U.S. patent application number 13/243675 was filed with the patent office on 2012-02-16 for carbon fiber composite material and method of producing the same, formed product of carbon fiber composite and method of producing the same, carbon fiber-metal composite material and method of producing the same, and formed product of carbon fiber-metal composite and method of producing the same.
This patent application is currently assigned to NISSIN KOGYO CO., LTD.. Invention is credited to Akira Magario, Toru NOGUCHI.
Application Number | 20120040176 13/243675 |
Document ID | / |
Family ID | 33493955 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120040176 |
Kind Code |
A1 |
NOGUCHI; Toru ; et
al. |
February 16, 2012 |
CARBON FIBER COMPOSITE MATERIAL AND METHOD OF PRODUCING THE SAME,
FORMED PRODUCT OF CARBON FIBER COMPOSITE AND METHOD OF PRODUCING
THE SAME, CARBON FIBER-METAL COMPOSITE MATERIAL AND METHOD OF
PRODUCING THE SAME, AND FORMED PRODUCT OF CARBON FIBER-METAL
COMPOSITE AND METHOD OF PRODUCING THE SAME
Abstract
A method of producing a carbon fiber composite material
including: mixing an elastomer which includes an unsaturated bond
or a group having affinity to carbon nanofibers with metal
particles; and dispersing the carbon nanofibers into the elastomer
including the metal particles by a shear force.
Inventors: |
NOGUCHI; Toru; (Ueda-shi,
JP) ; Magario; Akira; (Chiisagata-gun, JP) |
Assignee: |
NISSIN KOGYO CO., LTD.
Ueda-shi
JP
|
Family ID: |
33493955 |
Appl. No.: |
13/243675 |
Filed: |
September 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10895351 |
Jul 21, 2004 |
8053506 |
|
|
13243675 |
|
|
|
|
Current U.S.
Class: |
428/323 |
Current CPC
Class: |
B82Y 30/00 20130101;
B22F 2999/00 20130101; C08K 7/06 20130101; C22C 2026/002 20130101;
B29C 43/24 20130101; B29K 2105/162 20130101; C08K 7/18 20130101;
C08J 2321/00 20130101; B22F 2999/00 20130101; C22C 47/08 20130101;
B22F 1/0059 20130101; C08J 5/042 20130101; C08K 7/18 20130101; C22C
49/14 20130101; C08K 7/06 20130101; C22C 26/00 20130101; C22C 47/06
20130101; Y10T 428/25 20150115; C08J 5/005 20130101; C22C 49/14
20130101; C08L 21/00 20130101; C08L 21/00 20130101; C08L 21/00
20130101; B22F 1/0018 20130101 |
Class at
Publication: |
428/323 |
International
Class: |
B32B 5/16 20060101
B32B005/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2003 |
JP |
2003-278186 |
Aug 18, 2003 |
JP |
2003-294244 |
Jun 8, 2004 |
JP |
2004-169668 |
Claims
1. A carbon fiber composite material comprising: an elastomer; and
metal particles and carbon nanofibers uniformly dispersed in the
elastomer, wherein the elastomer includes an unsaturated bond or a
group having affinity to the carbon nanofibers, the elastomer in
the composite material is in a uncrosslinked form and the composite
material has a first spin-spin relaxation time (T2n) of 100 to
3,000 .mu.sec, a second spin-spin relaxation time (T2nn) of 1,000
to 10,000 .mu.sec or without the second spin-spin relaxation time,
and a fraction (fin) of components having the second spin-spin
relaxation time of less than 0.2, as measured at 150.degree. C. by
Hahn-echo method using a pulsed NMR technique with .sup.1H as an
observing nucleus, the metal particles have an average particle
diameter of 500 .mu.m or less, and the metal particles are not
ferromagnetic.
2. The carbon fiber composite material as defined in claim 1,
wherein the amount of the metal particles is 10 to 3,000 parts by
weight for 100 parts by weight of the elastomer.
3. The carbon fiber composite material as defined in claim 1,
wherein the metal particles have an average particle diameter
greater than an average diameter of the carbon nanofibers.
4. The carbon fiber composite material as defined in claim 1,
wherein the metal particles are aluminum particles or aluminum
alloy particles.
5. The carbon fiber composite material as defined in claim 1,
wherein at least one of a main chain, a side chain and a terminal
chain of the elastomer includes at least one of a double bond, a
triple bond, .alpha.-hydrogen, a carbonyl group, a carboxyl group,
a hydroxyl group, an amino group, a nitrile group, a ketone group,
an amide group, an epoxy group, an ester group, a vinyl group, a
halogen group, a urethane group, a biuret group, an allophanate
group and a urea group.
6. The carbon fiber composite material as defined in claim 1,
wherein a network component of the elastomer in an uncrosslinked
form has a spin-spin relaxation time (T2n) measured at 30.degree.
C. by a Hahn-echo method using pulsed nuclear magnetic resonance
(NMR) technique of 100 to 3,000 .mu.sec.
7. The carbon fiber composite material as defined in claim 1,
wherein a network component of the elastomer in a crosslinked form
has a spin-spin relaxation time (T2n) measured at 30.degree. C. by
a Hahn-echo method using pulsed nuclear magnetic resonance (NMR)
technique of 100 to 2,000 .mu.sec.
8. The carbon fiber composite material as defined in claim 1,
wherein the carbon nanofibers have an average diameter of 0.5 to
500 nm.
9. A formed product of carbon fiber composite obtained by forming
the carbon fiber composite material as defined in claim 1 into a
predetermined shape.
10. A formed product of carbon fiber composite obtained by
crosslinking the carbon fiber composite material as defined in
claim 1.
11. A formed product of carbon fiber composite obtained by
crosslinking the carbon fiber composite material as defined in
claim 1 and forming the carbon fiber composite material into a
predetermined shape.
12. The formed product of carbon fiber composite as defined in
claim 10, having a spin-lattice relaxation time (T1) measured at
150.degree. C. by a Hahn-echo method using pulsed nuclear magnetic
resonance (NMR) technique per 1 vol % of the carbon nanofibers, the
spin-lattice relaxation time (T1) for the formed product being at
least one .mu.sec shorter than the spin-lattice relaxation time
(T1) of the elastomer.
13. A carbon fiber-metal composite material obtained by mixing the
carbon fiber composite material as defined in claim 1 into a molten
metal and casting the mixture.
14. A carbon fiber-metal composite material obtained by mixing the
formed product of carbon fiber composite as defined in claim 9 into
a molten metal and casting the mixture.
15. A formed product of carbon fiber-metal composite obtained by:
permeating a molten metal into the formed product of carbon fiber
composite as defined in claim 9 to replace the elastomer with the
metal.
16. The carbon fiber-metal composite material as defined in claim
13, wherein the molten metal is the same metal as the metal
particles.
17. The carbon fiber-metal composite material as defined in claim
14, wherein the molten metal is the same metal as the metal
particles.
18. A carbon fiber-metal composite material obtained by
powder-forming the carbon fiber composite material as defined in
claim 1.
19. A carbon fiber-metal composite material obtained by
powder-forming the formed product of carbon fiber composite as
defined in claim 9.
Description
[0001] This is a Division of application Ser. No. 10/895,351 filed
Jul. 21, 2004, which claims the benefit of Japanese Patent
Application No. 2003-278186, filed on Jul. 23, 2003, Japanese
Patent Application No. 2003-294244, filed on Aug. 18, 2003, and
Japanese Patent Application No. 2004-169668, filed on Jun. 8, 2004,
are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a carbon fiber composite
material and a method of producing the same, a formed product of
carbon fiber composite and a method of producing the same, a carbon
fiber-metal composite material and a method of producing the same,
and a formed product of carbon fiber-metal composite and a method
of producing the same.
[0003] In recent years, composite materials using carbon nanofibers
have attracted attention. These composite materials are expected to
exhibit improved mechanical strength and the like due to the
presence of the carbon nanofibers.
[0004] As a casting method for a metal composite material, a
casting method in which a molten metal permeates a porous formed
product consisting of oxide ceramics by causing magnesium vapor to
permeate and become dispersed in the porous formed product and by
introducing nitrogen gas has been proposed (see Japanese Patent
Application Laid-open No. 10-183269, for example).
[0005] However, since the carbon nanofibers have strong aggregating
properties, it is very difficult to uniformly disperse the carbon
nanofibers in a substrate of a composite material. Therefore, it is
difficult to obtain a carbon nanofiber composite material having
desired properties, and the expensive carbon nanofibers cannot be
efficiently utilized.
