U.S. patent number 3,639,953 [Application Number 05/060,608] was granted by the patent office on 1972-02-08 for method of producing carbon fibers.
This patent grant is currently assigned to Kanegafuchi Boseki Kabushiki Kaisha. Invention is credited to Hidetsugu Habata, Isao Kimura.
United States Patent |
3,639,953 |
Kimura , et al. |
February 8, 1972 |
METHOD OF PRODUCING CARBON FIBERS
Abstract
Nonflammable fibers are produced by subjecting a composite fiber
comprising a pitch and a synthetic organic polymer bonded uniformly
along the longitudinal direction of the fiber to an oxidation
treatment to render it infusible and then to a set treatment in air
or gaseous nitrogen at a temperature of 200.degree. to 500.degree.
C. for at least 2 hours. The nonflammable fiber is converted to
carbon fiber by heating to a temperature higher than 800.degree. C.
in gaseous nitrogen. Suitable pitches include petroleum asphalt,
coal tar pitch, and pitch obtained by baking polyvinyl chloride.
Suitable synthetic organic polymers include polyamides, polyesters,
polyolefins, polyvinyl chloride, polyvinylidene chloride,
polyurethane, epoxy resins, and phenol resins.
Inventors: |
Kimura; Isao (Osaka,
JA), Habata; Hidetsugu (Osaka, JA) |
Assignee: |
Kanegafuchi Boseki Kabushiki
Kaisha (Tokyo, JA)
|
Family
ID: |
27297845 |
Appl.
No.: |
05/060,608 |
Filed: |
August 3, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Aug 7, 1969 [JA] |
|
|
44/62461 |
Sep 30, 1969 [JA] |
|
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44/78353 |
Sep 30, 1969 [JA] |
|
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44/78354 |
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Current U.S.
Class: |
423/447.6;
8/115.54; 428/357; 264/172.14; 264/172.15; 264/172.17; 264/172.18;
8/115.51; 423/447.1 |
Current CPC
Class: |
D01F
9/21 (20130101); D01F 9/26 (20130101); D01F
9/145 (20130101); D01F 9/245 (20130101); D01F
8/04 (20130101); D01F 9/22 (20130101); D01F
9/28 (20130101); D01F 9/322 (20130101); Y10T
428/29 (20150115) |
Current International
Class: |
D01F
8/04 (20060101); D01F 9/145 (20060101); D01F
9/22 (20060101); D01F 9/21 (20060101); D01F
9/14 (20060101); D01F 9/32 (20060101); D01F
9/24 (20060101); D01F 9/26 (20060101); D01F
9/28 (20060101); C01b 031/07 () |
Field of
Search: |
;23/209.1,209.4
;264/29,171 ;161/175,172 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Meros; Edward J.
Claims
What is claimed is:
1. A method of producing nonflammable fibers, which comprises
spinning concurrently a pitch and a synthetic organic polymer
melted separately through a common nozzle to obtain a composite
fiber, in which both the components are bonded uniformly along the
longitudinal direction of the unitary filament, subjecting the
resulting composite fiber to an oxidation treatment to render it
infusible and thereafter to a set treatment in air or gaseous
nitrogen at a temperature of 200.degree. to 500.degree. C. for at
least 2 hours.
2. A method of producing carbon fibers which comprises spinning
concurrently a pitch and a synthetic organic polymer melted
separately through a common nozzle to obtain a composite fiber, in
which both the components are bonded uniformly along the
longitudinal direction of the unitary filament, subjecting the
resulting composite fiber to an oxidation treatment to render it
infusible and thereafter to a set treatment in air or gaseous
nitrogen at a temperature of 200.degree. to 500.degree. C. for at
least 2 hours, and then to a carbonization treatment at least once
in gaseous nitrogen at a temperature higher than 800.degree. C.
3. The method as claimed in claim 2, wherein said composite fiber
has a conjugate ratio (by weight) of the pitch to the synthetic
organic polymer of 1/1 to 10/1.
4. The method as claimed in claim 2, wherein said composite fiber
has a conjugate ratio of the pitch to the synthetic organic polymer
of 2/1 to 6/1.
5. The method as claimed in claim 2, wherein said composite fiber
has a conjugate ratio of the pitch to the synthetic organic polymer
of 3/1 to 5/1.
