JP7642201B2 - Polyrotaxane-coated carbon fibers, carbon fiber composites, and prepregs - Google Patents

Description

(1) Described in the master's thesis public hearing abstract "Molecular design with environmentally friendly composite functions and their applications" published on August 24, 2020. (2) Presented at the "Master's thesis public hearing of the Department of Organic Materials Systems, Graduate School of Organic Materials Systems, Yamagata University, National University Corporation" held on August 24, 2020. (3) Described in the master's thesis "Molecular design with environmentally friendly composite functions and their applications" published in September 2020. (4) Described on page 109 of the "Collection of Abstracts of the Reiwa 2 Graduation Research Presentations of the Department of Polymer and Organic Materials Engineering, Faculty of Engineering, Yamagata University, National University Corporation" distributed on February 5, 2021. (5) Presented at the "Reiwa 2 Graduation Research Presentations of the Department of Polymer and Organic Materials Engineering, Faculty of Engineering, Yamagata University, National University Corporation" held on February 10, 2021. (6) Described in the bachelor's thesis "Development of carbon fiber composites with interface design using reactive slide-ring polymers" published on March 2, 2021.

The present invention relates to polyrotaxane-coated carbon fibers, carbon fiber composites, and prepregs.

Carbon fiber reinforced plastics are a material that combines strength and lightness, and are being put to practical use in a variety of applications. Carbon fibers are sometimes coated with a coating agent (sizing agent) to prevent damage to the carbon fibers and improve handling. Epoxy resins and the like are widely used as coating agents. Meanwhile, various coating agents are being investigated to impart desired physical properties to the carbon fiber surface or to improve the physical properties of carbon fiber reinforced plastics.

Patent Document 1 discloses a sizing-coated reinforcing fiber in which a sizing agent containing polyrotaxane is applied to the reinforcing fiber for the purpose of imparting high toughness to the fiber-reinforced composite material.

Patent Document 2 also discloses a copolymer containing a 2-oxazoline monomer and a nitrogen-containing heterocyclic monomer as constituent units as a dispersion promoter that can impart hydrophilicity and adhesiveness to the surface of a carbon material.

International Publication No. 2015/137206 JP 2018-24788 A

The carbon fiber coated with the copolymer of Patent Document 2 is chemically bonded to a resin having an acidic group, etc., and therefore the breaking strength of the carbon fiber reinforced plastic is improved. However, it was found that the elongation performance of the carbon fiber reinforced plastic is reduced.

The present invention solves the above problems by providing polyrotaxane-coated carbon fibers that can be used to produce carbon fiber composites with high breaking strength, excellent elongation performance, and excellent toughness, as well as carbon fiber composites and prepregs that use the polyrotaxane-coated carbon fibers and have high breaking strength and excellent elongation performance.

The polyrotaxane-coated carbon fiber according to the present invention comprises a carbon fiber (A), a compound (B) having two or more oxazolyl groups in one molecule, and a polyrotaxane (C) having a cyclic molecule,
A chemical bond is formed between the carbon fiber (A) and a part of the oxazolyl group of the compound (B),
A chemical bond is formed between the cyclic molecule of the polyrotaxane (C) and a part of the oxazolyl group of the compound (B).

In one embodiment of the polyrotaxane-coated carbon fiber, the compound (B) is a polymer or copolymer containing a structural unit derived from 2-vinyl-2-oxazoline.

In one embodiment of the polyrotaxane-coated carbon fiber, at least one of the cyclic molecules of the polyrotaxane (C) has a functional group that is reactive with an oxazolyl group.

In one embodiment of the polyrotaxane-coated carbon fiber, the functional group of the polyrotaxane (C) that is reactive with the oxazolyl group is an acidic group.

In one embodiment of the polyrotaxane-coated carbon fiber, the functional group of the polyrotaxane (C) that is reactive with the oxazolyl group includes one or more selected from a carboxy group, a thiol group, a phenolic hydroxyl group, and a group having an acid anhydride structure.

The carbon fiber composite material according to the present invention contains the polyrotaxane-coated carbon fiber and a resin (D).

One embodiment of the carbon fiber composite material has a chemical bond between the polyrotaxane (C) and the resin (D).

One embodiment of the carbon fiber composite material includes the polyrotaxane-coated carbon fiber, a resin (D), and a crosslinking agent (E),
The polyrotaxane (C) and the resin (D) are bonded via a crosslinking agent (E).

In one embodiment of the carbon fiber composite material, the resin (D) has an acidic group, and the crosslinking agent (E) contains a compound having two or more oxazolyl groups in one molecule.

The present invention also provides a prepreg containing the carbon fiber composite material.

The present invention provides polyrotaxane-coated carbon fibers that can be used to produce carbon fiber composites with high breaking strength, excellent elongation performance, and excellent toughness, and carbon fiber composites and prepregs that use the polyrotaxane-coated carbon fibers and have high breaking strength and excellent elongation performance.

The polyrotaxane-coated carbon fiber, carbon fiber composite, and prepreg according to the present invention will be described below.
In the present invention, (meth)acrylate is a general term for acrylate and methacrylate, and (meth)acrylic acid and the like are equivalent to this.
In this specification, the group represented by formula (1) may be simply referred to as "group (1)." The same applies to other substituents, chemical formulas, etc.
In the present invention, the term "cyclic molecule" refers to a molecule having a ring structure through which a linear molecule can penetrate. In addition, in the present invention, the term "cyclic structure" refers to the portion of the cyclic molecule excluding the groups (1) and (2).
In this specification, the term "to" indicating a range of values includes the lower and upper limits, unless otherwise specified.
In this specification, the solid content in a composition refers to the components constituting the composition excluding the solvent.

[Polyrotaxane-coated carbon fiber]
The polyrotaxane-coated carbon fiber according to the present invention (hereinafter, sometimes referred to as the present coated carbon fiber) comprises a carbon fiber (A), a compound (B) having two or more oxazolyl groups in one molecule, and a polyrotaxane (C) having a cyclic molecule,
A chemical bond is formed between the carbon fiber (A) and a part of the oxazolyl group of the compound (B),
A chemical bond is formed between the cyclic molecule of the polyrotaxane (C) and a part of the oxazolyl group of the compound (B).

This coated carbon fiber has a structure in which the carbon fiber (A) is chemically bonded to the cyclic molecules of the polyrotaxane (C) via the compound (B). The polyrotaxane is a compound characterized by a structure in which the axial molecule passes through the inside of the cyclic molecule and has a blocking group at the end of the axial molecule that prevents the cyclic molecule from being detached, forming a stable composite structure, and having no chemical crosslink between the cyclic molecule and the axial molecule, allowing the cyclic molecule to move on the axis. In this coated carbon fiber, the mechanism of dispersion of fracture stress due to the mobile crosslinking points of the polyrotaxane is adapted to the carbon fiber-base resin (resin (D)) interface adhesion site, and fracture due to stress concentration at the interface adhesion site is suppressed, thereby achieving an improvement in fracture strength without losing elongation performance.
Hereinafter, each component of the present coated carbon fiber will be described in detail.

