Note: Descriptions are shown in the official language in which they were submitted.
PROCESS FOR PRODUCING ELASTIC GRAPHITE MOLDED PRODUCTS
TEC~NICAL FIELD
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This invention relates to a process for molding a
carbonaceous material and, more particularly, to a
process for producing an elastic graphite molded product
having light weight and excellent elasticity.
BACKGROUND_ART
In general, molded products containing a
carbonaceous material as an a filler have been produced
by adding a binder to a carbonaceous powder such as
graphite or coker kneading them, molding the knead,
curing it, optionally firing, and graphitizing the cured
product. Required characteristics vary depending upon
- 15 the purpose or use of the produced carbonaceous molded
products, and therefore the molded products have been
produced by using many molding processes and many
binders. Many reports and proposals thereEor are found
in literatures. (e.g., "Revised Introduction to Carbon
~aterial", p.l35, Carbon Material Association; Mizushima
and Okada, "Carbon Material" p.55, Kyoritsu Shuppan;
Ishikawa and Nagaoki, "New Carbon Engineering", p.173,
Kindai Hensyusha)
These conventional carbonaceous molded products have
characteristics inherent to carbonaceous materials, i.e.,
light weight, high strength, high young's modulus,
conduction property, corrosion resistance, heat
resistance and sliding property. While such carbonaceous
molded products having high young modulus are
3Q advantageous when rigidity is required, they lack
flexibility because they have no yield point. From the
standpoint of sa~ety faster, carbonaceous molded products
having much higher strength have been required.
We have proposed an elastic graphite structure
having excellent elasticity characteristics as
carbonaceous materials (Japanese Patent Application No~
164808/1987). This elastic graphite structure ~ se is
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of light weight and exhibits good elasticity. The
elastic graphite structure has excellent characteristics
which could not be obtained by the conventional
carbonaceous materials.
However, in the conventional molding technique, it
is not necessarily easy to mold the carbonaceous
materials into a specific molded product in such a state
that characteristics inherent__to starting carbonaceous
materials are utilized, even if the carbonaceous
materials Per se have good material characteristics.
Molding processes conformed to material characteristics
have not established yet so far.
DISCLOSURE OF INVENTION
The present invention has been accomplished in view
of the foregoing. An object of the present invention is
to provide a process for producing an elastic molded
product having light weight and excellent compressive
elasticity.
In order to achieve the object described above, a
process for producing an elastic graphi~e molded product
according to the present invention comprises the steps of
mixing elastic graphite particles as fillers with a
binder resin, thereby to adhere the binder resin to the
surface of the elastic graphite particles as in the form
of a spider web, and thereafter molding the mixture.
BRIEF DESCRIPTION OF DRAWINGS
FIG.l is a microphotograph sho~ing the structure of
a texture of an elastic graphite molded product obtained
by Example 1 of the present invention; and
FIG.2 is a microphotograph showing the stxucture of
a texture of a molded product obtained by Comparative
Example.
BEST MODE FOR CARRYING OUT THE INVENTION
The feature of the present invention resides in a
process for molding elastic graphite particles without
impairing their elasticity. The outline of the present
process is described hereinafter.
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Elastic graphite structure for use herein as the
startiny material include those known in the art.
Particularly preferred elastic graphite structures which
can be used include those obtained by treating
carbonaceous mesophases prepared by heat treatment of
pitches such as petroleum pitches and coal pitches and/or
green coke with nitric acid or a mixture of nitric and
sulfuric acids, heat treating_ the treated mass and
graphitizing the same; and those obtained by treating the
carbonaceous mesophares and/or green coke with nitric
acid or a mixture of nitric and sulfuric acids,
contacting the treated mass with a basic aqueous solution
to solubilize it, adding an acid solution to precipitate
the carbonaceous component, heat treating the
carbonaceous component and graphitizing it. Details of a
process for producing such graphite structures having
excellent elasticity characteristic are described in, for
example, Japanese Patent Application No. 164808/1987.
In the present invention, particulates oE the
elastic graphite structures as described above are used
as the starting materials. It is preferred that the
particle size of graphite particles of the order of 10 ~m
to 1 mm Erom the standpoint of mo]dability~
The resin used as a binder in the present invention
is preferably a dispersed resin wherein thermosetting
resin or thermoplastic resin is dispersed in a suitable
dispersion medium. The reasons why the dispersed resin
is used are as follows.
Heretofore, in the production of molded products
such as carbon products, binders such as coal tar
pitches, phenol resins and furan resins have been used.
These melt at about 100C, and the molten binders are
kneaded with a filler, and the knead is cured, molded,
fired and/or graphitized to obtain a molded product.
