Process for producing carbon fiber tows

A process for producing a carbon fiber tow from an acrylic fiber tow wherein the acrylic fiber tow is treated to uniformily contain throughout the two (1) an aminosiloxane and (2) a chemical substance selected from glycerine, an alkylene glycol, and a polyalkylene glycol prior to heat-treating said acrylic fiber tow to produce the carbon fiber tow whereby problems such as fluffiness, spreading, and filament breakage are diminished.

The present invention relates to a process for producing carbon fiber tows 
(hereinafter referred to as carbon tows, which include graphite fiber 
tows). More particularly, the invention is concerned with a process for 
producing high-quality carbon tows suitable for use as reinforcements, 
wherein an acrylic fiber tow (hereinafter referred to as precursor tow) 
prepared so as to contain a particular aminosiloxane and a particular 
chemical substance in a uniform state is subjected to thermal 
stabilization and carbonization treatments. 
It is already known that carbon fibers can be obtained by thermally 
stabilizing acrylic fibers in an oxidizing atmosphere and then carbonizing 
the thus thermally stabilized acrylic fibers in a non-oxidizing 
atmosphere. But it is to be noted that the thermal stabilization reaction 
(oxidation reaction) of the acrylic fibers is an exothermic reaction, so 
that when the fibers are heated rapidly, local accumulation of heat takes 
place and non-uniform reactions are liable to occur; because of this, in 
the thermal stabilization step, the fibers are fused or agglutinated 
together or become brittle, and therefore it is very difficult to obtain 
high-quality carbon fibers. To overcome such technical difficulties, 
various proposals have been made, for example, such as a process wherein 
the thermal stabilization is carried out at a low temperature and for a 
long time, or a process as described in Laid-open Japanese Patent 
Application No. 117724/1974 wherein the precursor substrate is impregnated 
with or caused contain an organic silicone substance and thereafter it is 
thermally stabilized. However, these processes still have problems 
remaining unsolved. Namely, when such a particular substance is employed, 
the agglutination and fusion of the acrylic fibers can be reduced to some 
extent indeed, but on the other hand, owing to the water repellency of the 
silicone substance used, the acrylic fibers are liable to generate static 
electricity. When static electricity is generated, there will be caused 
grave difficulties such as fiber entanglement upon taking out fibers, 
fiber winding about rollers or guides in the steps of thermal 
stabilization and carbonization, generation of fluff, etc. and the 
operation is made seriously unstable. 
Among others, when a precursor tow produced by wet-spinning process is 
used, the tow shape is markedly disordered by the repulsion due to static 
electricity between single fibers, and therefore it has been difficult to 
obtain a satisfactory carbon tow. As an attempt to solve this difficulty, 
it is possible to employ the method proposed in Japanese Patent 
Publication No. 24136/1977, but the addition of a prescribed amount of 
aminosiloxane only will still cause various problems upon handling a 
precursor tow composed of a large number of single filaments. Namely, when 
the number of single filaments composing the precursor tow exceeds 10,000, 
a remarkable quantity of static electricity is generated between single 
filaments in the drying step (before the thermal stabilization step) and 
in the thermal stabilization step and puts the two shape into disorder. 
Also, accompanied with the increase in the number of single filaments, the 
diffusion of the heat generated by condensation, cyclization etc. 
reactions in the thermal stabilization step will become markedly slow, so 
that an effective diffusion of heat is impeded. This results in a tendency 
of local formation of pitch- or tar-like substances. 
Thus, when static electricity is generated between single filaments of a 
precursor tow and agglutination or fusion is induced therefrom, there will 
be caused, in the heat treatment steps, troubles such as entanglement of 
tow filaments around rollers or guides, generation of fluff, etc.; these 
troubles not only further lower the operation efficiency but also finally 
make it difficult to produce a high-quality carbon tow having excellent 
physical properties. 
