Method of manufacturing composite material of clay mineral and rubber

The present invention provides a method of manufacturing a composite material made of a rubber and a clay mineral dispersed uniformly therein. The method proceeds exchanging inorganic ions of the clay mineral with organic onium ions to organize the clay mineral; mixing the organized clay mineral and a process oil and/or a plasticizer; and mixing the rubber material with the mixture of the organized clay mineral and the process oil and/or the plasticizer. Process oil and/or plasticizer are intercalated into the organized clay mineral. As a result, the interlayer distance of the clay mineral is enlarged. The most favorable mode of the present invention is for a barrier material against water, gas and the like and for a rubber material required for an improved mechanical property.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing a composite 
material comprising a rubber and a clay mineral, dispersed uniformly 
therein in a level of molecule. 
2. Description of the Related Art 
In order to improve the mechanical property of a rubber material, there 
have been made researches for mixing clay mineral with the rubber 
material. For example, in the method disclosed in Japanese Laid-Open 
Patent Publication No. 1-198645, the clay mineral is organized by using 
oligomer having onium ions introduced into the end or the side chains 
thereof, and the organized clay mineral is applied into the rubber 
material. 
In the method disclosed in Japanese Laid-Open Patent Publication No. 
60-4541, mica treated with ammonium chloride or choline chloride and 
process oil are mixed with the rubber material. 
The above-mentioned methods have the following problems: 
In the art disclosed in Japanese Laid-Open Patent Publication No. 1-198645, 
the oligomer having the onium ions introduced into the end or the side 
chains thereof cannot be prepared easily. Further, because the oligomer is 
intercalated in the clay mineral directly, there are cases in which the 
clay mineral swells in a low degree. 
In the art disclosed in Japanese Laid-Open Patent Publication No. 60-4541, 
the process oil and the mica are added to the rubber material. The mica 
treated with ammonium chloride or choline chloride is unmiscible with the 
process oil. Thus, the mica cannot be dispersed into the rubber material 
uniformly, with the increase in the amount of the process oil. 
SUMMARY OF THE INVENTION 
The present invention has been made to solve the above-described problems. 
It is accordingly an object of the present invention to provide a method 
of manufacturing a composite material comprising a rubber and a clay 
mineral, which allows the clay mineral to be dispersed uniformly into the 
rubber. 
In one aspect of the present invention, there is provided a method of 
manufacturing a composite material comprising a rubber and a clay mineral 
comprising the steps of exchanging an inorganic ion of a clay mineral with 
an organic onium ion to organize the clay mineral; mixing the organized 
clay mineral and a process oil and/or a plasticizer; and mixing a rubber 
material with the mixture of the organized clay mineral and the process 
oil and/or the plasticizer and dispersing the clay mineral uniformly in 
the rubber material. 
The clay mineral will swell in water in a high degree, but in an organic 
solvent in a very low degree . 
In order to solve this problem, according to the present invention, an 
inorganic ion such as a sodium ion and a lithium ion present between 
silicate layers of the clay mineral is exchanged with an organic onium ion 
to organize the clay mineral. The resultant clay mineral is hydrophobic. 
Consequently, the clay mineral can be swelled in the hydrophobic organic 
solvent. 
Then, process oil and/or plasticizer are intercalated into the organized 
clay mineral. As a result, the interlayer distance of the clay mineral is 
enlarged. Then, the mixture of the process oil and/or plasticizer and the 
clay mineral is mixed with a rubber material. Then, the mixture of the 
process oil and/or plasticizer, the clay mineral, and the rubber material 
is kneaded. Consequently, the clay mineral can be dispersed uniformly into 
the rubber material, with interlayer distance of the clay mineral, much 
larger than in the conventional method. 
The above phenomenon is explained as follows: 
That is, as shown in FIG. 1, a large number of spaces is formed between 
silicate layers of a clay mineral 7 when the clay mineral 7 is organized 
by exchanging the inorganic ions of the clay mineral with organic onium 
ions 6. This enables a process oil 1 and/or a plasticizer 1 to intercalate 
into the clay mineral 7. 
