JP7260379B2 - Polyacrylonitrile-based copolymer, carbon fiber precursor fiber, method for producing carbon fiber precursor fiber, and method for producing carbon fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyacrylonitrile-based copolymer used for carbon fiber precursor fibers. More particularly, it relates to a polymer composition comprising a polyacrylonitrile-based copolymer having at least an acrylonitrile component and a vinyl-based monomer component having a metalloid atom.

Carbon fiber has excellent mechanical properties, particularly high specific strength and high specific modulus, and is therefore widely used as a reinforcing material for various reinforcing materials such as those related to aerospace, leisure goods, and industrial materials. In addition, due to its excellent mechanical properties, it is expected to reduce the weight of automobiles, etc., and is attracting attention as a part of the increasingly serious problem of reducing carbon dioxide.

Carbon fibers are produced by subjecting fibers prepared from an organic polymer, which is a precursor, to a flameproofing treatment in the presence of oxygen, followed by carbonization. Examples of precursors include cellulose, phenolic resin, polyvinyl alcohol, vinylidene chloride, pitch, polyacrylonitrile (hereinafter sometimes simply referred to as PAN), and the like. It has excellent mechanical properties such as strength and specific elastic modulus, and can be manufactured in a stable manner with uniform quality and performance, so it is mass-produced industrially. Further cost reduction and higher performance are important for the development of its applications.

PAN-based fibers, which are carbon fiber precursor fibers, are generally produced by a wet spinning method or a dry-wet spinning method. In order to reduce the manufacturing cost of carbon fibers, it is required to improve the spinning speed of PAN-based fibers, which are precursor fibers. In order to improve the fiber spinning speed, it is effective to raise the processing temperature in the drying process and the drawing process of the yarn. However, PAN, which is used as a carbon fiber precursor, has low thermal stability, and it has been difficult to improve the yarn drying speed and drawing speed by raising the heat treatment temperature. Therefore, many techniques have been proposed.

For example, for the purpose of speeding up the stretching process, a steam stretching apparatus and its processing method (for example, Patent Document 1) have been proposed, but the thermal stability of PAN remains low and the drying process can be speeded up. It is difficult. Also, a technique for improving the thermal stability of the dope solution has been proposed (for example, Patent Document 2). remains low and it is difficult to increase the spinning speed.

On the other hand, Patent Document 3 proposes imparting a boron compound to precursor fibers in order to improve the productivity of carbon fibers. It was still difficult to obtain sufficient productivity without dispersing to

JP 2016-17229 A JP-A-8-246230 JP-A-3-174019

The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve excellent thermal stability, enable improvement of the heat treatment temperature, and achieve both productivity and quality of carbon fiber precursor fibers. An object of the present invention is to provide a polyacrylonitrile-based copolymer capable of

The inventors of the present application have made intensive studies to solve the above problems, and found that a polyacrylonitrile-based copolymer having a vinyl-based monomer component having a metalloid atom other than carbon exhibits sufficient thermal stability, and carbon The inventors have found that it is suitable as a polymer composition for fiber production, etc., and have completed the present invention.

The polyacrylonitrile-based copolymer of the present invention is a polyacrylonitrile-based copolymer having at least an acrylonitrile-based monomer and a vinyl-based monomer having a metalloid atom other than carbon as copolymer components, and the polyacrylonitrile-based copolymer It is a polyacrylonitrile-based copolymer containing 0.01% by mass or more and less than 0.08% by mass of metalloid atoms in the polymer relative to the total amount of the polyacrylonitrile-based copolymer.

In the present invention, the vinyl-based monomer having a metalloid atom other than carbon is preferably a vinyl-based monomer having a boron atom as a metalloid atom. More preferably, the component is derived from at least one selected from the group consisting of vinylphenyl boric acid derivatives and allyl boric acid derivatives. The polyacrylonitrile-based copolymer of the present invention preferably further contains at least one selected from the group consisting of itaconic acid, acrylic acid and methacrylic acid as a copolymer component.

The present invention provides a carbon fiber precursor fiber comprising the polyacrylonitrile copolymer of the present invention, a method for producing a carbon fiber precursor fiber comprising a spinning step of spinning a spinning solution containing the polyacrylonitrile copolymer of the present invention, and , includes a method for producing a carbon fiber by carbonizing the carbon fiber precursor fiber of the present invention to obtain a carbon fiber.