The inner bulkhead of the elastic graphite particles
described above has a spongy microstructure divided by
thin carbon walls. It is thought that this is because
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characteristics such as light weight and excellent
compressive elasticity are developed. Accordingly, in
the molded products produced by a molding process using
the prior art binder, molten binder penetrates into the
interior of the elastic graphite particles to impair the
elasticity o the elastic graphite structure. We have
carried out studies while paying attention to the
drawbacks described above. We_have now found that the
use of a dispersed resin as a binder causes the bonding
of particles in such a state that the resin surrounds the
elastic graphite particles and therefore resin dues not
penetrate into the interior of a spongy structure of the
elastic graphite particles whereby a good molded product
can be obtained without impairing structure and elastic
characteristic.
It has turned out that, according to our finding,
the dispersed resin having a low viscosity is dispersed
in the dispersion medium in the form of spheres and
therefore the resin is stretched ln the form of a yarn by
mixing and kneading such a resin with the elastic
graphite particle filler, whereby there is developed such
a state the resin adheres to and entangles with the
surrounding of the elastic graphite partic]es in the form
of a spider web. Because the binder resin adhered to and
entanyled with the elastic graphite particles in the form
of a yarn or spider web acts as a binder by adhering so
that the binder resin covers onto only the surface of the
graphite particles without penetrating into the interior
of the spongy structure of the graphite particles,
elastic characteristic inherent to the elastic graphite
particles ~ se as the fillers is not reduced.
The resins which constitute the dispersed resins as
the binder as described above can be suitably selected
depending upon the type of desired molded products.
Particularly preferred resins are tetrafluoroethylene
resins, epoxy resinst phenols resins, unsaturated
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polyester resins in that they improve molding
characteristic.
Materials such as water, alcohols and inorganic
acids are preferably used as the dispersion medium.
In the present invention, a desirable binder is one
obtained by adding from 0.1 to 4.0 parts by weight,
preferably from 0.2 to 1.5 parts by weight of the resin
to 1 part by weight of the dispersion medium described
above.
In the present invention, a dispersed resin solution
is added to and thoroughly mixed with the elastic
graphite particle described above so that the amount of
the resin is ~rom 0.1 to 4.5 parts by weight,
particularly preferably from 0.5 to 4.5 parts by weight
based on 1 part by weight of the elastic graphite
particle. If the amount of the resin exceeds 4.5 parts
by weight based on 1 part by weight of the elastic
graphite particle, the bulk density of the resulting
molded product tends to be increased alld thus such an
amount is undesirable.
In the mixing step, an appropriate amount o water
can be added so that the mixture becomes highly viscous
just like a rice cake. Water may be previously added to
the binder resin solution.
When the amount of the binder excessively large to
prepare a mudd~ mi~ture, moisture can be suitabl~ removed
by drying after mixing.
In the present invention, there can be utilized a
mixing method whexein shear stress is applied in the
mixing step. The development o~ such a microstructure
that the binder resin described above surrounds the
graphite particles can be much accelerated by carrying
out this shear mixing. While such a mixing step can be
carried out by means of various apparatuses such as
static mixers, and ~enschel mixers, pulverizers such as
ball mills and kneaders can be used.
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In the present invention, the rice cake-like mixture
obtained by mixing or kneading as described above is
charged into a specific mold as such. ~lternatively, the
rice cake-like mixture is dried and the resulting powder
is charged into a specific mold. The mixture is molded
by conventional methods such as pressure molding. After
molding, the curing of the binder resin may be carried
out by heating or the like.
The molded products thus obtained have light weight
and excellent elasticity which cannot be obtained
conventional carbonaceous molded products. Of other
properties inherent to the carbonaceous materials,
properties such as heat resistance and corrosion
resistance are influenced by the properties of the binder
resin and therefore these properties are inferior to
those of the carbon products. However, properties such
as electroconductivity and sliding property are
maintained because the elastic graphite particle and the
resin are uniformly mixed.
The present invention is illustrated in more detail
by Examples.
EXAMPLE 1
Green coke obtained by delayed coking process was
pulveriæed to an average particle size of 10 ~mO The
elemental composition of the green coke was 95.1 wt% of
carbon, 3.1 wt% of hydrogen and 0.6 wt% of nitrogen.
Five grams of the green coke was added in small portions
to 100 ml of a mixed acid consisting 96% concentrated
sulfuric acid and 70% concentrated nitric acid in a
volumetric ratio of 50:50 in a Erlenmeyer flask of 300 ml
in volume. After the total amount of the green colce had
been added, the flask was heated for 4 hours in an oil
bath previously heated to 80C. Then, the product was
filtered out through a glass filter (No. 4), sufficiently
washed with water, and dried. The yield was 140% by
weight. The product was dispersed in water, and 2.5N -
NaOH was added with stirring until the pH was 10. The
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dispersion was then filtered through a glass filter (No.
