U.S. patent application number 11/475033 was filed with the patent office on 2009-12-10 for fiber composite material 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 | 20090306270 11/475033 |
Document ID | / |
Family ID | 37054558 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090306270 |
Kind Code |
A1 |
Noguchi; Toru ; et
al. |
December 10, 2009 |
FIBER COMPOSITE MATERIAL AND METHOD OF PRODUCING THE SAME
Abstract
A fiber composite material, including: an elastomer; carbon
nanofibers having an average diameter of 0.7 to 15 nm and an
average length of 0.5 to 100 micrometers; and fibers having an
average diameter of 1 to 100 micrometers and an aspect ratio of 50
to 500, the carbon nanofibers and the fibers being dispersed in the
elastomer, and the elastomer including an unsaturated bond or a
group exhibiting affinity to the carbon nanofibers.
Inventors: |
Noguchi; Toru; (Ueda-shi,
JP) ; Magario; Akira; (Ueda-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NISSIN KOGYO CO., LTD.
Ueda-shi
JP
|
Family ID: |
37054558 |
Appl. No.: |
11/475033 |
Filed: |
June 27, 2006 |
Current U.S.
Class: |
524/439 ;
524/496; 977/742 |
Current CPC
Class: |
B29K 2305/10 20130101;
B29K 2305/12 20130101; B29K 2707/04 20130101; B29K 2007/00
20130101; B29K 2995/0017 20130101; B29K 2311/10 20130101; B29K
2277/10 20130101; B29K 2011/00 20130101; B29C 70/12 20130101; B29C
70/02 20130101; B29K 2009/06 20130101; B29K 2305/00 20130101; B82Y
30/00 20130101 |
Class at
Publication: |
524/439 ;
524/496; 977/742 |
International
Class: |
C08K 3/08 20060101
C08K003/08; C08K 3/04 20060101 C08K003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2005 |
JP |
2005-191865 |
Apr 27, 2006 |
JP |
2006-123292 |
Claims
1. A fiber composite material, comprising: an elastomer; carbon
nanofibers having an average diameter of 0.7 to 15 nm and an
average length of 0.5 to 100 micrometers; and fibers having an
average diameter of 1 to 100 micrometers and an aspect ratio of 50
to 500, the carbon nanofibers and the fibers being dispersed in the
elastomer, and the elastomer including an unsaturated bond or a
group exhibiting affinity to the carbon nanofibers, wherein the
fiber composite material includes the carbon nanofibers in an
amount of 1 to 30 vol % and the fibers in an amount of 3 to 40 vol
%, and has an average coefficient of linear expansion of 100 ppm
(1/K) or less and a differential coefficient of linear expansion of
120 ppm (1/K) or less at -80 to 300.degree. C.
2. (canceled)
3. The fiber composite material as defined in claim 1, wherein the
fiber composite material has a ratio of a coefficient of linear
expansion in an arbitrary direction X and a coefficient of linear
expansion in a direction Y perpendicular to the direction X of 0.7
to 1.3 at -80 to 300.degree. C.
4. The fiber composite material as defined in claim 1, wherein the
carbon nanofibers have an aspect ratio of 50 or more.
5. The fiber composite material as defined in claim 1, wherein the
fiber composite material is in an uncrosslinked form.
6. The fiber composite material as defined in claim 1, wherein the
fiber composite material is in a crosslinked form.
7. The fiber composite material as defined in claim 1, wherein the
elastomer has a molecular weight of 5,000 to 5,000,000.
8. The fiber composite material as defined in claim 1, wherein at
least one of a main chain, side chain, and terminal chain of the
elastomer includes at least one unsaturated bond or group selected
from a double bond, a triple bond, and a functional group.
9. The 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 a pulsed nuclear magnetic resonance (NMR)
technique of 100 to 3,000 microseconds.
10. The 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 a pulsed nuclear magnetic resonance (NMR)
technique of 100 to 2,000 microseconds.
11. The fiber composite material as defined in claim 1, wherein the
fibers are natural fibers.
12. The fiber composite material as defined in claim 1, wherein the
fibers are metal fibers.
13. The fiber composite material as defined in claim 1, wherein the
fibers are synthetic fibers.
14. The fiber composite material as defined in claim 1, wherein the
fiber composite material has a heat resistant temperature of
300.degree. C. or more.
15. A method of producing a fiber composite material, the method
comprising: mixing carbon nanofibers having an average diameter of
0.7 to 15 nm and an average length of 0.5 to 100 micrometers and
fibers having an average diameters of 1 to 100 micrometers and an
aspect ratio of 50 to 500 into an elastomer including an
unsaturated bond or a group exhibiting affinity to the carbon
nanofibers; and dispersing the carbon nanofibers and the fibers by
applying a shear force, wherein the fiber composite material
includes the carbon nanofibers in an amount of 1 to 30 vol % and
the fibers in an amount of 3 to 40 vol.%, and has an average
coefficient of linear expansion of 100 ppm (1/K) or less and a
differential coefficient of linear expansion of 120 ppm (1/K) or
less at -80 to 300.degree. C.
Description
[0001] Japanese Patent Application No. 2005-191865, filed on Jun.
30, 2005, and Japanese Patent Application No. 2006-123292, filed on
Apr. 27, 2006, are hereby incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a fiber composite material
and a method of producing the same.
[0003] A composite material is generally provided with physical
properties corresponding to the application by combining a matrix
material and reinforcing fibers or particles. In the fields of
semiconductor manufacturing instruments, optical instruments,
microprocessing instruments, and the like, a reduction in the
effects of thermal expansion of parts has been demanded. To deal
with this demand, various composite materials using reinforcing
fibers such as carbon fibers have been proposed (see WO 00/64668,
for example).
[0004] However, it is difficult to provide a composite material
using fibers with a thermal expansion isotropy in comparison with a
composite material using particles. Therefore, the application is
limited to a product in the shape of a sheet or a plate, or a
three-dimensional structure such as a biaxial or triaxial weave
must be formed using fibers. The coefficient of linear expansion of
an elastomer changes to a large extent under different temperature
conditions. In particular, since an elastomer thermally
deteriorates at a relatively low temperature due to molecular chain
scission, the coefficient of linear expansion rapidly increases in
the vicinity of such a temperature (the temperature at which
thermal deterioration starts is hereinafter called "heat resistant
temperature"). Therefore, a composite material using an elastomer
matrix which exhibits a low and stable coefficient of linear
expansion over a wide temperature range has not been proposed.
[0005] The inventors of the invention have proposed a fiber
composite material in which carbon nanofibers are uniformly
dispersed (e.g. JP-A-2005-68386). In this fiber composite material,
the dispersibility of the carbon nanofibers exhibiting high
aggregating properties is improved by mixing the elastomer and the
carbon nanofibers.
SUMMARY
[0006] According to a first aspect of the invention, mere is
provided a fiber composite material, comprising:
[0007] an elastomer;
[0008] carbon nanofibers having an average diameter of 0.7 to 15 nm
and an average length of 0.5 to 100 micrometers; and
[0009] fibers having an average diameter of 1 to 100 micrometers
and an aspect ratio of 50 to 500,
[0010] the carbon nanofibers and the fibers being dispersed in the
elastomer, and the elastomer including an unsaturated bond or a
group exhibiting affinity to the carbon nanofibers.
[0011] According to a second aspect of the invention, there is
provided a method of producing a fiber composite material, the
method comprising:
[0012] mixing carbon nanofibers having an average diameter of 0.7
to 15 nm and an average length of 0.5 to 100 micrometers and fibers
having an average diameters of 1 to 100 micrometers and an aspect
ratio of 50 to 500 into an elastomer including an unsaturated bond
or a group exhibiting affinity to the carbon nanofibers; and
[0013] dispersing the carbon nanofibers and the fibers by applying
a shear force.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] FIG. 1 is a view schematically showing a method of mixing an
elastomer and carbon nanofibers utilizing an open-roll method
according to one embodiment of the invention.
[0015] FIG. 2 is a graph of "temperature-differential coefficient
of linear expansion" of Example 1 and Comparative Example 1.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0016] The invention may provide a fiber composite material in
which fibers and carbon nanofibers are uniformly dispersed and
which exhibits a small thermal expansion over a wide temperature
range, and a method of producing the same.
[0017] According to one embodiment of the invention, there is
provided a fiber composite material, comprising:
[0018] an elastomer;
[0019] carbon nanofibers having an average diameter of 0.7 to 15 nm
and an average length of 0.5 to 100 micrometers; and
[0020] fibers having an average diameter of 1 to 100 micrometers
and an aspect ratio of 50 to 500,
[0021] the carbon nanofibers and the fibers being dispersed in the
elastomer, and the elastomer including an unsaturated bond or a
group exhibiting affinity to the carbon nanofibers.
[0022] According to one embodiment of the invention, there is
provided a method of producing a fiber composite material, the
method comprising:
[0023] mixing carbon nanofibers having an average diameter of 0.7
to 15 nm and an average length of 0.5 to 100 micrometers and fibers
having an average diameters of 1 to 100 micrometers and an aspect
ratio of 50 to 500 into an elastomer including an unsaturated bond
or a group exhibiting affinity to the carbon nanofibers; and
[0024] dispersing the carbon nanofibers and the fibers by applying
a shear force.
[0025] According to the fiber composite material and the method of
producing the same in this embodiment, the fiber composite material
exhibits a small and stable coefficient of linear expansion over a
wide temperature range. Therefore, the fiber composite material may
be used in combination with a material having a small coefficient
of linear expansion, such as a metal or a ceramic. In particular,
since the fiber composite material can be used over a wide
temperature range in comparison with a common elastomer, a product
can be easily designed in which the fiber composite material is
combined with a material having a small coefficient of linear
expansion.
[0026] According to the fiber composite material and the method of
producing the same in this embodiment, since the unsaturated bond
or group of the elastomer is bonded to an active site of the carbon
nanofiber, in particular to a terminal radical of the carbon
nanofiber to reduce the aggregating force of the carbon nanofibers,
whereby the dispersibility of the carbon nanofibers can be
increased. In the resulting fiber composite material, the carbon
nanofibers are uniformly dispersed in the elastomer as a
matrix.
[0027] In this fiber composite material, the fiber composite
material may include the carbon nanofibers in an amount of 1 to 30
vol % and the fibers in an amount of 3 to 40 vol %, and may have an
average coefficient of linear expansion of 100 ppm (1/K) or less
and a differential coefficient of linear expansion of 120 ppm (1/K)
or less at -80 to 300.degree. C.
[0028] By reinforcing the entire elastomer with the fibers, thermal
expansion of the fiber composite material can be reduced by using a
relatively small amount of carbon nanofibers, whereby the
coefficient of linear expansion can be decreased.
[0029] In this fiber composite material, the fiber composite
material may have a ratio of a coefficient of linear expansion in
an arbitrary direction X and a coefficient of linear expansion in a
direction Y perpendicular to the direction X of 0.7 to 13 at -80 to
300.degree. C.
[0030] The fiber composite material according to this embodiment
does not exhibit anisotropy of the coefficient of linear expansion
due to the uniformly dispersed carbon nanofibers and fibers.
Therefore, the fiber composite material according to this
embodiment may be used not only in the form of a sheet or plate,
but also in various other forms.
[0031] In this fiber composite material, the carbon nanofibers may
have an aspect ratio of 50 or more.