In such a situation, we researched intensively to obviate the 
above-mentioned defects and to obtain carbon tows having excellent 
physical properties. As a result, we found that, by heat-treating a 
precursor tow produced so as to contain a particular chemical substance 
together with the above-mentioned aminosiloxane, and so as to diminish the 
variation in the contents of the two substances between divided portions 
of the tow, it is possible to obviate all the troubles such as the 
fluffiness, spreading, filament breakage, etc. of the precursor tow and at 
the same time, to markedly improve the stability in the operation of the 
carbon tow production process. The present invention is based on this 
finding. 
Therefore, an object of the present invention is to provide an improved 
process for producing carbon tows having excellent physical properties. 
Another object of the present invention is to provide a process for 
producing carbon tows, which makes it possible to eliminate such troubles 
as the fluffiness, spreading, fusion, etc. of the tow, and to produce 
carbon tows having a high tensile strength and a high modulus of 
elasticity and free from agglutination and fusion between single 
filaments, by heat treatment for a short time. 
Other objects of the present invention will become apparent from the 
following concrete explanation of the invention. 
In producing carbon tows from precursor tows, the above-mentioned objects 
of the present invention can be attained by heat-treating a precursor tow 
prepared in such a manner that the total number (X) of single filaments 
composing the pecursor tow is 10,000 or more, that said tow contains an 
aminosiloxane represented by the following general formula: 
##STR1## 
wherein each of R.sub.1, R.sub.2 and R.sub.3 represents hydrogen, methyl, 
ethyl or phenyl; R.sub.4 represents --C.sub.n H.sub.2n -- (wherein n is an 
integer from 1 to 10) or phenylene; each of R.sub.5 and R.sub.6 represents 
hydrogen or --C.sub.n H.sub.2n+1 (wherein n is an integer from 1 to 5); 
each of M and N represents an integer from 1 to 100,000 (wherein M+N&gt;10); 
and A represents 
##STR2## 
(wherein each of R.sub.7 and R.sub.8 represents hydrogen, alkyl whose 
number of carbon atoms is not more than 10 or phenyl), or 
##STR3## 
(wherein R.sub.9 represents H, C.sub.n H.sub.2n+1 (n=1.about.5) or phenyl, 
and R.sub.10 represents C.sub.n H.sub.2n (n=1.about.10) or phenylene), and 
a chemical substance selected from the group consisting of glycerine, an 
alkylene glycol whose number of carbon atoms is not more than 6 and a 
polyalkylene glycol whose number of carbon atoms is not more than 20, and 
in such a manner that when the precursor tow composed of X single 
filaments is so divided into Y portions (divided tows) that each divided 
tow will be composed of 1000 filaments 
##EQU1## 
the number of divided tows whose content in the aminosiloxane is not more 
than 0.05 weight % based on the dry weight of the fibers, is not more than 
10% relative to Y, and the number of divided tows whose content in said 
chemical substance is not more than 0.08 weight % based on the dry weight 
of the fibers, is not more than 20% relative to Y. 
In this way, by introducing two kinds of the particular treating substances 
into the structure of the precursor tow, the generation of static 
electricity is suppressed and at the same time appropriate bundling 
properties are given to the tow. This prevents fluff generation and 
entanglement of filaments around guides and rollers in the thermal 
stabilization step, and furthermore markedly suppresses the agglutination 
and fusion between single filaments. Consequently, there are no fluff 
generation and no entanglement of filaments around guides and rollers in 
the subsequent carbonization step. All these effects are outstanding 
characteristics of the present invention. In other words, the technical 
effects peculiar to the present invention are exhibited as a result of a 
synergetic action of the two particular substances employed, and if any 
one of said substances is lacking, the objects of the present invention 
cannot be attained. 
