Tire tread for ice traction

This invention relates to a tire with a rubber tread reinforced with silica and containing one or more additives designed to aid ice traction for the tread. Such additive is selected from at least one of (i) at least one organic fiber having hydroxyl groups on the surface thereof selected from cellulose fibers and wood fibers and (ii) small, hollow, spherical ceramic particles having silanol groups on the surface thereof. The rubber is composed of at least one or more diene-based sulfur vulcanizable elastomers having a Tg of less than -30.degree. C. and containing silica as predominant particulate reinforcement and other traditional rubber compound ingredients. In particular, a coupler is used to couple the silica as well as the said additive(s) to the elastomer(s) in the tire tread composition.

FIELD 
This invention relates to a tire having a tread containing silica 
reinforcement and composed of one or more diene-based sulfur vulcanizable 
elastomers having a Tg below -30.degree. C., together with at least one 
additive designed to enhance ice traction for the tire tread and together 
with a coupler for coupling the silica and the additive to the 
elastomer(s) of the tire tread. 
BACKGROUND 
In some countries with relatively harsh, long winters, such as for example 
some parts of some Scandinavian countries, studded winter tires are used 
relatively extensively to enhance tire tread traction on icy roads. 
However, the use of studded tires, namely tire treads containing metallic 
studs, have sometimes been somewhat restricted at least in part due to 
potential damage to roads. 
For many years, non-studded winter tires have been used which have tread 
rubber compositions composed of elastomers which have low glass transition 
temperatures (Tg's), namely Tg's below -30.degree. C. Such low Tg 
elastomers are typically used to inhibit or at least reduce excessive 
hardening of the tread rubber composition at the very low ambient 
operating temperatures. 
Also, silica reinforcement of selected elastomers have been used for tire 
treads intended for winter conditions. For example, see U.S. Pat. No. 
5,616,639. 
Other winter tread rubber compositions designed to improve tire traction on 
ice include the aforesaid use of low Tg rubbers, as well as use of low 
temperature plasticizers designed to provide a general reduction of the 
tread composition's hardness at low temperatures. 
However, it is considered herein that it is still desired to provide tire 
treads with enhanced traction on roads which are icy for extended periods 
of time. 
Historically, substantial amounts of silica reinforcement in combination 
with a silica coupling agent has sometimes been used as a primary or 
predominant reinforcement for various rubber blends in rubber tire treads. 
For example, see U.S. Pat. Nos. 4,519,430; 5,066,721; 5,227,425 and 
5,616,639. Use of various coupling agents to achieve reinforcement of the 
rubber composition by coupling the silica to the elastomer(s) is well 
known. However, it is considered herein that such silica/coupler 
reinforcement is often not, by itself, entirely sufficient for suitably 
enhanced ice traction for a tire tread. 
While it is understood that cellulose fibers have been previously suggested 
for use in earthmover tire treads to reduce cut propagation in the tire 
tread rubber composition and that resorcinol/formaldehyde type bonding 
systems have sometimes been used to bond such fibers to the resin network 
of the tread rubber composition compounds, it is considered herein that 
the subject of ice traction for such tread compositions has not been 
addressed. 
In the description of this invention, the terms "rubber" and "elastomer" 
where used herein unless otherwise prescribed, are used interchangeably. 
The terms rubber "composition" or "compound" where used herein, unless 
otherwise prescribed, generally refers to a composition in which one or 
several rubbers are blended or mixed with various ingredients or 
materials. A term "compounding ingredient" where used herein unless 
otherwise prescribed, generally refers to ingredients used to prepare 
rubber compositions, or compounds. Such terms are well known to those 
having skill in the rubber mixing and compounding art. 
The term "phr", where used herein and according to conventional practice, 
refers to parts by weight of respective material per 100 parts by weight 
of rubber. 
The Tg of a rubber or rubber compound, as used herein unless otherwise 
prescribed, refers to its glass transition temperature which can be 
conventionally be determined, for example, by differential scanning 
calorimetrie at a heating rate of 10.degree. C. per minute. It is 
understood that such Tg determination is well known to those having skill 
in such art. 