<Carbon fiber (A)>
The carbon fiber refers to a fiber produced by carbonizing a precursor fiber at high temperature, and can be appropriately selected and used depending on the application of the coated carbon fiber, such as PAN-based carbon fiber or pitch-based carbon fiber. The precursor fiber can be acrylic, polyacrylonitrile, phenolic, rayon, or pitch-based fiber, or a plant-derived raw material, and one type can be used alone or two or more types can be used in combination. As a spinning method for producing a precursor fiber using a resin, a known spinning method such as a wet spinning method or a dry spinning method can be used. In addition, a commercially available carbon fiber can be used.

The total fineness of the carbon fiber is preferably 400 to 3,000 tex. The number of filaments in the carbon fiber is preferably 1,000 to 100,000, and more preferably 3,000 to 50,000. From the viewpoint of improving the adhesion between the carbon fiber and the resin (D) described below, carbon fiber having a surface roughness (Ra) of 6.0 to 100 nm is preferred. To obtain carbon fiber having a surface roughness (Ra) of 6.0 to 100 nm, it is preferable to spin the precursor fiber by a wet spinning method.

Fine carbon fibers are preferably used because they can provide carbon fibers with high strength and elastic modulus. Specifically, the single fiber diameter of the carbon fibers is preferably 10 μm or less, more preferably 7.5 μm or less, and even more preferably 6 μm or less. The lower limit of the single fiber diameter is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 4.5 μm or more, in order to prevent single fiber breakage during the manufacturing process, etc.

The carbon fiber preferably has an acidic group in terms of ease of chemical bonding with the compound (B). Examples of the acidic group include a carboxy group, a thiol group, and a phenolic hydroxyl group, and the carboxy group may have an acid anhydride structure. The acidic group in the carbon fiber may be generated during the carbonization treatment of the raw material resin, or the acidic group may be introduced onto the surface of the carbonized fiber by oxidizing the carbonized fiber. Examples of the oxidation treatment method include gas phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation. Liquid phase electrolytic oxidation is preferred in terms of high productivity and uniform treatment.

<Compound (B) Having Two or More Oxazolyl Groups in One Molecule>
In this coated carbon fiber, a part of the oxazolyl group of the compound (B) having two or more oxazolyl groups in one molecule is chemically bonded to the carbon fiber (A) to modify the surface of the carbon fiber, thereby contributing to improving the breaking strength of the carbon fiber (A). Furthermore, a part of the other oxazolyl group of the compound (B) is chemically bonded to the cyclic molecule of the polyrotaxane (C), thereby connecting the carbon fiber (A) to the cyclic molecule of the polyrotaxane (C). As a result, the resin (D) interacts with the carbon fiber (A) coated with the compound (B) via the polyrotaxane (C), thereby realizing dispersion of the fracture stress at the interface, and a carbon fiber composite material having high breaking strength and excellent elongation performance can be obtained.

The compound (B) may be any compound having at least two oxazolyl groups. Among them, from the viewpoint of ease of synthesis, a (co)polymer containing a structural unit derived from a monomer having an oxazolyl group is preferred, and from the viewpoint of reactivity with a carbon material, a (co)polymer containing a structural unit derived from a 2-oxazoline monomer is preferred.
Examples of monomers having an oxazolyl group include 2-vinyl-2-oxazoline, 4-methyl-2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, 4-ethyl-2-vinyl-2-oxazoline, 5-ethyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-2-oxazoline, 4,4-diethyl-2-vinyl-2-oxazoline, 4,5-dimethyl-2-vinyl-2-oxazoline, 4,5-diethyl-2-vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline, -oxazoline, 4-methyl-2-isopropenyl-2-oxazoline, 5-methyl-2-isopropenyl-2-oxazoline, 4-ethyl-2-isopropenyl-2-oxazoline, 5-ethyl-2-isopropenyl-2-oxazoline, 4,4-dimethyl-2-isopropenyl-2-oxazoline, 4,4-diethyl-2-isopropenyl-2-oxazoline, 4,5-dimethyl-2-isopropenyl-2-oxazoline, 4,5-diethyl-2-isopropenyl-2-oxazoline, and the like. Among these, from the viewpoint of reactivity with acidic groups and the like, 2-vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, or 4,4-dimethyl-2-vinyl-2-oxazoline is preferred, and 2-vinyl-2-oxazoline or 2-isopropenyl-2-oxazoline is more preferred.
The monomer having an oxazolyl group can be used alone or in combination of two or more kinds.

The (co)polymer containing a structural unit derived from a monomer having an oxazolyl group may further contain a structural unit derived from another monomer. Examples of the other monomer include a nitrogen-containing heterocyclic (excluding oxazolyl) monomer, a (meth)acrylate monomer, a monomer having a glycidyl group, and a monomer having an isocyanate group. The nitrogen-containing heterocyclic monomer and the (meth)acrylate monomer are preferably used in combination with a monomer having an oxazolyl group in order to adjust the ratio of the structural unit derived from the monomer having an oxazolyl group in compound (B). Among them, the nitrogen-containing heterocyclic monomer is preferred from the viewpoint of suppressing the aggregation of carbon fibers.

Examples of nitrogen-containing heterocyclic monomers include N-vinylpyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinylpiperidone, N-vinyl-3-morpholinone, N-vinylcaprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine. Among these, N-vinylpyrrolidone, N-vinylimidazole, N-vinylcaprolactam, and N-acryloylmorpholine are preferred in terms of affinity with carbon fibers and copolymerizability during production. The nitrogen-containing heterocyclic monomers can be used alone or in combination of two or more.

When compound (B) is a copolymer containing a constituent unit derived from a monomer having an oxazolyl group, the proportion of the monomer having an oxazolyl group is preferably 1 to 90 mol% based on the total amount of the constituent units constituting compound (B). When compound (B) is a (co)polymer, the weight average molecular weight is preferably 1,000 to 500,000, more preferably 2,000 to 200,000, and even more preferably 4,000 to 100,000. If the weight average molecular weight is 1,000 or more, the adhesion to the carbon fiber surface is excellent. If the weight average molecular weight is 500,000 or less, the increase in viscosity is suppressed, and the handling property is excellent.

(Co)polymers containing structural units derived from monomers having an oxazolyl group can be produced by known radical polymerization methods such as solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization.

<Polyrotaxane (C)>
Polyrotaxane is a complex in which a linear molecule penetrates a cyclic molecule and has blocking groups on both sides of the linear molecule via the cyclic molecule. The blocking groups suppress detachment from the linear molecule. The cyclic molecule can move in the linear direction of the linear molecule with the area between the blocking groups as the range of motion. The cyclic molecule remains movable relative to the linear molecule even after crosslinking. Therefore, the polyrotaxane is flexibly deformed, and the force applied between the resin (D) and the carbon fiber is relaxed. As a result, it is presumed that the coated carbon fiber and carbon fiber composite have excellent elongation performance.

