of the present invention has a high density, it has low rigidity (flexibility) and good surface uniformity. For this reason, the fiber-reinforced plastic molded body obtained by the production method of the present invention is suitable for use as, for example, electronic product housings, audio equipment components, and sports shoe components.

Figure 1 is a schematic diagram illustrating the configuration of the device in the process of electrically heating. As shown in Figure 1, the device used in the process of electrically heating has an insulator 3 that sandwiches a nonwoven fabric 4 containing carbon fiber and a thermoplastic resin. At least one of the insulators 3 is equipped with an electric terminal 5 to which an electric heating wire 1 is connected. The electric heating wire 1 is connected to a terminal of a DC power source or an AC power source, and when the power source is turned on, a current flows through the electric terminal 5. When a current flows through the electric terminal 5, the nonwoven fabric 4 in contact with the electric terminal 5 is heated, and the thermoplastic resin contained in the nonwoven fabric 4 is melted. The device in the process of electrically heating may further include a transformer mechanism that adjusts the heating temperature by voltage. By providing such a mechanism, it is easy to adjust the heating temperature of the nonwoven fabric 4 to a desired temperature.

Figure 2 is a schematic diagram illustrating the configuration of the apparatus in the press molding process. As shown in Figure 2, in the press molding process, a pair of press dies 6 are clamped together in the direction of the arrow to perform pressure molding. Note that in the press molding process, both of the pair of press dies 6 may be clamped in the direction of the arrow, or one of the pair of press dies 6 may be fixed and the other press die 6 may be clamped to apply press pressure.

In this embodiment, the nonwoven fabric 4 is heated by the above configuration, and the heat is also transferred to the inside of the nonwoven fabric 4, so that the entire nonwoven fabric 4 is heated. In addition, in this embodiment, the insulators 3 are disposed on both sides of the nonwoven fabric 4, so that the nonwoven fabric 4 can be heated uniformly. This increases the density of the resulting fiber-reinforced plastic molded body, and makes it possible to obtain a fiber-reinforced plastic molded body with low rigidity (flexibility).

The electrical heating process and the press molding process may be carried out simultaneously. For example, as shown in FIG. 2, the entire nonwoven fabric 4 sandwiched between the insulators 3 may be press molded using a pair of press dies 6. A press molding process may also be provided after the electrical heating process. In this case, the nonwoven fabric 4 heated in the electrical heating process is transported to the press process and press molded. At this time, the nonwoven fabric 4 sandwiched between the insulators 3 may be transported to the press process, or only the nonwoven fabric 4 may be transported to the press process.

The insulator used in the process of applying electrical current and heating is made of a solid insulating material. Solid insulating materials are broadly divided into three categories: organic fibrous materials, organic solid insulating materials, and inorganic solid insulating materials. Examples of organic fibrous materials include synthetic fibers such as paper, cotton, polyester, nylon, and rubber, as well as natural fibers. Examples of organic solid insulating materials include materials obtained by hardening epoxy resin, phenolic resin, polyester resin, melamine resin, and polyurethane resin. Examples of inorganic solid insulating materials include ceramics, glass, mica, and asbestos. Note that the insulator may be a composite of an organic solid insulating material and an inorganic solid insulating material, such as a glass epoxy resin plate, or may be coated with a resin-based insulating paint. Among these, in this embodiment, it is preferable to use an organic solid insulating material or an inorganic solid insulating material from the viewpoint of heat resistance and hardness.

The volume resistivity of the insulator used in the electrical heating step is preferably 10 ⁵ Ω·cm or more, more preferably 10 ⁸ Ω·cm or more, and even more preferably 10 ¹⁰ Ω·cm or more. In this embodiment, it is particularly preferable that the insulator used in the electrical heating step is a sheet-like material. When the insulator is a sheet-like material, the thickness of the insulator is preferably 0.1 to 100 mm. By configuring the insulator as described above, it becomes possible to heat the nonwoven fabric more uniformly in the electrical heating step, and a fiber-reinforced plastic molded product with better moldability can be obtained.

