JP2023159916A - Manufacturing method of high elastic modulus fiber-reinforced plastic - Google Patents

Abstract

To solve the problems that as a matrix resin of a fiber-reinforced plastic having high strength and high elastic modulus, an epoxide resin is widely used, however, with respect to molding using a metal mold like molding at a high cycle, it is necessary to correspond by a batch method of using a resin mold and hardening in an autoclave due to poor demolding properties, or a method of increasing a thickness and a weight so as to secure strength using the other matrix resin, therefore, a fiber-reinforced plastic excellent in moldability and having high strength and high elastic modulus cannot be achieved.SOLUTION: A fiber-reinforced plastic containing a reinforced fiber coated with graphene oxide, and a matrix resin is such that: a volume ratio of the reinforced fiber to the matrix resin in the fiber-reinforced plastic is 15:85-50:50; and the matrix resin contains 30-100 mass% of a radical hardening type resin.SELECTED DRAWING: None

Description

The present invention relates to fiber-reinforced plastics using reinforcing fibers coated with graphene oxide and a radical curable resin as part of the matrix resin.

Fiber-reinforced plastics are widely used as structural materials due to their high strength. Among them, carbon fiber reinforced plastics exhibit high strength and high modulus. Epoxy resins are widely used as matrix resins for molded products that require high strength and high elastic modulus. However, since epoxy resin has a small curing shrinkage, when continuous molding such as press molding or pultrusion molding using a mold is performed, it is difficult to release the resin or the mold gets clogged, making molding difficult. Therefore, molding is generally performed using a molding method using an autoclave, but one molding cycle takes a very long time and is inefficient. On the other hand, radical curable resins such as vinyl ester resins have excellent moldability, but are inferior to epoxy resins in terms of strength.
Additionally, there are precedent examples of coating carbon fibers with graphene oxide to further improve the strength of carbon fiber-reinforced plastics using epoxy resins, but there has been no discussion in terms of moldability (Patent Document 1) .

JP2020-169424

Until now, fiber-reinforced plastics with excellent moldability, high strength, and high elastic modulus have not been achieved by combining reinforcing fibers with radical-curing resins, which have excellent moldability but have problems in terms of strength.

In order to achieve the above object, the present inventors conducted various studies and came up with the present invention.
That is, a fiber-reinforced plastic containing reinforcing fibers coated with graphene oxide and a matrix resin, wherein the volume ratio of the reinforcing fibers to the matrix resin in the fiber-reinforced plastic is 15:85 to 50:50, and The matrix resin is a fiber-reinforced plastic characterized by containing 30 to 100% by mass of a radical curable resin.

By using the graphene oxide-coated reinforcing fiber of the present invention and the fiber-reinforced plastic containing a matrix resin, it becomes easy to use a fiber-reinforced plastic that has excellent moldability, high strength, and high elastic modulus.

The present invention will be explained in detail below.
Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[Graphene oxide and graphene oxide dispersion]
The graphene oxide used in the present invention is obtained by oxidizing graphite and exfoliating it. Although the method for producing graphene oxide is not particularly limited, for example, graphene oxide is preferably obtained by oxidizing graphite in sulfuric acid using an oxidizing agent and exfoliating it after purification.

The graphene oxide of the present invention preferably has 10 layers or less. The number of layers can be analyzed using an electron microscope or the like. From the viewpoint of more effective adhesion, the number of layers of graphene oxide is preferably 1 to 10 layers, more preferably 1 to 7 layers, even more preferably 1 to 5 layers, and most preferably 1 to 3 layers. In addition, from the viewpoint of adhesion to fibers and dispersibility, the carbon/oxygen ratio (O/C) in graphene oxide is preferably in the range of 0.1 to 2, more preferably 0.2 to 1.5, and .3 to 1.2 is most preferred. By appropriately adjusting these O/C, it is possible to adjust the miscibility with the resin and additives to be combined, as will be described later. O/C can be increased by increasing the amount of oxidizing agent during graphene oxide synthesis or by making the oxidation conditions stronger, and can be decreased by reducing graphene oxide.