(Cyclic molecules)
In the polyrotaxane (C), the cyclic molecules have a ring structure through which the linear molecules described below can penetrate. Furthermore, it is preferable that at least one of the multiple cyclic molecules has a functional group (hereinafter, sometimes simply referred to as a functional group) that is reactive with an oxazolyl group. The functional group forms a chemical bond with the oxazolyl group of the compound (B) and connects to the carbon fiber (A).
The functional group reactive with the oxazolyl group may be any group capable of reacting with the oxazolyl group to form a chemical bond with the compound (B). Examples of such a functional group include a carboxy group, a thiol group, a phenolic hydroxyl group, and a group having an acid anhydride structure.
The substituent having the functional group is preferably a group represented by the following formula (1).

ただし、
Ｒ^１１は、オキサゾリル基との反応性を有する官能基であり、
Ｘ^１１は、環構造に連結する連結基又は単結合であり、
＊は環構造側末端を示す。

however,
R ¹¹ is a functional group reactive with an oxazolyl group;
^X11 is a linking group or a single bond linked to a ring structure;
* indicates the end of the ring structure.

Specific examples of R ¹¹ include groups represented by the following formulas (11) to (17).

ただし、
Ｒ^１及びＲ^２は、各々独立に、水素原子、ハロゲン原子、又は、置換基を有していてもよく炭素鎖中に－Ｏ－、－Ｓ－、－Ｃ（＝Ｏ）－、－Ｏ－Ｃ（＝Ｏ）－、－ＮＨ－Ｃ（＝Ｏ）－、又は、－ＮＨ－Ｃ（＝Ｏ）－Ｏ－を有してもよい炭化水素基であり、
Ｒ^３は、単結合、又は置換基を有していてもよい炭化水素基であり、
＊は式（１）におけるＸ^１１側末端を示す。

however,
R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, or a hydrocarbon group which may have a substituent and which may have -O-, -S-, -C(=O)-, -O-C(=O)-, -NH-C(=O)-, or -NH-C(=O)-O- in the carbon chain;
^R3 is a single bond or a hydrocarbon group which may have a substituent;
* indicates the end on the ^X11 side in formula (1).

The halogen atom in R ¹ and R ² includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the hydrocarbon group in ^R1 and ^R2 include linear or branched hydrocarbon groups having 1 to 12 carbon atoms, preferably hydrocarbon groups having 1 to 8 carbon atoms, and more preferably hydrocarbon groups having 1 to 6 carbon atoms. When the hydrocarbon group has 2 or more carbon atoms, it may have -O-, -S-, -C(=O)-, -O-C(=O)-, -NH-C(=O)-, or -NH-C(=O)-O- in the carbon chain. For example, when the carbon chain has the above bond, the hydrocarbon group for R ¹ to R ³ can be represented as *-R'-QR" (wherein R' and R" are each independently a hydrocarbon group having 1 or more carbon atoms, the sum of the number of carbon atoms in R' and the number of carbon atoms in R" is 2 to 12, and Q is -O-, -S-, -C(=O)-, -O-C(=O)-, -NH-C(=O)-, or -NH-C(=O)-O-).
Examples of the substituent that the hydrocarbon group may have include a halogen atom and a phenyl group.

From the standpoint of ease of synthesis and molecular stability, ^R1 and ^R2 are each preferably a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 6 carbon atoms which may have the above-mentioned Q in the carbon chain, more preferably a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms not having Q, and further preferably a hydrogen atom or a methyl group.
From the standpoint of ease of synthesis and molecular stability, ^R3 is preferably a hydrocarbon group having 1 to 6 carbon atoms which may have the above-mentioned Q in the carbon chain, more preferably a hydrocarbon group having 1 to 6 carbon atoms not having Q, and further preferably a methyl group or an ethyl group.

The hydrocarbon group for ^R3 includes linear or branched hydrocarbon groups having 1 to 12 carbon atoms, preferably hydrocarbon groups having 1 to 8 carbon atoms, and more preferably hydrocarbon groups having 1 to 6 carbon atoms.
Examples of the substituent that the hydrocarbon group may have include a halogen atom and a phenyl group.
When ^R3 is a single bond, the group (11) is *-COOH and the group (12) is *-SH.

^X11 is a linking group linked to a ring structure or a single bond. When ^X11 is a single bond, the group (1) is * ^-R11 .
When X ¹¹ is a linking group, it is preferably a linking group represented by the following formula (X1).

ただし、
Ｘ^１２は、＊－Ｏ－Ｒ^１２－＊＊、＊－Ｏ－Ｃ（＝Ｏ）－Ｒ^１２－＊＊、＊－Ｃ（＝Ｏ）－Ｏ－Ｒ^１２－＊＊、＊－ＮＨ－Ｃ（＝Ｏ）－Ｒ^１２－＊＊、＊－Ｃ（＝Ｏ）－ＮＨ－Ｒ^１２－＊＊、＊－ＮＨ－Ｃ（＝Ｏ）－Ｏ－Ｒ^１２－＊＊、＊－Ｏ－Ｃ（＝Ｏ）－ＮＨ－Ｒ^１２－＊＊を表し、Ｘ^１２が複数ある場合、複数あるＸ^１２は同一であっても異なっていてもよく、
Ｒ^１２は置換基を有していてもよい炭化水素基であって、Ｒ^１２が複数ある場合、複数あるＲ^１２は同一であっても異なっていてもよく、
Ｌ^１１は、＊－Ｏ－＊＊、＊－Ｏ－Ｃ（＝Ｏ）－＊＊、＊－Ｃ（＝Ｏ）－Ｏ－＊＊、＊－ＮＨ－Ｃ（＝Ｏ）－＊＊、＊－Ｃ（＝Ｏ）－ＮＨ－＊＊、＊－ＮＨ－Ｃ（＝Ｏ）－Ｏ－＊＊、＊－Ｏ－Ｃ（＝Ｏ）－ＮＨ－＊＊であり、
ｍ１は、１～２００の整数であり、
ｎ１は、０又は１であり、
＊は環構造側末端、＊＊は基（１）におけるＲ^１１側末端を示す。

however,
X ¹² represents *-O-R ¹² -**, *-O-C(=O)-R ¹² -**, *-C(=O)-O-R ¹² -**, *-NH-C(=O)-R ¹² -**, *-C(=O)-NH-R ¹² -**, *-NH-C(=O)-O-R ¹² -**, *-O-C(=O)-NH-R ¹² -**; when there is a plurality of X ¹² , the plurality of X ¹² may be the same or different;
R ¹² is a hydrocarbon group which may have a substituent, and when there are a plurality of R ¹² , the plurality of R ¹² may be the same or different;
L ¹¹ is *-O-**, *-OC(=O)-**, *-C(=O)-O-**, *-NH-C(=O)-**, *-C(=O)-NH-**, *-NH-C(=O)-O-**, *-O-C(=O)-NH-**,
m1 is an integer from 1 to 200,
n1 is 0 or 1;
* indicates the end on the ring structure side, and ** indicates the end on the R ¹¹ side in group (1).

