Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From sulfur-containing reactant
Reexamination Certificate
2000-06-16
2002-02-05
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From sulfur-containing reactant
C528S378000, C528S380000, C252S406000
Reexamination Certificate
active
06344537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber vulcanizing agent and a rubber composition containing the same. More specifically, it relates to a rubber vulcanizing agent capable of preventing decreases in the physical properties of a vulcanized rubber after aging, of suppressing scorching due to premature vulcanization or reversion and of improving reversion resistance and aging resistance and also relates to a rubber composition containing the same.
2. Description of the Related Art
In the past, there has been the problem that since the bond strength of polysulfide bonds produced during the cross-linking are weak, the bonds break and reversion occurs during vulcanization of rubber or even after vulcanization, the polysulfide bonds in the rubber easily break, the physical properties of the rubber after aging, such as the strength at break or elongation at break, ended up falling. Further, it is known that a vulcanizing agent having a thiol group (SH—) exhibits a high reactivity with a diene rubber. The vulcanization of rubber can be speeded up, but then the problem arises that the reactivity becomes conversely too high and vulcanization ends up occurring during the kneading of the rubber, i.e., so-called scorching ends up occurs.
SUMMARY OF THE INVENTION
Accordingly, the objects of the present invention are to eliminate the above-mentioned problems in the prior art and to provide a rubber vulcanizing agent capable of preventing a decline in the physical properties of the vulcanized rubber after aging and of suppressing scorching due to premature vulcanization or reversion and also to a rubber composition containing the same.
Another object of the present invention is to provide a vulcanizing agent for rubber capable of improving reversion resistance and aging resistance and a rubber composition containing the same.
Other objects and advantages of the present invention will be apparent from the following description.
In accordance with the present invention, there is provided a rubber vulcanizing agent comprising a compound having at least two thiirane groups in one molecule thereof.
In accordance with the present invention, there is also provided a rubber composition containing a compound having at least two thiirane groups in one molecule thereof and a thiirane ring-opening agent.
In accordance with the present invention, there is still further provided a rubber composition comprising 100 parts by weight of a rubber, 0.1 to 30 parts by weight of a compound having the thiirane group and 0.1 to 30 parts by weight of the thiirane ring-opening agent.
In accordance with the present invention, there is still further provided a rubber composition comprising 100 parts by weight of a rubber, 0.1 to 30 parts by weight of a compound having at least two thiirane groups in one molecule thereof, 0.1 to 30 parts by weight of a sulfenamide type vulcanization accelerator and/or a sulfenimide type vulcanization accelerator and 0.01 to 5 parts by weight of sulfur.
In accordance with the present invention, there is still further provided a rubber composition further comprising 0.5 parts by weight or less of an organic fatty acid and/or 0.5 to 30 parts by weight of a metal oxide, both based upon 100 parts by weight of the rubber, in the above-mentioned rubber compositions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rubber vulcanizing agent according to the present invention is a compound having two or more thiirane groups (i.e., episulfide groups) shown in the following formula in one molecule (hereinafter referred as a thiirane group-containing compound). A thiirane group is a group having the following structure:
The present inventors found that, by blending a compound having two or more thiirane groups in one molecule thereof and a thiurane ring-opening agent such as a nucleophilic reagent, electrophilic reagent, or a compound having these functional groups protected into a rubber, the thiirane group-containing compound acts as a vulcanizing agent. That is, upon heating, the thiirane group-containing compound and thiirane ring-opening agent are reacted with each other to generate a thiolate ion or radical, whereby the rubber is cross-linked. In this way, a thiirane group-containing compound is a latent vulcanizing agent which does not act as a vulcanizing agent before heating and causes cross-linking by a reaction of a thiolate ion or radical produced from the thiirane group upon heating with a rubber polymer. Therefore, a vulcanizing agent capable of suppressesing scorching before vulcanization is obtained by the use of the thiirane group-containing compound. The vulcanizing agent thus formed provides a fast vulcanization rate during vulcanization. Further, the cross-linking bonds produced due to the vulcanization are monosulfide bonds. Unlike polysulfide bonds, these are not easily broken, and therefore, it is also possible to suppress reversion and decreases in the physical properties of the rubber such as strength at break and elongation at break of the vulcanized rubber after aging.
The present inventors also found that the modulus is increased by adding sulfur and the reaction between the thiirane group and the ring-opening agent is accelerated with a metal oxide. Furthermore, since an organic acid such as stearic acid is liable to inhibit the reaction between the thiirane group and the thiirane ring-opening agent, the compounding amount thereof should be preferably minimized or should not be used.
To obtain the thiirane group-containing compound used in the present invention, for example, it is possible to substitute all or part of the oxirane rings of the epoxy compound having at least two oxirane rings shown in the following formula in one molecule thereof with thiirane rings, whereby the compound is converted to the desired compound having at least two thiirane rings in one molecule thereof.
The epoxy compound used for obtaining the thiirane group-containing compound according to the present invention is, for example, a compound having the following formula (a), (b), (d), (e), or (f) where the substituent groups Y are all oxirane rings or a compound having the following formula (c) where Z is an oxygen atom. The n is 0 or a number of more than 0.
Further, these epoxy compounds may be compounds in which the hydrogen atoms or other groups in the molecule are substituted with halogen atoms. For example, they may be compounds having the following formula (g):
wherein Hal indicates a halogen atom.
Example of the halogen atom are bromine, chlorine, flourine, etc.
In the present invention, the thiirane group-containing compound is a compound of the above formula (a), (b), (c), (d), (e), (f), or (g) where at least two of Y are thiirane rings, a compound where the Y's other than the thiirane rings are oxirane rings, or a compound where at least one of Z is S and the other Z's are 0.
The specific examples of the thiirane group-containing compound are those shown by the following formulas. These include compounds having the following formulas where at least two of Y are thiirane rings and the Y's other than the thiirane rings are oxirane rings or compounds where at least one of Z is S and the other Z's are 0. Further, n is a number of 0 or more.
The thiirane group-containing compound can be produced by the method of reacting an epoxy compound and potassium thiocyanate (KSCN), thiourea, etc. in a polar solvent with vigorous stirring.
As the polar solvent, for example, methanol, ethanol, acetone, water, or mixed solvents of the same may be used. Further, to obtain a compound (A) with a substitution ratio of 100%, that is, a ratio of content of oxirane rings/thiirane rings of 0/100, it is preferable to use acetone as the solvent.
The reaction can usually be performed in the temperature range of 10 to 35° C., for example, room temperature, for a reaction time of 10 to 40 hours or so, for example, about 20 hours. Further, the atmosphere of the reaction may be air or a nitrogen or other inert gas atmosphere. By raising the
Chino Keisuke
Onoi Hidekazu
Arent Fox Kintner & Plotkin & Kahn, PLLC
Sanders Kriellion A.
The Yokohama Rubber Co. Ltd.
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