The graphene oxide used in the present invention is preferably in the form of a dispersion. By forming a dispersion liquid, it is possible to suppress (agglomeration) of graphene oxide and to cause graphene oxide to effectively act on the surface of reinforcing fibers. Preferred dispersion media include, but are not particularly limited to, water, alcohols such as methanol, ethanol, and 2-propanol, ketone solvents such as acetone and methyl ethyl ketone, ether solvents such as diethyl ether and cyclopentyl methyl ether, and halogen solvents such as chloroform. can be mentioned. Among these, water and alcohol solvents are preferred, and water is most preferred. The concentration of the dispersion liquid is preferably 0.0001 to 10%, more preferably 0.0001 to 5% from the viewpoint of productivity and performance, even more preferably 0.001 to 3%, and most preferably 0.01 to 2%. preferable. Within the above range, graphene oxide can be satisfactorily attached to the reinforcing fibers. Moreover, in order to improve the dispersibility of the dispersion liquid, it is preferable that the dispersion liquid be subjected to a dispersion treatment. Examples of the dispersion treatment include shearing treatment using a homogenizer, etc., and ultrasonic treatment.

[Reinforced fiber]
The reinforcing fibers used in the present invention are not particularly limited, and may include polyacrylonitrile-based (hereinafter, PAN-based) carbon fibers, pitch-based carbon fibers, glass fibers, basalt fibers, boron fibers, aromatic polyamide fibers, etc. . PAN-based carbon fibers and pitch-based carbon fibers can be suitably used because of their high interaction with graphene oxide.

[Reinforced fiber coated with graphene oxide]
The reinforcing fiber coated with graphene oxide of the present invention has graphene oxide attached to the surface of the reinforcing fiber. Graphene oxide has a small thickness and large surfaces, and exhibits high adhesion through interaction between the surfaces. In particular, when carbon fiber is used as the reinforcing fiber, the interaction between graphene oxide and graphene oxide is particularly strong since both are carbon materials. From the viewpoint of improving the mixability into the resin, the minimum amount of graphene oxide required for the reinforcing fibers depends on the diameter and density of the reinforcing fibers used. For example, taking carbon fiber as an example, if the diameter is 7 μm and the density is 1.78, the surface area per 1 kg of carbon fiber is 320 m ² , and the graphene oxide (theoretical area 1315 m ² /g) required to cover it is approximately It becomes 0.25g (0.25ppm). The composite amount ratio of reinforcing fibers and graphene oxide may be greater than this, but in consideration of handling and adhesion rate, it is preferably 1 ppm or more. Further, from the viewpoint of not diluting the effect of the reinforcing fibers themselves, the adhesion ratio is preferably 1% or less.

[Method for producing reinforced fiber coated with graphene oxide]
Although the method for producing reinforcing fibers coated with graphene oxide of the present invention is not particularly limited, it preferably includes a step of bringing the reinforcing fibers into contact with a graphene oxide dispersion. The dispersion medium during contact is not particularly limited, but includes, for example, water, alcohols such as methanol, ethanol, and 2-propanol, ketone solvents such as acetone and methyl ethyl ketone, ether solvents such as diethyl ether and cyclopentyl methyl ether, and halogen-based solvents such as chloroform. Examples include solvents. Among these, water and alcohol solvents are preferred, and water is most preferred.

The method of contacting the graphene oxide dispersion with the reinforcing fibers is not particularly limited, but from the viewpoint of efficiently using graphene oxide, there are methods such as adding the graphene oxide dispersion to the reinforcing fibers, and spraying the graphene oxide dispersion onto the reinforcing fibers. A method of doing so is preferred. For example, a method in which reinforcing fibers are sequentially impregnated into a channel through which a graphene oxide dispersion is flowing, or a graphene oxide dispersion is sprayed in a process in which reinforcing fibers are transferred in the fiber direction (for example, in a fiber winding process). Examples include a method of attaching the reinforcing fiber to reinforcing fibers.

