JPH04281008A - Acrylonitrile precursor fiber bundle - Google Patents

Abstract

PURPOSE:To obtain an acrylonitrile-based precursor fiber bundle having high productivity and capable of readily manifesting high strength and high modulus when it is converted into a carbon fiber. CONSTITUTION:An acrylonitrile-based precursor fiber bundle being a fiber consisting of a polymer containing >=95wt.% acrylonitrile and >=0.1wt.% acrylamide, having <60 degree contact angle with water and 0.8-3.2 intrinsic viscosity [eta], treated with a silicon-based lubricant and having iodine absorption amount of <1wt.% based on the fiber weight.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylonitrile precursor fiber bundle for producing carbon fibers or graphite fibers.

0002

[Prior Art] Conventionally, carbon fibers and graphite fibers (hereinafter collectively referred to as carbon fibers) using acrylic fibers as precursors have been used for aerospace applications, sports, and leisure applications due to their excellent mechanical properties. Carbon fiber is commercially produced and sold as a reinforcing fiber material for high-performance composite materials, but in order to improve the performance of these composite materials, demands for improving the quality and performance of carbon fiber are becoming increasingly strict.

Unlike acrylic fiber for clothing, acrylic fiber as a precursor of carbon fiber is an intermediate product for producing the final product, carbon fiber, so it is easy to convert into carbon fiber. It is essential to improve the quality and performance of the obtained carbon fibers, and at the same time, it is extremely important that the carbon fibers have high productivity, excellent stability during spinning operations, and can be provided at low cost.

From this point of view, many proposals have been made regarding acrylic fibers as precursors.
When focusing on the quality and performance of the carbon fibers obtained, there are inventions such as increasing the degree of polymerization of raw material polymers and reducing the content of copolymer components other than acrylonitrile. It is common to adopt

However, in the former case, the solubility of the raw material polymer in the solvent generally decreases, the stability of the spinning dope is impaired, and the precipitation and solidification of the polymer increases significantly.
It is not possible to stably produce precursor fibers. In addition, in the latter method, since the uncoagulated dope yarn passes through the air, there is a limit to the hole density of the nozzle, and it cannot be said to be advantageous in terms of spinning productivity.

[0006] On the other hand, attempts have been made to maintain productivity and cost reduction during spinning using a wet spinning method, but a characteristic of the spinning method is that the structure of the obtained precursor fiber is low. In addition, single fiber breakage and fuzzing easily occur in the fiber bundle, so that the mechanical performance and quality of the obtained carbon fibers are not satisfactory.

[0007] There are reports that refer to the denseness of the fiber structure while using the wet spinning method, such as Japanese Patent Application Laid-Open No. 58-214518, but this also focuses on improvements in process passability during firing and associated carbon fiber quality. This method is still insufficient from the viewpoint of improving the performance of carbon fiber.

Furthermore, by using an acrylonitrile copolymer containing a predetermined amount of (meth)acrylamide and a carboxyl group-containing vinyl monomer as the raw material polymer, and inserting a preoxidation step at a low temperature in the precursor firing step, Attempts have been made to improve the fusion between single fibers that occurs during firing or single fiber breakage due to shrinkage stress (Japanese Patent Application Laid-Open No. 52-34027, etc.), but recently there has been a demand for shorter times and faster speeds. It cannot be used for firing and processing, and a satisfactory effect cannot be obtained.

That is, in the present invention, the fusion between single fibers is remarkable due to the high speed firing required today, and the precursor fibers do not have a high degree of density, so the resulting carbon fibers are expensive. However, it has not yet reached a level that is satisfactory in terms of both performance. Furthermore, it has a significant impact on manufacturing costs.
Even in these inventions, no research has been conducted regarding the stability of the precursor fiber during continuous spinning operations.

[0010] Despite much research being done in the past, there is no carbon fiber precursor fiber that is stable in industrial production, has excellent spinning productivity, and is of high quality with reduced single fiber breakage, fuzz, etc. At present, carbon fibers that have a highly dense fiber structure and a high level of mechanical performance have not yet been obtained.