Summary and Practice of the Invention 
In accordance with this invention, a pneumatic tire is provided having a 
tread of a rubber composition characterized by having a Shore A hardness 
within a range of about 45 to about 65, preferably about 50 to about 60, 
and by being comprised of, based on 100 parts by weight rubber of (a) 
about 95 to 100 phr of at least one diene-based elastomer having a Tg 
below -30.degree. C. and, correspondingly, zero to about 5 phr of at least 
one diene-based elastomer having a Tg of -30.degree. C. or above, 
typically -30.degree. C. to -10.degree. C.; (b) about 30 to about 110, 
alternatively about 50 to about 100, phr of reinforcing filler selected 
from (i) precipitated silica containing silanol groups on the surface 
thereof and (ii) carbon black, wherein said reinforcing filler is composed 
of from about 10 to about 107, alternatively about 30 to about 97, phr of 
said silica and about 3 to about 20 phr of carbon black; (c) about 2 to 
about 30, alternatively about 5 to about 25, phr of at least one additive 
selected from (i) at least one organic fiber having hydroxyl groups on the 
surface thereof selected from cellulose fibers and wood fibers, and (ii) 
hollow, spherical, ceramic particles having silanol groups on the surface 
thereof; (d) at least one coupler, or coupling agent, having a moiety 
reactive with the silanol groups on said silica and said ceramic particles 
and with the hydroxyl groups on said cellulose and/or wood fibers and 
another moiety interactive with at least one of said diene-based 
elastomer(s). 
In practice, it is usually desired that a weight ratio of said coupler to 
silica plus said additive(s) of about 1/8 to about 1/20 is used, although 
such ratio may vary considerably depending somewhat upon the additive 
selected for use and the concentration of silanol or hydroxyl groups on 
the surface thereof or otherwise available to react, as the case may be. 
In practice, it is required that the tire tread rubber composition, in its 
sulfur cured condition, have a Shore A hardness within the recited range 
for enhancing ice traction. While it is to be appreciated that the Shore A 
hardness is determined at about room temperature (i.e.: about 23.degree. 
C.), a rather low range of Shore A hardness values is desired, which is 
indicative of a relatively softer, vulcanized, tread rubber composition. 
The Shore A hardness value determination is well known to those having 
skill in such art. 
In one aspect of the invention, the organic fibers can be cellulose fibers. 
In another aspect, the organic fibers can be wood fibers which are a form 
of cellulose fibers which also contains lignins. In the description of 
this invention the term "cellulose fibers" is intended to exclude "wood 
fibers" even though wood fibers are a relatively impure form of cellulose 
and are physically of a smaller aspect ratio characteristic. 
In a further aspect, the substantially spherical, hollow particles are 
contemplated as being of an aluminosilicate glass composition. 
For the purposes of this invention, the cellulose fibers desirably have an 
average fiber length of about 50 to about 5000 microns, preferably about 
100 to about 2000 microns, and an average aspect ratio (length to diameter 
ratio) of about 5/1 to about 200/1, preferably about 10/1 to about 100/1. 
The wood fibers for the purposes of this invention are substantially 
stubbier than the cellulose fibers with an average aspect ratio of about 
2/1 to about 50/1, preferably about 3/1 to about 20/1, and an average 
fiber length of about 20 to about 2500, preferably about 50 to about 1500, 
microns. 
The hollow ceramic particles desirably have an average diameter in a range 
of about 30 to about 500, preferably about 30 to about 150, microns. 
The combination of the particulate, precipitated silica and said 
additive(s) together with the chemical bonding of such materials to the 
low Tg elastomer(s) by a coupling agent in a tire tread rubber composition 
is considered to be novel and a significant departure from past practice. 
Indeed, this combination of features for a tire tread is considered an 
important aspect of the invention designed to enhance the ice traction for 
a tire tread. 
It is considered, for example, that a silane unit of an alkoxy silane based 
coupling agent reacts with the hydroxyl groups on the surface of the 
cellulose or wood fibers or the silanol groups of the hollow, spherical 
ceramic particles as well as the silanol groups on the surface of the 
silica particles, during the thermal mechanical mixing of the rubber 
composition while compounding ingredients are being mixed with the rubber. 
It is considered herein that an additional moiety of the coupling agent, 
such as for example a polysulfide bridge contained in the coupling agent, 
reacts with the diene-based elastomer(s) during the processing and curing 
of the rubber composition, and thereby coupling the silica and the said 
fibers and/or ceramic particles to the elastomer(s) of the rubber 
composition of the tread compound. 