The temperature in the step of bringing the graphene oxide dispersion into contact with the reinforcing fibers is not particularly limited, but is preferably in the range of 0 to 90°C from the viewpoint of effectively adhering graphene oxide. Outside this range, the adhesion ability of graphene oxide decreases. The temperature is more preferably 10 to 80°C, even more preferably 20 to 70°C.

A third component may be included in the step of bringing the graphene oxide dispersion into contact with the reinforcing fibers. Examples include additives that enhance the adhesion ability of graphene oxide, reducing agents that reduce graphene oxide, and the like. These additives may be included in the graphene oxide dispersion, or may be added at the same time or after the contacting step. As the additive for increasing the adhesion ability, amine and ammonium are preferable. Among these, low-molecular compounds such as alkylamines (e.g. laurylamine) and alkylammoniums (e.g. benzalkonium chloride), high-molecular compounds polyamines (e.g. polyethyleneimine, polyallylamine, etc.), polyammoniums (polydimethylallylamine hydrochloride, etc.) ) is preferred.
Preferred reducing agents include hydrazine, hydrogen iodide, and L-ascorbic acid.

It is also preferable to include a purification step of removing excess graphene oxide and additives after the step of bringing the graphene oxide dispersion into contact with the reinforcing fibers. When carbon fibers are used as the reinforcing fibers, graphene oxide has a strong interaction with the carbon fibers, so depending on the conditions, excessive graphene oxide may be attached, so it is preferable to remove this excess graphene oxide. In the purification step, washing with a solvent is preferable, and the solvent is preferably the above-mentioned dispersion medium, and water is particularly preferable.

The manufacturing method may include a drying step and a reduction step. The drying step is preferably performed at room temperature or under heating, and the atmosphere may be an inert atmosphere, air, or vacuum. Reduction by heating or reduction using a reducing agent is suitable for the reduction step. Reduction by heating is preferably carried out at a temperature of 120°C or higher, more preferably 150°C or higher. From the viewpoint of preventing decomposition of graphene oxide, the temperature is preferably 700°C or less. The atmosphere may be an inert atmosphere, air, or vacuum. When using a reducing agent, as described above, the reducing agent added in the mixing step may be used, or a reducing agent may be separately applied to the reinforcing fibers coated with graphene oxide.

[Fiber-reinforced plastic and its molding method]
The fiber-reinforced plastic of the present invention is a fiber-reinforced plastic containing reinforcing fibers coated with graphene oxide and a matrix resin, wherein the volume ratio of the reinforcing fibers to the matrix resin in the fiber-reinforced plastic is 15:85 to 15:85. 50:50, and the matrix resin is a fiber-reinforced plastic characterized in that it contains 30 to 100% by mass of a radical curable resin.

The volume ratio of reinforcing fibers to matrix resin in the fiber-reinforced plastic of the present invention is 15:85 to 50:50, more preferably 20:80 to 50:50, even more preferably 30:70 to 50:50. It is. By setting it as the above-mentioned range, it is possible to maintain a balance between moldability and strength.

Methods for molding the fiber-reinforced plastic of the present invention include, but are not particularly limited to, a hand lay-up method in which fiber aggregate is placed in a mold, and resin mixed with a curing agent is laminated in multiple layers while defoaming, and a spray-up method. In addition, there is the SMC press method, in which a sheet-like mixture of aggregate and resin is compression-molded in a mold, the RTM method, in which resin is injected into a mating mold lined with fibers similar to injection molding, and thermosetting resin is molded in an autoclave. One example is a method of curing and molding.

When molding fiber-reinforced plastics, although there are no particular limitations, appropriate amounts of curing agents, accelerators, co-promoters, chain transfer agents, etc. may be used.

[Matrix resin]
The matrix resin of the fiber-reinforced plastic of the present invention contains 30 to 100% by mass of radical curable resin. Preferably it is 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more.

Radical curing resins used as the matrix resin of the fiber reinforced plastic of the present invention include thermosetting acrylic resins, unsaturated polyester resins, allyl resins (diallyl phthalate resins), epoxy acrylate resins (vinyl ester resins), and urethane acrylate resins. can be used. These resins may be used alone or in combination. Among these, vinyl ester resins are preferred from the viewpoint of high strength and high elasticity, and bisphenol type vinyl ester resins are more preferred.