The process oil and the plasticizer have a high degree of affinity for the 
rubber material. Therefore, the rubber material intercalates into the clay 
mineral 7. As a result, the clay mineral 7 swells in a high degree. 
Accordingly, the clay mineral 7 is capable of dispersing uniformly into 
the rubber material. 
Because the clay mineral is allowed to be dispersed uniformly into the 
rubber material as described above, the mixture of the rubber material and 
the clay mineral prevents gas, water and the like from permeating 
therethrough in a high degree. Because rubber molecules of the composite 
material is restricted in moving in the vicinity of the silicate layer, 
mechanical properties of the composite material is improved. 
The composite material comprising the rubber and the clay mineral 
manufactured in accordance with the present invention can be applied to 
ordinary uses. Furthermore the most favorable mode of the present 
invention is for a barrier material against water, gas and the like and 
for a rubber material required for an improved mechanical property. 
This and other objects, features and advantages of the present invention 
will become apparent upon reading of the following detailed description 
and drawings.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described below in detail. 
Clay minerals having a great contact area with the process oil and/or the 
plasticizer can be preferably used because such clay minerals can be 
swelled in a great extent. 
Preferably, the ion-exchange capacity of positive ions of the clay mineral 
is 50 to 200 milligram equivalent/100 g. If the ion-exchange capacity of 
the positive ions is less than 50 milligram equivalent/100 g, the 
ion-exchange between the inorganic ions of the clay mineral and the 
organic onium ions is not accomplished sufficiently, which makes it 
difficult to swell the clay mineral. If the ion-exchange capacity of the 
positive ions is more than 200 milligram equivalent/100 g, the interlayers 
connection force in the clay mineral is great, which makes it difficult to 
swell the clay mineral. 
Preferably, smectite clay minerals (e.g., montmorillonite, saponite, 
hectolite, beidellite, stevensite, nontronite), vermiculite, halloysite or 
fluorine mica having swelling property are used as the clay mineral, 
regardless of whether these clay minerals are natural and synthetic. 
The clay mineral is organized by the ion-exchange between the inorganic ion 
of the clay mineral and the organic onium ion. 
Favorably, the number of carbon atoms of the organic onium ion is six or 
more. More favorably, the number of carbon atoms is 6 to 40. Most 
favorably, the number of carbon atoms is 6 to 30. The organic onium ion 
having the above-described number of carbon atoms, and the process oil 
and/or the plasticizer allow the clay mineral to swell in a high extent. 
Preferably, as the organic onium ion, hexyl ammonium ion, octyl ammonium 
ion, 2-ethylhexyl ammonium ion, dodecyl ammonium ion, octadecyl ammonium 
ion, dioctyl dimethyl ammonium ion, trioctyl ammonium ion, and distearyl 
dimethyl ammonium ion can be used. 
It is possible to mix oligomer containing a polar group with the clay 
mineral organized by the ion-exchange, treat the mixture by heating and 
the like, and then add the process oil and/or the plasticizer to the 
mixture to swell the clay mineral. As the oligomer containing the polar 
group, hydrogenated polybutadiene oligomer (manufactured by Mitsubishi 
Kagaku, trade name: Polytail H) and polyisoprene oligomer (LIR506 
manufactured by Kuraray) can be used. 
Then, the organized clay mineral is mixed with the process oil and/or the 
plasticizer. 
The process oil means petroleum oils to be used to improve the 
processability of rubber. 
The process oil is not limited to a specific one. 
Preferably, the process oil comprises one or more oils selected from 
paraffinic oils, naphthenic oils, and aromatic oils. These process oils 
allow the clay mineral to swell in a high degree. 