6. The method as claimed in claim 2, wherein said pitch and said
synthetic organic polymer are bonded in a side-by-side relation in
the composite fiber.
7. The method as claimed in claim 2, wherein said pitch and said
synthetic organic polymer are bonded in a sheath-core relation in
the composite fiber.
8. The method as claimed in claim 7, wherein said pitch forms the
core in the composite fiber.
9. The method as claimed in claim 2, wherein said synthetic organic
polymer is a thermoplastic polymer selected from the group
consisting of polyethylenes, polypropylenes, polyamides, and
polyesters.
10. The method as claimed in claim 2, wherein said synthetic
organic polymer is a thermosetting polymer selected from the group
consisting of epoxy resins and phenol resins.
11. The method as claimed in claim 2, wherein said pitch is a
substance selected from the group consisting of petroleum asphalt,
coal tar, and pitch obtained by baking polyvinyl chloride.
12. The method as claimed in claim 2, wherein said oxidation
treatment is effected in a gas selected from the group consisting
of oxygen, air, ozone and hydrogen peroxide.
13. The method as claimed in claim 2, wherein said oxidation
treatment is effected by means of at least one of permanganates
selected from the group consisting of sodium permanganate,
potassium permanganate, calcium permanganate and barium
permanganate.
14. The method as claimed in claim 2, wherein said oxidation
treatment is effected by means of an aqueous solution of hydrogen
peroxide containing at least one of salts of metals selected from
the group consisting of manganese, iron, cobalt and nickel with an
acid selected from the group consisting of inorganic and organic
acids.
15. The method as claimed in claim 14, wherein said inorganic acid
is an acid selected from the group consisting of hydrochloric acid,
sulfuric acid and phosphoric acid.
16. The method as claimed in claim 14, wherein said organic acid is
an acid selected from the group consisting of acetic acid and
oxalic acid.
17. The method as claimed in claim 2, wherein said set treatment is
effected at a temperature of 200.degree. to 350.degree. C. for 2 to
4 hours.
18. The method as claimed in claim 2, wherein said carbonization
treatment is effected at a temperature of 800.degree. to
1,800.degree. C.
19. The method as claimed in claim 2, wherein said carbonization
treatment is effected in two heat treatment steps, the temperature
of the first heat treatment being 800.degree. to 1,800.degree. C.
and the temperature of the second heat treatment being
2,000.degree. to 3,500.degree. C.
20. The method as claimed in claim 2, wherein said carbonization
treatment is effected in one step at a temperature of 2,000.degree.
to 3,500.degree. C.
Description
The present invention relates to an improved method of producing
carbon fibers.
Recently, carbon fibers have been drawn attention as fibrous
materials having various excellent properties, for example, fire
resistance, heat resistance, corrosion resistance, electric
conductivity and insulating property.
Carbon fibers have the same or higher fire resistance, corrosion
resistance, insulating properties and the like as glass fibers and
are substantially the same in strength as glass fibers.
Furthermore, some carbon fibers have electric conductivity which
has never been possessed by glass fibers and further carbon fibers
are particularly superior in heat resistance under nonoxidizing
atmosphere to glass fibers and are low in specific gravity.
However, carbon fibers have particularly low elongation and are
broken even by applying a very slight elongation and it has been
impossible to obtain carbon fibers having a satisfactory length by
conventional production processes. Heretofore, carbon fibers have
been produced by spinning inexpensive pitches and carbonizing the
resulting fibers.
The starting fibers obtained from pitches have a much higher carbon
content than fibers of cellulose, polyacrylonitrile and lignin and
therefore the yield in the carbonization step is considerably
higher and lost materials are few and consequently the
carbonization step can be easily carried out in a short time. On
the other hand, the handling in the spinning or after the spinning
is considerably difficult as compared with starting fibers such as
polyacrylonitrile and the like.
The inventors have made investigations for solving these problems
in conventional production of carbon fibers and accomplished the
present invention.
The object of the present invention is to provide carbon fibers
having excellent physical properties.
Another object is to provide carbon fibers having excellent
physical properties commercially easily in a high yield.
