JP4887219B2 - Method for producing carbon fiber precursor acrylonitrile fiber - Google Patents

Description

  The present invention relates to a method for producing a carbon fiber precursor acrylonitrile fiber.

Conventionally, carbon fibers have been used in a wide range due to their excellent mechanical properties, such as a reinforcing fiber for composite materials for aerospace use, sports and leisure use. Currently, further expansion to industrial material applications is expected, and in order to improve the performance of these composite materials, it is required to improve the quality and performance of carbon fibers, reduce manufacturing costs, and the like.
Carbon fiber precursors used in the production of carbon fibers are generally shaped into fibers by dissolving the polymer in an organic or inorganic solvent to form a solution (dope) and then performing wet or dry wet spinning. It is manufactured by stretching, washing, and drying and densifying. As a method for producing carbon fiber, the carbon fiber precursor is heat-treated in an oxidizing atmosphere at 200 to 300 ° C. to form a flame-resistant fiber, and subsequently carbonized (fired) in an inert atmosphere at least 1000 ° C. The method is widely adopted industrially.

Acrylonitrile polymers are widely used as raw materials for acrylonitrile fibers (carbon fiber precursor acrylonitrile fibers) used as carbon fiber precursors.
In producing carbon fiber using carbon fiber precursor acrylonitrile fiber, a method for producing carbon fiber precursor acrylonitrile fiber by adding amines and peroxides has been proposed in order to perform firing in a short time. (See Patent Documents 1 and 2). However, this method adversely affects the stability of the dope and the carbon fiber precursor acrylonitrile fiber and is not an industrially excellent method.
In addition, a method of introducing a carboxy group into the acrylonitrile polymer as a reaction initiating group for promoting the cyclization condensation reaction of the nitrile group has been proposed (see Patent Document 3).
On the other hand, since the carboxy group is difficult to be incorporated into the ring structure at the firing stage, it exists as a defect point in the obtained carbon fiber and may deteriorate the mechanical properties. Therefore, the carboxy group is randomly added to the acrylonitrile-based polymer. Proposals for dispersion have also been made (see Patent Document 4).
Japanese Patent Publication No.51-7209 JP-A-48-87120 JP-A-5-339813 JP 2000-119342 A

However, in the above method in which carboxy groups are introduced by copolymerization, if it is desired to produce varieties that change the amount of carboxy groups, it is necessary to clean the production line and store multiple polymers. Is significantly worse.
The present invention has been made in view of the above circumstances, and has a high degree of freedom in productivity and composition design, and is suitable for producing a high-performance carbon fiber precursor acrylonitrile fiber. An object of the present invention is to provide a method for producing a fiber.

The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention that solves the above-mentioned problems is a kneader comprising an acrylonitrile polymer (A) not containing a carboxy group, a polymer (B) containing a carboxy group, and a solvent. in mixed dissolved by heating after, characterized by spinning with the acrylonitrile polymer (a) and the polymer (B), prepare uniformly dissolved acrylonitrile polymer solution.

According to the present invention, productivity and a high degree of freedom in composition design, it can provide a method for producing a suitable carbon fiber precursor acrylonitrile fiber to produce a high-performance carbon textiles.

In the method for producing a carbon fiber precursor acrylonitrile fiber of the present invention, first, an acrylonitrile polymer (A) not containing a carboxy group and a polymer (B) containing a carboxy group are blended.
Here, in the present specification and claims, the acrylonitrile-based polymer (A) that does not contain a carboxy group means that the ratio of acrylonitrile units in the polymer is 90% by mass or more and 100% by mass or less. . The ratio of the acrylonitrile unit in the polymer is more preferably 95% by mass or more and 100% by mass or less. Within the above range, the more acrylonitrile units, the higher the strength and the quality and performance of the carbon fiber when the resulting carbon fiber precursor acrylonitrile fiber is baked into carbon fiber.