Such coupling reaction for silica particles is known to be important for 
the effective reinforcement of rubber compositions for use in tire treads. 
In this invention, it is considered that the aforesaid coupling reaction 
between the said fibers and/or ceramic particles, as the case may be, is 
important to enhance the tire tread's ice traction by tending to 
chemically anchor and bond such additives in the tire tread rubber 
composition. 
In practice and in one aspect of the invention, it is believed that the 
said spherical particles and fibrous additives work by increasing the 
effective surface of the tire tread that contacts the ice, such as for 
example, by the friction of the tire tread on the road surface causing the 
rubber to abrade away and partially expose the said incorporated 
additives, resulting in an increased surface of the tire tread compared to 
a smooth tread surface without such additives. After running the tires on 
the road, a visual observation of the tire tread surface may show numerous 
fibers and/or spherical particles, as the case may be, somewhat anchored 
in the surface which are partially exposed. It is acknowledged that, as 
the spherical particles may be abraded against a road surface as the tire 
is run on a road, a portion of the particles may have their spherical 
shape become modified, or fractured or otherwise broken, so that they do 
not remain in a spherical shape during use. However, such particles may 
still be referred to herein as spherical particles. Additionally when such 
fibers or ceramic particles are removed by the friction of the tire on the 
road, the tire's exposed surface is significantly rougher than that of a 
tire tread without such additives contained in the tire tread rubber 
composition. It is readily apparent that a rougher tread surface has a 
larger surface area for contact with the ice than a smoothly worn 
traditional tread surface. This is a hypothesis as how improved, or at 
least enhanced, icy road traction might be obtained for the tire tread. 
In the practice of this invention, it is considered important that the 
elastomers for the tire tread rubber composition have a Tg below 
-30.degree. C. A purpose in restricting the elastomers to those having a 
Tg below -30.degree. C. is to inhibit, or avoid, excess tread rubber 
composition hardening at very low ambient temperature operating 
conditions. 
Representative elastomers for use in this invention include, for example 
and so long as they have a Tg of less than -30.degree. C. are, for 
example, high cis 1,4-polybutadiene containing at least 92 percent cis 
1,4-structure, medium cis 1,4-polybutadiene having about 35 to about 45, 
usually about 42, percent cis 1,4-structure, medium vinyl polybutadiene 
having about 40 to about 70 percent vinyl 1,2-content and a Tg in a range 
of about -30.degree. C. to about -60.degree. C., cis 1,4-polyisoprene 
which may be natural rubber, isoprene/butadiene copolymers, 
styrene/butadiene copolymers, styrene/isoprene copolymers and 
styrene/isoprene/butadiene terpolymers. It is recognized that one or more 
of such elastomers may also have variations which exhibit Tg's at or above 
-30.degree. C., however, it is an important aspect of this invention that 
only the variations of such elastomers which have Tg's lower than 
-30.degree. C. are selected. Thus, elastomers such as 3,4-polyisoprene, 
emulsion polymerization prepared styrene/butadiene copolymer elastomers 
containing at least about 40 percent units derived from styrene, and high 
vinyl polybutadiene elastomers containing greater than 70 percent 
1,2-vinyl groups, to the extent that such elastomers Tg's are above 
-30.degree. C., are intended to be excluded from use in the tire treads 
for this invention. 
While elastomers exclusively having Tg's below -30.degree. C. are 
prescribed, it is contemplated, for the practice of this invention that up 
to about five weight percent of other elastomers, including elastomers 
listed above, might be included in the rubber composition, some of which 
might have a Tg of -30.degree. C. or above, although this is not the 
preferred rubber composition for this invention. 
The cellulose fibers for the purposes of this invention, are a chemically 
refined product and, thus, intended to be differentiated from wood fibers. 
Wood fibers, which may chemically be a form of cellulose, are not 
generally so highly refined and, as hereinbefore discussed, are a 
relatively impure cellulose fiber in a sense that they also contain 
lignines and other organic substances as is well known to those skilled in 
such art. The cellulose fibers might be prepared by various processes such 
as, for example, grinding or hammer milling wood or wood chips to yield a 
fibrous wood pulp and subsequently chemically refining the wood pulps to 
produce a pulp that is fibrous in nature but with the lignin removed. 