The present invention consists in a method of producing carbon
fibers which comprises spinning concurrently a pitch and a
synthetic organic polymer melted separately through a common nozzle
to obtain a composite fiber in which both the components are bonded
uniformly along the longitudinal direction of the unitary filament,
subjecting the resulting composite fiber to an oxidation treatment
and to a set treatment in air or gaseous nitrogen at a temperature
of 200.degree. to 500.degree. C. for at least 2 hours and then to a
carbonization treatment at least once in gaseous nitrogen at a
temperature higher than 800.degree. C.
The term "carbon fibers" used in the present invention means ones
composed of carbon and the fibers include nonflammable fibers, in
which carbon does not show a crystal structure but shows an organic
amorphous structure, carbon fibers, in which carbon is
microcrystalline and graphite fibers, in which carbon shows a
distinct crystal structure.
In the above described nonflammable fibers, the carbon constituting
the fibers has an amorphous structure, so that said fibers have a
heat resistant temperature of about 250.degree. to 300.degree. C.
and show an electrical insulating property. The carbon fibers
composed of microcrystalline carbon have a higher heat resistance
than the nonflammable fibers and an electric conductivity. The
graphite fibers are superior in heat resistance and electric
conductivity to the above-described nonflammable fibers and carbon
fibers.
Pitches to be used in the present invention include petroleum
asphalt, coal tar pitch, petroleum slag and pitch obtained by
baking polyvinyl chloride, all of which can be melt spun. These
pitches can provide carbon fibers by melt spinning them along and
subjecting the resulting filament to an oxidation treatment and
then to a baking treatment. Petroleum asphalt and coal tar pitch
are most preferably in view of the carbon content ratio.
Thermoplastic synthetic organic polymers to be used in the present
invention are all known synthetic organic polymers having a
thermoplasticity, for example, polyamide, polyester, polyester
ether, polyolefin, polyvinyl chloride, polyvinylidene chloride,
polyurethane, polyacryl and copolymers, modified polymers and
blends thereof. Polyolefins, such as, polyethylene, polypropylene,
etc., are particularly preferable.
Thermosetting synthetic organic polymers include, for example,
epoxy resins, phenol resins, etc., and it is preferable not to
contain any heat-setting agent.
Conjugate spinning of these pitches and thermoplastic or
thermosetting polymers can be carried out according to conventional
conjugate spinning processes and any particular attention is not
necessary in the spinneret and the conjugate spinning of both the
components and for example, the melt conjugate spinning of
petroleum asphalt and polyamide can be carried out at a temperature
of 200.degree. to 300.degree. C. by means of a spinneret provided
with orifices having a diameter of 0.1 to 0.4 mm.
The structure bonding the above-described both components may be
either a side-by-side relation or a sheath-core relation and can be
selected by considering easiness in treatment and handling of the
spun fibers.
In order to obtain a high yield when the starting fibers are
carbonized to obtain carbon fibers, the starting fibers having a
high carbon content ratio are preferably in view of the yield and
other points. Accordingly, the starting fibers having a high ratio
of pitch are preferable, but considering easiness of various steps,
such as, spinning, taking-up, unwinding and the like or spinning
rate, the conjugate ratio of pitch and the thermoplastic or
thermosetting synthetic organic polymer is preferred to 1/1-10/1,
more preferably 2/1-6/1, most preferably 3/1-5/1.
In the case of a conjugate ratio of pitch and the synthetic organic
polymer being less than 1:1, the spinnability and the succeeding
handlings are easy but the carbon content ratio is lower and
consequently, the carbonization cannot be easily carried out and
further the yield of carbon fibers lowers.
When the conjugate ratio is more than 10:1, the setting and the
carbonization of the resulting fibers become easy and the yield of
carbon fibers increases, but yarn breakage occurs frequently in the
spinning and the conjugate spinning is difficult. In order to
decrease such yarn breakage, the takeup velocity must be lowered to
about 500-700 m./min., which is a usual takeup velocity in spinning
of a monofilament composed of only pitch, but in such a low rate it
is difficult to obtain uniform composite fibers.
If a draft to be applied to usual synthetic organic polymers is
conducted in the spinning of pitches, a stress is concentrated just
below the nozzle and therefore the fibers are broken. However, when
the synthetic organic polymer and pitch are conjugate spun as in
the present invention, the synthetic organic polymer endures the
stress and the melt spinning can be carried out stably and the
takeup velocity increases to 1,000 to 2,000 m./min. Furthermore,
the spinning draft can be increased, so that carbon fibers having a
fine denier can be produced.
