JP3223452B2 - Method for producing carbon fiber precursor fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber precursor (precursor), and more particularly to 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 fiber.

[0002]

2. Description of the Related Art With respect to high strength and high elasticity of carbon fibers, many techniques relating to firing techniques and post-treatment techniques have been proposed, while many techniques relating to improvement of acrylic fibers as carbon fiber precursors have been proposed. Proposed. As one means for increasing the strength and elasticity, it has been proposed to increase the density of acrylic fibers as a carbon fiber precursor.

[0003] Conventionally, as a measure of the compactness of an acrylic fiber as a carbon fiber precursor, the amount of iodine adsorbed on the precursor fiber, the thickness of a skin layer for adsorbing iodine, or a process in a swollen state are considered. The degree of swelling of the yarn is adopted. (JP-A-58-214518, JP-B-63
No. 21916).

However, in these techniques, for example, in the method using iodine, only the density of the surface layer of the fiber can be measured, so that the density of the entire fiber cannot be known. Further, the amount of adsorbed iodine depends on the amount and type of oil agent attached. Unlike the above, there is a problem in that the fiber matrix structure is easily affected by factors other than the denseness. In addition, the method of defining the swelling degree of the coagulated yarn and the swelling ratio which is the ratio of the swelling degree of the coagulated yarn to the swelling degree of the bath drawn yarn only represents the composition ratio of the solid portion and the liquid portion of the swollen yarn. However, it is not enough as a measure of compactness taking into account the fineness of microstructure. As described above, the evaluation method conventionally used is not sufficient for accurately grasping the denseness of the fiber. For this reason, a sufficiently high-density fiber could not be obtained depending on a method for producing a precursor fiber employing a conventional evaluation method.

[0005]

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

[0006]

Means for Solving the Problems The present inventors have developed a high strength,
In order to obtain a carbon fiber with high elasticity, as a result of intensive examination of a method for producing a highly dense acrylic fiber, the average pore radius and porosity are used as a scale for evaluating the denseness of the structure of the precursor fiber. The present inventors have found that the denseness can be accurately evaluated, and have completed the present invention for producing a highly dense precursor fiber.

That is, according to the present invention, a solvent solution of an acrylic polymer containing 95% by weight or more of acrylonitrile unit and 0.5% by weight or more of acrylamide unit is wet-spun to obtain an average pore radius of 140 ° or less and an empty space. 55% porosity
After the following coagulated yarn, the average pore radius of 110Å or less which was washed with stretching in boiling water, porosity 40
% Of water-swelled yarn, and then subjecting the water-swelled yarn to a silicone oil treatment and a dry densification treatment.

In the present invention, the acrylic fiber-forming polymer must contain acrylonitrile units in an amount of 95% by weight or more and acrylamide units in an amount of 0.5% by weight or more. 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-methylolacrylamide, 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-vinyl pyridine and 2-methyl-5-vinyl pyridine, methacryl Examples thereof include sulfonic acid derivatives such as sodium sulfonic acid, vinyl acetate, methacrylonitrile and the like, and these can be used alone or in combination.

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

[0010] In wet spinning the spinning solution described above, the average pore radius is 140Å or less and a porosity makes with the following coagulated yarn 55%. To obtain a small solidification yarn having such an average pore radius and porosity, polymer spinning dope - the concentration as well as 18% or more as described above, the temperature of the spinning dope 60 ° C.
The above can be achieved and the temperature of the coagulation bath can be reduced to 50 ° C. or lower, preferably 40 ° C. or lower.

[0011] In the present invention, the coagulated yarn described above, first, is given to the air drawn into 1.0 to 2.0 times preferred. Then, stretching while washing the solvent contained in the coagulated yarn in boiling water. At this time, the film is preferably stretched 1 to 10 times.
As the stretching method, a multi-stage stretching method of two or more stages can be used. This method is advantageous because it reduces the occurrence of voids due to sudden deformation of the yarn.

Further, it is effective to set the stretching bath temperature as high as possible within a range in which the single yarns do not fuse with each other, and to make the temperature as high as possible than the coagulation bath temperature. From this viewpoint, the temperature of the stretching bath is preferably set to a high temperature of 70 ° C. or higher.
In the case of the multi-stage stretching method, it is preferable that the temperature of the final bath is 90 ° C. or higher.

[0013] The average water-swellable yarns pore radius 110Å or less by optimizing such stretching conditions, the porosity can be 40% or less.

In the present invention, the average pore radius and the porosity are values measured by the following mercury intrusion method. The yarns from the coagulation bath and the drawing bath are collected, washed with water, and the structure is fixed using a freeze-drying method using liquid nitrogen. About 0.2 g of the dried sample is precisely weighed and placed in a dilatometer. Next, the inside of the container was vacuumed (0.05
Torr or less) and then filled with mercury. Then, the measurement is performed using a porosimeter. The pore radius is determined from the external pressure, and the pore volume is determined from the mercury intrusion amount. The pressure is applied up to 3000 bar. The porosity was determined using the following equation. Porosity = ρVp / (ρVp + 1) [where ρ = specific gravity, Vp = measured value (pore volume per g)] The average pore radius was determined as follows.

