A pneumatic tire having a multi-colored tread of a cap/base construction and a lug and groove construction wherein a visible portion of said grooves have walls of a non-black colored, devoid of carbon black, silica reinforced, rubber composition wherein and a majority of the visible portion of the surface of said tread is of a black-colored, carbon black-containing, rubber composition wherein said tread is comprised of co-extruded laminae of
- (A) a layer of a carbon black-containing, black colored tread cap rubber composition configured with lugs and grooves wherein the outer surface, or face, said tread lugs are designed to be ground-contacting,
- (B) a layer of a carbon black-containing, black-colored tread base which underlies said tread cap and is not designed to be ground contacting,
- (C) a pair of carbon black-containing, black-colored tread miniwings extending from the peripheral edges of said tread, and
- (D) at least one thin overlaying layer of said non-black colored, silica reinforced, outer rubber layer, exclusive of carbon black and containing a colorant other than of a black color, overlaying at least a portion of the surface of said at least a portion of said tread grooves;
- wherein said thin, non-black colored outer rubber layer is comprised of 100 phr of elastomer comprised of
- (1) about 50 to about 100 phr of at least one diene-based elastomer and
- (2) from zero to about 50 phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or chlorine,
- (B) about 25 to about 100 phr of silica comprised of particulate synthetic amorphous silica selected from at least one of
- (1) aggregates of precipitated silica having hydroxyl groups on the surface thereof, and
- (2) pre-hydrophobated aggregates of precipitated silica having been pre-hydrophobated by treating silica in an aqueous colloidal form thereof with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from 10/90 to 90/10;
- wherein said alkylsilane is of the general Formula (I)
- Xn—Si —R4-n (I)
- wherein R is an alkyl radical having from one to 18 carbon atoms, n is a value of from 1 to 3 and X is a radical selected from chlorine or bromine or alkoxy radical as (OR1)—, wherein R1 is an alkyl radical selected from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):
- (X)n(R2O)3-n—Si—R3—SH (II)
- wherein X is a radical selected from chlorine, bromine, and alkyl radicals having from one to 16 carbon atoms;
- wherein R2 is an alkyl radical having from one to 16 carbon atoms and R3 is an alkylene radical having from one to 16 carbon atoms;
- and n is a value from zero to 3;
- (3) from zero to about 15 phr of a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of said aggregates of precipitated silica and another moiety interactive with said diene-based elastomer(s);
- (4) about 0.5 to about 20 phr of an organo phosphite, where said elastomer includes said halogenated copolymer, as at least one of organo diphosphites selected from diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite and organo monophosphites selected from the general formulas (III) and (IV):
- ((OR4)2—P—O—R5)2—R6 (IV)
- wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals;
- wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, wherein R5 is a phenyl radical;
- and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms;
- wherein said organo phosphite is provided by one or more of the following:
- (a) by mixing said organo phosphite with said elastomer(s) and saic synthetic silica in an internal rubber mixer,
- (b) by pre-reacting said hydrogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
- (c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphite/silica composite thereof,
- (d) mixing said organo phosphite with said elastomer(s) and said synthetic silica according to any of said steps (a), (b) or (c) wherein said synthetic silica includes at least one of said pre-hydrophobated silica aggregate. which has been pre-hydrophobated prior to mixing with said elastomers,
- (e) mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (I) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
- (f) pre-reacting said organo phosphite and said alkylsilane of Formula (I) with
- (i) said aggregates of synthetic precipitated silica or
- (ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof.