JPH06264310A - Production of high-performance carbon fiber and/or graphite fiber - Google Patents

Abstract

PURPOSE:To produce a high-performance carbon fiber and/or a high-performance graphite fiber by preventing rapid absorption of moisture in the atmosphere while a flameproof fiber being sent from a flameproofing device to a carbonizing device or drying the fiber to remove absorbed water, and then carbonizing. CONSTITUTION:A device for preventing moisture absorption of a flameproof fiber or a device for removing water of the flameproof fiber having absorbed moisture is set between a flameproofing device and a carbonizing device, the water content of the flameproof fiber is reduced to <=2wt.%, preferably <=1.5wt.% and the flameproof fiber is carbonized. Or the carbon fiber thus carbonized is optionally graphitized.

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 high performance carbon fiber and / or graphite fiber.

[0002]

2. Description of the Related Art Carbon fibers and / or graphite fibers are precursor fibers of acrylonitrile-based, rayon-based, polyvinyl alcohol-based, etc. organic fibers and pitch-based inorganic fibers heated at 200 to 300 ° C. It is industrially produced by converting it into an oxidized fiber (often called flame-resistant fiber) in an oxidizing atmosphere, and then heat treating it in an inert atmosphere.

The flameproofed fiber obtained by the oxidation treatment is
It has long been known that water in the atmosphere can be easily absorbed (see, for example, Japanese Patent Publication No. 51-25487).

It is considered that this is because hydrophilic hydroxyl groups, carbonyl groups, imino groups, amino groups and the like are produced by the oxidation treatment (for example, Carbon Vol. 29, No. 8, 108).
See page 1, 1991).

Even though it is known that the flameproof fiber is hygroscopic as described above, the effect of the flameproof fiber subjected to carbonization on the quality of the carbon fiber and / or the graphite fiber when absorbing moisture. Has not been reported at all in the literature or patents.

The present inventors have found that even if the flameproof fiber absorbs water, the temperature inside the carbonization furnace is high and water is easily removed.
It has been considered that the moisture content of the flame-resistant fiber does not affect the quality of the formed carbon fiber and / or graphite fiber, and thus far, carbon fiber and / or graphite fiber have been produced without any measures.

However, in recent years, when ultra-high strength carbon fibers and graphite fibers are required, and as a result of continuing detailed research to find a more suitable manufacturing method for these, the moisture content of the flame-resistant fiber is reduced. , It has been found that the quality of the carbon fiber and graphite fiber obtained by processing it, in particular, has a great influence on the strength and elongation.

That is, when the water content of the flame-resistant fiber is increased, the strength of the carbon fiber and / or the graphite fiber is decreased, and the carbon fiber called ultra high strength and the high performance carbon called high strength and high elasticity. It was confirmed that the fibers, or the high-performance graphite fibers obtained by treating these high-performance carbon fibers at a higher temperature, are more likely to be adversely affected by this moisture.

The moisture absorption rate of the flameproofed fiber is quite rapid, and even if it is dried, the water content becomes more than 2% by weight in a normal atmosphere in a few minutes. In particular, when the temperature and humidity of the atmosphere are high as in the summer of Japan, both the moisture absorption rate and the moisture absorption amount of the flameproof fiber are remarkably increased. As shown in the reference example described later, it has been found that the moisture absorption rate of the flameproof fiber is much higher than that of silica gel which is well known as a desiccant.

In the carbon fiber industrial production facility, a roller for transferring the flame resistant fiber and a roller for adjusting the tension of the fiber are installed between the flame resistance device and the carbonization device. Due to reasons such as having to secure a space for inspecting and repairing these devices, it takes about 5 minutes or more for the flame-resistant fibers that have left the flame-resistant device to enter the carbonization device. Is needed.

Therefore, since the flameproof fiber that has exited the flameproofing device absorbs moisture in the atmosphere before entering the next carbonizing device, the content of moisture is 2% by weight before the carbonization reaction starts.
It becomes bigger. For this reason, especially when the humidity and temperature in the atmosphere are high, the water content becomes high, and it becomes difficult to stably produce the high performance carbon fiber and / or the high performance graphite fiber.

