JPH04257313A - Production of precursor fiber for carbon fiber - Google Patents

Abstract

PURPOSE:To produce the subject precursor fiber for carbon fiber, having a high density and suitable for production of a carbon fiber having a high strength and a high elasticity. CONSTITUTION:A method for producing a precursor fiber for carbon fiber by wet spinning a solvent solution of an acrylic polymer composed of acrylonitrile and acrylamide, washing the resultant coagulated yarn having <=140Angstrom average pore radius and <=55% porosity while stretching it in boiling water, and then applying silicone-based oil treatment and drying-densification treatment to the resultant water-swallen yarn having <=110Angstrom average pore radius and <=40% porosity. The object can be achieved by setting the average pore radius and the porosity to the above-mentioned values.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for producing a carbon fiber precursor (precursor), and in particular a highly dense carbon fiber precursor suitable for producing carbon fibers having high strength and high elasticity. The present invention relates to a method for producing body fibers.

0002

[Prior Art] Many techniques related to firing and post-treatment techniques have been proposed to increase the strength and elasticity of carbon fibers.On the other hand, there are also many techniques related to improving acrylic fibers as carbon fiber precursors. Proposed. As one means of achieving high strength and high elasticity, it has been proposed to increase the density of acrylic fibers as carbon fiber precursors.

[0003] Conventionally, as a measure of the density of acrylic fibers as carbon fiber precursors, the amount of iodine adsorbed by the precursor fibers, the thickness of the skin layer that adsorbs iodine, or the process in which the fibers are in a swollen state. The degree of swelling of the thread is used. (Japanese Unexamined Patent Publication No. 58-214518, Japanese Patent Publication No. 63-
21916).

However, with these techniques, for example, the method using iodine can only measure the density of the surface layer of the fiber, so the density of the entire fiber cannot be determined, and the amount of iodine adsorbed depends on the amount and type of oil agent. However, there is a problem in that it is easily influenced by factors other than the denseness of the fiber matrix structure. In addition, the method of specifying the degree of swelling of coagulated yarn and the swelling degree ratio, which is the ratio of the degree of swelling of coagulated yarn to the degree of swelling of bath-drawn yarn, only represents the composition ratio of the solid part and liquid part of the swollen yarn. However, it is extremely insufficient as a measure of compactness that takes into account the fineness of the microstructure. As described above, the evaluation methods that have been used in the past have not been sufficient to accurately grasp the denseness of fibers. Therefore, it has not been possible to obtain fibers with sufficiently high density depending on the method for producing precursor fibers that employs conventional evaluation methods.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing acrylic fibers as a highly dense carbon fiber precursor for obtaining high-strength, high-elasticity carbon fibers.

[0006]

[Means for Solving the Problems] The present inventors have developed high strength,
In order to obtain highly elastic carbon fibers, as a result of intensive studies on the manufacturing method of highly dense acrylic fibers, we found that the average pore radius and porosity were used as measures to evaluate the denseness of the structure of the precursor fibers. They discovered that the density can be accurately evaluated, and completed the present invention for producing precursor fibers with high density.

That is, the present invention involves wet-spinning a solvent solution of an acrylic polymer containing 95% by weight or more of acrylonitrile units and 0.5% by weight or more of acrylamide units to form voids with an average pore radius of 140 Å or less. Porosity is 55%
After forming the following coagulated thread, it is washed while being stretched in boiling water to have an average pore radius of 110 Å or less and a porosity of 40%.
This is a method for producing a precursor fiber for carbon fibers, which is characterized in that the following water-swellable yarns are prepared, and then the water-swellable yarns are subjected to a silicone oil treatment and a dry densification treatment.

In the present invention, the acrylic fiber-forming polymer must contain at least 95% by weight of acrylonitrile units and at least 0.5% by weight of acrylamide units. Examples of copolymerization components other than acrylonitrile and acrylamide include acids such as acrylic acid, methacrylic acid, and itaconic acid, acrylic acid derivatives such as methyl acrylate and methyl methacrylate, methacrylamide, N-methylol-acrylamide, N,N - Acrylamide derivatives such as dimethyl acrylamide, alkyl vinyl ketones such as methyl vinyl ketone and ethyl vinyl ketone, acrolein derivatives such as acrolein and methacrolein, vinyl pyridine derivatives such as 2-vinylpyridine and 2-methyl-5-vinylpyridine, methacryl Examples include sulfonic acid derivatives such as sodium sulfonate, vinyl acetate, methacrylonitrile, and the like, and these may be used alone or in combination.