It is preferable that the insulator covers the entire surface of the nonwoven fabric. For example, if the area of one side of the nonwoven fabric is P and the area of one side of the insulator is Q, it is preferable that Q≧P. By covering the entire surface of the nonwoven fabric with the insulator, it becomes possible to heat the nonwoven fabric more uniformly while ensuring insulation in the electrical heating process, and a fiber-reinforced plastic molded product with better moldability can be obtained. In addition, a release agent may be applied to the insulator or release paper may be placed on it in order to improve releasability after press molding.

As shown in FIG. 1, it is preferable that the current-carrying terminal 5 is joined to the insulator 3. Even if the current-carrying terminal 5 is not joined, it is possible to heat the nonwoven fabric by direct current. However, there is a concern that the resin component of the nonwoven fabric will melt and become too low in viscosity because an excessive current flows through the contact point with the electrode and the nonwoven fabric will be heated. For this reason, it is preferable that the current-carrying terminal 5 is joined to the insulator 3, and the current-carrying terminal 5 is preferably a metal tape, and more preferably an aluminum tape. The volume resistivity of the current-carrying terminal 5 is preferably 10 ⁻⁴ Ω·cm or less, and the thickness is preferably 0.01 to 5 mm. The area of the current-carrying terminal 5 is preferably 0.1 to 30% of the area of the insulator 3.

The current-carrying terminal 5 may be embedded in the insulator 3, or may simply be laminated on top of the insulator 3. However, to improve ease of handling, it is preferable that the current-carrying terminal 5 and the insulator 3 are joined with an adhesive or the like.

In this embodiment, after the nonwoven fabric is sandwiched between metal dies such as SUS, the entire product may be sandwiched between an insulator. By sandwiching the nonwoven fabric between metal dies such as SUS, the surface properties of the resulting fiber-reinforced plastic molded body are improved, and moldability is further improved. In this case, in order to prevent the heating and cooling time from increasing, it is preferable that the thickness of the metal die is 10 mm or less.

The heating temperature in the electrical heating process is preferably equal to or higher than the softening temperature of the thermoplastic resin, and more preferably equal to or higher than the softening temperature of the thermoplastic resin + 20°C. For example, when polypropylene is used as the thermoplastic resin, the heating temperature in the electrical heating process is preferably equal to or higher than 170°C, more preferably equal to or higher than 185°C, and even more preferably equal to or higher than 200°C. The heating temperature in the electrical heating process is preferably equal to or lower than 250°C. The softening temperature of the thermoplastic resin can be measured using a microscope, DSC, or the like. Usually, the softening temperature of a crystalline resin is the melting point, and the softening temperature of a non-crystalline resin is the glass transition temperature.

The press mold used in the press molding process may be, for example, a mold made of steel or stainless steel. In the press molding process, the press mold is positioned so that it is parallel to each surface of the nonwoven fabric and the insulator.

The press pressure in the press molding step is preferably 10 kgf/ ^cm2 or more, more preferably 20 kgf/ ^cm2 or more, and even more preferably 30 kgf/ ^cm2 or more. The press pressure in the press molding step is preferably 500 kgf/ ^cm2 or less, more preferably 400 kgf/ ^cm2 or less, and even more preferably 300 kgf/ ^cm2 or less.

The temperature of the nonwoven fabric subjected to the press molding process is preferably equal to or higher than the softening temperature of the thermoplastic resin contained in the nonwoven fabric, and more preferably equal to or higher than the softening temperature of the thermoplastic resin. For example, when polypropylene is used as the thermoplastic resin, the temperature of the nonwoven fabric subjected to the press molding process is preferably equal to or higher than 150°C, more preferably equal to or higher than 165°C, and even more preferably equal to or higher than 180°C. The temperature of the nonwoven fabric subjected to the press molding process is preferably equal to or lower than 230°C.

