JPS58220821A - Acrylic carbon fiber bundle with high strength and elongation and its production - Google Patents

Abstract

PURPOSE:An acrylic polymer solution is filtered, extruded into a coagulation bath to form a precursoy yarn, then subjected to heat treatment under specific conditions, thus producing the titled fiber bundle with high strength and elongation as well as high reliability, because of its little deviation in qualities and performances. CONSTITUTION:A solution of an acrylic polymer mainly containing acrylonitrile is filtered by means of a filter with less than 5 micron aperture and extruded into a coagulation bath at a draft of 2.0-5.0. The resultant wet yarn is washed with water, drawn, treated with a finishing oil and dried to give the precursor yarn. The resultant precursor yarn is oxidized by heating it in an atmosphere of the air filtered through a filter of less than 1 micron aperture at 200-350 deg.C, then carbonized in an inert atmosphere at a temperature over 1,000 deg.C to produce the objective carbon fiber bundle consisting of more than 1,000 carbon filaments more than 85% of which are free from defects caused by foreign matters sticking thereto at the broken surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high strength and elongation acrylic carbon fiber bundle and a method for producing the same, and more specifically, it is used as a reinforcing fiber for composite materials, with small variations in quality and performance, and high reliability. The present invention relates to carbon fiber bundles.

Conventionally, carbon fiber has been used for aviation, space, sports equipment such as golf club shafts, fishing rods, tennis rackets, high-speed rotating bodies, automobiles, ships, etc. due to its excellent mechanical properties, especially specific strength and specific modulus. It is said that it will be used in many types of transportation machinery, and its uses are wide and diverse. Carbon fibers used in these applications, for example, as structural materials for aviation, space, and transportation machinery, have strong demands for improved quality and performance in order to improve the durability and reliability of these structural materials. However, it is not easy to manufacture carbon fibers that meet these demands with good productivity and at low cost.

That is, carbon fibers, especially high-strength carbon fibers commonly referred to as "high grade", are produced using precursor fibers 1. That is, fiber yarns made of an acrylonitrile polymer as precursors are used in air at 2oO' to 350°C. A method of converting the fibers into oxidized fibers by heating in an oxidizing atmosphere such as, etc., and then carbonizing or graphitizing the oxidized fibers by heating in an inert atmosphere represented by nitrogen at at least 1000'C. However, the productivity of carbon fiber.

In order to increase the carbonization rate and reduce the manufacturing cost, the usual methods are to increase the number of single fibers as a precursor as much as possible or to increase the rate of acidification and carbonization. All of these methods often degrade the physical properties, quality, and performance of carbon fibers, and are not industrially viable.

The present inventors have discovered that the mechanical properties of carbon fiber bundles consisting of multiple single fibers are caused by cracks, voids, foreign matter, etc., and that they rapidly decrease as the number of single fibers with structural defects increases. The number of single fibers that exhibit such structural defects is related to the number of single fibers that make up the precursor carbon fiber yarn, and moreover, if the number of single fibers that make up this carbon fiber bundle exceeds a certain number, the above-mentioned We have discovered that even if we suppress the occurrence of structural defects, we cannot expect a dramatic improvement in the mechanical properties of carbon fiber bundles, and we have conducted extensive studies to develop the present invention.

That is, the present invention provides a high-quality, high-performance carbon fiber bundle that can be used as a reinforcing material for composites in which the single fibers constituting the carbon fiber bundle have few structural defects and have small variations in mechanical properties.

The object of the present invention is to reduce the number of single fibers constituting the carbon fiber bundle to at least i ooo, preferably 2000 to 3.
．． , , 0.000, and when the fracture surface of the fiber obtained by subjecting the fiber bundle to a tensile fracture test was observed, fracture had started due to deposits. This can be achieved by using a fiber bundle in which the number of single fibers is 15% or less based on the number of single fibers constituting the carbon fiber bundle.

Here, the ≠ Nakasho defect caused by deposits is a defect that is detected and quantified by carrying out a tensile break test as detailed below and observing the fractured surface of a single fiber obtained by this test using an electron microscope.

First, in the tensile breakage test, a fiber group with a length of about 10 crn is taken out from a carbon fiber bundle sample that has been pre-washed with a caulking solvent, etc., and the fibers are appropriately opened and single fibers are randomly extracted from the fiber group. As shown in FIG. 1, this sampled single fiber (1) was punched out to a length of 5 an x 1 cm, which exactly corresponds to the length of the 50 samples.

Place the center line of the mount (2) on the perforated mount (2) with dimensions (
Make a test piece by straightening it along 3) and fixing it with adhesive (4).