[0011]

[Problems to be Solved by the Invention] In response to such conventional techniques, the present inventors traced back to the composition and characteristics of the raw material acrylonitrile polymer, and improved the stability of precursor fiber production and improved the fiber structure. The present invention was developed through intensive studies on finer grain size, densification, and optimization of firing reactivity. That is, an object of the present invention is to provide an acrylonitrile precursor fiber bundle that is highly productive and can easily exhibit high strength and high elastic modulus when made into carbon fibers.

0012

[Means for Solving the Problems] The object of the present invention is to provide a material containing 95% by weight or more of acrylonitrile and 0.1 to 2.5% by weight of acrylamide as essential components, and having a contact angle with water of less than 60 degrees. ,, intrinsic viscosity [η] is 0.8 to 3.
This can be achieved by using an acrylonitrile precursor fiber bundle which is a fiber treated with a silicone oil agent and which is made of an acrylonitrile polymer (2) and has an iodine adsorption amount of less than 1% by weight per fiber weight.

In the present invention, when the amount of iodine adsorbed in the precursor fiber is 1% by weight or more, the denseness of the fiber structure decreases, making it difficult to obtain carbon fibers with excellent mechanical properties such as strength and elastic modulus. In addition, an increase in the amount of iodine adsorption is also related to excessive penetration of oil components into the fiber matrix, and in addition to the above-mentioned negative impact on carbon fiber performance,
This may cause problems such as quality deterioration due to fusion between single fibers and problems due to adhesion of oil thermal decomposition products to the inside of the kiln.

The fiber of the present invention consists of a copolymer containing 95% by weight or more of acrylonitrile and 0.1 to 2.5% by weight of acrylamide as essential components. At this time, other comonomers copolymerizable with acrylonitrile and acrylamide may be used to control the solubility in solvents, spinnability, or flame resistance reactivity of the polymer as a precursor.

For example, (meth)acrylic acid, itaconic acid,
Examples include crotonic acid and its esters, acid amides other than acrylamide, and (meth)acrylic acid or itaconic acid is preferably used.

[0016] When the acrylonitrile content is less than 95% by weight, the structure of the precursor fiber obtained lacks denseness and cannot exhibit high performance as a carbon fiber. Furthermore, if the amount of acrylamide, which is an essential copolymerization component, is less than 0.1% by weight, excellent results in terms of spinning stability cannot be obtained, and at the same time, troubles such as burning of the fibers are likely to occur during the firing stage, and the flame resistance reaction time is shortened. is significantly hindered.

On the other hand, if the acrylamide content exceeds 2.5% by weight, it may cause problems in the production of the copolymer, cause the denseness of the precursor fibers, cause fusing between single fibers due to thermal decomposition products, etc. Therefore, it becomes difficult to obtain the performance of the carbon fiber.

In the present invention, the acrylonitrile polymer used has an intrinsic viscosity [η] of 0.8 to 3.2. If [η] does not reach 0.8, the mechanical properties of the obtained precursor fiber will deteriorate, and it will be difficult to apply an appropriate tension during the firing process, making it impossible to achieve high performance of the carbon fiber. do not have. On the other hand, if [η] exceeds 3.2, the viscosity of the spinning dope increases, making stable spinning difficult.

The present inventors have discovered a relationship between the contact angle of the raw material polymer with water and phenomena that impair the quality of the precursor fiber bundle, such as thread breakage and fuzz during spinning. That is, the contact angle of the acrylonitrile polymer in the present invention with water is 6.
When the temperature is less than 0 degrees, yarn breakage and fuzz are significantly reduced during spinning using the polymer (especially wet spinning method), and the quality of the resulting precursor fiber bundle can be stably improved. The contact angle of the polymer with water is determined by the content of acrylamide, a comonomer, or by factors including the type and content of other copolymer components when added.

Furthermore, in the fiber manufacturing process using this acrylamide-containing polymer, the production of macrovoids is extremely suppressed, especially in the coagulation process, and the working range of coagulation conditions is dramatically expanded. The density of the fiber structure, expressed in terms of the amount, is significantly improved.

[0021] As the silicone oil agent in the present invention,
For example, polyether-modified polysiloxanes such as polydimethylpolysiloxane ethylene oxide copolymers, alcohol-modified polysiloxanes, amino-modified polysiloxanes, dimethylpolysiloxanes used in combination with some emulsifiers, alkyl-modified polysiloxanes, etc. are desirable.

