JPS58169518A - Preparation of high-strength carbon fiber having improved uniformity - Google Patents

Abstract

PURPOSE:To obtain the titled fibers having a high strength and little variation in physical properties, by coagulating a spinning solution consisting of an acrylic polymer, drawing the resultant coagulated fibers in a specific coagulation bath, secondly drawing the drawn fibers, and calcining the secondly drawn fibers. CONSTITUTION:An acrylic polymer consisting of 90wt% or more acrylonitrile is dissolved in a solvent to prepare a spinning solution, which is then extruded through a spinneret into a coagulation bath and coagulated. The resultant coagulated fibers are drawn in a drawing bath containing a solvent, e.g. dimethylformamide, in a higher concentration, preferably 3wt% or more, higher than the concentration of the coagulation bath at 3-8 draw ratio, secondly drawn at 1.3-5 draw ratio and then calcined.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides high-strength carbon fibers with excellent uniformity (in this specification, "carbon fibers" include "graphite fibers").

). More specifically, as a precursor for high-strength carbon fibers, acrylic fibers produced by stretching coagulated fibers obtained in a wet spinning process in a solvent-containing drawing bath and then secondly drawing them are used, and the fibers are fired. This invention relates to a method for producing high-strength carbon fiber with excellent uniformity.

The production of charcoal bulk fibers from acrylic fibers is well known and widely practiced. However, there are still large variations in the physical properties of carbon fiber, so it cannot be said that the original ability of carbon fiber is fully demonstrated. The current situation is that there are many cut threads during the heat treatment process to make the sheath flame resistant, reducing productivity. In order to solve these problems, the strength, elastic modulus, and oriented island crystals of precursors for carbon fibers have been improved.
Several improvements have been proposed. In addition, the cut threads in the flameproofing process are rounded to prevent fugitive adhesion and fusion, which are thought to occur due to adhesion and fusion during the flameproofing process of the precursor, and optimization of flameproofing conditions and oil agents. The development of Despite this proposal, the strength of carbon fiber is estimated to be theoretically achievable, with a modulus of 1O of 50-1.
This has only been achieved to a certain extent. Furthermore, with regard to problems such as cut threads during flame resistance, fully satisfactory results have not been obtained.

An object of the present invention is to obtain carbon fibers that have high strength and small variations in strength and other physical properties. Still another object is to provide a precursor that reduces cut threads during flame resistance and enables stable operation.

The method for producing carbon fibers according to the present invention involves dissolving an acrylonitrile polymer in a solvent to create a spinning stock solution, extruding the spinning stock solution from a spinneret into a coagulation bath to coagulate it, and coagulating the obtained coagulated thread. It is characterized by firing an acrylic fiber tube produced by stretching in a stretching bath containing a solvent at a concentration higher than that of the coagulating liquid in the bath, and then subjecting it to secondary stretching.

As described above, a uniform structure can be obtained by sufficiently coagulating the prepared spinning dope in a coagulation bath and then stretching it in a solvent-containing stretching bath while containing the solvent. In other words, in a solvent-containing stretching bath, the polymer aggregates formed by coagulation are in a mobile state, making it possible to stretch more uniformly, forming a uniform structure, and making the degree of orientation uniform. .

(9) By pre-stretching the fiber in a solvent-containing state, the secondary stretchability is good, it is also possible to achieve a higher stretching ratio, and the physical properties of the obtained fibers are improved. When the acrylic fiber thus obtained is used as a precursor and fired, a uniform carbon fiber with high strength and other physical properties and small variations in these properties can be obtained.

Furthermore, the acrylic fiber precursor obtained by the method of the present invention has less variation in strength and other physical properties, fewer structural defects, and lastly, cut threads are extremely reduced when flame resistant, improving operating efficiency when flame resistant. do.

In the method of the present invention, by fully coagulating in a coagulation bath and then stretching in a stretching bath containing a solvent, more uniform stretching is achieved, the orientation is increased, and the degree of swelling is reduced. This will advance the refinement. in this way,
In order to reduce IlIMf and promote densification, it is necessary to make the solvent concentration in the solvent-containing drawing bath higher than the coagulation solution concentration in the coagulation bath, and it is desirable that the difference in concentration between the two is 3 weight centimeters or more. . Further, it is preferable that the temperature is -5° C. or more higher than the temperature in the solvent-containing drawing bath, since the degree of swelling decreases and densification proceeds more quickly. The stretching ratio in a solvent-containing stretching bath is preferably 3 to 8'.

As mentioned above, fibers uniformly drawn in a solvent-containing drawing bath have a uniform degree of orientation and extremely excellent secondary drawability. Therefore, by performing secondary stretching, the total abrasiveness is increased, and a precursor having an even greater degree of orientation and crystal orientation can be obtained.

