JPH0329890B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a method for producing high-strength and elongation acrylic carbon fiber bundles, particularly as fibers for reinforcing composite materials, with small variations in quality and performance and reliability. The present invention relates to a method for producing carbon fiber bundles with enhanced carbon fiber bundles.

[Prior Art] Conventionally, carbon fiber has been used for aerospace, tennis rackets, golf club shafts,
In addition to sports equipment such as fishing rods, high-speed rotating bodies, and transportation equipment such as automobiles and ships, it is expected to be used in a wide range of fields. Carbon fibers used in these applications, such as structural materials for aerospace and transportation machinery, are in strong demand 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 that are generally referred to as "high grade", are manufactured by using fiber threads made of acrylonitrile polymer as their precursor fibers, i.e., precursors, at temperatures of 200 to 350°C.
The fibers are heated in an oxidizing atmosphere such as air to convert the fibers into oxidized fibers, and then heated in an inert atmosphere such as nitrogen at a temperature of at least 1000°C to carbonize or graphitize. .

[Problems to be Solved by the Invention] In the production of the above-mentioned carbon fibers, in order to increase productivity and reduce production costs, it is usually necessary to increase the number of single fibers as a precursor as much as possible, or to increase the rate of oxidation and carbonization. However, these methods often deteriorate the physical properties, quality, and performance of the carbon fiber.

The present inventors have discovered that the mechanical properties of carbon fiber bundles consisting of multiple single fibers rapidly decrease as the number of single fibers with structural defects due to cracks, voids, foreign objects, etc. increases, and that It was discovered that when the number of single fibers exceeds a certain value, dramatic improvement in the mechanical properties of the carbon fiber bundle cannot be expected, and this led to the present invention.

That is, an object of the present invention is to provide a high-quality, high-performance carbon fiber bundle as a reinforcing material for a composite in which the single fibers constituting the carbon fiber bundle have few structural defects and have small variations in mechanical properties.

[Means for Solving the Problems] The above-mentioned object of the present invention is to filter an acrylic polymer solution containing acrylonitrile as a main component through a filter with a mesh opening of 5 μm or less, and to reduce the actual draft to 2.0 to 2.0 μm.
5.0 and discharged into the coagulation bath, and apply a pressure of 1.5 using a Nitsu roller etc. to the resulting wet yarn with at least 1000 constituent single fibers.
Kg/cm ² or less, the fibers are washed with water, stretched, and treated with a silicone oil, and then dried to form precursor fiber threads. After that, the threads are opened and passed through a filter with a diameter of 1μ or less. A high strength and elongation acrylic system characterized by being oxidized by heating at a temperature range of 200 to 350°C in an air atmosphere that has been purified by using acrylic resin, and then carbonized by heating to at least 1000°C in an inert atmosphere. This can be achieved by a method for producing carbon fiber bundles.

That is, in the present invention, first, the precursor spinning dope is prepared by spinning in order to substantially remove impurities caused by the polymerization tank, transportation pipes, etc., and gel-like substances caused by side reactions during polymerization, thermal deterioration, etc. Prior to washing, filter and clean using a filter with a viscosity of 5μ or less.

This cleaned spinning stock solution has a number of holes.
It is discharged into a coagulation bath through a multi-hole spinneret of 1000 or more holes, and the actual draft, that is, the take-up speed (V ₁ )
The ratio of free discharge linear velocity (V _f ) to V ₁ /V _f is 2.0
-5.0, preferably within the range of 2.5-4.5. At this time, if the actual draft is smaller than 2.0, fusion between the single filaments tends to occur, while if it exceeds 5.0, the smoothness of the obtained carbon fiber will be impaired.

Next, the coagulated yarn spun in such a substantial draft is subjected to pressure of 1.5 kg/cm ² or less with a nip roller or the like, at least in the process until the yarn is dried and densified. In addition to maintaining
It is important to pass through each process such as coagulation, stretching, washing with water, and application of silicone oil. As a result, it is possible to significantly reduce not only inter-filament fusion of carbon fibers but also defects in the surface layer portion.

The pressure exerted by the nip roller, etc. here is the value obtained by dividing the total load (total of its own weight, air pressing force, mechanical loss, etc.) applied to the nip roller, etc. by the nipped area of the yarn, and the nipped area is the total yarn width. It is the product of the nip length in the longitudinal direction of the yarn, measured with pressure-sensitive paper (for example, "Prescale" manufactured by Fuji Film Corporation).

At this time, it is desirable to use water, chemicals, oils, etc. in each process such as coagulation, stretching, oil treatment, etc. that have been filtered with a filter with a mesh opening of 5 μm or less, as in the case of the spinning dope.
In particular, cleaning by filtration is desirable when a part of the coagulation bath liquid is recycled and reused.

