JP2020147876A - Sizing agent for carbon fiber, aqueous dispersion thereof, sizing agent-attached carbon fiber, and method of producing carbon fiber-reinforced composite material - Google Patents

Abstract

To provide a sizing agent for carbon fiber providing a carbon fiber-reinforced composite material that achieves both the tensile strength in the lengthwise direction of the fiber and the tensile strength in directions perpendicular to the lengthwise direction of the fiber.SOLUTION: The sizing agent for carbon fiber contains a compound represented by the formula (1) in the figure, where R1 represents a hydrogen atom or methyl group, and m represents an integer from 2 to 4.SELECTED DRAWING: None

Description

The present invention relates to a sizing agent for carbon fibers, an aqueous dispersion thereof, and carbon fibers to which the sizing agent for carbon fibers is attached.

Carbon fiber reinforced composite materials are lightweight and have excellent mechanical properties such as strength and elastic modulus, and are materials for components of sports and leisure equipment, equipment for vehicles and aerospace, and industrial materials for energy and civil engineering and construction. The application is being developed in a wide range of fields. The carbon fiber reinforced composite material is formed of a reinforcing material made of carbon fibers and a matrix resin, and various resins such as epoxy resin, unsaturated polyester resin, vinyl ester resin, and phenol resin are used as the matrix resin. Among them, epoxy resin is widely used. When applying carbon fiber reinforced composite materials to vehicle / aerospace equipment applications and industrial material applications, in addition to the tensile strength in the fiber length direction, the tensile strength in the direction perpendicular to the fiber length direction is applied. It is required to have a high level.
On the other hand, since carbon fiber itself has a small elongation and a brittle property, fluff is likely to occur due to mechanical friction or the like. Therefore, a sizing agent is attached to the carbon fibers for the purpose of suppressing the generation of fluff.
Furthermore, since the sizing agent affects the characteristics of the interface between the matrix resin and the carbon fiber, it is possible to improve the performance of the carbon fiber reinforced composite material by the sizing agent, and it has a function of improving the performance of the carbon fiber reinforced composite material. Sizing agents have been proposed.
For example, Patent Document 1 proposes a sizing agent containing a dimer acid type epoxy resin as a main component of the epoxy resin in the sizing agent. The carbon fiber reinforced composite material using the carbon fiber to which the sizing agent was attached as a reinforcing material had high tensile strength in the fiber length direction, but insufficient tensile strength in the direction perpendicular to the fiber length direction. Further, Patent Document 2 proposes a sizing agent containing a bisphenol A type epoxy resin as a main component. The carbon fiber reinforced composite material using the carbon fiber to which the sizing agent is attached as a reinforcing material has an excellent balance between the tensile strength in the fiber length direction and the tensile strength in the direction perpendicular to the fiber length direction. However, further improvement of the sizing agent has been desired in order to sufficiently bring out the performance of the ultra-high strength carbon fiber.

JP-A-2004-149721 JP-A-57-171767

The present invention has been made in view of the above circumstances, and is a sizing for carbon fibers that provides a carbon fiber reinforced composite material having both a tensile strength in the fiber length direction and a tensile strength in the direction perpendicular to the fiber length direction. It is an object of the present invention to provide an aqueous dispersion of an agent and a sizing agent. Another object of the present invention is to provide a carbon fiber to which the sizing agent is attached, and further, a carbon fiber reinforced composite material having excellent mechanical properties obtained by using the carbon fiber.

The present invention includes the following aspects.
[1] A sizing agent for carbon fibers containing a compound represented by the following formula (1) or (2).
... (1)
In formula (1), R ¹ represents a hydrogen atom or a methyl group, and m represents an integer from 2 to 4.
... (2)
In formula (2), R ² , R ³ and R ⁴ each independently represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 3.

[2] The sizing for carbon fibers according to [1], wherein the content of the compound represented by the formula (1) or (2) is 20 to 80% by mass with respect to the total mass of the sizing agent for carbon fibers. Agent.