Representative examples of cellulose fibers are sometimes referred to 
according to their source such as, for example, as leafwood cellulose, 
soft wood and hard wood cellulose. 
The wood and cellulose fiber descriptions presented above are simply 
intended to be illustrative and are not intended to be otherwise limiting. 
The cellulose fibers may have a purity of about 90% to about 100%. It is to 
be appreciated that the wood fibers are considered herein to be a somewhat 
less pure version of cellulose fibers and in a sense that they contain 
lignins, as well as other organic substances, in addition to the 
cellulose. 
Various cellulose fibers may be those such as, for example, Arbocel.RTM. of 
various grades from the Rettenmaier company exemplary of which is, for 
instance, Arbocel.RTM. B400. Various wood fibers may be those such as, for 
example, Lignocel.RTM. of various grades from the Rettenmaier company 
exemplary of which is, for instance, Lignocel.RTM. HB120. 
The hollow, substantially spherical, ceramic particles are composed an 
aluminosilicate glass composition. A representative example of such 
particles are ceramic microspheres which are sometimes called 
"cenospheres". Such materials may be obtained, for example, Tecfil of 
various grades from the Filtec Ltd company in Great Britain exemplary of 
which are, for instance, Tecfil T85LD and Tecfil 125. 
The hollow spherical ceramic particles for use in this invention, as 
hereinbefore discussed, may be characterized by having an average particle 
size of about 30 to about 500 microns, preferably about 30 to about 150, 
microns. The wall thickness of the hollow spherical particles is variable 
which may lead to an apparent specific gravity in a range of about 0.7 to 
about 1.1. 
Numerous coupling agents taught for use in coupling silica and diene-based 
elastomers may be used in the practice of this invention for coupling both 
the silica and the said additives to the diene-based elastomer(s) of the 
tire tread rubber composition. For example, various alkoxy silane based 
coupling agents recited in the aforesaid enumerated patents might be used 
which contain a polysulfide bridge such as, for example, 
bis(trialkoxysilylalkyl) polysulfide having from about 2 to about 8, 
usually an average of about 2 to about 5, sulfur atoms in the sulfur 
bridge where such alkyl groups may be selected from, for example, methyl, 
ethyl and propyl radicals, with the alkoxy groups preferably being 
selected from methoxy and ethoxy groups. A representative example might be 
bis(triethoxysilylpropyl) polysulfide. 
The commonly employed siliceous pigments used in rubber compounding 
applications can be used as the silica in this invention, including 
pyrogenic and precipitated siliceous pigments (silica), although 
precipitate silicas are preferred. 
The siliceous pigments preferably employed in this invention are 
precipitated silicas such as, for example, those obtained by the 
acidification of a soluble silicate, e.g., sodium silicate. 
The siliceous pigment (silica) may, for example, have an ultimate particle 
size in a range of 50 to 10,000 angstroms, preferably between 50 and 400 
angstroms. The BET surface area of the pigment, as measured using nitrogen 
gas, is in a range of about 80 to about 300, although more usually in a 
range of about 100 to about 200, although perhaps even up to about 360, 
square meters per gram. The BET method of measuring surface area is 
described in the Journal of the American Chemical Society, Volume 60, page 
304 (1930). 
The silica may typically have a dibutylphthalate (DBP) adsorption value in 
a range of about 150 to about 350, and usually about 200 to about 300 
cubic centimeters per 100 grams. 
The silica might have an average ultimate particle size, for example, in a 
range of about 0.01 to 0.05 micron as determined by the electron 
microscope, although the silica particles may be even smaller in size. 
Various commercially available silicas may be considered for use in this 
invention such as, for example only and without limitation, silicas 
commercially available from PPG Industries under the Hi-Sil trademark with 
designations 210, 243, etc; silicas available from Rhone-Poulenc. such as, 
for example, Zeosil 1165MP and silicas available from Degussa AG with 
designations such as, for example, VN2, VN3, BV 3370GR and silicas from J. 
M Huber company such as, for example, Hubersil 8745. 
