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
1999-05-06
2002-06-04
Niland, Patrick D. (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...
C152S151000, C152S152100, C152SDIG002, C264S501000, C524S366000, C524S368000, C524S376000, C524S377000, C524S492000, C524S493000, C524S495000, C524S496000
Reexamination Certificate
active
06399692
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to silica-filled rubber compositions and, more particularly, to silica-filled rubber compositions containing poly(alkylene oxide) compounds having alkali metal salts dissolved therein to improve the electrical conductivity of the rubber compositions. These rubber compositions are particularly useful in tires as silica-reinforced tread compositions and are particularly suitable for preventing or dissipating any electrostatic charges which might accumulate in the tire. The invention also relates to a method for dissipating electrostatic charges in silica-filled rubber compositions and, more particularly, for preventing the accumulation of electrostatic charges in tires having silica-reinforced tread compositions.
BACKGROUND OF THE INVENTION
It is known that electrostatic charges may be produced by any of a number of different ways within a motor vehicle. For instance, the mechanical and electrical components operating within a motor vehicle such as, for example, a rotating shaft within a bearing, can result in an electrostatic charge being generated within the vehicle, or even the friction of the rubber tire rolling on the road can generate an electrostatic charge. Typically, these charges are dissipated through the rubber tires that contact the ground since the tires typically include a sufficient amount of electrically conductive materials therein. Were such dissipation not to occur, interference with electronic components within the motor vehicle could occur. Furthermore, static shock could be experienced by the vehicle's passengers as they exit the vehicle. Such high electric charges can also lead to safety hazards upon refueling of the vehicle.
Although rubber tires have typically acted as an adequate conduit for the dissipation of such static charges produced from the mechanical or electrical components of a motor vehicle, the use of less conductive materials within tires has resulted in a decrease in the ability of the tires to effectively dissipate these static charges. This is particularly true in rubber tire compositions employing silica as a reinforcing filler. The advantages of silica-filled tires are well known in the art as silica has been found to provide excellent wet traction, excellent wear, and low rolling resistance in tires, while reducing hysteresis.
Inasmuch as silica-filled tires are advantageous, attempts have been made to produce tires, and particularly, tire tread compositions, that are silica filled, or at least partially silica filled and yet, adequately dissipate static electricity.
Initial attempts at increasing the conductivity of tires, including those having silica-filled tread compositions, have focused on the use of electro-mechanical means as an alternative conduit for dissipating the electrostatic charges. For example, U.S. Pat. No. 5,518,055 teaches a tire having an electrostatic discharge ring positioned on at least one shoulder of the tire. The discharge ring has a relatively low volume resistivity, which is on the order of 100 megohm cm. The discharge ring is critically positioned so as to contact the ground surface and dissipate static charge built-up within the inner portions of the tire. Likewise, European Patent Application Nos. 681,931 Al and 718,126 A2 teach tires or tire treads having a thin conductive layer on the outermost portion of the tread. In one case, the thin layer extends continuously in a circumferential direction over the tire tread; and in another embodiment the conductive portion has a width that is 15 percent of the tire strip width.
European Patent Application Nos. 0 705 722 A1 and 0 732 229 A1 teach silica reinforced rubber treads that contain a thin overcoat or cap, containing a quantitative amount of electrically conductive carbon black. In one embodiment, the outer top cap extends across the outer surface of the tread and in an alternative embodiment the outer cap extends only over the outer portion or peripheral edges of the tread surface that is intended to be contacted with the ground.
Similarly, European Patent Application Nos. 0 718 127 A1 and 0 747 243 A1 teach tires having one or more tread strips that provide ground contact and that are electrically conductive. These strips also extend radially inwardly to contact the body plies of the tire or the tire bead area.
More recently, attempts have been made which employ chemical additives to improve the electrical conductivity of the rubber compounds. For example, nonionic surfactants or phosphoric esters have been used in rubber tire compounds to improved electrical conductivity. In U.S. Pat. No. 5,714,533, a rubber composition having improved conductivity properties is disclosed which includes a rubber component, a filler such as silica, and a nonionic surfactant or phosphoric ester. Typical examples of the nonionic surfactant are adducts of ethylene oxide of 2 to 30 moles to linear, cyclic or branched, and saturated or unsaturated, and monohydric or polyhydric aliphatic alcohol having carbon atoms of 6 to 25, or adducts of ethylene oxide of 2 to 30 moles to alkylphenol, while representative phosphoric esters include those represented by the following formula (I) and (II):
wherein R′ represents a linear or branched, and saturated or unsaturated aliphatic hydrocarbon group having 8 to 25 carbon atoms or an aryl group; and q and r each are an integer satisfying a relation of q+r=1 to 30, or
wherein R′ and R″ each represent a linear or branched, and saturated or unsaturated aliphatic hydrocarbon group having 8 to 25 carbon atoms or and aryl group and may be the same or different; and s is an integer of 1 to 30.
Addition of other chemical ingredients, such as carbon black fibers or ultra fine carbon fibrils, have been reported to provide superior reinforcing and electrical conductivity compared to compounds with conventional carbon black reinforcing fillers.
Still further, it is believed that other chemical additives, namely polyoxyethylene deriviatives of phenol, commercially available under the trade name “Triton”, have been tested as electrically conductive additives. However, it has been found that the use of poly(alkylene oxide) derivatives alone do not provide a significant antistatic effect (as noted in Col. 7, lines 40-46 of U.S. Pat. No. 5,714,533) or, if they are able to provide the desired effect, quickly bleed out of the rubber.
Thus, a need continues to exist for an effective silica-reinforced tread composition, which will dissipate electrostatic charges while maintaining or improving upon the physical properties currently associated with silica-filled tire tread compositions and which will not bleed out of the composition. It is further desired that the means by which electrical conductivity of the tread composition is improved also act as a dispersing agent for the silica.
SUMMARY OF INVENTION
It is therefore, an object of the present invention to provide a silica-reinforced rubber composition having adequate electrostatic dissipation properties.
It is another object of the present invention to provide a silica-reinforced rubber composition, as above, suitable for use in a tread composition of a tire.
It is yet another object of the present invention to provide the rubber composition, as above, wherein the means used to increase the electrical conductivity of the rubber composition further acts as a dispersing agent for the silica.
It is still another object of the present invention to provide a rubber composition containing an additive which will not bleed out of the composition.
It is a further object of the present invention to provide tires having improved electrostatic dissipation properties.
It is still a further object of the present invention to provide a method for the dissipation of electrostatic charges in tires having silica-reinforced tread compositions.
At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to silica reinforced tires or tire treads having adequate electrostatic dissipation p
DeTrano Mario
Hergenrother William L.
Hogan Terrence E.
Bridgestone Corporation
Niland Patrick D.
Palmer Meredith E.
Skoglund Rodney
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