[3] The sizing agent for carbon fibers according to [1] or [2], which contains 5 to 25% by mass of a surfactant with respect to the total mass of the sizing agent for carbon fibers.

[4] An aqueous dispersion of a carbon fiber sizing agent in which the carbon fiber sizing agent according to any one of [1] to [3] is dispersed in water.

[5] A carbon fiber having a sizing agent attached, wherein the sizing agent for carbon fiber according to any one of [1] to [3] is attached to the surface of the carbon fiber.

[6] The carbon fiber according to [5], wherein the amount of the sizing agent attached to the carbon fiber is 0.1 to 5% by mass with respect to the total mass of the carbon fiber attached to the sizing agent.

[7] Production of a carbon fiber reinforced composite material comprising impregnating the sizing agent-attached carbon fiber according to [5] or [6] with a thermosetting resin composition and heat-curing the thermosetting resin composition. Method.

[8] A carbon fiber bundle composed of carbon fibers to which a compound represented by the following formula (1) or (2) is attached.
... (1)
In formula (1), R ¹ represents a hydrogen atom or a methyl group, and m represents an integer from 2 to 4.
... (2)
In formula (2), R ² , R ³ and R ⁴ each independently represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 3.

[9] The carbon fiber bundle according to [8], which contains 0.1 to 4.5% by mass of the compound represented by the formula (1) or (2).

[10] A method for producing a carbon fiber reinforced composite material, which comprises impregnating the carbon fiber bundle according to [8] or [9] with the thermosetting resin composition and heat-curing the thermosetting resin composition.

According to the present invention, it is possible to obtain a carbon fiber that provides a carbon fiber reinforced composite material having good tensile strength in both the length direction of the reinforcing fiber and the tensile strength in the direction perpendicular to the length direction of the reinforcing fiber.

The sizing agent for carbon fibers of the present invention
It contains a compound represented by the following formula (1) or (2).
... (1)
In formula (1), R ¹ represents a hydrogen atom or a methyl group, and m represents an integer from 2 to 4.
... (2)
In formula (2), R ² , R ³ and R ⁴ each independently represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 3.

By containing the compound represented by the formula (1) or (2) in the carbon fiber sizing agent, the tensile strength in the fiber length direction and the tension in the fiber length direction of the carbon fiber reinforced composite material It is possible to achieve both strength. Although the action of containing the compound represented by the formula (1) or (2) is not clear, it is considered as follows. The compound represented by the formula (1) or (2) has low compatibility with, for example, a bisphenol A type epoxy resin often used as a component of a matrix resin, and has a small epoxy equivalent, so that the compound has an appropriate adhesion. It is presumed that a layer having properties and toughness was formed at the interface. This prevented the breakage of the single fiber caused by the tension in the length direction of the fiber from propagating to the entire composite material, and at the same time, the breakage at the interface with respect to the tension in the direction perpendicular to the length direction of the fiber. It is thought that the effect of suppressing it appeared.
The compound represented by the formula (1) or (2) is preferably contained in an amount of 20% by mass or more and 80% by mass or less. By setting the content of the compound represented by the formula (1) or (2) to 20% by mass or more and 80% by mass or less, the tensile strength in the fiber length direction and the tensile strength in the fiber length direction can be adjusted. In both cases, a good carbon fiber reinforced composite material can be obtained.
As a material composed of the compound represented by the formula (1) or (2), a commercially available product such as Epicron HP-6000 (manufactured by DIC Corporation) can be used.

The sizing agent for carbon fibers of the present invention may contain a resin component other than the compound represented by the formula (1) or (2) as long as the effects of the present invention are not impaired. Examples of the resin component other than the compound represented by the formula (1) or (2) include bisphenol A type epoxy resin, bisphenol F type epoxy resin, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and alkanediol diglycidyl. Examples thereof include epoxy resins such as ether, (poly) ester compounds, (poly) urethane compounds, (poly) amide compounds, and (poly) imide compounds. Of these, it is more preferable to use a bisphenol A type epoxy resin because it can be obtained at low cost. The resin components other than the compound represented by the formula (1) or (2) are the compound represented by the formula (1) or (2) and the resin component other than the compound represented by the formula (1) or (2). It is preferable that the total amount is 80 parts by mass or less with respect to 100 parts by mass.