The matrix resin of the present invention may contain resin components other than the radical curable resin. It is preferable that the other resin components are compatible with the radical curable resin. These resins are not particularly limited, but thermosetting resins such as epoxy resins, urethane resins, alkyd resins, urea resins, and melamine resins can be used. Among them, it is preferable to use epoxy resin from the viewpoint of high strength and high elasticity.

The content of other resin components is preferably 0 to 70% by mass of the matrix resin, more preferably 0 to 50% by mass, and even more preferably 0 to 30% by mass. If the amount of radical curable resin in the matrix resin is less than 30% by mass, it is not preferable because molding becomes difficult.

Various additives may be used in the matrix resin as long as they do not go against the spirit of the present invention. Examples of additives include ultraviolet absorbers, antistatic agents, mold release agents, extenders, colorants, flame retardants, lubricants, plasticizers, and the like.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, unless otherwise specified, "parts" shall mean "parts by mass" and "%" shall mean "% by mass."

[Raman spectrum measurement]
Raman spectroscopic analysis was performed using the following equipment and conditions.
Measuring device: Raman microscope (JASCO NRS-3100)
Measurement conditions: 532 nm laser used, 20x objective lens, CCD capture time 1 second, 32 integration times (resolution = 4 cm ^-1 )
Measurement details: The presence of graphene oxide is confirmed by the presence or absence of characteristic G and D bands.

[X-ray photoelectron spectroscopy (XPS)]
It was analyzed under the following conditions and the oxygen and carbon contents were confirmed.
Shimadzu Kratos AXIS-NOVAX-ray source/output AlKα-100W pass energy 40eV neutralization gun ON

[Microdroplet test]
After molding resin droplets on carbon fibers, the interfacial shear strength was analyzed using a composite material interface property evaluation device HM410 manufactured by Toei Sangyo Co., Ltd., five times at a drawing speed of 0.12 mm/m. The minimum and maximum values were excluded, and the average of the three intermediate values was taken as the result for that test.

[Dynamic viscoelasticity (DMA) evaluation]
A molded product was cut out to have a thickness of 3 mm, a width of 5 mm, and a length of 50 mm, and the elastic modulus at 30° C. was evaluated using a dynamic rheological modulus (DMA) measuring device “RSA-G2”.

[Evaluation of elastic modulus (Young's modulus)]
The molded product was cut out to have a thickness of 3 mm, a width of 10 mm, and a length of 80 mm. Using an Instron universal testing machine, the elastic modulus was determined by three-point bending at a bending width of 40 mm and a bending speed of 1.5 mm/m. evaluated.

[Example of preparation of graphene oxide]
A graphene oxide dispersion liquid was synthesized using the following steps. 15 g of graphite (Z-25, manufactured by Ito Graphite Co., Ltd.) and 640 g of sulfuric acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) were placed in a reaction container in advance, and potassium permanganate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added while adjusting the temperature to 30°C. (manufactured by) was added. After the addition, the temperature was raised to 35° C. for 30 minutes, and the reaction was allowed to proceed for 2 hours.

After the reaction, 1070 ml of water and 42 ml of 30% hydrogen peroxide solution (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) were added to the reaction solution to stop the reaction. The obtained reaction solution was purified by static sedimentation by repeated removal of the supernatant and redispersion with ion-exchanged water. After purification, a peeling operation was performed using a homogenizer to prepare a graphene oxide dispersion (1) (0.1% water dispersion). The obtained graphene oxide was found to be a single layer by electron microscopy. O/C determined by XPS analysis was 0.55.

[Example of preparation of carbon fiber coated with graphene oxide]
Graphene oxide dispersion (1), carbon fibers (as they are, and those with surface impurities removed at 350°C in the atmosphere, referred to as CF-P and CF-H), carbon fiber cloth, and carbon fiber paper (all manufactured by Nissei Co., Ltd.) After impregnating the sample with 100% graphene oxide (manufactured by the same company) for 1 minute, the sample was washed with water to remove excess graphene oxide. By drying with air at 40° C., graphene oxide-covered carbon fibers, graphene oxide-covered carbon fiber cloth, and graphene oxide-covered carbon fiber paper were obtained.

