Note: Descriptions are shown in the official language in which they were submitted.
WO 95/07316 PCT/US94/10168
A RUBBER COMPOSITION CONTAINING
CARBON FIBRILS AND A PNEUMATIC TIRE
FIELD OF THE INVENTION
This invention relates to a novel rubber
compasition of superior hardness and strength. More
particularly, this invention relates to a rubber
compasition containing carbon fibrils in which specified
carban fibrils are compounded with synthetic rubber
and/ar natural rubber and to tires in which the
compasition is used.
BACKGROUND OF THE INVENTION
Concerns over the limited oil resources in
recent years has let to the imposition of certain fuel
cost standards in an effort to bring about improvement in
controlling automobile fuel costs. In order to meet the
strict standards of the future, it will be necessary to
improve existing materials and technology. One method is
to reduce the weight of the tire itself, which would be
effective in bringing about great improvement in
automobile fuel costs.
Lowering the specific gravity of the rubber
companent that forms the tire can be considered. From
this standpoint, it would be desirable to effect a great
decrease in the quantity of use of carbon black, which
has a high specific gravity. Carbon black has
approximately twice the specific gravity as that of
rubber. However, when the quantity of carbon is
decreased, hardness, tensile strength and modulus during
low extension are decreased and wear resistance is
insufficient.
Another way of lowering the weight of the tire
that has been considered is to decrease the size of the
tire. However, when the tire is made smaller, the
strength of the tire cannot be maintained. When the
quantity of carbon black that is used is increased,
hardness is increased. However, increase in strength is
not sufficient. When an ever larger amount of carbon
black is used, strength is decreased, the processing
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2
capacity of the rubber composition becomes poor and heat
generated from vulcanized rubber is increased. In
addition, there are the problems that the specific
gravity of the rubber composition increases and the '
weight of the tire increases.
Consequently, it is desirous to have a '
reinforcing material which has a greater reinforcing
capacity than conventional carbon black and that has
greater hardness and wear resistance when used in small
quantities. Most recently, fine, filiform carbon fibrils
have been developed and it has been discovered that
rubber compositions having hardness and good tensile
strength and wear resistance can be obtained by addition
of small amounts of reinforcing material. However,
problems such as deterioration in the physical
properties, and, of tensile strength in particular, of
these rubber compositions at high temperatures remain.
OBJECTS OF THE INVENTION
It is therefore a general object of the
invention to provide a rubber composition that has a low
specific gravity.
It is a further object of the invention to
provide a rubber composition having a high degree of
hardness, tensile strength and modulus.
It is a yet another object to provide a rubber
composition having a high wear resistance.
It is another object to provide a pneumatic
tire in which the surface layer of the tire is composed
of a rubber composition having a low specific gravity,
high degree of hardness, tensile strength and modulus,
and a high wear resistance.
These and other objects, features and
advantages of the invention will become readily apparent
from the ensuing description, and the novel features will
be particularly pointed out in the appended claims.
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SUMMARY OF THE INVENTION
The invention is broadly directed to a rubber
composition containing carbon fibrils in which 0.5 to 60
parts by weight of carbon fibril material comprised
primarily of an aggregate having an average particle
diameter of 0.05 to 50 ~m in which fine, filiform carbon
fibrils of 3.5 to 75nm in diameter are intertwined with
each other is mixed with 99.5 to 40 parts by weight of
synthetic rubber and/or natural rubber.
The invention is also broadly directed to a
pneumatic tire in which the surface layer of the tire is
provided with the rubber composition as described.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be understood more clearly
and fully from the following detailed description, when
read with reference to the accompanying figures, in
which:
Fig. 1 shows TEM (transmission electron
microscope) image of the carbon fibril material used in
the manufacture of the rubber composition of this
invention;
Fig. 2 shows the oxygen of fibril after
oxidation;
Fig. 3 shows the ESCA spectra of fibril
oxidized by nitric acid in various time periods;
Fig. 4 shows the ESCA wave separations of C-is
for fibrils oxidized with nitric acid for 20 hours;
Fig. 5 shows the structures of oxygen-
containing groups in fibrils;
Fig. 6 shows the change of oxygen content of
fibrils;
Fig. 7 shows an XPS spectrum of nitric acid
oxidized BN fibrils; and
Fig. 8 shows a high resolution spectrum of the
carbon is peaks in the spectrum of Fig. 7.
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DETAILED DESCRIPTION OF THE INVENTION
The invention is broadly directed to a rubber
composition containing carbon fibrils and is mixed with
synthetic and/or natural rubber.