The sizing agent for carbon fibers of the present invention may further contain a surfactant such as a nonionic surfactant or an anionic surfactant.
The surfactant is used to disperse the compound represented by the above formula (1) or (2) and other resin components in water. One type of surfactant may be used alone, or two or more types may be used in combination.

The sizing agent for carbon fibers of the present invention can be used by dispersing the sizing agent for carbon fibers in water or an organic solvent having low solubility for imparting to carbon fibers, or sizing to an organic solvent having high solubility. The agent can also be dissolved and used.
It is superior to use it by dispersing it in water because it is easier to handle than using it by dispersing or dissolving it in an organic solvent.
The content of the surfactant can be appropriately determined in consideration of the stability of the aqueous dispersion in which the sizing agent for carbon fibers is dispersed in water.
The content of the surfactant is preferably 5 to 25% by mass, more preferably 10 to 20% by mass, based on the total mass of the sizing agent for carbon fibers. When it is 5% by mass or more, the stability of the aqueous dispersion of the carbon fiber sizing agent is good, and when it is 25% by mass or less, the effect of the carbon fiber sizing agent of the present invention is satisfactorily exhibited.

As nonionic surfactants, as aliphatic nonionic surfactants, block polymers of ethylene oxide and propylene oxide (so-called pluronic type), higher alcohol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid esters Examples include ethylene oxide adducts, glycerol fatty acid esters, sorbitol and sorbitan fatty acid esters, pentaerythritol fatty acid esters, and the like. Moreover, as a phenol-based nonionic surfactant, an alkylphenol-based nonionic, a polycyclic phenol-based nonionic, and the like can be mentioned.
As the anionic surfactant, a compound having ammonium in as a counter ion and a phenolic group to which an alkylene oxide is added as a hydrophobic group is preferable. As the anionic surfactant, a surfactant such as a carboxylate, a sulfate ester salt, a sulfonate salt, and a phosphoric acid ester salt can be used. Of these, sulfate ester salts are preferable.

The aqueous dispersion of the carbon fiber sizing agent of the present invention contains the carbon fiber sizing agent of the present invention and water. In preparing the aqueous dispersion of the carbon fiber sizing agent of the present invention, there is no limitation on the method of dispersing the carbon fiber sizing agent in water, but for example, a uniform product is obtained by mixing the carbon fiber sizing agent and the surfactant. This can be prepared by gradually adding water while stirring to invert emulsification.
As used herein, the term "dispersion" means a suspension in which the sizing agent is suspended as particles or micelles having a size of about 1 nm to 10 μm in a dispersion medium such as water or an organic solvent.
The sizing treatment for adhering the sizing agent for carbon fiber to the surface of the carbon fiber of the present invention is a sizing agent solution for carbon fiber or a dispersion liquid of the sizing agent for carbon fiber (hereinafter, "sizing agent solution for carbon fiber or" Immerse carbon fibers or carbon fiber bundles (hereinafter, "carbon fibers or carbon fiber bundles" are referred to as "carbon fibers (bundles)") in a "sizing agent for carbon fibers" (referred to as "sizing liquid"). This can be done by applying the sizing liquid to the carbon fibers (bundles) by a method, a method of contacting the carbon fibers (bundles) with the rollers to which the sizing liquid is attached, or the like, and drying the carbon fibers (bundles). The amount of the sizing agent attached to the carbon fibers (bundles) can be adjusted by adjusting the concentration of the sizing agent in the sizing solution and adjusting the amount of drawing. Further, the drying can be performed by using hot air, a hot plate, a heating roller, various infrared heaters and the like.
Further, the concentration of the sizing agent in the aqueous dispersion of the carbon fiber sizing agent of the present invention, that is, the concentration of the components other than the volatile components (such as water dried and removed in the sizing treatment) in the aqueous dispersion of the carbon fiber sizing agent. Is usually adjusted to a concentration of about 10 to 50% by mass. The concentration may be less than 10% by mass at the stage of preparing the aqueous dispersion of the sizing agent for carbon fibers, but the proportion of water in the aqueous dispersion of the sizing agent for carbon fibers increases, and the water of the sizing agent for carbon fibers becomes large. It may be uneconomical in terms of transportation and storage from the preparation of the dispersion to its use (carbon fiber sizing treatment). Therefore, when using the aqueous dispersion of the carbon fiber sizing agent (sizing the carbon fiber), the concentration of the sizing agent is adjusted so that the desired amount of the carbon fiber sizing agent adheres to the aqueous dispersion. , It is preferable to dilute the sizing agent for carbon fibers so as to be 0.1 to 10% by mass with respect to the total mass of the aqueous dispersion.

