JP2015071833A - Fused blend fiber and method for producing carbon fiber using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fused blend fiber capable of producing a carbon fiber precursor fiber at a low cost by subjecting a polymer based thermoplastic carbon precursor and a non-polymer based thermoplastic carbon precursor to fusion blend spinning, and to remarkably improve a carbonization yield by bringing the polymer based thermoplastic carbon precursor and the non-polymer based thermoplastic carbon precursor into cooperative carbonization reaction.SOLUTION: Provided is a fused blend fiber made of a mixture of a polymer based thermoplastic carbon precursor of 20 to 80 mass% and a non-polymer based thermoplastic carbon precursor of 80 to 20 mass%.

Description

  The present invention relates to a melt blended fiber and a method for producing carbon fiber using the same.

  Carbon fiber has a specific strength and a specific elastic modulus which are superior to those of other fibers, and is used as a reinforcing material in obtaining a composite material due to its light weight and excellent mechanical properties. In addition to conventional sports and aerospace applications, it is also being widely deployed in general industrial applications such as automobiles, civil engineering / architecture, pressure vessels, and windmill blades.

  In particular, in recent years, the development of automotive applications has attracted a great deal of attention, and its adoption is being promoted for some luxury vehicles. However, since carbon fiber is expensive, there has been little progress in adopting it in passenger cars, and there is a demand for cost reduction of carbon fiber.

  By the way, carbon fibers are roughly classified into acrylonitrile-based carbon fibers and pitch-based carbon fibers due to the difference in raw materials, and pitch-based carbon fibers are further divided into mesophase pitch-based carbon fibers and isotropic pitch-based carbons depending on the crystal state of pitch used for spinning. Classified as fiber.

  Acrylonitrile-based carbon fiber has a characteristic that strength is easily obtained as compared with pitch-based carbon fiber. However, since acrylonitrile monomer as a raw material is expensive, there is a limit to reducing the cost of acrylonitrile-based carbon fiber.

  Pitch-based carbon fiber, on the other hand, is a fiber made by carbonizing by-products such as petroleum, coal, coal tar, etc. at high temperature, and the production cost can be reduced because the raw material is cheap and the carbonization yield is high. There is an advantage. However, since the pitch has poor spinnability and is difficult to spin, it is rarely produced with long fibers, particularly when isotropic pitch is used as a raw material.

  Various studies have been conducted to reduce the cost of acrylonitrile heavy carbon fibers. For example, a method of obtaining heat-resistant acrylonitrile fibers by subjecting fibers obtained by melt spinning acrylonitrile polymers to liquid phase oxidation has been proposed (Patent Document 1). In this method, although melt spinning reduces the cost at the spinning stage, it is necessary to use a mixed aqueous solution of potassium permanganate and nitric acid for the liquid phase treatment, and industrialization is extremely difficult.

  Patent Document 2 proposes a method in which a melt blend of a thermoplastic resin and a thermoplastic carbon precursor is infusibilized to carbonize the fibrous carbon precursor to obtain carbon fibers. However, this method is a method for obtaining ultrafine carbon fibers, and it is necessary to remove the thermoplastic resin before the carbonization step, which leads to an increase in cost.

JP-A-62-149918 JP 2010-31439 A

  An object of the present invention is to provide melt blended fibers and carbon fibers that can be produced at low cost.

  According to the present invention, there is provided a carbon fiber precursor fiber comprising a mixture of 20 to 80 mass percent of a polymeric thermoplastic carbon precursor and 80 to 20 mass percent of a non-polymeric thermoplastic carbon precursor.

  The polymer thermoplastic carbon precursor is preferably a polyacrylonitrile polymer, and the non-polymer thermoplastic carbon precursor is preferably pitch.

  In the present invention, a melt blended fiber in which a polymer thermoplastic carbon precursor and a non-polymer thermoplastic precursor have a co-continuous structure is obtained.

  Further, by controlling the weight ratio, a melt blended fiber in which the polymer thermoplastic carbon precursor and the non-polymer thermoplastic precursor have a sea-island structure can be obtained.

  These melt blended fibers are infusibilized and fired to provide carbon fibers.

  A melt blended fiber having a spinning speed of 20 m / min or more is provided.