As the paraffinic oils, for example, PX-90, PW-90, PS-90, and PW-380 
manufactured by Idemitsu Kosan Co., Ltd. are used. As the naphthenic oils, 
for example, FLEX1400N manufactured by Fuji Kosan, SUNSEN459 manufactured 
by Nippon Sun Sekiyu Co., Ltd., NS-100 manufactured by Idemitsu Kosan Co., 
Ltd., and NM-280 manufactured by Idemitsu Kosan Co., Ltd. are used. As the 
aromatic oils, for example, AC-460 and AH-58 manufactured by Idemitsu 
Kosan Co., Ltd. are used. 
Of the process oils, the naphthenic oils are most favorable because they 
allow the clay mineral to swell in a high extent and are compatible with 
the rubber material. 
The plasticizer is not limited to a specific one. 
Preferably, the plasticizer comprises one or more compounds selected from 
ester compounds, phosphate ester compounds, and sulfonamide compounds. 
These plasticizers allow the clay mineral to swell in a high extent. 
As the ester compounds, for example, dibutyl phthalate, butyl benzyl 
phthalate, ethyl phthalyl ethyl glycolate, dibutyl sebacate, methyl 
acetylricinolate, di(-2-ethylhexyl)adipate, di(-2-ethylhexyl)azelate are 
used. As the phosphate ester compounds, tributyl phosphate and the like 
are used. As the sulfonamide compounds, N-butyl benzene sulfonamide and 
the like are used. 
Preferably, the rubber material comprises at least one rubber selected from 
natural rubber, isoprene rubber, chloroprene rubber, styrene rubber, 
nitrile rubber, ethylene-propylene rubber, butadiene rubber, 
styrene-butadiene rubber, butyl rubber, epichlorohydrin rubber, acrylic 
rubber, urethane rubber, fluorine rubber, and silicone rubber. 
Preferably, the mixing ratio of the organized clay mineral to the process 
oil and/or the plasticizer is 10:1 to 100. The mixing ratio allows the 
clay mineral to swell in a high degree. If the mixing ratio of the former 
to the latter is 10: less than 1, it may be difficult to swell the former 
in a high extent. If the mixing ratio of the former to the latter is 10: 
more than 100, there is a possibility that the property of rubber 
deteriorates. 
In exchanging the inorganic ion with the organic onium ion, the clay 
mineral is dispersed sufficiently in water. Then, the organic onium 
ion-dispersed water is added to the clay mineral-dispersed water to 
prepare the organized clay mineral. 
The organized clay mineral and the process oil and/or the plasticizer may 
be mixed with each other at the room temperature. But preferably, they may 
be mixed with each other at 150.degree. C. to swell the organized clay 
mineral efficiently. 
Then, the mixture of the swelled clay mineral and the rubber material is 
kneaded at the temperature ranging from the room temperature to 
150.degree. C. by means of a kneader such as a mixing roll, a Banbury 
mixer or a biaxial extruder to knead the mixture efficiently. The mixing 
roll is most preferable. 
In kneading the mixture, an appropriate amount of carbon black, vulcanizing 
agent, vulcanizing accelerator or the like may be added to the mixture. 
The kneaded mixture of the swelled clay mineral and the rubber material is 
subjected to vulcanizing molding such as press molding to mold the kneaded 
mixture into products. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
EMBODIMENT 1 
The method of manufacturing the composite material comprising the rubber 
and the clay mineral according to the embodiment 1 is described below. 
The outline of the method of manufacturing the composite material 
comprising the rubber and the clay mineral is described below. First, a 
clay mineral is organized by exchanging inorganic ions of the clay mineral 
with organic onium ions. Then, the organized clay mineral and a process 
oil for rubber are mixed with each other. Then, the mixture is mixed with 
a rubber material. In this manner, the composite material comprising the 
rubber and the clay mineral dispersed uniformly therein is obtained. 
As the clay mineral, montmorillonite of sodium type (produced in Yamagata 
Prefecture, ion-exchange capacity: 120 meq/100 g) was used. As the organic 
onium ion, distearyl dimethyl ammonium ion in which the number of carbon 
atoms was 38 was used. As the process oil, FLEX1400N (manufactured by Fuji 
Kosan Co., Ltd.) was used. As the rubber material, natural rubber was 
used. 