Examples of the hydrocarbon group for R ¹² include a linear alkylene group, a branched alkylene group, a cycloalkylene group, an arylene group, and a group consisting of a combination thereof.
The linear alkylene group preferably has 1 to 12 carbon atoms, more preferably has 1 to 8 carbon atoms, and still more preferably has 1 to 6 carbon atoms. Examples of the linear alkylene group include a methylene group, an ethylene group, a propylene group, and a hexylene group.
The branched alkylene group is preferably a structure having an alkyl group as a substituent of the linear alkylene group. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.
The cycloalkylene group may be a monocyclic or condensed ring having 5 to 12 carbon atoms, and is preferably a cyclopentylene group or a cyclohexylene group.
Examples of the arylene group include a phenylene group, a naphthylene group, and an anthracenylene group.
An example of a group consisting of these combinations is a group in which a methylene group is connected to a phenylene group, etc. Examples of the substituent that R ¹² may have include a halogen atom and an alkoxy group having 1 to 6 carbon atoms.

^L11 and n1 represent the connection between ^X12 and ^R11 , and are appropriately selected from the viewpoint of ease of synthesis depending on the structure of ^X12 and ^R11 . For example, when the atom at the ^X11 end of ^R11 is O, n1 is preferably 0. On the other hand, when the atom at the ^X11 end of ^R11 is C or N, n1 may be either 0 or 1. When the atom at the ^X11 end of ^R11 is C, n1 is preferably 1 from the viewpoint of ease of synthesis.
From the standpoint of ease of synthesis, L ¹¹ is preferably *--O--C(═O)--**.

When m1 is 2 or more, the linking group (X1) is a polymer. In the linking group (X1), all ^X12 may be the same homopolymer, or ^X12 may be a copolymer having different structures. When the linking group (X1) is a copolymer, the bonding order is not particularly limited, and the linking group (X1) may be any of a random copolymer, a block copolymer, and an alternating copolymer.
From the viewpoints of breaking strength and elongation performance, m is preferably 1 to 200, more preferably 1 to 100, and even more preferably 1 to 40.

When the linking group (X1) is a polymer, specific examples of the polymer include polyether, polyester, polyamide, polyurethane, etc. In the polyrotaxane (C), from the viewpoints of ease of synthesis and chemical stability, it is preferable that the linking group (X1) is a polyether, polyester, polyamide, or a copolymer thereof.
The polyester structure can be suitably synthesized, for example, by ring-opening polymerization of lactone. Examples of the lactone include ε-caprolactone, δ-valerolactone, and γ-butyrolactone. The polyamide structure can be suitably synthesized, for example, by ring-opening polymerization of lactam. Examples of the lactam include ε-lactam, δ-lactam, and γ-lactam. These can be used alone or in combination of two or more.

The ring structure constituting the cyclic molecule may be appropriately selected from those capable of encapsulating the linear molecule described below. Specific examples of the ring structure include cyclodextrin, crown ether, cyclophane, calixarene, etc., and from the viewpoint of ease of introducing a substituent, cyclodextrin, cyclophane, and calixarene are preferred, and cyclodextrin is more preferred. Examples of cyclodextrin include α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. When the ring structure is cyclodextrin, it is preferable that the hydroxyl group of the cyclodextrin contains a structure substituted with the group (1).

The number of groups (1) per cyclic molecule is not particularly limited, and may be appropriately adjusted within the range of, for example, 1 to 24, taking into consideration the toughness of the resulting cured product.
For example, when the ring structure is α-cyclodextrin, the number of groups (1) per cyclic molecule is preferably 1 to 12, more preferably 1 to 10, and even more preferably 1 to 8, from the viewpoint of toughness of the resulting cured product.
When the ring structure is β-cyclodextrin, the number of groups (1) per cyclic molecule is preferably 1 to 15, more preferably 1 to 12, and even more preferably 1 to 10, from the standpoint of toughness of the resulting cured product.
When the ring structure is γ-cyclodextrin, the number of groups (1) per cyclic molecule is preferably 1 to 18, more preferably 1 to 15, and even more preferably 1 to 12, from the viewpoint of toughness of the resulting cured product.
In the case of a polyrotaxane having a plurality of cyclic molecules, some of the cyclic molecules may not have the group (1).

The cyclic molecule may have a substituent different from the above group (1) within the scope of the effects of the present invention. Examples of such a substituent include a group represented by the following formula (2).
Formula (2) *-X ¹¹ -R ²¹
however,
^X11 is a linking group or a single bond linked to a ring structure;
R ²¹ is a group having a hydroxyl group, an amino group, an epoxy group or an isocyanate group,
* indicates the end of the ring structure.

^X11 is the same as in group (1), and preferred embodiments are also the same.
The number of groups (2) per cyclic molecule is not particularly limited, but may be, for example, 0 to 23. Specifically, when the ring structure is α-cyclodextrin, the number of groups (2) per cyclic molecule is preferably 0 to 17. When the ring structure is β-cyclodextrin, the number of groups (2) per cyclic molecule is preferably 0 to 20. When the ring structure is γ-cyclodextrin, the number of groups (2) per cyclic molecule is preferably 0 to 23.

The polyrotaxane (C) may have at least two cyclic molecules. From the viewpoint of the breaking strength and elongation performance of the resulting carbon fiber composite material, the number of cyclic molecules is preferably 2 to 250, more preferably 3 to 200, and even more preferably 4 to 150.

The number of functional groups per cyclic molecule is not particularly limited, but is preferably 1 to 24 from the viewpoint of the breaking strength and elongation performance of the resulting carbon fiber composite. For example, when the ring structure is α-cyclodextrin, the number of functional groups per cyclic molecule is preferably 1 to 12, more preferably 1 to 10, and even more preferably 1 to 8 from the viewpoint of the breaking strength and elongation performance of the resulting carbon fiber composite. When the ring structure is β-cyclodextrin, the number of functional groups per cyclic molecule is preferably 1 to 15, more preferably 1 to 12, and even more preferably 1 to 10 from the viewpoint of the breaking strength and elongation performance. When the ring structure is γ-cyclodextrin, the number of functional groups per cyclic molecule is preferably 1 to 18, more preferably 1 to 15, and even more preferably 1 to 12 from the viewpoint of the breaking strength and elongation performance.
In the case of a polyrotaxane having a plurality of cyclic molecules, some of the cyclic molecules may not have a functional group.