It is readily understood by those having skill in the art that the rubber 
composition of the tread rubber would be compounded by methods generally 
known in the rubber compounding art, such as mixing the various 
sulfur-vulcanizable constituent diene polymers with various commonly used 
additive materials such as, for example, curing aids, such as sulfur, 
activators, retarders and accelerators, processing additives, such as 
oils, resins including tackifying resins, and plasticizers, pigments, 
fatty acid, zinc oxide, waxes, antioxidants and antiozonants, peptizing 
agents and reinforcing fillers such as, for example, silica and 
silica-carbon black mix. As known to those skilled in the art, depending 
on the intended use of the sulfur vulcanizable and sulfur vulcanized 
compounds or tread compounds, the additives mentioned above are selected 
and commonly used in conventional amounts. 
Typical additions of carbon black and silica, for this invention, are 
hereinbefore set forth. Various carbon blacks, particularly rubber 
reinforcing blacks might be used. For example, although such examples are 
not intended to be limitive, are of the ASTM designation type N-299, 
N-234, N-220, N-134, N-115, and N-110. The selection of the type of carbon 
black is well within an optimization skill by one having skill in the 
rubber compounding for tire treads, depending somewhat upon the intended 
use, purpose and properties for the tire tread. Typical amounts of 
tackifier resins, if used, comprise about 0.5 to about 10 phr, usually 
about 1 to about 5 phr. Typical amounts of processing aids comprise about 
1 to about 80 phr. Such processing aids can include, for example, 
aromatic, naphthenic, and/or paraffinic processing oils or plasticizer or 
medium molecular weight polyesters. Typical amounts of antioxidants 
comprise about 1 to about 5 phr. Representative antioxidants may be, for 
example, diphenyl-p-phenylenediamine and others, such as, for example, 
those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-346. 
Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts 
of fatty acids, if used, which can include stearic acid comprise about 0.5 
to about 4 phr. Typical amounts of zinc oxide comprise about 2 to about 5 
phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often 
microcrystalline waxes are used. Typical amounts of peptizers comprise 
about 0.1 to about 1 phr. Typical peptizers may be, for example, 
pentachlorothiophenol and dibenzamidodiphenyl disulfide. An antioxidant 
may be, for example, of the para-phenylene diamine and/or 
dihydrotrimethylquinoline type. 
The vulcanization is conducted in the presence of a sulfur vulcanizing 
agent. Examples of suitable sulfur vulcanizing agents include elemental 
sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, 
an amine disulfide, polymeric polysulfide or sulfur olefin adducts. 
Preferably, the sulfur vulcanizing agent is elemental sulfur. As known to 
those skilled in the art, sulfur vulcanizing agents are used in an amount 
ranging from about 0.5 to about 4 phr, with a range of from about one to 
about 2.5, being preferred. 
Accelerators are used to control the time and/or temperature required for 
vulcanization and to improve the properties of the vulcanizate. Retarders 
are also used to control the vulcanization on-set. 
In one embodiment, a single accelerator system may be used, i.e., primary 
accelerator. Conventionally and preferably, a primary accelerator(s) is 
used in total amounts ranging from about 0.5 to about 4, preferably about 
0.8 to about 2.5, phr. In another embodiment, combinations of a primary 
and/or a secondary accelerator might be used, with the secondary 
accelerator being used in amounts of about 0.05 to about 3 phr, for 
example, in order to activate the cure and to improve the properties of 
the vulcanizate. Suitable types of accelerators that may be used in the 
present invention are, for example, amines, disulfides, guanidines, 
thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and 
xanthates. Preferably, the primary accelerator is a sulfenamide. If a 
second accelerator is used, the secondary accelerator is preferably a 
guanidine, dithiocarbamate or thiuram compound. 
The selection and amounts of the various compounding ingredients are not 
considered to be critical for the purposes of this invention, except where 
they may be especially emphasized elsewhere in this description, and can 
be adjusted or modified by the practitioner as deemed suitable for the 
desired tire tread properties. 
The tire can be built, shaped, molded and cured by various methods which 
will be readily apparent to those having skill in such art and the rubber 
compounded as set forth in the representative examples. The parts and 
percentages are by weight unless otherwise indicated. 
In the following examples, rubber compositions are prepared with materials 
presented in Tables 1, 2 and 3. The values in the tables for the materials 
are represented in terms of "phr" which are, for the most part, values 
rounded off to the nearest whole part. 