[0006] Moreover, since the conventional casting method in which a
molten metal is caused to permeate the porous formed product
consisting of oxide ceramics includes complicated processing,
production on an industrial scale is difficult.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention may provide a carbon fiber composite
material in which carbon nanofibers are uniformly dispersed, and a
method of producing the same. The present invention may also
provide a formed product of carbon fiber composite in which carbon
nanofibers are uniformly dispersed, and a method of producing the
same. The present invention may further provide a carbon
fiber-metal composite material in which carbon nanofibers are
uniformly dispersed, and a method of producing the same. The
present invention may further provide a formed product of carbon
fiber-metal composite in which carbon nanofibers are uniformly
dispersed, and a method of producing the same.
[0008] According to one aspect of the present invention, there is
provided a carbon fiber composite material comprising: an
elastomer; and metal particles and carbon nanofibers dispersed in
the elastomer, wherein the elastomer includes an unsaturated bond
or a group having affinity to the carbon nanofibers.
[0009] In the carbon fiber composite material of the present
invention, the carbon nanofibers are further uniformly dispersed in
the elastomer as a substrate for reasons described later. In
particular, it is difficult to disperse carbon nanofibers with a
diameter of about 30 nm or less or carbon nanofibers in the shape
of a curved fiber. However, these carbon nanofibers can be
uniformly dispersed in the elastomer.
[0010] The elastomer used in the present invention may be either a
rubber elastomer or a thermoplastic elastomer. In the case of using
the rubber elastomer, the elastomer may be either a crosslinked
form or an uncrosslinked form. As the raw material elastomer, an
uncrosslinked form is used in the case of using the rubber
elastomer. The carbon nanofibers are dispersed to only a small
extent in ethylene propylene rubber (EPDM) among thermoplastic
elastomers. However, according to the present invention, the carbon
nanofibers can be uniformly dispersed in EPDM due to the carbon
nanofiber dispersion effect of the metal particles.
[0011] In a formed product of carbon fiber composite obtained by
crosslinking the carbon fiber composite material according to the
present invention and a formed product of carbon fiber composite
obtained from the carbon fiber composite material without
crosslinking the carbon fiber composite material, the carbon
nanofibers are uniformly dispersed due to the presence of the metal
particles in the same manner as in the carbon fiber composite
material.
[0012] In a carbon fiber-metal composite material obtained by
powder-forming the carbon fiber composite material or the formed
product of carbon fiber composite according to the present
invention, the carbon nanofibers are uniformly dispersed due to the
presence of the metal particles in the same manner as in the carbon
fiber composite material.
[0013] In a carbon fiber-metal composite material obtained by
mixing the carbon fiber composite material or the formed product of
carbon fiber composite according to the present invention into a
molten metal and casting the mixture, the carbon nanofibers are
uniformly dispersed due to the presence of the metal particles in
the same manner as in the carbon fiber composite material.
[0014] In a formed product of carbon fiber-metal composite obtained
by permeating a molten metal into the formed product of carbon
fiber composite according to the present invention to replace the
elastomer with the metal, the carbon nanofibers are uniformly
dispersed due to the presence of the metal particles in the same
manner as in the carbon fiber composite material. In particular, if
a formed product of carbon fiber composite comes in contact with a
molten metal, the molten metal permeates the formed product of
carbon fiber composite while thermally decomposing the elastomer,
and the elastomer is replaced by solidified metal, so that a formed
product of carbon fiber-metal composite in which carbon nanofibers
are uniformly dispersed can be cast. In the formed product of
carbon fiber composite, the amount of the metal particles is 10 to
3,000 parts by weight, and preferably 100 to 1000 parts by weight
for 100 parts by weight of the elastomer. If the amount of the
metal particles is less than 10 parts by weight, the permeation
rate of the molten metal is decreased due to a small degree of
capillary phenomenon, thereby giving rise to problems from the
viewpoint of productivity and cost. If the amount of the metal
particles exceeds 3,000 parts by weight, permeation into the
elastomer becomes difficult when producing the carbon fiber
composite material.
[0015] According to another aspect of the present invention, there
is provided a method of producing a carbon fiber composite
material, comprising:
[0016] mixing an elastomer which includes an unsaturated bond or a
group having affinity to carbon nanofibers with metal particles;
and
[0017] mixing the carbon nanofibers into the elastomer including
the metal particles and dispersing the carbon nanofibers by a shear
force.
[0018] According to this method, since the unsaturated bond or
group of the elastomer bonds to an active portion of the carbon
nanofiber, in particular, a terminal radical of the carbon
nanofiber, the aggregation force of the carbon nanofibers can be
reduced, whereby dispersibility can be increased. Turbulent flows
of the elastomer occur around the metal particles when dispersing
the carbon nanofibers by a shear force by using the elastomer
including the metal particles. As a result, the carbon fiber
composite material of the present invention has a structure in
which the carbon nanofibers are further uniformly dispersed in the
elastomer as a substrate. In particular, even carbon nanofibers
with a diameter of about 30 nm or less or carbon nanofibers in the
shape of a curved fiber can be uniformly dispersed in the
elastomer.
[0019] The step of dispersing the carbon nanofibers in the
elastomer by a shear force may be carried out by using (a) an
open-roll method with a roll distance of 0.5 mm or less, (b) a
closed kneading method, (c) a multi-screw extrusion kneading
method, or the like.
[0020] A method of producing a formed product of carbon fiber
composite having a step of crosslinking the carbon fiber composite
material according to the present invention can produce a formed
product of carbon fiber composite in which the carbon nanofibers
are uniformly dispersed due to the presence of the metal particles
by crosslinking the carbon fiber composite material in which the
carbon nanofibers are uniformly dispersed. A formed product of
carbon fiber composite having a desired shape in which the carbon
nanofibers are uniformly dispersed can be obtained by performing
the crosslinking step while forming the carbon fiber composite
material in a die having a desired shape. A method of producing a
formed product of carbon fiber composite having a step of forming
the carbon fiber composite material according to the present
invention into a desired shape without crosslinking the carbon
fiber composite material can produce a formed product of carbon
fiber composite in which the carbon nanofibers are uniformly
dispersed.
[0021] A method of producing a carbon fiber-metal composite
material having a step of mixing the carbon fiber composite
material or the formed product of carbon fiber composite according
to the present invention into a molten metal and casting the
mixture in a die having a desired shape can produce a carbon
fiber-metal composite material in which the carbon nanofibers are
uniformly dispersed due to the presence of the metal particles by
casting the formed product of carbon fiber composite in which the
carbon nanofibers are uniformly dispersed as described above.
[0022] A method of producing a formed product of carbon fiber-metal
composite including: disposing a metal ingot above the formed
product of carbon fiber composite according to the present
invention; heating the metal ingot to melt into a molten metal and
heating the formed product of the carbon fiber composite to
vaporize the elastomer in the formed product of carbon fiber
composite; and replacing the elastomer with the molten metal, can
produce a formed product of carbon fiber-metal composite in which
the elastomer in the formed product of carbon fiber composite in
which the carbon nanofibers are uniformly dispersed is replaced
with the metal. In particular, in the formed product of carbon
fiber composite, the amount of the metal particles is 10 to 3,000
parts by weight, and preferably 100 to 1000 parts by weight for 100
parts by weight of the elastomer. If the amount of the metal
particles is less than 10 parts by weight, the permeation rate of
the molten metal is decreased due to a small degree of capillary
phenomenon, thereby giving rise to problems from the viewpoint of
productivity and cost. If the amount of the metal particles exceeds
3,000 parts by weight, impregnation with the elastomer becomes
difficult when producing the carbon fiber composite material. It is
preferable that the formed product of carbon fiber composite is
formed in an uncrosslinked state, because the elastomer is easily
decomposed, whereby the molten metal can swiftly permeate the
formed product of carbon fiber composite.
[0023] A method of producing a carbon fiber-metal composite
material including a step of powder-forming the carbon fiber
composite material or the formed product of carbon fiber composite
according to the present invention can produce a carbon fiber-metal
composite material in which the carbon nanofibers are uniformly
dispersed by using the carbon fiber composite material or the
formed product of carbon fiber composite in which the carbon
nanofibers are uniformly dispersed as described above.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0024] FIG. 1 is a diagram schematically showing a kneading method
for an elastomer and carbon nanofibers using an open-roll method,
according to one embodiment of the present invention.
[0025] FIG. 2 is a diagram schematically showing a device for
producing a formed product of carbon fiber-metal composite by a
pressureless permeation method.
[0026] FIG. 3 is a diagram schematically showing another device for
producing a formed product of carbon fiber-metal composite by a
pressureless permeation method.