Since the polyacrylonitrile-based copolymer of the present invention has sufficient thermal stability, carbon fiber precursor fibers can be obtained with both productivity and quality.

Hereinafter, examples of embodiments for carrying out the present invention will be described, but the present invention is not limited to the following examples.

The polyacrylonitrile-based copolymer of the present invention is a polyacrylonitrile-based copolymer having, as copolymer components, at least an acrylonitrile-based monomer and a vinyl-based monomer having a metalloid atom other than carbon. Here, the copolymer component means a repeating unit derived from each monomer in the molecular chain of the polyacrylonitrile-based copolymer. A metalloid atom refers to an atom in which a single substance has intermediate properties between metallic properties and non-metallic properties, and includes boron, silicon, carbon, and phosphorus atoms. In the present invention, hereinafter, metalloid atoms refer to metalloid atoms other than carbon unless otherwise specified. A vinyl-based monomer component having a metalloid atom other than carbon refers to a repeating unit derived from a vinyl-based monomer having a metalloid atom in its molecular structure. In the present invention, a boron atom is preferable as the metalloid atom used in the vinyl-based monomer having a metalloid atom.

Furthermore, the polyacrylonitrile-based copolymer of the present invention contains 0.01% by mass or more and less than 0.08% by mass of metalloid atoms in the polyacrylonitrile-based copolymer based on the total amount of the polyacrylonitrile-based copolymer. . In the present invention, the proportion of metalloid atoms in the copolymer is determined by proton nuclear magnetic resonance ( ¹ H-NMR) measurement, unless otherwise specified. It means the content calculated from the ratio of

By containing metalloid atoms within this range, the thermal stability of PAN is improved, and carbon fiber precursor fibers can be obtained with good productivity. If the metalloid atom content in the polyacrylonitrile-based copolymer is too high, a longer time or a higher temperature is required for flame resistance during the production of the carbon fiber, and productivity tends to decrease. On the other hand, if the metalloid atom content in the polyacrylonitrile-based copolymer is too low, the thermal stability of PAN will be insufficient, and the productivity of carbon fiber precursor fibers will tend to decrease. More preferably, the metalloid atom content is 0.01% by mass or more and less than 0.05% by mass.

In the present invention, the proportion of the acrylonitrile component in the polyacrylonitrile copolymer is preferably 90% by mass or more. When the acrylonitrile component is in this range, the yield of carbon fibers in the carbonization treatment is high, and the mechanical properties of the obtained carbon fibers are improved, so that high-quality carbon fibers can be obtained with good productivity. .

The proportion of the acrylonitrile component in the polyacrylonitrile-based copolymer is preferably 90 to 99.5% by mass, more preferably 94 to 99.5% by mass.

The vinyl-based monomer having a metalloid atom in the polyacrylonitrile-based copolymer is not particularly limited as long as it is a monomer having a carbon=carbon double bond and a metalloid atom in the molecule. A vinyl-based monomer containing at least one selected from atoms is preferred, and a vinyl-based monomer containing a boron atom is particularly preferred.

The vinyl-based monomer containing a boron atom is not particularly limited, but at least one selected from the group consisting of vinyl boric acid, vinyl phenyl boric acid, allyl boric acid, vinyl boric acid derivatives, vinyl phenyl boric acid derivatives, and allyl boric acid derivatives. Or it is preferable to use a combination thereof. Examples of boric acid derivatives include boric acid esters and boric acid amides.

Specific examples of such vinyl monomers containing boron atoms include 4-vinylphenyl boric acid, 4-vinylphenyl boric acid diethyl ester, 4-vinylphenyl boric acid pinacol ester, and 4-vinylphenyl boric acid dibutyl ester. , 2-vinylphenyl borate, vinyl borate, allyl borate, vinyl borate diethyl ester, vinyl borate pinacol ester, allyl borate diethyl ester, allyl borate pinacol ester, etc., of which one or a combination thereof may be used. can do.