After the press molding process, it is preferable to provide a step of cooling the fiber-reinforced plastic molded body formed from the nonwoven fabric. In this case, it is preferable that the fiber-reinforced plastic molded body is cooled to at least the softening temperature of the thermoplastic resin minus 50°C or less before being removed from the press mold.

<Nonwoven fabric>
The nonwoven fabric subjected to the electrical heating step contains carbon fibers and a thermoplastic resin. In particular, the nonwoven fabric is preferably one containing carbon fibers and thermoplastic resin fibers, and more preferably a wet-laid nonwoven fabric containing carbon fibers and thermoplastic resin fibers.

The density of the nonwoven fabric is preferably 0.05 g/ ^cm3 or more, more preferably 0.08 g/ ^cm3 or more, even more preferably 0.10 g/ ^cm3 or more, even more preferably 0.20 g/ ^cm3 or more, and particularly preferably 0.30 g/ ^cm3 or more. The density of the nonwoven fabric is preferably 95% or less of the theoretical density of the constituent material. By setting the density of the nonwoven fabric to be subjected to the electric heating step within the above range, the rigidity (flexibility) of the obtained fiber reinforced plastic molded body can be reduced, and a fiber reinforced plastic molded body with excellent moldability can be easily obtained.

The weight of the nonwoven fabric is preferably 10 g/ ^m2 or more, more preferably 20 g/ ^m2 or more, and even more preferably 30 g/ ^m2 or more. The weight of the nonwoven fabric is preferably 1000 g/ ^m2 or less. By setting the weight of the nonwoven fabric within the above range, the rigidity (flexibility) of the obtained fiber reinforced plastic molded body can be reduced, and a fiber reinforced plastic molded body with excellent moldability can be easily obtained. In the present embodiment, the nonwoven fabric may be laminated so that the total weight is within the above range.

The nonwoven fabric subjected to the electrical heating process may be a preliminary press sheet. Here, the preliminary press sheet is a sheet obtained by heating and pressurizing a nonwoven fabric containing carbon fiber and a thermoplastic resin at low pressure. In this specification, the preliminary press sheet refers to a sheet for molding that has been heated and pressurized once or multiple times to the extent that there is room (remaining) for molding.

<Carbon fiber>
As the carbon fiber, polyacrylonitrile (PAN)-based, petroleum/coal pitch-based, rayon-based, lignin-based, and other carbon fibers can be used. These carbon fibers may be used alone or in combination of two or more types. Among these carbon fibers, polyacrylonitrile (PAN)-based carbon fibers are preferred from the viewpoints of productivity and mechanical properties on an industrial scale.

The number average fiber length of the carbon fibers is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 5 mm or more. The number average fiber length of the carbon fibers is preferably 50 mm or less, more preferably 40 mm or less, and even more preferably 30 mm or less. By setting the number average fiber length of the carbon fibers within the above range, it is possible to prevent the carbon fibers from falling off during the production of the nonwoven fabric. Furthermore, by setting the number average fiber length of the carbon fibers within the above range, it is possible to mold a fiber-reinforced plastic molded body with excellent strength.

The average fiber diameter of the carbon fibers is preferably 3 μm or more and 20 μm or less. By setting the average fiber diameter of the carbon fibers within the above range, the strength of the fiber-reinforced plastic molding can be increased.

The single fiber strength of the carbon fiber is preferably 4,500 MPa or more, and more preferably 4,700 MPa or more. Single fiber strength refers to the tensile strength of the monofilament. The single fiber strength can be measured in accordance with JIS R7601 "Carbon Fiber Testing Method."

The carbon fiber content in the nonwoven fabric is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, based on the total mass of the nonwoven fabric. The carbon fiber content in the nonwoven fabric is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, based on the total mass of the nonwoven fabric. By setting the carbon fiber content within the above range, it becomes easier to obtain a fiber-reinforced plastic molded body with excellent moldability. Also, by setting the carbon fiber content within the above range, it becomes possible to mold a fiber-reinforced plastic molded body with excellent strength.