[0015]

(Equation 1)

[Where ni = number of pores, N = number of total pores, ri = pore radius (Å)] The equation for obtaining r is as follows. πr ² p = −2πrσcos θ [where, σ: surface tension of mercury, θ: contact angle]

The above-mentioned water-swelled yarn is thereafter subjected to a silicone-based or modified silicone-based oil treatment. At this time, the amount of the oil agent attached is 0.01 to 5% by weight per fiber, and control is performed so that the single yarns do not fuse with each other and the bunching property is good. After the silicon-based oil treatment, the fibers are dried and densified to obtain highly dense fibers. Further, after the drying, the drawing can be further enhanced by performing a dry heat drawing with a heating roller.

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

[0019]

The present invention will be described more specifically with reference to the following examples. The physical property values used in the text and the examples are as follows:
It was measured by the following method. (1) The performance (strength and elastic modulus) of carbon fiber is measured according to JIS R
It measured according to -7601. It was determined from the physical properties of the strand impregnated with the epoxy resin. (2) The average pore radius and porosity were based on the mercury porosimetry described above.

Example 1 Acrylonitrile (AN) and acrylamide (AAm)
Acrylic copolymer obtained by copolymerizing methacrylic acid (MAA) with methacrylic acid (MAA) as a third component at a weight ratio shown in Table 1 is dissolved in dimethylacetamide, and a spinning stock solution (polymer concentration 21% by weight, stock solution temperature 70 ° C.) Was prepared. The spinning solution using a spinneret having a diameter of 0.075 mm, hole number 3000, concentration 72%, coagulated yarn ungated discharged in dimethylacetamide bath liquid bath temperature 35 ° C., which is 1.5 times of the air The film was stretched, then stretched 4.3 times in a stretching bath at 70 ° C., further stretched 1.3 times in a boiling water stretching bath, and washed.

[0021] was then confer silicon-based oil agent with a controlled concentration so this water-swollen yarn, convergence does not occur fusion of single yarn each other is in good condition. Then heat at 130 ° C
Drying and densification treatment were performed with a slurry to obtain a carbon fiber precursor fiber of the present invention. The average pore radius and porosity of coagulated yarn and water-swelling yarn and the physical properties of carbon fibers produced from the precursor fibers are shown in Table 1.

[0022]

[Table 1]

[0023] Table 1 from coagulated yarn and an average pore radius smaller water-swellable yarns, also as low precursor fiber porosity, it can be seen that the strength and modulus can be produced with high carbon fiber.
In the first column of Table 1, acrylonitrile (AN) units are used.
An example using a copolymer of 90% by weight.
Was.

Comparative Example 1 In Example 1, methyl acrylate (MA) was used as a copolymer 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. Table 2 shows the results.

[0025]

[Table 2]

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

The spinning conditions, drawing conditions, oil treatment, and dry densification are the same as in Example 1. After the dry densification treatment, a carbon fiber precursor fiber subjected to dry heat drawing by 1.2 times with a heating roller at 180 ° C. and a carbon fiber precursor fiber not subjected to the dry heat drawing are produced, respectively. The physical properties of carbon fibers produced from Co., Ltd. were examined. Table 3 shows the results.

[0028]

[Table 3]

By performing dry heat drawing after the dry densification treatment, carbon fibers having higher strength and higher elasticity can be produced.

Example 3 A spinning dope was prepared using a polymer having the same polymer composition as in Example 2 and a solvent. The concentration of the coagulation bath was kept constant at 72%, and the temperature was changed in the range of 25 to 55 ° C., and the same wet spinning as in Example 1 was performed. Table 4 shows the results.

[0031]

[Table 4]

The average pore radius and porosity of the water-swollen yarn after solidification yarn及<br/> beauty stretching according to lower the temperature of the coagulation bath is reduced, carbon fibers produced from each precursor fiber It was found that the performance (strength and elastic modulus) was also significantly improved.

[0033]

According to the present invention, it is possible to produce a carbon fiber precursor acrylic fiber having high density. Therefore, high strength, high elasticity carbon fibers can be produced from the precursor fibers.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yukio Kasobo 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside of Mitsubishi Rayon Co., Ltd. Otake Office (56) References JP-A-59-88925 (JP, A) JP-A-63-256713 (JP, A) JP-A-61-41326 (JP, A) JP-A-62-117814 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 1/00-6/96 D01F 9/00-9/04

Claims (2)

(57) [Claims] 1. A solvent solution of an acrylic polymer containing at least 95% by weight of acrylonitrile unit and at least 0.5% by weight of acrylamide unit is wet-spun to obtain an average pore radius of 140 ° or less and a porosity of at least 140%. After forming a coagulated yarn of 55% or less, the coagulated yarn is washed while being stretched in boiling water to form a water-swelled yarn having an average pore radius of 110 ° or less and a porosity of 40% or less. A method for producing a precursor fiber for carbon fiber, comprising subjecting a yarn to a silicone oil treatment and a dry densification treatment. 2. An acrylonitrile unit of at least 95% by weight,
A composition containing 0.5% by weight or more of acrylamide units
The solvent solution of the cryl polymer is wet-spun and the average pore half
A coagulated yarn with a diameter of 140 ° or less and a porosity of 55% or less
After that, this is first stretched 1-2 times in air, then in boiling water
Washing while stretching 1 to 10 times with an average pore radius of 11
0% or less, water-swelling yarn having a porosity of 40% or less
The water-swollen yarn is treated with a silicone oil agent, and then dried and densified.
Of precursor fiber for carbon fiber characterized by applying
Method.