As long as the acrylonitrile-based polymer (A) containing no carboxy group used in the present invention satisfies the above conditions, acrylic acid esters, methacrylic acid esters, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, It can be produced by copolymerizing monomers that do not contain a carboxy group, such as acetone acrylamide, methacrylonitrile, styrene, and α-methylstyrene. One or more types of monomers may be used.
The production method of the acrylonitrile-based polymer (A) not containing a carboxy group is not particularly limited, and any of the known polymerization methods such as solution polymerization and suspension polymerization is used, and the carboxy group is not contained. A monomer may be polymerized.
The polymerization initiator and catalyst used for the polymerization are not particularly limited, and examples thereof include azo compounds, organic peroxides, or redox catalysts such as persulfuric acid / sulfurous acid, chloric acid / sulfurous acid, or ammonium salts thereof.
As an optimal method for producing an acrylonitrile-based polymer (A) containing no carboxy group, an overflow type polymerization vessel is charged with monomer, distilled water, ammonium persulfate, ammonium bisulfite and sulfuric acid as polymerization initiators per minute. There is a method in which a fixed amount is supplied, stirring is continued while maintaining a constant temperature, and an acrylonitrile-based polymer is obtained from the overflowed polymerization slurry through washing and drying.

  The degree of polymerization of the acrylic polymer (A) containing no carboxy group is determined by the drawing characteristics in the spinning step after blending the acrylic polymer (A) containing no carboxy group and the polymer (B) containing the carboxy group. From the viewpoint of carbon fiber performance, etc., the intrinsic viscosity [η] is preferably 1 or more, more preferably 1.4 or more.

  As the acrylic polymer (A) not containing a carboxy group, one kind may be used alone, or a mixture of two or more kinds of polymers may be used.

The polymer (B) containing a carboxy group refers to a polymer containing monomer units containing a carboxy group.
Examples of the monomer containing a carboxy group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid and the like, and also include a monomer containing an acid anhydride group that becomes a carboxy group by hydrolysis. It is. Examples of the monomer containing an acid anhydride group include maleic anhydride. One of these monomers may be used alone, or two or more thereof may be used in combination.
As a monomer containing a carboxy group, acrylic acid and / or methacrylic acid and / or itaconic acid are preferable.

The ratio of the monomer unit containing a carboxy group in the polymer (B) containing a carboxy group is preferably 0.014% by mass or more and 100% by mass or less. When the carboxy group is contained in an amount of 0.014% by mass or more, the firing time can be advanced in a short time. As long as the polymer (B) containing a carboxy group can be dissolved in a solvent during dope preparation, all the monomer units may be monomer units containing a carboxy group.
The more monomer units containing carboxy groups, the easier it is to adjust the amount of carboxy groups in the carbon fiber precursor acrylonitrile fiber, so the proportion of monomer units containing carboxy groups is 0.1% by mass or more and 100% by mass or less. More preferably, the content is 1% by mass or more and 100% by mass or less.

The polymer (B) containing a carboxy group may have a monomer unit other than the monomer unit containing a carboxy group as long as the effects of the present invention are not impaired.
The component other than the monomer containing a carboxy group is not particularly limited, but acrylonitrile, acrylamide, methacrylamide, diacetone acrylamide, methacrylonitrile and the like are preferable because they are easily incorporated into the carbon skeleton at the time of firing. One of these monomers may be used alone, or two or more thereof may be used in combination.
In addition, a compound containing a group that promotes the cyclization condensation reaction of a nitrile group, such as a sulfonic acid group-containing vinyl monomer and a sulfuric acid group-containing vinyl monomer, may be copolymerized without impairing the effects of the present invention. it can.

  The manufacturing method of the polymer (B) containing a carboxy group is not specifically limited, It can manufacture by the method similar to the acrylonitrile type polymer (A) which does not contain the said carboxy group.

  The degree of polymerization of the polymer (B) containing a carboxy group is remarkably dissolved out of the system in the spinning step after blending the acrylonitrile polymer (A) not containing a carboxy group and the polymer (B) containing a carboxy group. However, there is no particular limitation as long as it does not impair the drawing characteristics and the performance of the carbon fiber.

  As a polymer (B) containing a carboxy group, 1 type may be used independently and 2 or more types may be used together.