[0032] In this fiber composite material, the fibers may be natural
fibers, metal fibers, or synthetic fibers.
[0033] In this fiber composite material, the fiber composite
material may have a heat resistant temperature of 300.degree. C. or
more. Since the fiber composite material has a heat resistant
temperature as high as 300.degree. C. or more, the fiber composite
material may also be utilized for parts used at a high
temperature.
[0034] The elastomer according to this embodiment may be a rubber
elastomer or a thermoplastic elastomer. When using a rubber
elastomer, the elastomer may be in a crosslinked form or an
uncrosslinked form. Note that it is preferable to use an elastomer
in an uncrosslinked form.
[0035] Embodiments of the invention are described below in detail
with reference to the drawings.
[0036] The elastomer preferably has characteristics such as a
certain degree of molecular length and flexibility in addition to
high affinity to the carbon nanofibers. When dispersing the carbon
nanofibers in the elastomer by applying a shear force, it is
preferable that the carbon nanofibers and the elastomer be mixed at
as high a shear force as possible.
(I) Elastomer
[0037] 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
exhibits excellent elasticity for dispersing the carbon nanofibers.
The elastomer can easily enter the space between the aggregated
carbon nanofibers due to viscosity, and can separate the carbon
nanofibers due to elasticity. 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 due to low elasticity, even if a shear force
is applied in the subsequent step. If the molecular weight of the
elastomer is greater than 5,000,000, since the elastomer becomes
too hard, it is difficult to process the elastomer.
[0038] 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 a pulsed nuclear
magnetic resonance (NMR) technique of preferably 100 to 3,000
microseconds, and still more preferably 200 to 1,000 microseconds.
If the elastomer has a spin-spin relaxation time (T2n/30.degree.
C.) within the above range, the elastomer is flexible and has a
sufficiently high molecular mobility. That is, the elastomer
exhibits ah appropriate elasticity for dispersing the carbon
nanofibers. Moreover, since the elastomer exhibits viscosity, when
mixing the elastomer and the carbon nanofibers, 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 microseconds, the elastomer
cannot have a sufficient molecular mobility. If the spin-spin
relaxation time (T2n/30.degree. C.) is longer than 3,000
microseconds, since the elastomer tends to flow and exhibits a low
elasticity, it is difficult to disperse the carbon nanofibers.
[0039] The network component of the elastomer in a cross linked
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 microseconds. The reasons therefor are
the same as for the uncrosslinked form. Specifically, when
crosslinking an uncrosslinked form which satisfies the above
conditions, the spin-spin relaxation time (T2n) of the resulting
crosslinked form almost falls within the above range.
[0040] The spin-spin relaxation time obtained by the Hahn-echo
method using the pulsed NMR technique is an index of the molecular
mobility of a substance. In more detail, when measuring the
spin-spin relaxation time of the elastomer by the Hahn-echo method
using the pulsed NMR technique, a first component having a shorter
first spin-spin relaxation time (T2n) and a second component having
a longer second spin-spin relaxation time (T2nn) 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 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.
[0041] 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 also be used instead of the Hahn-echo
method. Since the elastomer according to this embodiment has a
medium spin-spin relaxation time (T2), the Hahn-echo method is most
suitable. In general, the solid-echo method and the 90-degree pulse
method are suitable for measuring a short spin-spin relaxation time
(T2), the Hahn-echo method is suitable for measuring a medium
spin-spin relaxation time (T2), and the CPMG method is suitable for
measuring a long spin-spin relaxation time (T2).
[0042] At least one of the main chain, side chain, and terminal
chain of the elastomer includes an unsaturated bond or a group
having affinity to a terminal radical of the carbon nanofiber, or
the elastomer has properties of readily producing such a radical or
group. The unsaturated bond or group may be at least one
unsaturated bond or group selected from a double bond, a triple
bond, and functional groups such as alpha-hydrogen, a carbonyl
group, a carboxyl group, a hydroxyl group, an amino group, a
nitrite 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.
[0043] The carbon nanofiber generally has a structure in which the
side surface is formed of a six-membered ring of carbon atoms and
the end is closed by introduction of a five-membered ring. Since
the carbon nanofiber has a forced structure, a defect easily
occurs, and a radical or a functional group tends to be formed at
the defect. In this embodiment, since at least one of the main
chain, side chain, and terminal chain of the elastomer includes an
unsaturated bond or a group having high affinity (reactivity or
polarity) to the radical of the carbon nanofiber, the elastomer and
the carbon nanofiber can be bonded. This allows the carbon
nanofibers to be easily dispersed by overcoming the aggregating
force of the carbon nanofibers. When mixing the elastomer and the
carbon nanofibers, free radicals produced due to breakage of the
elastomer molecules attack the defects of the carbon nanofibers to
produce radicals on the surfaces of the carbon nanofibers.
[0044] As the elastomer, an elastomer 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 (IIR), 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), or
polysulfide rubber (T); a thermoplastic elastomer such as an
olefin-based elastomer (TPO), poly(vinyl chloride)-based elastomer
(TPVC), polyester-based elastomer (TPEE), polyurethane-based
elastomer (TPU), polyamide-based elastomer (TPEA), or styrene-based
elastomer (SBS); or a mixture of these elastomers may be used. In
particular, a highly polar elastomer which readily produces free
radicals during mixing of the elastomer, such as natural rubber
(NR) or nitrile rubber (NBR), is preferable. An elastomer having a
low polarity, such as ethylene propylene rubber (EPDM), may also be
used in this embodiment, since such an elastomer also produces free
radicals by setting the mixing temperature at a relatively high
temperature (e.g. 50 to 150.degree. C. for EPDM).
[0045] The elastomer according to this embodiment may be a rubber
elastomer or a thermoplastic elastomer. When using a rubber
elastomer, the elastomer may be in a crosslinked form or an
uncrosslinked form. Note that it is preferable to use an elastomer
in an uncrosslinked form.
