KR20110078242A - Method of preparing polyacrylonitrile-based precursors for carbon fibers - Google Patents

Abstract

PURPOSE: A method of manufacturing the polyacrylonitrile group precursor fiber for carbon fiber is provided to prevent acrylonitrile group polymer from doing a cyclization reaction by controlling production of a amine compound by hydrolysis in the production and storage of the dope undiluted solution, and to maintain stability of the dope undiluted solution. CONSTITUTION: The method of manufacturing the polyacrylonitrile group precursor fiber for carbon fiber is as follows. The doped undiluted solution throws in an acrylonitrile copolymer and organic solvent in a dissolver, and dissolves the acrylonitrile copolymer in the organic solvent. The precursor fiber production is emits the dope undiluted solution and manufactures the acrylonitrile-group precursor fiber for carbon fiber. The dope undiluted solution production is done by throwing nitrogen.

Description

Method for producing polyacrylonitrile precursor fiber for carbon fiber {METHOD OF PREPARING POLYACRYLONITRILE-BASED PRECURSORS FOR 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 copolymerizable vinylic monomer is conventionally used for the polymer solution which uses organic solvents, such as dimethyl sulfoxide, dimethyl formamide, and 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.

However, the dope stock solution may be hydrolyzed by moisture. That is, the amine compound is formed in the dope solution by hydrolysis of the dope solution, whereby the acrylonitrile polymer easily forms a cyclized structure. As a result, a problem of lowering the stability of the dope stock solution may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and prevents the cyclization reaction of acrylonitrile-based polymers caused by amine compounds by inhibiting the production of amine compounds by hydrolysis during preparation and storage of the dope stock solution, and furthermore, It is an object of the present invention to provide a method for producing a precursor for carbon fiber of good quality while maintaining the stability of the stock solution.

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 is prepared by the step of preparing a dope stock solution and the dope stock solution to dissolve the acrylonitrile-based copolymer in the organic solvent by adding an acrylonitrile-based copolymer and an organic solvent in the dissolution tank A method for producing acrylonitrile precursor fiber for carbon fiber, comprising the step of preparing a precursor fiber for producing acrylonitrile precursor fiber for carbon fiber, wherein the dope is prepared in order to remove moisture in the dope solution It provides a method for producing acrylonitrile precursor fiber for carbon fiber, characterized in that the input.

In addition, the method for producing acrylonitrile precursor fiber for carbon fiber according to the present invention is characterized in that the nitrogen is continuously added for 30 to 90% of the time of the dope solution preparation time.

In addition, the method for producing acrylonitrile precursor fiber for carbon fiber according to the present invention further includes the step of storing the dope stock solution in a storage tank after the dope stock solution manufacturing step, 50% of the storage time in the storage tank Nitrogen is continuously added for the above time.

According to the method for producing acrylonitrile precursor fiber for carbon fiber of the present invention, by continuously adding nitrogen to the dope solution during the preparation and storage of the dope solution, the production of the amine compound by hydrolysis and the resulting acrylonitrile polymer It can suppress the cyclization reaction of.

Therefore, by spinning the dope stock solution in which the risk of deterioration of the dope stock solution by the cyclization reaction of the acrylonitrile-based polymer is reduced, it is possible to obtain precursor fibers with uniform quality and excellent quality.

As a result, defects in the precursor fibers and defects in the carbon fibers due to the modification of the dope stock solution can be reduced, whereby high strength / high elastic carbon fibers can be produced.

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

The precursor for carbon fiber produced 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 sulfone group include allyl sulfonic acid, metharylsofonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesul And 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, can also 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. In this case, an amine compound by hydrolysis is formed in the dope stock solution during the preparation and storage of the dope stock solution, whereby the acrylonitrile polymer can easily form a cyclized structure. In this case, the cyclized structure of the acrylonitrile polymer inhibits the stability of the dope stock solution.

In addition, when spinning the dope solution, internal defects are formed during solidification / extension of the precursor fiber by the cyclized acrylonitrile polymer present in the dope solution. Such precursor fibers undergo a firing process, causing defects that lower the physical properties of the carbon fibers.

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. If the amount of the organic solvent used is too small or too large, it is difficult to spin the polymer or prevent the formation of voids.