The solvent for the acrylic polymer used in preparing the spinning dope is not particularly limited, but may include dimethylformamide, dimethylsulfoxide, dimethylacetamide,
Nitric acid, rhodan soda aqueous solution, zinc chloride aqueous solution, etc. can be used. In the present invention, the concentration of the polymer in the spinning dope is 18% by weight or more. Further, the temperature of the spinning dope is preferably 60°C or higher. Although the solution viscosity of the spinning dope is determined by the intrinsic viscosity, concentration, and temperature of the polymer, it is preferable to set the concentration of the polymer to be as large as possible within the range of solution viscosity allowable as manufacturing conditions.

[0010] The above spinning dope is wet-spun to form a coagulated thread having an average pore radius of 140 Å or less and a porosity of 55% or less. In order to obtain a coagulated yarn with such a small average pore radius and porosity, the polymer concentration of the spinning stock solution should be set to 18% or more as described above, and the temperature of the spinning stock solution should be set to 60°C or higher. This can be achieved by controlling the temperature of the coagulation bath to 50°C or lower, preferably 40°C or lower.

[0011] In the present invention, it is preferable that the above-mentioned coagulated thread is first drawn in the air to a ratio of 1.0 to 2.0 times. Next, the coagulated thread is drawn in boiling water while washing the solvent contained in the coagulated thread. At this time, it is preferable to stretch the film by 1 to 10 times. Moreover, as a method for this stretching, it is also possible to use a multi-stage stretching method of two or more stages. This method is advantageous because it reduces the occurrence of voids due to rapid deformation of the yarn.

Furthermore, it is effective to set the drawing bath temperature as high as possible within a range where the single filaments do not fuse together, and to make it as high as possible above the coagulation bath temperature. From this point of view, it is preferable that the temperature of the drawing bath be a high temperature of 70° C. or higher. In the case of a multistage stretching method, it is preferable that the final bath be heated to a high temperature of 90° C. or higher.

By optimizing the stretching conditions as described above, the average pore radius of the water-swollen yarn is 110 Å or less, and the porosity is 4.
It can be reduced to 0% or less.

In the present invention, the average pore radius and porosity are values measured by the following mercury intrusion method. The threads coming out of the coagulation bath and drawing bath are collected, washed with water, and the structure is fixed using a freeze-drying method using liquid nitrogen. Approximately 0.2 g of this dry sample is accurately weighed and placed in a dilatometer. The inside of the container is then evacuated (0.05 Torr or less) using a mercury injection device, and then filled with mercury. Then, measurement is performed using a porosimeter. The pore radius is determined by external pressure, and the pore volume is determined by the amount of mercury intrusion. Pressure is up to 30
Apply up to 00 bar. The porosity was determined using the following formula. Porosity=ρVp/(ρVp+1) [where, ρ=specific gravity, Vp=measured value (pore volume per g)] Further, the average pore radius was determined as follows.

[0015]

[Math 1]

[Here, ni=number of pores, N=total number of pores, ri=pore radius (Å)] The formula for determining r is as follows. πr2p=-2πrσcosθ [where, σ: surface tension of mercury, θ: contact angle]

The water-swollen yarn is then treated with a silicone-based or modified silicone-based oil. At this time, the amount of oil applied is 0.01 to 5% by weight per fiber, and controlled so that the single yarns do not fuse together and have good cohesiveness. After the silicone oil treatment, the fibers are dried and densified to produce highly densified fibers. Moreover, if dry heat stretching is further performed using a heating roller after drying, the denseness can be further improved.

[0018] Since the acrylic fiber obtained by the method for producing a carbon fiber precursor fiber bundle of the present invention has high density as a whole fiber, the carbon fiber obtained by firing the acrylic fiber has high strength and high elasticity. .