Next, when extremely brittle fibers such as carbon fibers are tensilely fractured in the air, the impact at the time of fracture tends to cause secondary fractures in several places in addition to the primary fracture. Using a constant speed tension type tensile testing machine modified to perform a tensile fracture test, the test piece is attached to the test machine and a tensile fracture test is conducted at a tensile strain rate of 1%/depth.

This tensile fracture test is performed on at least 1 single fiber per total number of single fibers constituting the fiber bundle, the single fiber is taken out from the tensile fractured test piece, gold coating is applied to the primary fracture surface of the single fiber, and the single fiber is scanned. The fractured surface is observed using an electron microscope at an acceleration voltage of 25 KV and a magnification of 10,000 times, and a photograph is taken. FIG. 2 is an electron micrograph showing a typical example of a glutinous defect caused by deposits according to the present invention. As shown in FIG. 2, there is deposits attached to the fractured surface of the single fibers, and it can be seen that this deposits are the cause of the single fibers breaking.

In general, cracks and voids are widely known as typical structural defects in carbon fibers, and such cracks and void defects occur in the precursor itself and in the process of converting the precursor into carbon fiber. However, the deposit dust defects of the present invention are thought to be caused by impurities or foreign substances that adhere to the glare sensor during the manufacturing process and firing process of the precursor. The cause of occurrence is different from defects such as cracks and voids.

In other words, as will be explained later, in the production of carbon fiber, a sufficiently filtered and purified spinning stock solution is usually used as a breaker to ensure that the fibers are homogeneous without fusing between single fibers and without defects such as cracks or voids. Precursor fibers, especially acrylic fibers, are used, and it is necessary to apply an anti-fusing oil for flame resistance, such as a silicone oil, to this breaker, and to consider the conditions for flame resistance, carbonization, and carbonization. This prevents the occurrence of deposit defects in the resulting single fibers constituting the carbon fiber bundle, and reduces the uniformity of physical properties among the single fibers constituting the carbon fiber bundle.

In particular, when the number of single fibers becomes less than 1,000, not only does productivity drop and costs increase,
Adhesive deposits = It becomes difficult to reduce the number of single fibers with defects, and if the number of single fibers is too large, especially over 30,000, it is difficult to prevent deposits from occurring. Although this method is effective to some extent, it becomes difficult to achieve a wide range of mechanical properties as a carbon fiber bundle, and the object of the present invention cannot be achieved in either case.

Since the relationship between the number of single fibers constituting the carbon fiber bundle of the present invention and the deposits of the single fibers≠large defects and the physical properties of the carbon fiber bundle is related to the manufacturing conditions of the carbon fiber bundle, preferred embodiments of the present invention will be described below. A specific and detailed explanation will be given using a manufacturing method as an example.

First, as a spinning stock solution, in order to substantially remove impurities caused by the polymerization tank and transportation pipes, and gel-like substances caused by side reactions during polymerization, thermal deterioration, etc., the spinning solution is filtered through a filter with a mesh opening of 5μ or less. A stock solution is used. This spinning dope is passed through a multi-hole spinneret hole with a hole number of at least 1".000 into a coagulation bath, where it has a substantial draft, that is, a free discharge linear velocity (V f
) (D ratio Vt/'V f 2.0.~5.
It is discharged so that Os is preferably in the range of 2.5 to 4.5.

If the actual draft is less than 2.0, it is undesirable because it tends to cause fusion between the single filaments, and if it exceeds 5.0, the smoothness of the obtained carbon fiber tends to be impaired, which is undesirable. What is important is that the coagulated yarn spun in such a substantially draft manner is treated at least once in the process until the yarn is dried and densified.
．． To 5! It is necessary to pass through various processes such as coagulation, stretching, and water washing without being pressed by pressure exceeding /cdl. That is, if the wet yarn is pressed under a pressure exceeding 1.5 Kp/ctll in the step before the drying step, it is not preferable because not only inter-filament fusion but also carbon fibers with defects on the surface layer are likely to be formed. .

Furthermore, in addition to the above-mentioned filtration of the spinning solution, the water, chemicals, and oils used in each process such as coagulation, water washing, stretching, and process lubrication must be sufficiently purified or filters with an aperture of 5 μm or less should be used. It is preferable to use one that has been filtered in the same way as the spinning dope. Particularly for liquids such as coagulation bath liquids, a part of which is recycled and reused, it is recommended to strengthen purification by filtration.

Steps after drying include secondary stretching in steam or pressurized steam, application of an oil agent, and opening treatment, which can be applied as necessary.