In order to maintain the stability of the dope stock solution, the present invention is characterized in that nitrogen is added to both the dissolution tank for preparing the dope stock solution, the storage tank for storing the dope stock solution, or both the dope stock solution in the dissolution tank and the storage tank.

First, nitrogen is added to the dope solution dissolving tank to remove all moisture present therein, and then an organic solvent such as acrylonitrile copolymer (PAN) and dimethyl sulfoxide (DMSO) is added to prepare a dope solution. Nitrogen is continuously added until the preparation of the dope is completed. At this time, the dope stock solution of the dissolution tank is moved to a defoaming tank and subjected to a defoaming process as necessary. In addition, prior to transferring the prepared dope solution to the dope solution storage tank, by introducing nitrogen into the dope solution storage tank to remove all the moisture present therein to suppress the formation of cyclization structure of the amine compound and acrylonitrile.

In the manufacturing step of the dope stock solution, the time in which nitrogen is added may vary depending on the dope stock solution manufacturing time, the nitrogen input time is typically 30 to 90%, preferably 50 to 90% of the stock preparation time, most preferably It is 60-80%. If the nitrogen is less than 30%, the moisture is not completely removed, the dope solution is easily denatured, the storage period of the dope solution is shortened and the physical properties of the precursor fiber is changed to produce high strength / high elastic carbon fiber. Difficult to do However, when the nitrogen input time is 90% of the preparation time of the stock solution and 80%, there is almost no difference in the physical properties of the precursor fiber. none.

In addition, nitrogen should be continuously added to the dope stock storage tank and the time of nitrogen input depends on the storage time of the dope stock solution, but the nitrogen input time is usually 50% or more of the storage time, preferably 60% or more, Most preferably at least 80%.

In this way, by introducing nitrogen into the dope stock solution of the dissolution tank during the preparation of the dope stock solution, a part of the water is first removed, and nitrogen is continuously added to the dope stock solution in the storage tank, so that the dope stock solution can be easily changed. By removing it, the stability of the dope stock solution can be ensured.

As described above, a carbon fiber precursor having reduced internal defects can be produced by spinning a dope stock solution having a stable stability by adding nitrogen.

The spinning can be carried out wet or wet. The spun carbon fiber precursor, i.e. acrylonitrile-based fiber, was drawn in hot water of 50 ° C. or higher, and then treated with 0.01-5.0 wt% aqueous solution of an emulsion including a modified silicone emulsion, an epoxy-modified silicone emulsion, fine particles, and an ammonium compound. Then, if necessary, it is stretched again in a high temperature fruit such as steam, and can be produced as precursor fibers for carbon fibers. At this time, the total draw ratio of the prepared precursor fiber is usually 7 to 25 times, and the short fiber fineness is 0.5 to 2.0 dtex.

The carbon fiber precursor thus fired was flameproofed in an oxygen atmosphere and at 200 to 400 ° C. and carbonized at 800 to 2000 ° C. in an inert atmosphere, 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 invention, but the scope of the 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. The viscosity of the dope stock 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.

Example 1 Preparation of Carbon Fiber Precursor

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% by weight of itaconic acid (IA) Was injected at a rate of 36 cc / min, and 0.15% by weight of sulfuric acid and redox-based catalyst in which 2.0% by weight of acidic ammonium sulfite and 0.2% by weight of ammonium persulfate were injected, and 100 parts by weight of the reactant was used. The ratio of total amount to ion-exchanged water) was 1 / 5.5, so that it was continuously supplied. The polymerization temperature was 55 ℃, the polymerization was carried out so that the average residence time is 8 hours through sufficient stirring. A polymer aqueous dispersion was continuously obtained from the outlet of the reactor, and ion-exchanged water was added to wash thoroughly, and the wet polymer obtained by dehydration was dried with a vacuum dryer to obtain an acrylonitrile-based polymer shown in Table 1 below.

The dried polymer was dissolved in dimethyl sulfoxide (DMSO) at a concentration of 20% by weight in a dope stock solution maintained at 50 ° C. for 3 hours, and nitrogen (1 kgf / cm 2, purity 99.5% for 1.8 hours, 60% of the dissolution time). Or more). The dope stock solution subjected to the defoaming process was transferred to a storage tank maintained at 40 ° C., and nitrogen (1 kgf / cm 2, purity 99.5% or more) was added to the storage tank for 1.6 hours, which is 80% of the storage time. After 2 hours, the dope was spun dry at 40 ° C. using a nozzle of 3000 holes and a diameter of 0.15 mm, and then solidified in a 40 ° C. solidification bath (35 wt% DMSO aqueous solution). This was washed, stretched, emulsified and dried to densify to obtain polyacrylonitrile precursor fiber. Viscosity, UV transmittance, and tensile strength and tensile strength change rate (CV%) of the dope stock solution immediately before spinning were measured, and the results are shown in Table 1 together.