A rubber composition containing specified
carbon fibrils is disclosed in Japanese Patent Disclosure -
No. 2-235945 [1990] as a means of solving the
aforementioned problems. That disclosure indicated the
diameter of the aggregate of carbon fibrils is 0.10 to
0.25 mm and the rupture strength TB of the rubber sheet
that is obtained is decreased at smaller diameters.
However, the inventors of this invention, who
conducted further intensive and repeated research,
discovered as a result that the dispersibility of the
carbon fibril material and the external appearance of the
compact surface could be improved without impairing the
TB and HS, even when the average particle diameter of the
carbon fibril aggregate was even smaller. It was further
ascertained that the conductive properties of the rubber
composition could be improved and that equal resistance
values could be obtained by means of a small quantity of
carbon fibril material.
As a result of research for the purpose of
applying the results of the foregoing study industrially,
it was discovered that rubber compositions in which a
specified carbon fibril material was compounded in a
suitable quantity with any commercial synthetic rubber
and/or natural rubber are of superior processing capacity
and that they form a vulcanized rubber of high hardness
and of superior tensile strength and wear resistance as a
result of vulcanization.
The essential aspects of this invention are
that it is a rubber composition containing carbon fibrils
in which 0.5 to 60 parts by weight of carbon fibril
material comprised primarily of an aggregate of fibrils
having an average particle diameter of 0.05 to 50 ~m in
which fine, filiform carbon fibrils of 3.5 to 75 nm in
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WO 95/07316 ~ PCT/US94/10168
diameter are intertwined with each other is mixed with
99.5 to 40 parts by weight of synthetic rubber and/or
natural rubber and that pneumatic tire in which the
surface layer of the tire is provided with this rubber
5 composition.
Here, the tire surface layer refers to the
tread, the side wall or various types of covering rubber.
In tread that is comprised of several layers, the tread
includes not only the outside layer of tread, but also
the inside layer of tread that is exposed on the surface
of the tire after it has run. In this invention, the
aforementioned rubber composition should be provided with
a tread.
The term "90~ diameter" is used in the
explanation of this invention. It is defined as follows.
The distribution obtained by taking d as
particle diameter and the volumetric ratio of particle
diameter Vd as the probability variable is called the
particle size distribution D. When the minimum particle
diameter in the particle size distribution D is taken as
dmin and the maximum particle diameter is taken as dmax,
the average particle diameter dm satisfies the following
formula.
Formula 1:
dmax
0.5=~ Vd or 0.5=~ V d
dmin
In addition, "90~ diameter" d9o satisfies the
following formula:
Formula 2:
d90
0.9=~ Yd
dmin
The carbon fibril material that is used in this
invention is comprised of an aggregate of an average
particle diameter of 0.05 to 50 ~m in which fine,
filifarm carbon fibrils of 3.5 to 75 nm in diameter are
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CA 02171466 2004-03-10
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intertwined with each other. The average parti.c:le
diameter of the aggregate should be U.2 to 30 ~,x~, and,
preferably, 0.5 to 20 Vim.
The particle size distribution of the aggregate
ire °this invea~tion is as follows. ~pecif ically, 90%
diameter as defined previously should ordinarily be less
than :x.00 stn, preferably, less than E30 ~,m, and, mare
preferably, less than 50 ~Sm. further, 90% dia~ttteter
should be less than '7~5 times the average particle
1.0 diameter.
'then f~he ave~~age particle diameter of. the
aggregate exceeds 50 Vim, the carbon fibra_1 material in the
rubber° corc~position is poorly dispersed, the tensile
strength of the vulcanized material is decreased and the
external appearance of the molded compact is impaired.
Manufacture is difficult w~a~an tree aver°age particle
diameter .i_s less that 0.05 Vim.
'fhe proportion of aggregate in the carbon
fibril material should be greater than 30%, and,
preferak~ly, greater than 50%.
The carbran f ibx i is that f orm the carbon f ibr ~_ 1
aggregate are filaments of which the va~°iation in
diameter should be less than 150 of the average diameter
o~ several tens of samples and of which the aspect ratio
should ordinarily be greater than 5, preferably, greater
than 100, and, mare preferably,, greater than 1000.
Moreover, they should ordinarily be tubular fibrils with
hollow cores.
Moreover, the carbon fibrils should have
several graphite layers that are parallel to the fibril
axis and should not have a continuous thermal carbon
coating. The proportion of the surface area that is
coated by the thermal carbon coating should ordinarily be
less thal7 500, preferably, less than 25%, and, mare
preferably, less than 50.
