JP7026442B2 - Stabilized mesophase pitch modified product and its manufacturing method - Google Patents

Description

The present invention relates to a stabilized mesophase pitch modified product and a method for producing the same. More specifically, the present invention relates to a stabilized mesophase pitch modified product obtained by heating a composite containing a stabilized mesophase pitch in a thermoplastic resin under a specific atmosphere, and a method for producing the same.

Carbon nanomaterials, especially ultrafine carbon fibers having an average fiber diameter of 1 μm or less, have excellent properties such as high crystallinity, high conductivity, high strength, high elastic modulus, and light weight, and thus have high performance. It is used as a nanofiller for composite materials. Its applications are not limited to reinforcing nanofillers aimed at improving mechanical strength, but by taking advantage of the high conductivity of carbon materials, it is an additive material for electrodes of various batteries and capacitors, electromagnetic shielding materials, and antistatic materials. It is being studied for use as a conductive nanofiller for resin or as a nanofiller to be blended in an electrostatic coating material for resins. In addition, it is expected to be used as a field electron emission material such as a flat display by taking advantage of its chemical stability, thermal stability, and fine structure as a carbon material.

For example, Patent Document 1 describes (1) a step of forming a precursor molded product from a mixture of 100 parts by mass of a thermoplastic resin and 1 to 150 parts by mass of a mesophase pitch which is a thermoplastic carbon precursor, (2). ) A step of subjecting the precursor molded body to a stabilizing treatment to stabilize the thermoplastic carbon precursor in the precursor molded body to form a stabilized resin composition, (3) From the stabilized resin composition to the thermoplastic resin. Is disclosed under reduced pressure to form a fibrous carbon precursor, and (4) a step of carbonizing or graphitizing the fibrous carbon precursor, and a method for producing carbon fiber.

International Publication No. 2009/125857

The method described in Patent Document 1 removes the thermoplastic resin from the mixture molded body under reduced pressure to form a stabilized mesophase pitch modified product. Therefore, in the step of removing the thermoplastic resin, a reduced pressure treatment is required, which makes the step longer and more complicated. Furthermore, since the method described in Patent Document 1 heats under reduced pressure, the heat conduction to the thermoplastic resin to be removed becomes low. Therefore, depending on the degree of decompression (degree of vacuum), a part of the thermoplastic resin may not be removed and may remain (residual coal formation). As a result, amorphous carbon derived from the thermoplastic resin may remain as a foreign substance in the finally obtained ultrafine carbon fibers, resulting in a decrease in conductivity, strength, and elastic modulus. Therefore, it is necessary to sufficiently lower the basis weight of the mixture molded body to suppress the formation of residual coal, which is low efficiency.

An object of the present invention is to provide a stabilized mesophase pitch modified product in which residual coal formation is suppressed from a composite in which a stabilized mesophase pitch is contained in a thermoplastic resin, and a method for producing the same.

As a result of diligent studies in view of the above-mentioned prior art, the present inventors have set specific conditions for removing the thermoplastic resin to efficiently modify the stabilized mesophase pitch having predetermined properties. A body can be obtained, and the obtained stabilized mesophase pitch modified product is high in carbon fiber because it does not contain amorphous carbon derived from a thermoplastic resin as a foreign substance even after undergoing a carbonization step and / or a graphitization step. We have found that ultrafine carbon fiber with physical properties can be provided. Based on the above findings, the present invention has been completed.

That is, the present invention that solves the above problems is described below.

[1] The elemental composition ratio (O / C) of oxygen O and carbon C measured by the elemental analysis method is 0.1 or more, and the elemental composition ratio (N / C) of nitrogen N and carbon C is 0. Stabilized mesophase characterized by having a peak of 02 or more and having a peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy containing a pyridine-type aromatic N (398 eV) and a pyrrole-type aromatic NH (400 eV). Pitch denatured body.

[2] The stabilized mesophase pitch modified product according to [1], wherein the stabilized mesophase pitch modified product has a fibrous morphology and an average fiber diameter of 100 to 900 nm.

[3] The method for producing a stabilized mesophase pitch modified product according to [1], wherein the complex composed of the thermoplastic resin and the stabilized mesophase pitch is heated in the presence of a solvent.

[4] The method for producing a stabilized mesophase pitch modified product according to [3], wherein the heating temperature is equal to or higher than the melting point of the solvent and lower than the boiling point, and the heating time is 0.5 to 5 hours.

[5] The composite is a composite composed of 100 parts by mass of the thermoplastic resin and 1 to 150 parts by mass of the stabilized mesophase pitch with respect to 100 parts by mass of the thermoplastic resin. [3] Alternatively, the method for producing a stabilized mesophase pitch modified product according to [4].

[6] Production of the stabilized mesophase pitch modified product according to any one of [3] to [5], wherein the complex is a complex in which the stabilized mesophase pitch is dispersed in the thermoplastic resin. Method.

[7] The method for producing a stabilized mesophase pitch modified product according to any one of [3] to [6], wherein the basis weight of the complex is 20000 g / m ² or less.