Precursor tows, after once packed up in boxes or wound on spools, are 
introduced into the thermal stabilization and carbonization steps. Upon 
such packing up in boxes, winding on spools, or taking the tows out of 
boxes or spools, when the tows have been treated with the two kinds of the 
particular substances according to the present invention, there is no 
substantial generation of static electricity, and the tows can be handled 
with ease, and finally it is possible to produce carbon tows with 
excellent physical properties and free from agglutination and fusion. 
Furthermore, when the contents of the two kinds of the particular treating 
substances are made uniform between the divided tows (each composed of 
1000 filaments of the precursor tow) by a prescribed means, substantially 
the same heat treatment behavior as in the case of a tow composed of 1000 
filaments can be attained, so that even if the total number of single 
filaments composing the tow is 10,000 or more, it is possible to produce 
carbon tows with excellent physical properties. 
Moreover, it is possible to prevent rapid local accumulation of heat due to 
slow heat diffusion resulting from an increased number of constituent 
single filaments. 
The precursor tows used in the present invention are those produced from an 
acrylonitrile copolymer containing combined therewith at least 85 mol %, 
preferably more than 90 mol % acrylonitrile, and copolymerized with 0.3-6 
mol % preferably 0.5-3 mol % of a carboxyl group-containing unsaturated 
monomer, in accordance with any of the usual spinning processes (for 
example wet-spinning process, dry-wet-spinning process, etc.) and 
after-treatments (cold water stretching, hot water stretching, gel 
treatment, steam stretching, drying, etc.), and are fiber bundles composed 
of 10,000 or more single filaments. Among the above-mentioned carboxyl 
group-containing unsaturated monomers, there can be mentioned acrylic 
acid, methacrylic acid, itaconic acid, etc. Besides such unsaturated 
monomers, it is also permissible to use known unsaturated vinyl compounds 
such as allyl alcohol, methallyl alcohol, oxypropioacrylonitrile, methyl 
acrylate, methyl methacrylate, acrylamide, N-methylol acrylamide, etc. 
As the precursor tows to be used in the present invention, it is preferable 
to employ water-swollen tows (in a gel state) after spinning and heat 
stretching, because the tow shape related with its handling, bundling, 
etc. properties is maintained in a good state throughout the precursor tow 
and carbon tow production steps, and also upon the treatment with the 
above-mentioned two kinds of the particular substances, it is possible to 
cause said two substances to penetrate into the core of the filaments of 
the tow. The above-mentioned water-swollen tows mean those containing 
20-200 weight % water based on the dry weight of the fibers after spinning 
and before drying. 
The aminosiloxanes to be used in the present invention are those 
represented by the following general formula and are liquids having a 
viscosity (at room temperature) of 50 to 1,000,000 centipoises, preferably 
100 to 10,000 centipoises; 
##STR4## 
wherein each of R.sub.1, R.sub.2 and R.sub.3 represents hydrogen, methyl, 
ethyl or phenyl; R.sub.4 represents --C.sub.n H.sub.2n -- (wherein n is an 
integer from 1 to 10), or phenylene; each of R.sub.5 and R.sub.6 
represents hydrogen or --C.sub.n H.sub.2n+1 (wherein n is an integer from 
1 to 5); each of M and N represents an integer from 1 to 100,000 wherein 
M+N&gt;10); and A represents 
##STR5## 
(wherein each of R.sub.7 and R.sub.8 represents hydrogen, alkyl whose 
number of carbon atoms is not more than 10, or phenyl). 
Such an aminosiloxane is preferably contained in the precursor tow in an 
amount of 0.01-5 weight % based on the dry weight of the fibers. 
On the other hand, the chemical substance to be used together with the 
aminosiloxane is selected from the group consisting of glycerine, an 
alkylene glycol whose number of carbon atoms is not more than six, 
preferably not more than three, and a polyalkylene glycol whose number of 
carbon atoms is not more than 20, preferably from 5 to 15. As concrete 
examples of such chemical substances, there can be mentioned glycerine, 
ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol, 
polypropylene glycol, polybutylene glycol, etc. (these glycols are not 
limited for the molecular weight). It is also desirable that such a 
chemical substance should be contained in the prescursor tow finally in an 
amount of 0.01-5 weight % based on the dry weight of the fibers. 