When the flameproof fiber absorbs moisture as described above,
As will be described later, the quality of the obtained carbon fibers and graphite fibers deteriorates, but it was found that the degree of this quality deterioration depends on the moisture absorption amount.

Therefore, it has been found that it is impossible to satisfactorily achieve the purpose of supplying a stable product with the least quality fluctuation, which is the most important for industrial products such as always providing carbon fiber or graphite fiber of constant quality. .

[0014]

As a result of intensive studies on means for solving such problems, the present invention has reached a method for producing high-performance carbon fibers and / or high-performance graphite fibers with stable quality.

That is, an object of the present invention is to treat high-performance carbon fiber and / or high-performance carbon fiber of stable quality by treating the flame-resistant fiber which easily absorbs moisture so as not to absorb the moisture, or by removing the absorbed moisture. It is an object of the present invention to provide a manufacturing method for making it possible to manufacture graphite fibers by an industrially advantageous method.

[0016]

The object of the present invention is to convert acrylonitrile-based precursor fibers (hereinafter referred to as precursors) containing 90% by weight or more of acrylonitrile into flame-resistant fibers in an oxidizing atmosphere, and In the carbonization treatment in an active atmosphere, the moisture resistance of the flameproofed fiber is maintained at 200 ° C. or less and 2% by weight or less, preferably 1.5% by weight or less, or
This can be achieved by heat treatment in an inert atmosphere and conversion into carbon fibers and / or graphite fibers.

There are the following methods for holding or reducing the water content of the flameproof fiber to 2% by weight or less, preferably 1.5% by weight or less, and the conceptual diagrams thereof are shown in FIGS. 2 and 3. .

1. Method for preventing moisture absorption of the flameproofing fiber from the flameproofing device and keeping the water content at 2% by weight or less: As shown in FIG. 2, since normally flameproofing is performed in an oxidizing atmosphere at 200 ° C. or higher, The moisture content of the flameproof fiber 9 at the outlet 1'of the flameproof device 1 is usually 1% by weight or less. Therefore, it suffices that the flameproof fiber 9 is not exposed to the high-humidity atmosphere. For this purpose, a moisture absorption prevention device 3 is provided between the outlet 1'of the flameproofing device 1 and the inlet 2'of the carbonization device 2, and dry air or dry gas is introduced thereinto.
This is easily accomplished by insufflating air from the air and isolating it from the moist atmosphere. In FIG. 1, 4a, 4b, 4c, 4d and 4e are flame resistant fiber transfer rollers, and 6a and 6b are entrance and exit slits of the moisture absorption prevention device 3.

2. Method for reducing water content of moisture-absorbed flameproofing fiber: When the distance between the flameproofing device 1 and the carbonization device 2 is long as shown in FIG. 3 or the device is complicated and it is difficult to shield the atmosphere, the carbonization device 2 The drying device 7 is provided immediately before, and drying is performed using the heating rollers 8a, 8b or dried heated air (not shown) to reduce the water content of the flame resistant fiber 9 to 2% by weight or less, and It may be introduced into the rectification device 2. In this case, after leaving the drying device 7, the carbonization device 2
It is necessary to prevent re-absorption of water by setting the time until entering into the water to 2-3 minutes or less.

Although any one of the above methods 1 or 2 or a method combining 1 and 2 may be adopted, when preventing the moisture absorption of the flameproof fiber or drying the water content, The temperature must be 200 ° C. or lower. This is because when exposed to an atmosphere having a temperature higher than 200 ° C. as described later, the flame-resistant fiber may be further oxidized or may be thermally shrunk, so that it may be introduced into the carbonization device in an optimum oxidation state. Because it turned out to be difficult.

In the present invention, the drying degree of the dry air used for blocking the atmosphere to prevent the moisture absorption of the flameproof fiber or for dehumidifying depends on the contact time between the flameproof fiber and the dry air, the temperature, etc. Low humidity air having an absolute humidity of 5 g / kg of water or less than dry air is preferable. Since the moisture absorption rate of the flameproofed fiber is affected not only by humidity but also by temperature, the degree of drying of the dry air used here is better than the relative humidity as a guideline.
Since it is more appropriate to regulate by absolute humidity or dew point, the method of controlling by absolute humidity was adopted.