As mentioned above, the conjugate spinning of pitches and the
synthetic organic polymers is very important even in any bonding
structure of both the components. For example, in view of
penetration of an oxidizing agent in the oxidation treatment, it is
preferable to conjugate spin the above-described polymer and pitch
in a side-by-side relation or in a sheath-core relation, in which
the synthetic organic polymer is arranged as the core component and
the pitch is arranged as the sheath component.
However, when both the components are conjugate spun in a
side-by-side relation, it is desirable to select such a bonding
structure that both the components are not separated in the
treatment. According to the present invention it is preferable to
arrange both the components in a sheath-core relation, in which the
above-described pitch forms the core and the synthetic organic
polymer forms the sheath. In this case, since the core pitch is
surrounded by the synthetic organic polymer in the composite fiber,
it is possible to handle such a composite fiber in the same manner
as in a conventional composite fiber, but considering penetration
of an oxidizing agent in the oxidation treatment, the sheath is
preferred to be thin and it is desirable that the thickness of the
sheath of the synthetic organic polymer in the cross section of the
composite fiber is less than one-fifth of the diameter. When the
pitch and the synthetic organic polymer are conjugate spun in a
sheath-core relation, the number of core may be more than 2.
The spun fibers obtained by conjugate spinning of the pitch and the
synthetic organic polymer according to the present invention are
much more flexible than the fibers obtained by melt spinning pitch
alone and are considerably improved in a resistance against
elongation stress and further the spun fibers are very easily
taken-up.
According to the present invention, the spun fibers are firstly
subjected to an oxidation treatment. For the oxidation, inorganic
or organic substances, such as oxygen, air, ozone, hydrogen
peroxide, hypochlorites, bichromates, permanganates, benzoyl
peroxide, cumen peroxide, and the like are used.
This oxidation treatment makes the pitch and the synthetic organic
polymer constituting the composite fiber infusible and insoluble to
heat and solvent.
The oxidation treatment is carried out in a gaseous phase or an
aqueous phase by using the above-described oxidizing agent. The
gaseous oxidation is carried out by using oxygen, air, ozone, and
hydrogen peroxide and the aqueous oxidation is carried out by using
hydrogen peroxide, hypochlorites, bichromates, permanganates,
benzoyl peroxide, cumen peroxide, etc.
When the pitch forms the surface of the fiber, it is preferable to
effect the oxidation in a gaseous phase by means of ozone and the
like and in the case of oxidation by ozone, the oxidation is
carried out at a temperature of 20.degree. to 200.degree. C. for 10
minutes to 5 hours.
When the oxidation treatment is effected in an aqueous phase there
is a fear of stickiness of the fibers and it is preferable to use
an aqueous solution of hydrogen peroxide containing at least one of
manganese, iron, cobalt and nickel salts of organic or inorganic
acids or an aqueous solution of sodium, potassium, calcium and
barium salts of permanganic acid in order to prevent the
stickiness.
When an aqueous solution of hydrogen peroxide is used, the
above-described manganese, iron, cobalt and nickel salts of organic
or inorganic acids are added in order to prevent the
above-described stickiness. As the acids constituting the
above-described metal salts mention may be made of inorganic acids,
such as, hydrochloric acid, sulfuric acid and phosphoric acid or
organic acids, such as acetic acid, and oxalic acid.
The concentration of hydrogen peroxide in the aqueous solution is
selected properly within the range of 1 to 30 percent by weight and
the content of the above-described metal salts in the aqueous
solution is 0.05 mg. to 5 g. as the anhydrous salts per 1 l. of
aqueous solution of hydrogen peroxide, preferably, 0.2 mg. to 1
g.
When the concentration of the metal salts in the aqueous solution
of hydrogen peroxide is less than the lower limit, the
decomposition rate of hydrogen peroxide is too slow and therefore,
it is difficult to oxidize the spun fibers sufficiently and to make
the fibers infusible and insoluble. On the other hand, when the
concentration is higher than the upper limit, the decomposition
rate of hydrogen peroxide is too rapid and hydrogen peroxide is
decomposed in a short time, and therefore, it is difficult to
generate nascent oxygen continuously.