[0027] FIG. 4 shows a scanning electron microscope (SEM) image of a
formed product of carbon fiber-metal composite according to one
embodiment of the present invention.
[0028] FIG. 5 is a graph showing the distribution of the closest
distance between carbon nanofibers in a formed product of carbon
fiber-metal composite.
[0029] FIG. 6 shows an SEM image of a fracture plane of a formed
product of carbon fiber-metal composite according to one embodiment
of the present invention.
[0030] FIG. 7 is a graph showing the relationship between stress
and strain of a formed product of carbon fiber-metal composite.
[0031] FIG. 8 is a graph showing yield strength of a formed product
of carbon fiber-metal composite.
[0032] FIG. 9 is a graph showing the relationship between
temperature and modulus of elasticity (E't/E'30) of a formed
product of carbon fiber-metal composite.
[0033] FIG. 10 is a graph showing the relationship between
temperature and loss factor (tan .delta.) of a formed product of
carbon fiber-metal composite.
[0034] FIG. 11 is another graph showing the relationship between
temperature and loss factor (tan .delta.) of a formed product of
carbon fiber-metal composite.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] Embodiments of the present invention will be described in
detail below with reference to the drawings.
[0036] According to one embodiment of the present invention, there
is provided a carbon fiber composite material comprising: an
elastomer; and metal particles and carbon nanofibers dispersed in
the elastomer.
[0037] A formed product of carbon fiber composite according to one
embodiment of the present invention can be obtained by forming the
carbon fiber composite material into a desired shape with or
without crosslinking the carbon fiber composite material.
[0038] A carbon fiber-metal composite material according to one
embodiment of the present invention can be obtained by
powder-forming the carbon fiber composite material, or the formed
product of carbon fiber composite.
[0039] A carbon fiber-metal composite material according to one
embodiment of the present invention can be obtained by mixing the
carbon fiber composite material or the formed product of carbon
fiber composite into a molten metal and casting the mixture.
[0040] A formed product of carbon fiber-metal composite according
to one embodiment of the present invention can be obtained by
permeating a molten metal into the formed product of carbon fiber
composite to replace the elastomer with the metal.
[0041] According to one embodiment of the present invention, there
is provided a method of producing a carbon fiber composite
material, comprising: mixing an elastomer which includes an
unsaturated bond or a group having affinity to carbon nanofibers
with metal particles; and mixing the carbon nanofibers into the
elastomer including the metal particles and dispersing the carbon
nanofibers by a shear force.
[0042] According to one embodiment of the present invention, there
is provided a method of producing a formed product of carbon fiber
composite, comprising: forming the carbon fiber composite material
into a desired shape. According to one embodiment of the present
invention, there is provided a method of producing a formed product
of carbon fiber composite, comprising: crosslinking and forming the
carbon fiber composite material.
[0043] A method of producing a carbon fiber-metal composite
material according to one embodiment of the present invention
includes a step of casting the carbon fiber composite material or
the formed product of carbon fiber composite and a molten metal in
a die.
[0044] According to one embodiment of the present invention, there
is provided a method of producing a formed product of carbon
fiber-metal composite comprising: disposing a metal ingot above the
formed product of carbon fiber composite; heating the metal ingot
to melt into a molten metal and heating the formed product of the
carbon fiber composite to vaporize the elastomer in the formed
product of carbon fiber composite; and replacing the elastomer with
the molten metal.
[0045] A method of producing a carbon fiber-metal composite
material according to one embodiment of the present invention
includes a step of powder-forming the carbon fiber composite
material or the formed product of carbon fiber composite.
[0046] The elastomer preferably has characteristics such as a
certain degree of molecular length and flexibility in addition to
high affinity to the carbon nanofibers.
[0047] In the step of dispersing the carbon nanofibers in the
elastomer by a shear force, it is preferable that the carbon
nanofibers and the elastomer be kneaded at a shear force as high as
possible.
1. ELASTOMER
[0048] The elastomer has a molecular weight of preferably 5,000 to
5,000,000, and still more preferably 20,000 to 3,000,000. If the
molecular weight of the elastomer is within this range, since the
elastomer molecules are entangled and linked, the elastomer easily
enters the space between aggregated carbon nanofibers. Therefore,
the effect of separating the carbon nanofibers is increased. If the
molecular weight of the elastomer is less than 5,000, since the
elastomer molecules cannot be sufficiently entangled, the effect of
dispersing the carbon nanofibers is reduced even if a shear force
is applied in the subsequent step. If the molecular weight of the
elastomer is greater than 5,000,000, the elastomer becomes too
hard, thereby making processing difficult.
[0049] The network component of the elastomer in an uncrosslinked
form has a spin-spin relaxation time (T2n/30.degree. C.) measured
at 30.degree. C. by a Hahn-echo method using pulsed nuclear
magnetic resonance (NMR) technique of preferably 100 to 3,000
.mu.sec, and still more preferably 200 to 1,000 .mu.sec. If the
elastomer has the spin-spin relaxation time (T2n/30.degree. C.)
within the above range, the elastomer is flexible and has
sufficiently high molecular mobility. Therefore, when the elastomer
and the carbon nanofibers are mixed, the elastomer can easily enter
the space between the carbon nanofibers due to high molecular
mobility. If the spin-spin relaxation time (T2n/30.degree. C.) is
shorter than 100 .mu.sec, the elastomer cannot have sufficient
molecular mobility. If the spin-spin relaxation time
(T2n/30.degree. C.) is longer than 3,000 .mu.sec, the elastomer
tends to flow as a liquid, whereby it becomes difficult to disperse
the carbon nanofibers.
[0050] The network component of the elastomer in a crosslinked form
preferably has a spin-spin relaxation time (T2n) measured at
30.degree. C. by the Hahn-echo method using the pulsed NMR
technique of 100 to 2,000 .mu.sec. The reasons therefor are the
same as those for the uncrosslinked form. Specifically, when an
uncrosslinked form which satisfies the above conditions is
crosslinked according to the method of the present invention, the
spin-spin relaxation time (T2n) of the resulting crosslinked form
almost falls within the above range.
[0051] The spin-spin relaxation time obtained by the Hahn-echo
method using the pulsed NMR technique is a measure which represents
molecular mobility of a substance. In more detail, when the
spin-spin relaxation time of the elastomer is measured by the
Hahn-echo method using the pulsed NMR technique, a first component
having a first spin-spin relaxation time (T2n) which is shorter and
a second component having a second spin-spin relaxation time (T2nn)
which is longer are detected. The first component corresponds to
the network component (backbone molecule) of the polymer, and the
second component corresponds to the non-network component (branched
component such as a terminal chain) of the polymer. The shorter the
first spin-spin relaxation time, the lower the molecular mobility
and the harder the elastomer. The longer the first spin-spin
relaxation time, the higher the molecular mobility and the softer
the elastomer.
[0052] As the measurement method in the pulsed NMR technique, a
solid-echo method, a Carr-Purcell-Meiboom-Gill (CPMG) method, or a
90.degree. pulse method may be applied in addition to the Hahn-echo
method. However, since the carbon fiber composite material
according to one embodiment of the present invention has a medium
spin-spin relaxation time (T2), the Hahn-echo method is most
suitable. Generally, the solid-echo method and the 90.degree. pulse
method are suitable for the measurement of a short spin-spin
relaxation time (T2), the Hahn-echo method is suitable for the
measurement of a medium spin-spin relaxation time (T2), and the
CPMG method is suitable for the measurement of a long spin-spin
relaxation time (T2).
[0053] The elastomer includes an unsaturated bond or a group having
affinity to the carbon nanofiber, in particular, to a terminal
radical of the carbon nanofiber in at least one of the main chain,
side chain, and terminal chain, or has properties of readily
forming such a radical or group. The unsaturated bond or group may
be at least one selected from a double bond, a triple bond, and
functional groups such as a-hydrogen, a carbonyl group, a carboxyl
group, a hydroxyl group, an amino group, a nitrile group, a ketone
group, an amide group, an epoxy group, an ester group, a vinyl
group, a halogen group, a urethane group, a biuret group, an
allophanate group, and a urea group.
[0054] A carbon nanofiber generally consists of six-membered rings
of carbon atoms on the side surface, and five-membered rings are
introduced at the end to form a closed structure. However, since
the carbon nanofiber has a forced structure, a defect tends to
occur and a radical or a functional group tends to be formed at the
defect. In one embodiment of the present invention, since the
elastomer includes an unsaturated bond or a group having high
affinity (reactivity or polarity) to the radical of the carbon
nanofiber in at least one of the main chain, side chain, and
terminal chain of the elastomer, the elastomer and the carbon
nanofiber can be bonded. This enables the carbon nanofibers to be
easily dispersed by overcoming the aggregation force of the carbon
nanofibers.