The upper limit of the absolute humidity of the dry air is not limited to the relationship with the contact time with the dry air and the temperature as described above, but also the wetness of the atmosphere, the moisture content of the target flameproof fiber and the atmosphere. It is difficult to set it in a general way because it is related to the airtightness and the air volume of the shielding device for shutting off, but the moisture content of the flameproof fiber should be at least 2% by weight or less before entering the carbonization device. It goes without saying that it must be dry air that can be adjusted to.

In addition to dry air, other inert dry gas or the like can be used, but industrially dry air is inexpensive and safe, and is preferably used.

An example of the relationship between the water content of the flameproof fiber introduced into the carbonization apparatus and the strength of the carbon fiber obtained by carbonizing the same is shown in Example 1 and FIG. 1 described later.

As is apparent from FIG. 1, it is understood that it is difficult to obtain a carbon fiber having high strength when the water content of each flameproof fiber used for carbonization exceeds 2% by weight. The details will be described later.

Particularly when higher strength carbon fibers are required, the water content of each flame-resistant fiber is preferably 1.5% by weight or less.

In order to reduce the fluctuations in the strength and elongation of the carbon fibers and graphite fibers, the fluctuation of the water content of the flame-resistant fiber before being carbonized is controlled within ± 0.2% by weight. More preferably, it is fed to a carbonizer.

[0028]

[Function] Although there is no clear reason why the strength of the carbon fiber obtained when the moisture content of the flame-resistant fiber is high decreases, a side reaction other than the carbonization reaction (for example, the carbon material is changed to steam) in the carbonization process. It is presumed that this is because the reaction such as conversion to activated carbon by activation) is caused by water in the flame-resistant fiber or water released from the flame-resistant fiber.

A carbon fiber obtained from a flame-resistant fiber having a high water content was subjected to a tensile test of its single fiber,
When measuring the strength of single fibers and observing the fracture surface with a scanning electron microscope, it seems that the fracture starts from defects such as small dents and grooves on the outer surface. It seems certain that water increases the defects on the outer surface of the carbon fiber, as it is more than the carbon fiber obtained from the synthetic fiber.

[0030]

EXAMPLES In order to explain the present invention more specifically, representative examples and reference examples are shown below, but the present invention is not limited to the scope thereof by these examples. The% shown in the following examples and reference examples is% by weight unless otherwise specified.

The water content of the flame-resistant fiber, the physical properties of the strand and the humidity of the air in this example were measured by the following methods.

(1) Water content of flame resistant fiber: About 5 g of flame resistant fiber was dried at 70 ° C. for 2 hours using a vacuum dryer (about 30 mmHg), and the weight change before and after drying was calculated.

(2) Measurement of physical properties of strand: JIS-76
According to the method of 01, ARALD is used as the matrix resin liquid.
A resin-impregnated strand was prepared by using a mixed solution of ITE XD911 (trade name of epoxy resin, manufactured by Nagase Ciba Co., Ltd.) / Furfuryl alcohol = 3/2, and the resin-impregnated strand was prepared at 45 ° C. at 150 ° C.
Tensile test was performed on the cured product for
The elastic modulus was calculated.

(3) Humidity of air and dry air: Temperature, relative humidity and absolute humidity were measured using a temperature and humidity measuring device FC-452 manufactured by Testterm Co., Ltd. The absolute humidity was converted to g / kg of water and dry air.

Example 1 Five kinds of precursor A shown in the following Table 1 having different single yarn denier to which an amino-modified polysiloxane oil agent was applied,
A ', B, C and D were continuously passed through three hot air circulation type flameproofing devices having different temperatures shown in Table 1 so as to be retained for 20 minutes each to obtain a flameproofing fiber. The specific gravity of the flameproof fiber was adjusted by changing the set temperatures of the three flameproofing devices. Also, A and A'are the same precursors, but are different in that they are treated with different flameproofing temperatures.

[0036]

By changing the absolute humidity of the air fed from the flame resistant fibers 9 from 5 by using the moisture absorption preventing device 3 as shown in FIG. 2 within the range of 0.5 to 15 kg of water / dry air, The moisture content of the flameproof fiber entering the carbonization device 2 was changed. Here, the outlet slit 6b of the moisture absorption prevention device 3
Since the distance from the carbonizer to the inlet 2'of the carbonizer 2 was designed to be as short as possible, the residence time during this period was only 10 minutes.
Seconds.