However, the acrylic fiber yarn obtained as described above has a single yarn fineness of 0.5 to 1.5 d and a tensile strength and elongation of 5.7 f/d or more, preferably 6. O~Z5p/d and 8~12%, fineness fluctuation rate is 8 inches or less, preferably 5
It is preferable to select the manufacturing conditions for the acrylic fiber yarn of the breaker with a yarn having such physical properties as the target.

In order to stably produce the carbon fiber bundle of the present invention with good reproducibility, the heating atmosphere used in the firing process, especially the oxidation process, of the obtained acrylic fibers, such as dust contained in the air, inorganic metal fine particles, etc. etc. to be removed. Specifically, it is important to filter and clean using a filter with an eye opening of 1 μm or less.

This kind of filtration prevents iron and other inorganic metal oxides, which are generated due to heating and oxidative deterioration inside the air piping of the heating furnace, from adhering to the fiber surface and deteriorating the fiber surface. In addition, the above-mentioned acids, compounds, etc. once attached react with the carbon fibers in the carbonization process to form carbides, etc., thereby effectively preventing the formation of local defects on the carbon fiber surfaces. Therefore, in the present invention, it is preferable to filter and purify not only the oxidizing atmosphere but also the inert gas typified by nitrogen used in the carbonization step.

Next, in the present invention, the number of monofilaments is at least 10 as the precursor acrylic fibers to be subjected to the flame resistant process.
00, preferably 2,000 to 30,000 bundled yarns are required.

That is, when the number of single fibers of the acrylic fibers decreases to less than 1000, thermal decomposition products such as tar or pitch-like substances generated during the flame-retardant process adhere to the periphery of the fiber bundle, and Small amounts of dust, inorganic metal particles, etc. present in the flame-retardant atmosphere adhere and become fixed, leading to an increase in the number of single filaments that cause visual defects.

Therefore, the conditions for flame resistance are to always supply fresh air to prevent thermal decomposition products from adhering to the precursor, or to recirculate all or part of the heated air to save thermal energy. It is important to perform cleaning treatment, such as by oxidizing and decomposing thermal decomposition products in the air, before use.

However, if the number of single fibers in the acrylic fiber bundle used for flame resistance is too large, it becomes difficult to produce an acrylic fiber bundle with uniform fineness, shape, and physical properties. In addition, during the flame-proofing and carbonization processes, it becomes difficult to impart tension and heat transfer evenly to the constituent fibers of the fiber bundle, resulting in significant differences in physical properties between the fibers.

Hereinafter, the present invention will be specifically explained with reference to Examples. Example 1: 98 mol of acrylonitrile (AN) and 1. Ammonia was blown into a copolymer of 2 mol acrylic acid with an intrinsic viscosity [η] of 1.76 to create a modified polymer in which the terminal hydrogen of the carboxyl group of the copolymer was replaced with an ammonium group.
A dimethyl sulfoxide (DMSO) solution having a concentration of this modified polymer of 20% by weight was prepared. This solution was used as a door material, and after filtering through a 6μ sintered metal filter, the temperature was adjusted to 60℃, and the concentration was 50%.
was discharged into a DMSO aqueous solution. For the cap, hole diameter 1
], 05 m+++, and 5000 holes were used, the solidification take-off speed was set to 8 m191-, and the actual draft was set to 6.5. The coagulation bath solution was circulated and filtered through a micro-wind filter with a mesh opening of 5 μm. After washing the obtained coagulated yarn with water and stretching it five times in hot water, it was immersed in a corn oil bath at a pressure of 1.0 O.
Ky/cd! After reducing the moisture content of the fiber bundle by squeezing the fiber bundle in Nip Row 2, the fiber bundle is brought into contact with a roller surface heated to 160 to 160°C for drying and densification, and then 4. o
Stretched 2.5 times in pressurized steam at 2.5 y/crd.

Obtained single yarn fiber fineness: 1. Od,) - Tal Denir 3
Using a ring nozzle on a fiber bundle of 000D, the pressure was 0.7.
After the KF/CRD air opening process, the air was purified using a sintered metal filter with a mesh opening of 1μ, and the ambient temperature was maintained at 250°C and 260°C, respectively, in a hot air circulation heating furnace. The oxidation treatment was carried out by sequentially passing the sample in a substantially constant length state. Next, the obtained oxidized fiber bundle was carbonized at a maximum temperature of 1'500° C. in a nitrogen atmosphere that had been purified using a sintered metal filter having a mesh opening of 1 μm.

This carbon fiber bundle was subjected to a single fiber tensile rupture test using the method described in the text, and single fibers with scanning electron microscopic defects were observed, but the frequency was very low at 8%.