[0055] As the elastomer, elastomers such as natural rubber (NR),
epoxidized natural rubber (ENR), styrene butadiene rubber (SBR),
nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene
rubber (EPR or EPDM), butyl rubber (ITR), chlorobutyl rubber
(CIIR), acrylic rubber (ACM), silicone rubber (Q), fluorine rubber
(FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR),
epichlorohydrin rubber (CO or CEO), urethane rubber (U), and
polysulfide rubber (T); thermoplastic elastomers such as
olefin-based elastomers (TPO), polyvinyl chloride)-based elastomers
(TPVC), polyester-based elastomers (TPEE), polyurethane-based
elastomers (TPU), polyamide-based elastomers (TPEA), and
polystyrene-based elastomers (SBS); and mixtures of these
elastomers may be used. The present inventors have confirmed that
it is difficult to disperse the carbon nanofibers in ethylene
propylene rubber (EPR or EPDM).
2. METAL PARTICLES
[0056] The metal particles are mixed and dispersed in the elastomer
in advance, and allow the carbon nanofibers to be further uniformly
dispersed when mixing the carbon nanofibers. As the metal
particles, particles of aluminum and an aluminum alloy, magnesium
and a magnesium alloy, iron and an iron alloy, and the like may be
used either individually or in combination of two or more. The
metal particles preferably have an average particle size greater
than the average diameter of the carbon nanofibers to be used. The
average particle size of the metal particles is 500 .mu.m or less,
and preferably 1 to 300 .mu.m. In the case of using a pressureless
permeation method in a casting step, the amount of the metal
particles is 10 to 3,000 parts by weight, and preferably 100 to
1,000 parts by weight for 100 parts by weight of the elastomer. If
the amount of the metal particles is less than 10 parts by weight,
the permeation rate of a molten metal is decreased due to a small
degree of capillary phenomenon, thereby giving rise to problems
from the viewpoint of productivity and cost. If the amount of the
metal particles exceeds 3,000 parts by weight, impregnation with
the elastomer becomes difficult when producing a carbon fiber
composite material. The shape of the metal particles is not limited
to spherical. The metal particles may be in the shape of a sheet or
a scale insofar as turbulent flows occur around the metal particles
during mixing.
[0057] In the case where the metal particles are aluminum
particles, an oxide on the surfaces of the aluminum particles is
reduced by a radical generated by thermal decomposition of the
elastomer when causing the aluminum molten metal to permeate. This
improves wettability between the aluminum particles and the
aluminum molten metal, whereby the bonding strength can be
increased. Moreover, flows accompanying permeation of the aluminum
molten metal cause the carbon nanofibers to enter the aluminum
particles. The above-described preferable effects are obtained in
the case where the metal particles are particles having an oxide on
the surface, such as aluminum particles.
3. CARBON NANOFIBER
[0058] The carbon nanofibers preferably have an average diameter of
0.5 to 500 nm. In order to increase the strength of the carbon
fiber composite material, the average diameter of the carbon
nanofibers is still more preferably 0.5 to 30 nm. The carbon
nanofibers may be in the shape of a linear fiber or a curved
fiber.
[0059] The amount of the carbon nanofibers to be added is not
particularly limited and may be determined depending on the
application. In the carbon fiber composite material according to
one embodiment of the present invention, a crosslinked elastomer,
an uncrosslinked elastomer, or a thermoplastic polymer may be
directly used as the elastomer material. The carbon fiber composite
material may be used as a raw material for a metal composite
material. In the case where the carbon fiber composite material is
used as a raw material for a metal composite material, the carbon
fiber composite material may include the carbon nanofibers in an
amount of 0.01 to 50 wt %. Such a raw material for a metal
composite material may be used as a masterbatch as a carbon
nanofiber source when mixing the carbon nanofibers into a
metal.
[0060] As examples of the carbon nanofibers, a carbon nanotube and
the like can be given. The carbon nanotube has a single-layer
structure in which a graphene sheet of a hexagonal carbon layer is
closed in the shape of a cylinder, or a multi-layer structure in
which the cylindrical structures are nested. Specifically, the
carbon nanotube may consist of only the single-layer structure or
only the multi-layer structure, or the single-layer structure and
the multi-layer structure may be present in combination. A carbon
material partially having the structure of the carbon nanotube may
also be used. The carbon nanotube is also called a graphite fibril
nanotube.
[0061] The single-layer carbon nanotube or the multi-layer carbon
nanotube is produced to a desired size by an arc discharge method,
a laser ablation method, a vapor-phase growth method, or the
like.
[0062] The arc discharge method is a method in which an arc is
discharged between electrode materials made of a carbon rod in an
argon or hydrogen atmosphere at a pressure, lower than atmospheric
pressure to some extent to obtain a multi-layer carbon nanotube
deposited on the cathode. The single-layer carbon nanotube is
obtained from soot adhering to the inner side surface of a
processing vessel by mixing a catalyst such as nickel/cobalt into
the carbon rod and discharging an arc.
[0063] The laser ablation method is a method in which a target
carbon surface into which a catalyst such as nickel/cobalt is mixed
is irradiated with a strong pulse laser light from a YAG laser in
noble gas (argon, for example) to melt and evaporate the carbon
surface, thereby obtaining a single-layer carbon nanotube.
[0064] The vapor-phase growth method is a method in which a carbon
nanotube is synthesized by thermally decomposing hydrocarbons such
as benzene or toluene in a vapor phase. A floating catalyst method,
a zeolite-supported catalyst method, and the like can be given as
specific examples.
[0065] The carbon nanofibers may be provided with improved adhesion
and wettability with the elastomer by subjecting the carbon
nanofibers to a surface treatment such as an ion-injection
treatment, sputter-etching treatment, or plasma treatment before
kneading the carbon nanofibers and the elastomer.
4. MIXING THE CARBON NANOFIBERS INTO THE ELASTOMER AND DISPERSING
THE CARBON NANOFIBERS BY A SHEAR FORCE
[0066] An example using an open-roll method with a roll distance of
0.5 mm or less is described as the step of mixing the metal
particles and the carbon nanofibers into the elastomer.
[0067] FIG. 1 is a view schematically showing the open-roll method
using two rolls. In FIG. 1, a reference numeral 10 denotes a first
roll, and a reference numeral 20 denotes a second roll. The first
roll 10 and the second roll 20 are disposed at a predetermined
distance d of preferably 1.0 mm or less, and still more preferably
0.1 to 0.5 mm. The first and second rolls are rotated normally or
reversely. In the example shown in FIG. 1, the first roll 10 and
the second roll 20 are rotated in the directions indicated by the
arrows. The surface velocity of the first roll 10 is denoted by V1,
and the surface velocity of the second roll 20 is denoted by V2.
The surface velocity ratio (V1/V2) of the first roll 10 to the
second roll 20 is preferably 1.05 to 3.00, and still more
preferably 1.05 to 1.2. A desired shear force can be obtained by
using such a surface velocity ratio. When an elastomer 30 is wound
around the second roll 20 in a state in which the first and second
rolls are rotated, a bank 32 in which the elastomer is deposited
between the rolls 10 and 20 is formed. The step of mixing the
elastomer 30 and metal particles 50 is performed by adding the
metal particles 50 to the bank 32 and rotating the first and second
rolls 10 and 20. Carbon nanofibers 40 are added to the bank 32 in
which the elastomer 30 and the metal particles 50 are mixed, and
the first and second rolls 10 and 20 are rotated. The distance
between the first and second rolls 10 and 20 is reduced to the
distance d, and the first and second rolls 10 and 20 are rotated at
a predetermined surface velocity ratio. This causes a high shear
force to be applied to the elastomer 30, and the aggregated carbon
nanofibers are separated by the shear force so that the carbon
nanofibers are pulled out one by one, and dispersed in the
elastomer 30. The shear force due to the rolls causes turbulent
flows to occur around the metal particles dispersed in the
elastomer. These complicated flows cause the carbon nanofibers to
be further dispersed in the elastomer 30. If the elastomer 30 and
the carbon nanofibers 40 are mixed before mixing the metal
particles 50, since the movement of the elastomer 30 is restricted
by the carbon nanofibers 40, it becomes difficult to mix the metal
particles 50. Therefore, it is preferable to perform the step of
mixing the metal particles 50 before adding the carbon nanofibers
40 to the elastomer 30.
[0068] In this step, the elastomer and the carbon nanofibers are
mixed at a comparatively low temperature of preferably 0 to
50.degree. C., and still more preferably 5 to 30.degree. C. in
order to obtain a shear force as high as possible. In the case of
using the open-roll method, it is preferable to set the roll
temperature at the above temperature. The distance d between the
first and second rolls 10 and 20 is set to be greater than the
average particle size of the metal particles 50 even in the
smallest state. This enables the carbon nanofibers 40 to be
uniformly dispersed in the elastomer 30.
[0069] Since the elastomer in this embodiment has the
above-described characteristics, specifically, the above-described
molecular configuration (molecular length), molecular motion, and
chemical interaction with the carbon nanofibers, dispersion of the
carbon nanofibers is facilitated. Therefore, a carbon fiber
composite material and a formed product of carbon fiber composite
excelling in dispersibility and dispersion stability (reaggregation
of carbon nanofibers rarely occurs) can be obtained. In more
detail, when the elastomer and the carbon nanofibers are mixed, the
elastomer having an appropriately long molecular length and high
molecular mobility enters the space between the carbon nanofibers,
and a specific portion of the elastomer bonds to a highly active
portion of the carbon nanofiber through chemical interaction. When
a high shear force is applied to the mixture of the elastomer and
the carbon nanofibers in this state, the carbon nanofibers move
accompanying the movement of the elastomer, whereby the aggregated
carbon nanofibers are separated and dispersed in the elastomer. The
carbon nanofibers which have been dispersed are prevented from
reaggregating due to chemical interaction with the elastomer,
whereby excellent dispersion stability can be obtained.
[0070] Since a predetermined amount of the metal particles are
included in the elastomer, a shear force also functions in the
direction in which the carbon nanofibers are separated due to a
number of complicated flows such as turbulent flows of the
elastomer around the metal particles. Therefore, since even carbon
nanofibers with a diameter of about 30 nm or less or carbon
nanofibers in the shape of a curved fiber move in the flow
directions of the elastomer molecules to which the carbon
nanofibers have bonded due to chemical interaction, the carbon
nanofibers are uniformly dispersed in the elastomer.
[0071] The step of dispersing the carbon nanofibers in the
elastomer by a shear force may be performed by using a closed
kneading method or a multi-screw extrusion kneading method in
addition to the open-roll method. In other words, it suffices that
this step apply shear force sufficient to separate the aggregated
carbon nanofibers to the elastomer.
[0072] A carbon fiber composite material obtained by the step in
which the metal particles and the carbon nanofibers are mixed and
dispersed in the elastomer (mixing and dispersion step) may be
crosslinked using a crosslinking agent and formed, or formed
without crosslinking the carbon fiber composite material. A formed
product of carbon fiber composite may be obtained by performing a
compression forming step or an extrusion forming step, for example.
The compression forming step includes a step of forming the carbon
fiber composite material in which the metal particles and the
carbon nanofibers are dispersed in a pressurized state for a
predetermined period of time (20 min, for example) in a forming die
having a desired shape and set at a predetermined temperature
(175.degree. C., for example).
[0073] In the mixing and dispersing step of the elastomer and the
carbon nanofibers or in the subsequent step, additives usually used
for processing of elastomers such as rubber may be added. As the
additives, conventional additives may be used. Examples of
additives include a crosslinking agent, a vulcanizing agent, a
vulcanization accelerator, a vulcanization retarder, a softener, a
plasticizer, a curing agent, a reinforcing agent, a filler, an
aging preventive, a colorant, and the like.
5. CARBON FIBER COMPOSITE MATERIAL AND FORMED PRODUCT OF CARBON
FIBER COMPOSITE
[0074] In the carbon fiber composite material and the formed
product of carbon fiber composite according to one embodiment of
the present invention, the carbon nanofibers are uniformly
dispersed in the elastomer as a substrate. In other words, the
elastomer is restrained by the carbon nanofibers. The mobility of
the elastomer molecules restrained by the carbon nanofibers is
smaller than that in the case where the elastomer molecules are not
restrained by the carbon nanofibers. Therefore, the first spin-spin
relaxation time (T2n), the second spin-spin relaxation time (T2nn),
and the spin-lattice relaxation time (T1) of the carbon fiber
composite material and the formed product of carbon fiber composite
are shorter than those of the elastomer which does not include the
carbon nanofibers. In particular, in the case of mixing the carbon
nanofibers into the elastomer including the metal particles, the
second spin-spin relaxation time (T2nn) becomes shorter than that
of the elastomer including the carbon nanofibers. The spin-lattice
relaxation time (T1) of the crosslinked form (formed product of
carbon fiber composite) varies in proportion to the amount of the
carbon nanofibers mixed.
[0075] The number of non-network components (non-reticulate chain
components) is considered to be reduced in a state in which the
elastomer molecules are restrained by the carbon nanofibers for the
following reasons. Specifically, when the molecular mobility of the
elastomer is entirely lowered by the carbon nanofibers, since the
number of non-network components which cannot easily move is
increased, the non-network components tend to behave in the same
manner as the network components. Moreover, since the non-network
components (terminal chains) easily move, the non-network
components are easily adsorbed to the active point of the carbon
nanofibers. As a result, the number of non-network components is
decreased. Therefore, the fraction (fnn) of components having the
second spin-spin relaxation time becomes smaller than that of the
elastomer which does not include the carbon nanofibers. In
particular, in the case of mixing the carbon nanofibers into the
elastomer including the metal particles, the fraction (fnn) of
components having the second spin-spin relaxation time becomes
further smaller than that of the elastomer including the carbon
nanofibers.
[0076] Therefore, the carbon fiber composite material and the
formed product of carbon fiber composite according to this
embodiment preferably have values measured by the Hahn-echo method
using the pulsed NMR technique within the following range.
[0077] Specifically, in the uncrosslinked form (carbon fiber
composite material), it is preferable that the first spin-spin
relaxation time (T2n) measured at 150.degree. C. be 100 to 3,000
.mu.sec, the second spin-spin relaxation time (T2nn) measured at
150.degree. C. be absent or 1,000 to 10,000 .mu.sec, and the
fraction (fnn) of components having the second spin-spin relaxation
time be less than 0.2.
[0078] In the crosslinked form (formed product of carbon fiber
composite), it is preferable that the first spin-spin relaxation
time (T2n) measured at 150.degree. C. be 100 to 2,000 .mu.sec, the
second spin-spin relaxation time (T2nn) measured at 150.degree. C.
be absent or 1,000 to 4000 .mu.sec, and the fraction (fnn) of
components having the second spin-spin relaxation time be less than
0.08.
[0079] The carbon fiber composite material and the formed product
of carbon fiber composite according preferably have values measured
by the Hahn-echo method using the pulsed NMR technique within the
following range. Specifically, the amount of change (.DELTA.T1) in
the spin-lattice relaxation time (T1) measured at 150.degree. C. of
the crosslinked form (formed product of carbon fiber composite) per
vol % of the carbon nanofibers is preferably 1 msec or more, and
still more preferably 2 to 15 msec smaller than that of the
elastomer.
[0080] The spin-lattice relaxation time (Ti) measured by the
Hahn-echo method using the pulsed NMR technique is a measure which
represents molecular mobility of a substance in the same manner as
the spin-spin relaxation time (T2). In more detail, the shorter the
spin-lattice relaxation time of the elastomer, the lower the
molecular mobility and the harder the elastomer. The longer the
spin-lattice relaxation time of the elastomer, the higher the
molecular mobility and the softer the elastomer.
[0081] The carbon fiber composite material and the formed product
of carbon fiber composite preferably have a flow temperature,
determined by temperature dependence measurement of dynamic
viscoelasticity, 20.degree. C. or more higher than the flow
temperature of the raw material elastomer. In the carbon fiber
composite material and the formed product of carbon fiber
composite, the metal particles and the carbon nanofibers are
uniformly dispersed in the elastomer. In other words, the elastomer
is restrained by the carbon nanofibers as described above. The
elastomer in this state exhibits molecular motion smaller than that
of the elastomer which does not include the carbon nanofibers. As a
result, flowability is decreased. The carbon fiber composite
material and the formed product of carbon fiber composite having
such flow temperature characteristics exhibit small temperature
dependence of dynamic viscoelasticity. As a result, the carbon
fiber composite material and the formed product of carbon fiber
composite have excellent thermal resistance.
