JPS62257422A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To produce a carbon fiber having high strength and elastic modulus, by carrying out a multi-stage flame-resisting treatment of an acrylonitrile fiber in an oxidizing atmosphere while controlling the stretching ratio at a specific level and carbonizing the treated fiber. CONSTITUTION:An acrylonitrile fiber bundle having a single filament fineness of 0.3-1.5d and total fiber fineness of 1,000-20,000d is introduced into a flame- resisting treatment furnace consisting of plural furnaces maintained at respective different temperatures and containing oxidizing atmosphere and is stretched under a condition satisfying the formula [k is total stage number of the flame- resisting treatment furnace; rhoo, rhok and rhon are fiber densities (g/ml) of the fed fiber, fiber after the completion of the flame-resisting treatment and fiber after the completion of the n-th treatment, respectively; tn* is treating time (min) in the n-th stage furnace] while suppressing the stretching ratio to <=30 until the fiber density reaches 1.22g/ml. The stretching is continued keeping the total stretching ratio to <=50 until the fiber density reaches 1.26g/ml. Thereafter, the fiber is treated in a manner to get a fiber density of 1.34-1.40g/ml while suppressing the shrinkage of the fiber. The produced flame-resistant fiber is carbonized in an inert gas atmosphere..

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing carbon fj, which has high strength and high elasticity.

[Background technology]

In recent years, carbon fiber composite materials have been widely applied to sports, aerospace, industrial applications, etc., and their quantitative expansion is remarkable. In response to this situation, the performance of the carbon fibers used is also rapidly improving. Focusing on the modulus of elasticity, ten years ago it was 20 tons, on/M2, but a few years ago, 23-24 tons/mm2 became the standard, and more recently, the trend has been towards around 30 tons, 7 mm2. It has been pointed out that this may become mainstream in the future.

However, if such an improvement in the elastic modulus is achieved while the strength of the carbon fiber remains constant, it will naturally lead to a decrease in the elongation of the carbon fiber, making the carbon fiber composite material brittle. This will be the case.

Therefore, there is a strong demand for carbon fibers with high elasticity and high elongation, that is, carbon fibers that have both high elongation and high strength.

The conventional method for improving the elastic modulus has been to increase the carbonization temperature, that is, the final heat treatment temperature.

However, with this method, the strength decreases as the elastic modulus increases,
Therefore, there was a drawback that the elongation of the carbon fiber was reduced. For example, in order to maintain an elastic modulus of 28 tons/ran2, the carbonization temperature must be approximately 1800°C, but at this temperature, the strength is 100 kg/ran2 compared to 1600°C.
With this, high strength cannot be achieved at all. This decrease in strength as the carbonization temperature increases corresponds well to the decrease in density, and is likely due to the generation of micropores in the fibers that cause a decrease in strength during the process of increasing the carbonization temperature. Presumed. In addition, when acrylonitrile polymer fiber bundles with a total fiber fineness of 1,000 to 20,000 deniers are subjected to flame-retardant treatment and then carbonized, fiber bundles that frequently fluff or break during the carbonization process must have high strength, It cannot be made into a carbon fiber bundle with high elongation. The reasons for this are that flame-resistant dead spots between the single fibers that make up the flame-resistant fiber bundle to be subjected to the carbonization process and spots in the longitudinal direction of each flame-resistant fiber are large, and that there are small flame-resistant spots in the flame-resistant fiber itself. Examples include having defects.

[Problems to be solved by the present invention]

Conventionally, when obtaining high elastic fibers, carbonization treatment is performed at a high temperature of 1800° C. or higher, but it is extremely difficult to obtain high strength and high elongation carbon fibers using this method.

[Means for Solving the Problem] The present inventors completed the present invention as a result of conducting research on a method for producing high-strength and high-elastic carbon fiber.

