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
2000-10-23
2002-02-05
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...
C525S189000, C525S535000, C525S536000, C528S374000, C528S376000
Reexamination Certificate
active
06344510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber vulcanization agent and a rubber composition containing the same. More specifically, it relates to a rubber vulcanization agent capable of suppressing scorching at the time of processing, of improving the heat stability of the vulcanized rubber, and of facilitating production and a rubber composition containing the same.
2. Description of the Related Art
When the generally widely used sulfur is used as a vulcanization agent for a vulcanizable rubber, a polysulfide bond is mainly formed as the cross-linking structure between carbon chains of the rubber. A bond between sulfurs in polysulfide bonds is susceptible to heat and is easily cut, and therefore, a vulcanized rubber containing a large number of polysulfide cross-linking structures inevitably becomes inferior in the heat resistance. Therefore, as the cross-linking form of the vulcanized rubber, vulcanization agents and vulcanization accelerators for mainly forming monosulfide bonds and/or disulfide bonds have been actively studied. However, most of the vulcanization agents which have been reported to achieve the above object in the past have generated carcinogenic nitroso amines during vulcanization and, therefore, have been problematic in the safety. Further, while the resistance to heat aging of the vulcanized rubber has been improved to a certain extent by the use of the vulcanization accelerator, there has been the problems that the resistance to fatigue aging and resistance to cracking by bending is decreased.
As a rubber vulcanization agent for improving the heat stability of the vulcanized rubber without forming nitroso amines during the vulcanization, a polysulfide polymer containing a large amount of sulfur in the molecular chain has been reported (for example, see (1) Gomu Kogyo Binran (Rubber Industry Handbook, New Edition, p. 167, ed. by Society of Rubber Industry Japan Rubber (1973) and (2) Gosei Gomu Handbukku (Synthetic Rubber Handbook), p. 237, ed. by Shu Kanbara, Kyoichi Kawasaki, Magoichi Kitajima, and Masayuki Furuya (1960)). Further, since a polysulfide polymer is liquid, there is no worry of bloom after vulcanization unlike with vulcanization by sulfur, when used as a vulcanization agent (Japanese Unexamined Patent Publication (Kokai) No. 57-170939). However, a conventional polysulfide polymer is volatile and has a strong odor, and therefore, a vulcanized rubber using this as a vulcanization agent gives a strong odor and is not suitable for practical use (U.S. Pat. No. 2,235,621).
On the other hand, even among polysulfide polymers, since what has been developed as sealing materials have been nonvolatile substances with little odor, the use thereof as a vulcanization agent mixing well with rubber substances is possible. However, when the above liquid polysulfide polymer per se is used as a vulcanization agent, since the end group structure of the polymer is a thiol group, so-called “scorching” where the vulcanization proceeds early at the time of processing easily occurs. Further, since the average number of sulfur bonds in the repeating units is not more than 2, there have been the problems such that a long vulcanization time is required, for example. Thus, to prevent scorching during processing or shorten the vulcanization time, the technique has been adopted of capping the end thiol group in the polysulfide polymer, then increasing the number of sulfur bonds in the repeating units (Japanese Unexamined Patent Publication (Kokai) No. 10-120788). If a reaction with sulfur is caused to increase the number of sulfur bonds in the main chain, without capping the end thiol group in the thiol-terminated polysulfide polymer, the polymer is an unstable substance which generates hydrogen sulfide in the air and is changed to a highly sticky substance. Therefore, the increase in the number of sulfur bonds in a polysulfide polymer main chain should be carried out after capping the end thiol group. That is, the important process in producing a rubber vulcanization polysulfide polymer is the process for producing a polysulfide polymer by capping the end thiol group of a thiol group terminated polysulfide polymer.
The conventional methods of capping a thiol group of a thiol group terminated polysulfide polymer include the method of reacting a halogenated alkyl compound with a thiol group terminated polysulfide polymer and trapping the halogenated hydrogen produced by an amine compound and the method of capping the end with a halogenated alkyl simultaneously with forming the thiol group terminated polysulfide polymer. In both techniques, amine salts or sodium salts are formed as by-products and the complicated operations of filtering out these salt compounds and washing becomes necessary. Therefore, a polysulfide polymer having a capped end thiol group is capable of producing more simply had been sought.
Further, Japanese Unexamined Patent Publication (Kokai) No. 11-322931 discloses polysulfides having various substituents at the end group thereof. Among those, polysulfides having a benzothiazole group, a thiocarbamyl group, etc. which have vulcanization accelerating effects. In fact, these polar groups can accelerate the vulcanization speed, but the scorch time is shortened and therefore causes big problems in the viewpoint of a practical use thereof.
As mentioned above, the prior polysulfide polymers are produced so as to terminate the end thiol group which causes the scorch and also so as to shorten the vulcanization time. However, when the prior polysulfide polymers having the polar groups cannot provide practically sufficient unvulcanized rubber characteristics and also the properties of the vulcanized rubber are not sufficient.
SUMMARY OF THE INVENTION
Accordingly, the objects of the present invention are to maintain the sufficient unvulcanized characteristics (i.e., scorch and vulcanization time) and to easily provide a rubber vulcanization agent capable of improving the properties and the vulcanized rubber and the heat stability thereof.
In accordance with the present invention, there is provided a rubber vulcanization agent comprising a polysulfide polymer having the formula (I):
R—S&Parenopenst;Y—S
x
&Parenclosest;
n
Y—S—R (I)
wherein Y indicates an alkylene group which may include a hetero atom, n is an integer of 1 to 100, x is more than 2 but not more than 6, and R is a residue obtained by reacting a polysulfide polymer having the formula (II):
HS&Parenopenst;Y—S
x
&Parenclosest;
n
Y—SH (II)
wherein Y, n and x are as defined above
with (i) an unsaturated alicyclic compound or (ii) a compound having the structure (III) or (IV)
R
2
OOC—CH═CH—COOR
2
(IV)
wherein R
1
indicates a hydrogen atom or a methyl group and R
2
indicates a C
1
to C
18
hydrocarbon group having no polar groups, so as to cap the end thiol group.
In accordance with the present invention, there is also provided a rubber vulcanization agent having the average number of sulfur bonds of 3 to 5.
In accordance with the present invention, there is further provided a rubber vulcanization agent wherein R
2
in the formula (III) or (IV) indicates a C
3
to C
8
alkyl group.
In accordance with the present invention, there is further provided a rubber composition comprising 0.1 to 30 parts by weight of a rubber vulcanization agent, based upon 100 parts by weight of a diene rubber.
In accordance with the present invention, there is still further provided a rubber composition further comprising a sulfur at a weight ratio of the rubber vulcanization agent/the sulfur of at least 0.5, provided that the total amount of the rubber vulcanization and the sulfur is 0.5 to 20 parts by weight based upon 100 parts by weight of a diene rubber.
DESCRIPTION OF PREFERRED EMBODIMENTS
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
The singular forms “a”, “an” and “the” include plural referents unless the context clearly di
Ishikawa Kazunori
Maruyama Tsukasa
Arent Fox Kintner & Plotkin & Kahn, PLLC
Cain Edward J.
The Yokohama Rubber Co. Ltd.
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