(II) Fiber and Carbon Nanofiber
[0046] The fibers exhibit flexibility and excellent bending
properties and have an average diameter of 1 to 100 micrometers and
an aspect ratio of 50 to 500. If the average diameter of the fibers
is less than 1 micrometer, processing (mixing) is difficult. If the
average diameter of the fibers is greater than 100 micrometers, the
fibers exhibit an insufficient reinforcing effect.
[0047] The carbon nanofibers have an average diameter of 0.7 to 15
nm and an average length of 0.5 to 100 micrometers. If the average
diameter of the carbon nanofibers is less than 0.7 nm, the carbon
nanofibers may be damaged during mixing. If the average diameter of
the carbon nanofibers is greater than 15 nm, the confinement effect
due to the carbon nanofibers and the fibers is not obtained,
whereby the reinforcing effect becomes insufficient. If the average
length of the carbon nanofibers is less than 0.5 micrometers, the
reinforcing effect is insufficient If the average length of the
carbon nanofibers is greater than 100 micrometers, processing
(mixing) is difficult.
[0048] The carbon nanofibers preferably have an aspect ratio of 50
or more, and still more preferably 100 to 20,000. If the aspect
ratio is less than 50, the effect of confining the elastomer is not
obtained, whereby the resulting fiber composite material may flow
or be thermally deteriorated at 300.degree. C. or less, for
example.
[0049] It is preferable that the fiber composite material include
the carbon nanofibers in an amount of 1 to 30 vol %, and still more
preferably 1 to 15 vol %, and include the fibers in an amount of 3
to 40 vol %. A fiber composite material including the fibers and
the carbon nanofibers at such a volume ratio exhibits a low and
stable coefficient of linear expansion at -80 to 300.degree. C.,
that is, an average coefficient of linear expansion of 100 ppm
(1/K) or less and a differential coefficient of linear expansion of
120 ppm (1/K) or less. If the amount of carbon nanofibers is less
than 1 vol %, since the elastomer cannot be restrained, the
coefficient of linear expansion cannot be reduced. The coefficient
of linear expansion can be reduced by increasing the amount of
carbon nanofibers to greater than 15 vol %. In practice, it is not
desirable to use the carbon nanofibers in an amount of greater than
30 vol %, since a large amount of expensive carbon nanofibers is
required. If the amount of fibers is less than 3 vol %, the
coefficient of linear expansion cannot be reduced without adding a
large amount of carbon nanofibers. If the amount of fibers is
greater than 40 vol %, processing (mixing) becomes difficult.
[0050] As the fiber, a flexible fiber exhibiting excellent bending
properties is preferable. For example, a natural fiber, metal
fiber, synthetic fiber, or combination of these fibers may be
used.
[0051] As the natural fiber, a vegetable fiber such as cotton or
hemp or an animal fiber such as sheep wool or silk may be
appropriately used. As the metal fiber, a stainless steel fiber,
copper fiber, or the like may be appropriately used. As the
synthetic fiber, an aliphatic polyamide fiber or the like may be
used. Note that a polyester fiber, aromatic polyamide fiber,
ceramic fiber, and the like are not suitable due to rigidity and
the absence of bending properties.
[0052] As examples of the carbon nanofiber, a carbon nanotube and
the like can be given. The carbon nanotube has a single-wall
structure in which a graphene sheet of a hexagonal carbon layer is
closed in the shape of a cylinder, or a multiwall structure in
which the cylindrical structures are nested. Specifically, the
carbon nanotube may be formed only of either the single-wall
structure or the multi-layer structure, or may have the single-wall
structure and the multiwall structure in combination. A carbon
material having a partial carbon nanotube structure may also be
used. The carbon nanotube may also be called a graphite fibril
nanotube.
[0053] A single-wall carbon nanotube or a multiwall carbon nanotube
is produced to a desired size using an arc discharge method, laser
ablation method, vapor-phase growth method, or the like.
[0054] In the arc discharge method, an arc is discharged between
electrode materials made of carbon rods in an argon or hydrogen
atmosphere at a pressure lower than atmospheric pressure to a small
extent to obtain a multiwall carbon nanotube deposited on the
cathode. When a catalyst such as nickel/cobalt is mixed into the
carbon rod and an arc is discharged, a single-wall carbon nanotube
is obtained from soot adhering to the inner side surface of the
processing vessel.
[0055] In the laser ablation method, a target carbon surface into
which a catalyst such as nickel/cobalt is mixed is irradiated with
strong pulse laser light from a YAG laser in a noble gas (e.g.
argon) to melt and vaporize the carbon surface to obtain a
single-wall carbon nanotube.
[0056] In the vapor-phase growth method, a carbon nanotube is
synthesized by thermally decomposing a hydrocarbon such as benzene
or toluene in a vapor phase. As specific examples of the
vapor-phase growth method, a floating catalyst method,
zeolite-supported catalyst method, and the like can be given.
[0057] The carbon nanofibers may be provided with improved adhesion
to 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
mixing the carbon nanofibers into the elastomer.
(III) Mixing Fibers and Carbon Nanofibers into Elastomer and
Dispersing Fibers and Carbon Nanofibers by Applying Shear Force
[0058] This step may be carried out using an open-roll method, an
internal mixing method, a multi-screw extrusion kneading method, or
the like.
[0059] In this embodiment, an example using an open-roll method
with a roll distance of 0.5 mm or less is illustrated as the step
of dispersing the carbon nanofibers in the elastomer by applying a
shear force.
[0060] FIG. 1 is a view schematically showing the open-roll method
using two rolls. In FIG. 1, a reference numeral 10 indicates a
first roll, and a reference numeral 20 indicates a second roll. The
first roll 10 and the second roll 20 are disposed at a
predetermined distance d (e.g. 1.5 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.