[0082] As described above, the carbon fiber composite material and
the formed product of carbon fiber composite in this embodiment can
be used as an elastomer material, or as a raw material for a metal
composite material or the like. The carbon nanofibers are generally
entangled and dispersed in a medium to only a small extent.
However, if the carbon fiber composite material or the formed
product of carbon fiber composite in this embodiment is used as a
raw material for a metal composite material, since the carbon
nanofibers are present in the elastomer in a dispersed state, the
carbon nanofibers can be easily dispersed in a medium by mixing the
raw material and the medium such as a metal.
6. CASTING OF A CARBON FIBER-METAL COMPOSITE MATERIAL AND FORMED
PRODUCT OF CARBON FIBER-METAL COMPOSITE
[0083] The casting step of the carbon fiber-metal composite
material may be performed by a step of mixing the carbon fiber
composite material or the formed product of carbon fiber composite
obtained in the above embodiments into a molten metal, and casting
the mixture in a die having a desired shape, for example. In the
casting step, a metal mold casting method, a diecasting method, or
a low-pressure diecasting method, in which a molten metal is poured
into a die made of steel, may be employed. A method classified into
a special casting method, such as a high-pressure casting method in
which a molten metal is caused to solidify at a high pressure, a
thixocasting method in which a molten metal is stirred, or a
centrifugal casting method in which a molten metal is cast in a die
by utilizing centrifugal force may also be employed. In the above
casting method, a molten metal is caused to solidify in a die in a
state in which the carbon fiber composite material or the formed
product of carbon fiber composite is mixed into the molten metal to
form a carbon fiber-metal composite material or a formed product of
carbon fiber-metal composite. In this casting step, the elastomer
in the carbon fiber composite material or the formed product of
carbon fiber composite is decomposed and removed by the heat of the
molten metal.
[0084] The molten metal used in the casting step may be
appropriately selected from metals used in a conventional casting
process, such as iron and an iron alloy, aluminum and an aluminum
alloy, magnesium and a magnesium alloy, copper and a copper alloy,
zinc and a zinc alloy, either individually or in combination of two
or more depending on the application. If the metal used as the
molten metal is the same metal as the metal particles mixed in
advance into the carbon fiber composite material or the formed
product of carbon fiber composite, or an alloy containing the same
metal element as the metal particles, wettability with the metal
particles is increased, whereby the strength of the carbon
fiber-metal composite material or the formed product of carbon
fiber-metal composite as the product can be increased.
[0085] A casting step using a pressureless permeation method in
which a molten metal is caused to permeate the formed product of
carbon fiber composite according to one embodiment of the present
invention is described below in detail with reference to FIGS. 2
and 3.
[0086] FIGS. 2 and 3 are schematic configuration diagrams of a
device for producing a formed product of carbon fiber-metal
composite by using the pressureless permeation method. As the
formed product of carbon fiber composite obtained in the above
embodiment, a formed product of carbon fiber composite 4 which is
compression-formed in a forming die having the shape of the final
product may be used, for example. It is preferable that the formed
product of carbon fiber composite 4 be not crosslinked. If the
formed product of carbon fiber composite 4 is not crosslinked, the
permeation rate of the molten metal is increased. In FIG. 2, the
formed product of carbon fiber composite 4 formed in advance (metal
particles such as aluminum particles 50 and carbon nanofibers 40
are mixed into uncrosslinked elastomer 30, for example) is placed
in a sealed container 1. A metal ingot such as an aluminum ingot 5
is disposed on the formed product of carbon fiber composite 4. The
formed product of carbon fiber composite 4 and the aluminum ingot 5
disposed in the container 1 are heated to a temperature equal to or
higher than the melting point of aluminum by using a heating means
(not shown) provided to the container 1. The heated aluminum ingot
5 melts to become aluminum molten metal (molten metal). The
elastomer 30 in the formed product of carbon fiber composite 4
which is in contact with the aluminum molten metal is decomposed
and vaporized, and the aluminum molten metal (molten metal)
permeates the space formed by decomposition of the elastomer
30.
[0087] In the formed product of carbon fiber composite 4, the space
formed by decomposition of the elastomer 30 allows the aluminum
molten metal to permeate the entire formed product due to a
capillary phenomenon. The aluminum molten metal permeates the space
between the aluminum particles 50 of which wettability is improved
by being reduced due to the capillary phenomenon, whereby the
inside of the formed product of carbon fiber composite is entirely
filled with the aluminum molten metal. The heating by the heating
means of the container 1 is then terminated, and the molten metal
which has permeated the mixed material 4 is allowed to cool and
solidify to obtain a formed product of carbon fiber-metal composite
6 as shown in FIG. 3 in which the carbon nanofibers 40 are
uniformly dispersed. The formed product of carbon fiber composite 4
used in the casting step is preferably formed in advance using
metal particles of the same metal as the molten metal used in the
casting step. This enables the molten metal and the metal particles
to be easily mixed, whereby a homogeneous metal can be
obtained.
[0088] The atmosphere inside the container 1 may be removed by a
decompression means 2 such as a vacuum pump connected with the
container 1 before heating the container 1. Nitrogen gas may be
introduced into the container 1 from an inert-gas supply means 3
such as a nitrogen gas cylinder connected with the container 1.
[0089] In the case of using aluminum as the metal particles and the
molten metal, since the surfaces of the aluminum particles 42 and
the aluminum ingot 5 are covered with an oxide, wettability between
the aluminum particles 42 and the aluminum ingot 5 is poor.
However, wettability between the aluminum particles 42 and the
aluminum ingot 5 is excellent in this embodiment. The reason
therefor is considered to be as follows. Specifically, when the
aluminum molten metal is caused to permeate, the molecular end of
the thermally decomposed elastomer becomes a radical, and the oxide
(alumina) on the surfaces of the aluminum ingot 5 and the aluminum
particles 42 is reduced by the radical. Therefore, in this
embodiment, since the reducing atmosphere can be generated even
inside the formed product of carbon fiber composite by
decomposition of the elastomer included in the formed product of
carbon fiber composite, the casting process using the pressureless
permeation method can be performed without providing a reducing
atmosphere processing chamber as in a conventional method. As
described above, since wettability between the reduced surfaces of
the aluminum particles and the permeated aluminum molten metal is
improved, a more homogeneously integrated metal material or metal
formed product can be obtained. Moreover, flows due to permeation
of the aluminum molten metal cause the carbon nanofibers to enter
the aluminum particles. Furthermore, the surfaces of the carbon
nanofibers are activated by the radicals of the decomposed
elastomer molecules, whereby wettability with the aluminum molten
metal is improved. The formed product of carbon fiber-metal
composite thus obtained includes the carbon nanofibers uniformly
dispersed in the aluminum matrix. The aluminum molten metal is
prevented from being oxidized by performing the casting step in an
inert atmosphere, whereby wettability with the aluminum particles
is further improved.
7. POWDER-FORMING METHOD
[0090] The carbon fiber-metal composite material or the formed
product of carbon fiber-metal composite according to one embodiment
of the present invention may be obtained by a step of
powder-forming the carbon fiber composite material or the formed
product of carbon fiber composite obtained by the above-described
steps. In more detail, the carbon fiber composite material obtained
in the above embodiment is compressed in a die after optionally
mixing the carbon fiber composite material with other metal
materials, and is sintered at the sintering temperature of the
metal particles (550.degree. C. when the metal particles are
aluminum particles, for example) to obtain a carbon fiber-metal
composite material.
[0091] The powder-forming in this embodiment is the same as
powder-forming in a metal forming process and includes powder
metallurgy. The powder-forming in this embodiment includes not only
the case of using a powder raw material, but also the case of using
a raw material formed in the shape of a block by compression
preforming the carbon fiber composite material. As the sintering
method, a generally-used sintering method, a spark plasma sintering
method (SPS) using a plasma sintering device, or the like may be
employed.
[0092] The carbon fiber composite material and particles of other
metal materials may be mixed by dry blending, wet blending, or the
like. In the case of using wet blending, it is preferable to mix
(wet-blend) the carbon fiber composite material with particles of
other metal materials in a solvent. Since the carbon fiber
composite material or the formed product of carbon fiber composite
which is ground in the shape of a particle can be used in wet
blending or dry blending, the material is easily utilized for
metalworking.
[0093] The carbon fiber-metal composite material or the formed
product of carbon fiber-metal composite produced by such
powder-forming is obtained in a state in which the carbon
nanofibers are dispersed in the metal material as the matrix. The
particles of other metal materials used in this step may be a
material either the same as or different from the material for the
metal particles. A carbon fiber-metal composite material having
desired properties can be produced by adjusting the ratio of the
metal material and other metal particles.