(Linear molecule)
The linear molecule has a linear structure that passes through the ring structure of the cyclic molecule, and a blocking group that inhibits the cyclic molecule from being released.
The linear structure may be a linear polymer, etc. The linear structure may have a branched structure as long as the movement of the cyclic molecules is not hindered.
Specific examples of the linear polymer include vinyl polymers such as polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, and vinyl chloride-vinyl acetate copolymers; acrylic polymers such as poly(meth)acrylic acid, poly(meth)acrylamide, polymethyl(meth)acrylate, and acrylonitrile-methyl acrylate copolymers; cellulose polymers such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; polyethers such as polyethylene oxide, polyethylene glycol, polypropylene glycol, and polyacetal; Examples of the polyolefin include polyolefins such as polypropylene and polyolefins such as nylon; polyamides such as nylon; polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and other polystyrenes; polysiloxanes such as polydimethylsiloxane; polydienes such as polyisoprene and polybutadiene; polyesters, polyamines, polyimides, polyanilines, polyurethanes, polycarbonates, polyethyleneimines, casein, gelatin, and starch; polysulfones, polyimines, polyacetic anhydrides, polyureas, polysulfides, polyphosphazenes, polyketones, polyphenylenes, polyhaloolefins, and derivatives thereof.
From the standpoint of the stability of the linear molecule and the toughness of the cured product, the linear structure is preferably polyethylene glycol, polyisoprene, polyisobutylene, polybutadiene, polypropylene glycol, polytetrahydrofuran, polydimethylsiloxane, polyethylene, polypropylene, polyvinyl alcohol, or polyvinyl methyl ether, more preferably polyethylene glycol, polypropylene glycol, polytetrahydrofuran, polydimethylsiloxane, polyethylene, or polypropylene, and among these, polyethylene glycol is even more preferable.

The blocking group may be appropriately selected from substituents that are bulkier than the opening of the cyclic molecule. Specific examples of the blocking group include aryl groups such as phenyl, naphthyl, and pyrenyl; alkyl groups having an aryl group as a substituent, such as trityl; cyclic alkyl groups such as adamantyl; known compounds having a condensed ring, such as fluoresceins and steroids, and cyclodextrins. These blocking groups may further have a substituent. Examples of the substituent include alkyl groups, oxyalkyl groups, hydroxy groups, cyano groups, sulfonyl groups, carboxy groups, amino groups, aryl groups, and halogen atoms.
In the polyrotaxane (C), from the viewpoint of molecular stability, the blocking group is preferably a dinitrophenyl group, an adamantyl group, a trityl group, a pyrenyl group, a fluorescein, or a cyclodextrin, and more preferably an adamantyl group or a trityl group.
In addition, the blocking groups present in the linear molecule may be the same or different, but from the viewpoint of ease of synthesis, it is preferable that the blocking groups are the same substituents.

The molecular weight of the linear molecule may be adjusted as appropriate depending on the number of cyclic molecules contained in the polyrotaxane (C) and the range of motion required for the cyclic molecules. The weight average molecular weight of the linear molecule may be adjusted, for example, in the range of 1,000 to 1,000,000, preferably 2,000 to 500,000, and more preferably 3,000 to 200,000.

The number of functional groups per polyrotaxane (C) may be adjusted appropriately depending on the molecular weight of the linear molecule, the number of cyclic molecules, the physical properties required for the cured product, and the like. When the cyclic molecules are compounds derived from cyclodextrin, the modification rate (= number of functional groups/number of reactive hydroxyl groups (hydroxyl value) of the raw polyrotaxane × 100 [%]) can be adjusted as a guide. The number of reactive hydroxyl groups of the raw polyrotaxane is the number of reactive hydroxyl groups of the polyrotaxane before the functional groups are introduced, and is given as a hydroxyl value mgKOH/g that is known in the art. For example, the commercially available product, CELMS Super Polymer SH1300P of CELMS Super Polymer of ASM Co., Ltd., has a hydroxyl value of 85 mgKOH/g and has 1.52 mmol of reactive hydroxyl groups per 1 g of the polyrotaxane. The above modification rate can be calculated as an average value using NMR. In this polyrotaxane (C), the average modification rate is preferably 1 to 99%, more preferably 1 to 80%, and even more preferably 1 to 70%.

Polyrotaxane (C) may be synthesized, for example, by the method described below or the method described in International Publication No. 2011/105532, or a commercially available product may be used. Examples of commercially available products include the Selm Super Polymer series from ASM Corporation.

<Method of producing polyrotaxane-coated carbon fiber>
The method for producing the coated carbon fiber will be described with an example. First, carbon fiber (A) is prepared. The carbon fiber (A) may be a commercially available product and may be washed or dispersed as necessary. It is preferable to disperse the carbon fiber (A) in a solvent. Examples of the solvent include water; alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, propyl acetate, and butyl acetate; ethers such as ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether, and ethylene glycol monomethyl ether; tetrahydrofuran, toluene, xylene, chloroform, N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, dimethylacetamide, dimethylsulfoxide, cyclohexane, and silicone oil, and cationic, anionic, amphoteric, or nonionic surfactants may be combined. The solvent may be used alone or in a mixture of two or more types.

Also, a compound (B) having two or more oxazolyl groups in one molecule is prepared. The ratio of compound (B) is appropriately adjusted depending on the application, material, etc., but from the viewpoint of obtaining a carbon fiber composite material having high breaking strength and excellent elongation performance, it is preferable to adjust the coating amount of compound (B) to be 0.1 to 100 mg/ ^m2 , and more preferably 0.1 to 80 mg/ ^m2 , relative to the surface area of carbon fiber (A).

Methods for reacting carbon fiber (A) with compound (B) include (1) a method in which the carbon fiber (A) and compound (B) are mixed in a solvent and dispersed while being heated, thereby contacting the carbon fiber (A) with compound (B) and causing a reaction; and (2) a method in which the carbon fiber (A) and compound (B) are mixed in a solvent, and then a composite in which compound (B) is attached to the carbon fiber (A) is taken out from the dispersion liquid, and the composite is heated to cause a reaction.

In the above method (1), the heating temperature varies depending on the structure of compound (B), etc., but is preferably 40 to 200°C, more preferably 60 to 180°C. In this method, the dispersion of carbon fiber (A) and the adhesion reaction with compound (B) proceed simultaneously, so it is more preferable to use a stirring device with a mixing effect, an ultrasonic cleaner, a bead mill disperser, etc. The required processing time varies depending on the dispersion method, device, and temperature, but can be appropriately adjusted within the range of 10 minutes to 10 hours. The obtained surface-modified carbon material may be used in the next step while still dispersed in the dispersion liquid, or may be removed from the dispersion liquid and left in a wet state or dried.

In the above method (2), a dispersion treatment is first performed. The dispersion treatment can be performed, for example, at a temperature of -20 to 40°C for 10 minutes to 10 hours. The carbon fibers to which the compound (B) is attached are removed from the obtained dispersion liquid and dried. Next, the carbon fibers are heated (calcined) to react with the carbon fibers (A) and the compound (B). The carboxyl groups and phenolic hydroxyl groups on the carbon fiber surface are reacted with the oxazolyl groups of the compound (B) to obtain a surface-modified carbon material. The heating temperature during calcination is, for example, 80 to 240°C, preferably 100 to 220°C, and more preferably 120 to 200°C. By setting the calcination temperature to 240°C or less, the thermal decomposition and oxidation of the compound (B) can be suppressed. The surface-modified carbon material produced by this method is a solid material, and may be used in the next step in the solid form or may be redispersed.