[0061] When causing an elastomer 30 to be wound around the second
roll 20 while rotating the first and second rolls 10 and 20, a bank
32 of the elastomer is formed between the rolls 10 and 20. After
the addition of fibers 50 and carbon nanofibers 40 to the bank 32,
the first and second rolls 10 and 20 are rotated to obtain a
mixture in which the fibers and the carbon nanofibers are mixed
with the elastomer. The mixture is then removed from the open
rolls. After reducing the distance d between the first roll 10 and
the second roll 20 to preferably 0.5 mm or less, and still more
preferably 0.1 to 0.5 mm, the mixture of the elastomer and the
carbon nanofibers is supplied to the open rolls and tight-milled.
Tight milling is preferably performed about ten times, for example.
When the surface velocity of the first roll 10 is indicated by V1
and the surface velocity of the second roll 20 is indicated by V2,
the surface velocity ratio (V1/V2) of the first roll 10 to the
second roll 20 during tight milling 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.
[0062] As the order of adding the fibers and the carbon nanofibers
to the elastomer, it is preferable to add the fibers before adding
the carbon nanofibers.
[0063] This causes a high shear force to be applied to the
elastomer 30 so that the aggregated carbon nanofibers 40 are
separated in such a manner that the carbon nanofibers 40 are
removed by the elastomer molecules one by one and are dispersed in
the elastomer 30.
[0064] In this step, the elastomer and the carbon nanofibers are
mixed at a relatively low temperature of preferably 0 to 50.degree.
C., and still more preferably 5 to 30.degree. C. in order to obtain
as high a shear force as possible. When using EPDM as the
elastomer, it is preferable to perform two-stage mixing steps. In
the first mixing step, EPDM and the carbon nanofibers are mixed at
a first temperature which is 50 to 100.degree. C. lower than the
temperature in the second mixing step in order to obtain as high a
shear force as possible. The first temperature is preferably 0 to
50.degree. C., and still more preferably 5 to 30.degree. C. A
second temperature of the rolls is set at a relatively high
temperature of 50 to 150.degree. C. so that the dispersibility of
the carbon nanofibers can be improved.
[0065] In this step, free radicals are produced in the elastomer
shorn by the shear force and attack the surfaces of the carbon
nanofibers, whereby the surfaces of the carbon nanofibers are
activated. When using natural rubber (NR) as the elastomer, the
natural rubber (NR) molecule is cut while being mixed by the rolls
to have a molecular weight lower than the molecular weight before
being supplied to the open rolls. Radicals are produced in the cut
natural rubber (NR) molecules and attack the surfaces of the carbon
nanofibers during mixing, whereby the surfaces of the carbon
nanofibers are activated.
[0066] Since the elastomer according to this embodiment has the
above-described characteristics, that is, the above-described
molecular configuration (molecular length), elasticity due to
molecular motion, viscosity, and particularly chemical interaction
with the carbon nanofibers, dispersion of the carbon nanofibers is
facilitated. Therefore, a fiber composite material exhibiting
excellent dispersibility and dispersion stability (i.e. dispersed
carbon nanofibers rarely reaggregate) of the carbon nanofibers can
be obtained. In more detail, when mixing the elastomer and the
carbon nanofibers, the elastomer exhibiting viscosity enters the
space between the carbon nanofibers, and a specific portion of the
elastomer bonds to a highly active site of the carbon nanofiber
through chemical interaction. When a high shear force is applied to
the mixture of the elastomer having an appropriately long molecular
length and high molecular mobility (elastic) and the carbon
nanofibers, the carbon nanofibers move accompanying deformation of
the elastomer, and the elastomer exhibits a restoring force due to
elasticity after shearing, whereby the aggregated carbon nanofibers
are separated and dispersed in the elastomer. According to this
embodiment, when the mixture is forced out from the narrow space
between the rolls, the mixture is deformed to have a thickness
greater than the distance between the rolls due to the restoring
force of the elastomer resulting from the elasticity. The
deformation causes the mixture to which the strong shearing force
is applied to flow more complexly, whereby the carbon nanofibers
are dispersed in the elastomer. The dispersed carbon nanofibers do
not reaggregate due to the chemical interaction with the elastomer,
whereby the carbon nanofibers are provided with excellent
dispersion stability.
[0067] In this step, the above-mentioned internal mixing method or
multi-screw extrusion kneading method may be used instead of the
open-roll method. In other words, it suffices that this step apply
a shear force to the elastomer sufficient to separate the
aggregated carbon nanofibers and to produce radicals due to
breakage of the elastomer molecules.
[0068] After the above step of dispersing the carbon nanofibers in
the elastomer, an extrusion step, molding step, crosslinking step,
and the like may be carried out using a known method.
[0069] In the step of dispersing the carbon nanofibers in the
elastomer, or before or after this step, a compounding ingredient
usually used in processing of an elastomer such as rubber may be
added. As the compounding ingredient, a known compounding
ingredient may be used. As examples of the compounding ingredient,
a coloring agent (e.g. fiber), filler (e.g. calcium carbonate),
reinforcing agent (e.g. silica, talc, and clay), crosslinking agent
(e.g. peroxide), vulcanizing agent, vulcanization accelerator,
vulcanization retarder, softener, plasticizer, curing agent,
reinforcing agent, filler, aging preventive, and the like can be
given.
(IV) Fiber Composite Material Obtained by (III)
[0070] The fiber composite material according to this embodiment
includes an elastomer, 3 to 40 vol % of fibers, and 1 to 30 vol %
of carbon nanofibers, the fibers and the carbon nanofibers being
dispersed in the elastomer, the fiber composite material having an
average coefficient of linear expansion of 100 ppm (1/K) or less
and a differential coefficient of linear expansion of 120 ppm (1/K)
or less.