[8] The method for producing a stabilized mesophase pitch modified product according to [1], wherein the composite composed of the thermoplastic resin and the stabilized mesophase pitch is heated in a steam atmosphere.

[9] The method for producing a stabilized mesophase pitch modified product according to [8], wherein the heating temperature is 350 to 600 ° C. and the heating time is 0.01 to 5 hours.

[10] The composite is a composite composed of 100 parts by mass of the thermoplastic resin and 1 to 150 parts by mass of the stabilized mesophase pitch with respect to 100 parts by mass of the thermoplastic resin. [8] Alternatively, the method for producing a stabilized mesophase pitch modified product according to [9].

[11] The method for producing a stabilized mesophase pitch modified product according to any one of [8] to [10], wherein the water vapor atmosphere is a water vapor atmosphere having an oxygen concentration of 50% by volume or less.

[12] Production of the stabilized mesophase pitch modified product according to any one of [8] to [11], wherein the complex is a complex in which the stabilized mesophase pitch is dispersed in the thermoplastic resin. Method.

[13] The method for producing a stabilized mesophase pitch modified product according to any one of [8] to [12], wherein the complex has a basis weight of 20000 g / m ² or less.

[14] The basis weight X (kg / m ² ) of the complex and the heating time Y (minutes) are given by the following formula (1).
Y ≧ 2.5X + 3 ・ ・ ・ (Equation 1)
The method for producing a stabilized mesophase pitch modified product according to any one of [8] to [13].

According to the present invention, it is possible to provide a stabilized mesophase pitch modified product in which residual carbon formation is suppressed, and the obtained stabilized mesophase pitch modified product is carbon fiber through a carbonization step and / or a graphitization step. However, since amorphous carbon derived from the thermoplastic resin is not contained as a foreign substance, ultrafine carbon fibers having high physical characteristics can be provided.

3 is an SEM photograph (200 times) of the mesophase pitch denatured product of Example 2. It is an XPS spectrum of the mesophase pitch modified product of Example 2. 3 is an SEM photograph (200 times) of the mesophase pitch denatured product of Example 3. 6 is an SEM photograph (1000 times) of the mesophase pitch denatured product of Comparative Example 1. 6 is an SEM photograph (5000 times) of the mesophase pitch denatured product of Comparative Example 1.

Hereinafter, the present invention will be described in detail. In the present invention, the average fiber length means a volume average value measured by using an image analysis particle size distribution meter unless otherwise specified. Further, the average fiber diameter means an average value measured by image analysis of an electron micrograph, unless otherwise specified. Further, in the present invention, the mesophase pitch after the stabilization treatment is also referred to as "stabilized mesophase pitch".

The stabilized mesophase pitch modified product of the present invention has an elemental composition ratio (O / C) of oxygen O and carbon C measured by an elemental analysis method of 0.1 or more, and an elemental composition ratio of nitrogen N and carbon C. (N / C) is 0.02 or more, and the peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy contains pyridine-type aromatic N (398 eV) and pyrrole-type aromatic NH (400 eV). ..

The O / C is preferably 0.1 to 0.3, and more preferably 0.1 to 0.2.

The N / C is preferably 0.02 to 0.1, more preferably 0.02 to 0.05.

The peaks derived from the N1s orbital measured by X-ray photoelectron spectroscopy show that the pyridine-type aromatic N (398 eV) and the pyrrole-type aromatic NH (400 eV) have an intensity of 0.1 E + 4 or more with respect to the baseline, respectively. It is preferably 0.2E + 4 or more.

If the stabilized mesophase pitch modified product is in the above range, it has high physical characteristics because the amorphous carbon derived from the thermoplastic resin is not contained as a foreign substance even as carbon fibers through the carbonization step and / or the graphitization step. It can be carbon fiber.

The stabilized mesophase pitch modified product of the present invention is fibrous in morphology, and the average fiber diameter thereof is preferably 100 to 900 nm, more preferably 100 to 600 nm, and particularly preferably 150 to 400 nm. preferable.

Within such a range, the carbon fiber obtained through the carbonization step and / or the graphitization step is a so-called nanocarbon material. Due to its properties, it can be suitably used as a filler for high-performance composite materials.

The stabilized mesophase pitch modified product of the present invention is fibrous in morphology, and its average fiber length is preferably 1 μm or more, more preferably 1 to 200 μm, and particularly preferably 20 to 150 μm. .. When the fiber length is about the above-mentioned constant length, the degree of imparting high conductivity as a filler is further improved.

In converting the stabilized mesophase pitch modified product into carbon fibers, a conventional method may be followed, and ultrafine carbon fibers can be produced by setting known carbonization and / or graphitization conditions.

The ultrafine carbon fiber thus produced has a linear structure having substantially no branched structure, and has an average fiber diameter of 10 to 900 nm, preferably 100 to 600 nm. Here, "substantially having no branch structure" means that the degree of branching is 0.01 pieces / μm or less.

