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
2001-09-11
2003-10-28
Wu, David W. (Department: 1713)
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...
C524S504000, C430S058050, C430S059500, C430S110100, C430S108100, C138S137000
Reexamination Certificate
active
06639003
ABSTRACT:
FIELD OF THE INVENTION
The present invention is a rubber additive comprising a low molecular weight polyethylene wax. The additive is used in rubber compounding and increases the processability of the rubber compounds and also enhances the rubber compound's resistance to attack by ozone.
BACKGROUND OF THE INVENTION
Rubber is inherently difficult to process and mold because of its high viscosity. Rubber is also subject to degradation and attack by ozone and ultraviolet (“UV”) light. Both of these phenomena are well known to those practiced in the art of compounding rubber.
Rubber formulations also contain a number of additives, which are used for purposes, such as, but not limited to, improve the processability of the rubber, and reduce the degradation of rubber caused by the effects of ozone and UV light.
Traditional additives used to improve processability of rubber have included polyethylene waxes. A commonly used polyethylene wax for use in improving process ability is commercially available from Honeywell (Morristown, N.J.) and is sold under the A-C®617 name. This polyethylene wax is a relatively soft with a hardness (@25 degrees C.) of 6-9 dmm, a Mettler drop point of 101 degrees C., a molecular weight of approximately 3000, and a density of 0.91 g/cc. There are several other suppliers of similar polyethylene waxes including Eastman Chemical (Kingsport, Tenn.) Epolene® wax and Mitsui (Tokyo Japan) Hi-Wax™
Polyethylene waxes are derived from polymerization of ethylene under conditions that restrict the polymer length there by rendering the final product with wax like characteristics. The traditional polyethylene waxes used in rubber processing have molecular weights in the 2000 to 3000 Mn range. Traditional polyethylene waxes used as processing aids in rubber compounds have been used sparingly because of their effects on reducing adhesion and green tack of rubber. In fact suppliers promote traditional polyethylene waxes as tack reducing compounds for those instances where reduced tack is desirable. In most instances, however, such as tire building, high levels of green tack aids in building of tires and is generally a desirable property.
To improve the resistance of rubber to the effects of ozone and UV light, rubber compounders have traditionally used combinations of static and dynamic antidegradants. Commonly used dynamic antiozonants include 2,4,6-Tris-(N-1,4-Dimethylpentyl-p-Phenylenediamino)-1,3,5-Triazine supplied by Uniroyal Chemical under the brand name Durazone®37, or N-isopropyl-N′-phenyl-p-phenylenediamine- supplied by Monsanto Chemicals. Another dynamic antiozonant is N-(1-methylhexyl)-N′-phenyl-p-phenylenediamine (6PPD), which is supplied by several chemical companies.
Rubber additives that are used to protect against static ozone attack are microcrystalline waxes that are sold under a variety of tradenames, such as Astor® (Honeywell, Inc., Morristown N.J.); Norcheck®, by IGI International. Antiozonant microcrystalline waxes are derived from petroleum, and refined from slack wax to fractionate and separate out the microcrystalline fraction. The molecular weights of microcrystalline waxes are typically in the 600-700 Mn range. The microcrystalline waxes are used to provide a physical barrier on the surface of a rubber article, such as a tire. This physical barrier prevents attack on the rubber from ozone present in the atmosphere. The surface film of microcrystalline wax is sacrificial and is constantly being regenerated through a phenomenon called blooming. Blooming is the process where the microcrystalline wax, due to its incompatibility with rubber, continually migrates to the rubber surface. The rate of migration is a complex situation effected by time, heat, concentration of wax, chemical make-up of the rubber, and other factors. Microcrystalline wax use in tires has been limited due to the adverse effect high levels have on adhesion and green tack of the rubber compound.
Various applications of polyethylene waxes and microcrystalline waxes have been described in the prior art.
In U.S. Pat. No. 4,161,202 Powell et al. disclose using a low molecular weight (approximately 2000) polyethylene wax, having a melting point of approximately 78 degrees C., as an internal coating in a tire to render the tire puncture resistant. The polymer has the properties of a stiff grease which will not liquefy, but which will penetrate voids such as a puncture under the influence of inflation pressure.
Messerly et al. (U.S. Pat. No. 4,096,898) disclose using low molecular weight polyethylenes (molecular weights ranging from 1000-50,000, and having a density of approximately 0.88), as an internal tire lubricant. The compound is described as being a polyolefin grease, becoming liquid at a temperature of approximately 85 degrees C.
Ganster et al (U.S. Pat. No. 4,309.378) discloses using polyethylene wax as a release agent in tire manufacturing. The particular polyethylene is a polyethylene adipate having a molecular weight of approximately 2000.
In U.S. Pat. No. 3,992,502, Krishman discloses the use of polyethylene or polyethylene waxes as mold release agents in the formation of rubber products, to prevent adhesion of the finished product to the mold.
In U.S. Pat. No. 4,082,706 Danielson describes problems that occur when waxes are used as an antiozonant in a rubber formulation. He notes the limited success of waxes because of the difficulty of insuring that the wax layer remains intact. The wax film often separates or tears, causing cracks to develop of greater magnitude than articles having no wax, under the stresses to which the articles are subjected. The antiozonant compounds described are enamines.
Wheeler et al. (U.S. Pat. No. 4,956,405) describe the use of waxes to inhibit ozone cracking in articles under stress in static conditions by incorporating the wax into rubber compounds before vulcanization. They indicate the wax migrates to the surface of the article, forming a film which acts as a physical barrier to protect the article from ozone attack. The problem they note is that the wax film becomes cracked or disrupted during use of the article, and may cause cracks of greater severity than if no wax were used in the formulation, leading them to state “for many service conditions, the use of wax is impractical due to the dynamic conditions under which the article is expected to perform”(col. 1, lines 63-col. 2, line 7). The novel antiozonant compounds of this invention are tris-(N-alkyl-p-phenylenediamino)-1,3,5-triazines, and their use in a variety of elastomeric products, such as industrial belts, hoses, air springs, and roofing membranes are described.
In U.S. Pat. No. 5,120,779 Cornell et al. disclose the use of novel triazine compounds as antiozonants for rubber. Noteworthy is the statement at col. 2, lines 13-16 that the novel arylenediamine triazine of the invention provided exceptional long term ozone protection under static conditions without using wax. At col. 9, lines 5-8 Cornell et al. state that their inventive compounds may be used in combination with other antiozonant agents, and less preferably with microcrystalline waxes as are commonly used to protect against static ozone attack.
U.S. Pat. No. 6,201,049 Sakamoto et al.)discloses the use of N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine (“6PPD”) and N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (“8PPD”) as antioxidant agents in a rubber composition used for tire sidewalls.
In U.S. Pat. No. 4,696,753 Umland et al. disclose the use of between 50-70 per cent by weight of polyethyleneglycol or polyglycol ether in combination with aluminum bronze, in conjunction with a wetting agent, as a lubricant for a tire and wheel assembly. The lubricant is applied as a thin layer, external to the tire, between the tire and rim assembly, to prevent damage or destruction of the tire due to slippage when the tire is operated for a long period of time in a deflated state.
In U.S. Pat. No. 4,501,616 Fink et al. disclose the use of polyoxypropylenediols or polyoxypropylenepolyoxyethyl
Borsinger Gregory G.
Cawley Craig
Adams Thomas L.
Hu Henry
Wu David W.
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