In order to cause these two substances to be contained in the precursor 
tow, a combination of the following methods is suitably employed: a 
spinning solution containing the aminosiloxane and/or chemical substance 
is spun; a method wherein a precursor tow in a water-swollen state 
obtained by spinning is treated with the aminosiloxane and/or chemical 
substance so that these substances can be introduced into said tow; a 
method wherein a precursor tow after drying and before the thermal 
stabilization treatment is treated with the aminosiloxane and/or chemical 
substance so that these substances can be introduced and contained in said 
tow, etc. In this way, the prescribed amounts of the aminosiloxane and 
chemical substance can be dispersed and introduced into the precursor tow 
before the thermal stabilization treatment. As mentioned above, when a 
water-swollen tow is used as the precursor tow according to the present 
invention, it is necessary, of course, that the treatment with the 
aminosiloxane and/or chemical substance should be carried out or 
accomplished while the tow is in a water-swollen state. 
Thus, for the precursor tow used in the present invention, the prescription 
on the total number of single filaments and the introduction of the two 
particular treating substances are indispensable. An additional important 
matter besides these factors is to make the content of said two particular 
treating substance uniform throughout the whole precursor tow. 
That is to say, when the presursor tow composed of X single filaments is so 
divided into Y portions (divided tows) that each divided tow will be 
composed of 1000 filaments 
##EQU2## 
it is indispensable that the number of divided tows whose content in the 
aminosiloxane is not more than 0.05 weight % based on the dry weight of 
the fibers, is not more than 10% relative to Y (total number of divided 
tows), and the number of divided tows whose content in said chemical 
substance is not more than 0.08 weight % based on the dry weight of the 
fibers, is not more than 20% relative to Y. If the number of divided tows 
containing the aminosiloxane in said weight % exceeds 10%, or if the 
number of divided tows containing the chemical substance in said weight % 
exceeds 20%, there will be observed the generation of static electricity 
between single filaments of the precursor tow, poor bundling properties, 
agglutination, fusion, etc., and it is impossible to produce a 
high-quality carbon tow having excellent physical properties. 
For example, suppose that the total number of single filaments (X) of a 
precursor tow is 20,000, then the number of divided tows (Y) will be 20 
##EQU3## 
For each of the 20 divided tows, the average content of the aminosiloxane 
and that of the chemical substance (for instance polyethylene glycol) are 
measured. When all of the 20 divided tows contain an amount exceeding 0.05 
weight % aminosiloxane and an amount exceeding 0.08 weight % polyethylene 
glycol, there is no problem. But if there are three or more tow in the 20 
divided tow containing not more than 0.05 weight % aminosiloxane, the 
above-mentioned troubles will occur and it is impossible to obtain carbon 
tows having excellent physical properties. 
To diminish the variation in the content of the chemical substances such as 
aminosiloxane and polyethylene glycol between the divided tows, the 
treating concentration, treating time and treating temperature of the 
treating substances for the precursor tow should be suitably modified. As 
regards the treating concentration of the treating substances, it is 
recommended to use a concentration of 0.5-5.0% for aminosiloxane and a 
concentration of 0.7-7% for the chemical substance (both for the treatment 
with each single substance and with the two substances at the same time). 
