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
2000-08-16
2001-08-14
Moore, Margaret G. (Department: 1712)
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...
C523S209000, C523S212000
Reexamination Certificate
active
06274662
ABSTRACT:
TECHNICAL FIELD
This invention relates to vulcanizable elastomeric compositions containing surface treated barium sulfate and vulcanizates obtained therefrom, and, more particularly, to a vulcanized elastomeric product, such as a tire, containing a unique surface treated barium sulfate product that offers enhanced dampening properties among other things.
BACKGROUND OF THE INVENTION
Natural barium sulfate (also commonly referred to as barite or barytes) is frequently used as an extender pigment and/or filler due to its chemical inertness (in both acid and alkali environments), high refractive index, low abrasiveness, low oil absorption, and resistance to corrosion. Barium sulfate is also known to promote flame retardancy and smoke suppression in polymeric end use applications. Given their high refractive index, barium sulfates of high brightness are desirable to use as a replacement for titanium dioxide (TiO
2
) in certain compositions such as pigmented polymeric compounds. Barite can be utilized to replace a portion of the more expensive TiO
2
pigment without having a deleterious impact on the compound's brightness and whiteness properties. Synthetic, precipitated barium sulfate pigments are used in a like fashion, but are typically available in finer particle size grades versus the mechanically ground, natural barites. Precipitated barium sulfate is commonly referred to as blanc fixe.
Despite barium sulfate's many end use advantages, it is not readily wetted or dispersed in organic based formulations such as polymeric compounds given its inert inorganic surface. Accordingly, lengthy processing times are typically required to obtain desired levels of dispersibility of the barite in such compounds. Further, fine and ultrafine particle barites in dry form tend to cake when stored and/or transported. Caking creates processing problems when the barite particles are added to end use formulations via automated dry feeders and the like. Consequently, a general need for barium sulfite with improved processability and dispersibility has existed.
In the vulcanized rubber product fields, fillers have been used to stiffen or reinforce rubber and/or reduce the cost of the rubber formulations, such used as in tires, v-belts, hoses, and so forth. Fillers used in for rubber tire components, for instance, have primarily involved carbon black and/or silicas. Besides, silicas, other non-carbon black fillers for tire rubbers also have been mentioned in the prior art, including calcium silicate, aluminum silicate, clay, talc, calcium carbonate, magnesium carbonate, alumina hydrate, diatomaceous earth, barium sulfate, mica, alumina sulfate and titanium oxide (e.g., see U.S. Pat. No. 5,959,039). Vulcanized rubber applications would be advanced if rubber fillers, which implicitly must be compatible with vulcanizable rubber formulations, could be developed which would enhance the vibration and/or noise dampening properties of the end product without causing a sacrifice of the performance needed in other respects, such as in abrasion/cutting/wear resistance, grip (if applicable), flexibility, rolling resistance (if applicable), and/or manufacturability.
SUMMARY OF THE INVENTION
The above and other objectives are fully met by the present invention, which is directed to vulcanizable elastomeric compositions having enhanced dampening properties, among other things, in which the elastomeric composition contains surface-treated barium sulfate particles formed of a plurality of barium sulfate particles and a reaction product of the barium sulfate and silicon-hydride containing polysiloxane integrally located on the surfaces of the barium sulfate particles. The invention also covers the vulcanized products thereof. The inventive elastomeric compositions can be vulcanized to retain appropriate shapes to provide tire parts (e.g., treads), v-belts, conveyor belts, sealants, shoe parts, and so forth, having enhanced vibration and noise dampening attributes, but without adversely impacting other performance-related properties of the rubber products.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In accordance with the preceding summary, the present invention is directed toward a surface treated barium sulfate product having excellent dispersibility in vulcanizable elastomeric compositions, resulting in reduced processing times and yielding elastomeric products having improved dampening attributes, such as vibration and/or noise dampening. The surface-treated barium sulfate can be made by mixing a linear and non-crosslinked silicon-hydride containing polysiloxane as described herein, in neat or in aqueous emulsion form, with a quantity of barium sulfate particles and then optionally drying the resultant mixture. The silicon-hydride containing polysiloxane is then directly deposited on and chemically bonded to the surface of the barium sulfate particles to form a barium sulfate/ silicon-hydride containing polysiloxane reaction product integrally on the surfaces of the barium sulfate particles. Thereafter, the surface treated barium sulfate particles are incorporated into and dispersed within an elastomeric composition before it is cured.
The elastomers used in this invention are rubbers such as polyisoprene (natural rubber), polybutadiene, polychloroprene, polyisobutylene, styrene-butadiene rubber, acrylonitrile-butadiene, terpolymers of ethylene/propylene
on-conjugated dienes (EPDM), ethylene-vinylacetate copolymer, ethylene-propylene, chlorobutadiene, chlorinated polyethylene, chlorosulfonated polyethylene and ethylene-acrylate copolymer, as used singly or in blends thereof. Diene-based rubbers, copolymers of diene-based rubbers with other prepolymers, and blends thereof, are preferred for tire rubber applications encompassed by this invention. The diene rubbers preferably are conjugated dienes having 1,3 or 1,4 bonds. An exemplary rubber blend, especially for tire tread applications, is (a) styrene-butadiene rubber and (b) polybutadiene rubber. Rubber components (a) and (b) generally can have a mixing ratio of approximately 60-80/40-20 wt %/wt %, respectively, for tire tread rubber implementations of the invention. The above-listed rubbers, once combined in the elastomeric compositions with the surface treated barium sulfate described herein and other ingredients, are vulcanized, i.e., cured by formation of chemical cross-links between high molecular weight linear molecules of the base rubber material(s). Curing of elastomers used in elastomeric compositions according to this invention can proceed along conventional lines using sulfur-based chemical systems, and/or by using organic peroxide catalyzed systems.
In addition to the surface-treated barium sulfate additive of this invention, elastomeric compositions of this invention typically also contain conventional rubber adjuvants and additives such as antioxidants, antiozonants, oil extenders and other processing aids, stiffening fillers, pigments, and/or reinforcing fillers, added in conventional respective amounts. For instance, sulfur is a known curing agent for rubbers, but acts too slowly by itself at most practical temperatures, so combinations of accelerators and activators including sulfur are often used. Examples of accelerators in this regard include diphenyl guanidine, hexamethylamine tetramine, mercaptobenzothiazole disulfide, tetramethylthiuram disulfide, zinc diethyl dithiocarbamate, sulfenamides, and so forth. Common activators include stearic acid and zinc oxide. Protective agents used to suppress or reduce the deteriorating effects of oxygen and ozone on the rubber include alkyl paraphenyl diamines and phenyl &bgr;-naphthylamine. As reinforcing fillers, carbon black and silica can be used, while useful non-reinforcing fillers include clay, calcium carbonate and so forth. Fluids used to soften the rubber or reduce the stiffness of the rubber include paraffin waxes and mineral oils.
One exemplary elastomeric formulation of this invention includes, styrene-butadiene rubber (e.g., solution polymerized SBR), polybutadiene rubber (PB), the
Evans Larry R.
Freeman Gary M.
Lynch Thomas J.
J.M. Huber Corporation
Moore Margaret G.
Nieves Carlos
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