In the sizing agent-attached carbon fiber of the present invention, the carbon fiber sizing agent of the present invention is attached to the surface of the carbon fiber. By using the sizing agent-adhered carbon fiber of the present invention as the reinforcing material of the carbon fiber reinforced composite material, both the tensile strength in the fiber length direction and the tensile strength in the direction perpendicular to the fiber length direction are good carbon. A fiber reinforced composite material is obtained. Further, in the present invention, the bundle of sizing agent-attached carbon fibers is referred to as a sizing-attached carbon fiber bundle.
The amount of the sizing agent for carbon fibers attached to the sizing agent-attached carbon fibers of the present invention is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, based on the total mass of the sizing agent-attached carbon fibers. preferable.
The carbon fiber to which the sizing agent for carbon fiber of the present invention is attached may be obtained from any raw material such as pitch-based, rayon-based or polyacrylonitrile-based, and is a high-strength type (low elasticity carbon fiber). ), Medium and high elastic carbon fiber or high elastic carbon fiber may be used.
Since the sizing agent-attached carbon fiber bundle containing the sizing agent for carbon fibers of the present invention has less fluffing, it is easy to handle in processing processes such as opening and weaving, and fibers such as woven fabrics with less fluff and multiaxial warp knits. A base material can be obtained.

By impregnating the matrix resin composition, the sizing agent-adhered carbon fiber bundle containing the sizing agent for carbon fibers of the present invention is an intermediate material such as a unidirectional prepreg, a cross prepreg, a tow prepreg, a short fiber sheet prepreg, and a short fiber matte prepreg. Can be processed into a carbon fiber reinforced composite material in the form of. The matrix resin composition is not particularly limited, and examples thereof include epoxy resin, vinyl ester resin, unsaturated polyester resin, and phenol resin as long as it is a thermosetting resin, and it may be a thermoplastic resin. Examples thereof include polyolefin resins, polyester resins, polyamide resins, polyimide resins, polyamideimide resins, polyetherimide resins, polyether ketone resins, polyether ketone ketone resins, polyether ether ketone resins, and polyphenylene sulfide resins.

The method for producing a carbon fiber composite material of the present invention includes impregnating a carbon fiber bundle with a sizing agent of the present invention with a thermosetting resin composition, and then heat-curing the thermosetting resin composition.
The ratio of the thermosetting resin composition is preferably 30 to 70 parts by mass, more preferably 40 to 60 parts by mass with respect to 100 parts by mass of the sizing agent-attached carbon fiber bundle.
The heating conditions for heat-curing the thermosetting resin composition are preferably 60 to 200 ° C, preferably 130 to 180 ° C. Further, it is preferable to heat at the above temperature for 1 to 200 minutes, and more preferably to heat for 15 to 60 minutes.

Further, the carbon fiber bundle of the present invention is a carbon fiber bundle composed of carbon fibers to which the compound represented by the formula (1) or (2) is attached. The amount of the compound represented by the formula (1) or (2) contained in the carbon fiber bundle is preferably 0.1 to 0.45% by mass with respect to the mass of the carbon fiber bundle, and is 0.2 to 2.6. Mass% is more preferred.