The spun fibers are treated in the above-described aqueous solution
of hydrogen peroxide at 0.degree. to 90.degree. C., preferably,
10.degree. to 80.degree. C. for 1 min. to 2 hours. The pH value of
the aqueous solution of hydrogen peroxide may be 1 to 13.
In this case the oxidation treatment of the spun fibers is carried
out in the above-described aqueous solution of hydrogen peroxide
and the treating process is not limited, if the spun fibers are
contacted with an aqueous solution of hydrogen peroxide containing
the metal salt and oxidized and converted into infusible and
insoluble fibers.
For example, the spun fibers may be passed through the aqueous
solution of hydrogen peroxide or the spun fibers may be formed into
a skein and then dipped in the aqueous solution or the spun fibers
may be wound around a perforated bobbin and then dipped in the
aqueous solution.
In order to contact the spun fibers with the treating solution
effectively, 0.01 to 3 percent by weight of a surfactant may be
dissolved in the treating solution. In this case the surfactant may
be anionic, cationic, nonionic or amphoteric type, such as
anionnonionic surfactant.
In this case hydrogen peroxide is rapidly decomposed in the
oxidation treatment of the spun fibers, by the catalytic function
of the metal salt and by heating to discharge nascent oxygen and
the nascent oxygen acts effectively the spun fibers and oxidizes
them and the spun fibers are converted into infusible and insoluble
fibers.
When the spun fibers are oxidized in an aqueous phase by an aqueous
solution of hydrogen peroxide containing metal salts, such an
oxidation treatment in an aqueous phase may be repeated several
times, if necessary and further after the oxidation treatment in an
aqueous phase an additional oxidation treatment may be performed in
a gaseous phase. The oxidation treatment in a gaseous phase is
performed under air or an oxidizing atmosphere at a temperature
lower than 260.degree. C. by depositing hydrogen peroxide or other
oxidizing agent on the fibers in a solution state or other proper
manner or without depositing it.
When the oxidation treatment is carried out by means of an aqueous
solution of a permanganate, potassium salt is particularly
preferable. In this case, the treatment for making the spun fibers
infusible and insoluble may be effected in an aqueous solution of a
permanganate or after the spun fibers are deposited with an aqueous
solution of a permanganate, an oxidation in a gaseous phase may be
effected in air.
The concentration of the permanganate in the aqueous solution is
preferred to be at least 0.6 percent by weight. As far as the
concentration of salt is more than 0.6 percent by weight, a
saturated concentration may be used but if the concentration is
less than 0.6 percent by weight, the spun fibers cannot be
sufficiently oxidized and it is impossible to make the spun fibers
infusible and insoluble sufficiently. Furthermore, the
concentration of permanganate in the aqueous solution can be
properly selected in relation to the treating conditions,
particularly, treating temperature. pH value of the aqueous
solution of the above salt is not particularly limited. The
oxidation treatment with such a solution may be effected in the
same manner as described in the aqueous solution of hydrogen
peroxide.
When the spun fibers are made infusible and insoluble by an
oxidation in a gaseous phase after effecting the oxidation in an
aqueous phase it is preferable that the spun fibers have been
previously deposited with the above-described aqueous solution of
the salt uniformly.
In order to deposit the above-described aqueous solution of the
salt on the fibers, the fibers are dipped in the aqueous solution
of the salt or are sprayed with the aqueous solution of the
salt.
An amount of an aqueous solution of permanganate deposited on the
surface of the fibers before the oxidation in a gaseous phase is at
least 0.1 part by weight in pure salt component per 100 parts by
weight of the fibers. When the amount of pure salt component
deposited is less than the lower limit, it is impossible to make
sufficiently the spun fiber infusible and insoluble and such an
amount is not preferable. As in the case of aqueous solution of
hydrogen peroxide, the above-described aqueous solution may be
added with a surfactant. The oxidation treatment may be carried out
either in an aqueous phase or in a gaseous phase or a plurality of
oxidation treatments may be effected.
The temperature in the above oxidation treatment in an aqueous
phase is 0.degree. to 90.degree. C., preferably, 10.degree. to
80.degree. C. and in the case of the oxidation in a gaseous phase
the temperature of hot air is preferred to be lower than
260.degree. C. Furthermore, the treating time is about 1 minute to
3 hours in any case of an aqueous phase and a gaseous phase and is
selected by considering the concentration of salt in the aqueous
solution, treating temperature and the other operating
conditions.