~Phe surfaces of carbon fibrils which have been
denatured can be used. Denaturing can be performed, for
ezcample, by chemical reactions, such as oxidation and by
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procedures such as coating with polymers, like epoxy
resins.
The carbon fibrils that are used in this
invention should be partially oxidized carbon fibrils in
which the relative ration of CIS and OIS (CIS/OIS) as
determined by X-ray photoelectron spectrometry is in the
range of 92/8 to 98/2. When the ratio is less than 92/8,
dispersion in the rubber is not sufficient, causing the
tensile strength of the vulcanized rubber to decreased.
When the ratio of CIS and OIS is greater than 98/2, the
tensile strength after maintenance at high temperatures
is decreased. This type of rubber composition is suited
for use in automobile tires and passenger automobile
tires in particular.
The proportion of carbon fibril material in the
composition of this invention should be 0.5 to 60~ by
weight, preferably, 1 to 50% by weight, and, more
preferably, 5 to 40o by weight. In tires, the proportion
of carbon fibrils should be 15 to 60~ by weight, and,
preferably, 20 to 50~ by weight. In tires, the
proportion of carbon fibrils should be 15 to 60~ by
weight, and, preferably, 20 to 50~ by weight. When it is
less than 0.5~ by weight, the effect attributable to the
carbon fibril material is not manifested. When it
exceeds 60~ by weight, there are the drawbacks that the
processing capacity of the composition is markedly poor
and that the hardness of vulcanized composition is
excessively great.
The method of manufacturing the carbon fibrils
that are used in this invention is described in Japanese
Patent Application 2-503334 [1990]. A specific example
is described below.
The carbon fibrils are manufactured in a
vertical tubular reactor by introducing catalyst
particles containing metal into a gas flow containing
carbon by means of its own weight or by injection of a
gas such as an inert gas. The reaction temperature is
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550 to 1200°C. The catalyst particles may be formed in
the reaction vessel by decomposition of a precursor
compound, for example, ferrocene. An internal plug of
quartz wool for catching the catalyst particles and a
quartz tube equipped with a thermocouple for monitoring
the temperature of the reaction vessel are used in the
reaction vessel. In addition, it is equipped with an
inlet port for introducing the catalyst, the reaction gas
and a purge gas such as argon and with an outlet port for
removing the gas from the reaction vessel.
Suitable gases containing carbon include
saturated hydrocarbons, for example, methane, ethane,
propane, butane, hexane and cyclohexane, unsaturated
hydrocarbons, for example, ethylene, propylene, benzene
and toluene, hydrocarbons containing oxygen, for example,
acetone, methanol and tetrahydrofuran and carbon
monoxide. The preferable gases are ethylene and propane.
Preferably, hydrogen gas is added. Typically, the ratio
of gas containing carbon to hydrogen gas is in the range
of 1:20 to 20:1. Desirable catalysts include iron,
molybdenum-iron, chromium-iron, cerium-iron and
manganese-iron particles attached to deposited alumina.
In order to cause the fibrils to grown, the
reaction tube is heated to 550 to.1200°C, and, at the
same time, purging is performed with, for example, argon.
When the reaction tube reaches a specified temperature,
introduction of the hydrogen flow and the flow of gas
containing carbon is begun. A hydrogen flow volume of
approximately 100 millimeters/minute and a flow of gas
containing carbon of approximately 200 millimeters/minute
are suitable for a reaction tube of 1 inch in length.
After the reaction tube has been purged for over 5
minutes with the reaction gases at the aforementioned
flow volumes, the catalyst is dropped onto the quartz
wool plug. Next, the reaction gases are reacted with the
catalyst (typically for 0.5 to 1 hour) throughout the
entire body of the reaction vessel. When the reaction
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9
period is completed, the flow of reaction gases is
stopped, purging is effected with a gas not containing
carbon, for example, argon, the reaction vessel is cooled
to roam temperature and the fibrils are recovered from
the reaction tube. The yield of fibrils is greater than
30 times the iron content of the catalyst.
The carbon fibril material that is used in this
invention consists of carbon fibrils in unaltered form
manufactured as described above, or, in many cases, is
obtained by pulverizing them to a specified size. The
pulverization apparatus may be, for example, a pneumatic
grinder (jet mill) or an impact grinder. Because these
grinders can be operated continuously and the quantity
treated per unit time is greater than with a ball mill or
a vibrating mill, pulverization costs can be lowered. In
addition, a uniform carbon fibril aggregate of a narrow
particle size distribution can be obtained by installing
a classifying mechanism in the grinder or by installing a
classifier such as a cyclone in the line.