In the present invention, acrylonitrile polymer fiber bundles having a single fiber fineness of 0.3 to 1.5 denier and a total fiber fineness of 1000 to 20000 denier are processed in a plurality of furnaces maintained in an oxidizing atmosphere at different oxidation treatment temperatures. Supplied to flame retardant treatment furnace,
The density of the fibers passed through each flameproofing furnace is calculated by the following formula [where ρ is]. is the density of acrylonitrile polymer fiber C &
/ml, ~7 is the density of the flame-resistant treated yarn (g/me
), ρ. is the density of the fiber after passing through the n-th flame-retardant furnace (CEI/ml), and tn is the flame-retardant treatment time in the n-th furnace (
minutes), k indicates the total number of stages of the flame-retardant treatment furnace], the fiber density of the flame-retardant treatment system was 1.22 i / m
The elongation is carried out with the elongation rate kept below 60% until the fiber density reaches 1.26 i/ml, and then the elongation is carried out within a range where the total elongation rate is within 50% until the fiber density reaches 1.26 i/ml. Shrinkage is substantially suppressed, and the fiber density at the end of flame resistance is 1.34 to 1.40! This is a method for producing carbon fibers, which is characterized by subjecting the fibers to flame resistance so that the fibers become 9/111, and carbonizing the obtained flame-resistant fibers in an inert gas atmosphere.

The acrylonitrile polymer fiber used in the present invention is
It can be produced by spinning a (co)polymer obtained from 90% by weight or more of acrylonitrile and 10% by weight or less of another copolymerizable vinyl monomer.

Other copolymerizable vinyl monomers are components that promote the flame resistance reaction of acrylonitrile polymer fibers and contribute to shortening the flame resistance time, such as hydroxyethyl acrylonitrile, methyl vinyl ketone, methyl acrylate, and acrylic acid. , methacrylic acid, itaconic acid, t-butyl methacrylate, etc. are used. The polymerized units of acrylonitrile are 90% by weight or more, preferably 95% by weight or more. Fibers obtained from polymers containing less than 90% by weight of acrylonitrile units have low flame retardant reactivity, so it is necessary to raise the flame retardant initiation temperature, and once the flame retardant reaction is initiated, it is likely to cause a runaway reaction. .

Acrylonitrile polymers are usually produced by wet spinning or dry spinning.
The fibers are spun using a wet spinning method to obtain an acrylonitrile polymer fiber bundle having a single fiber fineness of 0.3 to 1.5 deniers and a total fiber fineness of 1000 to 20000 deniers. Single fiber fineness is 0.
Fibers with a single fiber brightness of less than 3 denier tend to lack strength and are therefore undesirable.On the other hand, fibers with single fiber brightness exceeding 1.5 denier require an abnormally long time to become flame resistant in the flame resistant process. In order to achieve the object of the present invention, it is unavoidable that the acrylonitrile fiber bundle has a total fiber fineness of more than 20,000 deniers. After flame-retardant fiber bundles, there is a large difference in fiber density between the inner and outer surfaces of the fiber bundles, and such flame-retardant fiber bundles tend to become fluffy and break during the carbonization process, making it difficult to use high-performance carbon fibers. is difficult to obtain.

In carrying out the present invention, the acrylonitrile polymer fiber bundle is maintained in an oxidizing atmosphere at 200 to 350°C and fed to a flameproofing furnace composed of a plurality of stages having different treatment temperatures.

As the flame-retardant furnace composed of a plurality of furnaces, a flame-retardant furnace having two or more stages, preferably three to six stages, is used. If the number of stages in the flameproofing furnace is too large, the equipment will become bulky and operability will decrease, which is undesirable. In order to maintain an oxidizing atmosphere inside the furnace, air is usually used, but -nitrogen oxide, sulfur dioxide gas, etc. can also be used.

The fiber bundle thus supplied has a fiber density of 1゜2'1g.
The elongation rate is set to 30% or less until the fiber density reaches 1.26fi/ml, and then elongation is performed within a range where the total elongation rate is 50% or less until the fiber density reaches 1.26fi/ml, and the density of the fibers passing through each stage ( Flame-retardant treatment is carried out under conditions such that tn) satisfies the above formula and the fiber density at the end of flame-retardation is 1.34 to 1.40 l/ml.

The relationship between flame resistant fiber density and treatment time will be explained with reference to the drawings.

Conventionally, in order to flame-proof acrylonitrile-based polymer fibers at high speed, as shown in curve 1 in the figure, the temperature rise gradient at the beginning of the flame-proofing treatment is increased, and the temperature rise gradient in the latter half of the flame-proofing treatment is lowered. For example, Japanese Patent Publication No. Sho 47-35938 discloses a method in which 1Σ, tn is used, but in this method, fusion and sticking phenomena are observed between acrylonitrile synthetic fibers, and in inconvenient cases, The flame retardant treatment reaction may go out of control and the treated fibers may catch fire.