One example of a method for reacting compound (B) with polyrotaxane (C) is to heat a carbon fiber coated with compound (B) while it is infiltrated with a solution of polyrotaxane (C). This method allows for an even coating of polyrotaxane (C).

[Carbon fiber composite material]
The carbon fiber composite material according to the present invention (hereinafter, sometimes referred to as the present carbon fiber composite material) is characterized by containing the above-mentioned polyrotaxane-coated carbon fiber and a resin (D). The present carbon fiber composite material has high breaking strength and excellent elongation performance.

<Resin (D)>
Resin (D) is a matrix resin that is usually impregnated into the polyrotaxane-coated carbon fiber. Resin (D) can be appropriately selected depending on the application of the carbon fiber composite material, and may be a thermoplastic resin or a thermosetting resin.
Examples of thermoplastic resins include polyolefins such as polyethylene and polypropylene; polyamides such as nylon 6 and nylon 66; polystyrene, acrylonitrile-butadiene-styrene copolymers; and poly(meth)acrylic acid-based resins.
Examples of the thermosetting resin include unsaturated polyester resin, vinyl ester resin, epoxy resin, phenol resin, melamine resin, urea resin, thermosetting polyimide resin, cyanate ester resin, and bismaleimide resin.
The resin (D) may be used alone or in combination of two or more kinds.

It is preferable that at least a portion of the resin (D) is chemically bonded to the polyrotaxane (C) of the polyrotaxane-coated carbon fiber (I) or is linked to the polyrotaxane (C) via the crosslinking agent (E) (II).

The resin (D) used in the carbon fiber composite material in which the polyrotaxane (C) and the resin (D) are chemically bonded preferably has a group reactive with the substituent (1) or group (2) of the cyclic molecule of the polyrotaxane (C). As an example, when the cyclic molecule of the polyrotaxane (C) has a carboxy group, the resin (D) preferably has an epoxy group, an amino group, a hydroxyl group, an isocyanate group, an oxazolyl group, or the like.

In addition, when the polyrotaxane (C) and the resin (D) are linked via a crosslinking agent (E), the crosslinking agent (E) preferably has a group reactive with the substituent (1) or group (2) of the cyclic molecule of the polyrotaxane (C). As an example, when the cyclic molecule of the polyrotaxane (C) has a carboxy group, the crosslinking agent (E) preferably has an epoxy group, an amino group, a hydroxyl group, an isocyanate group, an oxazolyl group, or the like.
In addition, the resin (D) preferably has the same type of substituent as the cyclic molecule of the polyrotaxane (C).

The crosslinking agent (E) may have two or more groups in one molecule that are reactive with the substituent (1) or group (2) of the cyclic molecule of polyrotaxane (C). For example, compound (B) may be used, or a known crosslinking agent or curing agent that is generally used in the relevant field for the target resin (D) may be used. When compound (B) is used as the crosslinking agent (E), the preferred embodiment is as described above.

[Prepreg]
The prepreg according to the present invention is characterized by containing the carbon fiber composite material. The prepreg has high breaking strength and excellent elongation performance. The prepreg may be made of the carbon fiber composite material as is, but may contain various additives depending on the application. Examples of additives include antioxidants, light stabilizers, ultraviolet absorbers, and fillers such as rubber particles and inorganic particles.

The filler may be appropriately selected from known fillers, and suitable examples include insulating fillers such as aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, and boron nitride, and conductive fillers such as gold, silver, copper, nickel, aluminum, carbon, and graphite.

The carbon fiber composite and the prepreg can be produced, for example, by a wet method in which the resin (D) is dissolved in a solvent to reduce the viscosity, and the crosslinking agent (E) and the additives are added as necessary, and the polyrotaxane-coated carbon fiber is impregnated with the resin, or a hot melt method in which the resin (D) is heated to reduce the viscosity, and the polyrotaxane-coated carbon fiber is impregnated with the resin.

This carbon fiber composite and this prepreg can be suitably used, for example, as housings for electronic devices, components for aircraft and automobiles, blades for wind turbines, etc.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[Production of polyrotaxane (C)]
Production Example 1: Step of introducing carboxyl group into polyrotaxane (3%)
10.0 g of polyrotaxane (SH2400P, hydroxyl value 76 mgKOH/g) and 40.7 mg of succinic anhydride (Tokyo Chemical Industry Co., Ltd.) were dissolved in 60 mL of ethyl acetate (Kanto Chemical Co., Ltd.), and after 0.5 hours of nitrogen bubbling, 71.6 mg of triethylamine (Tokyo Chemical Industry Co., Ltd.) dissolved in 2.0 mL of ethyl acetate (Kanto Chemical Co., Ltd.) was added as a base, and the mixture was stirred for 24 hours at 70° C. under a nitrogen atmosphere. The solvent was distilled off from the reaction solution under reduced pressure to obtain a crude compound of carboxy-modified polyrotaxane.

Production Example 2: Step of introducing carboxyl group into polyrotaxane (5%)
10.0 g of polyrotaxane (SH2400P, hydroxyl value 76 mgKOH/g, manufactured by ASM Co., Ltd.) and 67.8 mg of succinic anhydride were dissolved in 58 mL of ethyl acetate, and after bubbling with nitrogen for 0.5 hours, a solution of 00 mg of triethylamine in 2.0 mL of ethyl acetate was added as a base, and the mixture was stirred for 24 hours at 70° C. under a nitrogen atmosphere. The solvent was distilled off from the reaction solution under reduced pressure to obtain a crude carboxy-modified polyrotaxane compound.

Production Example 3: Step of introducing carboxyl group into polyrotaxane (5%)
10.0 g of polyrotaxane (ASM Corporation: SC1300P, hydroxyl value 43 mgKOH/g) and 38.3 mg of succinic anhydride were dissolved in 58 mL of ethyl acetate, and after bubbling with nitrogen for 0.5 hours, a solution of 77.5 mg of triethylamine in 2.0 mL of ethyl acetate was added as a base, and the mixture was stirred for 24 hours at 70° C. under a nitrogen atmosphere. The solvent was distilled off from the reaction solution under reduced pressure to obtain a crude carboxy-modified polyrotaxane compound.

Production Example 4: Step of introducing carboxyl group into polyrotaxane (5%)
10.0 g of polyrotaxane (SH1300P, hydroxyl value 84 mgKOH/g, manufactured by ASM Co., Ltd.) and 74.9 mg of succinic anhydride were dissolved in 58 mL of ethyl acetate, and after bubbling with nitrogen for 0.5 hours, a solution of 151.5 mg of triethylamine dissolved in 2.0 mL of ethyl acetate was added as a base, and the mixture was stirred for 24 hours at 70° C. under a nitrogen atmosphere. The solvent was distilled off from the reaction solution under reduced pressure to obtain a crude compound of carboxy-modified polyrotaxane.