After the oxidation treatment in a gaseous phase and in an aqueous
phase, the spun fibers are treated in air or gaseous nitrogen at
200.degree. to 500.degree. C. for at least 2 hours and they are
set. The fibers after this treatment are nonflammable fibers. The
heat-resistant and flame-resistant temperatures of these fibers are
at most 250.degree. to 300.degree. C. and the fibers are electric
insulator. Accordingly, when the heat-resistant temperature is
within the above-described range or the fibers are used for an
electric insulator, the nonflammable fibers can be used as such.
The set treatment is generally carried out in air at 200.degree. to
350.degree. C. for 2 to 4 hours.
The nonflammable fibers obtained by the above-described treatment
are carbonized at least once under nitrogen atmosphere at a high
temperature higher than 800.degree. C. In the set treatment, a heat
treatment in the presence of air is rather preferable in order to
promote the reaction, while since the carbonization treatment is a
reaction at a high temperature, the treatment must be effected in
an inert gas, such as nitrogen. When the temperature for
carbonization treatment is 800.degree. to 1,800.degree. C., carbon
fibers having microcrystalline carbon structure can be obtained.
When the temperature for carbonization treatment is raised to
2,000.degree. to 3,500.degree. C., carbon fibers having graphite
structure, namely, graphite fibers can be obtained. The
carbonization treatment may be two step treatments, in which the
nonflammable fibers are heat treated at a temperature of
800.degree. to 1,800.degree. C. and then further treated at a
temperature of 2,000.degree. to 3,500.degree. C. or one step
treatment in which the nonflammable fibers are treated at a
temperature of 800.degree. to 1,800.degree. C. or a temperature of
2,000.degree. to 3,500.degree. C.
The time of carbonization varies depending upon pitches and
synthetic organic polymers to be used, conditions for the conjugate
spinning and temperature of carbonization and the like but
generally is 10 minutes to 10 hours.
According to the present invention, the set treatment or the
carbonization treatment of the oxidized fibers can be selected in a
proper stage depending upon the properties of the aimed carbon
fibers.
According to the present invention, the spun fibers can be easily,
uniformly and rapidly oxidized and be converted into infusible and
insoluble fibers and the oxidized fibers have no stickiness and are
flexible and can be very easily handled while maintaining the shape
of the spun fibers. Accordingly, the fibers are not deformed by the
succeeding carbonization treatment as in the conventional case, the
shape of the spun fibers is maintained and carbon fibers having a
sufficient flexibility can be easily obtained. The thus obtained
spun fibers are superior in flexibility and in a resistance against
an elongation stress to the spun fibers obtained by the
conventional method for producing carbon fibers and further yarn
breakage does not occur in the spinning and the taking-up is easy
and such fibers can be produced commercially easily. Carbon fibers
having improved properties and satisfactory length can be obtained.
Consequently, according to the present invention the carbon fibers
can be produced commercially advantageously.
The following examples are given in illustration of this invention
and are not intended as limitations thereof. The percent used in
the examples means by weight, unless otherwise mentioned.
EXAMPLE 1
Nylon-6 chips having an intrinsic viscosity of 1.2 measured in
m-cresol at 30.degree. C. was used as a core component. Petroleum
asphalt containing 85.8 percent of carbon, which had been obtained
by subjecting blown asphalt (made by Maruzen Sekiyu K.K.) having a
softening point of 150.degree. C. to dry distillation under
nitrogen atmosphere, was used as a sheath component. These spinning
materials were conjugate spun in a conjugate ratio (by weight) of
core/sheath of one-fourth at a melter temperature of 280.degree. C.
through nozzles having a diameter of 0.2 mm. and for producing
sheath-core composite fibers into air at room temperature. The spun
fibers were taken up on a bobbin spaced 6 m. just under the nozzles
at a takeup velocity of 500 m./min.
When the resulting composite fibers were unwound from the bobbin,
the fibers were not broken nor deformed at all. Moreover, adhesion
between the starting asphalt and nylon-6 was favorable.
The spun fibers were dipped into 36.5 percent aqueous solution of
hydrogen peroxide at 25.degree. C. for 24 hours in the form of a
skein to oxidize the surface. The resulting fibers were suspended
in a tube, heated up to 280.degree. C. at a rate of 5.degree.