Since the flame-retardant treatment system thus obtained contains many yarn defects, fuzz and yarn breakage occur frequently during the carbonization process, and carbon fibers tend to have many voids, making it difficult to produce high-performance carbon fibers. On the other hand, as shown by curve 2 in the figure, there is a method in which the temperature increase gradient at the initial stage of the flameproofing treatment is kept low and the temperature increase gradient in the latter half is increased. -163729, this flame-retardant method first produces an incompletely flame-retardant yarn with no interfiber fusion, and then rapidly performs a highly flame-retardant treatment. The degree of flame resistance increases between the fibers of the yarn and in the longitudinal direction of the fibers, and fluff and yarn breakage occur during the carbonization process, making it impossible to carry out efficient carbonization treatment, making it difficult to use high-performance carbon fibers. can't get it.

In contrast, in the present invention, acrylonitrile-based polymer fiber bundles are flame-retardant treated under conditions that satisfy formula (1). This maintains a nearly linear relationship between the increase in fiber density and the flame-retardant treatment time. As a result, it was possible to prevent the rapid rise of the flame-retardant reaction from occurring during the flame-retardant process of acrylonitrile-based polymer fibers, thereby reducing the rate of oxygen diffusion into the acrylonitrile-based fibers and the oxygen diffusion into the acrylic fiber bundles. Since the speed can be made significantly more uniform compared to conventional methods, it is possible to prevent inconvenient phenomena such as fusion and sticking between acrylic fibers and the occurrence of fiber white defects such as voids due to rapid thermal decomposition. . Furthermore, the flame-resistant fiber bundle thus obtained does not generate fuzz or thread breakage even when subjected to a carbonization process, and can be made into extremely high-performance carbon fiber.

Furthermore, according to the flame-retardant treatment method of the present invention, acryloni)
Even if the flame-retardant treatment time for IJ-type synthetic fiber bundles is shortened to within 90 minutes, especially within 60 minutes, which was unimaginable with conventional methods, there will be no inconvenience. Can be done.

In addition, the elongation rate is kept below 30% until the fiber density reaches 1.22 i / rne, and the fiber density reaches 1.26 j;
It is necessary to elongate it within a range where the total elongation rate is 50% or less until it reaches 1/ml, and then apply flame-retardant treatment.

A flame-retardant treatment system that can be used as a high-performance carbon fiber is one that has a highly oriented structure that facilitates the formation of a graphite network surface.

The density of acrylonitrile polymer fiber is usually 1.18
g/ml, and the density of this fiber is 1.22117
It is possible to elongate about 50% until reaching m1, but
If the elongation rate exceeds 30%, the flame-resistant fibers obtained may have larger irregularities and yarn defects may occur. In addition, the total elongation rate was 50 until the fiber density reached 1.26 g/;nl.
% or less, the graphite crystal structure is likely to develop in the carbonization process, and highly oriented and defect-free carbon fibers can be obtained.

In addition, in a region where the fiber density exceeds 1.26 i/ml, it is necessary to carry out flameproofing treatment under conditions that do not cause substantial elongation of the fibers. If substantial elongation of the fiber occurs in this region, many microvoids will be embedded in the carbon fiber, degrading the performance of the fiber. Furthermore, if the fibers shrink during this step, the fine structure of the flame-resistant fibers will be disturbed, and the strength of the resulting carbon fibers will decrease.

A method for elongating the fibers is, for example, by bringing the fibers into contact with a number of rotating rolls, increasing the roll speed for a while until the density reaches 1°'16 g/ml, and then keeping the roll speed constant. good.

Furthermore, the fiber density ρ7 when flame resistance is completed is 1.34 to 1,4
09 ml preferably 1.345-1.385 g/
It is necessary to set it in the range of ml. ρega 1.34
Flame-resistant fibers with g/rn of less than 1 exhibit rapid thermal decomposition during the carbonization process, resulting in frequent thread breakage and fuzzing, making it impossible to carry out efficient carbonization treatment, and the performance of the carbon fibers is also poor. . Furthermore, flame-resistant fibers with a rho value exceeding 1°4 Q g/ml cannot be subjected to orientation during the carbonization process, and cannot be made into high-performance carbon fibers with a tensile strength exceeding 400 kg/+uc2.