Rubber composition, or compound, physical properties are also provided in 
Tables 1, 2 and 3. Such properties include compound stiffness as reflected 
in its 300 percent modulus, as well as compound hardness as reflected by 
its Shore A hardness. Such properties are well known to those having skill 
in such art. 
A tire's performance is also reflected in Tables 1, 2 and 3, relating to 
acceleration and braking on ice is provided in normalized values. 
Comparative values above 100 represent improved tire performance. Ice 
acceleration values on artificial or natural ice, are measured by time to 
accelerate from one set speed to a given higher speed, the starting and 
ending speed of the test depending on the track used to perform the test 
(e.g.: length of test lane and available braking space) and the test 
vehicle used. Ice braking values are determined by measuring the braking 
distance to bring the vehicle to a complete stop from a given starting 
speed, with the starting speed, as in the case of the acceleration values, 
being dependant upon the test track used to perform the test. For 
comparative acceleration and braking testing of different tire rubber 
compositions, the test conditions were the same for experimental and 
control tires. 
The rubber compositions, or compounds, were prepared by mixing the 
ingredients in several sequential non-productive stages (without the 
sulfur and associated accelerator(s) curatives together with 
antidegradants) to temperatures of about 165.degree. C. followed by a 
final productive mixing stage to a temperature of about 105.degree. C. in 
which the curatives and antidegradants are added. An internal rubber mixer 
(Banbury type) was used. 
The resulting rubber compounds were than extruded to form tread strips 
which, in turn, were built onto tire carcasses and the resulting assembly 
vulcanized in a suitable mold at a temperature of about 160.degree. C. to 
form a tire of size 195/65R15.

EXAMPLE I 
Control rubber composition A is a silica reinforced rubber composition. It 
does not contain wood or cellulose fibers or ceramic spheres. The 
composition has Shore A hardness and dynamic stiffness (300 percent 
modulus) properties considered herein to be normally desirable for winter 
tire tread compositions. 
Control rubber composition B is composed of relatively low Tg elastomers 
reinforced with silica, together with a silica coupler, with hardness and 
dynamic stiffness values lower than those of Control rubber composition A. 
Such means to improve ice performance of tires (tire treads) is considered 
herein to be well known to those having skill in such art. Composition B 
does not contain any wood or cellulose fibers or ceramic spheres. As is 
apparent from the data shown in Table 1, the tire with tread of 
composition B provided a significant improvement of acceleration on ice of 
almost 18 percent as compared to a tire with a tread of composition A. 
However, no significant improvement in ice braking was obtained with 
composition B. Thus, it is considered herein that such classical means of 
compounding to improve the tire performance on ice, as illustrated by the 
tread of composition B as compared to composition A, are only able to 
improve ice acceleration but not ice braking. 
Experimental compositions C and D represent modifications of composition B 
by containing 20 phr of wood or cellulose fibers in place of 20 phr of the 
silica. Compositions C and D also contained an additional 20 phr of rubber 
processing oil to maintain a Shore A hardness similar to composition B. It 
is apparent from the data in Table 1 that the tires with tread 
compositions which contained the fibers (compounds C and D) provided 
significant improvements in ice acceleration and braking as compared to a 
tire with a tread of composition B without the fibers. Therefore, it is 
concluded herein that the inclusion of the wood or cellulose fibers in 
place of a portion of the silica improved the ice braking performance of 
the tires. 
Composition E is a modification of composition B by containing 20 phr of 
hollow ceramic spheres in place of 20 phr of the silica. It is evident 
that the utilization of the ceramic spheres improved the ice performance 
of composition E as compared to the Control B without the ceramic spheres. 
As is apparent from the ice performance test results of compounds C, D and 
E as compared to the Control B, partial replacement of the silica filler 
in the tread rubber composition by either the fibers or the hollow ceramic 
spheres improved the general ice performance of the tires containing these 
additives in the tread rubber composition, particularly improved the 
braking on natural ice. 