In particular, when a nitric acid aqueous solution is used as a spinning dope adjustment compatibilizer, coagulation liquid, and drawing bath liquid, it becomes extremely difficult to draw heat due to the stretching ratio when drawing under the same manufacturing conditions as coagulation. In contrast, when, as in the method of the present invention, after sufficient coagulation in a coagulation bath, stretching is carried out in an aqueous nitric acid solution with a higher concentration of nitric acid than the concentration of nitric acid in the coagulation bath, the effectiveness of the present invention is extremely limited. It is. Further preferred conditions for the solvent-containing rectangular stretching bath are a concentration higher than that of the coagulation bath by 3 weight or more and a temperature higher than that of the coagulation bath (by 5° C. or more). Stretching under these conditions can sufficiently increase the stretching ratio and enable uniform stretching, and at the same time, the secondary stretching properties are good, the total abrasive stretching ratio is high, the degree of orientation is improved, and It becomes easy to spin fine fibers t* and fibers with a denier of less than .5 denier.

In the method of the present invention, the solvent for preparing the spinning dope, the coagulating solution in the coagulating bath, and the solvent in the solvent-containing drawing bath can be selected from those known as solvents for -artaryl polymers. Examples of such solvents include organic solvents such as dimethyl formand, dimethylacetamide, and dimethyl sulfoxide, and inorganic solvents such as rhodan salt, zinc chloride, nitric acid, and sulfuric acid. Among these, inorganic acid solvents such as nitric acid, which are coagulated at low temperatures to avoid denaturation during spinning, are most effective. Although they may be different, it is preferable that they be the same substance from the viewpoint of recovery.

The "acrylic polymer" used in the method of the present invention refers to polyacrylonitrile and copolymers of acrylonitrile containing at least 90% by weight of acrylonitrile and other unsaturated monomers, etc. Examples of unsaturated monomers include ethylenically unsaturated compounds such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, vinyl acetate, and itaconic acid. Acrylic polymers can be obtained by commonly used polymerization means.

The following margins The spinning itself in the method of the present invention may be carried out by any generally known water washing method, and the drying method may be used as long as it can remove moisture, and is not particularly determined. .

After stretching in a solvent-containing stretching bath or further washing with water7
j He then performs secondary stretching. The stretching method in the secondary stretching may be any conventionally known stretching method such as hot water stretching method, steam stretching method, pressurized saturated steam stretching method, heated steam stretching method, dry heat stretching method, hot pin stretching method, etc. A combination of two or more of these methods may also be used. The stretching temperature is also not particularly limited, and may be the same as conventionally used conditions as long as the fibers are sufficiently heated and the desired uniform stretching is achieved. The stretching ratio applied in the secondary stretching is based on the # fiber length of the stretching film in a solvent-containing stretching bath, and any conventionally known casting method can be adopted. Generally, 150 to 400 in an oxidizing atmosphere
A preferred firing method is a flameproofing step in which the material is heated to C to cyclize it, and then a carbonization step in which it is carbonized or graphitized by firing at a high temperature in a non-oxidizing atmosphere or under reduced pressure. Air is suitable as the atmosphere for the flameproofing process, and nitrogen, helium, argon, etc. are suitable as the atmosphere for carbonization or graphitization.

The carbon fibers obtained by the method of the present invention are not only strong but also have good uniformity in quality, and have a high degree of strength and uniformity in quality. It has the best performance as a sot forming material. Furthermore, there are very few cut threads during the flame-retardant process, and carbon fibers can be manufactured with high productivity.

Typical examples of the method of the present invention are shown below.
Percentages are expressed on a weight basis unless otherwise specified.Example 1 An acrylonitrile copolymer consisting of 97% acrylonitrile and 30% acrylic acid was dissolved in 7OS nitric acid, and a spinning stock solution having a polymer concentration of 16.3- was prepared by lI! The purified liquid was extruded from a spinneret into a 35.3 inch nitric acid aqueous solution at -3°C and sufficiently coagulated. After that, the conditions of the nitric acid-containing drawing bath were variously changed (conditions are described later in M1!). !), the film was stretched at a stretch ratio of 5 times by 6'6°, and then a second stretching was carried out at a stretch ratio of 3 times in hot water or saturated steam. Thereafter, 11 precursors with a single yarn fineness of 1.5 denibe and a filament number of 6.00Of were prepared by washing with normal water and drying at 150°C. For comparison, the same spinning stock solution as above was used at 35.3%. .

After extruding into a nitric acid aqueous solution at -3℃ and solidifying it sufficiently,
Washed with water without stretching in a solvent-containing stretching bath,
Stretched 5 times in hot water, dried at 15015℃,
Single yarn fineness 1.5 denier, number of filaments 6.00Of
A precursor was created.