Next, the flame-resistant fiber is carbonized at a temperature of 1600 to 1800° C. in an atmosphere of an inert gas such as nitrogen gas or argon gas. By performing the primary carbonization treatment in the temperature range of 300 to 800° C. prior to this carbonization treatment, the subsequent carbonization treatment at a high temperature can be performed more efficiently.

Following the first carbonization treatment, the second carbonization treatment, that is, the final heat treatment, is performed at 1300 to 1800 ℃ in an inert gas atmosphere.
They are kept under tension at a temperature range of 10°C for tens of seconds to several minutes.

In the heat treatment, the maximum temperature in the treatment process is 1300℃.
If the temperature is less than 0.degree. C., a predetermined elastic modulus cannot be obtained. On the other hand, when the maximum temperature exceeds 1800°C, the strength and density decrease and become below a predetermined value. Further, it is preferable that the temperature profile during the heat treatment is set such that the temperature rises gradually from around 1000° C. to reach the maximum temperature. Further, the tension applied to the fibers during heat treatment must be at least 250 m97 denier, preferably at least 350 m9/denier. If the tension is lower than this value, it will be difficult to obtain a predetermined elastic modulus.

[Effects of the present invention]

According to the method of the present invention, the degree of flame resistance of the fibers on the inner and outer surfaces of the fiber bundle is made uniform, and the degree of flame resistance in the fiber axis direction is made uniform, and a specific elongation operation is applied in this flame resistance process. Because it has a flame-resistant fiber structure with no defect structure and a highly oriented graphite crystal structure that is easy to develop, we have created a high-performance carbon fiber with a tensile strength of 450 kg/ran2 or higher and an elastic modulus of 27 bon/-2 or higher. It can be produced with extremely high productivity.

The carbon fiber obtained by the present invention has high elasticity and high strength, so it can be used for sports applications such as aircraft secondary structural materials, fishing rods, golf shafts, and industrial applications such as high-speed centrifuges and robots.
It can be used in a wide range of applications such as ground high-speed transportation vehicles.

The strand strength and strand elastic modulus in the following examples are J! It was measured by the method of SR7601.

Moreover, the density was measured by the density gradient tube method.

An acrylonitrile polymer fiber bundle consisting of 12,000 filaments was processed in 5 temperature zones, each with a processing length of 1.
Using a hot air circulation multi-stage flameproofing furnace consisting of 8m each for the 4th to 4th tiers and 5.3m for the 5th tier, the treatment time was 45 minutes.
When flame-retardant treatment is performed so that the density at the end of flame-retardation is 1.36 fi/ml, the density range after each film treatment is calculated using formula (1) and is in the range shown in Table 1. .

Next, the treatment temperature for achieving the above calculated density range was read from the curve of density change versus flameproofing treatment time under constant temperature conditions at various temperatures determined in advance. The determined temperature conditions are shown in Table 1. Under this temperature condition, 50 acrylonitrile polymer fiber bundles were arranged so that the width between the fiber bundles was approximately 5.2B, and at a take-up speed of 0 m/hour, 20% in the first stage and 20% in the second stage. A flame-retardant treatment was performed to give an elongation of 8% and a treatment time of 45 minutes.

The fiber bundle being conveyed through the flameproofing furnace was in the form of a sheet with virtually no gaps. This flame-retardant treatment was carried out continuously for 24 hours, but there was no ignition due to runaway reaction, and the flame-retardant fiber bundle obtained was satisfactory, with no fusion or fuzz.

After 24 hours of operation, samples were taken from the fibers after each membrane treatment and the densities were measured using a density gradient tube.As shown in Table 1, the densities at all stages were within the range of the calculated densities.

The obtained flame-resistant fiber bundle was subsequently carbonized by passing continuously through a carbonization furnace with a maximum temperature of 600° C. and a carbonization furnace with a maximum temperature of 1500° C. under a nitrogen cloud atmosphere.

At this time, when the elongation rate in the carbonization furnace at 600° C. was varied until fluff was generated, there was no fluff at all up to 20%, and slight fluff was observed at 22%. then 60
The elongation rate in the 0°C carbonization furnace was set to 8%, and then carbonization treatment was performed at 1600'C while applying 4% shrinkage. obtained n
Carbon fiber has very little fuzz and has a tensile strength of 5.
! 15 k'i/mrtt2 and modulus of elasticity 28.5'',
on /@112, which was a very high performance.

