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
1998-12-02
2001-10-02
Henderson, Christopher (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...
C525S329800, C525S330900, C525S332600
Reexamination Certificate
active
06297327
ABSTRACT:
The present invention relates to cure promoters and methods for vulcanizing elastomers.
Many uses of elastomeric materials require that the polymer chains in the elastomer be cross-linked. Crosslinking of the polymer chains in an elastomeric matrix is typically referred to as curing or vulcanization. Crosslinking is commonly accomplished using sulfur or an organic sulfur compound at an elevated temperature. As a result of crosslinking, the cured elastomer is elastic, i.e., it deforms under stress yet returns to the shape it had when the stress is removed, has improved tensile strength, reduced temperature sensitivity, higher elongation, greater tear resistance and increase hardness or durometer.
During the vulcanization reaction, elastomers are typically reacted with sulfur in the presence of a cure activator or promoter. Commonly used cure activators are oleic and stearic acids combined with zinc oxide and a cure accelerator. However, oleic and stearic acids are relatively expensive and since they are used in large quantities in rubber formulations, they contribute to the high cost of many elastomeric products.
Various alternatives to stearic acid have been proposed including the use of tall oil fatty acid mixtures as described in U.S. Pat. Nos. 4,870,135 and 4,895,911 to Mowdood et al. However, these products are also relatively expensive and are subject to price fluctuations which lead to market instabilities.
It is therefore an object of the invention to provide a cost effective cure promoter and method of using the same for vulcanizing elastomeric materials.
Another object of the invention is to provide a low cost alternative to stearic acid as a cure promoter for an elastomeric material.
A further object of the present invention to provide a cure promoter for an elastomeric formulation which is readily available and which may be substituted directly for stearic acid in an elastomeric composition without adversely affecting the properties of the resulting cured elastomer.
An additional object of the invention is to provide a method for promoting the cure of elastomers using a relatively inexpensive cure promoter.
Having regard to the above and other objects, the invention provides a method for making a cross-linked elastomer which comprises compounding a mixture including a vulcanizable elastomer, a sulfur source and from about 0.1 to about 6% by weight of a monomeric distillate by-product from the clay-catalyzed dimerization of fatty acids. The compounded mixture is then heated to a temperature sufficient to cause substantial crosslinking of the elastomer.
The monomeric distillate by-product used in the present invention is a low cost alternative to stearic acid, oleic acid and tall oil fatty acid (TOFA) and is available in plentiful supply. The monomeric distillate by-product may be obtained from the clay-catalyzed dimerization of fatty acids obtained from oils selected from the group consisting of linseed, canola, soybean, rapeseed and tall oils or blends of the fatty acids obtained from two or more of the foregoing oils. It is especially preferred to use the monomeric distillate by-product from the clay-catalyzed dimerization reaction of tall oil fatty acids (TOFA). Although TOFA is produced in large quantities from renewable resources and is itself a known cure promoter for vulcanization, the monomeric distillate by-product from the clay-based dimerization of TOFA has not been recognized as having utility in such applications. The composition of the distillate is quite different from that of either the dimer product or the TOFA raw material. In fact, as described in U.S. Pat. No. 3,925,342 to Scharrer, incorporated herein by reference, it was observed that the dimerization by-product from the clay-based dimerization of TOFA has very limited utility due to the presence of the branched chain isomers produced during the dimerization process, the TOFA being characterized as containing principally straight chain fatty acids.
However, it has now been discovered that the dimerization distillate by-product does in fact provide an excellent alternative to TOFA as well as the traditional substantially pure stearic or oleic acid materials as a promoter for vulcanization reactions. When it is realized that recent increased production of TOFA dimer products for other uses will inevitably result in substantially increased accumulation of the monomeric distillate by-product, the advantages of the invention which provide a highly beneficial utility for this material become very significant. Also, disposal problems associated with increased production of the TOFA dimer by-products are considerably lessened and the goal of full utilization of components of the renewable resource (wood) from which these products are derived is furthered to a great extent.
The invention is applicable to a wide range of elastomers including, but not limited to, polymers, copolymers and terpolymers of substituted and unsubstituted olefinic compounds, arene compounds and olefinic and arene compounds such as natural and synthetic rubber. Synthetic rubbers include polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, butyl rubber, halogenated butyl rubbers such as chlorobutyl and bromobutyl rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene, nitrile rubber, chloroprene rubber, ethylene-propylene terpolymer rubber such as ethylene-propylene-diene monomer, silicone rubber, neoprene rubber, polysulfides, polyacrylate rubber, epichlorohydrin rubber, fluoroelastomers, polyurethanes and thermoplastic rubber.
The amount of elastomer present in an elastomeric formulation may vary widely depending on the desired product qualities. Typically, the elastomeric formulation will contain from about 55 to about 85% by weight of elastomer which may be a single elastomer or a mixture of elastomers.
Elemental sulfur is the most commonly used sulfur source for providing the vulcanizing agent, however, an organic sulfur compound such as an olefin adduct, an amine disulfide or a polymeric polysulfide may also be used as a source of sulfur. The amount of sulfur required in the elastomeric formulation to produce substantial crosslinking may range from about 0.5 to about 5% by weight free sulfur based on the total weight of the formulation.
It is known that low sulfur ratios tend to improve the resistance of the vulcanizate to deterioration during aging. Accordingly, when it is desired to produce elastomeric compositions having a low sulfur ratio and short curing time, organic accelerators are often combined with vulcanization promoters such as stearic acid or oleic acid and/or metal oxide activators such as zinc oxide, calcium oxide, magnesium oxide and lead oxide.
According to a preferred embodiment of the invention, the vulcanization promoter is provided by the monomeric distillate by-product from the clay-catalyzed dimerization of TOFA. The distillate by-product from the clay-based dimerization of TOFA is believed to be composed of a mixture of C
16
to C
18
monounsaturated fatty acids which are predominantly randomly branched isomers having the single double bond located at random positions in the molecules. If the distillate by-product is obtained from a fatty acid mixture other than tall oil, the by-product may contain a significant quantity of branched C
20
to C
22
monounsaturated fatty acids. The by-product will typically be effective as a promoter in a concentration ranging from about 0.1 to about 6% by weight based on the total weight of the composition mixture prior to vulcanization. Preferably, the by-product comprises about 0.7 to about 1.4 wt. % of the pre-vulcanized mixture.
The clay-catalyzed dimerization of TOFA is conventionally carried out by contacting TOFA with a naturally occurring bentonite, montmorillonite clay, classified by Chemical Abstracts Number (CAS#) 1302-78-9 in a reaction vessel. The reaction mixture is held at a temperature in the range of from about 200° C. to about 260° C., under steam pressure in the range of from about 3.4 atm. to about 6.8 atm., for
Conte Alexander J.
Phillips, Jr. Claude Frank
Arizona Chemical Company
Henderson Christopher
Luedeka Neely & Graham P.C.
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