[0071] The average coefficient of linear expansion of the fiber
composite material differs depending on the volume ratio of the
fibers and the carbon nanofibers. The average coefficient of linear
expansion decreases as the volume ratio of the fibers and the
carbon nanofibers increases, and the average coefficient of linear
expansion increases as the volume ratio of the fibers and the
carbon nanofibers decreases. Specifically, the average coefficient
of linear expansion of the fiber composite material can be
controlled by the volume ratio of the fibers and the carbon
nanofibers. If the amount of carbon nanofibers is less than 1 vol
%, since the elastomer cannot be restrained, the coefficient of
linear expansion cannot be reduced. The coefficient of linear
expansion can be reduced by increasing the amount of carbon
nanofibers to greater than 15 vol %. In practice, it is not
desirable to use the carbon nanofibers in an amount of greater than
30 vol %, since a large amount of expensive carbon nanofibers is
required. If the amount of fibers is less than 3 vol %, the
coefficient of linear expansion cannot be reduced without adding a
large amount of carbon nanofibers. If the amount of fibers is
greater than 40 vol %, processing (mixing) becomes difficult.
[0072] The carbon nanofibers and the fibers have a correlation in
regard to the volume ratio. A low coefficient of linear expansion
is maintained by increasing the amount of the fibers when the
amount of the carbon nanofibers is small and increasing the amount
of the carbon nanofibers when the amount of the fibers is
small.
[0073] The differential coefficient of linear expansion of the
fiber composite material is as low as 120 ppm (1/K) or less and is
stable over a wide temperature range, so that an instantaneous
increase in thermal expansion does not occur. The maximum value of
the differential coefficient of linear expansion of the fiber
composite material differs depending on the volume ratio of the
fibers and the carbon nanofibers. The maximum value of the
differential coefficient of linear expansion decreases as the
volume ratio of the fibers and the carbon nanofibers increases, and
the maximum value of the differential coefficient of linear
expansion increases as the volume ratio of the fibers and the
carbon nanofibers decreases. Specifically, the maximum value of the
differential coefficient of linear expansion of the fiber composite
material can be controlled by the volume ratio of the fibers and
the carbon nanofibers. If the amount of carbon nanofibers is less
than 1 vol %, the fiber composite material exhibits an unstable
coefficient of linear expansion at -80 to 300.degree. C. and
exhibits a heat resistant temperature of lower than 300.degree. C.
When the volume ratio of the carbon nanofibers is less than 15 vol
% and the volume ratio of the fibers is less than 3 vol %, the
maximum value of the differential coefficient of linear expansion
exceeds 120 ppm (1/K). As a result, the differential coefficient of
linear expansion changes to a large extent in the temperature range
of -80 to 300.degree. C., whereby thermal expansion shows an
unstable behavior in a specific temperature range.
[0074] The fiber composite material according to this embodiment
has a ratio of the coefficient of linear expansion in an arbitrary
direction X to the coefficient of linear expansion in a direction Y
perpendicular to the direction X of 0.7 to 13 at -80 to 300.degree.
C.
[0075] When the arbitrary direction X is the rotational direction
of the open roll, rigid fibers such as polyester fibers are
generally oriented to exhibit anisotropy in which the coefficient
of linear expansion significantly decreases in the direction Y
perpendicular to the direction X. On the other hand, the fiber
composite material according to this embodiment exhibits an
isotropic coefficient of linear expansion.
[0076] In the fiber composite material according to this
embodiment, the elastomer as the matrix is surrounded by the fibers
and the carbon nanofibers, whereby a restraint region is formed. In
the restraint region, the movement of the elastomer is limited and
restrained. In a fiber composite material including 1 to 30 vol %
of thin carbon nanofibers with an average diameter of 0.7 to 15 nm
and 3 to 40 vol % of fibers, since the restraint region becomes
significantly small in an arbitrary plane, the elastomer is
restrained as if the elastomer is crosslinked. Moreover, the
restraint region formed by the carbon nanofibers can provide a
coefficient of linear expansion stable against heat over a wide
temperature range (e.g. -80 to 300.degree. C.).
[0077] The fiber composite material may be either an uncrosslinked
form or a crosslinked form, which may be appropriately selected
depending on the application. When the fiber composite material is
an uncrosslinked form, the fiber composite material may be
recycled.
[0078] The fiber composite material according to this embodiment
exhibits a heat resistant temperature of 300.degree. C. or
more.
[0079] The heat resistant temperature may be determined by a rapid
increase in coefficient of linear expansion resulting from breakage
of the molecular chain of the elastomer of the fiber composite
material.
[0080] In the fiber composite material according to this
embodiment, the fibers and the carbon nanofibers are uniformly
dispersed in the elastomer as the matrix. In other words, the
elastomer is restrained by the fibers and the carbon nanofibers.
The mobility of the elastomer molecules restrained by the fibers
and the carbon nanofibers is low in comparison with the case where
the elastomer molecules are not restrained by the fibers and 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 fiber composite material
according to this embodiment are shorter than those of an elastomer
which does not include the fibers and the carbon nanofibers.
[0081] In a state in which the elastomer molecules are restrained
by the fibers and the carbon nanofibers, the number of non-network
components (non-reticulate chain components) is considered to be
reduced for the following reasons. Specifically, when the molecular
mobility of the elastomer is decreased over the entire elastomer by
the fibers and 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 tend to
be adsorbed on the active sites of the fibers and the carbon
nanofibers. It is considered that these phenomena decrease the
number of non-network components.
[0082] Therefore, the fiber composite material according to this
embodiment preferably has values within the following range
measured by the Hahn-echo method using the pulsed NMR
technique.