The copolymerization composition ratio of the vinyl-based monomer component containing metalloid atoms in the polyacrylonitrile-based copolymer can be controlled by the reaction charge ratio, and the greater the reaction charge ratio, the larger the polymerization composition ratio. However, the copolymerization composition ratio and the reaction charge ratio do not necessarily match. In particular, when a vinyl monomer containing a boron atom is used, in the range where the reaction charge ratio of the vinyl monomer containing a boron atom in the monomer component is 0.5% by mass or less, the amount of the vinyl boron monomer component as a copolymerization composition ratio tends to be greater than or equal to the reaction charge ratio.

The copolymerization monomer that leads to the copolymerization component other than the acrylonitrile component and the vinyl-based monomer component containing a metalloid atom in the polyacrylonitrile-based copolymer is not particularly limited, and a known copolymerizable polymerizable unsaturated compound is used. be able to. Examples of such components include unsaturated carboxylic acids, unsaturated carboxylic acid esters, unsaturated carboxylic acid amides, aromatic vinyl compounds, heterocyclic vinyl compounds, and the like. can be preferably used.

From the viewpoint of carbon fiber productivity, it is preferable to use a polymerizable unsaturated compound having an effect of promoting flame resistance as a copolymerization monomer. Examples of such polymerizable unsaturated compounds include acrylic acid, methacrylic acid, itaconic acid, methyl methacrylate, methyl acrylate, acrylamide, itaconic acid ester, vinyl sulfonic acid, and the like. Or a combination of these can be used. Among these, it is more preferable to use at least one selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid, or a combination thereof.

The proportion of the polymerizable unsaturated compound having the effect of promoting flame resistance in the polyacrylonitrile-based copolymer is preferably 10% by mass or less, more preferably 6% by mass or less.

The method for producing the polyacrylonitrile-based copolymer in the present invention is not particularly limited, and a known polymerization method can be applied, and a free radical polymerization method can be preferably applied.

When performing free radical polymerization, known polymerization methods such as solution polymerization, suspension polymerization and emulsion polymerization can be used. In particular, from the viewpoint of productivity, solution polymerization or suspension polymerization is preferred. Polymerization initiators and catalysts used for radical polymerization are not particularly limited, and examples thereof include azo compounds, organic peroxides, redox catalysts such as persulfuric acid/sulfuric acid, chloric acid/sulfuric acid, or sodium salts or ammonium salts thereof. . When using a redox initiator, a catalyst and a pH adjuster can be added as appropriate in order to allow the redox reaction to proceed efficiently.

When solution polymerization is carried out, a known solvent such as an aqueous solution of zinc chloride, dimethylsulfoxide, dimethylformamide and the like can be used as a polymerization solvent. In particular, an aqueous solution of zinc chloride or dimethylsulfoxide is desirable because it causes less side reactions.

Since the polyacrylonitrile-based copolymer of the present invention thus obtained has sufficient thermal stability, carbon fiber precursor fibers and carbon fibers can be obtained with both productivity and quality.

Carbon fiber precursor fibers and carbon fibers using the polyacrylonitrile-based copolymer of the present invention are not particularly limited, but can be produced, for example, by the following method.

<Precursor fiber>
Carbon fiber precursor fibers can be produced by spinning a spinning solution containing the polyacrylonitrile-based copolymer of the present invention. The spinning method is not particularly limited, but wet spinning or dry-wet spinning is preferred.

Precursor fibers are obtained by washing, drying, drawing, and oiling the spun raw material fibers. The treatment temperature in these treatment steps is not particularly limited, but from the viewpoint of productivity, the heat treatment (drying treatment and/or stretching treatment) is preferably performed at a temperature of 180° C. or higher. The number of filaments of the precursor fiber is preferably 1,000 or more, more preferably 12,000 or more, and even more preferably 24,000 or more, in terms of production efficiency.

<Flame resistant treatment>
The obtained precursor fiber is heated in heated air at 200 to 300° C. for 10 to 100 minutes to be flameproofed. In the flameproofing treatment, the precursor fiber is preferably drawn at a draw ratio of 0.90 to 1.20.

<Carbonization treatment>
A carbon fiber can be obtained by carbonizing the flame-resistant precursor fiber at 300 to 2000°C. In order to obtain a carbon fiber bundle having a denser internal structure with higher tensile strength, a two-step carbonization process is carried out in which low-temperature carbonization is performed at 300 to 1,000°C and then high-temperature carbonization is performed at 1,000 to 2,000°C. It is preferable to carry out a carbonization treatment. If a higher modulus of elasticity is required, the graphitization treatment may be further carried out at a high temperature of 2000 to 3000°C.