The raw materials used for the carbon fiber sizing agents of Examples and Comparative Examples are shown below.
Naftylene ether type epoxy resin: HP-6000 (manufactured by DIC Corporation)
Bisphenol A type epoxy resin: jER828 (manufactured by Mitsubishi Chemical Corporation)
Dimer acid type epoxy resin: jER871 (manufactured by Mitsubishi Chemical Corporation)
Anionic emulsifier: Hytenol NF-17 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)

<Preparation of aqueous dispersion of sizing agent for carbon fiber>
For each of Examples 1 to 4 and Comparative Examples 1 and 2, the above components were mixed at the ratios (parts by mass) shown in Table 1 to obtain a sizing agent for carbon fibers. Ion-exchanged water was added to the obtained sizing agent for carbon fibers, and phase inversion emulsification was performed using a homomixer to obtain an aqueous dispersion of the sizing agent for carbon fibers. Further, the concentration of the sizing agent in the aqueous dispersion was adjusted to be 30% by mass.

<Carbon fiber sizing treatment>
A carbon fiber bundle without a sizing agent (“Pyrofil MR 60H24P” manufactured by Mitsubishi Chemical Co., Ltd .: 24,000 filaments, fiber diameter 5 μm, strand tensile test strength 5700 MPa, elastic modulus 285 GPa) is applied to an aqueous dispersion of a sizing agent. After being immersed and passed through the immersion tank filled with the above, it was dried by contacting it with a roller heated to 150 ° C. for 30 seconds to obtain a carbon fiber bundle with a sizing agent attached. Then, the sizing agent-attached carbon fiber bundle was wound around the bobbin. At this time, the concentration of the sizing agent in the aqueous dispersion of the sizing agent in the immersion tank was adjusted so that the amount of the sizing agent attached to the carbon fibers was 0.8% by mass with respect to the total mass of the carbon fibers having the sizing agent attached.

<Measurement of sizing agent adhesion to carbon fiber>
The amount (% by mass) of the sizing agent for carbon fibers attached to the total mass of the carbon fibers adhering to the sizing agent was measured by the Soxhlet extraction method using methyl ethyl ketone. The extraction time was 1 hour.

<Preparation of matrix resin composition>
50 parts by mass of bisphenol A type epoxy resin (“jER828” manufactured by Mitsubishi Chemical Corporation), 50 parts by mass of tetraglycidyl type epoxy resin (“jER604” manufactured by Mitsubishi Chemical Corporation), and phenoxy resin (“jER604” manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. 10 parts by mass of YP-70 ") and 32 parts by mass of 4,4'-diaminodiphenyl sulfone (manufactured by Wakayama Seika Kogyo Co., Ltd.) were mixed to prepare a matrix resin composition.

<Making prepreg>
The matrix resin composition was uniformly applied to a release paper having a mold release treatment on one side surface at 54 g / m ² per unit area with a roll coater to obtain a resin-supported sheet. A carbon fiber bundle with a sizing agent adhered to the resin-supporting sheet was attached to the resin-supported sheet by aligning them in one direction so that the fiber basis weight was 200 g / m ² . Then, the surface on the carbon fiber side was uniformly coated with the same matrix resin at 54 g / m ² per unit area as described above, and the surface on the resin side of the separately prepared resin-supporting sheet was superposed, and these were placed at a temperature of 100 ° C. and a wire. A unidirectional carbon fiber prepreg was prepared by impregnating the matrix resin composition with pressure and heating at a pressure of 2 kgf / cm. Then, the release paper on one side was peeled off, and a protective film was attached to that side. The unidirectional carbon fiber prepreg had a carbon fiber grain of 200 g / m ² and a resin content of 35% by mass.