The mass ratio ((B) / (A)) of the polymer (B) containing a carboxy group and the acrylonitrile-based polymer (A) containing no carboxy group blended in the present invention is 0.0001 or more and 2. It is preferable that it is 3 or less. When (B) / (A) is 0.0001 or more, the firing time can be advanced in a short time, and when it is 2.3 or less, the amount of carboxy groups in the carbon fiber precursor acrylonitrile-based fiber is reduced. It is preferable because it is easy to adjust.
From the balance between the effect of advancing the firing time in a short time and the ease of adjusting the amount of carboxy groups in the precursor, (B) / (A) is more preferably 0.001 or more and 1.5 or less, and 0.002 or more. 1 or less is more preferable.

As a spinning method, a dope in which an acrylonitrile-based polymer (A) containing no carboxy group and a polymer containing a carboxy group (B) are dissolved in a solvent is wet-spun from a spinneret (such as a nozzle hole having a circular cross section). A method of spinning by a method or a dry-wet spinning method is preferred.
The dope solvent is not particularly limited as long as it can uniformly dissolve the acrylonitrile-based polymer (A) not containing a carboxy group and the polymer (B) containing a carboxy group. For example, dimethylformamide, dimethylacetamide, dimethylsulfoxide , Zinc chloride aqueous solution, thiocyanic acid aqueous solution and the like.
The method for dissolving the acrylonitrile-based polymer in the solvent is not particularly limited. For example, the acrylonitrile-based polymer and the solvent can be dissolved by mixing with a kneader and then heated.
At this time, the acrylonitrile-based polymer (A) not containing a carboxy group and the polymer (B) containing a carboxy group may be blended and then dissolved in a solvent, or an acrylonitrile-based polymer containing no carboxy group ( A) and the polymer (B) containing a carboxy group may be dissolved separately, and then the solutions may be mixed. Alternatively, the other polymer may be added to a solution in which one of the polymers is dissolved and dissolved. For example, the gelation of the dope can be suppressed by adding the polymer (B) containing a carboxy group immediately before spinning.
From the viewpoint of spinnability, the dope preferably has a polymer concentration (the total concentration of the acrylonitrile-based polymer (A) not containing a carboxy group and the polymer (B) containing a carboxy group) of 10% by mass or more. 17 mass% or more is more preferable, and 19 mass% or more is further more preferable. The upper limit of the acrylonitrile-based polymer concentration is preferably 30% by mass or less and more preferably 27% by mass or less in consideration of spinnability.
The spinning draft (which part should be stretched during the spinning process) may be appropriately set so as to obtain a desired fineness according to the acrylonitrile polymer concentration and the stretching ratio.
When used as a precursor fiber for carbon fiber, the single yarn fineness of the acrylonitrile fiber is preferably 2.0 dtex or less, more preferably 1.5 dtex or less, from the viewpoint of the mechanical properties of the carbon fiber.

In the case of the wet spinning method, the dope is discharged directly from the spinneret into the coagulation bath to obtain a coagulated yarn. In the case of dry and wet spinning, the dope is once discharged into the air from the spinneret and then immediately set in the coagulation bath. To do.
The coagulation bath is preferably set to a condition with sufficient margin for taking up the coagulated yarn and subsequent drawing, and the coagulation bath concentration and temperature are preferably set so as to satisfy these requirements.
For the coagulation bath, an aqueous solution containing a solvent used for the dope is preferably used, and the concentration of the contained solvent is appropriately adjusted.
The temperature of the coagulation bath is preferably lower from the viewpoint of the density of the coagulated yarn, but considering the point that if the temperature is lowered too much, the take-up speed of the coagulated yarn is lowered and the productivity is lowered. It is preferably 50 ° C. or lower, more preferably 20 ° C. or higher and 40 ° C. or lower. In dry-wet spinning, it is preferably 30 ° C. or lower, more preferably 0 ° C. or higher and 20 ° C. or lower.

  The coagulated yarn is usually subjected to an oil agent treatment after being washed and stretched. Further, after the oil agent treatment, it is dried and densified, and is stretched again under a heating roll or pressurized steam as necessary. Thereby, a carbon fiber precursor acrylonitrile fiber is obtained.