The treating time is closely related to the treating speed, and at a 
treating speed of 100 m/min, a treating time of 0.5 second or more, and at 
a treating speed of 150 m/min, a treating time of 0.8 second or more is 
preferable. As regards the treating temperature, a temperature from room 
temperature to 70.degree. C. is desirable. As an additional means for 
preventing the variation in the amounts of absorption, it is desirable to 
employ the following method: the method consists in adjusting the width of 
the precursor tow travelling in the treating bath to 5-10 cm for a number 
of constituent single filaments of 10,000, and the width of the tow after 
leaving the treating bath to 0.5 to 2 cm for a number of constituent 
single filaments of 10,000. An adjusting means for the former is to spread 
the tow width by blowing the treating liquid against the tow through a 
nozzle installed in the treating bath and then to bundle the tow with a 
roller installed outside the bath, this spreading and bundling operation 
being repeated. An adjusting means for the latter is to use tow width 
controlling rollers installed outside the treating bath. As other 
adjusting means for the former and the latter, there may be mentioned the 
use of cross rollers, the use of a folding operation, etc. according to 
circumstances. 
Upon producing a carbon tow from a precursor tow into which such a 
particular aminosiloxane and chemical substance have been introduced 
uniformly, conventional known heat treating processes can be employed. In 
general, there is employed a heat treating process consisting of a thermal 
stabilization step in which the tow is heated at 200.degree.-350.degree. 
C. in an oxidizing atmosphere and a subsequent carbonization step in which 
the tow is heated at a higher temperature (above 800.degree. C.) in a 
non-oxidizing atmosphere or under reduced pressure. As the atmosphere for 
thermal stabilization, air is suitable, but it is also possible to employ 
a thermal stabilization method which is carried out in the presence of 
sulfurous acid gas or nitrogen monoxide gas, or under the irradiation of 
light. As the atmosphere for carbonization or graphitization, nitrogen, 
helium, argon, etc. are used by preference. Additionally, in order to 
produce a carbon tow with a higher tensile strength and a higher modulus 
of elasticity, it is preferable to carry out the heat treatment under 
tension (generally 0.1-0.5 g/d). Particularly effective is to apply 
tension in the thermal stabilization step and the carbonization step or 
the graphitization step. 
Thus, by employing the process of the present invention, it has become 
possible to produce carbon tows having an excellent tensile strength and 
modulus of elasticity at a high production efficiency and in a short time. 
Accordingly, such carbon tows having excellent properties are now used in 
the wide field of reinforcements, heating elements, refractory materials, 
etc.

For a better understanding of the present invention, representative 
examples are shown in the following. In the examples percentages and parts 
are by weight unless otherwise indicated. 
EXAMPLE 1 
A spinning solution prepared by dissolving 9 parts of an acrylonitrile 
copolymer consisting of 98% acrylonitrile and 2% methacrylic acid in 91 
parts of a 47% aqueous solution of sodium thiocyanate, was extruded 
through a spinnerette (40,000 spinning orifices) into a 12% aqueous 
solution of sodium thiocyanate to coagulate the spinning solution. After 
water-washing, cold stretching (three times in length), and hot water 
stretching (4 times) in boiling water, a precursor tow in a water-swollen 
state containing 135% water was obtained. Thereafter, this precursor tow 
was immersed into an aqueous emulsion of the aminosiloxane (NH.sub.2 
content 0.5%) shown in the following formula: 
##STR6## 
and a precursor tow (single-filament denier 1.5) containing 0.3% of the 
above-mentioned aminosiloxane was obtained. 
Thereafter, this tow was further immersed into an aqueous solution of 
polyethylene glycol (400), and Sample Nos. 1-6 in Table 1 were prepared by 
suitably regulating the mangle squeeze ratio. These tows were thereafter 
supplied through rollers to a heating furnace (180.degree. C.), and then 
to the thermal stabilization step. The state of the generation of static 
electricity and operability in this step are also shown in Table 1. 
TABLE 1 
______________________________________ 
Quantity of 
polyethylene 
Generation of 
Sample glycol intro- 
static 
no. duced (%) electricity Operability 
______________________________________ 
1 0.05 a little fairly bad 
2 0.1 no good 
3 0.25 no good 
4 0.50 no good 
5 5.20 no bad; rollers were 
polluted 
6 0 remarkable very bad 
______________________________________ 
It is understood from the results in Table 1 that good operability can be 
obtained when the two kinds of the particular treating substances of the 
present invention are used in combination. On the other hand, it was 
attempted to once dry the water-swollen tows and then to supply them to 
said heating furnace. In the case of Sample Nos. 1 and 6, the generation 
of static electricity was remarkable, and much fluff was generated, so 
that continuous treatment was difficult. In the case of Sample Nos. 2-5, 
some fluff was generated but continuous operation was not hindered. 
