Compositions – Compositions containing a single chemical reactant or plural... – Organic reactant
Reexamination Certificate
1998-08-24
2001-11-27
Anthony, Joseph D. (Department: 1714)
Compositions
Compositions containing a single chemical reactant or plural...
Organic reactant
C252S182130, C252S182150, C252S182230
Reexamination Certificate
active
06322721
ABSTRACT:
FIELD OF INVENTION
The present invention is directed toward rubber and plastic accelerator formulations that exhibit unique, superior effectiveness for accelerating the vulcanization of rubber and plastic compounds. Such effectiveness is achieved in natural rubber, synthetic rubbers, elastomers and fluoroelastomers and in blends of natural and synthetic rubbers and plastics.
BACKGROUND OF THE INVENTION
Chemicals that are used to accelerate the vulcanization process may be referred to as accelerator chemicals, rubber accelerators or plastic accelerators. Such chemicals accelerate the vulcanization or curing process during which cross-linking reactions take place that cause the product rubbers, plastics or rubber/plastic blends to have a desired set of characteristics. The accelerator chemicals, rubber accelerators or plastic accelerators may also, therefore, be referred to as cross-linking agents.
Chemicals that are typically used to accelerate the rubber vulcanization process are toxic. Many such chemicals cause defects by bleeding out of the rubber compound after having been cured. Many accelerator chemicals cause staining and discoloring of light-colored rubber compounds. Certain widely used accelerators lack storage stability, breaking down chemically after 4-6 months. Many accelerator chemicals have foul, pungent odors and are difficult to work with.
For many rubbers such as EPDM rubbers (which are ethylene-propylene-diene-monomer-based rubber compounds), nitrile rubber, Hypalon and Neoprene, ultra and secondary accelerators are required in addition to the primary accelerator to quickly obtain full cure. Two to as many as four of the ultra and one of the secondary accelerators are typically used in small amounts, usually from about 1 wt % to 2 wt %. These chemicals are toxic and very costly and, furthermore, pose a difficult problem to admix correctly and uniformly into rubber compounds in the small amounts required. If a slightly higher amount, on the order of 0.25 wt %, of an ultra accelerator is inadvertently added into the rubber compound, the rubber compound scorches badly during processing and becomes overcured, causing lower physical properties than what is typically required or desired. Usually such rubber batches are scraped as a total loss.
If the amount of the ultra accelerators is slightly lower than what is required the rubber compound becomes undercured. This causes the rubber compound to have physical properties of lower quality than what is required in properly cured rubber compounds. Such batches are also usually scraped or offered at much lower prices as off-specification.
For EPDM and nitrile rubbers, two to four ultra accelerators are typically required in addition to the primary accelerator so as to obtain fast, complete cure. The ultra accelerators are usually captax, methyl tuads, sulfads, ethyl tellurac, as made, for example, by R. T. Vanderbilt. The primary accelerator is usually Santocure NS, as provided by Monsanto.
To cure Hypalon (made by E. I. Dupont) a high percentage of litharge (lead monoxide, PbO) is typically required, that is, about 10%. Since litharge is a lead-based chemical, it is very toxic. Furthermore, litharge tends to cause rubber compounds to become very scorchy during processing. In addition, Hypalon typically requires additional accelerators, plus the litharge vulcanizing agent, to obtain a fast and complete cure. The secondary accelerators that are typically used are zinc oxide and Tetrone A.
For neoprene rubber, which tends to be scorchy during processing, zinc oxide and Magalite D are typically used to obtain a fast and complete cure. During such processing steps undesirable toxic fumes may be produced.
ADVANTAGES AND SUMMARY OF THE INVENTION
The present invention is directed to accelerator formulations that are useful for accelerating the vulcanization of rubber and plastic compounds. Such formulations are capable of producing rubbers having improved properties as well as reducing or eliminating some of the disadvantages of prior art rubber accelerators. For example, if the rubber and plastic accelerator formulations of the present invention are used to replace the prior art primary accelerators that are typically used for curing EPDM or nitrile rubbers, the ultra and secondary accelerators are unnecessary and may be eliminated.
In addition, if the accelerators of the present invention and Tetrone A are used to cure Hypalon rubber, the litharge can be eliminated and the secondary accelerators are also not required to quickly develop a complete cure.
If the accelerators of the present invention are used to cure neoprene rubber, Magalite D and all other secondary accelerators that are typically used, including peroxide and/or sulfur, are unnecessary and may be completely eliminated. The accelerators of this invention, in combination with only about 5% zinc oxide, may be characterized as functioning as cross-linking agents. As a result, this is a new “curing process” that is as fast or faster than current rubber curing processes.
Further objectives and advantages of the present invention will be apparent to those skilled in the art from the detailed description of the disclosed invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail for specific preferred embodiments of the invention, it being understood that these embodiments are intended only as illustrative examples and the invention is not to be limited thereto.
The present invention is directed to rubber and plastic accelerator formulations that may be used to accelerate the vulcanization of rubber and/or plastic compounds so as to produce rubbers and plastics having improved properties. Such vulcanization processes may require no additional or secondary accelerators to obtain fast, complete cure. The vulcanization or curing process may involve treatment of a composition comprised of a single rubber compound or a single plastic compound, a blend of rubber compounds, a blend of plastic compounds or a blend of rubber and plastic compounds. The term “rubber and plastic accelerator” formulation is, thus, used generally to refer to an accelerator that may be used in vulcanizing or curing a rubber and/or plastic composition without regard to whether the specific rubber and plastic accelerator is particularly preferred for a specific rubber and/or plastic composition.
The formulations of the present invention are directed to formulations containing an accelerator compound comprised of an organic-based quaternary ammonium salt. Preferably, the organic-based quaternary ammonium salt may include, for example, a salt selected from the group consisting of trimethylbetahydroxyethyl ammonium hydroxide (TMBHEAH), carboxymethyltrimethyl ammonium hydroxide (CMTAH), methylallylbenzylphenol ammonium iodide, benzyltriethyl ammonium chloride, hexadecyltrimethyl ammonium chloride and imidazolium compounds.
The accelerator compounds of the present invention are preferably present as a halide or a hydroxide. The accelerator compounds may be included in a rubber and plastic accelerator formulation that may further include additional ingredients such as:
a hydrated silica compound, for example, Tixocil 38 AB, which is available from Rhone-Poulenc of Cranbury, N.J., and which functions as an absorbent that produces an end product in powdered form;
an inorganic peroxide, for example, CaO
3
, which functions as a cross-linking agent by providing free oxygen to oxidize the carbon double bonds;
an additional inorganic compound, for example, ZnO, which may transiently form ZnO
2
for accelerating the peroxide oxidation step;
an alkaline silicate, for example, Na
2
O
3
Si, for increasing the overall alkalinity of the formulation;
a silicone copolymer fluid, for example, “L7602,” available from Witco Chemical Co. of Greenwich, Conn., which is a polyalkalene-oxide-modified polydimethylsiloxane that functions to wet-out the rubber and plastic compounds for fast interaction and synergize the entire process;
a free fatty acid ester, for example, iso
Wright Susan
Yankner Paul R.
Anthony Joseph D.
Kenyon & Kenyon
Technical Processing, Inc.
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