  ADVANTAGE OF THE INVENTION According to this invention, a carbon fiber precursor fiber can be manufactured at low cost by carrying out melt blend spinning of a high molecular thermoplastic carbon precursor and a non-polymeric thermoplastic carbon precursor at high shear. Further, the carbonization yield can be greatly improved by the cooperative carbonization reaction of the high-molecular thermoplastic carbon precursor and the non-polymeric thermoplastic carbon precursor.

Cross-sectional TEM image of melt blended fiber obtained by the operation of Example 1 Cross-sectional TEM image of melt blended fiber obtained by the operation of Example 4

  Such melt blended fibers and carbon fibers can be suitably obtained by the production method of the present invention described later.

  Below, the manufacturing method of the melt blend fiber and carbon fiber of this invention is demonstrated in detail.

  The melt blended fiber obtained in the present invention is obtained by melt spinning a polymer thermoplastic carbon precursor and a non-polymer thermoplastic carbon precursor.

  The polymer-based thermoplastic carbon precursor used in the present invention is a polymer that can maintain the spinning stability of the melt blended fiber, has a molecular weight of 10,000 or more, and has undergone infusibilization treatment and chemical treatment to obtain carbon after Any polymer can be used as long as it can maintain the fiber form by the reaction. From the viewpoint of easy melting and kneading, it is preferable to have a softening point of 150 ° to 400 °.

  Examples of such thermoplastic carbon precursors include melt-formable acrylonitrile-based polymers, melt-shaped cellulose polymers, phenol resins, polyvinyl chloride, and polyvinyl alcohol. Among these, it is preferable to use an acrylonitrile-based polymer that can be melt-shaped from the viewpoint of the carbonization yield in the subsequent carbonization reaction.

  As the acrylonitrile-based polymer that can be melt-shaped, a homopolymer of acrylonitrile and / or a copolymer with other monomers can be used. It is only necessary to maintain melt shapeability. When a homopolymer is used, water may be coordinated with the nitrile group to impart thermoplasticity.

  In the case of using an acrylonitrile copolymer, water may be coordinated similarly to the homopolymer to impart thermoplasticity, or the amount of copolymerization may be controlled to impart thermoplasticity. It is preferable that acrylonitrile is 80 weight percent or more for the purpose of reducing defects caused by the copolymerization component when the carbon fiber is formed and improving the quality and performance of the carbon fiber.

  The copolymerization component monomer of the acrylonitrile-based polymer is not particularly limited. For example, acrylic acid esters represented by methyl acrylate and ethyl acrylate; methacrylic acid represented by methyl methacrylate and ethyl methacrylate Esters; unsaturated monomers represented by acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, styrene, vinyltoluene, etc .; methallylsulfonic acid, allylsulfonic acid, styrenesulfonic acid and their alkali metals Is mentioned. These may be one type or two or more types. From the viewpoint of maintaining melt spinnability, the copolymerization amount is preferably 5 weight percent or more.

  The melt-shaped acrylonitrile-based polymer can be produced by any of the usual solution polymerization method, suspension polymerization method, emulsion polymerization method and the like, but as an anionic surfactant, an aliphatic soap, Molecular weight regulators using emulsifiers such as alkyl sulfates, dialkyl sulfosuccinates, sulfonated esters, sulfonated amides, fatty acid esters such as polyethylene glycol and polypropylene glycol, and sorbitan aliphatic esters as nonionic surfactants It is more preferable to use an emulsion polymerization method using a relatively large amount of propyl mercaptan, isopropyl mercaptan, butyl mercaptan, benzyl mercaptan, octyl mercaptan, lauryl mercaptan, and the like.

  The non-polymer thermoplastic carbon precursor is a substance having a molecular weight of less than 10,000 and higher than the carbonization yield of the polymer thermoplastic carbon precursor.

  Examples of such non-polymer thermoplastic carbon precursors include lignin, mesophase pitch exhibiting optical anisotropy, and isotropic pitch that is optically isotropic. Among these, it is preferable to use an isotropic pitch from the viewpoint that it has a relatively low softening point and is easily melt-shaped.

  The blend ratio X of the non-polymer thermoplastic carbon precursor to the melt blend fiber is preferably 20 or more and 80 weight percent or less. If the non-polymer thermoplastic carbon precursor blend ratio X is less than 20 percent by weight, the carbonized yield of the carbon fiber obtained by infusibilizing and carbonizing the melt blend fiber will be low, and the non-polymer thermoplastic carbon will be reduced. If the precursor blend ratio X is 80% by weight or more, the melt blend fiber becomes brittle, so that the spinnability is remarkably lowered, and the resulting fiber becomes extremely brittle.