<Thermoplastic resin>
Examples of thermoplastic resins include polyester, polyethylene, polypropylene, polycarbonate (PC), polyamide (PA6, PA66, PA9T), ABS, polyether ether ketone (PEEK), polyamide imide (PAI), polyphenylene sulfide (PPS), polyether imide (PEI), polyether ketone ketone (PEKK), and polystyrene (PS).

In this specification, thermoplastic resins are also called matrix resins because they form a matrix or bonding points at the intersections of fiber components during heat and pressure treatment. Nonwoven fabrics using such thermoplastic resins do not require autoclave treatment and can be processed in a shorter time for heat and pressure molding than sheets using thermosetting resins, thereby increasing productivity.

In the nonwoven fabric used in this embodiment, the thermoplastic resin is preferably in a fibrous form. When the thermoplastic resin is in a fibrous form, the thermoplastic resin fibers maintain the fibrous form before heating and pressure molding, so the sheet itself is flexible and has drapeability before the fiber-reinforced plastic molded body is formed. For this reason, the nonwoven fabric can be stored and transported in a rolled up form, and has the characteristic of excellent handleability.

When the thermoplastic resin is in a fibrous form, the number average fiber length of the thermoplastic resin fibers is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 5 mm or more. The number average fiber length of the thermoplastic resin fibers is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 15 mm or less. By setting the number average fiber length of the thermoplastic resin fibers within the above range, it is possible to prevent the thermoplastic resin fibers from falling off when producing a nonwoven fabric. Furthermore, by setting the number average fiber length of the thermoplastic resin fibers within the above range, it is possible to mold a fiber-reinforced plastic molded body with excellent strength.

When the thermoplastic resin is in the form of fibers, the average fiber diameter of the thermoplastic resin fibers is preferably 3 μm or more and 50 μm or less. By setting the average fiber diameter of the thermoplastic resin fibers within the above range, the strength of the fiber-reinforced plastic molding can be increased.

The content of the thermoplastic resin in the nonwoven fabric is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, based on the total mass of the nonwoven fabric. The content of the thermoplastic resin in the nonwoven fabric is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, based on the total mass of the nonwoven fabric. By setting the content of the thermoplastic resin within the above range, it becomes easier to obtain a fiber-reinforced plastic molded body with excellent moldability. Also, by setting the content of the thermoplastic resin within the above range, it becomes possible to mold a fiber-reinforced plastic molded body with excellent strength.

<Optional ingredients>
The nonwoven fabric subjected to the electrical heating step may contain optional components in addition to the carbon fibers and the thermoplastic resin, such as a binder component.

Binder components that can be used include polyester resins such as polyethylene terephthalate and modified polyethylene terephthalate, which are generally used in the manufacture of nonwoven fabrics, and binder fibers with a core-sheath structure that combine these, acrylic resins, styrene-(meth)acrylic acid ester copolymer resins, urethane resins, PVA resins, various starches, cellulose derivatives, sodium polyacrylate, polyacrylamide, polyvinylpyrrolidone, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymer alkali salts, isobutylene-maleic anhydride copolymer alkali salts, polyvinyl acetate resins, styrene-butadiene copolymers, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, styrene-butadiene-(meth)acrylic acid ester copolymers, etc.

The content of the binder component is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the nonwoven fabric. By keeping the content of the binder component within the above range, the strength of the nonwoven fabric can be increased and the handleability can be improved.

Optional components include, for example, coupling agents, antioxidants, light stabilizers, flame retardants, and colorants such as carbon black.

In this embodiment, the nonwoven fabric may be made by laminating and press-molding an appropriate resin film depending on the purpose and application. Examples of such resin films include PP, PE, PC, PA, PEI, and PET films.

(Fiber-reinforced plastic molding)
The present invention may also relate to a fiber-reinforced plastic molded body manufactured by the above-mentioned manufacturing method. The fiber-reinforced plastic molded body manufactured by the above-mentioned manufacturing method has low rigidity (flexibility) and excellent moldability.

