KR101148428B1 - Method of preparing precursors for polyacrylonitrile-based carbon fibers - Google Patents

Abstract

The present invention relates to a method for producing a polyacrylonitrile precursor which is particularly suitable for the production of carbon fibers having high strength and high elasticity by maintaining the stability of the dope stock solution, the acrylonitrile of at least 95% by weight and less than 5% by weight of comonomer A method for producing a polyacrylonitrile precursor fiber for carbon fibers comprising the step of preparing a dope solution using a polyacrylonitrile polymer comprising a polymer, wherein the comonomer is methyl acrylate, acrylic acid, methacryl It is made of two or more selected from the group consisting of acid, itaconic acid, the dope solution preparation step provides a method for producing a polyacrylonitrile precursor fiber for carbon fibers, characterized in that carried out at 25 ~ 50 ℃.

According to the present invention, the viscosity stability of the dope stock solution can be improved by dissolving the PAN polymer at low temperature during the preparation of the dope stock solution. In addition, since the stable dope solution is not easily deteriorated, it is excellent in radioactivity and can reduce trimming and moor occurrence. As a result, the internal defects of the fibers are reduced, thereby making it possible to produce precursor fibers and carbon fibers of good quality. In addition, the present invention helps to save energy and reduce costs by preparing the dope solution at a low temperature.

Dope stock, viscosity stability, paste, trimmed, precursor fiber, low temperature melting

Description

Manufacturing method of polyacrylonitrile precursor fiber for carbon fiber {METHOD OF PREPARING PRECURSORS FOR POLYACRYLONITRILE-BASED CARBON FIBERS}

The present invention relates to a method for producing polyacrylonitrile (PAN) -based precursor fibers for carbon fibers, and more particularly, to polyacrylonitrile (PAN) -based precursor fibers, in particular polyacrylonitrile (PAN) -based polyacrylonitrile. It relates to a method for producing a ronitrile precursor.

Carbon fibers produced from acrylonitrile polymers, so-called PAN (Polyacrylonitrile) carbon fibers, have excellent strength and are widely used as raw materials for carbon fibers. Recently, more than 90% of all carbon fibers are PAN-based carbon fibers. In addition, since PAN-based carbon fibers have applicability to carbon electrode materials for secondary batteries, carbon films, and the like, research and development on these have been actively conducted.

In the case of producing carbon fibers from acrylonitrile-based polymers, the acrylic fibers obtained by spinning acrylonitrile-based polymers, that is, precursors for carbon fibers, are flameproofed at 200 to 400 ° C. in an oxidizing atmosphere. It is called chloride fiber.

The flame resistant fiber thus obtained is carbonized at 800 to 2000 ° C. in an inert gas atmosphere to produce carbon fiber. In addition, the carbon fibers thus obtained are sometimes treated in a higher temperature inert gas, and the fibers thus obtained are called graphite fibers.

In the method for producing a dope stock solution (polymer solution) for producing a precursor of such carbon fiber, factors that affect polymer concentration, viscosity, molecular weight, molecular structure, etc., which are characteristics of the dope stock solution, are largely attributable to the dope stock solution. It is divided into what originates after manufacture.

Examples of the dope stock solution may include variations in basic conditions such as raw materials, additives, injection amount of solvent, injection time, dissolution tank temperature, pressure, stirring speed, reaction time, and the like.

In addition, after the preparation of the dope solution, the storage time (retention time) of the polymer solution, the change in the thermal history and the change in the concentration of the polymer due to the post-polymerization of the remaining residual monomers, the change in the molecular weight distribution, the deterioration of the polymer, etc. Can be.

Such fluctuations and deterioration cause quality fluctuations and deterioration of fibers, films, resin products, etc., which are manufactured in a subsequent process, and further act as a factor causing out of specification products.

The polymer for acrylonitrile precursor fiber which consists of 90 weight% or more of acrylonitrile and a vinylic monomer copolymerizable is conventionally used in the polymer solution which uses an organic solvent, such as dimethyl sulfoxide, dimethyl formamide, or dimethylacetamide, as a solvent. It is susceptible to deterioration by cyclization / crosslinking due to thermal history of the remaining polymerization initiator or redox process. This altered polymer is likely to form three-dimensional cyclization / crosslinking between polymer rings in the polymer solution, causing internal defects in the yarn or final product.