In this way, the flame-resistant fibers having different water contents have maximum temperatures of 500 ° C., 1000 ° C. and 1400 ° C., respectively.
It was continuously carbonized by being retained in the carbonization apparatus 2 at 0 ° C. for 1 minute each. However, in the case of the precursor D, the maximum temperature of the last carbonization device 2 was 1300 ° C.

The carbon fiber thus obtained is surface-treated by an electrolytic oxidation method using ammonium bicarbonate as an electrolyte, washed with water, and a sizing agent made of a water-soluble epoxy resin is added to the carbon fiber, which is dried and wound with a winder. I took it.

The strand strength, elastic modulus, specific gravity of the flameproof fiber, and water content of the flameproof fiber immediately before entering the carbonization apparatus are shown in Table 2 below.

The relationship between the water content of the flameproof fiber and the strength of the carbon fiber is shown in FIG.

As is clear from this result, when the moisture content of the flameproof fiber immediately before entering the carbonization device is 2% or less,
Those containing more than 2% of water have low strength of the obtained carbon fiber. It can be seen that this tendency is particularly strong in the precursors A, B, and C for the purpose of obtaining carbon fibers having high strength.

Reference Example 1 The precursor C of Example 1 had a specific gravity of 1.34 g / cc and 1.3 by changing the temperatures of the three flameproofing apparatuses 1.
6 g / cc and 1.38 g / cc of 3 types of flameproof fibers were created, lightly defibrated by hand, and then dried under the same conditions as for moisture measurement, temperature 35 ° C, relative humidity 52% (absolute Humidity 1
The moisture absorption rate was measured in a room of 8.3 g / kg / dry air). Further, silica gel, which is often used as a desiccant, was similarly dried and the moisture absorption rate was measured in the same room. The results are shown in FIG.

As is clear from FIG. 4, the moisture absorption rate of the flameproof fiber is very high, and if the humidity and temperature in the atmosphere are high, the moisture content exceeds 2% after only a few minutes of exposure.

Therefore, it is necessary to take measures to prevent moisture absorption between the time when the flameproofing device is left and the time when the carbonizing device is entered, or to keep the water content at 2% or less unless it is dried just before entering the carbonization device. Understood difficult. In particular, when the specific gravity of the flame-resistant fiber is high, the moisture absorption speed is higher and the amount of moisture absorbed is larger, so that special consideration as in the present invention is required.

Example 2 Instead of providing the moisture absorption preventing device 3 as shown in FIG. 2 in the flame resistance to carbonization process of the precursor B of Example 1, a heating and drying roller 8a as shown in FIG. 8
A carbon fiber was prepared in the same manner as in Example 1 except that the drying device 7 provided with b was installed to improve the flameproof fiber to be dried and then subjected to carbonization.

The specific gravity of the flameproof fiber used here is 1.3.
It is 4 g / cc. The water content of the flameproof fiber was adjusted by changing the temperature of the heating roller and the residence time by changing the number of windings on the roller. The time from the exit of the heating roller to the carbonization device was set to 30 seconds or less.

Table 3 shows the water content of the flame-resistant fiber thus dried and the strand strength of the carbon fiber obtained by carbonizing the same.

As is clear from the results shown in Table 3, the carbonized product which has not been dried has a water content of more than 2%, and high strength carbon fibers cannot be obtained. On the other hand, the one dried at 220 ° C has a low water content, but due to the stress generation due to the shrinkage of the fiber during drying (the stress generated by the heat shrinking fiber being wound around the roller, free contraction does not occur and becomes a tension state). The commercial value was inferior because the tension of the fiber in the carbonization device increased and many fluffs occurred during the carbonization process. Also, the strength of the carbon fiber was even lower than that when it was not dried.

This is because the heat-shrinkable stress presses the flame-resistant fiber against the heated roller with a strong force, so that the fiber is unevenly heated, and the heat diffusion due to the exothermic reaction is prevented, so that the fibers are separated from each other. It is thought that this is because adhesion has occurred and the suitable properties as a flame-resistant fiber have been impaired. Therefore, the drying roller temperature does not cause shrinkage or flame resistance reaction. 2
A temperature of 00 ° C or lower is suitable.