In the same way as above except that in place of the above-mentioned 
spinnerette, spinnerettes having 1000 and 5000 orifices were used, two 
kinds of precursor filament bundles with a single-filament denier of 1.5 
were obtained. Without using polyethylene glycol in combination, there was 
no problem in operation for both, but when eight tows each composed of 
5000 single filaments were produced and united, and the united tow was 
subjected to thermal stabilization and carbonization, there was a 
remarkable generation of static electricity, and consequently much 
entanglement of filaments around rollers took place. Moreover, ply 
separation occurred between the united bundles composing the tow, and 
therefore it was difficult to apply a uniform tension to the tow. In 
addition, because of thickness unevenness of the tow in the direction of 
tow width, there occurred, in the thermal stabilization step, filamenent 
breakage owing to heat accumulation at thicker portions, and it was 
impossible to obtain a thermally stabilized satisfactory tow continuously. 
EXAMPLE 2 
The water-swollen precursor tow obtained in Example 1 was treated in a 
treating bath in which the aminosiloxane and polyethylene glycol of 
Example 1 were present together, while varying the treating conditions as 
shown in Table 2, so as to fix them to the tow in amounts of 0.25% and 
0.4% based on the dry weight of the fibers, respectively. Six kinds of the 
thus obtained tows (Sample Nos. 7-12) were each divided into 40 portions, 
and the contents of the treating substances in the respective divided tows 
were evaluated. The results are shown in Table 2. 
Each of the presursor tows (Sample Nos. 7-12) was supplied continuously to 
a heating furnace so that the tow would stay in the furnace for three 
minutes. Thereafter, each of the tows was introduced into a thermal 
stabilization furnace at 240.degree. C. so that it would be subjected to a 
thermal stabilization treatment for 60 minutes, followed by a 
carbonization treatment at 300.degree.-800.degree. C. for two minutes in a 
nitrogen atmosphere to obtain carbon tows. The physical properties of the 
carbon tows are also shown in Table 2. 
From the results in Table 2, it is understood that, from Sample Nos. 9-12 
whose variation in the contents of the treating substances is outside the 
limits prescribed in the present invention, it is impossible to obtain a 
carbon tow having satisfactory physical properties. 
TABLE 2 
__________________________________________________________________________ 
Physical properties 
Treating conditions Percent of divided 
Percent of divided 
of carbon tow 
Width of 
tows whose content 
tows whose content 
Tensile 
Tensile 
Sample 
Conc. of 
Conc. of 
Time 
immersed 
AM is not more 
in PEG is not more 
strength 
Modulus 
no. AM (%) 
PEG (%) 
(sec.) 
tow (cm) 
than 0.05 wt % 
than 0.08 wt % 
(kg/mm.sup.2) 
(ton/mm.sup.2) 
__________________________________________________________________________ 
7 1.0 1.5 1.2 30 10 10 324 24.7 
8 1.0 0.8 1.2 30 10 20 314 24.5 
9 0.3 1.5 1.2 30 20 10 256 23.7 
10 1.0 1.5 0.48 
30 20 20 253 23.6 
11 1.0 0.5 1.2 30 10 30 245 23.7 
12 1.0 1.5 1.2 15 30 40 240 23.6 
__________________________________________________________________________ 
Note: 
Treating speed: 100 m/min 
Treating temperature: 40.degree. C. 
The tow width leaving the treating bath was maintained constant at 4 cm. 
AM = aminosiloxane 
PEG = polyethylene glycol