The ultrafine carbon fiber obtained from the above is useful as a conductive auxiliary material constituting an electrode for, for example, a non-aqueous electrolyte secondary battery. When used as a conductive auxiliary material constituting an electrode for a non-aqueous electrolyte secondary battery, the ratio (aspect ratio: L / D) between the average fiber length (L) and the average fiber diameter (D) of the ultrafine carbon fibers is 30 or more. It is preferably 50 or more, more preferably 100 or more, and even more preferably 100 or more. By setting the aspect ratio to 30 or more, a conductive path made of ultrafine carbon fibers is efficiently formed in the electrode, and the cycle characteristics of the obtained battery can be improved. If it is less than 30, the formation of the conductive path by the ultrafine carbon fibers tends to be insufficient in the electrode, and the resistance value in the film thickness direction of the electrode may not be sufficiently lowered. The upper limit of the ratio (L / D) is not particularly limited, but is generally 10,000 or less, preferably 1000 or less, and more preferably 800 or less.

It should be noted that the ultrafine carbon fibers may have a fibrous form as a whole, and for example, those having an aspect ratio less than the preferable range may come into contact with or bond with each other to have an integral fiber shape. (For example, those in which spherical carbons are connected in a bead shape, those in which at least one or a plurality of extremely short fibers are connected by fusion or the like) are also included.

Further, in the above-mentioned ultrafine carbon fiber, the average plane spacing d002 of the (002) plane measured by the X-ray diffraction method is in the range of 0.335 to 0.350 nm.

As described above, the ultrafine carbon fibers obtained from the stabilized mesophase pitch modified product of the present invention have extremely high crystallinity, and thus are excellent in electrical conductivity and thermal conductivity.

When this ultrafine carbon fiber is used as a conductive auxiliary material, it may be used alone or in combination with a known conductive auxiliary agent such as acetylene black.

As a method for producing a stabilized mesophase pitch modified product of the present invention, for example, by heating a composite composed of a thermoplastic resin and a stabilized mesophase pitch in the presence of a solvent, the heat from the composite is obtained. A method of removing the plastic resin can be adopted.

The heating temperature is preferably equal to or higher than the melting point of the solvent and lower than the boiling point from the viewpoint of handleability. The heating time is related to the heating temperature or the thermoplastic resin dissolving ability of the solvent, but may be set to about 0.5 to 5 hours.

As the solvent, any solvent that dissolves the thermoplastic resin and does not affect the mesophase pitch can be used. Depending on the thermoplastic resin to be dissolved, a more soluble solvent is used. For example, if the thermoplastic resin is polyolefin, cyclohexane, decalin, toluene and the like can be used, and if it is polycarbonate, methylene chloride and tetrahydrofuran can be used.

In the production method of the present invention, it is preferable to hold the complex on a supporting substrate at a basis weight of 20000 g / m ² or less. By holding it on the supporting substrate, it is possible to suppress the aggregation of the stabilized mesophase pitch modified product when the thermoplastic resin is removed. Further, it becomes possible to maintain the solvent permeability, improve the efficiency of solvent removal, and facilitate the discharge of the melt of the thermoplastic resin to the outside of the system. As the material of the supporting base material, it is necessary that the material does not deform or corrode due to the solvent or heating. Further, as the heat resistant temperature of the supporting base material, any of them can be adopted as long as it is not deformed by the heating temperature of the above-mentioned thermoplastic resin removing step. Metallic materials such as stainless steel and ceramic materials such as alumina and silica can be used.

Further, the shape of the supporting base material is preferably a shape having solvent permeability in the direction perpendicular to the plane. A network structure is exemplified as such a shape.

In the present invention, examples of the composite composed of the thermoplastic resin and the stabilized mesophase pitch include a composite having a sea-island structure having the thermoplastic resin as a sea component and the stabilized mesophase pitch as an island component. A mesophase pitch composition as a raw material to be described later is dispersed in a matrix resin made of a thermoplastic resin to prepare a mesophase pitch composition, and the mesophase pitch composition is formed into various shapes to be dispersed in the thermoplastic resin. The shape of the mesophase pitch is controlled. After the mesophase pitch becomes the desired shape and the matrix resin is no longer needed, the matrix resin is removed.

Further, as a method for producing a stabilized mesophase pitch modified product of the present invention, for example, a composite composed of a thermoplastic resin and a stabilized mesophase pitch is heated from the composite to the above in a steam atmosphere. A method of thermally decomposing and removing the thermoplastic resin can be adopted.

The water vapor atmosphere referred to here means that the water vapor at 200 ° C. or higher is filled with 50% by volume or more, preferably 80% by volume or more.

The thermoplastic resin is removed while the inert atmosphere is maintained by the water vapor atmosphere. The inert atmosphere referred to here preferably has an oxygen concentration of 50% by volume or less, more preferably 30% by volume or less, and even more preferably 20% by volume or less. Further, an inert gas other than water vapor may be contained. Examples of the inert gas include carbon dioxide, nitrogen, argon and the like.

The thermal decomposition temperature is preferably 350 to 600 ° C, more preferably 380 to 550 ° C. When the thermal decomposition temperature is less than 350 ° C., the thermal decomposition of the stabilized mesophase pitch can be suppressed, but the thermal decomposition of the thermoplastic resin may not be sufficiently performed. On the other hand, if the temperature exceeds 600 ° C., the thermoplastic resin can be sufficiently thermally decomposed, but the stabilized mesophase pitch may be thermally decomposed, and the yield tends to decrease. The thermal decomposition time is preferably 0.01 to 5 hours, more preferably 0.05 to 3 hours.