The present invention has been made to solve the above problems, to prevent the cyclization reaction of the acrylonitrile-based polymer during the preparation and storage of the dope stock solution, and further to maintain the stability of the dope stock solution to produce a precursor for carbon fiber of excellent quality It aims to provide a way to.

In addition, an object of the present invention is to provide a method for producing a precursor for a carbon fiber that can produce a high strength / high elastic carbon fiber by maintaining the stability of the dope stock solution for a long time.

In order to solve the above problems, the present invention provides a carbon comprising a dope stock solution preparing a dope stock solution using a polyacrylonitrile polymer comprising at least 95% by weight acrylonitrile and less than 5% by weight comonomer A method for producing a polyacrylonitrile-based precursor fiber for fibers, wherein the comonomer is composed of two or more selected from the group consisting of methyl acrylate, acrylic acid, methacrylic acid and itaconic acid, and the dope stock preparation step is 25 to It provides a method for producing a polyacrylonitrile-based precursor fiber for carbon fibers, characterized in that carried out at 50 ℃.

According to the manufacturing method of the PAN system precursor fiber for carbon fiber of this invention, the viscosity stability of a dope stock solution can be improved by melt | dissolving a PAN polymer at low temperature at the time of preparation of a dope stock solution. In addition, since the stable dope solution is not easily deteriorated, it is excellent in radioactivity and can reduce trimming and moor occurrence. As a result, the internal defects of the fibers are reduced, thereby making it possible to produce precursor fibers and carbon fibers of good quality. In addition, the present invention helps to save energy and reduce costs by preparing the dope solution at a low temperature.

Hereinafter, the features and advantages of the present invention will be described in detail.

PAN precursor fiber for carbon fiber according to the present invention is obtained from an acrylonitrile-based polymer. The properties of the precursor for carbon fiber are basically dependent on the composition of the acrylonitrile-based polymer. The main component of the acrylonitrile polymer used in the present invention is an acrylonitrile unit, and the content of the acrylonitrile unit is 90% by weight or more, preferably 95% by weight or more based on the total acrylonitrile polymer. If the content of the acrylonitrile unit is too small, the mechanical properties of the carbon fiber may be lowered, such as the strength of the carbon fiber obtained by the firing process is lowered.

The acrylonitrile-based polymer may be, as necessary, a unit containing at least one copolymerization component (an auxiliary component other than acrylonitrile), including a densification accelerator component, an extension promoter component, and the like in the spinning process; A unit containing a flame resistance promoting component in the flame resistance process; It may further include a unit including an oxygen permeation promoting component. The content of the additional copolymerization component is 10% by weight or less, preferably 5% by weight or less based on the total acrylonitrile-based polymer.

The structural unit which becomes the said densification promotion component is produced by copolymerization of the vinyl compound monomer which has hydrophilic functional groups, such as a carboxyl group, a sulfone group, and an amide group. Examples of the monomer containing a densification promotion component having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, maleic acid, alkyl esters thereof (methyl acrylate, etc.), and the like. Among them, acrylic acid, methacrylic acid, itaconic acid, etc. are preferably used. In addition, specific examples of the densification-promoting component having the sulfonic group include allyl sulfonic acid, metharylsofonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (2-acrylamido-2-methyl propane sulfonic acid), vinyl sulfonic acid, and sulfo propyl methacrylate. Specific examples of the structural unit of the densification-promoting component having the amide group may include acrylamide, methacrylamide, and dimethylacrylamide.

In addition, alkylamines such as octyl amine, dodecyl amine and lauryl amine in order to improve oxygen permeability between single fibers in a flame resistant furnace; Dialkyl amines such as dioctyl amine; Trialkylamines such as trioctylamine; Diamine components such as ethylene diamine and hexamethylene diamine may be used. Among these, in order to improve the uniformity of polymerization, it is preferable to use a component having solubility in a polymerization solvent, a medium, a spinning solvent and the like.

In addition, the unit including the oxygen permeation promoting component may be introduced by copolymerization of an alkyl ester of one unsaturated carboxylic acid structure, for example, ethyl methacrylate. The acrylonitrile-based copolymer can be obtained by subjecting such an auxiliary component (comonomer) and the main component to aqueous suspension polymerization using an inorganic redox catalyst according to a conventional method.

In order to spin the acrylonitrile-based polymer, the acrylonitrile-based polymer is dissolved in a solvent to prepare a dope stock solution.