The partially oxidized carbon fibrils that are
used in this invention can be manufactured using carbon
fibrils as the carbon fibrils and by oxidizing their
surfaces. They can be manufactured by gaseous phase
oxidation at normal temperature or high temperatures with
such oxidating gases as air, oxygen, ozone, water vapor
and plasma and by liquid phase oxidation with
concentrated nitric acid, potassium permanganate,
potassium dichromate and sodium hypochlorite. To prevent
environmental contamination, gaseous phase oxidation is
preferably conducted with an industrial oxidizing gas.
Manufacture can be carried out by combining the oxidation
treatment process with the process of manufacturing the
carbon fibrils. These oxidation treatments can also be
carried out after the raw material carbon fibrils have
been pulverized.
Figure 1 shows an example of the carbon fibril
material that is used in this invention. The portions
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WO 95!07316 PCTIUS94110168
2~ 7 ~ ~b6
that are shaded in black are the carbon fibril aggregate
obtained as described above. The matter that appears as
lines is the fibrils themselves.
The synthetic rubbers that are used in this
5 invention include polyisoprene rubber, polybutadiene
rubber, butadiene-styrene copolymer rubber, butadiene- ,
acrylonitrile copolymer rubber, polychloroprene rubber,
ethylene-olefinic copolymer rubber, ethylene-acrylic
copolymer rubber, ethylene-vinyl acetate copolymer,
10 acrylic rubber, epichlorohydrin rubber, halogenated
polyethylenes, cholorsulfonated polyethylenes, silicone
rubber, fluorine rubber and phosphazene rubber.
Modified substances obtained by adding malefic
acid anhydride, a, j3-unsaturated carboxylic acids and
esters thereof, various types of vinyl compounds and
acenaphthylene to the aforementioned rubbers and modified
substances obtained by hydrogenating those of the
aforementioned rubbers having unsaturated groups in the
polymer main chain can also be cited.
Diene polymers, specifically, polybutadiene
rubber, butadiene-styrene copolymer rubber and
polyisoprene rubber can be used suitably in tires.
The vinyl content of the butadiene component of
tl~e (co)polymer in the butadiene rubber compound should
be greater than 15~, preferably, greater than 20~, and,
more preferably, greater than 30%. From the standpoints
of manufacture and effect, it should be less than 90~.
When it is less than 15~, it is difficult to
improve wet skid characteristics and roll friction
resistance characteristics are improved, roll friction
resistance characteristics at the same time. That is,
when wet skid characteristics are impaired, and, when
roll friction resistance characteristics are improved,
wet skid characteristics are impaired.
The glass transition temperature (Tg) of the
aforementioned butadiene (co)polymers should be greater
than -70°C, and, preferably, greater than -60°C. For
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il
effectiveness, it should be less than -30°C. When the
glass transition temperature is less than said
temperature, wet skid characteristics are impaired. This
is nat desirable. The glass transition temperatures (Tg)
indicates values determined by DSC. In this connection,
the value for Li butadiene rubber of a 12~ vinyl bond
content is -180°C, the value for natural rubber is
-76°C and the value for styrene-butadiene copolymer
rubber (SBR #1500: brand name) obtained by emulsion
polymerization is -64°C.
Conjugated diene (co)polymers that are
desirable for use in tires can be obtained by subjecting
a conjugated diene alone or a conjugated diene together
with one or more other conjugated dienes or aromatic
vinyl compounds to solution polymerization, after which
the product is reacted with a reactive compound such as
an isocyanate compound.
Styrene-butadiene copolymers having a styrene
content of greater than 5~ are particularly desirable
because they exhibit excellent wet skid characteristics
and roll friction resistance characteristics and because
they are also of superior tensile strength and processing
capacity.
~ Although there are no particular limitations on
the aforementioned styrene content, it should be less
than 50~ by weight, and, preferably, less than 45~ by
weight.
Additives, vulcanization accelerators,
auxiliary vulcanization accelerators, aging inhibitors,
softeners and fillers that are commonly used in the
rubber industry can be compounded with the rubber
composition of this invention.
Further, as required, fillers such as carbon
black, silica, diatomaceous earth, pulverized quartz,
talc, clay, mica, calcium silicate, magnesium silicate,
glass powder, calcium silicate, magnesium silicate, glass
powder, calcium carbonate, barium sulfate, zinc
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WO 95/07316 PCT/US94/10168
12
carbonate, titanium oxide, alumina, glass fibers, other
types of carbon fibers and organic fibers and known
additives such as softeners, plasticizers, auxiliary
processing agents, lubricants, aging inhibitors and
ultraviolet ray absorbents can also be added.