TABLE 1 
______________________________________ 
A B C D E 
(Control) 
(Control) 
(Exp) (Exp (Exp) 
______________________________________ 
Compounded Compositions 
IBR-1 50/50.sup.1 
32 0 0 0 0 
IBR-2 30/70.sup.2 
33 0 0 0 0 
Oil extended MV-BR*.sup.3 
0 48.1 48.1 48.1 48.1 
Oil extended cis-BR.sup.4 
43.8 81.3 81.3 81.3 81.3 
Silica.sup.5 95 85 65 65 65 
Wood Fibers.sup.6 
0 0 6 14 0 
Cellulose Fibers.sup.7 
0 0 14 6 0 
Hollow ceramic spheres.sup.8 
0 0 0 0 20 
Coupling agent.sup.9 
15.2 10.2 10.2 10.2 10.2 
PEG.sup.10 0 1 1 1 1 
Antidegradants 
3.5 3.5 3.5 3.5 3.5 
Waxes 1.5 1.5 1.5 1.5 1.5 
Rubber processing oil 
42 25 45 45 25 
Fatty acids 3 3 3 3 3 
Zinc oxide 2.5 2.5 2.5 2.5 2.5 
Sulfur 1.4 1.4 1.4 1.4 1.4 
Accelerators 3.9 4 4.5 4.5 3.4 
Vulcanized Compound 
Properties 
Modulus 300% 5.7 5.7 4.6 4.5 4.7 
Shore A hardness 
58 53 52 49 51 
Dynamic stiffness at 
9.2 4.7 2.9 2.4 3.7 
-20.degree. C. 
Tire Performance on Ice 
Tire Size 195/65R15 
Natural Ice Braking 100 108.4 
104.7 
104 
Artificial Ice Braking 
99.6 100 101.6 
101.2 
101 
Artificial Ice 
82.1 100 102 103.9 
103.3 
Acceleration 
______________________________________ 
*43.8 phr oil extended rubber corresponds to 35 phr of dry rubber and 8.8 
phr of oil 
81.3 phr extended rubber corresponds to 65 phr of dry rubber and 16.3 phr 
of oil 
1. IBR-1 is an isoprene/butadiene copolymer rubber containing about 50 
percent units derived from isoprene and having a Tg of about -45.degree. 
C. obtained from The Goodyear Tire & Rubber Company. 
2. IBR-2 is an isoprene/butadiene copolymer rubber containing about 30 
percent units derived from isoprene and having a Tg of about -85.degree. 
C. obtained from The Goodyear Tire & Rubber Company. 
3. An oil extended medium vinyl polybutadiene rubber having a vinyl content 
of about 53 percent and a Tg of about -55.degree. C. obtained as 
BUDENE.RTM. 1255 from The Goodyear Tire & Rubber Company. 
4. Cis-1,4-polybutadiene rubber having a cis 1,4- content of about 95 
percent and a Tg of about -98.degree. C. obtained as BUDENE.RTM. 1254 from 
The Goodyear Tire & Rubber Company. The rubber contained 37.5 phr of 
rubber processing oil. 
5. A silica obtained as Zeosil 1165 MP from Rhone Poulenc. 
6. Lignocel.RTM. HB120, from the J. Rettenmaier & Sohne GMBH & Co company, 
is a natural wood fiber which is understood to contain some lignin and 
wood polyoses and understood to have a fiber length of about 40 to about 
120 microns and an average aspect ratio of about 10/1. 
7. Arbocel.RTM. B400, from the J. Rettenmaier & Sohne GMBH & Co company, is 
a highly pure cellulose fiber reportedly having a purity of about 95% to 
99.5% and understood to have an average fiber length of about 900 microns 
and an average aspect ratio of about 45/1. 
8. Hollow ceramic spheres as Tecfil T85LD from the Filtec Ltd company 
having an average diameter of about 65 microns. 
9. The coupling agent is a bis-3-(triethoxysilylpropyl) tetrasulfide (50% 
active) commercially available as X50S from Degussa as a 50/50 blend of 
the tetrasulfide with N330 carbon black (thus, considered 50% active). 
Technically, the tetrasulfide is believed to be an organosilane 
polysulfide as a composite, or mixture, having an average number of sulfur 
atoms in a polysulfide bridge in a range of about 3.5 to about 4 
connecting sulfur atoms, although the composite, or mixture, may contain 
individual organosilane polysulfides with about 2 to about 8 connecting 
sulfur atoms. 
10. Poly(ethylene glycol) as Berox 4000 from the Caldic company having a 
softening point range (interval) of about 55 to 61.degree. C. and a 
molecular weight of about 4000. 
EXAMPLE II 
The following Table 2 represents the Control composition F and an 
Experimental composition G. The Control composition F is presented without 
a special additive material included in Experimental composition G. 