As a solvent for preparing the dope solution, acrylonitrile polymers such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), and dimethyl acetamide (DMAc) can be dissolved. A conventional organic solvent, an aqueous solution of an inorganic compound such as an aqueous zinc chloride solution or an aqueous sodium thiocyanate solution may be used, but dimethyl sulfoxide, which is an organic solvent having no amide bond, is most preferably used. The use amount of the said solvent is 18 to 22 weight% normally with respect to the weight of an acrylonitrile-type polymer.

Next, a polyacrylonitrile precursor fiber for carbon fibers prepared by sequentially passing the dope stock solution through a known spinning process, drying process, washing process and stretching process is prepared.

The present invention is characterized in that the dope is prepared at a low temperature of 25 ~ 50 ℃ to increase the stability of the dope. If the temperature is less than 25 ° C., dimethyl sulfoxide, which is an organic solvent, is coagulated, and thus it is difficult to prepare a dope solution, and even if it is prepared, a uniform dope solution is not produced. It is difficult to manufacture. In addition, when the temperature is higher than 50 ℃, the dope solution is easily modified to shorten the effective storage period of the dope solution, the physical properties of the precursor fiber is difficult to produce a high strength / high elastic carbon fiber.

As described above, when the dope is prepared and stored at a low temperature, the formation of a cyclized structure by intermolecular or intramolecular crosslinking is reduced, thereby reducing the occurrence of trimming and shaving in subsequent spinning or firing processes.

Specifically, according to the present invention, an acrylonitrile-based polymer comprising at least 90% by weight of acrylonitrile and the stretching and densification promoting component in the spinning process, the flame resistance promoting component and the oxygen permeation promoting component in the flameproofing process is used, and dimethyl Preparation of the dope stock solution at a concentration of 18% to 22% at a temperature of 25 to 50 ° C. using an organic solvent such as dimethyl sulfoxide, dimethyl formamide, or dimethyl acetamide desirable. The dope stock solution is spun by a wet or dry wet spinning method, and firstly stretched with hot water of 60 ° C. or higher, and then is secondly stretched with a high temperature fruit such as steam by imparting an emulsion including a silicone-based emulsion, a modified epoxy emulsion, and an ammonium compound. At this time, it is preferable to make the total draw ratio 7 to 20 times. The elongated fibers have a fineness of 0.5 to 2 dtex.

The spun carbon precursor is flameproofed in an oxygen atmosphere and at 200 to 400 ° C. and carbonized at an inert atmosphere and at 800 to 2000 ° C. according to a conventional method, thereby having uniform physical properties and defects caused by voids. Less carbon fiber can be produced.

Carbon fiber prepared using the precursor fiber produced by the manufacturing method according to the invention is useful as a material for forming energy-related substrates such as CNG tanks, wind turbine blades, turbine blades and structural reinforcement materials such as roads, bridges, etc. Can be used.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are intended to illustrate the present invention, but the scope of the present invention is not limited by the following examples.

In the following examples, in order to confirm the stability of the dope stock solution, the viscosity and UV transmittance change of the dope stock solution in the dope storage tank were checked with time. The UV transmittance was measured using an ultraviolet spectrometer (UV spectrometer) and dimethyl sulfoxide as a base solution (reference solution), and the transmittance (%) at wavelengths of 450 nm and 550 nm was measured. Viscosity of the dope solution was measured using a Brookfield viscometer and the viscosity in a thermostat maintained at 40 ℃. In addition, the uniformity of the precursor fibers was confirmed by measuring the tensile strength and the rate of change (CV%, coefficient of variation) of the precursor fibers.

Hereinafter, the Example and comparative example of this invention are demonstrated in detail.

< Example  1> Carbon fiber  Preparation of Precursors

In a 50 liter reactor equipped with a stirrer, 38.4 kg of ion-exchanged water (pH = 2.5) was charged, 96% by weight of acrylonitrile (AN), 3% by weight of methyl acrylate (MA) and 1 weight of itaconic acid (IA) % Was injected at a rate of 36 cc / min. To the total weight of the reactants, 0.15 wt% of sulfuric acid was injected with a redox-based catalyst combining 2.0 wt% of acidic ammonium sulfite and 0.2wt% of ammonium persulfate, and the ratio (the ratio of total monomer to ion-exchanged water) was It fed continuously at 1 / 5.5. At this time, polymerization temperature was 55 degreeC. The polymerization was carried out for an average residence time of 8 hours through sufficient stirring. Next, ion-exchanged water was added to the polymer aqueous dispersion obtained continuously from the outlet of the reactor, followed by sufficient washing and dehydration to obtain a wet polymer. The wet polymer thus obtained was dried with a vacuum dryer to obtain an acrylonitrile-based polymer shown in Table 1 below.