These compounding substances can be kneaded
with kneading machines that are commonly used such as
rolling machines and Bumbury mixers, after which molding
and vulcanization can be carried out under ordinary
conditions for manufacturing vulcanized rubber.
Mixing of the carbon fibril material of this
invention and the rubber can be carried out by the wet
master batch method.
The invention will be more fully described and
understood with reference to the following examples which
are given by way of illustration.
In determination of the diameter of the
aggregate of the carbon fibril material, the carbon
fibrils were first added to water to which a surfactant
had been added and were dispersed using an ultrasonic
homogenizer. Following that, the carbon fibril
dispersion was analyzed using a laser diffraction
scattering type particle size distribution meter and the
particle diameter of the aggregate was determined.
Compounding for the purpose of vulcanization
tests in the examples and comparative examples was as
indicated in Table 1 through Table 3. The unit of
compounding was parts by weight in all cases. Carbon
fibrils or HAF carbon (high reinforcing carbon black)
were added to the compounding materials based on
compounding formulation 1 and compounding formulation 2
in Table 1 by compounding as indicated in Table 2 and
Table 3. As specified in Table 2 and Table 3, the types
of rubbers were SBR rubber and EP rubber.
Table 2 and Table 3 also show the properties of
the carbon fibril material and the test results for the
examples and comparative examples.
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[Table 1]
Compounding Compounding
1 2
Rubber (SBR rubber 100 100
or EP rubber)
Carbon fibrils
HAF carbon
(ASTM 330)
Stearic acid 2 1
Zinc white 3 5
N-butyl-N-isopropyl- 2 -
p-phenylenediamine
Diphenylguanidine 1 -
Dibenzothiazole 0.6 -
disulf ide
N-cyclohexyl-2- - 1.5
benzothiazole
disulfide
Dipentamethylene - 0.75
thiuram tetrasulfide
Tellurium diethyl - 0.75
dithiocarbamate
Sulfur 1.5 1.5
Cases marked with * were compounded as indicated in Table
Z and Table 3.
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14
. . r~ roH x ro~ x~ c~~n o ~ w d w c
c r~ r.~ ~ n o co roa~ ~ :~ ~
~ w
o w
re ro~ ~n - x~ n d ao ~ n b
O tn r D'LfN G ~t D''Cirt m C' IC Q
Cl. r .t
( ,..s
E F' G i F~ G ni f7 O O (D ~p fDO
fD tD E F-~r tD17 rr cYG w G G 00 w rrG O
cD ~.rt
I
~r w m co m w ~t m crw n o w ~q~co h,
r~ w
,~
n n w m rro cco c ~,w rr rr n ~, r.,
N. n m r00 o n cu o r w ~n w o ,r
g r,n x ~'N r" n o ~ awo~ w ~ n a
r
n
~ ~ p ~ ~ M FN'C ',D1~~-' 20~N~ 'rN O
~
~
u
rt a.0'7 G W n m . G
G ~ rn b G
N ~ ~' c C ~ ~p rt . '
.. r-rN o w ~ o r.
.. m f7w rt "~ 'Lip
n ~ a ~ w o o ~ ~ a
v ~ t r w r
~ r t
G' n N N O r't~ N
W r . O
!A QO P. ~ f
l7
O
B "
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v
C.J
O ~'~~-.N O ~"'' O~ G.7
Example
1
X ~ o c~ oo c i o I ~,,~ ~, ~
0 00 o c~ cu o o c~ cryca
o ,~ N o ,,., Comparative
X W --~c~ oo n. I o ~ I I I I ,....Example
1
o v. o00 ~ 0 0
w
w o0
N o ~ o W
X ( I N o ' o I i ,~ ~- cw,Example
2
o ~- W o o c~ cryc~.,
n Comparative
I I o -~ o I ,~ I I I I ~ Example
2
,.r c~ cry o o
0
V
2 5 ~
N ~. m v-.
X I v~o cry ~ i o i I I ( ,.rExample
3
0 o N o ~ o ca
~ o
c c ~-- Comparative
c o
"~ I I -~ ~ "'s 1 o I I i i ~ p
Exam le
3
3 0 E-. ~ ~" ~ o W
o cn
V
N
0
0o I ,a.oo a.. I o I c"~ ca ~ r- Example
4
o cn ~ 00 o cn ,~.,~ c.~
0
cn
35 ~ ~ o ~,j~ Comparative
X I o r ~ ,.~ I o o I I I ( ~ Examp le
4
o ao0 00 0 0
N
b
. r O
C7 r- ~-. f-. tV
X ca ( r.~-~ rt I o f ca ,cueoo ..... ,,~Comparative
0 0 0 o c~ Example
r 5 .