[0019]

EXAMPLES The present invention will be explained in more detail with reference to Examples below. The physical property values used in the text and examples are as follows:
It was measured by the following method. (1) Performance (strength, elastic modulus) of carbon fiber is JIS
Measured according to R-7601. It was determined from the physical properties of strands impregnated with epoxy resin. (2) The average pore radius and porosity were determined by the mercury intrusion method described above.

Example 1 Acrylonitrile (AN) and acrylamide (AAm)
An acrylic copolymer prepared by copolymerizing and methacrylic acid (MAA) as a third component in the weight ratio shown in Table 1 was dissolved in dimethylacetamide to make a spinning stock solution (polymer concentration 21% by weight, stock solution temperature 70°C). was prepared. Using a spinneret with a diameter of 0.075 mm and 3000 holes, this spinning stock solution was discharged into a dimethylacetamide water bath solution with a concentration of 72% and a bath temperature of 35°C to form a coagulated thread, which was then stretched 1.5 times in the air. The film was then stretched 4.3 times in a 70° C. stretching bath, further stretched 1.3 times in a boiling water stretching bath, and washed.

[0021] Next, this water-swollen thread was given a silicone oil agent whose concentration was controlled so that the single threads would not fuse together and would have good cohesiveness. Thereafter, a drying and densification treatment was performed using a heated roller at 130°C to obtain a carbon fiber precursor fiber of the present invention. Table 1 shows the average pore radius and porosity of the coagulated yarn and water-swollen yarn, as well as the physical properties of the carbon fiber produced from the precursor fiber.

[0022]

[Table 1]

From Table 1, it can be seen that the smaller the average pore radius of the coagulated yarn and the water-swellable yarn and the lower the porosity of the precursor fiber, the higher the strength and modulus of elasticity of the carbon fiber can be produced.

Comparative Example 1 In Example 1, methyl acrylate (MA) was used as a copolymerization component instead of acrylamide. The copolymerization weight ratio at this time was acrylonitrile/methyl acrylate/methacrylic acid=95/4/1. A carbon fiber precursor fiber was produced in the same manner as in Example 1 using this acrylic copolymer. The results at this time are shown in Table 2.

[0025]

[Table 2]

Example 2 Copolymerization of acrylonitrile, acrylamide, and methacrylic acid A dimethylacetamide solution of an acrylic copolymer having a weight ratio of acrylonitrile/acrylamide/methacrylic acid = 98/1/1 (polymer concentration 21% by weight, A stock solution temperature of 70° C.) was used for the spinning stock solution.

The spinning conditions, stretching conditions, oil treatment, and drying and densification conditions are the same as in Example 1. After dry densification treatment, carbon fiber precursor fibers were subjected to dry heat stretching of 1.2 times with a heating roller at 180°C, and carbon fiber precursor fibers that were not subjected to the dry heat stretching were prepared. The physical properties of carbon fibers manufactured from The results are shown in Table 3.

[0028]

[Table 3]

[0029] After the dry densification treatment, a carbon fiber with even higher strength and higher elasticity can be produced by performing dry heat stretching.

Example 3 A spinning stock solution was prepared using a polymer having the same polymer composition as in Example 2 and a solvent. Wet spinning was carried out in the same manner as in Example 1, with the concentration of the coagulation bath kept constant at 72% and the temperature varied within the range of 25 to 55°C. The results are shown in Table 4.

[0031]

[Table 4]

As the temperature of the coagulation bath is lowered, the average pore radius and porosity of the coagulated fiber and the water-swollen fiber after drawing become smaller, and the performance (strength,
It was found that the elastic modulus) was also significantly improved.

[0033]

According to the present invention, carbon fiber precursor acrylic fibers having high density can be produced. Therefore, high-strength, high-elasticity carbon fibers can be produced from this precursor fiber.

Claims (1)

[Claims] Claim 1: A solvent solution of an acrylic polymer containing 95% by weight or more of acrylonitrile units and 0.5% by weight or more of acrylamide units is wet-spun, and the average pore radius is 140 Å or less and the porosity is After forming a coagulated thread of 55% or less, this is washed while being stretched in boiling water to form a water-swellable thread with an average pore radius of 110 Å or less and a porosity of 40% or less, and then the water-swellable thread is A method for producing a precursor fiber for carbon fibers, which comprises subjecting the fibers to a silicone oil treatment and a dry densification treatment.