<Surface oxidation treatment>
The carbon fibers obtained above are preferably subjected to a surface treatment in order to improve wettability with the sizing agent and the matrix resin. The surface treatment can be performed by any conventionally known method, but electrolytic oxidation is generally used industrially because the equipment is simple and the process is easy to manage.

<Sizing treatment>
The carbon fibers thus obtained are preferably subjected to a sizing treatment with a sizing agent.

The polyacrylonitrile-based copolymer of the present invention has sufficient thermal stability. When manufactured, carbon fibers can be obtained with both productivity and quality.

Using the carbon fiber thus obtained, it is combined with a matrix resin such as a thermosetting resin or thermoplastic resin, for example, by known means and methods such as autoclave molding, press molding, resin transfer molding, and filament winding molding. A composite material is obtained. The carbon fiber reinforced composite material obtained in this manner is low cost and has high performance, so it is preferably used as a reinforcing material for various reinforcing materials such as automobile applications, aerospace applications, leisure goods and industrial materials.

Hereinafter, the method of the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by these examples.

〔Measuring method〕
<Copolymer composition>
The composition ratio of each component in the copolymer was obtained by the following method.
The vinylphenylboric acid copolymerization ratio was calculated by ¹ H-NMR measurement. An NMR apparatus (manufactured by JEOL Ltd., JNM-ECA600) was used as the measurement apparatus, and deuterated dimethyl sulfoxide was used as the measurement solvent.

The itaconic acid copolymerization ratio was calculated by neutralization titration measurement. As a measuring device, an automatic potentiometric titrator (916Ti-touch manufactured by Metrohm) was used. In the measurement, the polymer was dissolved in dimethylformamide, and an ethanol solution of potassium hydroxide was used as the titrant.

<Weight average molecular weight of copolymer>
The weight average molecular weight of the copolymer was obtained by gel permeation chromatography (GPC) measurement. A GPC measuring device (GPC101 manufactured by Showa Denko KK) was used as a measuring device. TSK gel α-M (manufactured by Showa Denko KK) was used as the column, and a differential refractive index detector (Shodex RI-71S, manufactured by Showa Denko KK) was used as the detector. Dimethylformamide was used as a mobile phase, and lithium bromide was added as an eluent so as to be 10 mM. Polystyrene was used as a standard substance.

<Thermal Properties of Polymer>
Thermal properties of the polymers were evaluated by differential scanning calorimetry (DSC measurements). A differential scanning calorimeter (DSC Q2000, manufactured by TA Instruments) was used as a measuring device. In the measurement, 5 holes with a diameter of 0.5 mm were made in the upper lid of the aluminum pan, and the temperature was raised from 30°C to 400°C at 10°C/min under the inflow of air (20 ml/min). The exothermic start temperature of the exothermic peak was taken as the measured value t0, the peak top temperature of the first peak was taken as the measured value t1, and the peak top temperature of the second peak was taken as the measured value t2.

When t0 is 240° C. or higher and t1 is 265° C. or higher, sufficient thermal stability is exhibited during the production of precursor fibers. Further, when t0 is less than 250°C and t1 is less than 275°C, flameproofing reaction easily occurs, and carbon fibers can be obtained with good productivity.

[Example 1]
A 1 L separable flask was charged with 449.54 parts by mass of ion-exchanged water deoxygenated by nitrogen blowing, 0.05 parts by mass of concentrated sulfuric acid as a pH adjuster, and 0.0005 parts by mass of iron (II) sulfate as a catalyst. . A nitrogen atmosphere was created in the separable flask while stirring, and the separable flask was immersed in a hot water bath adjusted to 50°C. .50 parts by weight was added. After confirming that the internal temperature of the separable flask reached 48° C. or higher, 0.37 parts by mass of a 50% ammonium hydrogensulfite aqueous solution and 0.15 parts by mass of ammonium peroxodisulfate were added as polymerization initiators. A polymerization reaction was carried out by holding the separable flask after the addition at 50° C. for 1 hour. After completion of the reaction, white particles were collected from the reaction mixture by filtration, thoroughly washed with deionized water, and dried in an electric dryer at 70° C. overnight to obtain a copolymer (P-1).