In the production method of the present invention, it is preferable to hold the complex on a supporting substrate at a basis weight of 20000 g / m ² or less. By holding it on the supporting substrate, it is possible to suppress the aggregation of the stabilized mesophase pitch modified product when the thermoplastic resin is removed. Further, it becomes possible to maintain the air permeability, improve the efficiency of heating, and facilitate the discharge of the decomposition product of the thermoplastic resin to the outside of the system. As the material of the supporting base material, it is necessary that the material does not deform or corrode due to the solvent or heating. Further, the heat resistant temperature of the supporting base material is preferably 600 ° C. or higher because it is necessary that the supporting base material is not deformed by the thermal decomposition temperature of the above-mentioned thermoplastic resin removing step. Examples of such a material include a metal material such as stainless steel and a ceramic material such as alumina and silica.

Further, the shape of the supporting base material is preferably a shape having air permeability in the direction perpendicular to the plane. A network structure is exemplified as such a shape.

The basis weight X (kg / m ² ) of the resin composite stabilized fiber and the thermal decomposition time Y (minutes) are given by the following formula (1).
Y ≧ 2.5X + 3 ・ ・ ・ (Equation 1)
It is preferable to satisfy. By satisfying the above relationship, a stabilized mesophase pitch modified product having a low residual coal ratio can be produced.

In the present invention, examples of the composite composed of the thermoplastic resin and the stabilized mesophase pitch include a composite having a sea-island structure having the thermoplastic resin as a sea component and the stabilized mesophase pitch as an island component. By dispersing the mesophase pitch in a matrix resin made of a thermoplastic resin to prepare a mesophase pitch composition and molding the mesophase pitch composition into various shapes, the shape of the mesophase pitch dispersed in the thermoplastic resin is controlled. Will be done. After the mesophase pitch becomes the desired shape and the matrix resin is no longer needed, the matrix resin is removed.

<Thermoplastic resin>
The thermoplastic resin in the present invention is a thermoplastic resin that can be removed from the system by thermal decomposition or a solvent. Examples of such thermoplastic resins include polyacrylate-based polymers such as polyolefin, polymethacrylate, and polymethylmethacrylate; polystyrene, polycarbonate, polyarylate, polyester, polyamide, polyester carbonate, polysulfone, polyimide, polyetherimide, polyketone, and polylactic acid. Etc. are preferable. Among these, polyolefin is preferably used.

Specific examples of the polyolefin include polyethylene, polypropylene, poly-4-methylpentene-1, and a copolymer containing these. From the viewpoint of easy removal from the system, it is preferable to use polyethylene. Examples of polyethylene include low-density polyethylene such as high-pressure method low-density polyethylene, vapor-phase method / solution method / high-pressure method linear low-density polyethylene, medium-density polyethylene, homopolymers such as high-density polyethylene, or ethylene and α-olefin. Copolymer; Examples thereof include a copolymer of polyethylene such as an ethylene / vinyl acetate copolymer and another vinyl-based monomer.

The thermoplastic resin used in the present invention preferably has a melt mass flow rate (MFR) of 0.1 to 25 g / 10 min measured in accordance with JIS K 7210 (1999), preferably 0.1 to 15 g / min. It is more preferably 10 min, and particularly preferably 0.1 to 10 g / 10 min. When the MFR is in the above range, the mesophase pitch can be satisfactorily microdispersed in the thermoplastic resin. Further, when the mesophase pitch composition is formed, the mesophase pitch in the thermoplastic resin is stretched, so that the obtained stabilized mesophase pitch modified product can be formed into a fiber shape. The thermoplastic resin used in the present invention has a glass transition temperature of 250 ° C. or lower in the case of amorphous and a melting point of 300 ° C. or lower in the case of crystalline from the viewpoint that it can be easily melt-kneaded with the mesophase pitch. preferable.

<Raw material mesophase pitch>
The mesophase pitch is a pitch that can form an optically anisotropic phase (liquid crystal phase) in a molten state. The mesophase pitch as a raw material used in the present invention (hereinafter, may be referred to as “raw material mesophase pitch”) is a material obtained from a distillation residue of coal or petroleum, or an aromatic hydrocarbon such as naphthalene as a raw material. Things can be mentioned. For example, the coal-derived raw material mesophase pitch can be obtained by a treatment mainly for hydrogenation / heat treatment of coal tar pitch, a treatment mainly for hydrogenation / heat treatment / solvent extraction, and the like.

The optically anisotropic content (mesophase ratio) of the raw material mesophase pitch is preferably 80% or more, and more preferably 90% or more.

The softening point of the raw material mesophase pitch is preferably 100 to 400 ° C, more preferably 150 to 350 ° C.