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WO 95/07316 7 ~ ~ ~ ~ pCTlUS94/10168
[Table 3]
ExampleExampleExample Comparative Comparative
5 6 7 Ex. 6 Ex. 1
Type of 1 1 1 1 1
C unding
Carbon fibril
roperties
C / O 97/3 95/5 97/3 99/1
Diameter 12 12 12 13.5 -
(nm)
Average 2.9 2.9 2.9 3.2 -
particle
diameter
of
aggregate
(N.m)
Compounding
Carbon fibrils30 30 40 30 -
HAF carbon - - _ _ 7 5
(ASTM N-30)
SBR rubber 100 100 100 100 100
Results
of
evaluation
Rol t good good good good good
processing
capacity
Properties
of
vulcanized
material
Hardness 84 85 93 83 85
(HS)
(JIS-A)
After 48 89 89 96 92 92
hours
at 100C
Tensi le 226 225 247 223 218
strength
(TB)
(kgf/cm~
After 48 180 182 181 161 160
hours
et '100C
Pico wear 100 100 112 99 gl
(index)
DIN wear 116 112 84 118 133
(mg)
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. 16
Example 1
An aggregate of an average particle diameter of
3.5 ~cm and a 90~ diameter as described previously of 8.2
~Cm in which fine, filiform tubular graphitic carbon '
fibrils of an average diameter of 13 nm were intertwined
were used as the carbon fibril material.
This was compounded on the basis of compounding
formulation 1 and compounding formulation 2 as shown in
Table 1 in accordance with the compounding conditions
described in Table 2. SBR 1502 manufactured by Japan
Synthetic Rubber was used as the SBR rubber. The
compounded material was kneaded using a laboplast mill
and a roller, after which vulcanization was carried out
for 30 minutes at 145°C, with a rubber sheet of
approximately 2 mm in thickness being obtained.
Tests were carried out in accordance with the
tensile test method for vulcanized rubber specified in
JIS K6301 and the for hardness (Hs) and rupture strength
(Ts) shown in Table 2 were obtained. Pico wear tests as
specified in ASTM D-2228 were carried out wear resistance
was expressed by an index obtained by taking the values
in Table 1 as 100.
Comparative Example 1
Tests were conducted in the same way as in
Example 1 except that 70 parts of HAF carbon (ASTM No. N-
330) was used instead of 30 parts of carbon fibrils.
When Example 1 and Comparative Example 1 were
compared, it was found that hardness and tensile strength
equal to that with HAF carbon was obtained with
approximately half the quantity carbon fibrils. Wear
resistance was also superior.
Example 2 and Comparative Example 2
Tests were carried out in the same way as in
Example 1 except that EP rubber (EP21 manufactured by
Japan Synthetic Rubber) was used in compounding
formulation 2 in Table 1 and that carbon fibrils and HAF
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17
carbon were used as in Example 1 and Comparative Example
1, respectively.
In EP rubber as well, carbon fibrils were more
effective in increasing hardness than HAF carbon.
Volumetric intrinsic resistance was approximately
1/10,000 in Example 2. Thus, carbon fibrils were
extremely good in increasing conductivity.
Example 3
Tests were conducted in the same way as in
Example 1, except that 3 parts of carbon fibrils was
used.
Comparative Example 3
Test were carried out in the same way as in
Comparative Example 1 except that 3 parts of HAF carbon
was used. From a comparison of Example 3 and Comparative
Example 3, it was found that carbon fibrils in small
amounts had the effect of bringing about marked decreases
in the volumetric intrinsic resistance of vulcanized
rubber.
Example 4
An aggregate of an average particle diameter of
7.4 ~m and a 90~ particle diameter as described
previously of 34 ~m in which fine, filiform tubular
graphitic carbon fibrils of 13 nm in average diameter
were intertwined was used as the carbon fibril material.
This aggregate was tested in the same way as in Example 1
using compound formulation 1 in Table 1 and under the
compounding conditions of Table 2.
The quantity of carbon fibrils was increased by
5 parts by comparison to Example 1, for which reason
there was high hardness and tensile strength as well as
high conductivity. There was little wear.
Comparative Example 4
Tests were carried out in the same way as in
Comparative Example 2 except that 100 parts carbon were
used. Roller processing capacity was poor and tensile
strength was also low.