Production Example 5-1: Purification of crude carboxy-modified polyrotaxane 1.0 g of the crude carboxy-modified polyrotaxane prepared in Production Example 1 was dissolved in 2.0 mL of 1,4-dioxane (Kanto Chemical Co., Ltd.), and 0.05 mL of 1N hydrogen chloride diethyl ether solution (Tokyo Chemical Industry Co., Ltd.) was added dropwise to neutralize the base used in the reaction, and 6 to 15 ml of methanol (Kanto Chemical Co., Ltd.) was added under cooling until a white precipitate was formed, to obtain a white precipitate of the target compound. The target compound isolated by centrifugation was dissolved again in 2 mL of 1,4-dioxane, washed successively with 10 mL of ion-exchanged water and 6 to 15 mL of methanol, and then separated into solid and liquid by centrifugation. The obtained white solid was dried under reduced pressure to obtain 0.4 g of the target carboxy-modified polyrotaxane. The introduction rate of the introduced carboxy group was determined by NMR, and it was confirmed that it was introduced at 2.4% with respect to the hydroxyl value of the raw material.

Production Examples 5-2 to 5-4: Purification of Crude Carboxy-Modified Polyrotaxane [0213] The crude carboxy-modified polyrotaxane was purified in the same manner as in Production Example 5-1, except that the crude carboxy-modified polyrotaxane of Production Example 1 was replaced with the crude carboxy-modified polyrotaxanes of Production Examples 2 to 4, respectively.

[Production of Compound (B) Having Two or More Oxazolyl Groups in One Molecule]
Production Example 6: Process for synthesizing poly 2-vinyl-2-oxazoline (Pvozo) 10.0 g of vinyloxazoline (KJ Chemicals Co., Ltd.) and 0.169 g of azoisobutyronitrile (Kanto Chemical Co., Ltd.) were dissolved in 56.7 g of N,N-dimethylformamide (Kanto Chemical Co., Ltd.) in a 100 mL three-neck flask equipped with a reflux condenser, and after 1 hour of nitrogen bubbling, the mixture was stirred at 70°C for 6 hours. The progress of the reaction and the polymerization rate were calculated using NMR (86.5%). 1200 mL of diethyl ether (Kanto Chemical Co., Ltd.) was added to the reaction solution to obtain 5.3 g of the target compound as a white precipitate.

[Coating of compound (B)]
Production Example 7: Process of coating carbon fiber with polyvinyloxazoline The poly(2-vinyl-2-oxazoline) synthesized in Production Example 6 was dissolved in propylene glycol monomethyl ether (Kanto Chemical Co., Ltd.) to 1.0 wt%, and this was added to carbon fiber (Toray Industries, Inc.: T700, desized) cut to 9 cm in size, about 0.1 g, so that the entire fiber was immersed. After heating this in an oil bath at 100°C for 3 hours, the excess poly(2-vinyl-2-oxazoline) was washed five times with 10 mL of methanol for 2 minutes. The obtained poly(2-vinyl-2-oxazoline-coated carbon fiber was dried at 100°C for 10 minutes to obtain the desired poly(2-vinyl-2-oxazoline-coated carbon fiber.

[Production of polyrotaxane-coated carbon fibers]
Example 1: Process of coating polyvinyloxazoline-coated carbon fiber with carboxyl-modified polyrotaxane The 2-vinyl-2-oxazoline-coated carbon fiber prepared in Production Example 7 was infiltrated with a polyrotaxane solution in which 50 mg of the carboxyl-modified polyrotaxane obtained through Production Examples 1 and 5-1 was dissolved in 10 g of propylene glycol monomethyl ether. After heating this for 3 hours at 100°C in an oil bath, the excess carboxyl-modified polyrotaxane was washed five times for 2 minutes with 10 mL of acetone (Kanto Chemical Co., Ltd.). The obtained coated carbon fiber was dried for 10 minutes at 100°C to obtain a poly2-vinyl-2-oxazoline-coated carbon fiber (also referred to as the polyrotaxane-coated carbon fiber of Example 1) coated with the desired carboxyl-modified polyrotaxane.

Examples 2 to 4: Production of polyrotaxane-coated carbon fibers Polyrotaxane-coated carbon fibers of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the carboxy group-modified polyrotaxane in Example 1 was changed to the carboxy group-modified polyrotaxanes obtained via Production Examples 2 to 4 and Production Examples 5-2 to 5-4, respectively.

[Manufacturing of carbon fiber composite materials]
Example 5: Process for preparing carbon fiber-reinforced polypropylene composite material using polyrotaxane-coated carbon fiber 0.2 g of the polyrotaxane-coated carbon fiber of Example 1 was melt-kneaded with 1.746 g of polypropylene (Japan Polypropylene Corporation), 0.054 g of Ma-g-PP (product name: UMEX 1001, Sanyo Chemical Industries, Ltd.), and 0.010 g of Pvozo synthesized in Production Example 6 in a twin-screw kneader (Labo Plastomill μ, a batch-type twin-screw kneader manufactured by Toyo Seiki Seisakusho) at 200°C, 60 rpm, and 10 minutes to form pellets.
The prepared composite pellets were crushed to 2 mm mesh, and this was filled into a mold for preparing dumbbell-shaped test specimens with handles on both sides extended by 5 mm in accordance with JIS K6251-7. The molded specimens were then preheated at 200°C for 5 minutes and press molded at 5 MPa at 200°C for 5 minutes. The molded specimens were then quenched at 5 MPa for 2 minutes to prepare a carbon fiber composite material (also referred to as the carbon fiber composite material of Example 5).

Examples 6 to 8: Production of carbon fiber composite materials Carbon fiber composite materials of Examples 6 to 8 were obtained in the same manner as in Example 5 above, except that the polyrotaxane-coated carbon fiber of Example 1 was changed to the polyrotaxane-coated carbon fiber of Examples 2 to 4, respectively.

Comparative Example 1: Process for preparing a carbon fiber reinforced polypropylene composite material using carbon fiber 0.378 g of carbon fiber (Toray Industries, Inc.: T700, desized) was melt-kneaded with a resin consisting of 3.3 g of polypropylene and 0.1 g of maleic anhydride modified polypropylene (Ma-g-PP) (product name: UMEX 1001, Sanyo Chemical Industries, Ltd.) at a ratio of 10 wt% at 200°C, 60 rpm, and 10 minutes in a twin-screw kneader, and this was made into pellets. The prepared composite pellets were crushed to 2 mm mesh, filled into a mold for preparing dumbbell-shaped test pieces similar to those in Example 5, preheated at 200°C for 5 minutes, and then press-molded at 5 MPa, 200°C, for 5 minutes, and then quenched at 5 MPa for 2 minutes to prepare a carbon fiber composite material of Comparative Example 1.