<Complex>
In the present invention, the composite composed of the thermoplastic resin and the stabilized mesophase pitch (hereinafter, also simply referred to as “composite”) includes the thermoplastic resin and 1 to 150 parts by mass with respect to 100 parts by mass of the thermoplastic resin. An example is a complex comprising a stabilizing mesophase pitch of the moiety. The content of the stabilized mesophase pitch is preferably 5 to 100 parts by mass. If the content of the stabilized mesophase pitch exceeds 150 parts by mass, the mesophase pitch may not be well dispersed in the thermoplastic resin. Further, if the content of the stabilized mesophase pitch is less than 1 part by mass, the processing cost for removing the thermoplastic resin to obtain the stabilized mesophase pitch increases.

The method for producing the stabilized mesophase pitch modified product of the present invention and the ultrafine carbon fiber will be described below.

First, the raw material mesophase pitch is dispersed in the thermoplastic resin to prepare a mixture of the thermoplastic resin and the raw material mesophase pitch (hereinafter, also referred to as “mesophase pitch composition”).

The mesophase pitch composition can be prepared by kneading the thermoplastic resin and the raw material mesophase pitch in a molten state.

The melt-kneading of the thermoplastic resin and the raw material mesophase pitch can be performed using a known device. For example, one or more types selected from the group consisting of a uniaxial kneader, a biaxial kneader, a mixing roll, and a Banbury mixer can be used. Among these, it is preferable to use a biaxial kneader for the purpose of satisfactorily microdispersing the raw material mesophase pitch in the thermoplastic resin, and in particular, use a biaxial kneader in which each axis rotates in the same direction. Is preferable.

The kneading temperature is not particularly limited as long as the thermoplastic resin and the raw material mesophase pitch are in a molten state, but is preferably 100 to 400 ° C, preferably 150 to 350 ° C. If the kneading temperature is less than 100 ° C., the raw material mesophase pitch does not become a molten state and it is difficult to micro-disperse it in the thermoplastic resin, which is not preferable. On the other hand, if the temperature exceeds 400 ° C., the decomposition of the thermoplastic resin and the raw material mesophase pitch proceeds, which is not preferable.

The melt-kneading time is preferably 0.5 to 20 minutes, more preferably 1 to 15 minutes. If the melt-kneading time is less than 0.5 minutes, microdispersion of the raw material mesophase pitch is difficult, which is not preferable. On the other hand, if it exceeds 20 minutes, the productivity is significantly lowered, which is not preferable.

The raw material mesophase pitch used in the present invention may be denatured by reacting with oxygen during melt-kneading, and may hinder microdispersion in the thermoplastic resin. Therefore, it is preferable to perform melt kneading in an inert atmosphere to suppress the reaction between oxygen and the raw material mesophase pitch. The melt-kneading is preferably carried out in an inert atmosphere having an oxygen gas content of less than 10% by volume, more preferably in an inert atmosphere having an oxygen gas content of less than 5% by volume, and having an oxygen gas content of less than 5% by volume. It is particularly preferred to carry out under an inert atmosphere of less than 1% volume.

In order to produce a fibrous stabilized mesophase pitch modified product having an average fiber diameter of 100 to 900 nm, it is preferable that the dispersion diameter of the raw material mesophase pitch in the mesophase pitch composition is 0.01 to 50 μm. It is more preferably 01 to 30 μm. If the dispersion diameter of the raw material mesophase pitch in the mesophase pitch composition deviates from the range of 0.01 to 50 μm, it may be difficult to produce ultrafine carbon fibers. That is, when it is less than 0.01 μm, it is difficult to maintain the fiber shape, and the fiber length tends to be short. Further, when it exceeds 50 μm, it is difficult to produce ultrafine fibers, and the fiber diameter tends to be large.

In the mesophase pitch composition, the raw material mesophase pitch forms a spherical or elliptical island phase, but the dispersion diameter in the present invention means the diameter when the island component is spherical, and in the case of an elliptical shape. Means its major axis diameter.

The dispersion diameter of 0.01 to 50 μm is preferably maintained within the above range even after the mesophase pitch composition is held at 300 ° C. for 3 minutes, and is maintained even after being held at 300 ° C. for 5 minutes. It is more preferable that the product is maintained at 300 ° C. for 10 minutes, and it is particularly preferable that the product is maintained at 300 ° C. for 10 minutes. In general, when the mesophase pitch composition is kept in a molten state, the raw material mesophase pitch aggregates in the thermoplastic resin over time. If the raw material mesophase pitch is aggregated and the dispersion diameter exceeds 50 μm, it may be difficult to produce a desired stabilized mesophase pitch modified product or carbon fiber. The aggregation rate of the raw material mesophase pitch in the mesophase pitch composition varies depending on the thermoplastic resin used and the type of the raw material mesophase pitch.

The mesophase pitch composition is molded by spinning or the like in order to form the raw material mesophase pitch dispersed in the thermoplastic resin into a fiber shape (hereinafter, the molded mesophase pitch composition is also referred to as "resin composite fiber").

Examples of the method for forming the mesophase pitch composition include a method of melt-spinning the mesophase pitch composition from a spinning cap, a method of melt-forming a mesophase pitch composition from a rectangular cap, injection molding, and the like. As a result, the raw material mesophase pitch contained in the mesophase pitch composition can be extended and formed into a fiber form with high initial orientation.

