JPS58214529A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To reduce the occurrence of microvoids or cracks, etc. in fibers and obtain carbon fibers of high quality without fluffs or broken fibers, by specifying a heating rate of yarns in a furnace and the rate of an inert gas to be fed into the furnace in carbonizing flameproofed yarns of organic polymer fiber yarns. CONSTITUTION:Yarns obtained by flameproofing organic polymer fiber yarns are carbonized in an inert atmosphere at >=1200 deg.C maximal temperature. In the process, the heating rate (UT1) of the yarns to be treated within 300-700 deg.C temperature region in the interior of a carbonization furnace 1 is set at 100- 1,100 deg.C/min, and the heating rate (UT2) within 700-1,000 deg.C temperature region is set at 300-5,000 deg.C/min. Furthermore, the heating rate (UT3) within 1,000- 1,200 deg.C temperature region is set at 100-1,800 deg.C/min to satisfy conditions expressed by formulas I and II. The rate of the inert gas based on the yarns to be treated is made to satisfy the condition of 3-10Nm<3>/kg in the carbonization furnace 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing carbon fibers, particularly a flame-resistant yarn obtained from an organic polymer fiber yarn at a maximum temperature of at least 1200°C.
During carbonization treatment in an inert atmosphere, we specified the rate of temperature rise of the treated yarn in the carbonization furnace and the amount of inert gas supplied here. By reducing minute voids or cracks inside the fibers that occur due to the reaction, and quickly discharging the decomposition reaction products (hereinafter simply referred to as decomposition products), there is less fuzz and single fiber breakage, and the physical properties are improved. The present invention relates to a method of manufacturing excellent high quality carbon fiber.

Carbon fiber is an organic polymer fiber in an oxidizing atmosphere of 200 to 4
A common industrial manufacturing method is to make the material flameproof at 00° C. and then carbonize it in a heating furnace in a non-oxidizing atmosphere.

In addition, in order to obtain high-quality carbon fibers, various studies have been carried out, including clarifying the composition of raw polymers, setting conditions for the atmosphere during flame-retardant and carbonization treatments, treatment temperature and time, and tension. This is also true.

However, in the production of the above-mentioned carbon fibers, defects on the fiber surface (
In addition, tar compounds, which are part of the decomposition products in the decomposition reaction, adhere to the fiber surface or the furnace inner wall, causing fuzz and single fiber breakage, as well as the formation of carbon fibers. There were problems such as a decrease in physical properties (strength, elastic modulus) and further operational troubles. This point is still an unresolved technical problem in the carbonization process.

By the way, in the carbonization process, the cracked gas, which is a part of the decomposition products generated by the rapid decomposition reaction, is generally heated to a processing temperature of 3.
Concentrated around 00 to 700℃ and 1000 to 1200℃ (BADEN-BADEN, CARBON
2. International CarbonThe present inventors have focused on the fact that the generation of decomposition gas in the carbonization process is generally concentrated in a specific treatment temperature range, and that this is closely related to the decomposition reaction of the treated yarn. In order to solve all of the above-mentioned problems associated with the decomposition reaction of the processing system, the present invention was developed as a result of intensive studies. That is, the purpose of the present invention is to specify the temperature increase rate of the treated yarn in the carbonization process during carbon fiber production and the amount of inert gas supplied there, and to control the mainly rapid decomposition reaction during carbonization. The object of the present invention is to reduce defects (micro voids, cracks) on the fiber surface caused by carbon fibers, and to obtain high-quality carbon fibers in which the decomposition products are quickly discharged. Another purpose is to prevent operational troubles caused by tar compounds that are part of the decomposition products.

The object of the present invention is to carbonize flame-resistant yarn obtained from organic polymer fiber yarn in an inert atmosphere with a maximum temperature of at least 1200°C, so that the temperature increase rate of the treated yarn in the carbonization furnace is The following (1) to ■) formula % formula % (1) () ) () (where uT is the average temperature increase rate of the treated yarn in the temperature range of 300 to 70°C.

UT is the average temperature increase rate of the treated yarn in the temperature range of 7oO to 10oOoC.

UTs is the average temperature increase rate of the treated yarn in the temperature range of 10,00 to 12 oo<0>C.