[0083] Specifically, it is preferable that the uncrosslinked fiber
composite material have a first spin-spin relaxation time (T2n)
measured at 150.degree. C. of 100 to 3,000 microseconds, a second
spin-spin relaxation time (T2nn) measured at 150.degree. C. of
1,000 to 10,000 microseconds, and a fraction (fnn) of components
having a second spin-spin relaxation time of less than 0.2.
[0084] It is preferable that the crosslinked fiber composite
material have a first spin-spin relaxation time (T2n) measured at
150.degree. C. of 100 to 2,000 microseconds, a second spin-spin
relaxation time (T2nn) measured at 150.degree. C. of zero or 1,000
to 5,000 microseconds, and a fraction (fnn) of components having a
second spin-spin relaxation time of less than 0.2.
[0085] The spin-lattice relaxation time (T1) measured by the
inversion recovery method using the pulsed NMR technique is an
index of the molecular mobility of a substance together with 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. Therefore, the
fiber composite material, in which the fibers and the carbon
nanofibers are uniformly dispersed, exhibit a reduced molecular
mobility to exhibit T2n, T2nn, and fnn within the above ranges.
[0086] The fiber composite material according to this embodiment
preferably has 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 fiber composite material according to this
embodiment, the fibers and the carbon nanofibers are uniformly
dispersed in the elastomer. In other words, the elastomer is
restrained by the fibers and the carbon nanofibers, as described
above. In this state, the elastomer exhibits a molecular motion
smaller than that of the elastomer which does not include the
fibers and the carbon nanofibers, whereby flowability is decreased.
The fiber composite material according to this embodiment having
such flow temperature characteristics shows a small temperature
dependence of dynamic viscoelasticity to exhibit excellent heat
resistance.
[0087] The fiber composite material according to this embodiment
exhibits stable thermal expansion characteristics over a wide
temperature range, as described above. Moreover, the fiber
composite material exhibits a small thermal expansion over a wide
temperature range due to a small average coefficient of linear
expansion. Since the maximum value of the differential coefficient
of linear expansion of the fiber composite material is small, the
fiber composite material is stable over a wide temperature range.
Therefore, an instantaneous increase in thermal expansion does not
occur.
[0088] Examples according to the invention and comparative examples
are described below. Note that the invention is not limited to the
following examples.
Examples 1 to 8 and Comparative Examples 1 to 3
(1) Preparation of Sample
[0089] An elastomer shown in Table 1 was mixed with predetermined
amount of fibers and carbon nanofibers using the open-roll method
to obtain samples. As the samples, an uncrosslinked sample and a
crosslinked sample were prepared using the following methods.
(a) Preparation of Uncrosslinked Sample
[0090] 1) The elastomer was supplied to six-inch open rolls (roll
temperature: 10 to 20.degree. C.) and wound around the roll.
[0091] 2) Fibers and carbon nanofibers (indicated by "CNT1" and
"CNT13" in Table 1) were added to the elastomer. The roll distance
was set at 1.5 mm.
[0092] 3) After the addition of the fibers and the carbon
nanofibers, the mixture of the elastomer, the fibers, and the
carbon nanofibers was removed from the rolls.
[0093] 4) After reducing the roll distance from 1.5 mm to 0.3 mm,
the mixture was supplied to the rolls and tight-milled. The surface
velocity ratio of the rolls was set at
1.1. Tight Milling was Repeatedly Performed Ten Times.
[0094] 5) After setting the roll distance at a predetermined
distance (1.1 mm), the mixture subjected to tight milling was
supplied to the rolls and sheeted.
[0095] Uncrosslinked samples of Examples 1 to 8 and Comparative
Examples 1 to 3 were thus obtained. In Table 1, the raw material
elastomer "NR" is natural rubber, and the raw material elastomer
"EPDM" is ethylene-propylene rubber. In Table 1, "CNT1" indicates
single-wall carbon nanotubes with an average diameter (fiber
diameter) of about 1 nm and an average length of 1 to 10
micrometers, and "CNT13" indicates multiwall carbon nanotubes with
an average diameter of about 13 nm and an average length of 1 to 25
micrometers. In Table 1, "cotton" indicates cotton yarn with an
average diameter (fiber diameter) of about 10 micrometers and an
average length of about 6 mm, "silk" indicates silk yarn with an
average diameter of about 3 micrometers and an average length of
about 6 mm, and "stainless steel fiber" indicates stainless steel
fibers exhibiting high bending properties with an average diameter
of about 10 micrometers and an average length of about 6 mm. In
Examples 1 and 3 to 8 and Comparative Examples 1 to 3, 2 phr of a
peroxide ("PO") was added to 100 phr of the elastomer as a
crosslinking agent before adding the carbon nanofibers and the
fibers. Example 2 is an uncrosslinked sample of Example 1.
(b) Preparation of Crosslinked Sample
[0096] The uncrosslinked samples of Examples 1 and 3 to 8 and
Comparative Examples 1 to 3 cut into a die size were placed in a
die and press-crosslinked at 175.degree. C. and 100 kgf/cm.sup.2
for 20 minutes.
[0097] Table 1 shows the volume ratio of each material added to the
fiber composite materials of Examples 1 and 3 to 8 and Comparative
Examples 1 to 3.
(2) Electron Microscope Observation
[0098] The dispersion state of the carbon nanofibers and the fibers
in the uncrosslinked and crosslinked samples was observed using an
electron microscope (SEM). The carbon nanofibers and the fibers
were uniformly dispersed in the elastomer in all the samples.
