Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-03-04
2001-10-09
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332500, C525S332600, C525S391000, C525S333100, C525S333300, C525S333500, C525S341000, C525S345000, C525S354000
Reexamination Certificate
active
06300421
ABSTRACT:
FIELD
The invention relates to EPDM and EPR-based rubber compositions which are vulcanized with peroxide together with a specified combination of sulfur and acrylate co-agents. The invention further relates to articles having at least one component thereof.
BACKGROUND
Various industrial products are prepared which have at least one component as a rubber composition which is based upon an EPDM or EPR rubber.
It is sometimes desired to improve the cure efficiency for peroxide curing of an EPDM-based, or EPR-based rubber composition, namely providing a faster cure system for a reduction in cure time, commensurate with a suitable processing safety, or processing without generating scorched rubber.
In practice, EPDM (ethylene/propylene
on-conjugated diene terpolymer elastomers) based rubber compositions, as well as rubbery ethylene/propylene polymer (EPR) based rubber compositions, are often cured (vulcanized) with peroxide curatives and sometimes with a combination of peroxide and a co-agent such as, for example, sulfur or acrylate co-agent.
However, it is not seen where a combination of sulfur and acrylate co-agents have contemplated for peroxide curing of EPDM or EPR elastomers.
It is to be appreciated that peroxide curatives generate free radicals for the EPDM or EPR, as the case may be, curing process which serve to crosslink the EPDM or EPR with carbon-to-carbon crosslinks. Some peroxide curatives promote faster curing of EPDM and EPR rubbers than others.
For peroxide curing of EPDM and EPR rubbers, free radicals formed during its peroxide-based curing is typically accompanied by a small amount of side reactions such as, for example, beta scission of a portion of the rubber itself which reduces the molecular weight of the polymer, and tends to degrade physical properties.
In order to minimize, or retard, the effects of such side reactions, a co-agent may be used in combination with the peroxide curative to react with the free radicals formed during the curing process and to stabilize the said radicals. In this manner, a co-agent tends to improve the overall crosslinking efficiency, thereby leading to higher cure rate and state of cure. This is well known to those having skill in such art.
Processing safety, for the purposes of this invention, relates to the processing of a rubber composition with conventional rubber mixing apparatus up to temperatures of about 130° C., or sometimes even up to about 150° C., for reasonable periods of time without appreciably scorching the rubber composition itself. The term “scorching” relates to prematurely curing the rubber composition while it is being mixed, or processed, in the aforesaid rubber mixer, particularly in an internal rubber mixer. The undesirable aspect of scorching, or pre-curing, of rubber during its mixing in an internal rubber mixer is well known to those having skill in such art.
Accordingly, peroxide curatives for EPDM and EPR rubbers are often selected according to their decomposition rate, namely their rate of forming free radicals during the curing of an EPDM or EPR.
For example, product manufacturing operations that desire relatively fast curing times, or relatively short molding times, typically use peroxide curatives with a relatively short half-life such as, for example, diacyl peroxides, although such peroxides may have a reduced processing safety, or a greater tendency to result in a scorched rubber composition.
On the other hand, peroxide curatives that typically exhibit slower curing times for curing EPDM's and EPM's, such as for example, di-tert-alkyl peroxides, usually exhibit good process safety, or resistance to scorching of the EPDM, or EPR, as the case may be, yet require relatively long cure times.
A philosophy of selection of peroxide curatives to balance curing speed with elimination of at least reduction of scorching of EPDM and EPR rubber compositions is well known to those having skill in such art.
In practice, sulfur is sometimes used as a co-agent for peroxide curing of EPDM's and EPR's, as is well known to those having skill in such art.
Other co-agents sometimes used as additives for peroxide-based cure systems for rubber compositions are typically polyfunctional chemicals that react readily with free radicals which are generated by the peroxide cure system. Such reaction by a co-agent tends to reduce the side reactions of free radicals generated by the peroxide curative during the curing of the EPDM rubber, including chain scission of the rubber itself. In practice, such co-agents are basically used to improve both the cure rate and the state of cure of the rubber composition.
Examples of use of sulfur and various co-agents in peroxide curing of polymers may be found, for example, in
Rubber Chem. and Tech.
, vol 61, page 238 (1988) by R. C. Keller.
In one aspect of this invention, it is desired to provide a method for appreciably increasing a cure rate for an EPDM-based or EPM-based rubber composition while substantially retaining, or even improving, its processability, or scorch safety.
In the description of this invention, the term “phr” as used herein, and according to conventional practice, refers to parts of a respective material per 100 parts by weight of rubber. In the description herein, rubber and elastomer are used interchangeably unless otherwise noted. The terms “cure”, “vulcanized” and “crosslinked” also used interchangeably unless otherwise noted. Further, the terms “uncured”, “unvulcanized” and “uncrosslinked” are used interchangeably to refer to a rubber composition which has not been cured, vulcanized or crosslinked” unless otherwise noted.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a process is provided which comprises blending an EPDM-based and/or EPR-based rubber composition with a peroxide curative together with a combination of sulfur and acrylate co-curing agents, followed by peroxide curing the rubber composition at an elevated temperature.
In particular, a process of preparing a composition is provided which comprises
(A) blending, preferably at a temperature in a range of about 100° C. to about 130° C. and based upon 100 phr of elastomer;
(1) about 10 to about 100, preferably about 100, and alternately about 40 to about 80, phr of at least one low unsaturation rubber or saturated rubber selected from EPDM and EPR and about zero to about 90, preferably zero and alternately about 20 to about 60, phr of at least one high unsaturation rubber selected from homopolymers and copolymers of conjugated dienes and copolymers of at least one conjugated diene with a vinyl aromatic compound selected from styrene and alpha-methylstyrene;
(2) about 20 to about 200, alternately about 90 to about 110, phr of particulate reinforcement selected from at least one of clay, carbon black and precipitated silica, preferably clay and/or silica with only a minor amount, if any, of carbon black;
(3) about 0.5 to about 10, alternatively about 2 to about 6, phr of peroxide curative for said low unsaturation rubber(s);
(4) about 0.25 to about 10, alternately about 1.5 to about 5.5, phr of acrylate co-curing agent which is homogeneously dispersed within said elastomer(s), wherein said acrylate is selected from at least one of monoacrylate, diacrylate, triacrylate, tetraacrylate, pentaacrylate and hexaacrylate co-curing agents for peroxide curative, and mixtures thereof; and
(5) about 0.05 to about 0.6, alternatively about 0.2 to about 0.4, phr of elemental sulfur co-curing agent; wherein the weight ratio of said sulfur and acrylate co-curing agents to said peroxide curative is in a range of about 1/1 to about 1/30 and the weight ratio of said acrylate co-curing agent to said sulfur co-curing agent is in a range of about 2/1 to about 200/1, followed by
(B) heating and curing the prepared composition at a temperature in a range of about 150° C. to about 180° C.
Thus, it is required that the acrylate co-curing agent is clearly in the majority of the sulfur and acrylate co-curing agents.
In further accordance with this invention, an article is provide
Blok Edward John
Gordon Larry Ashley
Kralevich, Jr. Mark Leslie
Sandstrom Paul Harry
Taucher James Edward
Harlan R.
The Goodyear Tire & Rubber Company
Wu David W.
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