At the same time, the amount of inert gas supplied to the treated yarn in the carbonization furnace is within the specified range of the amount of inert gas supplied per yarn weight (
This can be achieved by a carbon fiber manufacturing method characterized by satisfying the following relationships.

The constituent elements and effects of the present invention will be explained in detail below.

First, the organic polymer fiber yarn in the present invention is cellulose-based or polyacrylonitrile-based.

Any material that can be carbonized may be used, such as polyvinyl alcohol-based organic synthetic polymer fibers, lignin, pitch fibers, etc.
Preferably polyacrylonitrile fibers, especially fibers made from AN polymers containing at least 9 a mol % of acrylonitrile (AN), such as polyacrylonitrile.

Acrylic acid and methacrylic acid as copolymerization components.

Itaconic acid or its lower alkyl esters.

Oxyalkyl acrylic compound, acrolein.

Fibers made of a copolymer of at least one of methacrolein, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, and salts thereof are preferable.

These fiber yarns usually have a single yarn tenier of 0.5 to 1.5.
d. There are continuous filament thread forms with a range of 500 to 30,000 filaments, or continuous tow forms with 30,000 or more filaments.

The above-mentioned yarn usually has a molecular weight of 200 to
Flame retardant treated at 400℃ and continued to 400~1600
Carbonization is carried out in an inert atmosphere (e.g. nitrogen gas) heating furnace at a temperature of 1200°C, but the key point in the present invention is the temperature in the carbonization furnace during carbonization treatment in an inert atmosphere with a maximum temperature of at least 1200°C. The conditions, particularly the rate of temperature rise of the yarn to be processed and the amount of inert gas supplied thereto, have been specified.

In other words, regarding the heating rate conditions for the treated yarn, as mentioned above, during the normal carbonization stage, defects such as micro voids or cracks are likely to occur on the fiber surface due to the rapid decomposition reaction, which affects the quality of the carbon fiber. However, in this respect, the present invention reduces the temperature increase rate of the treated yarn to the above (1) to
For the specified range of formula (to), preferably for formula (1) to (to), UT, = 200 to 500'C/m1n UT, = 400 to 30 [1''C/rrlinUT, =
Carbonization treatment is carried out in the range of 200 to 1000°C and 7 m1n.

The temperature increase rate conditions are as shown in FIG.
At ~700℃ and 1000~1200℃, the temperature increase rate is reduced to allow the decomposition reaction to proceed slowly, thereby preventing defects such as minute voids or cracks that occur on the fiber surface, and improving the quality of carbon fiber. Therefore, in the present invention, especially UTl<UT2, UT, >
It is important to satisfy the relationship UT.

Here, the lower limit defined by formulas (1) and (2) is a value determined in consideration of the economic speed of yarn processing, and the upper limit is a value determined in consideration of the physical properties of the carbon fiber.

Since the decomposition reaction at this stage needs to proceed sufficiently, sufficient consideration should be given to the length of the furnace that maintains a predetermined temperature range or the traveling speed of the yarn, and should be determined in accordance with the purpose of the present invention.

Next, regarding the amount of inert gas supplied, the decomposition products generated during carbonization should be discharged outside the furnace as quickly as possible. It adheres near the seal part that corresponds to the entrance and exit,
Since this prevents fuzz, single yarn breakage, deterioration of physical properties, and operational troubles, the condition of formula (b) above must be fully satisfied.

Here, if the inert gas supply amount, ■ (where ■ is the inert gas supply amount per yarn weight to be treated, Nm'/), is less than 3, the decomposition products wandering outside the furnace tB- will be insufficient. As a result, various troubles, especially those caused by tar compounds, begin to occur. On the other hand, when (■) exceeds 10, the effect of improving the physical properties and processability of carbon fibers is saturated, which is economically disadvantageous on an industrial scale.

In addition, as a method for more appropriately discharging such decomposition products to the outside of the furnace, for example, particularly in the temperature range 400 to 7
Carbonization treatment at 00°C is carried out using one carbonization furnace,
It is also possible to carry out the subsequent carbonization treatment in a high temperature range using a different carbonization furnace.

Further, a vertical carbonization furnace as shown in FIG. 2 may be used to facilitate the discharge of decomposition products from the furnace.

In the figure, a carbonization furnace 1 has a yarn entrance/exit seal portion 2.3, an inert gas supply port 4.5, and an inert gas discharge port 6 provided near the center of the furnace length, and carbonization is generated within the furnace.

The decomposition products are discharged from the furnace through the discharge port 6 together with the inert gas.

Of course, even in the above-mentioned sideways method, it is important to satisfy the condition of formula (b) above in order to promptly discharge the decomposition products out of the furnace.

As described above, according to the present invention, the rate of temperature increase of the treated yarn in the carbonization furnace and the amount of inert gas supply during carbonization treatment are fully defined,
Due to these single weight effects, defects such as minute voids or cracks on the fiber surface, as well as the adhesion of decomposition products, especially tar compounds, to the fiber surface are significantly reduced, resulting in less fluff and single fiber breakage. In addition, high-quality carbon fibers with excellent strength and elastic modulus can now be easily obtained.

Furthermore, as the adhesion of the tar compounds to the inner wall of the furnace decreased, the number of operational troubles decreased by a large +11.

The present invention will be specifically described below with reference to Examples.

Example 1 Acrylic fiber yarn (single yarn denier 1.Od, number of filaments 6000) was placed in a flameproofing furnace heated to 240 to 270°C in air and subjected to flameproofing treatment for 40 minutes.

The obtained flame-resistant yarn was carbonized in a carbonization furnace with a maximum temperature of 1300°C in nitrogen gas while varying the heating rate of the yarn.

However, in the carbonization treatment in this case, the nitrogen gas supply amount (1) was set to 5, and the temperature increase rate in the temperature range of 1200 to 1300°C was set to 1500/mH1.

The carbonization conditions and the quality of the obtained carbon fibers are shown in Table 1.

Table 1 Example 2 The flame-resistant yarn obtained in Example 1 was treated in a carbonization furnace with a maximum temperature of 1300° C. Carbonization treatment was carried out by varying the amount of nitrogen scum supplied per yarn.

However, the heating rate of the yarn in the carbonization treatment in this case is UT+: 300'c/min UTt'2000
”/-1nUT, :5oo℃/, and 1200~
The temperature increase rate in the ln temperature range of 1300°C was 1500°C/r11in.

The carbonization conditions and the quality of the obtained carbon fibers are shown in Table 1.

Table 2 Example 3 Acrylic fiber (single yarn denier 1d, number of filaments 60
00 yarns) were continuously unwound using a creel with 10 twists per meter, and the yarns were pulled two by two into one groove of a grooved roller and doubled, and heated in air to 240°C to 260°C. It was passed through a flameproofing furnace and subjected to flameproofing treatment for 50 minutes.

Next, carbonization treatment was performed in a carbonization furnace with a maximum temperature of 1300° C. in nitrogen gas. However, under the carbonization treatment conditions in this case, the heating rate of the yarn is UT: 300'C/
min, UT, : 2000℃/min, UTs
:500℃/・1500mtn in the temperature range of 1200-1300℃.

℃, stitching, and nitrogen gas supply amount (■) was set to 4.

ln On the other hand, as a comparative example, the heating rate of the yarn was the same, and the nitrogen gas supply amount v was 2.

This operation was carried out continuously for one month, and the quality of the carbon fibers and the state of tar-like substances adhering to the inner wall of the furnace were examined during this period.
It is shown in Table 3.

Table 6

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a state in which the temperature of yarn is increased in a carbonization furnace according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a carbonization furnace according to an embodiment of the present invention. 1: Furnace body 2.6: Yarn inlet/outlet seal part 4.5: Inert gas supply port 6: Inert gas discharge port

Claims (1)

[Claims] When carbonizing flame-resistant yarn obtained from organic polymer fiber yarn in an inert atmosphere with a maximum temperature of at least 1200°C, the rate of temperature increase of the treated yarn in the carbonization furnace is as follows: (1
) ~ (G) Formula % Formula % () () () () () However, UT is the temperature increase rate of the treated yarn in the temperature range of 300 to 700°C. UT2 is the temperature increase rate of the treated yarn in the temperature range of 700 to 1000°C. UT is the temperature increase rate of the treated yarn in the temperature range of 1000 to 1200°C. At the same time, the amount of inert gas supplied to the treated yarn in the carbonization furnace is within the specified range of N
A system made of carbon fiber characterized by satisfying the following relationships: ′/to, ).