Example 3 Using the flameproofed fibers obtained from the precursors A and B shown in Example 1, the moisture absorption was adjusted by the method shown in FIG. Further, heat treatment was performed for 3 minutes at 2450 ° C. in an argon atmosphere while giving 2% elongation to obtain a graphite fiber. Table 4 shows the physical properties of the obtained graphite fiber.

It was confirmed that the water content of the flameproofed fiber greatly affects not only the carbon fiber but also the quality of the graphite fiber obtained by graphitizing the carbon fiber. The water content of the flameproofed fiber has a greater effect on the graphitized fiber than on the carbon fiber. It is considered that this is because the defects on the surface of the fiber are further increased by the graphitization, and these defects serve as the starting points of the breakage, which seriously affects the strength.

By subjecting the flame-resistant fiber to moisture reduction as much as possible and then subjecting it to carbonization and graphitization as in the present invention, a highly elastic graphite fiber having an elongation of 1% or more, which has hitherto been unattainable. Was obtained for the first time.

[0054]

[0055]

[0056]

[0057]

According to the present invention described in detail above, in the step of introducing the flameproof fiber into the carbonization device after converting the precursor into the flameproof fiber in an oxidizing atmosphere, the flameproof fiber is rapidly exposed to the atmosphere. Prevents absorption of internal moisture, or removes absorbed moisture by drying at 200 ° C or lower to reduce the moisture content of the flame-resistant fiber to 2% by weight or less and then carbonizes it to achieve high quality and high performance. Facilitates industrial production of carbon fibers and / or high performance graphite fibers.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the water content of flame-resistant fibers and the strength of carbon fibers.

FIG. 2 is a schematic diagram of an apparatus for preventing the moisture absorption of flame resistant fibers before they enter the carbonizer.

FIG. 3 is a schematic diagram of an apparatus for drying to reduce the moisture content of flame-resistant fibers.

FIG. 4 is a diagram showing the moisture absorption rates of flameproofed fibers and silica gel.

[Explanation of symbols]

 1 Flameproofing Device 2 Carbonization Device 3 Moisture Absorption Prevention Device 4a Flameproofing Fiber Transfer Roller 4b Flameproofing Fiber Transfer Roller 4c Flameproofing Fiber Transfer Roller 4d Flameproofing Fiber Transfer Roller 4e Flameproofing Fiber Transfer Roller 5 Air Supply Mouth 6a Inlet slit of flame resistant fiber 6b Outlet slit of flame resistant fiber 7 Drying device 8a Heat drying roller 8b Heat drying roller 9 Flame resistant fiber

[Procedure amendment]

[Submission date] July 23, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

(2) Measurement of physical properties of strands: JIS-R7
According to the method of 601 , AR is used as the matrix resin liquid.
A resin impregnated strand was prepared using a mixed solution of ALDITE XD911 (trade name of epoxy resin, manufactured by Nagase Ciba Co., Ltd.) / Furfuryl alcohol = 3/2, and 150
A tensile test was performed on the cured product at 45 ° C. for 45 minutes to determine the strength and elastic modulus.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

The absolute humidity of the air sent from 5 to these flameproof fibers 9 by using the moisture absorption preventing device 3 as shown in FIG. 2 is changed within the range of 0.5 to 15 g / kg of water and dry air. As a result, the moisture content of the flameproof fiber entering the carbonization device 2 was changed. Here, since the distance from the outlet slit 6b of the moisture absorption prevention device 3 to the inlet 2'of the carbonization device 2 is devised so as to be as short as possible, the residence time during this period is only 10 seconds.

Claims (1)

[Claims] 1. An acrylonitrile-based precursor fiber containing 90% by weight or more of acrylonitrile is converted into a flame-resistant fiber in an oxidizing atmosphere, and then heat-treated in an inert atmosphere. A method for producing high-performance carbon fibers and / or graphite fibers, which comprises holding the moisture content at 2% by weight or less at a temperature of ℃ or less or reducing it, and then heat treating it in an inert atmosphere.