Experimental G composition is similar to Control F composition except that 
some of the silica is replaced by cellulose and wood fibers. 
The wood fibers and cellulose fibers were the same as those used in Example 
I as were the rubber compounding ingredients, except where noted. 
The results confirm the improvement in ice performance of tires containing 
cellulose and wood fibers as a partial replacement of the silica filler 
(Experimental composition G) as compared to a similar silica reinforced 
rubber composition (Control F) without the fibers. 
It might be noted that a different combination of elastomers and different 
concentrations of silica and fibers were used than in the compositions of 
Example I. This supports an aspect of the invention that the addition of 
the ice performance enhancing materials is not limited to the elastomer 
blends and fiber and filler levels of Example I. 
TABLE 2 
______________________________________ 
F G 
(Control) 
(Exp) 
______________________________________ 
Compound Compositions 
Natural rubber 50 50 
Oil extended cis-BR* 
62.5 62.5 
Silica 95 75 
Wood fibers 0 6.5 
Cellulose fibers 0 10 
Coupling agent 15.2 15.2 
Antidegradants 3.5 3.5 
Waxes 1.5 1.5 
Rubber processing oil 
35.3 48.3 
Sulfur 1.4 1.4 
Accelerators 3.6 3.5 
Fatty acids 3 3 
Zinc oxide 2.5 2.5 
Vulcanized Compound 
Properties 
Modulus 300% 5.6 6.1 
Shore A hardness 59.2 58.2 
Tire Performance on Ice 
Tire Size 175/70R15 
Testing on Natural Ice 
Acceleration 100 103.9 
Braking 100 106.4 
______________________________________ 
*62.5 phr oil extended cis 1,4polybutadiene rubber correspond to 50 phr o 
dry rubber and 12.5 phr of oil 
EXAMPLE III 
In the following Table 3, the Control rubber composition H is similar to 
Control composition B used in Example I. 
The recited Experimental rubber compositions I and J are of the same 
composition as Control rubber composition H except that a small amount of 
either wood fibers or cellulose fibers are used in addition to a small 
amount of additional coupling agent. No silica was replaced by the added 
fibers. Also, no additional rubber processing oil was added which thereby 
resulted in rubber compositions having higher Shore A hardness values as 
compared to Control composition H. 
The wood fibers and cellulose fibers were those used in the previous 
Examples as were the compounding ingredients except where noted. 
It is readily observed that the tires with treads composed of the 
Experimental rubber compositions I and J with the fiber additions 
evidenced very significant improvements in ice acceleration as compared to 
the tire with tread of the Control rubber composition H. 
For ice braking, however, the tire with tread of Experimental composition K 
containing the wood fiber evidenced a slight reduction in performance and 
the tire with tread of Experimental composition J containing the cellulose 
fibers evidenced a significant improvement in performance. 
TABLE 3 
______________________________________ 
H I J 
(Control) 
(Exp) (Exp) 
______________________________________ 
Compound Composition 
IBR-1 50/50 32 32 32 
IBR-2 30/70 33 33 33 
Oil extended cis BR 
43.8 43.8 43.8 
Wood fibers 0 6 0 
Cellulose fibers 
0 0 6 
Silica 85 85 85 
Coupling agent 13.6 15 15 
PEG 1 1 1 
Antidegradants 2.5 2.5 2.5 
Waxes 2.5 2.5 2.5 
Rubber processing oil 
41.3 41.3 41.3 
Sulfur 1.4 1.4 1.4 
Accelerators 4.1 4.1 4.1 
Fatty acids 3 3 3 
Zinc oxide 2.5 2.5 2.5 
Compound Properties 
Modulus 300% 6.4 6.6 6.9 
Shore hardness 56.8 61.3 62.5 
Dynamic stiffness at -20.degree. C. 
8.5 11.4 10.6 
Tire Size 
Tire Performance on Ice 195/65R15 
Artificial ice acceleration 
100 117.8 125.5 
Artificial ice braking 
100 97.8 107.6 
______________________________________ 
*43.8 phr oil extended rubber corresponds to 35 phr of dry rubber and 8.8 
phr of oil 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the invention, it will be apparent to those 
skilled in this art that various changes and modifications may be made 
therein without departing from the spirit or scope of the invention.