  More preferably, the blend ratio X of the non-polymeric thermoplastic carbon precursor is 40 to 60 weight percent. If the blend ratio X of the non-polymer thermoplastic carbon precursor is less than 40 percent by weight, a sea island structure is formed in which the polymer thermoplastic carbon precursor is a matrix and the non-polymer thermoplastic carbon precursor is finely dispersed. To do. If the blend ratio X is greater than 60 weight percent, a sea-island structure is formed in which the non-polymer thermoplastic carbon precursor is a matrix and the polymer thermoplastic carbon precursor is finely dispersed.

  On the other hand, when the blend ratio X is 40 to 60 weight percent, the polymer thermoplastic carbon precursor and the non-polymer thermoplastic precursor form a co-continuous structure. Thus, the contact area between the polymeric thermoplastic precursor and the non-polymeric thermoplastic precursor is significantly increased. If the contact area is large, the amount of high-molecular thermoplastic precursor and non-polymeric thermoplastic precursor cooperatively carbonized during the subsequent carbonization reaction will increase, thus improving the carbonization yield. It leads to.

  The temperature at which the polymeric thermoplastic carbon precursor and the non-polymeric thermoplastic carbon precursor are kneaded is preferably 150 degrees or more and 400 degrees or less, although it depends on the substance used. If it is less than 150 degrees, melting becomes insufficient, and if it is 400 degrees or more, the polymer thermoplastic carbon precursor is thermally decomposed to cause a structural change. If the polymeric thermoplastic precursor is a melt-formable acrylonitrile polymer and the non-polymeric thermoplastic carbon precursor is a combination of isotropic pitches, the kneading temperature is 150 ° C. or more from the viewpoint of the softening point It is preferable that it is 300 degrees or less.

  Melting and kneading of the polymeric thermoplastic carbon precursor and the non-polymeric thermoplastic carbon precursor can be performed by a known method, for example, a uniaxial melt kneading extruder, a biaxial melt kneading extruder, a mixing roll, mixing A mixer etc. are mentioned. Among these, it is preferable to knead with a biaxial conical screw for the purpose of uniformly mixing with high shear. Moreover, it is preferable to carry out in inert atmosphere in order to prevent the oxidation reaction during melt-kneading.

  The melt kneading temperature is preferably 150 to 400 degrees. When the melt kneading temperature is less than 150 ° C., the plasticity becomes insufficient and uniform kneading becomes difficult, which is not preferable. On the other hand, when it exceeds 400 degrees, the thermal decomposition of the polymer thermoplastic carbon precursor and the non-polymer thermoplastic carbon precursor proceeds, and the spinning stability is lowered. The melt kneading time is 1 to 20 minutes, preferably 1 to 15 minutes. When the melt kneading time is less than 1 minute, kneading is insufficient and uniform kneading becomes difficult, which is not preferable. On the other hand, when it exceeds 20 minutes, productivity of a melt blend fiber and carbon fiber will fall. Melt spinning is performed by a known method, and an undrawn yarn can be obtained. The winding speed of the undrawn yarn is preferably 20 m / min or more. The film may be continuously stretched without being wound, or may be wound and then subjected to the next stretching process while being unwound. The stretching treatment can be performed in a hot stove, a hot plate, or a steam atmosphere, and may be performed in one stage or in multiple stages.

  The melt blended fiber obtained as described above is subsequently subjected to an infusibilization reaction. The infusibilization treatment can be performed by a known method. It is preferable to carry out at 150 to 400 degrees in air. If it is less than 150 degrees, the progress of the infusibilization reaction is slow. On the other hand, if it is higher than 400 degrees, the thermal decomposition reaction proceeds. The infusibilization treatment is preferably performed for 5 hours or less, preferably 3 hours or less from the viewpoint of productivity.

  The infusible melt blended fiber is subsequently subjected to carbonization or graphitization reaction. In the carbonization or infusibility reaction, the reaction is performed in an inert gas such as nitrogen or argon, and the temperature is 500 ° C. or more and 3500 ° C. or less, preferably 800 It is not less than 3000 degrees and not more than 3000 degrees.