Table 1 Comparative Example 1 In Example 1, flameproofing treatment was carried out by changing the temperature conditions to the temperatures shown in Table 2. The flame-retardant treatment was stable with no fuzz or fusion. Next, carbonization treatment was performed in the same manner as in Example 1, but fluffing occurred frequently in the carbonization furnace with a maximum temperature of 600°C, and no elongation could be imparted.

Furthermore, although the fibers were passed through a carbonization furnace with the elongation rate set to zero, a large amount of fuzz occurred in the carbonization furnace, and the obtained carbon fibers could not be evaluated.

In addition, as a result of measuring the fiber density after each stage of flameproofing treatment in the same manner as in Example 1, as shown in Table 2, the fiber densities of the first to third stages are as shown in Table 1. The value was outside the calculated density range.

Table 2 Example 2 The process was carried out in the same manner as in Example 1, except that 20% elongation was applied in the first stage until the fiber density of the flame-retardant treated system reached 1.22 ji/ml, and then the fiber density was 1.269
An additional 15% elongation was applied in the second stage until reaching /ml, resulting in a total elongation rate of 38% for flame resistance. The properties of the obtained carbon fiber were a tensile strength of 555 kFl/mrx2 and an elastic modulus of 29.2 ton/Hg''.

Comparative Example 2 In Example 1, the fiber density of the flame-resistant treated system was 1.22.
f! When elongation of 38% was applied in the first stage until reaching /ml, frequent fluffing and breakage of fiber bundles occurred in the elongated region.

Comparative Example 3 Processed in the same manner as in Example 1, except that 30% elongation was applied in the first stage until the fiber density of the flame-retardant treated system reached 1.22 g/ml, and then the fiber density reached 1.26 g/ml. An additional 15% elongation was applied in the second stage until reaching /ml, making the total elongation rate for flame resistance 50%. As a result, some fuzz was observed during the flame-retardant process, and the performance of the obtained carbon fiber was
Osteoderm 525 kg/mrn2 and elastic modulus 29.6 to
It decreased to n/mu2.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between the flame-retardant fiber density and the flame-retardant treatment time for detailed explanation of the present invention. Curve 1 shows a conventional method in which the initial temperature increase gradient is increased and the latter half temperature increase gradient is increased. Curve 2 shows the case where the temperature increase gradient in the initial stage is low and the temperature increase gradient in the latter half is high.

Claims (1)

[Claims] Single fiber fineness 0.3 to 1.5 denier, total fiber fineness 100
An acrylonitrile polymer fiber bundle of 0 to 20,000 deniers is supplied to a flameproofing furnace consisting of multiple furnaces maintained in an oxidizing atmosphere with different oxidation treatment temperatures, and the density of the fibers passing through each flameproofing furnace is determined. The following formula (ρ_O-0.0.1) + (ρ_k-ρ_O) (Σ^n
_n_=_1t_n)/(Σ＾k_n_=_1t_n≦
ρ_n≦(ρ_O+0.01)+(ρ_k−ρ_O)(
Σ＾n_n_=_1t_n)/(Σ＾k_n_=_1t
_n) (1) [In the formula, ρ_O is the density of the acrylonitrile polymer fiber (g/ml), ρ_k is the density of the flame-retardant finished yarn (g/ml), and ρ_n is after passing through the n-th flame-retardant furnace. The fiber density of the flame-retardant yarn (g/ml), t_n is the flame-retardant treatment time of the n-th furnace (minutes), and t_n is the total number of stages of the flame-retardant furnace. Density is 1.2
The elongation is carried out with the elongation rate kept below 30% until the fiber density reaches 2 g/ml, and then the elongation is carried out within a range where the total elongation rate is within 50% until the fiber density reaches 1.26 g/ml. The flame resistant fibers are subjected to flame resistant treatment so that the shrinkage of the fibers is substantially suppressed and the fiber density is 1.34 to 1.40 g/ml at the end of flame resistant flame resistant fibers, and the obtained flame resistant fibers are carbonized in an inert gas atmosphere. A carbon fiber manufacturing method characterized by: