JPS5887321A - Continuous production of carbon fiber - Google Patents

Abstract

PURPOSE:The starting yarns for making carbon fiber are twisted individually, then doubled and made flame resistant and, further the resultant yarns are untwisted into individual yarns and carbonized to produce high-quality carbon fiber with no strength reduction in high productivity. CONSTITUTION:Preferably, starting yarns for carbon fiber such as acrylic fibers, are twisted by means of a creel separately and several of the resulting yarns are doubled into a bundle without twisting. The resultant fiber bundle is sent into the furnace for imparting it flame resistance where the bundle is heated and calcined in an oxidative atmosphere to give a flame resistant fiber bundle. Then, the resulting bundle is separated into two or more bundle to the same number of the yarns. Thus, the separated yarns are carbonized in a non-oxidative atmosphere of such as nitrogen gas or hydrogen gas to produce the objective carbon fiber. The product of the filament denier in the starting fiber and the filament count is 500-30,000 and the twisting number is desirably 5-100/m.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing carbon fibers, particularly a method for producing high-quality carbon fibers with high efficiency from carbon-Na Hosokawa threads such as acrylic fibers. be.

Carbon fiber has extremely high specific strength and specific modulus, as well as excellent heat resistance and chemical resistance, so it is widely used as a reinforcing material for aerospace applications and for sporting goods such as golf clubs and fishing rods. It's used a lot.

Taking acrylic carbon fiber as an example, the method for manufacturing carbon fiber is to make the precursor fiber flame resistant by fermenting it in an oxidizing atmosphere at a temperature of 200 to 350 degrees Celsius over a relatively long period of time. It can be obtained by heating and carbonizing the fiber in a non-oxidizing atmosphere at a temperature of 1000° C. or higher.

During this process, especially in the initial so-called flameproofing process, the heat generated by the oxidation reaction is significant and the fibers need to be retained for a long time, so it is necessary to enlarge the furnace body or arrange many furnaces. Furthermore, in general, the flameproofing process requires a long time, from several tens of minutes to several hours, to treat the fibers, so even if relatively large equipment is used, the threads are small and productivity is extremely low. As described above, the flame resistance process was the biggest bottleneck in carbon fiber productivity.

In order to compensate for this low productivity, JP-A-56-9
It has been proposed that two or more precursor fibers heated in 1015 are aligned and subjected to flameproofing and carbonization treatment in the heated state.

According to this type of method, the number of filaments constituting the precursor fibers supplied to the flame-retardant and carbonization process can be increased, which certainly improves the productivity of carbon fibers, but on the other hand, the carbon fibers obtained There was a problem in that the strength of the steel was significantly reduced.

Furthermore, in JP-A No. 48-41040, it has been proposed to improve the productivity of carbon fibers by applying electricity to the precursor fibers and then carbonizing the precursor fibers in a state in which several fibers are aligned and combined. As mentioned above, the bottleneck in fiber production is mainly in the flame-retardant process, so no matter how much you ignore the productivity of the flame-retardant process and improve only the carbonization process or production efficiency, the overall production of carbon fibers will be affected. The productivity through the process did not necessarily improve, and as in the case of the above proposal, the decrease in strength of the carbon fibers could not be avoided.

The present inventors have arrived at the present invention as a result of intensive research aimed at achieving both improved productivity and high-quality adhesiveness in the production of carbon fibers as described above.

That is, an object of the present invention is to provide a method for producing carbon fibers of excellent quality with high efficiency.

The object of the present invention is to heat the raw yarn for carbon fiber and to heat the raw yarn for carbon fiber. M'I&, at least two bundles of flame-retardant fibers, which are made by pulling and doubling the yarns without heating and continuously firing them in an oxidizing atmosphere to form a bundle of flame-retardant yarns, or the heated raw material. This is achieved by a continuous carbon fiber production method characterized by dividing into thread units and then carbonizing in a non-oxidizing atmosphere.

The yarn for carbon fiber in the method of the present invention is an organic polymer fiber that has been made flame resistant by heating and oxidation in a fermenting atmosphere, and that carbon fiber can be obtained by heating at high temperature in a non-oxidizing atmosphere. For example, acrylic fibers, polyvinyl alcohol fibers, petroleum-based or coal-based pitch fibers, and acrylic fibers are preferred.

The yarn for carbon fiber usually has a single yarn denier of 0.5 to 2,0
d The number of constituent filaments is 500 to 30 OoO, preferably 500 to . Poooo within the scope of the book.

For example, 0.5 a x 6000, 1.0 a
X 6000a, X, 5dX3000 lines, '2.0dX
There are 3000 pieces.

In addition, the raw yarn is used 5 to 100 times per meter, preferably 5 to 2 times per meter.
A twist within the range of 0 twists is given, but if the number of twists is less than 5 twists, the fibers become entangled with each other when a plurality of raw yarns are combined, making it impossible to divide them smoothly after flame resistance. On the other hand, when the number of twists increases, the physical properties of the carbon fiber, especially the strength, are observed to decrease, and when the number of twists exceeds 100, the decrease is significant.