Further, steps after drying include secondary stretching in steam or pressurized steam, application of an oil agent, fiber opening treatment, etc., and these can be applied as necessary.

The acrylic fiber obtained in this way can be used as a carbon fiber precursor with a single yarn fineness of 0.5 to
1.5d, a fineness fluctuation rate of 8% or less, especially 5% or less, a tensile strength of 5.7g/d or more, especially 6.0 to 7.5g/d, and an elongation of 8 to 12%.

The precursor is supplied to a firing process for oxidation and carbonization, but at this time, dust, inorganic metal fine particles, etc. contained in the heating atmosphere in the oxidation process, that is, air, must be removed. Specifically, before the air is supplied to the oxidation process, it is filtered using a filter with a mesh opening of 1μ or less.
It is important to keep it clean. This cleaning of the heating atmosphere prevents iron and other inorganic metal oxides, which are produced by 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, it is possible to effectively prevent the above-mentioned oxides and the like once attached from forming carbides and the like in the carbonization process, thereby effectively preventing local defects from occurring on the carbon fiber surface. Of course, in the present invention, it is desirable to filter and clean not only the oxidizing atmosphere but also the atmospheric gas in the carbonization step.

Further, as a precursor, it is desirable to use a bundled yarn having a number of single fibers of 1000 or more, particularly 2000 to 30000. In other words, when the number of single fibers in the precursor decreases to less than 1000, thermal decomposition products generated during the flame retardant process, such as tar or pitch-like substances, adhere to the periphery of the fiber bundle and are present in small amounts in the flame retardant atmosphere. In some cases, dust, inorganic metal particles, etc., may adhere and become fixed, leading to an increase in the number of single yarns, which causes deposit defects.

In addition, in the flameproofing treatment of the precursor, when all or part of the heated air is recycled to save thermal energy, in addition to the above-mentioned cleaning treatment of the circulating air, the oxidative decomposition of the thermal decomposition products derived from the precursor is also carried out. It is desirable to carry out treatment.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

In this example, the single fiber physical properties and strand physical properties of the carbon fibers, as well as the tensile rupture test of the single fibers, were conducted as follows.

Single fiber tensile strength and elongation were measured according to the single fiber test method described in JIS-R-7601.

Strand strength and elongation were measured according to the resin-impregnated strand test method described in JIS-R-7601. At this time, the resin composition was Chitsonox 221/boron trifluoride monoethylamine/acetone = 100/3/4 parts.

Tensile breakage test for single fibers First, the carbon fiber bundle is washed with a solvent or the like in advance. A fiber group with a length of about 10 cm is taken out from the fiber bundle sample, opened as appropriate, and single fibers are randomly extracted from the fiber group. This extracted single fiber 1 is
As shown in the figure, stick it straight along the center line 3 of the mount 2 with adhesive 4 on a perforated mount 2 with dimensions of 5 cm x 1 cm that has been punched out to a length that exactly corresponds to the sample length of 5 cm. Fix it and prepare a test piece.

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, so in order to avoid this, Using a constant speed tension type tensile testing machine modified to be able to perform a tensile rupture test, the test piece is attached to the testing machine,
A tensile rupture test is performed at a tensile strain rate of 1%/min.

This tensile rupture test is performed on at least 1% of the single fibers based on the total number of single fibers constituting the fiber bundle.

A single fiber was taken out from the tensile fractured test piece, gold coating was applied to the primary fracture surface of the single fiber, and using a scanning electron microscope, the accelerating voltage was
Observe and photograph the fractured surface at 25KV and 10,000x magnification. FIG. 2 is an electron micrograph showing a typical example of defects caused by deposits on carbon fibers.

Example 1 Ammonia was blown into a copolymer of 98 mol% acrylonitrile (AN) and 2 mol% acrylic acid with an intrinsic viscosity [η] of 1.73, and the terminal hydrogens of the carboxyl groups of the copolymer were replaced with ammonium groups. A dimethyl sulfoxide (DMSO) solution with a modified polymer concentration of 20% by weight was prepared as a modified polymer.

This solution was filtered using a sintered metal filter with a mesh opening of 3μ as a filter medium, the temperature was adjusted to 60°C, and the solution was discharged into a DMSO aqueous solution at a temperature of 60°C and a concentration of 50%. As for the cap, the hole diameter is 0.05mm and the number of holes is 3000.
using a coagulation drawing speed of 8 m/min.
The actual draft was set at 3.5.

The coagulation bath solution was circulated and filtered through a micro-wind filter with a mesh opening of 5 μm.