The density of the fiber reinforced plastic molded body is preferably 0.70 g/ ^cm3 or more, more preferably 0.80 g/ ^cm3 or more, even more preferably 0.90 g/ ^cm3 or more, and particularly preferably 1.00 g/ ^cm3 or more. The density of the fiber reinforced plastic molded body is preferably the theoretical density or less. In the present invention, by employing the above-mentioned manufacturing method, a high-density fiber reinforced plastic molded body can be manufactured.

Applications of fiber-reinforced plastic molded bodies include, for example, "casings for office automation equipment, mobile phones, smartphones, personal digital assistants, tablet PCs, digital video cameras and other portable electronic devices, air conditioners and other home appliances, as well as reinforcing materials such as ribs attached to the casings, diaphragms for speakers in home and car audio and electronic musical instruments, sports and leisure goods such as golf clubs, fishing rods and running shoes, aircraft materials, civil engineering and building material parts such as "pillars, panels and reinforcing materials," exterior panels or body parts and their reinforcing materials such as "various frames, various wheel bearings, various beams, doors, trunk lids, side panels, upper back panels, front bodies, underbodies, various pillars, various frames, various beams and various supports," and "instrument panels, systems, etc." It is suitable for use in components such as "interior parts such as car frames," "fuel system, exhaust system, or intake system parts such as gasoline tanks, various pipes, and various valves," "engine coolant joints, thermostat bases for air conditioners, headlamp supports, pedal housings," and other automobile and motorcycle parts, "aircraft parts such as winglets and spoilers," "railroad vehicle parts such as seat components for railroad cars, exterior panels, reinforcing materials attached to exterior panels, ceiling panels, and air conditioner outlets," and "reinforcing materials for molded bodies made of resin (thermosetting resin, thermoplastic resin), reinforcing materials for molded bodies made of resin and reinforcing fibers, and reinforcing materials for plant-derived sheets (kraft paper, cardboard, greaseproof paper, insulating paper, conductive paper, release paper, impregnated paper, glassine paper, cellulose nanofiber sheets, etc.)."

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

Example 1
(Production of carbon fiber paper bodies)
50 parts by mass of polypropylene fiber (fiber diameter 20 μm, fiber length 10 mm), 40 parts by mass of carbon fiber (fiber diameter 7 μm, fiber length 6 mm), and 10 parts by mass of polyvinyl alcohol fiber (fiber diameter 11 μm, fiber length 3 mm) were prepared by a wet papermaking method, and a carbon fiber article (basis weight 80 g/ ^m2 ) was produced. The density of the carbon fiber article was 0.08 g/ ^cm3 .

(Molding process)
The obtained carbon fiber sheet was heated by applying electricity. The device shown in FIG. 1 was used as the device for applying electricity. First, the carbon fiber sheet was cut into a 200 mm x 200 mm square and mounted on a 5 mm thick glass epoxy resin plate (insulating) with terminals for electricity (aluminum tape) connected to both ends. Next, a glass epoxy resin plate (insulating) was placed on top of the carbon fiber sheet to sandwich the carbon fiber sheet. In this state, the AC power source was turned on and electricity was applied to heat the carbon fiber sheet. After the surface temperature of the end of the carbon fiber sheet reached 200°C, the carbon fiber sheet was sandwiched between the glass epoxy resin plate (insulating) and electricity was applied, and the carbon fiber sheet was set in a press machine whose mold had been heated to 40°C in advance, and molded for 1 minute at a pressure of 50 kgf/ ^cm2 . One minute after the molding, the current was stopped and the sheet was cooled. When the surface temperature of the sheet reached 80°C, the press was opened. The density of the obtained fiber-reinforced plastic molded body was 0.85 g/ ^cm3 .