C./min. in the presence of air and maintained at this temperature
for 2 hours, whereby the fibers were heat set. Following to this
heat set, the fibers were heated up to 1,000.degree. C. at the same
rate under nitrogen atmosphere, maintained at this temperature for
30 minutes to effect a carbonization treatment, and then cooled to
room temperature to obtain carbon fibers. The resulting carbon
fibers had a strength of 8 t./cm..sup.2 and an elongation of 1.8
percent.
COMPARATIVE EXAMPLE
The petroleum asphalt obtained by dry distillation under the same
condition as described in Example 1 alone was heated and melted at
280.degree. C. in a melter and spun through nozzles having a
diameter of 0.2 mm. into air at room temperature. The spun fibers
were taken up on a bobbin spaced 1 m. from the nozzles at a takeup
velocity of 200 m./min.
When the spun fibers were taken up under the same condition as
described in Example 1, that is, the space was 6 m. and the takeup
velocity was 500 m./min., the fibers were broken and were not able
to be taken up, and the workability was considerably inferior to
that in the method of the present invention shown in Example 1.
Furthermore, the fibers taken up under the above-mentioned
condition had a very low strength, and moreover the fibers were
deformed during unwinding from the bobbin, oxidation and heat set.
Therefore, it was impossible to produce long filamentary carbon
fibers.
EXAMPLE 2
Epikote 1009 (trademark of an epoxy resin made by Shell
international Chemicals Corp.) was used as a core component. Coal
tar pitch containing 86.2 percent of carbon was used as a sheath
component. These spinning materials were melted and conjugate spun
in a conjugate ratio (by weight) of core/sheath of 1/6 at a
temperature of 220.degree. C. through the same nozzles having a
diameter of 0.2 mm. and for producing a sheath-core composite
fibers as used in Example 1, and the spun fibers were taken up at a
takeup rate of 400 m./min.
The resulting composite fibers were not broken nor deformed at all
during various treatments.
The composite fibers were subjected to an oxidation treatment at
70.degree. C. for 1.5 hours in air containing 8-11 g./m..sup.3 of
ozone to make the fibers insoluble and infusible. Then, the fibers
were heat set in the presence of air and subjected to a
carbonization treatment under nitrogen atmosphere in the same
manner as described in Example 1 to obtain carbon fibers. The
resulting carbon fibers had a strength of 9 t./cm..sup.2 and an
elongation of 1.5 percent.
EXAMPLE 3
A spinneret for producing side-by-side composite fibers, in which
one component is entered into the other component in the form of a
neck so that both components do not separate, was used. Petroleum
asphalt used in Example 1 was used as one component. Yukaron YM-60
(trademark of a high pressure process polyethylene resin made by
Mitsubishi Yuka K.K.) was used as the other component. These
spinning materials were melted and conjugate spun in a conjugate
ratio of petroleum asphalt/polyethylene of 2/1 at 260.degree. C.,
and the spun fibers were taken up under the same condition as
described in Example 1.
The resulting composite fibers were able to be subjected to various
treatment under the same condition as described in Example 1, while
keeping filamentary configuration without breakage and deformation.
Carbon fibers having a strength of 11 t./cm..sup.2 and an
elongation of 2.0 percent were obtained.
EXAMPLE 4
The petroleum asphalt used in Example 1 was used as a core
component, and Noblen MA-3A (trademark of a polypropylene resin
made by Mitsubishi Yuka K.K.) was used as a sheath component. These
spinning materials were melted and conjugate spun in various
conjugate ratio at a melter temperature of 290.degree. C. through
nozzles having a diameter of 0.2 mm. and for producing sheath-core
composite fibers into air at room temperature in the same manner as
described in Example 1. The spun fibers were contacted with 5
percent solution of benzoyl peroxide in benzene between the nozzles
and a bobbin, whereby the benzoyl peroxide was applied to the fiber
surface, and then the fibers were taken up on the bobbin. The
resulting fibers were oxidized at 80.degree. C. for 4 hours in air
having the same ozone concentration as described in Example 2 to
make the fibers insoluble and infusible, and then the fibers were
heat set in the presence of air and further subjected to a
carbonization treatment at 1,000.degree. C. under nitrogen
atmosphere in the same manner as described in Example 1 to obtain
carbon fibers. The obtained result is shown in the following Table
1. ##SPC1##
EXAMPLE 5
Thermally cracked polyvinyl chloride pitch having a softening point
of 170.degree. C. was used as a core component, and a novolack
resin having an average molecular weight of 1,200 was used as a
sheath component. The pitch was melted at a melter temperature of
220.degree. C. and the novolack resin was melted at a melter
temperature of 170.degree. C. and both the components were
conjugate spun in a conjugate ratio of core/sheath of 5/1 through
nozzles having a diameter of 0.3 mm. and for producing sheath-core
composite fibers at a nozzle temperature of 220.degree. C. into air
at room temperature, and the spun fibers were taken up on a bobbin
at a takeup velocity of 1,000 m./min.