Table 1 shows the composition ratio of each component in the obtained copolymer. Also, the weight average molecular weight obtained by GPC measurement was 481,000.

The obtained polymer (P-1) was dissolved in dimethylsulfoxide, stretched into a thin film, and the solvent was removed to obtain a transparent film (F-1). Table 1 shows the results of DSC measurement of the obtained transparent film (F-1).

[Example 2]
Copolymer (P-2) was prepared by the method described in Example 1, except that 49.36 parts by mass of acrylonitrile, 0.14 parts by mass of p-vinylphenylboric acid, and 0.50 parts by mass of itaconic acid were added as monomers. got Table 1 shows the composition ratio of each component in the obtained copolymer. The weight average molecular weight obtained by GPC measurement was 481,000.

The obtained polymer (P-2) was dissolved in dimethylsulfoxide, stretched into a thin film, and the solvent was removed to obtain a transparent film (F-2). Table 1 shows the results of DSC measurement of the obtained transparent film (F-2).

[Comparative Example 1]
Copolymer (rP-1) was prepared by the method described in Example 1, except that 48.81 parts by mass of acrylonitrile, 0.69 parts by mass of p-vinylphenylboric acid, and 0.50 parts by mass of itaconic acid were added as monomers. got Table 1 shows the composition ratio of each component in the obtained copolymer. The weight average molecular weight obtained by GPC measurement was 594,000.

The resulting polymer (rP-1) was dissolved in dimethylsulfoxide, stretched into a thin film, and the solvent was removed to obtain a transparent film (rF-1). Table 1 shows the results of DSC measurement of the obtained transparent film (rF-1).

[Comparative Example 2]
A copolymer (rP-2) was obtained by the method described in Example 1 except that 49.50 parts by mass of acrylonitrile and 0.50 parts by mass of itaconic acid were added as monomers. Table 1 shows the composition ratio of each component in the obtained copolymer. The weight average molecular weight obtained by GPC measurement was 398,000.

The resulting polymer (rP-2) was dissolved in dimethylsulfoxide, stretched into a thin film, and the solvent was removed to obtain a transparent film (rF-2). Table 1 shows the results of DSC measurement of the obtained transparent film (rF-2).

[Comparative Example 3]
The copolymer (rP-2) obtained in Comparative Example 2 was dissolved in dimethyl sulfoxide by adding 0.6 parts by mass of boric acid to 100 parts by mass of the polymer. The resulting solution was stretched into a thin film, and the solvent was removed to obtain a transparent film (rF-3). Table 1 shows the results of DSC measurement of the obtained transparent film (rF-3).

The polyacrylonitrile copolymers obtained in Examples 1 and 2 were copolymers having sufficient thermal stability to withstand the heat treatment during spinning and a sufficient flame retarding rate in the flame retarding treatment.

Claims (6)

A polyacrylonitrile-based copolymer having at least an acrylonitrile-based monomer and a vinyl-based monomer having a metalloid atom other than carbon as copolymerization components,
Containing metalloid atoms in the polyacrylonitrile-based copolymer in an amount of 0.01% by mass or more and less than 0.08% by mass with respect to the total amount of the polyacrylonitrile-based copolymer,
the vinyl-based monomer having a metalloid atom other than carbon is a vinyl-based monomer having a boron atom as a metalloid atom, and
The vinyl-based monomer having a boron atom is a component derived from at least one selected from the group consisting of vinylboric acid, vinylphenylboric acid, allylboric acid, vinylphenylboric acid derivatives and allylboric acid derivatives.
A polyacrylonitrile-based copolymer characterized by: 2. The polyacrylonitrile copolymer according to claim 1 , further comprising at least one selected from the group consisting of itaconic acid, acrylic acid and methacrylic acid as a copolymer component. A carbon fiber precursor fiber comprising the polyacrylonitrile-based copolymer according to claim 1 or 2 . A method for producing a carbon fiber precursor fiber, comprising a spinning step of spinning a spinning solution containing the polyacrylonitrile-based copolymer according to claim 1 or 2 . The method for producing a carbon fiber precursor fiber according to claim 4 , wherein heat treatment is performed at a temperature of 180°C or higher in the spinning step. A method for producing a carbon fiber, comprising carbonizing the carbon fiber precursor fiber according to claim 3 to obtain a carbon fiber.