[0022] During the adhesion treatment, it is necessary to perform the adhesion process evenly among the single fibers and without variation in the amount of adhesion, and it is preferable that the amount of the adhesion oil agent be 0.05 to 3% by weight based on the weight of the fibers. The precursor fiber bundle according to the present invention does not cause various troubles in its manufacturing process, has high productivity,
The carbon fibers have high quality and high density, and the carbon fibers obtained by firing can exhibit high performance.

It is necessary that the amount of iodine adsorbed in the precursor fiber of the present invention is less than 1% by weight based on the weight of the fiber. If the amount of iodine adsorbed in the precursor fiber exceeds 1% by weight, the denseness and fineness of the fiber structure will be impaired and the fiber will become non-uniform, resulting in the formation of defect points in the fiber. Therefore, fiber breakage occurs due to the tension generated in the firing process, and at the same time, the density of the obtained carbon fiber decreases and structural defects remain, making it impossible to exhibit excellent performance in terms of tensile strength, elastic modulus, and compressive strength.

An example of manufacturing the acrylonitrile precursor fiber bundle of the present invention will be explained. The acrylonitrile copolymer of the present invention may be polymerized by any known method such as solution polymerization or slurry polymerization. Further, the obtained copolymer can be made into a precursor fiber by any known method, and any known organic or inorganic solvent can be used for spinning.

In the present invention, this acrylonitrile copolymer solution is spun, stretched (in air and in a bath, or in a bath), and dried and densified according to known methods. The spinning method may be a wet method or a dry/wet method, but it is preferable to perform the spinning under conditions such that the degree of swelling of the coagulated yarn is 200% or less.

[0026] The bath drawing may be carried out directly on the spun yarn, or
Alternatively, the stretching may be carried out after the spun yarn is once drawn in the air. Stretching in a bath is usually performed in a stretching bath at 50 to 98° C. once or in two or more stages, and washing with water may be performed before, during, or after the stretching, but the present invention is limited to this. It hasn't been done.

[0027] Through these operations, it is preferable that the coagulated filament be stretched by about 6 times or more by the time the bath stretching is completed. The yarn after bath drawing and washing can be dried and densified by any known method, but in consideration of drying speed, simplicity of equipment, fiber densification effect, etc., a method using heated rollers at 130°C or higher is recommended. is preferred. Furthermore, if necessary, the yarn may be further stretched using a high-temperature heated roller or pressurized steam before or after drying and densification. Furthermore, the silicone oil treatment is carried out by employing a conventional method such as applying it as a process oil.

[0028]

[Examples] The present invention will be explained in detail with reference to Examples below. "%" represents weight %. (a) "Intrinsic viscosity of copolymer [η]" Measured using a dimethylformamide solution at 25°C. (b) "Contact angle of copolymer with water" A dimethylformamide solution of the copolymer was cast onto a smooth glass plate, dried and the solvent was removed to create a film with a thickness of approximately 20μ, and then Distilled water for injection was dropped, and the contact angle was measured using a contact angle measuring device (model CA-P, manufactured by Kyowa Kagaku Co., Ltd.).

(c) "Iodine adsorption amount of fiber" 2 g of precursor fiber was accurately weighed and placed in a 100 ml Erlenmeyer flask. Add to this an iodine solution (100 g of potassium iodide, 9 g of acetic acid)
0g, 2,4 dichlorophenol 10g, iodine 50g
Dissolve in distilled water to make 1000ml solution) 100ml
1 and shaken at 60°C for 50 minutes to perform iodine adsorption treatment. Thereafter, the adsorption treated yarn was washed with ion-exchanged water for 30 minutes, further rinsed with distilled water, and then centrifugally dehydrated. Place the dehydrated thread in a 300ml beaker and add 200ml of dimethysulfoxide.
ml and heat to dissolve at 60°C. This solution is N/1
The amount of iodine adsorbed was determined by potentiometric titration with a 0.00 silver nitrate aqueous solution. (d) “Strand strength and elastic modulus of carbon fiber” JI
It was measured according to the method described in S-7601.