Comparative Example 2: Process for preparing a carbon fiber reinforced polypropylene composite material using carbon fiber 0.378 g of the 2-vinyl-2-oxazoline-coated carbon fiber prepared in Production Example 7 was melt-kneaded for 10 minutes at 200°C, 60 rpm in a twin-screw kneader so that the ratio was 10 wt% with respect to a resin consisting of 3.3 g of polypropylene and 0.1 g of Ma-g-PP, and this was made into pellets. The prepared composite pellets were crushed to 2 mm mesh, and filled into a mold for preparing a dumbbell-shaped test piece similar to that in Example 5, and then preheated at 200°C for 5 minutes, and then press-molded at 5 MPa, 200°C, for 5 minutes, and then quenched at 5 MPa for 2 minutes to prepare a carbon fiber composite test piece of Comparative Example 2.

Example 9: Process for preparing a carbon fiber reinforced polyacrylic acid composite material using polyrotaxane-coated carbon fiber 0.24 g of the carbon fiber (SH1300P-05 coated) prepared in Example 1 was melt-kneaded with 2.16 g of ethylene-methacrylic acid copolymer resin (EMAA) (product name: Nucrel AN4233C, Mitsui Dow Polychemical Co., Ltd.) and 0.6059 g of Pvozo synthesized in Production Example 6 at 200 ° C., 60 rpm, 10 minutes in a twin-screw kneader, and this was made into a pellet. The prepared composite pellet was crushed to a 2 mm mesh, filled into a mold for preparing a dumbbell-shaped test piece similar to that in Example 5, preheated at 200 ° C. for 5 minutes, then press-molded at 5 MPa, 200 ° C., for 5 minutes, and then quenched at 5 MPa for 2 minutes to prepare a carbon fiber composite material of Example 9.

Comparative Example 3: Process for preparing a carbon fiber reinforced polyacrylic acid composite material using carbon fiber 0.24 g of carbon fiber (Toray Industries, Inc.: T700, desized) was melt-kneaded with 2.16 g of ethylene-methacrylic acid copolymer resin (EMAA) (product name: Nucrel AN4233C, Mitsui Dow Polychemical Co., Ltd.) and 0.6059 g of Pvozo synthesized in Production Example 6 at 200 ° C., 60 rpm, 10 minutes in a twin-screw kneader to prepare pellets. The prepared composite pellets were crushed to 2 mm mesh, filled into a mold for preparing a dumbbell-shaped test piece similar to that in Example 5, preheated at 200 ° C. for 5 minutes, then press-molded at 5 MPa, 200 ° C. for 5 minutes, and quenched at 5 MPa for 2 minutes to prepare a carbon fiber composite material of Comparative Example 3.

[evaluation]
For each of the carbon fiber composite materials of Examples 5 to 9 and Comparative Examples 1 to 3, a dumbbell-shaped tensile test piece was produced with reference to JIS K 7139:2009, and a tensile test was performed at a displacement rate of 10 mm/min to measure the tensile modulus, breaking strength, breaking elongation, and stress-strain curve.
The area under the strain curve refers to the value obtained by integrating the area of the stress-strain curve over the section up to breakage, and indicates the energy required for breakage. The area under the strain curve ratio is the ratio of the area under the strain curve of each example to Comparative Example 2 (area under the strain curve is 100%) for Examples 5 to 8 and Comparative Examples 1 to 2 in which the resin (D) contains polypropylene, and is similarly the ratio of the area under the strain curve of each example to Comparative Example 3 in which the resin (D) contains polyacrylic acid. The larger the area under the strain curve, the more excellent the toughness can be evaluated. The results are shown in Table 1, representing Examples 7 and 9.

In comparison with Comparative Example 1, which used carbon fiber that was not coated with either polyrotaxane or Pvozo, the carbon fiber of Comparative Example 2, which was coated only with Pvozo, had increased tensile modulus and breaking strength, but a smaller area under the strain curve and reduced energy required to break.
In contrast, the carbon fiber composite of Example 7, which used the polyrotaxane-coated carbon fiber of the present invention in which the carbon fiber was successively coated with Pvozo and polyrotaxane, showed improved tensile modulus and breaking strength compared to Comparative Example 1, and further showed an increased area under the strain curve and improved toughness.
A feature of the carbon fiber interface design according to the present invention is that chemical bonds are formed via Pvozo to functional groups on the carbon fiber surface, to which polyrotaxane has previously had difficulty forming chemical bonds, without restricting the axial movement of the cyclic molecules. This suppresses peeling at the fiber-resin interface that is expected to occur when an external force is applied to a carbon fiber reinforced composite material, and is presumably absorbing this force, thereby improving various physical properties.
A comparison of Comparative Example 1 and Comparative Example 2 shows that simply coating carbon fibers with Pvozo not only does not provide a significant effect on both breaking strength and elongation, but also tends to reduce the energy required to break the fibers. This suggests that appropriately arranging polyrotaxane at the interface leads to improved physical properties.
Similarly, in the carbon fiber composite material (Example 9) in which the resin (D) contained polyacrylic acid, the area under the strain curve was 1.3 times that of Comparative Example 3.
When a low modulus material is reinforced with carbon fiber, a remarkable increase in modulus is usually observed. However, with the polyrotaxane-coated carbon fiber of the present invention, it is possible to improve the breaking energy while maintaining low modulus, and it is believed that the strength can be improved without compromising currently required physical properties.

Claims (10)

The present invention relates to a method for producing a composite material comprising: a carbon fiber (A); a compound (B) having two or more oxazolyl groups in one molecule; and a polyrotaxane (C) having a cyclic molecule,
A chemical bond is formed between the carbon fiber (A) and a part of the oxazolyl group of the compound (B),
A polyrotaxane-coated carbon fiber having a chemical bond between a cyclic molecule of the polyrotaxane (C) and a part of the oxazolyl group of the compound (B). The polyrotaxane-coated carbon fiber according to claim 1, wherein the compound (B) is a polymer or copolymer containing a structural unit derived from 2-vinyl-2-oxazoline. The polyrotaxane-coated carbon fiber according to claim 1 or 2, wherein at least one of the cyclic molecules of the polyrotaxane (C) has a functional group reactive with an oxazolyl group. The polyrotaxane-coated carbon fiber according to claim 3, wherein the functional group reactive with the oxazolyl group is an acidic group. The polyrotaxane-coated carbon fiber according to claim 3 or 4, wherein the functional group reactive with the oxazolyl group includes one or more selected from a carboxy group, a thiol group, a phenolic hydroxyl group, and a group having an acid anhydride structure. A carbon fiber composite material comprising the polyrotaxane-coated carbon fiber according to any one of claims 1 to 5 and a resin (D). The carbon fiber composite material according to claim 6, which has a chemical bond between the polyrotaxane (C) and the resin (D). The polyrotaxane-coated carbon fiber according to any one of claims 1 to 5, a resin (D), and a crosslinking agent (E),
A carbon fiber composite material, in which the polyrotaxane (C) and the resin (D) are bonded via a crosslinking agent (E). The carbon fiber composite material according to claim 8, wherein the resin (D) has an acidic group, and the crosslinking agent (E) contains a compound having two or more oxazolyl groups in one molecule. A prepreg comprising the carbon fiber composite material according to any one of claims 6 to 9.