Example 2
A carbon fiber sheet produced in the same manner as in Example 1 was hot-pressed at a temperature of 170°C and a pressure of 10 kgf/ ^cm2 for 3 minutes to obtain a preliminary press sheet with a density of 0.50 g/ ^cm3 . A fiber-reinforced plastic molded article was obtained in the same manner as in Example 1, except that the preliminary press sheet obtained was used. The density of the obtained fiber-reinforced plastic molded article was 1.00 g/ ^cm3 .

Example 3
A carbon fiber paperboard produced in the same manner as in Example 1 was hot-pressed at a temperature of 185°C and a pressure of 10 kgf/ ^cm2 for 3 minutes, and cooled to 80°C to obtain a preliminary press sheet with a density of 0.80 g/ ^cm3 . A fiber-reinforced plastic molded article was obtained in the same manner as in Example 1, except that the preliminary press sheet obtained was used. The density of the obtained fiber-reinforced plastic molded article was 1.15 g/ ^cm3 .

(Comparative Example 1)
The preliminary press sheet obtained in the same manner as in Example 3 was heated using a far-infrared heater until the surface temperature reached 250° C. The heated preliminary press sheet was then moved to a press machine (SUS mold) that had been preheated to 40° C., and molded at a pressure of 50 kgf/cm ^2. The density of the obtained fiber-reinforced plastic molded body was 0.60 g/cm ³ .

(Evaluation: Uneven surface gloss)
The fiber-reinforced plastic moldings obtained in the Examples and Comparative Examples were visually evaluated for uneven gloss on the surfaces thereof.
⊚: The surface gloss is uniform with no unevenness.
A: Some unevenness in gloss is observed on the surface, but this does not cause any problems in practical use.
×: The surface has uneven gloss and no uniformity.

(Evaluation: Moldability)
The moldability of the fiber-reinforced plastic molded articles obtained in the Examples and Comparative Examples was evaluated comprehensively based on the following criteria.
⊚: Heating was sufficient, and the density of the obtained molded product was high and there was no unevenness in gloss.
◯: Heating was sufficient, and the density of the obtained molded product was high, but there was gloss unevenness at a level that did not pose a practical problem.
×: Heating was insufficient, the density of the obtained molded product was low, and uneven gloss was observed.

Compared to Comparative Example 1, Examples 1 to 3 produced fiber-reinforced plastic molded bodies with higher density and suppressed the occurrence of uneven gloss on the surface. Thus, the Examples produced fiber-reinforced plastic molded bodies with good moldability.

1 Electric heating wire 3 Insulator 4 Nonwoven fabric 5 Electric terminal 6 Press die

Claims (8)

A nonwoven fabric containing carbon fiber and a thermoplastic resin is sandwiched between insulators to which a current-carrying terminal is joined ,
A method for producing a fiber-reinforced plastic molded product, comprising: a step of electrically heating the nonwoven fabric; and a step of press-molding the nonwoven fabric. The method for producing a fiber-reinforced plastic molded body according to claim 1, wherein the electrical heating step and the press molding step are performed simultaneously. The method for producing a fiber-reinforced plastic molded body according to claim 1, wherein the press molding step is performed after the electrical heating step. The method for producing a fiber-reinforced plastic molded body according to any one of claims 1 to 3, wherein the nonwoven fabric has a density of 0.05 g/ ^cm3 or more. The method for producing a fiber-reinforced plastic molding according to any one of claims 1 to 4, wherein the number average fiber length of the carbon fibers is 3 to 50 mm. The method for producing a fiber-reinforced plastic molding according to any one of claims 1 to 5, wherein the content of the carbon fibers in the nonwoven fabric is 20 to 80 mass % relative to the total mass of the nonwoven fabric. The method for producing a fiber-reinforced plastic molded body according to any one of claims 1 to 6, wherein the heating temperature in the electrical heating step is equal to or higher than the softening temperature of the thermoplastic resin. The method for producing a fiber-reinforced plastic molded body according to any one of claims 1 to 7, wherein the insulator comprises at least one selected from the group consisting of ceramic, glass, and resin.

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