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Comparative Example 5
An aggregate of an average particle diameter of
80 um and a 90~ particle diameter as described previously
of 240 ~Cm in which fine, filiform tubular graphitic
carbon fibrils of 13 nm in average diameter were
intertwined was used as the carbon fibril material. This
aggregate was tested in the same way as in Example 1
using compound formulation 1 in Table 1 and was
compounded as indicated in Table 2. Roller processing
capacity was poorer and tensile strength was lower than
in Example 1, in which the same quantity of carbon
fibrils was compounded. Conductivity was inferior to
that in Example 1.
Examples 5 to 7
Concentrated nitric acid was added to the
carbon fibrils of Example 1, the materials were heated, a
reaction was carried out under reflux and carbon fibrils
of different degrees of oxidation was prepared. Table 3
shows their shapes and properties.
These fibrils were compounded as indicated in
the column for compounding formulation 1 of Table 1 and
the compounding column in Table 3. Vulcanization and
tests of physical properties were carried out in
accordance with the conditions described in Example 1.
In addition to tests at normal temperature (25°C),
hardness and tensile strength were tested at normal
temperature after the test strips were maintained at
100°C for 48 hours.
Comparative Example 6
The tests were carried out in the same way as
in Example 5 except that a material in which the CIS/OIS
ratio was 99/1 was used as the carbon fibril material and
that the other conditions were those indicated in Table
3.
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Comparative Example '7
The tests were carried out in the same way as
in Example 5 except that °75 parts of HAF carbon was used
instead of Carbon fibrils.
~7hen Examples 5 and 6 were compared with
Comparative Example 7, it was found that there was little
change (deterioration) of hardness and tensile strength
after maintenance at high temperatures when the carbon
fibrils of this invention were used.
4Jhen Example 5 and Comparative Example °7 were
compared, it was found that the carbon fibrils conferred
hardness and tensile strength on vulcana.zed rubber equal
to that with FiAF carbon when compounded in two--f fifths the
quantity of the latter.
Example 8
Using CC fibrils, films were cast f~°om the
formulations shown in the table below. The fibrils were
first ultrasonically dispersed in the Triton solution,
then the latex was added, followed by additional
sonication. The mixture was then dried as a film, after
which conductive paint stripes were applied for
resistivity determination.
Table 4
2 5 A11 amounts are parts by wezght
C~vNTRyLj TESTS
1 2 1 2 3 4
water- 2000 2000 2000 2000 2000
2000
2M
Triton X-1001 - ZO 10 10 10 10
3 0 BN Fibrils - 5 - 10
CC Fibrils 5 - 10 -
Natural Rubber2 100 100 100 100 100 100
Resistivity, ohm-c~ ~ ~ 1.1 98 0.3 13
1 'f~=~-tore ~~100 is ~ nana_onzc surface ar_°tive ac~en4
35manufactux°ed by J~ohm and Haas 2
2 Added as 1.61 pax-ts of 62 0 latex
WO 95/07316 2 PCT/US94/10168
As can be seen, the rubber containing CC
fibrils at 5 parts per hundred (Test 1) is 43 times more
conductive than its BN counterpart (Test 2). At the 10
phr loadings (Tests 3 & 4), the conductivity ration is
5 essentially unchanged. Accordingly, it was found that CC
fibrils imparted electrical conductivity substantially
more effectively than BN fibrils.
As described above, the rubber composition of
this invention exhibits good roller processing capacity.
10 Moreover, when the effects of the carbon fibrils of this
invention and carbon black are compared for SBR rubber
compositions, essentially the same physical properties in
respect to hardness, tensile strength and wear can be
obtained with carbon fibrils as with carbon black when
15 the carbon fibrils are compounded in amounts of less than
half the carbon black. Volumetric intrinsic resistance
values are approximately 1/70th, with vulcanized rubber
of high conductivity being obtained.
Example 9
20 Surface modifications of fibrils were
conducted. The gas-phase separation of geometric isomers
of hydrocarbons such as xylenes requests a tough and
strong polymer matrix for membrane formation which does
riot dissolve in hydrocarbon solvents.
One of favorable candidate polymers for this
purpose would be Nylon since Nylons are stable and tough
to hydrocarbon solvents. So, a target is aimed at Nylon
as a matrix in which the fibrils are well dispersed.
In order to have a well-dispersed state of
fibrils in Nylon, it would be necessary to modify the
surface structure of fibrils through chemical
modifications. A method for the surface modifications of
fibrils was carried out by surface oxidation with nitric
acid by the following procedure.
Fibrils were treated under following
conditions:
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Fibrils: 5g
36~ HN03: 70 ml in 200 mol flask
Heating: reflux at 110° for 5 hrs.