In addition, the average single fiber physical properties of this carbon fiber bundle were determined according to JIS4-7
The results were as follows: the strength was 405 to 9/mtM, the elongation was 1.62%, and the strand physical properties of this carbon fiber bundle were measured using the single fiber test method (n=60) described in 601. 455 Ni/mas elongation 1.84%
It showed very high physical properties.

Comparative Example 1 Acrylic fibers were continuously spun for 6 days in the same manner as in Example 1, except that the coagulation bath solution was not filtered through a microfist wind filter with a mesh opening of 5μ. did.

The obtained fiber yarn was subjected to oxidation treatment and carbonization treatment in the same manner as in Example 1 to produce carbon fibers.

When the fractured surface of the single fibers of the obtained carbon fibers was observed, it was found that the number of single fibers with defects caused by deposits was 66%, and the average single fiber strength was 500%. To! /
mA, elongation is 1.22%, strand flexibility is 365 K
l/rtta, the elongation was 1.47%.

Comparative Example 2 In Example 1, carbon fiber was produced in the same manner as in Example 1, except that the air used in the oxidation treatment step was not filtered using a sintered metal filter with an opening of 1μ. . When the fractured surface of the single fibers of the obtained carbon fibers was observed, it was found that the number of single fibers with pressing defects caused by deposits was 20%, and the average single fiber strength was 365/. A1 elongation is 1.39%, strand strength is 6
The elongation at 90/-1 was 1.58%.

Comparative Example 6゜In Example 1, the solidification take-off speed was extremely high at 2 m7 minutes! An acrylic fiber bundle was produced under the same conditions as in Example 1, except that the actual draft was set to 1.8.
. In Example 1, an acrylic fiber bundle was spun under the same conditions as in Example 1, except that the pick-up speed was very high at 18 m/min and the actual draft was 5.5, and then the acrylic fiber bundle was subjected to oxidation and carbonization treatments. carbon fiber was created.

When the fractured surface of the single fibers of the obtained carbon fibers was observed, it was found that the number of single fibers with non-M defects caused by deposits as shown in Fig. 2 was as large as 50%, and the average single fiber strength was 310K! /rtU elongation was 1.28%, strand strength was 660/-1 elongation was 1,49%.

Reference Example 1゜Example 1 except that the nip roller pressure was increased to 2.0 KF/aa in order to further reduce the moisture content of the fibers entering the drying and densification process. Acrylic fibers were spun in the same manner as in Example 1, and then fired in the same manner as in Example 1 to produce carbon fibers.

When the fractured surface of the single fibers of the obtained carbon fibers was observed, the number of single fibers with cracking defects caused by deposits was 24, the average single fiber strength was 320 KP/ma, and the elongation was 1.6.
2%, strand strength 575KP/mj, elongation 1.5
1chi was 0

[Brief explanation of drawings]

Fig. 1 is a plan view showing a test piece for a tensile rupture test used for detecting and quantifying cracks and defects caused by deposits in carbon fiber bundles according to the present invention, and Fig. 2 is a plan view showing a test piece according to the present invention. This is an electron micrograph showing a typical example of a lining defect caused by deposits on the patent.
it @ Aoi 2 161 ”” Ts7. I3.25 ”' Kazuo Wakasugi, Commissioner of the Japan Patent Office, 1, Indication of the case, 1982 Patent Application No. 97759
September 2, 1982, 2-2 Nihonbashi Muromachi, Chuo-ku, Tokyo
8th (shipment date) 5. Number of 4-lights that can be increased by amendment None & “Brief explanation of drawings” column of the specification subject to amendment (1) Page 18, line 6 to line 6 of the specification In the 7th line, "Figure 2 is an electron micrograph." is deleted and the following statement is inserted.

Claims (2)

[Claims] (1) Consisting of a carbon fiber bundle with a small number of single fibers, at least 8 of the single fibers constituting the fiber bundle.
No. 5 is a high-strength and elongated acrylic carbon fiber bundle that is a single fiber without any defects caused by deposits on its fractured surface. (2) Filter the acrylic polymer solution containing acrylonitrile as the main component through a filter with a mesh size of 5μ or less,
The net draft is set within the range of 2.0 to 5.0 and discharged into a coagulation bath, and the obtained wet yarn is washed with water, stretched, treated with an oil agent, and dried to form a precursor yarn. After that, the precursor thread was oxidized by heating within a temperature range of 200-350°C in a purified air atmosphere using a filter with an opening of 1μ or less, and then a small amount was oxidized in an inert atmosphere. A method for producing a high strength and elongation acrylic carbon fiber bundle, which comprises carbonizing both by heating to 1000°C.