<Measurement of 0 ° tensile strength>
The tensile strength in the fiber length direction of the carbon fiber reinforced composite material was evaluated by the method for measuring the 0 ° tensile strength shown below.
First, five unidirectional carbon fiber prepregs are laminated with the carbon fibers oriented in one direction, and then heated and pressure-cured using an autoclave (heated from room temperature to 180 ° C over 2 hours, and the temperature is 180 ° C. , And held at a pressure of 0.6 MPa for 2 hours) to prepare a cured plate having a thickness of 1 mm.
Then, a test piece having a length of 230 mm and a width of 12.5 mm was cut out from the obtained hardened plate. The 0 ° tensile strength of the test piece was measured according to ASTM-D3039 using a tensile tester (manufactured by Instron, “Universal Tester No. 5882”). The measurement conditions were that the crosshead speed of the tensile tester was 1.27 mm / min, each of the five test pieces was tested (n = 5), and the average value was 0 ° tensile strength. The results are shown in Table 1.

<Measurement of 90 ° tensile strength>
The tensile strength in the length direction and the direction perpendicular to the fiber length of the carbon fiber reinforced composite material was evaluated by the 90 ° tensile strength measuring method shown below.
First, 10 unidirectional carbon fiber prepregs are laminated with the carbon fibers oriented in one direction, and then heated and pressure-cured using an autoclave (heated from room temperature to 180 ° C over 2 hours, and the temperature is 180 ° C. , And held at a pressure of 0.6 MPa for 2 hours) to prepare a cured plate having a thickness of 2 mm.
Then, a test piece having a length of 150 mm and a width of 20 mm was cut out from the obtained hardened plate. The 90 ° tensile strength of the test piece was measured according to ASTM-D3039 using a tensile tester (manufactured by Instron, “Universal Tester No. 5882”). The measurement conditions were that the crosshead speed of the tensile tester was 1 mm / min, each of the five test pieces was tested (n = 5), and the average value was 90 ° tensile strength. The results are shown in Table 1.

As shown in Table 1, all of Examples 1 to 4 had good 0 ° tensile strength and 90 ° tensile strength. However, in Comparative Example 1, the 0 ° tensile strength and the 90 ° tensile strength were low, and in Comparative Example 2, the 0 ° tensile strength was good but the 90 ° tensile strength was low.

Claims (10)

A sizing agent for carbon fibers containing a compound represented by the following formula (1) or (2).
... (1)
In formula (1), R ¹ represents a hydrogen atom or a methyl group, and m represents an integer from 2 to 4.
... (2)
In formula (2), R ² , R ³ and R ⁴ each independently represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 3. The sizing agent for carbon fibers according to claim 1, wherein the content of the compound represented by the formula (1) or (2) is 20 to 80% by mass with respect to the total mass of the sizing agent for carbon fibers. The sizing agent for carbon fibers according to claim 1 or 2, which contains a surfactant and the content of the surfactant is 5 to 25% by mass with respect to the total mass of the sizing agent for carbon fibers. An aqueous dispersion of a carbon fiber sizing agent in which the carbon fiber sizing agent according to any one of claims 1 to 3 is dispersed in water. A carbon fiber bundle to which the sizing agent for carbon fibers according to any one of claims 1 to 4 is attached. The carbon fiber bundle with a sizing agent according to claim 5, wherein the amount of the sizing agent for carbon fibers attached is 0.1 to 5% by mass with respect to the total mass of the carbon fiber bundles with the sizing agent. A method for producing a carbon fiber reinforced composite material, which comprises impregnating the sizing agent-attached carbon fiber bundle according to claim 5 or 6 with the thermosetting resin composition and heat-curing the thermosetting resin composition. A carbon fiber bundle composed of carbon fibers to which a compound represented by the following formula (1) or (2) is attached.
... (1)
In formula (1), R ¹ represents a hydrogen atom or a methyl group, and m represents an integer from 2 to 4.
... (2)
In formula (2), R ² , R ³ and R ⁴ each independently represent a hydrogen atom or a methyl group, and n represents an integer from 1 to 3. The carbon fiber bundle according to claim 8, which contains 0.1 to 4.5% by mass of the compound represented by the formula (1) or (2). A method for producing a carbon fiber reinforced composite material, which comprises impregnating the carbon fiber bundle according to claim 8 or 9 with the thermosetting resin composition and heat-curing the thermosetting resin composition.