The obtained coagulated thread was washed with water, stretched 5 times in hot water, and then immersed in a silicone oil bath to reduce the pressure.
After squeezing the fiber bundle with a 1.0 Kg/cm ² Nitz Pro roller to reduce the moisture content, it was brought into contact with a roller surface heated to 130 to 160°C to dry and densify it, and then compressed with 4.0 Kg/cm ² pressurized steam for 2.5 Stretched twice.

Obtained single fiber fineness 1.0d, total denier
3000D precursors are air-opened using a ring-shaped nozzle at a pressure of 0.7 kg/cm ² and then cleaned using a sintered metal filter with a mesh opening of 1 μm at an ambient temperature of 250°C. ,260℃
The oxidation treatment was carried out by sequentially passing the sample in a substantially constant length state through a hot air circulation type heating furnace maintained at a constant temperature. Next, the obtained oxidized fiber bundle was carbonized at a maximum temperature of 1300° C. in a nitrogen atmosphere that had been cleaned using a sintered metal filter with a mesh opening of 1 μm.

The obtained carbon fiber bundle was subjected to a single fiber tensile fracture test, and the primary fracture surface was observed using a scanning electron microscope. As a result, defects caused by deposits were detected as shown in Figure 2. Although some single fibers were observed, their frequency was very low at 8%.
Also, the average tensile strength of this carbon fiber single fiber is 405
Kg/mm ² and the elongation is 1.62% (n=60 in both cases).
The strand strength of this carbon fiber bundle was 455 Kg/mm ² and the elongation was 1.84%, which were very high values.

Comparative Example 1 Carbon fibers were 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 a mesh opening of 1 μm.

When the fractured surface of the single fibers of the obtained carbon fibers was observed, the number of single fibers with defects due to deposits was 20%, and the average fiber strength was 335 Kg/mm ² .
The elongation was 1.39% (all average values for n=60), the strand strength was 390 Kg/mm ² , and the elongation was 1.58%.

Comparative Example 2 A precursor was produced under the same conditions as in Example 1, except that the coagulation and take-off speed was very slow at 2 m/min and the actual draft was 1.8. However, the adhesion between single yarns was Furthermore, during the oxidation or carbonization process of these fibers, fuzz, thread breakage, etc. occur significantly, making it difficult to produce carbon fiber bundles with stable quality and performance.

On the other hand, in Example 1, the solidification withdrawal speed was
Very fast at 18m/min, effectively reducing the draft to 5.5
A precursor was produced under the same conditions as in Example 1 except that the fiber was oxidized or carbonized to obtain carbon fiber.

When we observed the fractured surface of the single fibers of the obtained carbon fibers, we found that the number of single fibers with defects due to deposits was as high as 30%, and the average single fiber strength was 310 Kg/mm ² and the same elongation. is 1.28% (n=
60), the strand strength was 360 Kg/mm ² , and the elongation was 1.49%.

Comparative Example 3 In Example 1, the precursor was produced under the same conditions as in Example 1, except that the nip roller pressure was increased to 2.0 kg/cm ² in order to further reduce the moisture content of the fibers entering the drying and densification process. This fiber was then fired in the same manner as in Example 1 to obtain carbon fiber.

When we observed the single fiber fracture surface of the obtained carbon fibers, we found that the number of single fibers with defects due to deposits was 24%, and the average single fiber strength was
320Kg/mm ² , the same elongation is 1.32% (all average values of n=60), the strand strength is 375Kg/mm ² , the same elongation is
It was 1.51%.

[Effects of the Invention] According to the method of the present invention, deposit defects on the fractured surface of carbon fibers were reduced to about 15% or less of the total number of single fibers constituting a carbon fiber bundle. For this reason, the strand physical properties that are said to reflect the composite properties of carbon fiber well, that is, the strand strength,
This has a remarkable effect of significantly improving the elongation to 400Kg/mm ² or more and the elongation to 1.7% or more.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a test piece for a tensile fracture test of a carbon fiber bundle, and FIG. 2 is an electron micrograph showing a typical example of defects caused by deposits on the carbon fiber bundle.

Claims (1)

[Claims] 1 Filter an acrylic polymer solution containing acrylonitrile as the main component through a filter with a mesh opening of 5μ or less, set the actual draft within the range of 2.0 to 5.0, and discharge it into a coagulation bath.The number of constituent single fibers obtained At least 1,000 wet yarns are kept under pressure of 1.5 kg/cm ² or less using a Nitzpro roller, washed with water, stretched, and treated with silicone oil, and then dried to form precursor fiber yarns. After that, the yarn was heated for 200 minutes in an air atmosphere that had been purified using a filter with a mesh size of 1 μm or less.
A method for producing a high strength and elongation acrylic carbon fiber bundle, which comprises heating to oxidize the bundle at a temperature of ~350°C, and then carbonizing it by heating to at least 1000°C in an inert atmosphere.