As a method for drawing the coagulated yarn, a wet heat drawing method is preferably used in which the solvent contained in the coagulated yarn is washed in boiling water. When further stretching is performed after drying and densification, the stretching ratio at this time does not require a particularly large ratio, so it is sufficient if it is 2 to 5 times. When stretching is not applied after drying and densification, it is necessary to set the stretching ratio as much as necessary. Moreover, it is also possible to use a multistage stretching method of two or more stages as the wet heat stretching method. It is also possible to perform stretching in the air before wet heat stretching. The procedure of stretching in air and wet heat stretching is not particularly limited according to the present invention, and a known method can be applied.
It is effective to set the drawing bath temperature in the wet heat drawing method as high as possible within a range in which the single yarns are not fused. From this viewpoint, the temperature of the stretching bath is preferably 70 ° C. or higher. When wet heat stretching is performed in multiple stages, the final bath is preferably 90 ° C or higher.

There is no special limitation by this invention about an oil agent processing method, A well-known method is applicable. Although the kind of oil agent is not specifically limited, Amino silicone type oil agent is used suitably.
The temperature for drying and densification needs to be performed at a temperature exceeding the glass transition temperature of the fiber, but may be substantially different depending on the drying state from the water-containing state, and a method using a heating roller of about 100 to 200 ° C. is preferable. .
If the total draw ratio is low, the fiber orientation is lowered, which is disadvantageous in that the performance of the acrylonitrile fiber and the carbon fiber tends to be lowered. If the total draw ratio is high, yarn breakage tends to occur, which is disadvantageous in production. From this point of view, it is preferable to perform further stretching after drying and densification. As the stretching method, dry heat stretching performed between heating rollers, hot plate stretching performed on a heating plate, steam stretching performed in pressurized steam, or the like can be employed. In particular, steam stretching that can realize a high stretching ratio is preferable. From the same viewpoint, the total draw ratio including this draw is preferably 8 times or more and 20 times or less.

  The carbon precursor acrylonitrile fiber obtained as described above can be converted into a flame resistant fiber by heat treatment (flame resistant treatment) in an oxidizing atmosphere at 200 ° C. to 400 ° C. Furthermore, carbon fiber can be obtained by carbonizing the flame-resistant fiber in an inert atmosphere of about 1000 ° C. to 1500 ° C. by a known method.

Hereinafter, the present invention will be described in more detail with reference to examples.
In the examples, acrylonitrile, acrylamide and methacrylic acid are represented by AN, AAm and MAA, respectively, and% represents mass%.
(B) “Polymer composition”
The composition of the polymer (the ratio of each monomer unit (mass ratio)) was quantified by ¹ H-NMR method (manufactured by JEOL Ltd., GSZ-400 type superconducting FT-NMR).
(B) “Intrinsic viscosity of polymer [η]”
Measurement was performed using a Ubbelohde viscometer using a dimethylformamide solution at 25 ° C.
(C) “Strand characteristics of carbon fiber”
The strand strength and strand elastic modulus were measured according to the test method described in JIS-R-7601.

[Production Example 1: Production of polymer (A1)]
An AN, AAm, distilled water, and a constant amount of ammonium persulfate and ammonium hydrogen sulfite are supplied to an overflow type polymerization vessel every minute, and the stirring is continued while maintaining at 50 ° C., and the overflowed polymerization slurry is washed. A polymer (A1) was obtained through drying. The composition of this polymer was AN / AAm = 97.5 / 2.5. The intrinsic viscosity [η] of this polymer was 1.8.

[Production Example 2: Production of polymer (B1)]
A polymer (B1) was obtained in the same manner as in Production Example 1 except that AN, AAm, and MAA were used instead of AN and AAm. The composition of this polymer was AN / AAm / MAA = 95.7 / 2.5 / 1.8. The intrinsic viscosity [η] of this polymer was 1.8.

[Production Example 3: Production of polymer (C1)]
An acrylonitrile polymer (C1) was obtained in the same manner as in Production Example 1 except that the amounts of AN, AAm, and MAA used were changed. The composition of this polymer was AN / AAm / MAA = 96.6 / 2.5 / 0.9. The intrinsic viscosity [η] of this polymer was 1.8.