The temperature at the time of molding needs to be higher than the melting temperature of the raw material mesophase pitch, and is preferably 150 to 400 ° C, more preferably 180 to 350 ° C. When the temperature exceeds 400 ° C., the deformation relaxation rate of the raw material mesophase pitch increases, and it becomes difficult to maintain the morphology of the fibers.

The resin composite fiber may be cooled in the subsequent cooling step. As the cooling step, in the case of melt spinning, a method of cooling the atmosphere downstream of the spinneret is exemplified. In the case of melt film formation, a method of providing a cooling drum downstream of the rectangular base is exemplified. By providing the cooling step, the region where the raw material mesophase pitch is deformed by elongation can be controlled, and the strain rate can be controlled. Further, by providing the cooling step, the resin composite fiber after spinning or film formation can be immediately cooled and solidified to enable stable molding.

Next, the resin composite fiber is subjected to a stabilization treatment (also referred to as an infusibilization treatment) with respect to the raw material mesophase pitch contained therein. In the present invention, the raw material mesophase pitch after the stabilization treatment is also referred to as "stabilized mesophase pitch". The stabilization treatment is performed by contacting the resin composite fiber with a gas containing nitrogen oxides in a vapor phase state. (The resin composite fiber after the stabilization treatment is also referred to as "resin composite stabilized fiber".)

The gas may be nitrogen oxide alone or may be used in combination with other oxidizing gases. Examples of the oxidizing gas include air, oxygen and a mixture thereof. When used in combination with an oxidizing gas, the nitrogen oxides reduced by the stabilization reaction to the raw material mesophase pitch can be oxidized again to form nitrogen oxides, so that the nitrogen oxides can be used efficiently and productivity can be achieved. Is improved. Further, the gas may contain a gas other than the oxidizing gas. Examples of the gas other than the oxidizing gas include an inert gas such as carbon dioxide, nitrogen and argon.

The stabilization reaction temperature is preferably 25 to 100 ° C. By the stabilization treatment at a temperature in this range, thermal runaway due to the heat of reaction is suppressed, the resin composite fiber is prevented from being excessively fused, and the orientation of the stabilized mesophase pitch contained in the resin composite fiber is maintained high. Will be done.

The stabilization treatment time is preferably 10 to 300 minutes, preferably 20 to 200 minutes.

The softening point of the stabilized mesophase pitch obtained by the above stabilizing treatment is remarkably increased. The softening point of the stabilized mesophase pitch is preferably 400 ° C. or higher, more preferably 500 ° C. or higher. When the softening point is 400 ° C. or higher, the softening of the stabilizing mesophase pitch at the time of thermally decomposing the thermoplastic resin in the subsequent step is suppressed.

The form of the resin composite stabilized fiber is preferably 50 to 350 dtex when it is fibrous, and preferably 10 μm to 2 mm in thickness when it is in the form of a sheet or other.

Next, the resin composite stabilized fiber obtained as described above is heated in a solvent or steam atmosphere to remove the thermoplastic resin. In this step, the thermoplastic resin is removed while suppressing the decomposition of the stabilized mesophase pitch to obtain a stabilized mesophase pitch modified product in which the residual coal is suppressed. The conditions for removing the thermoplastic resin are as described above.

The stabilized mesophase pitch modified product produced by the method for removing a thermoplastic resin of the present invention is unlikely to generate foreign matter (residual carbon) derived from the thermoplastic resin. Specifically, the residual coal ratio is 0.1% by mass or less, preferably 0.01% by mass or less, based on the mass of the stabilized mesophase pitch modified product.

Within this range, even if the obtained stabilized mesophase pitch modified product is used as carbon fiber through a carbonization step and / or a graphitization step, the amorphous carbon derived from the thermoplastic resin is not contained as a foreign substance, so that the physical characteristics are high. Ultra-fine carbon fiber can be provided.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Various measurements and analyzes in the examples were carried out according to the following methods.

(1) Confirmation of the shape of the stabilized mesophase pitch modified product Observation and photography were performed using a scanning electron microscope (JCM-6000 manufactured by JEOL Ltd.).

(2) XPS measurement of stabilized mesophase pitch modified product Spectral measurement derived from N1s orbital was performed by Narrow Scan using an X-ray photoelectron spectrometer (manufactured by THERMO SCIENTIFIC).

(3) Elemental analysis (nitrogen, carbon)
Measurement was performed by the TCD detection method using an elemental analyzer NCH-22F type (manufactured by Sumika Chemical Analysis Service Co., Ltd.).

(4) Elemental analysis (oxygen)
Measurement was performed by the NDIR detection method using an elemental analyzer EMGA-920 (manufactured by HORIBA, Ltd.).

