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
2000-08-11
2002-01-29
Cain, Edward J. (Department: 1714)
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...
C524S492000, C524S442000, C524S445000, C524S447000, C106S468000, C106S469000, C106S481000, C106S482000, C523S351000
Reexamination Certificate
active
06342560
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention relates to chemically modified fillers and the use of such fillers in polymeric compositions. More particularly, this invention relates to particulate or amorphous fillers having minimum carbon and sulfur contents, a minimum Silane Conversion Index and a minimum Standard Tensile Stress @ 300% elongation and polymers, e.g., curable rubber compositions, containing such fillers. Most particularly, this invention relates to a functionalized and hydrophobized filler, hereinafter referred to as a “modified filler”, that improves the efficiency of producing polymeric compositions, such as in rubber compounding, and the performance of polymerized or cured products, e.g., tires.
In the production of polymeric compositions, it is common to incorporate fillers to improve the physical properties of the polymer. The surfaces of such fillers are often modified to increase the reactivity and consequently the two and three dimensional coupling of the filler within the polymeric composition. It is conventional in the rubber industry to incorporate carbon black and other reinforcing fillers into natural and synthetic rubber to increase the physical properties of the cured rubber vulcanizate. Fillers used to reinforce such polymeric compositions include natural and synthetic fillers.
One of the principal non-black fillers used in the rubber industry is amorphous precipitated silica. This siliceous filler is used to impart improved tensile strength, tear resistance and abrasion resistance to the rubber vulcanizate. Silica fillers are also used in combination with carbon blacks to obtain maximum mileage in passenger vehicle tires and off-the-road tires, e.g., tires for mining and logging operations and for road-building equipment. Such applications have become well established. When used as the sole reinforcing filler, silica fillers that are not well dispersed and/or coupled in the rubber do not provide the overall improved performance obtained by the use of carbon blacks alone. This is observed most readily in rubber vulcanizes used for tires, e.g., tire treads.
Various coupling agents, e.g., titanates, zirconates and silanes, have been suggested for use with fillers when such fillers are incorporated into polymeric compositions, e.g., rubber, in order to improve the performance of the rubber vulcanizate. Among the various organosilane coupling agents suggested for such use are the bis(alkoxysilylalkyl)polysulfides, e.g., 3,3′-bis(triethoxysilylpropyl)tetrasulfide. It has been reported that the use of appropriate amounts of such coupling agents, particularly 3,3′-bis(triethoxysilylpropyl)tetrasulfide, in siliceous filler-reinforced synthetic rubbers provides at least equivalent performance to carbon black-reinforced synthetic rubbers in several key physical properties such as 300% modulus, tensile strength and abrasion resistance.
The high cost of bis(alkoxysilylalkyl)polysulfides, and the time and energy required to mix them into polymeric compositions have deterred the more general use of siliceous fillers as the principal reinforcing filler in large volume applications. U.S. Pat. No. 4,436,847 describes increasing the efficiency of silane coupling agents, e.g., bis(alkoxysilylalkyl)polysulfide coupling agents, by using an alkoxysilane in combination with the silane to form a coupling composition. In one specific embodiment described in the '847 patent, the silane coupling composition is formulated with the siliceous filler in a suitable non-reactive liquid that is chemically inert with respect to the coupling composition and siliceous filler to prepare a rubber compounding additive, i.e., a silica-silane concentrate.
U.S. Pat. No. 5,116,886 describes a two-step process in which the surface of natural or synthetic, oxide or silicate fillers is modified by using certain organosilicon compounds. In the first step, the organosilicon compound is mixed intensely with the filler at a temperature below 60° C. In the second step, the homogenous mixture is subjected to a temperature of from 60 to 160° C. to complete the surface modification of the filler.
U.S. Pat. No. 5,908,660 also describes a two-step method for the preparation of hydrophobic silica. In the first step, an aqueous suspension of precipitated silica is contacted with an organosilicon compound in the presence of a catalytic amount of an acid to effect hydrophobizing of the precipitated silica. In the second step, the aqueous suspension of the hydrophobic precipitated silica is contacted with a water-immiscible organic solvent at a solvent to silica weight ratio greater than 5:1 to effect separation of the hydrophobic precipitated silica from the aqueous phase.
It has now been discovered that a modified filler, e.g., a particulate or amorphous inorganic oxide, that is characterized by a carbon content of greater than 1 weight percent, a sulfur content of greater than 0.1 weight percent, a Silane Conversion Index (described hereinafter) of at least 0.3 and a Standard Tensile Stress @ 300% elongation (also described hereinafter) of 7 or more can be prepared. The process described in U.S. Pat. No. 5,908,660 may be improved and used to produce the modified filler of the present invention by utilizing a certain combination of functionalizing and hydrophobizing agents in an aqueous suspension of inorganic oxide having a pH of 2.5 or less and treating the acidic aqueous suspension of modified fillers with acid neutralizing agents to increase the pH of the suspension to a range of from 3.0 to 10.
As used herein, a functionalizing agent is a reactive chemical which can cause an inorganic oxide to be covalently bonded to the polymeric composition in which it is used. A hydrophobizing agent is a chemical which can bind to and/or be associated with an inorganic oxide to the extent that it causes a reduction in the affinity for water of the inorganic oxide while increasing the inorganic oxide's affinity for the organic polymeric composition in which it is used.
The aforementioned Standard Tensile Stress @ 300% elongation (STS@300%) of at least 7 or greater indicates improved reinforcement of the rubber composition. Improved reinforcement translates into an improvement in the mechanical durability of the product which is evidenced by increased tear strength, hardness and abrasion resistance. In addition to the improved properties, the modified filler has the benefit of requiring less time and energy to get incorporated into the polymeric composition.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities, ratios, ranges, etc. used herein are to be understood as modified in all instances by the term “about”.
The modified filler of the present invention may be produced by any method that results in such a filler, i.e., an inorganic oxide, having a carbon content of greater than 1 weight percent, preferably, at least 1.5 weight percent, and more preferably, at least 2.0 weight percent; a sulfur content of greater than 0.1 weight percent, preferably, at least 0.3 weight percent, and more preferably, at least 0.6 weight percent; a Silane Conversion Index, of at least 0.3, preferably, at least 0.4, and most preferably, at least 0.5 and a Standard Tensile Stress @ 300% elongation of at least 7.0, preferably, at least 7.5 and more preferably at least 8.0. The modified filler of the present invention may also be characterized by a modified Brunauer-Emmett-Teller (BET), i.e., a single point surface area, of from 20 to 350 m
2
/g, preferably from 40 to 300 m
2
/g and most preferably of from 100 to 200 m
2
/g, a pH of from 5 to 10, preferably from 5.5 to 9.5, more preferably from 6.0 to 9.0 and most preferably, a pH of from 6.0 to 7.5 or the pH of the product may range between any combination of these values, inclusive of the recited ranges; and a Soxhlet Extractable percent carbon of less than 30 percent, preferably less than 25 percent and more preferably less than 20 pe
Cain Edward J.
Mallak Frank P.
Marmo Carol A.
PPG Industries Ohio Inc.
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