8. EXAMPLES 1 TO 7 AND COMPARATIVE EXAMPLES 1 AND 2
[0094] Examples according to the present invention and Comparative
Examples are described below. Note that the present invention is
not limited to the following examples.
8.1 Preparation of Samples
8.1.1 Uncrosslinked Sample (Carbon Fiber Composite Material)
[0095] Step 1: An open roll with a roll diameter of six inches
(roll temperature: 10 to 20.degree. C.) was provided with a
predetermined amount (100 g) of a polymer substance (100 parts by
weight (phr)) shown in Table 1, and the polymer substance was wound
around the roll.
[0096] Step 2: Metal particles were added to the polymer substance
in an amount (parts by weight) shown in Table 1. The roll distance
was set at 1.5 mm. The type of the metal particles added is
described later.
[0097] Step 3: Carbon nanofibers ("CNT" in Table 1) were added to
the polymer substance including the metal particles in an amount
(parts by weight) shown in Table 1. The roll distance was set at
1.5 mm.
[0098] Step 4: After the addition of the carbon nanofibers, the
mixture of the polymer substance and the carbon nanofibers was
removed from the rolls.
[0099] Step 5: The roll distance was reduced from 1.5 mm to 0.3 mm,
and the mixture was positioned and tight milled. The surface
velocity ratio of the two rolls was set at 1.1. The tight milling
was repeated ten times.
[0100] Step 6: The rolls were set at a predetermined distance (1.1
mm), and the mixture which had been tight milled was positioned and
sheeted.
[0101] Uncrosslinked samples of Examples 1 to 5 were obtained in
this manner. The steps 2 to 4 were omitted to obtain uncrosslinked
samples of Comparative Examples 1 and 2.
8.1.2 Crosslinked Sample (Formed Product of Carbon Fiber
Composite)
[0102] The steps 1 to 5 were conducted in the same manner as in the
case of the uncrosslinked samples.
[0103] Step 6: The rolls were set at a predetermined distance (1.1
mm), and the mixture which had been tight milled was positioned. A
predetermined amount of a crosslinking agent (2 parts by weight)
was added to the mixture. The mixture was then sheeted.
[0104] Step 7: The sample cut into a die size was placed in a die
and subjected to press-crosslinking at 175.degree. C. and 100
kgf/cm.sup.2 for 20 minutes.
[0105] Crosslinked samples of Examples 1 to 4 were obtained in this
manner. The steps 2 to 4 were omitted to obtain crosslinked samples
of Comparative Examples 1 and 2.
8.1.3 Formed Product of Carbon Fiber-Metal Composite
[0106] The uncrosslinked sample (formed product of carbon fiber
composite) obtained in each of Examples 1 to 5 was disposed in a
container (furnace). An aluminum ingot (metal) was placed on the
uncrosslinked sample, and the sample and the aluminum ingot were
heated to the melting point of aluminum in an inert gas (nitrogen)
atmosphere. The aluminum ingot melted to become aluminum molten
metal. The molten metal permeated the uncrosslinked sample to
replace the polymer substance in the uncrosslinked sample. After
permeation of the aluminum molten metal was completed, the aluminum
molten metal was allowed to cool and solidify to obtain a formed
product of carbon fiber-metal composite.
[0107] As the metal particles of Examples 1 to 5, aluminum
particles (average particle size: 50 .mu.m) were used. As the
carbon nanofibers, carbon nanofibers having a diameter (fiber
diameter) of 10 to 20 nm were used.
[0108] In Example 6, a formed product of carbon fiber-metal
composite (carbon nanofiber content was 0.4 vol %) was obtained by
changing the amount of the carbon nanofibers in Example 5 to 2.5
parts by weight. In Example 7, a formed product of carbon
fiber-metal composite (carbon nanofiber content was 0.8 vol %) was
obtained by changing the amount of the carbon nanofibers in Example
5 to 5 parts by weight. The carbon nanofiber content in the formed
product of carbon fiber-metal composite of Example 5 was 1.6 vol
%.
8.2 Measurement by Pulsed NMR Technique
[0109] The uncrosslinked samples and the crosslinked samples of
Examples 1 to 5 were subjected to measurement by the Hahn-echo
method using the pulsed NMR technique. The measurement was
conducted using "JMN-MU25" manufactured by JEOL, Ltd. The
measurement was conducted under conditions of an observing nucleus
of .sup.1H, a resonance frequency of 25 MHz, and a 90.degree. pulse
width of 2 .mu.sec, and a decay curve was determined while changing
Pi in a pulse sequence (90.degree.x-Pi-180.degree.x) of the
Hahn-echo method. The sample was measured in a state in which the
sample was inserted into a sample tube within an appropriate range
of a magnetic field. The measurement temperature was 150.degree. C.
The first spin-spin relaxation time (T2n), the second spin-spin
relaxation time (T2nn), and the fraction (fnn) of components having
the second spin-spin relaxation time were determined by the
measurement for the raw material elastomer and the uncrosslinked
sample and the crosslinked sample of the composite material. The
first spin-spin relaxation time (T2n) of the raw material elastomer
was determined at a measurement temperature of 30.degree. C. The
amount of change (.LAMBDA.T1) in the spin-lattice relaxation time
per part by weight of the carbon nanofibers was determined for the
crosslinked sample of the composite material. The measurement
results are shown in Table 1. The second spin-spin relaxation time
(T2nn) of the uncrosslinked sample of Example 1 was 4,500
(.mu.sec), and the fraction (fnn) of components having the second
spin-spin relaxation time was 0.127. The second spin-spin
relaxation time (T2nn) of the crosslinked sample of Example 1 was
3,180 (.mu.sec), and the fraction (fnn) of components having the
second spin-spin relaxation time was 0.034. The second spin-spin
relaxation time (T2nn) of Examples 2 to 5 was not detected.
Therefore, the fraction (fnn) of components having the second
spin-spin relaxation time was zero.
8.3 E' (Dynamic Viscoelasticity), TB (Tensile Strength), and EB
(Elongation at Break)
[0110] E', TB, and EB of the crosslinked samples of the composite
materials of Examples 1 to 5 were measured in accordance with JIS K
6521-1993. The results are shown in Table 1.
8.4 Flow Temperature
[0111] The flow temperature of the raw material elastomer and the
uncrosslinked samples of the composite materials of Example 1 to 5
was determined by dynamic viscoelasticity measurement (JIS K 6394).
In more detail, the flow temperature was determined by applying
sine vibration (.+-.0.1% or less) to the sample having a width of 5
mm, a length of 40 mm, and a thickness of 1 mm, and measuring the
stress and phase difference .delta. generated by applying the sine
vibration. The temperature was changed from -70.degree. C. to
150.degree. C. at a temperature rise rate of 2.degree. C./min. The
results are shown in Table 1. In Table 1, a case where a flow
phenomenon of the sample was not observed up to 150.degree. C. was
indicated as "150.degree. C. or higher".
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2
Example 3 Example 4 Example 5 Example 1 Example 2 Raw material
Polymer substance EPDM EPDM EPDM EPDM NR NR EPDM elastomer Polar
group Double bond Double bond Double bond Double bond Double bond
Double bond Double bond Norbornene Norbornene Norbornene Norbornene
Norbornene Average molecular weight 200,000 200,000 200,000 200,000
3,000,000 3,000,000 200,000 T2n (30.degree. C.) (.mu.sec) 520 520
520 520 700 700 520 T2n (150.degree. C.) (.mu.sec) 2,200 2,200
2,200 2,200 5,500 5,500 2,200 T2nn (150.degree. C.) (.mu.sec)
16,000 16,000 16,000 16,000 18,000 18,000 16,000 fnn (150.degree.
C.) 0.405 0.405 0.405 0.405 0.381 0.381 0.405 Flow temperature
(.degree. C.) 55 55 55 55 40 40 55 Composition Polymer (phr) 100
100 100 100 100 100 100 A1 particles (phr) 50 500 1,000 500 500 0 0
CNT (phr) 10 10 10 60 10 0 0 Uncrosslinked Flow temperature
(.degree. C.) 95 150 or 150 or 150 or higher 150 or higher -27.8 55
higher higher sample T2n (150.degree. C.) (.mu.sec) 1,450 1,400
2,000 1,050 1,640 5,450 2,200 Crosslinked T2n (150.degree. C.)
(.mu.sec) 540 560 600 580 880 1,280 640 sample E' (30.degree. C.)
