Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-11-22
2003-05-27
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S474000, C524S481000, C524S484000
Reexamination Certificate
active
06569936
ABSTRACT:
BACKGROUND OF THE INVENTION
1. (Technical Field to which the Invention Belongs)
The present invention relates to a rubber composition for a heat-resistant belt having excellent mechanical strength, heat resistance (including heat aging resistance), abrasion resistance, and roll processability, and more specifically to a conveyor belt having heat resistance and abrasion resistance for conveying a sintered product, a coke, a cement, a clinker, a quicklime, etc.
2. (Prior Art)
Since an ethylene/propylene copolymer rubber (EPM) and an ethylene/propylene/diene copolymer rubber (EPDM) do not have an unsaturated bond in the main chain, the above copolymers have better heat resistance and weatherbility than widely used diene-type rubbers and are used in many products such as automotive parts and industrial parts.
It is known that EPM and EPDM change their heat resistance (heat aging resistance) according to their compositions. It is known that as the ethylene content becomes higher, roll processability and low temperature flexibility become poorer. If the diene content is small, it is known that the amount of the vulcanizer should be increased, but obtained rubbers have excellent heat resistance (heat aging property).
It is known that as a method of vulcanization, vulcanization with an organic peroxide gives better heat resistance (heat aging property) than vulcanization with sulfur.
The conveyor belt for conveying a high temperature product such as a sintered product, a coke, a cement, a clinker, a quicklime, etc. should withstand the load of the conveyed product or the heat emitted from the conveyed product for long periods of time. Especially, the above conveyor belt should have heat resistance and abrasion resistance.
However, the heat-resistant belt obtained by crosslinking the conventional rubber composition for a heat-resistant belt has insufficient heat resistance (heat aging resistance) in conveying such high temperature product. Furthermore, since the conventional rubber composition. for a heat-resistant belt contains EPM as a base, it is still unsatisfactory because a large amount of a vulcanizer is required to obtain a high crosslinking density.
The object of the present invention is to solve the problem belonging to the conventional art, and to provide a rubber composition for a conveyor belt which belt is suitable for conveying a high temperature product and has excellent heat resistance and abrasion resistance.
Another object of the present invention is to provide a crosslinked product having a high crosslinking density and excellent heat resistance by using a smaller amount of a crosslinking agent, especially a conveyor belt.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a rubber composition for a conveyor belt comprising
(A) 100 parts by weight of an ethylene/an &agr;-olefin containing 3 to 20 carbon atoms/a conjugated polyene copolymer rubber having a diene unit derived from a non-conjugated diene of general formula (1)
wherein n is an integer of 0 to 10, R
1
represents a hydrogen atom or an alkyl group containing 1 to 10 carbon atoms, and R
2
represents a hydrogen atom or an alkyl group containing 1 to 5 carbon atoms,
or a non-conjugated diene of general formula (2)
R
3
represents a hydrogen atom or an alkyl group containing 1 to 10 carbon atoms,
B) 0.5 to 15 parts by weight of an organic peroxide,
C) 30 to 80 parts by weight of carbon black and
(D) 5 to 25 parts by weight of a softening agent.
In the above-mentioned rubber composition, the following embodiments 1 to 3 are preferred.
1. In the ethylene/&agr;-olefin containing 3 to 20 carbon atoms
on-conjugated polyene copolymer rubber (A), the &agr;-olefin is propylene, and the ethylene/propylene mole ratio is from 50/50 to 72/28.
2. In the ethylene/&agr;-olefin containing 3 to 20 carbon atoms
on-conjugated polyene copolymer rubber (A), the &agr;-olefin contains 4 to 20 carbon atoms, and the ethylene/&agr;-olefin mole ratio is from 60/40 to 82/18.
3. The ethylene/&agr;-olefin containing 3 to 20 carbon atoms
on-conjugated polyene copolymer rubber (A) has (i) a non-conjugated polyene content of 0.2 to 4% by weight, and (ii) an intrinsic viscosity (&eegr;), measured in decalin at 135° C., of 1.5 to 3 dl/g.
According to the present invention, a conveyor belt obtained by crosslinking the above rubber composition is also provided.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The rubber composition of the present invention for a conveyor belt is characterized by comprising (A) 100 parts by weight of an ethylene/&agr;-olefin containing 3 to 20 carbon atoms
on-conjugated polyene containing a diene unit derived from the non-conjugated diene of the above general formula (1) or (2), (B) 0.5 to 15 parts by weight of an organic peroxide, (C) 30 to 80 parts by weight of carbon black and (D) 5 to 25 parts by weight of a softening agent.
The non-conjugated diene in the copolymer rubber (A) used in the present invention is limited to that comprising a norbornene compound having a chemical structure of the above general formula (1) or (2) for the following reasons.
Cyclic non-conjugated polyenes include various types, for example, a type having a norbornene skeleton and a type having a dicyclopentadiene skeleton. If 5-ethylidene-2-norbornene (ENB) or dicyclopentadiene (DCPD) is used, when the non-conjugated polyene content of the copolymers is within the range of the present invention, it is difficult to increase the heat resistance (heat aging resistance) of the resulting crosslinked product.
On the other hand, if 5-vinyl-2-norbornene (VNB) or 5-(1-butenyl)-2-norbornene (BNB) represented by the following chemical structure:
is used, the use of a small amount of crosslinking agent enables the crosslinking to proceed effectively when the copolymer is crosslinked with a peroxide. In addition, the resulting crosslinked product has markedly good heat resistance (heat aging resistance) as well as excellent abrasion resistance (see Examples given below).
The following thought will be derived from the above fact.
When the non-conjugated polyene is copolymerized, one ethylenically unsaturated bond participates in copolymerization, and the remaining ethylenically unsaturated bond remain in the copolymer chains. In the case of cyclic non-conjugated polyenes represented by the general formula (1) and the general formula (2), the ethylenically unsaturated bonds outside the ring remain in greater amounts although detailed reasons are not known. Generally, ethylenically unsaturated bonds existing outside the ring have a larger degree of freedom than the ethylenically unsaturated bonds existing in the ring, and have a higher reactivity. Hence, in the copolymer rubber (A) of the present invention, by using a smaller amount of a crosslinking agent, crosslinking takes place effectively.
Since in a copolymer rubber prepared from a conjugated polyene, an ethylenically unsaturated bond remaining after vulcanization exists in the main chain, the unsaturated bonding in the main chain will adversely affect the heat resistance (heat aging resistance). On the other hand, since the copolymer rubber (A) of the present invention uses a cyclic non-conjugated diene represented by the general formula (1) or (2), the unsaturated bond which did not participate in the polymerization reaction but remained in the copolymer existed outside of the main chain, and after crosslinking of the coplymer rubber (A), the unsaturated bond still existed outside the main chain. Accordingly, the copolymer rubber (A) is considered to have excellent heat resistance (heat aging resistance).
The other components of the present invention, namely the organic peroxide (B), the carbon black (C) and the softening agent (D), are necessary components for obtaining the crosslinked product as a conveyor belt.
The rubber composition of the present invention can be subjected to a crosslinking reaction effectively in comparison with the amount of the organic peroxide to achieve a high crosslinking density.
In the rubber composi
Hakuta Takashi
Kawasaki Masaaki
Nakahama Hidenari
Tojo Tetsuo
Burns Doane , Swecker, Mathis LLP
Cain Edward J.
Mitsui Chemicals Inc.
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