After the treatment fibrils were collected by
filtration and washed with water, repeatedly and dried.
Surface structures of fibrils were
characterized by ESCA analyses. The content of oxygen on
the fibrils surface increased from 4.35 to 12.42. It
is expected that the increase of the oxygen content might
be due to the formation -COOH group on the surface of
fibrils .
Example 10
Further studies on surface modification of
fibrils by oxidation with nitric acid were carried out
under various conditions so that carboxylic acid groups
were incorporated onto the surface. At the initial stage
of the oxidation ether-type oxygen was incorporated and
then following oxidation reactions took place to produce
carbonyl and carboxylic acid moieties.
Surface analyses by ESCA indicate that the
incorporation of oxygen reached an equilibrium after 5
hr. treatment in 60~ nitric acid at 110°C.
Surface modification of fibrils was carried out
by means of oxidation with concentrated nitric acid so
that carboxylic acid groups were introduced on the
surface of fibrils. Oxidation reaction was carried out
as follows: lOg of fibrils~were suspended in 200 ml of
60~ nitric acid which were heated under reflux conditions
at 110°C. During the reaction nitrogen dioxide gas was
evolved which was neutralized with 5~ aqueous potassium
hydroxide solution. After a given time period of the
reaction, the suspension was poured into 21 of water and
the fibrils were filtered off. The oxidized fibrils were
washed repeatedly with water, followed by washing with
acetone and drying under vacuum at 50°C. Drying fibrils
directly after washing with water yielded a crammed mass
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which was difficult to disperse. Therefore, the washing
with acetone, followed by hexane was necessary to keep
fibril structure.
Surface analyses of fibrils was carried out by
means of ESCA(XPS), using JEOL Surface Science SSX-100,
and also by means of elemental analyses.
Fig. 2 indicates the total oxygen content of
fibrils after the oxidation. The initial content of
oxygen of fibril was 1.4%, which increased gradually by
the oxidation. The oxygen content of fibrils increased
up to 6.8% after one hr oxidation and reached an
equilibrium content of about 11% after ten hr.
Structural analyses of oxygen were carried out
by C-1s wave analyses which are shown in Figs. 3 and 4,
as ESCA spectra. Results of the structures of oxygen are
summarized in Fig. 5, which revealed that ether-type
oxygen -O-C was observed at the initial state, followed
by gradual increases in C=O and -COOH groups.
Presumably, peroxide groups would be formed at
the initial stage of the oxidation on the surface of the
fibrils, which then transformed into carbonyl and
carboxylic acid groups.
The oxygen contents and the structures of
oxygen groups did not significantly change after keeping
fibril for almost three months in air, as shown in Fig.
6.
Example il
XPS spectrum was conducted on nitric acid
oxidized fibrils. Fig. 7 is a XPS spectrum of nitric
acid oxidized BN fibrils. It shows carbon is and oxygen
is peaks. The calculated oxygen content from this
spectrum is 20.6% (atomic percentage). The fibrils were
oxidized in 35% nitric acid at 107°C for 48 hours. Fig.
8 was recorded from the same sample. It is a high
resolution spectrum of the carbon is peaks. The peaks at
283.94, 285.66 and 287.99 eV can be assigned to C, C-OH
and COOH (C=O), respectively.
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Rubber of high hardness can be obtained by
means of the rubber composition of this invention without
impairing processing capacity and rubber elasticity.
Consequently, stability of properties can be maintained
over long periods. The reason for this is that the
rubber composition of this invention makes it possible to
maintain hardness while decreasing the quantity of
fillers and sulfur compounded for the purpose of
increasing hardness.
Rubber compositions having sufficient hardness
so that they can be used for radial tire treads of large
vehicles while increase in heat generation by the rubber
is avoided can be obtained more readily than with high
reinforcing carbon black which is compounded for
reinforcement.
When partially oxidized carbon fibrils are
used, hardness, tensile strength and wear resistance are
of the same degree as with carbon black when the quantity
of carbon compounded is approximately two-fifths that
with carbon black. Moreover, there is little thermal
deterioration of the vulcanized rubber.
Thus, the rubber compositions of this invention
satisfy performance requirements which have been becoming
higher and higher in recent years, their performance as
products is stable over long periods and they can be used
effectively over an extremely broad range of industrial
fields. For example, they can be used for automobile
companents, tire components, rubber rollers, rolling,
pads and oil seals.
Having thus described in detail preferred
embodiments of the present invention, it is to be
understood that the invention defined by the appended
claims is not limited to particular details set forth in
this description as many variations thereof are possible
withaut departing from the spirit or scope of the present
invention.
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