First, 20 g of montmorillonite was dispersed in 2,000 ml of water having a 
temperature of 80.degree. C. Then, 21 g of distearyl dimethyl ammonium 
chloride was dissolved in 1,500 ml of water having a temperature of 
80.degree. C. The montmorillonite-dispersed liquid and the distearyl 
dimethyl ammonium ion-dissolved liquid were mixed with each other quickly. 
The precipitate was washed twice with water having a temperature of 
80.degree. C. In this manner, the organized montmorillonite was obtained 
by the ion-exchange between the inorganic ions of the montmorillonite and 
the distearyl dimethyl ammonium ions. The organized montmorillonite is 
hereinafter referred to as DSDM-montmorillonite. 
The inorganic content of the resultant DSDM-montmorillonite was 54.2 wt. %. 
The interlayer distance of the DSDM-montmorillonite was measured by means 
of X-ray diffractometry to observe the swelling behavior of the 
montmorillonite. The interlayer distance thereof was 36.5 .ANG.. 
Then, 1 g of the DSDM-montmorillonite and 1 g of FLEX1400N serving as the 
process oil were mixed with each other at 80.degree. C. for 12 hours. As a 
result, a clay composite material was obtained. 
Measuring the interlayer distance of the DSDM-montmorillonite of the clay 
composite material by X-ray diffractometry, it was 46.5 .ANG.. The result 
indicates that the addition of the FLEX1400N (process oil) to the 
DSDM-montmorillonite increased the interlayer distance of the 
DSDM-montmorillonite in comparison with the one to which the process oil 
is not added. That is, the addition of the FLEX1400N to the 
DSDM-montmorillonite allowed the DSDM-montmorillonite to swell. This 
indicates that the FLEX1400N intercalated into the DSDM-montmorillonite. 
Then, 100 parts by weight of natural rubber, 3 parts by weight of zinc 
white, 2.25 parts by weight of sulfur, and 2 parts by weight of 
vulcanizing accelerator were added to 20 parts by weight of the clay 
composite material containing 10 parts by weight of the clay mineral. The 
mixture was kneaded by a roll until the components were mixed with each 
other sufficiently to obtain a kneaded mixture in accordance with ASTM D 
3184. 
The kneaded mixture was vulcanized at 160.degree. C. for 10 minutes and 
molded into a sheet having a thickness of 2 mm. Specimens of dumbbell No. 
3 were cut off from the sheet and subjected to tensile tests. The result 
was that the specimens had a tensile strength of 27.5 MPa. The observation 
of the sheet by means of a permeable type electron microscope revealed 
that silicate (montmorillonite) layers having a thickness of 1 nm were 
uniformly dispersed in the rubber. 
In a manner similar to the above, a sheet having a thickness of 0.5 mm was 
formed by molding and evaluated in the water permeability coefficient 
thereof. The result was 3.9.times.10.sup.-5 g.mm/mm.sup.2 per day. 
COMISON 1 
In comparison 1, a sheet made of a rubber material was manufactured without 
using the clay composite material as a material of the sheet. 
That is, a mixture of 100 parts by weight of natural rubber, 3 parts by 
weight of zinc white, 2.25 parts by weight of sulfur, and 2 parts by 
weight of vulcanizing accelerator was kneaded until the components were 
mixed with each other sufficiently to form the sheet, similarly to the 
embodiment 1. 
The tensile strength of the sheet was 22.7 MPa. The water permeability 
coefficient thereof was 6.5.times.10.sup.-5 g.mm/mm.sup.2 per day. 
EMBODIMENT 2 
In embodiment 2, a composite material comprising the rubber and the clay 
mineral was manufactured by using plasticizer. 
A clay mineral was organized by means of octadecyl ammonium ions. As the 
plasticizer, methyl acetylricinolate was used. As the rubber material, 
EPDM (ethylene-propylene-diene terpolymer, trade name: EP22) manufactured 
by Nippon Gosei Gomu Co., Ltd. was used. 