Example 2 Preparation of Carbon Fiber Precursor

A polyacrylonitrile-based precursor fiber was obtained in the same manner as in Example 1, except that the dope solution was stored for 48 hours in a 40 ° C. storage tank and spun and spun with nitrogen for 38.4 hours, which is 80% of 48 hours. Viscosity, UV transmittance, and tensile strength and tensile strength change rate (CV%) of the dope stock solution immediately before spinning were measured, and the results are shown in Table 1 together.

Example 3 Preparation of Carbon Fiber Precursor

Same as Example 2, except that nitrogen was added to the dissolution tank for 0.9 hours, 30% of the dissolution time, and stored for 48 hours in a storage tank, and nitrogen was added for 24 hours, 50% of the 48 hours. Polyacrylonitrile precursor fiber was obtained by the method. Viscosity, UV transmittance, and tensile strength and tensile strength change rate (CV%) of the dope stock solution immediately before spinning were measured, and the results are shown in Table 1 together.

Comparative Example 1 Preparation of Carbon Fiber Precursor

A polyacrylonitrile precursor fiber was obtained in the same manner as in Example 1 except that nitrogen was not added to the dope stock solution dissolution tank and the storage tank. Viscosity, UV transmittance, and tensile strength and tensile strength change rate (CV%) of the dope stock solution immediately before spinning were measured, and the results are shown in Table 1 together.

Comparative Example 2 Preparation of Carbon Fiber Precursor

A polyacrylonitrile precursor fiber was obtained in the same manner as in Example 2 except that nitrogen was not added to the dope stock solution dissolution tank and the storage tank. Viscosity, UV transmittance, and tensile strength and tensile strength change rate (CV%) of the dope stock solution immediately before spinning were measured, and the results are shown in Table 1 together.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 polymer Polymerization composition and
Properties AN / MA / IN = 96/3/1
Intrinsic Viscosity = 2.0
Dope
Stock solution
Produce
Condition
Dissolution time 3 3 3 3 3 Melting bath
Nitrogen injection time 1.8 1.8 0.9 0 0 Storage time 2 48 48 2 48 Reservoir
Nitrogen injection time 1.6 38.4 24 0 0 Dope
Stock solution
Properties Viscosity 925 930 950 950 1500 At 450nm
UV transmittance (%) 68 65 62 55 44 At 550nm
UV transmittance (%) 93 92 90 85 82 Precursor
fiber Tensile strength (g / d) 7.8 7.9 7.9 7.6 7.5 Tensile Strength CV% 3.4 4.5 6.1 8.5 12.0

Comparing Examples 1 to 3 and Comparative Example 1 and Comparative Example 2 shown in Table 1, by continuously injecting nitrogen into the dope stock solution during the preparation and storage of the dope stock solution, the viscosity of the dope stock solution was lowered, and the precursor fiber It can be seen that the tensile strength of increases.

Claims (3)

Dopant solution preparation step of dissolving the acrylonitrile-based copolymer in the organic solvent by adding an acrylonitrile-based copolymer and an organic solvent to the dissolution tank and spinning the dope solution to produce acrylonitrile precursor fiber for carbon fibers As a method for producing acrylonitrile precursor fiber for carbon fiber comprising a precursor fiber manufacturing step, The method for producing acrylonitrile precursor fiber for carbon fiber, characterized in that the nitrogen is added in the dope preparation step. The method of claim 1, The method of preparing nitrogen in the dope preparation step is a method for producing acrylonitrile precursor fiber for carbon fibers, characterized in that 30 to 90% of the dope preparation time. The method according to claim 1 or 2, Further comprising the step of storing the dope stock solution in a storage tank after the dope stock solution manufacturing step, The storage tank is a method for producing acrylonitrile precursor fiber for carbon fiber, characterized in that the nitrogen is continuously added for more than 50% of the storage time.