  Carbonization yield of non-polymer thermoplastic carbon precursor when infusible and carbonized under the same conditions is A, carbonization yield of polymer thermoplastic carbon precursor is B, non-polymer heat When the blend ratio of the plastic carbon precursor is X, the yield C of the carbon fiber obtained by infusibilization and carbonization is (AB) X / 100 + B or more. This is because the melt-blended fibers form a sea-island structure or a co-continuous structure, so that the contact area between the polymeric thermoplastic carbon precursor and the non-polymeric thermoplastic carbon precursor increases, and the carbonization reaction occurs cooperatively. This significantly improves the carbonization yield.

  By such a method, a carbon fiber precursor fiber can be produced at a low cost by melt blend spinning a polymer thermoplastic carbon precursor and a non-polymer thermoplastic carbon precursor. Further, the carbonization yield can be greatly improved by the cooperative carbonization reaction of the high-molecular thermoplastic carbon precursor and the non-polymeric thermoplastic carbon precursor.

  Hereinafter, the present invention will be described more specifically with reference to examples. The examples described below are examples of the best mode of the present invention, but the present invention is not limited to these examples.

The infusibilization and carbonization reaction in the present invention was carried out in the following three ways using TG / DTA6300 manufactured by SII Nanotechnology, and the carbonization yield was calculated.
[Reaction A]
The infusibilization reaction was heated to 200 degrees in air (flow rate 200 ml), held for 60 minutes, then held at 225 degrees for 30 minutes, and then held at 250 degrees for 30 minutes. The heating rate was all 10 degrees / minute. Subsequently, the carbonization reaction was maintained at 250 ° C. for 10 minutes in nitrogen for replacement, and then the temperature was increased to 1000 ° C. at 50 ° / min. The weight loss at 1000 degrees was defined as the carbonization yield.
[Reaction B]
The infusibilization reaction was carried out in air (flow rate 200 ml), heated to 190 degrees and held for 30 minutes, then held at 210 degrees for 30 minutes, then held at 230 degrees for 20 minutes, and then at 250 degrees and 20 minutes. Held at 270 degrees for 20 minutes, and finally at 290 degrees for 20 minutes. The heating rate was all 10 degrees / minute. Subsequently, the carbonization reaction was carried out in nitrogen at 290 ° C. for 10 minutes for replacement, and then the temperature was increased to 1000 ° C. at 50 ° / min. The weight loss at 1000 degrees was defined as the carbonization yield.
[Reaction C]
The infusibilization reaction was carried out in air (flow rate 200 ml), heated to 190 degrees and held for 30 minutes, then held at 210 degrees for 30 minutes, then held at 230 degrees for 20 minutes, and then at 250 degrees and 20 minutes. Held at 270 ° C. for 10 minutes, and at 290 ° C. for 10 minutes, and finally at 320 ° C. for 10 minutes. The heating rate was all 10 degrees / minute. Subsequently, the carbonization reaction was carried out in nitrogen at 290 ° C. for 10 minutes for replacement, and then the temperature was increased to 1000 ° C. at 50 ° / min. The weight loss at 1000 degrees was defined as the carbonization yield.

Cross-sectional TEM observation of the melt blended fiber was performed using H-7600 manufactured by Hitachi. After melt blended fibers are polymer-embedded with UV curable PMMA resin, they are surfaced and trimmed with a microtome equipped with a glass knife to obtain a horizontal or vertical cross section, and with a diamond knife, the thickness is about 70 nm. Sections were cut out. The obtained sections were collected on a grid with a support film for TEM observation.
[Example 1]
An acrylonitrile-based polymer that can be melt-shaped is used as the polymer thermoplastic carbon precursor, and an isotropic pitch (Mitsubishi Resin Co., Ltd., softening point of about 200 degrees) is used as the non-polymer thermoplastic precursor. As the acrylonitrile-based polymer capable of being melt-shaped, a copolymer of 85% by weight of acrylonitrile and 15% by weight of methyl acrylate was obtained by emulsion polymerization. The softening point was about 210 degrees.

  Using a small kneader manufactured by DSM, 75% by weight of an acrylonitrile-based polymer capable of melt shaping and 25% by weight of an isotropic pitch were kneaded for 10 minutes at a screw speed of 200 rpm in a 220 ° nitrogen atmosphere. The melt blend was extruded from a 0.3 mm nozzle at a screw speed of 100 rpm and wound at 26 m / min to obtain a melt blend fiber. When the obtained fiber was observed by TEM, a sea-island structure was formed (FIG. 1). The fragility of the fiber was very good.