The method of manufacturing the composite material comprising the rubber 
and the clay mineral according to this embodiment is described below in 
detail. 
First 20 g of montmorillonite was dispersed in 2,000 ml of water having a 
temperature of 80.degree. C. Then, 8.8 g of octadecyl ammonium chloride 
was dissolved in 1,500 ml of water having a temperature of 80.degree. C. 
The montmorillonite-dispersed liquid and the octadecyl ammonium 
chloride-dissolved liquid were mixed with each other quickly. The 
precipitate was washed twice with water having a temperature of 80.degree. 
C. In this manner, the organized montmorillonite was obtained by the 
ion-exchange between the inorganic ions of the montmorillonite and the 
octadecyl ammonium ions. The organized montmorillonite is hereinafter 
referred to as C18-montmorillonite. 
The inorganic content of the resultant C18-montmorillonite was 69.5 wt. %. 
Measuring the interlayer distance of the C18-montmorillonite by means of 
X-ray diffractometry, it was 22.5 .ANG.. 
Then, 1 g of the C18-montmorillonite and 1 g of the methyl acetylricinolate 
serving as the plasticizer were mixed with each other at 80.degree. C. for 
four hours. As a result, a clay composite material was obtained. 
Measuring the interlayer distance of the C18-montmorillonite of the clay 
composite material by X-ray diffractometry, it was 50.7 .ANG.. The result 
indicates that the addition of the methyl acetylricinolate serving as the 
plasticizer to the C18-montmorillonite increased the interlayer distance 
of the C18-montmorillonite in comparison with the one to which the methyl 
acetylricinoleate is not added. That is, the addition of the methyl 
acetylricinolate to the C18-montmorillonite allowed the 
C18-montmorillonite to swell. This indicates that the methyl 
acetylricinolate intercalated into the C18-montmorillonite. 
Then, 100 parts by weight of EPDM, 20 parts by weight of carbon (Asahi 
Carbon #70), 3 parts by weight of zinc white, 1.5 parts by weight of 
sulfur, and 1 part by weight of vulcanizing accelerator were added to 20 
parts by weight of the clay composite material containing 5 parts by 
weight of the clay mineral. The mixture was kneaded by a roll until the 
components were mixed with each other uniformly to obtain a kneaded 
mixture in accordance with ASTM D 3568. 
The kneaded mixture was vulcanized at 160.degree. C. for 30 minutes and 
molded into a sheet having a thickness of 2 mm. Specimens of dumbbell No. 
3 were cut off from the sheet and subjected to tensile tests. The result 
was that the specimens had a tensile strength of 20 MPa. The observation 
of the sheet by means of a permeable type electron microscope revealed 
that silicate (montmorillonite) layers having a thickness of 1 nm were 
uniformly dispersed in the rubber. 
In a manner similar to the above, a sheet having a thickness of 0.5 mm was 
formed by molding and evaluated in the water permeability coefficient 
thereof. The result was 1.0.times.10.sup.-6 g.mm/mm.sup.2 per hour. 
COMISON 2 
In comparison 2, a sheet made of a rubber material was manufactured without 
using the clay composite material as a material of the sheet. 
That is, a mixture of 100 parts by weight of EPDM, 20 parts by weight of 
carbon, 3 parts by weight of zinc white, 1.5 parts by weight of sulfur, 
and 1 part by weight of vulcanizing accelerator was kneaded until the 
components were mixed with each other sufficiently to form the sheet, 
similarly to the embodiment 2. 
The tensile strength of the sheet was 12 MPa. The water permeability 
coefficient thereof was 1.2.times.10.sup.-6 g.mm/mm.sup.2 per day. 
While the invention has been described with reference to embodiments, it is 
to be understood that modification or variations may be easily made by a 
person of ordinary skill in the art without departing from the scope of 
the invention which is defined by the appended claims.