(5) Residual coal rate The mass (g) of the stabilized mesophase pitch modified product after removing the thermoplastic resin is A, the texture (g / m ² ) when removing the thermoplastic resin is B, and the mesophase pitch composition. Using the following formula with the mass ratio of the raw material mesophase pitch in the product as C, the residual coal ratio per 1 m ² was calculated.
Residual coal rate (%) = A / (B x 1 x C) x 100-100

[Reference Example 1] (Manufacturing method of raw material mesophase pitch)
A coal tar pitch with a softening point of 80 ° C. from which the quinoline insoluble matter was removed was hydrogenated at a pressure of 13 MPa and a temperature of 340 ° C. in the presence of a Ni—Mo catalyst to obtain a hydrogenated coal tar pitch. This hydrogenated coal tar pitch was heat-treated at 480 ° C. under normal pressure and then reduced in pressure to remove low boiling points to obtain a mesophase pitch. This mesophase pitch was filtered at a temperature of 340 ° C. using a filter to remove foreign substances in the pitch to obtain a purified raw material mesophase pitch.

[Reference Example 2] (Manufacturing method 1 of resin composite fiber)
As a thermoplastic resin, 80 parts by mass of linear low-density polyethylene (Exceed® 1018HA, ExxonMobil, MFR = 1 g / 10 min), and the raw material mesophase pitch obtained in Reference Example 1 (mesophase ratio 90.9%). , Softening point 303.5 ° C) 20 parts by mass is melt-kneaded with a twin-screw extruder in the same direction (“TEM-26SS” manufactured by Toshiba Machinery Co., Ltd., barrel temperature 300 ° C, under nitrogen stream) to prepare a mesophase pitch composition. did. The above mesophase pitch composition is spun from a spinneret at 340 ° C. using a cylinder type single-hole spinning machine, and a resin composite fiber (a sea island containing the raw material mesophase pitch as an island component and linear low-density polyethylene as a sea component). Mold composite fiber) was produced.

[Reference Example 3] (Manufacturing method 2 of resin composite fiber)
A resin composite fiber was produced in the same manner as in Reference Example 2 except that the linear low-density polyethylene was 60 parts by mass, the raw material mesophase pitch was 40 parts by mass, and the spinneret was 360 ° C.

[Reference Example 4] (Manufacturing method 1 of resin composite stabilized fiber)
2.5 kg of the resin composite fiber obtained in Reference Example 2 was charged into a reaction vessel (volume 33 L), and a mixed gas containing nitrogen dioxide was introduced into the reaction vessel system at room temperature over 300 minutes. As a result, the raw material mesophase pitch was stabilized, and a resin composite stabilized fiber was obtained.

[Reference Example 5] (Manufacturing method 2 of resin composite stabilized fiber)
2.5 kg of the resin composite fiber obtained in Reference Example 3 was charged into a reaction vessel (volume 33 L), and a mixed gas containing nitrogen dioxide was introduced into the reaction vessel system at room temperature over 720 minutes. As a result, the raw material mesophase pitch was stabilized, and a resin composite stabilized fiber was obtained.

[Example 1]
The composite stabilized fiber obtained in Reference Example 4 was placed in a flask and heated at 50 ° C. for 1 hour in cyclohexane as a solvent to remove the thermoplastic resin and obtain a stabilized mesophase pitch modified product. .. The average fiber diameter at this time was 280 nm. Further, the residual coal ratio was calculated from the mass of the obtained stabilized mesophase pitch modified product and found to be 0%.
When this fibrous stabilized mesophase pitch modified product was measured by an elemental analysis method, the elemental composition ratio (O / C) of oxygen O and carbon C was 0.12, and the elemental composition ratio of nitrogen N and carbon C (elemental composition ratio) ( N / C) was 0.03. Moreover, when the peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy was confirmed, the peaks of the pyridine type aromatic N (398 eV) and the pyrrole type aromatic NH (400 eV) were observed.
When the obtained mesophase pitch modified product was used as carbon fiber, one in which amorphous carbon derived from a thermoplastic resin was not contained as a foreign substance was obtained.

[Comparative Example 1]
The composite stabilized fiber obtained in Reference Example 4 was placed in a flask and heated in cyclohexane at 50 ° C. for 0.017 hours to remove the thermoplastic resin to obtain a stabilized mesophase pitch modified product. Electron micrographs of this stabilized mesophase pitch denatured product are shown in FIGS. 4 and 5. It was confirmed that the fibrous stabilized mesophase pitch modified product was present, but on the other hand, it was observed that the thermoplastic resin remained. The average fiber diameter at this time was 350 nm. Further, the residual coal ratio was calculated from the mass of the obtained stabilized mesophase pitch modified product and found to be 15%.
When this fibrous stabilized mesophase pitch modified product was measured by an elemental analysis method, the elemental composition ratio (O / C) of oxygen O and carbon C was 0.07, and the elemental composition ratio of nitrogen N and carbon C (elemental composition ratio) ( N / C) was 0.01. Moreover, when the peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy was confirmed, the peaks of the pyridine type aromatic N (398 eV) and the pyrrole type aromatic NH (400 eV) were not observed.
When the obtained mesophase pitch modified product was used as carbon fiber, amorphous carbon derived from a thermoplastic resin was contained as a foreign substance.