After drying the polymer, the dope solution was prepared by dissolving at 20 ° C. in dimethyl sulfoxide (DMSO) in a dope solution dissolution tank maintained at 35 ° C. The dope stock solution subjected to the defoaming process was stored in a reservoir maintained at 40 ℃. Within 2 hours after storage in a reservoir, the dope stock solution was spun dry at 45 ° C. using a nozzle of 3000 holes, 0.15 mm in diameter, and then solidified in a 35 ° C. coagulation bath (35 wt% DMSO aqueous solution). The coagulated yarn thus obtained was washed, stretched, emulsified, and dried and densified to obtain polyacrylonitrile precursor fiber. Tensile strength and tensile strength change rate (CV%) of the precursor fibers, the viscosity of the dope solution immediately before spinning and the UV transmittance and the viscosity of the dope solution 3 days after the production was measured and shown in Table 1.

< Example  2> Carbon fiber  Preparation of Precursors

A polyacrylonitrile precursor fiber was obtained in the same manner as in Example 1 except that the temperature of the dissolution tank was maintained at 50 ° C. during the preparation of the dope solution. The viscosity of the dope stock solution immediately before spinning and the viscosity of the dope stock solution 3 days after the preparation of the dope stock solution were measured and shown in Table 1. In addition, the tensile strength and the tensile strength change rate (CV%) of the precursor fibers were measured, and the results are shown in Table 1.

< Example  3> Carbon fiber  Preparation of Precursors

A polyacrylonitrile precursor fiber was obtained in the same manner as in Example 1 except that the temperature of the dissolution tank was maintained at 25 ° C. during the preparation of the dope solution. The viscosity of the dope stock solution immediately before spinning and the viscosity of the dope stock solution 3 days after the preparation of the dope stock solution were measured and shown in Table 1. In addition, the tensile strength and the tensile strength change rate (CV%) of the precursor fibers were measured, and the results are shown in Table 1.

< Comparative example  > Carbon fiber  Preparation of Precursors

A polyacrylonitrile precursor fiber was obtained in the same manner as in Example 1 except that the temperature of the dissolution tank was maintained at 65 ° C. during the preparation of the dope solution. The viscosity of the dope stock solution immediately before spinning and the viscosity of the dope stock solution 3 days after the preparation of the dope stock solution were measured and shown in Table 1. In addition, the tensile strength and the tensile strength change rate (CV%) of the precursor fibers were measured, and the results are shown in Table 1.

division Example 1 Example 2 Example 3 Comparative example polymer Polymerization composition and
Properties AN / MA / IA = 96/3/1
Intrinsic Viscosity 2.0 Dope
Manufacture conditions Melter temperature
(℃) 35 50 25 65

Dope
Properties
Immediately before radiation
Viscosity 920 920 920 930 Viscosity after 3 days of manufacture 940 950 930 1150 At 450nm
UV transmittance (%) 68 65 72 54 At 550nm
UV transmittance (%) 94 93 95 85
Precursor
fiber The tensile strength
(g / d) 7.9 7.9 7.8 7.3 The tensile strength
Rate of change (CV%) 3.5 4.5 6.1 10.2

Comparing Examples 1 to 3 and Comparative Example with reference to Table 1, when the PAN polymer was dissolved at low temperature, that is, at 25 to 50 ° C. during the preparation of the dope stock solution, the viscosity of the dope stock solution was low and did not change significantly after 3 days. I can see that it does not. In addition, it can be confirmed that the precursor fiber having excellent tensile strength can be prepared by using the dope stock solution having excellent viscosity stability.

Claims (1)

Preparation of polyacrylonitrile precursor fiber for carbon fiber comprising the step of preparing a dope solution using a polyacrylonitrile polymer containing 95% by weight or more acrylonitrile and less than 5% by weight comonomer As a method, The comonomer is made of two or more selected from the group consisting of methyl acrylate, acrylic acid, methacrylic acid, itaconic acid, The dope preparation step of producing a polyacrylonitrile precursor fiber for carbon fibers, characterized in that carried out at 25 ~ 50 ℃.