The precursor obtained by K as described above was continuously treated for 45 minutes while being stretched 1.5 times at 240°C in an air atmosphere using an electric furnace tube to obtain a flame-resistant yarn. , and then the flame-retardant yarn was heated at 300°C under a nitrogen atmosphere.
By gradually increasing the temperature from 1,200°C to 1,200°C over 3 minutes, the fibers were obtained. The physical properties of the resulting returned fibers were measured. The results are shown in Table 1 below.

From the following margin tlI and Table 1, it can be seen that according to the method of the present invention, carbon fibers with high strength and small variations in strength can be obtained. In addition, adhesion is reduced and the number of cut threads is extremely small.

Example 2 A drawn yarn obtained by drawing in a solvent-containing drawing bath in the same manner as in Example 1 was washed with water in a conventional manner to remove the solvent, and then heated at 150°C.
After drying using a cylinder of
A 5 denier, 6,000 filament precursor was prepared.

The precursor thus obtained was treated under the same conditions as in Example 1, and the strength and variation of carbon fiber obtained were compared. In addition, the presence or absence of cut threads and adhesion during flame resistance was also determined. The results are shown in Table 2 below.

Margin 2I below! From the results, it can be seen that according to the method of the present invention, high-strength carbon 1L edge fibers with excellent uniformity can be obtained.

Example 3 Apv Ronitrile 98 t, Methyl methacrylate t
-, an acrylonitrile-based copolymer consisting of 1.0% methacrylic acid was dissolved in an aqueous solution of 55% rhodan soda to prepare a spinning stock solution with a polymer concentration of 16%, and a spinning stock solution with a polymer concentration of 16% was prepared. 6,000) at -3℃, 15
．． After extrusion into a Rodan soda aqueous solution of No. 51 and solidifying it sufficiently, the conditions of the stretching bath containing Rodan soda were variously changed (conditions are shown in Table 3 below) to obtain a stretching ratio of 5.
Stretching was performed at 5 times. After that, wash thoroughly with water, then
Secondary stretching was performed at a stretching ratio of 3 times in heated steam at 20°C. It was dried at 150° C. to produce a precursor having a single yarn fineness of 1.5 denier and a number of filaments of 6.00 Of.

The precursor obtained by K as described above was subjected to flameproofing treatment and carbonization treatment in the same manner as in Example 1 to obtain carbon fibers. # The strength, elastic modulus, and stiffness variations of the fibers were compared and studied. The results were as shown in Table 3 below.

Below, samples A19 to -22 had very good cut threads in the margin flameproofing process, whereas sample A16 had many cut threads and had extremely poor operability.

Example 4 Using the coagulated thread prepared in Example 1, a zinc chloride aqueous solution (
Stretching was carried out at a stretching ratio of 6 times (at a concentration of 42° C. and a temperature of 15° C.). After washing with water, secondary stretching was carried out in hot water at 100° C. at a draw ratio of 2.5 times, followed by drying to produce a precursor having a single yarn fineness of 1, 2 deniers, and 6,000 filaments. This fiber was treated with flame resistance in the same manner as in Example 1.
Carbonization treatment was performed to obtain carbon fibers. The physical properties of this Ω carbon fiber were measured. The tensile strength is 435 k&/m2, and the variation σ is 2.2 Yu/W2, which shows extremely high strength and small variation. The elastic modulus is also the same, 25.5 Ton/sm and σ is 0.4 Ton/sm.
It was an excellent one. In addition, there were very few cut threads in the flame-retardant process, and there was good elongation during operation.

Claims (1)

[Claims] 1. When producing acrylic fibers or carbon fibers, an acrylic polymer containing 90 weight or more of acrylonitrile is dissolved in a solvent to create a spinning stock solution, and the spinning stock solution is passed through a spinneret. It is extruded into a coagulation bath to coagulate, and the resulting coagulated thread is drawn in a drawing bath containing a high concentration of solvent in addition to the coagulation solution in the coagulation bath, and then subjected to secondary drawing to create an acrylic material. A method for producing carbon fiber with excellent uniformity and high strength, which is characterized by firing the fibers. 2. Concentration of coagulating liquid in coagulating bath and solvent in solvent-containing drawing bath 1
The method for producing carbon fibers according to claim 1, wherein there is a difference of 3 weight or more in relation to f) &. 3. The method for producing carbon fibers according to claim 1, wherein the temperature of the coagulating liquid in the coagulating bath is 5° C. or more lower than the temperature of the solvent in the solvent-containing drawing bath. 4. The method for producing carbon fibers according to any one of claims 1 to 3, wherein an aqueous nitric acid solution is used as a solvent for preparing a spinning dope, a coagulation liquid, and a solvent in a solvent-containing drawing bath.