A suitable method for imparting twist here is, for example, rotating the spindle of a creel (unwinding machine) and continuously heating/firing.

The carbon fiber raw yarn heated in this way is doubled in the number of yarns in the range of 2 to 8, preferably 2 to 4. At this time, if the number of yarns is too large, the splitting properties after flame resistance will be reduced, fuzz will occur frequently, and in severe cases, yarn breakage will occur. Controlling heat generation/heat removal becomes difficult.

The combined yarn is sent to a flameproofing furnace and heated and fired under normal flameproofing conditions 2, for example, in air at 200 to 350°C.

The obtained flame-resistant yarn bundle is sent to the next carbonization process.

The filament is split into heated filament units or multiple filaments before being heated.

The filament 'fk' of the divided yarn is usually 500 to 30
000 fibers, and if this is too large, the physical properties of the carbon fiber, especially the strength, will be significantly reduced.On the other hand, the lower limit for fiber splitting is the heated raw fiber unit, and below that, the fiber splitting itself will be difficult;
Also, it is meaningless in that it damages the fibers.

The flame-retardant yarn that has been split is treated with nitrogen gas and hydrogen gas.

It is carbonized by a conventionally known method in a carbonization furnace maintained at 1000° C. or higher in an atmosphere of argon gas or the like to become carbon fibers.

In addition, in the present invention, the yarn for carbon fibers is a doubling yarn.

Alternatively, in order to efficiently split the flame-resistant yarn bundle,
It is usually desirable to use grooved rollers. This is because the grooved roller is superior to the comb-shaped guides that have been commonly used in the past in that it causes less damage to the fibers, especially less fuzz.

As detailed above, the present invention aims to improve productivity in a well-balanced manner throughout the production of carbon fibers, and at the same time maintain high quality. In the carbonization process, which requires a shorter processing time than the flame-retardant process, the flame-retardant yarn bundle obtained by the yarns is divided into raw yarn units or their own. Carbonization is performed after the fibers are split into multiple fibers, and this results in an easy and well-balanced increase in the productivity of carbon fiber manufacturing, while at the same time reducing the strength loss of carbon fibers that was unavoidable with conventional productivity improvement measures. The effect is remarkable, such as being able to sufficiently avoid problems.

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

Example 1 Acrylic fibers with 3000 filaments were twisted 15 times per meter using a creel and then continuously unwound 4
The yarns were drawn one by one into one groove of a grooved roller and put into a flameproofing furnace heated to 240°C to 270°C in air and subjected to oxidation treatment for 80 minutes. Next, the fibers are divided into two fibers using a roller with a roller, and the fibers are heated to a maximum temperature of 1300 ml in nitrogen gas.
Carbonization was carried out for 1 minute in a carbonization furnace at .degree.

The physical properties of the obtained carbon fiber are strength 3'72 kg/
am-modulus of elasticity was 23.9 t/wm".

Incidentally, the flame-resistant yarn bundle obtained by the same oxidation treatment as described above was not divided into fibers, but was subjected to carbonization treatment as it was as a four-ply yarn. The physical properties of the obtained carbon fiber are strength: 346 kg/wa", elastic modulus: 2
The amount was 3.6t/-.

Example 2 When heating an acrylic fiber with 6,000 filaments (hereinafter referred to as raw yarn) with a creel, the number of twists was variously changed, and the number of twists was 3 in the groove of a grooved roller to improve operability during fiber separation. The effect on carbon fiber quality (strength and elastic modulus) was investigated. The results are shown in Table 1.

Table 1 Example 3 Acrylic fibers with 3,000 filaments (hereinafter referred to as yarn) were continuously unwound using a creel while being twisted 15 times per meter under the same firing conditions as Example 1. Flameproofing and carbonization treatments were performed.

Here, various changes were made to the doubling during the flame-retardant treatment and the fiber splitting state during the carbonization treatment, and the effects of these on the carbon fiber quality (strength 9 elastic modulus) were investigated. These results are shown in Table 8.

Claims (5)

[Claims] (1) After heating the raw yarn for carbon fiber, combining multiple yarns without heating, and continuously firing in an oxidizing atmosphere to form a flame-resistant yarn bundle. , splitting the flame-resistant yarn bundle into at least two or the heated raw yarn units;
A continuous method for producing carbon fibers, which is then carbonized in a non-oxidizing atmosphere. (2) The method for continuously producing carbon fiber according to claim (1), wherein the carbon fiber yarn is an acrylic fiber. (3) The carbon fiber according to claim (1), wherein the carbon w, the single fiber denier of the textile yarn x the number of constituent filaments is 500 to 30,000, and the number of heating is 5 to 100 times/m. Continuous manufacturing method. (4) The method for continuously producing carbon fibers according to claim (1), wherein the number of yarns for carbon fibers supplied to the flameproofing step is 2 to 8. (5) The continuous method for producing carbon fibers according to claim (), wherein the number of constituent filaments of the split flame-resistant yarn supplied to the carbonization step is 500 to 30,000.