(3) Measurement of Coefficient of Linear Expansion and Heat
Resistant Temperature
[0099] The uncrosslinked sample of Example 2 and the crosslinked
samples of Examples 1 and 3 to 8 and Comparative Examples 1 to 3
were subjected to measurement of the coefficient of linear
expansion and the heat resistant temperature. The measurement
results are shown in Table 1. "TMASS" manufactured by SII was used
as the measurement instrument. The measurement sample had
dimensions of 1.5.times.1.0.times.10 mm. The measurement load was
25 KPa, the measurement temperature was -80 to 350.degree. C., and
the temperature rise rate was 2.degree. C./min. FIG. 2 is a graph
of "temperature (.degree. C.)-differential coefficient of linear
expansion (ppm (1/K)" of Example 1 (B in FIG. 2) and Comparative
Example 1 (A in FIG. 2).
TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 Raw Type of elastomer NR
NR NR NR NR NR material Polar group Double Double Double Double
Double Double elastomer bond bond bond bond bond bond Average
molecular weight 3,000,000 3,000,000 3,000,000 3,000,000 3,000,000
3,000,000 Uncrosslinked T2n (30.degree. C.) 700 700 700 700 700 700
form (.mu.sec) T2n (150.degree. C.) 5500 5500 5500 5500 5500 5500
(.mu.sec) T2on (150.degree. C.) 18000 18000 18000 18000 18000 18000
(.mu.sec) Inn (150.degree. C.) 0.381 0.381 0.381 0.381 0.381 0.381
Flow temperature 40 40 40 40 40 40 (.degree. C.) Fiber Volume ratio
CNT13 (vol %) 15 15 8 3 0 3 composite CNT1 (vol %) 0 0 0 0 1 0
material Cotton (vol %) 3 3 20 30 40 0 Silk (vol %) 0 0 0 0 0 30
Stainless steel fiber 0 0 0 0 0 0 (vol %) Crosslinking Cross-
Uncross- Cross- Cross- Cross- Cross- linked linked linked linked
linked linked Mixing capability Mixed Mixed Mixed Mixed Mixed Mixed
Average coefficient of linear 76 74 74 69 75 63 expansion (ppm/K)
Maximum value of differential 98 95 95 97 98 89 coefficient of
linear expansion (ppm/K) Heat resistant temperature 300 300 300 300
300 300 (.degree. C.) or more or more or more or more or more or
more Low elongation stress ratio 1.15 1.13 1.22 1.25 1.29 1.2
Example Comparative Example 7 8 1 2 3 Raw Type of elastomer NR EPDM
NR NR NR material Polar group Double Double Double Double Double
elastomer bond bond bond bond bond Narbomece Average molecular
weight 3,000,000 2,00,000 3,000,000 3,000,000 3,000,000
Uncrosslinked T2n (30.degree. C.) 700 520 700 700 700 form
(.mu.sec) T2n (150.degree. C.) 5500 2200 5500 5500 5500 (.mu.sec)
T2on (150.degree. C.) 18000 16000 18000 18000 18000 (.mu.sec) Inn
(150.degree. C.) 0.381 0.405 0.381 0.381 0.381 Flow temperature 40
55 40 40 40 (.degree. C.) Fiber Volume ratio CNT13 (vol %) 3 8 14 0
3 composite CNT1 (vol %) 0 0 0 0.5 0 material Cotton (vol %) 0 20 0
30 45 Silk (vol %) 0 0 0 0 0 Stainless steel fiber 30 0 0 0 0 (vol
%) Crosslinking Cross- Cross- Cross- Cross- Cross- linked linked
linked linked linked Mixing capability Mixed Mixed Mixed Mixed
Could not be mixed Average coefficient of linear 61 78 121 Not Not
expansion (ppm/K) calculated calculated Maximum value of
differential 88 99 141 Not Not coefficient of linear calculated
calculated expansion (ppm/K) Heat resistant temperature 300 300 300
250 -- (.degree. C.) or more or more or more Low elongation stress
ratio 1.29 1.25 1.1 1.8 --
[0100] As shown in FIG. 2, it was confirmed that the sample of
Example 1 had a low and stable coefficient of linear expansion over
the measurement temperature range in comparison with the sample of
Comparative Example 1. The sample of Comparative Example 1 showed a
large change in the differential coefficient of linear expansion in
several temperature ranges. On the other hand, the sample of
Example 1 according to the invention showed a small change in the
differential coefficient of linear expansion over the measurement
temperature range. It was also found that the sample of Example 1
had a differential coefficient of linear expansion smaller than
that of the sample of Comparative Example 1.
[0101] As shown in Table 1, the following items were confirmed by
Examples 1 to 8 according to the invention. Specifically, the fiber
composite materials of Examples 1 to 8 had an average coefficient
of linear expansion of 100 ppm (1/K) or less and a maximum value of
the differential coefficient of linear expansion of 120 ppm or less
at -80 to 300.degree. C. The fiber composite materials of Examples
1 to 8 and Comparative Example 1 had a heat resistant temperature
of 300.degree. C. or more. The fiber composite material of
Comparative Example 1 had an average coefficient of linear
expansion of 121 ppm (1/K) and a maximum value of the differential
coefficient of linear expansion of 141 ppm (1/K). In Comparative
Example 2, the coefficient of linear expansion was not calculated
since the coefficient of linear expansion was unstable at -80 to
300.degree. C. The sample of Comparative Example 2 had a heat
resistant temperature of 250.degree. C. Since the sample of
Comparative Example 3 could not be mixed, the coefficient of linear
expansion, heat resistant temperature, and low elongation stress
ratio could not be measured.
[0102] The uncrosslinked sample of Example 2 showed almost the same
results as the crosslinked sample of Example 1.
[0103] Therefore, it was confirmed that the fiber composite
material according to the invention shows a small and stable
thermal expansion over a wide temperature range.
[0104] Although only some embodiments of the invention have been
described in detail above, those skilled in the art will readily
appreciate that many modifications are possible in the embodiments
without departing from the novel teachings and advantages of this
invention. Accordingly, all such modifications are intended to be
included within the scope of this invention.
* * * * *