[Example 1, Example 2] Microdroplet test with vinyl ester resin 100 parts by mass of vinyl ester resin (RF-701, manufactured by Showa Denko K.K.), 0.3 mass of 8% cobalt octenoate as an accelerator Using 2 parts by mass of 328EM (manufactured by Kayaku Akzo Co., Ltd.) as a curing agent, the resin and accelerator were mixed for 5 minutes, the curing agent was added thereto, and after mixing for 3 minutes, carbon fibers coated with graphene oxide were prepared. (CF-P (Example 1) and CF-H (Example 2)) was coated, left at room temperature for 30 minutes, and then cured in a blower oven at 60°C for 4 hours to produce droplets.

[Comparative example 1, comparative example 2]
Droplets were produced in the same manner as in Examples 1 and 2, except that carbon fibers (CF-P and CF-H) not coated with graphene oxide were used.

The microdroplet test results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1. As a result, by coating with graphene oxide, we were able to improve the strength, which was an issue with vinyl ester. This made it possible to provide a carbon fiber reinforced plastic with excellent moldability, high strength, and high modulus of elasticity.

[Example 3, Example 4]
10 sheets each of carbon fiber cloth coated with graphene oxide (Example 3) and carbon fiber paper coated with graphene oxide (Example 4) were stacked, and 100 sheets of vinyl ester resin (RF-701, manufactured by Showa Denko K.K.) were stacked. After pressing for 60 minutes at a mold temperature of 80°C using 0.3 parts by mass of 8% cobalt octenoate as an accelerator and 2 parts by mass of Percmil H-80 (manufactured by NOF Corporation) as a hardening agent. After curing at 120° C. for 15 hours, a fiber-reinforced plastic was obtained.

[Comparative Example 3, Comparative Example 4]
Fiber-reinforced plastics were produced in the same manner as in Examples 3 and 4, except that carbon fibers (CF-P and CF-H) not coated with graphene oxide were used.

[Comparative Examples 5 and 6]
Ten sheets each of carbon fiber cloth coated with graphene oxide (Reference Example 1) and carbon fiber paper coated with graphene oxide (Reference Example 2) were stacked, and epoxy resin (828EL, manufactured by Mitsubishi Chemical Corporation) was used as the thermosetting resin. Using 100 parts by mass and 5 parts by mass of Curesol 1B2MZ (manufactured by Shikoku Kasei Kogyo Co., Ltd.) as a curing agent, they were pressed at a mold temperature of 110°C for 60 minutes, and then after-cured at 120°C for 15 hours to obtain a fiber-reinforced plastic. .

Table 2 shows the DMA and Instron evaluation results of Examples 3 and 4 and Comparative Examples 3, 4, 5, and 6. As a result, by coating with graphene oxide, we were able to improve the strength, which was an issue with vinyl ester. It was also found that by combining carbon fiber coated with graphene oxide and vinyl ester resin, strength equal to or higher than that of epoxy resin, a conventional thermosetting resin, was revealed. From this, by combining carbon fiber coated with graphene oxide and vinyl ester resin, it was possible to provide a carbon fiber reinforced plastic with excellent moldability, high strength, and high elastic modulus.

Claims (5)

A fiber-reinforced plastic containing reinforced fibers coated with graphene oxide and a matrix resin,
The volume ratio of reinforcing fibers and matrix resin in the fiber-reinforced plastic is 15:85 to 50:50,
The fiber-reinforced plastic is characterized in that the matrix resin contains 30 to 100% by mass of a radical curable resin. The fiber-reinforced plastic according to claim 1, wherein the reinforcing fibers are PAN-based or pitch-based carbon fibers. The fiber reinforced plastic according to claim 1, wherein the radical curable resin is a vinyl ester resin. The fiber reinforced plastic according to claim 2, wherein the radical curable resin is a vinyl ester resin. A method for molding the fiber-reinforced plastic according to claims 1 to 4, characterized in that a mold is used.