4) and lN-HNO3 was added to the filtrate until the pH
value was below 1 (the precipitate is hereinafter
referred to as an a~uamesophase). The aquamesophase was
filtered through a glass filter (No. 4) and dried. The
yield of the aquamesophase was 133% by weight based on
the green coke. This aquamesophase was placed in a
cylindrical glass vessel of 500 ml, and then it was in
turn held for 30 minutes in a salt bath previously heated
to 300C. Next, the product was heated to 2,800C at a
heating rate of 400C/hr in an argon gas flow and then
held at that temperature for 30 minutes for
graphitization. The yields were 85 and 52% by weight
based on the green coke, respectively.
The compressive elasticity (compressibility and
recovery ratio) of the graphitized sample (the elastic
graphite structure) was measured in the following manner.
In a cylindrical vessel of 10 mm inner diameter was
charged with 0.5 g of the sample pulverized to no more
than 0.33mm on which a load of 1 kg/cm2 was applied from
above. The sample's volume at this point was used as the
base volume (ho)~ Then, a predetermined load was applied
and the volume was measured. This volume was designated
as hl. Then, the load was removed and the volume h2 was
measured. The compressibility and recovery ratio were
calculated by the following equations:
compressibilitY (%) = {(ho~hl)/ho}Xl
Recovery ratio (%) = {~h2-hl)/(ho-hl)}xlO0
Furthermore, the packing density was calculated ~rom
ho according to the following formula;
Packing density (g/cm3) = sample weight . ho
The results are shown in Table 1.
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T~BLE l
Elastic Packing Density Load Compressi- Recovery
Graphite(l kg/cm2) [kg/cm2] bility Ratio
Structure[g/cm3] [%] [%]
0.23 -
5_0 ~4 88
5000 91 84
One gram of a tetrafluoroethylene resin
(manufactured by Mitsui/Dupont Fluorochemical, K,K. under
the trade name 30 - J; resin content of 60% by weight)
and 2 grams of water were added to 1 gram of the elastic
~raphite structure pulverized to no more than 45 ~m, and
the whole was well mixed by a glass rod. When the whole
became highly viscous just like a rice cake, it was
transferred to a 25 x 50 mm mold and pressure molded
under a pressure of 40 Icg/cm2. It was held for 30
minutes at 100 - 120C, and moisture was evaporated.
Thereafter, treatment was carried out for one hour at
350C to cure to obtain a molded product. The dimension
of this molded product was 25 x 50 x 3 mm. The
compressive elasticity of the molded product was
measured. Experiments were carried out by varying the
composition of the elastic graphite structure, resin and
water. The results (No~ l - 8) are shown in Table 2.
FIG. l is a microphotograph of a texture of the
molded product obtained. As can be seen from FIG.l, the
binder resin entangles with the surface of the graphite
particles in the form of a yarn or spider web.
EX~MPLE 2
One gram of the same elastic graphite structure as
used in Example l and 3 grams of the same resin as used
in Example l were placed in a beaker and well mixed by a
glass rod. The mixture was placed in a drier at 100 -
120C Eor 2 hours, dried and thereafter pressure molded
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120C for 2 hours, dried and thereafter pressure molded
under a pressure of 40 kg/cm2. This was treated for one
hour at 350C to cure to obtain a molded product. The
dimension of this molded product was 25 x 50 x 3 mm. The
compressive elasticity of the resulting molded product
was measured. The results (No. 9) are shown in Table 2.
No. 10 is an experimental example wherein only the
resin was molded. _
COMPARP.TIVE EXAMPLE
One gram of the same elastic graphite structure as
used in Example 1 and 3 grams of the same resin as used
in Example 1 were placed in a beaker, transferred to a
mold without any mixing step and pressure molded under a
pressure of 40 kg/cm2. The treated material was treated
for one hour at 350C to cure it to obtain a molded
product (No.ll). The dimension of the molded product was
25 x 50 x 3 mm, and its bulk density was 1.07 g/cm3.
~owever, man~ cracks occurred in portions of the surface
of the molded product.
FIG~ 2 is a microphotograph of a texture of the
resulting mo]ded product. It turned out that the binder
resin was unevenly dispersed in the surface of the
graphite particles in the form of a lump.
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As can be seen from the results of Examples
described above, according to the present invention,
molding can be carried out while utilizing elastic
characteristic inherent to the graphite structure which
is a molding material. Accordingly, elastic graphite
molded products having light weight and excellent
elasticity can be obtained.
IN~USTRIAL APPLICABILITY
The elastic graphite molded products obtained by the
present invention have characteristics such as
electroconductivity and sliding property inherent to
graphite materials; microporous structure which cannot be
obtained in the prior art; and excellent compressive
elasticity. Accordingly, the elastic graphite molded
proaucts can be utilized in many uses utilizing these
features, such as gaskets, packings, shock resistance-
improving materials, brake shoes, friction boards, wave-
absorbing materials, catalyst carriers, and heat
insulating materials.
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