The obtained melt blended fiber was cut into a 1 cm length and installed in a TG / DTA measuring apparatus. When the infusibilization and carbonization reactions were carried out under reaction A conditions, the carbonization yield was 58.0 percent.
[Example 2]
The same procedure as in Example 1 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 56.0 percent.
Example 3
The same procedure as in Example 1 was performed except that the infusibilization and carbonization reactions were performed under the reaction C conditions. The carbonization yield was 53.2 percent.
Example 4
A 50 weight percent melt-formable acrylonitrile polymer and 50 weight percent isotropic pitch were spun in the same manner as in Example 1. The winding speed was 105 m / min. When the obtained fiber was observed by TEM, a co-continuous structure was formed (FIG. 2). The fragility of the fiber was very good.

The obtained melt blended fiber was cut into a 1 cm length and installed in a TG / DTA measuring apparatus. When the infusibilization and carbonization reactions were carried out under reaction A conditions, the carbonization yield was 65.0 percent.
Example 5
The same procedure as in Example 4 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 68.3 percent.
Example 6
The same procedure as in Example 4 was performed except that the infusibilization and carbonization reactions were performed under the reaction C conditions. The carbonization yield was 61.4 percent.
Example 7
A 25 weight percent melt-formable acrylonitrile polymer and 75 weight percent isotropic pitch were spun in the same manner as in Example 1. The winding speed was 72 m / min. When the obtained fiber was observed with a TEM, a sea-island structure was formed. The fragility of the fiber was good.

The obtained melt blended fiber was cut into a 1 cm length and installed in a TG / DTA measuring apparatus. When the infusibilization and carbonization reactions were carried out under Reaction A conditions, the carbonization yield was 62.0 percent.
Example 8
The same procedure as in Example 7 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 73.1 percent.
Example 9
The same procedure as in Example 7 was performed except that the infusibilization and carbonization reactions were performed under the reaction C conditions. The carbonization yield was 65.6 percent.
[Comparative Example 1]
A melt-shaped acrylonitrile polymer was spun in the same manner as in Example 1. The winding speed was 40 m / min. The brittleness of the resulting fiber was very good.

The obtained melt blended fiber was cut into a 1 cm length and installed in a TG / DTA measuring apparatus. When the infusibilization and carbonization reactions were carried out under reaction A conditions, the carbonization yield was 36.3 percent.
[Comparative Example 2]
The same procedure as in Comparative Example 1 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 44.4 percent.
[Comparative Example 3]
The same procedure as in Comparative Example 1 was performed except that the infusibilization and carbonization reactions were performed under the reaction C conditions. The carbonization yield was 45.2 percent.
[Comparative Example 4]
An isotropic pitch was spun in the same manner as in Example 1. The winding speed was 15 m / min. The resulting fiber was extremely fragile.

The obtained melt blended fiber was cut into a 1 cm length and installed in a TG / DTA measuring apparatus. When the infusibilization and carbonization reactions were carried out under reaction A conditions, the carbonization yield was 58.2 percent.
[Comparative Example 5]
The same procedure as in Comparative Example 4 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 69.4 percent.
[Comparative Example 6]
The same procedure as in Comparative Example 4 was performed except that the infusibilization and carbonization reactions were performed under the reaction B conditions. The carbonization yield was 66.1 percent.

Claims (6)

  A melt blended fiber comprising a mixture of 20 to 80 weight percent of a polymeric thermoplastic carbon precursor and 80 to 20 weight percent of a non-polymeric thermoplastic carbon precursor.   The melt blend fiber according to claim 1, wherein the high molecular weight thermoplastic carbon precursor is a polyacrylonitrile-based polymer, and the non-high molecular weight thermoplastic carbon precursor is pitch.   The melt blend fiber according to claim 1 or 2, wherein the polymer thermoplastic carbon precursor and the non-polymer thermoplastic precursor have a co-continuous structure.   The melt blend fiber according to claim 1 or 2, wherein the polymer thermoplastic carbon precursor and the non-polymer thermoplastic precursor have a sea-island structure.   Carbon fiber obtained by infusibilizing and firing the melt-blended fiber according to any one of claims 1 to 4. The method for producing a melt-blended fiber according to claim 1, wherein the spinning speed is 20 m / min or more.