[Example 2]
The composite stabilized fiber obtained in Reference Example 4 was placed on a wire mesh made of SUS304 so as to have a grain size of 540 g / m ² , and charged into a furnace. By heating for 08 hours, the thermoplastic resin was removed to obtain a fibrous stabilized mesophase pitch modified product. The water vapor atmosphere immediately after the composite stabilized fiber was placed in the furnace was 100% by volume, and the water vapor atmosphere became 98% by volume with the removal of the resin (2% by volume is the decomposition gas of the resin). An electron micrograph of this fibrous stabilized mesophase pitch modified product is shown in FIG. 1, and it was observed that no thermoplastic resin remained. The average fiber diameter at this time was 267 nm. Further, the residual coal ratio was calculated from the mass of the obtained stabilized mesophase pitch modified product and found to be 0%. As can be seen from FIG. 1, the obtained stabilized mesophase pitch denaturants were not found to be aggregated or bundled, and were dispersed neatly.
When this fibrous stabilized mesophase pitch modified product was measured by an elemental analysis method, the elemental composition ratio (O / C) of oxygen O and carbon C was 0.11, and the elemental composition ratio of nitrogen N and carbon C (elemental composition ratio) ( N / C) was 0.03. Moreover, the peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy is shown in FIG. 2, and the peaks of the pyridine-type aromatic N (398 eV) and the pyrrole-type aromatic NH (400 eV) were observed.
When the obtained mesophase pitch modified product was used as carbon fiber, one in which amorphous carbon derived from a thermoplastic resin was not contained as a foreign substance was obtained.

[Example 3]
The composite stabilized fiber obtained in Reference Example 5 was placed in a furnace so as to have a texture of 1350 g / m ² , and heated at 500 ° C. for 0.17 hours in a steam atmosphere to obtain a thermoplastic resin. Was removed to obtain a fibrous stabilized mesophase pitch modified product. The water vapor atmosphere immediately after the composite stabilized fiber was placed in the furnace was 100% by volume, and the water vapor atmosphere became 96.5% by volume with the removal of the resin (3.5% by volume is the decomposition gas of the resin). .. An electron micrograph of this fibrous stabilized mesophase pitch modified product is shown in FIG. 3, and it was observed that no thermoplastic resin remained. The average fiber diameter at this time was 380 nm. Further, the residual coal ratio was calculated from the mass of the obtained stabilized mesophase pitch modified product and found to be 0%.
When this fibrous stabilized mesophase pitch modified product was measured by an elemental analysis method, the elemental composition ratio (O / C) of oxygen O and carbon C was 0.11, and the elemental composition ratio of nitrogen N and carbon C (elemental composition ratio) ( N / C) was 0.04. Moreover, when the peak derived from the N1s orbital measured by X-ray photoelectron spectroscopy was confirmed, the peaks of the pyridine type aromatic N (398 eV) and the pyrrole type aromatic NH (400 eV) were observed.
When the obtained mesophase pitch modified product was used as carbon fiber, one in which amorphous carbon derived from a thermoplastic resin was not contained as a foreign substance was obtained.

Claims (7)

The raw material mesophase pitch is dispersed in the thermoplastic resin to obtain a mesophase pitch composition composed of a mixture of the thermoplastic resin and the raw material mesophase pitch.
The mesophase pitch composition is melt-spun or melt-formed to extend the raw material mesophase pitch contained in the mesophase pitch composition and form it into a fiber form.
Next, the raw material mesophase pitch was subjected to a stabilization treatment to obtain a complex composed of the thermoplastic resin and the stabilized mesophase pitch.
By heating the complex in a steam atmosphere, the thermoplastic resin is thermally decomposed and removed from the complex .
The elemental composition ratio (O / C) of oxygen O and carbon C measured by the elemental analysis method is 0.1 to 0.3, and the elemental composition ratio (N / C) of nitrogen N and carbon C is 0. Stabilized mesophase pitch modification with a peak of 02 to 0.1 and from the N1s orbital measured by X-ray photoelectron spectroscopy containing pyridine-type aromatic N (398 eV) and pyrrole-type aromatic NH (400 eV). How to make a body. The method for producing a stabilized mesophase pitch modified product according to claim 1, wherein the heating temperature in a steam atmosphere is 350 to 600 ° C. and the heating time is 0.01 to 5 hours. The composite according to claim 1 or 2, wherein the composite is composed of 100 parts by mass of the thermoplastic resin and 1 to 150 parts by mass of the stabilized mesophase pitch with respect to 100 parts by mass of the thermoplastic resin. The method for producing a stabilized mesophase pitch modified product according to the above. The method for producing a stabilized mesophase pitch modified product according to any one of claims 1 to 3, wherein the water vapor atmosphere is a water vapor atmosphere having an oxygen concentration of 50 parts by volume or less. The method for producing a stabilized mesophase pitch modified product according to any one of claims 1 to 4, wherein the composite is a composite in which the stabilized mesophase pitch is dispersed in the thermoplastic resin. The method for producing a stabilized mesophase pitch modified product according to any one of claims 1 to 5, wherein the complex has a basis weight of 20000 g / m ² or less. The basis weight X (kg / m ² ) of the complex and the heating time Y (minutes) are given by the following formula (1).
Y ≧ 2.5X + 3 ・ ・ ・ (Equation 1)
The method for producing a stabilized mesophase pitch modified product according to any one of claims 1 to 6.

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