(MPa) 8.21 64.5 129 645 13.1 1.16 2.98 TB (MPa) 11.3 28.4 25.8 77.4
15.7 3.5 1.7 EB (%) 120 55 25 15 150 240 180 .DELTA.T1 (msec/CNF 1
vol %) 5.35 6.28 6.19 7.25 14.5 0 0 Carbon Metal forming state Good
Good Good Good Good -- -- fiber-metal (metallographical composite
microscope) material CNT dispersion state Good Good Good Good Good
-- -- (aluminum) (SEM observation)
[0112] As shown in Table 1, the following items were confirmed
according to Examples 1 to 5 of the present invention.
Specifically, the spin-spin relaxation times at 150.degree. C. (T2n
and T2nn/150.degree. C.) of the uncrosslinked sample (carbon fiber
composite material) and the crosslinked sample (formed product of
carbon fiber composite) including the metal particles and the
carbon nanofibers are shorter than those of the raw material
elastomer which does not include the metal particles and the carbon
nanofibers. The fraction (fnn/150.degree. C.) of the uncrosslinked
sample (carbon fiber composite material) and the crosslinked sample
(formed product of carbon fiber composite) including the metal
particles and the carbon nanofibers is smaller than that of the raw
material elastomer which does not include the metal particles and
the carbon nanofibers. The amount of change (.DELTA.T1) in the
spin-lattice relaxation time (T1) of the uncrosslinked sample
(carbon fiber composite material) and the crosslinked sample
(formed product of carbon fiber composite) including the metal
particles and the carbon nanofibers is smaller than that of the raw
material elastomer which does not include the metal particles and
the carbon nanofibers. These results show that the carbon
nanofibers are uniformly dispersed in the carbon fiber composite
materials according to the examples.
[0113] This is more clearly understood by comparing Example 1 with
Comparative Example 2. Specifically, in Comparative Example 2 which
does not include the carbon nanofibers, the spin-spin relaxation
times (T2n and T2nn/150.degree. C.) of the uncrosslinked sample are
similar to those of the raw material elastomer. On the other hand,
in Example 1 of the present invention, the spin-spin relaxation
times (T2n and T2nn/150.degree. C.) of the uncrosslinked sample
(carbon fiber composite material) are considerably shorter than
those of the raw material elastomer. The same fact was confirmed
for the fraction (fnn/150.degree. C.).
[0114] It was confirmed that the spin-spin relaxation times (T2n
and T2nn/150.degree. C.) of the crosslinked sample (f Hued product
of carbon fiber composite) are shorter than those of the raw
material elastomer. The same fact was confirmed for the fraction
(fnn/150.degree. C.). The amount of change (.DELTA.T1) in the
spin-lattice relaxation time per vol % of the carbon nanofibers was
confirmed to be smaller than that of the raw material
elastomer.
[0115] As is clear from the results for E', TB, and EB using the
crosslinked sample, according to Examples 1 to 5 of the present
invention, it was confirmed that the presence of the carbon
nanofibers improves dynamic viscoelasticity and tensile strength
while maintaining elongation at break, whereby the reinforcing
effect can be obtained by the carbon nanofibers. This fact is more
clearly understood by comparing Examples 1 to 5 with Comparative
Examples 1 and 2.
[0116] Since the flow temperature of the carbon fiber composite
material (uncrosslinked sample) including the metal particles and
the carbon nanofibers is 20.degree. C. or more higher than that of
the raw material elastomer, it is understood that the carbon fiber
composite material has a small temperature dependence of dynamic
viscoelasticity and exhibits excellent thermal resistance.
[0117] As a result of microscope observation of the carbon
fiber-metal composite materials (aluminum matrix) of Examples 1 to
5, a void was observed only to a small extent by observation of the
metal forming state using a metallographical microscope ("Good" in
Table 1), and aggregation of the carbon nanofibers was observed
only to a small extent by observation of the dispersion state of
the carbon nanofibers using an electron microscope (SEM) ("Good" in
Table 1). In Comparative Examples 1 and 2, microscope observation
was omitted since the materials did not include the carbon
nanofibers and were not cast ("-" in Table 1).
[0118] FIG. 4 is an SEM image of the fracture plane of the formed
product of carbon fiber-metal composite of Example 2. Thin fibrous
sections shown in FIG. 4 are carbon nanofibers in the shape of a
curved fiber with a diameter of about 10 to 20 nm. The carbon
nanofibers shown in FIG. 4 are thicker than the actual diameter.
This shows that the aluminum covers the surfaces of the carbon
nanofibers. A number of carbon nanofibers covered with aluminum are
dispersed in the aluminum matrix and are entangled only to a small
extent. The photographing conditions were set at an acceleration
voltage of 7.0 kV and a magnification of 20.0 k.
8.5 Closest Distance
[0119] The closest distance between the carbon nanofibers was
measured by observing the fracture plane of the formed product of
carbon fiber-metal composite of Example 5 using an electron
microscope. As shown in FIG. 6, since the carbon nanofibers are
covered with an aluminum compound and present as fibrous
substances, the closest distance between the fibrous substances was
measured. The measurement results are taken as an evaluation of
dispersibility of the carbon nanofibers in the formed product of
carbon fiber-metal composite of Example 5, and shown in FIG. 5 as
the distribution of the closest distance between the carbon
nanofibers. The distribution of the closest distance between the
carbon nanofibers showed an almost normal distribution in which the
average was 263 nm and the standard deviation was 74.8 mm.
Therefore, it was found that the carbon nanofibers were uniformly
dispersed in the formed product of carbon fiber-metal composite. In
the case of merely mixing the carbon nanofibers into the aluminum
molten metal, it is difficult to measure the closest distance and a
normal distribution is not obtained. The aluminum compound covering
the carbon nanofibers was a substance which did not melt at
660.degree. C., which is the melting point of the aluminum, and did
not fuse even at 1100.degree. C.
8.6 Compressive Stress and Yield Strength
[0120] The relationship between compressive stress and strain and
yield strength were measured using the formed product of carbon
fiber-metal composite samples of Examples 5, 6, and 7. The results
are shown in FIGS. 7 and 8. In FIG. 7, a curve A denotes aluminum
which does not include the carbon nanofibers, a curve B denotes the
formed product of carbon fiber-metal composite of Example 6, a
curve C denotes the formed product of carbon fiber-metal composite
of Example 7, and a curve D denotes the formed product of carbon
fiber-metal composite of Example 5. In FIG. 8, a straight line E
denotes aluminum which does not include the carbon nanofibers, and
a curve F denotes yield strength of the formed product of carbon
fiber-metal composites of Examples 5, 6, and 7. These results show
that compressive stress and yield strength of the formed product of
carbon fiber-metal composite are improved by adding only a small
amount of carbon nanofibers.
8.7 Modulus of Elasticity and Internal Friction
[0121] A modulus of elasticity and internal friction were measured
by performing a bending test using a dynamics test method (sine
vibration non-resonant method). FIG. 9 shows the relationship
between the temperature and the modulus of elasticity (E't/E'30).
FIGS. 10 and 11 show the relationship between the temperature and
the loss factor (tan .delta.) as internal friction. In FIG. 9, a
curve H denotes the formed product of carbon fiber-metal composite
of Example 7, and a curve G denotes an aluminum sample which does
not include the carbon nanofibers. In FIGS. 10 and 11, curves I and
K denote the formed product of carbon fiber-metal composite of
Example 7, and curves J and L denote an aluminum sample which does
not include the carbon nanofibers. The amount of bending in the
bending test shown in FIG. 9 was 10 .mu.m. The amount of bending
for the curves I and J in the bending test shown in FIG. 10 was 10
.mu.m, and the amount of bending for the curves K and L in the
bending test shown in FIG. 11 was 50 .mu.m. From the results shown
in FIGS. 9 to 11, it was found that a decrease in modulus of
elasticity and an increase in internal friction due to an increase
in temperature were prevented in the formed product of carbon
fiber-metal composite in comparison with the aluminum. The chuck
interval was 20 mm, the dimensions of the sample were 1 mm in width
and 3 mm in thickness, the temperature rise rate was 5.degree.
C./min, and the vibration frequency was 1 Hz.
[0122] As described above, according to the present invention, it
was found that the carbon nanofibers, which can be generally
dispersed in a substrate to only a small extent, can be uniformly
dispersed in the elastomer. In particular, it was found that the
carbon nanofibers can be uniformly dispersed in EPDM, which rarely
allow the carbon nanofibers to be dispersed therein. Furthermore,
it was found that even thin carbon nanofibers with a diameter of 30
nm or less or carbon nanofibers which are easily curved and
entangled can be sufficiently dispersed by mixing the metal
particles into the elastomer.
* * * * *