Example 1 A copolymer consisting of 97% acrylonitrile, 2% acrylamide, and 1% methacrylic acid, having a contact angle with water of 56 degrees and an intrinsic viscosity [η] of 1.7, was prepared at a copolymer concentration of 23%. % in dimethylformamide solution to prepare a spinning stock solution, 30%
Wet spinning was performed in a 70% dimethylformamide aqueous solution using a 00 hole nozzle. After washing and removing the solvent while stretching in boiling water, the film was immersed in a silicone oil bath solution for approximately 130°C. A precursor fiber bundle of 3000 filaments and a single yarn denier of 1.2 d was obtained by drying and densifying the fibers using a heating roller of C.

The amount of iodine adsorbed by this fiber was measured and was found to be 0.6%. Furthermore, during the spinning process, almost no single yarn breakage or occurrence of fuzz was observed. This fiber is 230~
The fibers were made into flame-retardant fibers with a fiber density of 1.36 g/cm3 while being elongated by 5% in a hot air circulating flame retardant furnace at 270°C, and then the fibers were heated at a maximum temperature of 600°C under a nitrogen atmosphere.
A low-temperature heat treatment was performed at an elongation rate of 5%, and further treatment was performed for about 1.5 minutes under the same atmosphere in a high-temperature heat treatment furnace with a maximum temperature of 1400°C under an elongation of -5%. The obtained carbon fiber had a strand strength of 496 Kg/mm2 and a strand elastic modulus of 27.6 ton/mm2.

Example 2 The comonomer composition ratio of the acrylonitrile copolymer is shown in Table 1.
A copolymer with an intrinsic viscosity [η] of 1.7 was produced by making the changes as shown in Figure 1. A dimethylacetamide solution with a copolymer concentration of 21% was used as the spinning stock solution, and a 70% Wet spinning was carried out in an aqueous dimethylacetamide solution.

[0033] The spun yarn was once stretched 1.5 times in air, and then washed and desolventized while being stretched in boiling water.
Thereafter, a precursor fiber was obtained in the same manner as in Example 1. These fibers were of good quality with very little single thread breakage and fuzz. Subsequently, these fibers were fired under the same conditions as in Example 1 to obtain carbon fibers. The results are shown in Table 1.

Comparative Example 1 Acrylonitrile/methyl acrylate/methacrylic acid (
A precursor fiber was obtained in the same manner as in Example 2 using a copolymer of 95/4/1). During spinning, single filament breakage was noticeable in the coagulation bath and drawing bath, and winding around the heating roller for drying and densification occurred. In addition, fuzz was observed in the obtained fiber. Table 1 shows the contact angle of the copolymer used with water and the amount of iodine adsorbed by the precursor fiber. Further, the carbon fiber performance obtained by firing the fiber under the same conditions as in Example 1 is shown in Table 1.

Example 3 The precursor fiber B in Example 2 was dried and densified, then stretched twice in pressurized steam, and dried again using a heated roller. The amount of iodine adsorbed in this fiber bundle was 0.4%. The obtained precursor fibers were fired under the same conditions as in Example 1 to obtain carbon fibers having a strand strength of 510 kg/mm 2 and a strand elastic modulus of 27.6 t/mm 2 .

Comparative Example 2 A precursor fiber bundle with an iodine adsorption amount of 0.9% was obtained in the same manner as in Example 2 except that the acrylonitrile copolymer was made of 99% acrylonitrile and 1% methacrylic acid. Ta. During spinning, single filament breakage occurred frequently in the coagulation bath and drawing bath, and the filament wound around the heated roller for drying and densification. The contact angle of the copolymer used with water was 62°. Further, the precursor fiber was fired in the same manner as in Example 2, and the strand strength was 380 kg/mm2.
, a carbon fiber having a strand elastic modulus of 24.2 t/mm2 was obtained.

[0037]

[Table 1]

Claims (1)

[Claims] Claim 1: Contains 95% by weight or more of acrylonitrile and 0.1 to 2.5% by weight of acrylamide as essential components, has a contact angle with water of less than 60 degrees, and has an intrinsic viscosity [η] of 0.
．． An acrylonitrile precursor fiber bundle, which is a fiber treated with a silicone oil agent and made of an acrylonitrile polymer having a molecular weight of 8 to 3.2, and has an iodine adsorption amount of less than 1% by weight per fiber weight.