[Example 1]
50 parts of the polymer (A1) produced in Production Example 1, 50 parts of the polymer (B1) produced in Production Example 2 and dimethylacetamide were mixed with a kneader and dissolved by heating to obtain a polymer concentration of 21. A mass% acrylonitrile-based polymer solution (dope) was prepared.
This dope was discharged into a 69% concentration dimethylacetamide aqueous solution (bath temperature 35 ° C.) using a spinneret having a pore diameter of 0.75 mm and a pore number of 3000 to obtain coagulated fibers, and the coagulated fibers were further washed in a washing tank. The solvent was removed and the film was stretched 3 times to obtain a water-swollen acrylonitrile fiber. Aminosilicone-based oil is added to this water-swelled acrylonitrile fiber, dried and densified with a heating roll having a surface temperature of 130 ° C., and stretched three times in a pressurized steam at 170 ° C. to give a carbon fiber precursor acrylonitrile fiber. Got.
The carbon fiber precursor acrylonitrile fiber is passed through a flameproof furnace having a temperature gradient of 230 ° C. to 270 ° C. over 60 minutes, and further fired in a carbonization furnace having a temperature gradient of 300 ° C. to 1400 ° C. in a nitrogen atmosphere. To obtain carbon fiber. Table 1 shows the strand characteristics of this carbon fiber.

[Comparative Example 1]
A predetermined amount of the polymer (C1) produced in Production Example 3 and dimethylacetamide were mixed at room temperature with a kneader, and then dissolved by heating to prepare a dope having a polymer concentration of 21% by mass.
Using this dope, a carbon fiber precursor acrylonitrile fiber was obtained in the same manner as in Example 1.
The carbon fiber precursor acrylonitrile fiber is passed through a flameproof furnace having a temperature gradient of 230 ° C. to 270 ° C. over 60 minutes, and further fired in a carbonization furnace having a temperature gradient of 300 ° C. to 1400 ° C. in a nitrogen atmosphere. To obtain carbon fiber. Table 1 shows the strand characteristics of this carbon fiber.

  As shown in the above results, in Example 1, the polymer (A1) and the polymer (B1) were blended and spun to use a single polymer (C) that apparently has the same composition. As a result, a carbon fiber precursor acrylonitrile-based fiber capable of obtaining high-performance carbon fibers at the same level as in Comparative Example 1 could be produced.

The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention is suitable for producing a high-performance carbon fiber precursor acrylonitrile fiber having high productivity and a high degree of freedom in composition design.
For example, according to the carbon fiber precursor acrylonitrile fiber produced according to the present invention, a carbon fiber precursor obtained by using a single polymer having the same composition as that of the blend of the polymer (A) and the polymer (B). A carbon fiber having the same performance (for example, strength, elastic modulus, etc.) as that using the body acrylonitrile fiber can be obtained. Therefore, compared with the case where a single polymer is used, a high-performance carbon fiber precursor acrylonitrile fiber can be easily produced.
Moreover, the amount of carboxy groups in the carbon fiber precursor acrylonitrile fiber can be easily changed simply by changing the blend ratio of the polymer (A) and the polymer (B).
In addition, since the polymer (B) can secure the amount of carboxy groups necessary for firing in the production of carbon fibers in a short time, the steric rule is difficult to copolymerize as the acrylonitrile-based polymer (A). It is possible to use polyacrylonitrile with controlled properties, ultrahigh molecular weight polyacrylonitrile, or the like, and to obtain a high-performance carbon fiber. “Polymer with controlled stereoregularity” means a polymer whose isotactic triad (mm) or syndiotactic triad (rr) quantifiable by ¹³ C-NMR measurement exceeds 0.3. . The ultrahigh molecular weight polyacrylonitrile has an intrinsic viscosity [η] of 3 or higher.

Claims (2)

The acrylonitrile-based polymer (A) not containing a carboxy group, the polymer (B) containing a carboxy group, and a solvent are mixed with a kneader and dissolved by heating to dissolve the acrylonitrile-based polymer (A) and the polymer. polymer (B) is method of producing a carbon fiber precursor acrylonitrile fiber spinning by, prepare homogeneously dissolved acrylonitrile polymer solution.   The carbon fiber according to claim 1, wherein the polymer (B) is composed of a monomer unit containing a carboxy group and at least one monomer unit selected from acrylonitrile, acrylamide, methacrylamide, diacetone amide, and methacrylonitrile. A method for producing a precursor acrylonitrile fiber.