The resulting raw fibers were dipped in 20 percent aqueous solution
of hexamethylenetetramine at 25.degree. C. for 2 hours, and then
the fibers were oxidized at 80.degree. C. for 2 hours in the
ozone-containing air used in Example 1 to make the fibers insoluble
and infusible. The fibers were further heat set in the presence of
air in the same manner as described in Example 1 to obtain
nonflammable fibers (8).
Then, the nonflammable fibers (8) were divided into two parts. One
part was heated up to 1,000.degree. C. at a rate of 3.degree.
C./min. under dried nitrogen atmosphere, maintained at this
temperature for 1 hour and cooled to room temperature under the
above described nitrogen atmosphere to obtain carbon fibers (9).
Another part was heated up to 2,500.degree. C. at a rate of
3.degree. C./min. under the same dried nitrogen atmosphere as
described above, maintained at this temperature for 30 minutes and
cooled to room temperature under the above described nitrogen
atmosphere to obtain graphite fibers (10).
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The properties of the resulting fibers are shown in the following
Table 2.
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TABLE 2
Specific Strength Elasticity Fiber gravity (t./cm..sup.2) 10.sup.3
t./cm..sup.2)
__________________________________________________________________________
Non- flammable 1.2 4.3 0.2 fibers (8) Carbon fibers 1.5 10 0.7
Graphite fibers 1.8 16.5 3.1 (10)
__________________________________________________________________________
EXAMPLE 6
Petroleum asphalt having a softening point of 240.degree. C., which
had been obtained by subjecting petroleum blown asphalt to dry
distillation at 280.degree. C. for 4 hours under a reduced pressure
of 2 mm.Hg. in the absence of air, was used as a core component.
Polyethylene terephthalate having a relative viscosity of 0.62
measured in o-chlorophenol at 30.degree. C. was used as a sheath
component. These spinning materials were conjugate spun in a
conjugate ratio of core/sheath of 4/1 at a melter temperature of
300.degree. C. through nozzles having a diameter of 0.25 mm. and
for producing sheath-core composite fibers into air at room
temperature in the same manner as described in Example 1. The spun
fibers were contacted with 2 percent aqueous solution of cobalt
chloride between the nozzles and a bobbin, whereby the cobalt
chloride was applied to the fiber surface, and then the fibers were
taken up on the bobbin. The thus obtained fibers were dipped in 36
percent aqueous solution of hydrogen peroxide at 25.degree. C. for
24 hours in the form of a skein to oxidize the surface. Then, the
fibers were heat set in the presence of air under the same
condition as described in Example 1, and further carbonized and
baked at 1,000.degree. C. under nitrogen atmosphere to obtain aimed
carbon fibers. The resulting carbon fibers had a strength of 10
t./cm..sup.2.
EXAMPLE 7
The sheath-core composite fibers obtained in Example 1 were dipped
and oxidized in an aqueous solution, which contained 10 percent by
weight of potassium permanganate and a small amount of an anionic
surfactant consisting of sodium alkylbenzenesulfonate and was kept
at a temperature of 60.degree. C. and at a pH of about 7, for 10
hours in the form of a skein.
The thus treated fibers were charged directly in an electric
furnace under nitrogen atmosphere without washing and drying,
heated up to 1,000.degree. C. at a rate of 5.degree. C./min.,
maintained at this temperature for 30 minutes to effect a
carbonization treatment, and cooled to room temperature to obtain
carbon fibers. The resulting carbon fibers had electric
conductivity and had a strength of 8.2 t./cm..sup.2 and an
elongation of 1.5 percent.
* * * * *