Rubber materials having excellent grip on ice

A rubber material having an excellent grip on ice comprising a mixture of an ordinary rubber and a powdered polymer, said powdered polymer having a maximum of tan .delta. at a temperature in the range of -5.degree. C. to +35.degree. C. when the tan .delta. is measured by a nonresonance, forced vibration apparatus at a frequency of 110 hertz and a heating rate of 2.degree. C./minute.

This invention relates to rubber materials having an excellent grip on ice. 
Known methods for preventing tires and other rubber articles from slipping 
on roads covered with ice or snow include (1) attaching of spikes to their 
surfaces (e.g. Japanese Patent Publication No. 71003/75), (2) 
incorporation of a hard powder, such as glass or sand (e.g. Japanese 
Patent Publication No. 31732/71), (3) insertion of steel wires (e.g. 
Japanese Patent Publication No. 52705/75) and (4) production of these 
articles from a polymer having a high grip on ice. The articles obtained 
by the methods (1) to (3), however, damage objects in contact with the 
articles in an atmosphere above room temperature and free of ice. For 
instance, a tire scars the road surface, causing a hydroplaning 
phenomenon, and a shoe sole causes damage to a floor covering. With the 
method (4), on the other hand, a marked improvement in ice grip is 
difficult to achieve. 
The object of the present invention, therefore, is to provide rubber 
materials capable of affording rubber articles which have an excellent 
grip on ice and cause no damage to surfaces in contact with the articles. 
We have found that the above object can be attained by incorporating in an 
ordinary rubber a powdered polymer which hardens at service temperatures 
on ice and softens at higher temperatures. Thus, the present invention 
provides a rubber material which is a mixture of an ordinary rubber and a 
powdered polymer, said powdered polymer being characterized in that its 
loss tangent (tan .delta.) is at a maximum at a temperature in the range 
of -5.degree. C. to +35.degree. C. when its tan .delta. is measured by a 
nonresonance, forced vibration apparatus at a frequency of 110 hertz and a 
heating rate of 2.degree. C./min. 
When the dynamic mechanical properties of a polymer are measured by a 
nonresonance, forced vibration apparatus at a constant frequency of 
vibration to check for their dependence on temperature, it is generally 
observed that the tan .delta. has a maximum value in a temperature region 
in the vicinity of the glass transition temperature of the polymer. 
MECHANICAL PROPERTIES OF POLYMERS, pages 146 and 163 (Reinhold Publishing 
Corporation, 1962), for instance, gives a detailed description of examples 
of the measuring method and the results of measurements. Such methods well 
known in the art are employed to perform measurements for defining the 
powdered polymer of the present invention. 
Polymeric materials which harden at service temperatures on ice, or at 
temperatures which they experience on ice, and which soften at room 
temperatures are known. These polymeric materials have glass transition 
temperatures or crystallization temperatures falling between the hardening 
temperature and the softening temperature. However, when these polymeric 
materials are kneaded with rubber, they either disperse in the rubber 
finely in sizes on the order of several microns or become compatible with 
the rubber; therefore, the addition of these polymeric materials cannot 
afford rubber articles having an improved grip on ice (see Sample Nos. 2 
and 3 of Example 1 to appear later). 
According to the present invention, a crosslinked powdered polymer or a 
very high-molecular-weight, uncrosslinked powdered polymer having an 
average molecular weight higher than 200 million, each of which does not 
lose the shape of powder due to heat experienced during shaping or curing 
is added to rubber in order to prevent such excessive fine dispersion or 
dissolution. The particle size of the powdered polymer is larger than 0.1 
mm. The crosslinked powdered polymer refers to a powder of a crosslinked 
product obtained by heating rubber, if desired, in the presence of an 
ordinary crosslinking agent and other compounding agents. 
The powdered polymer of the present invention, as has been earlier defined, 
must have a maximum tan .delta. at a temperature within the range of 
-5.degree. C. to +35.degree. C. If rubber is mixed with the powdered 
polymer having a maximum tan .delta. at a temperature below -5.degree. C., 
a rubber article produced from the mixture cannot have an improved grip on 
ice. If rubber is mixed with the powdered polymer having a maximum tan 
.delta. at a temperature above +35.degree. C., a rubber article formed 
from the mixture considerably damages the surface of an object which the 
article contacts. 
Examples of the powdered polymer usable in the present invention include a 
copolymer of styrene or .alpha.-methylstyrene with a conjugated diene such 
as butadiene or isoprene, the content of the styrene unit being relatively 
high; a high vinyl butadiene polymer; and a norbornene polymer disclosed, 
for example, in U.S. Pat. No. 3,546,183. Any other polymers are unable 
which satisfy the aforementioned definition. 
For production of tires, the use of those polymers which have a tan .delta. 
maximum measured at a relatively high temperature near +35.degree. C. is 
preferred so as to cope with heat build-up during running. 
The amount of the powdered polymer is 5 to 100 parts by weight, preferably 
5 to 50 parts by weight, per 100 parts by weight of rubber as a substrate. 
The powdered polymer and ordinary compounding agents for rubber, such as 
curing agents, fillers, and process oils, are added to an ordinary 
synthetic rubber, such as styrene-butadiene copolymer rubber, butadiene 
rubber, or isoprene ruber, or natural rubber to produce the rubber 
material of the present invention. Shaping and heating of this rubber 
material afford a rubber article having a good grip on ice and causing no 
damage to the surface in contact with the article in an atmosphere having 
a higher temperature than the service temperature on ice.

The following Examples illustrate the present invention. The parts therein 
are by weight. 
EXAMPLE 1 
Sixty parts of an aromatic process oil was caused to be absorbed by 100 
parts of a norbornene polymer(polymer of 5-norbornene, NORSOREX, a 
trademark for a product of CdF Company, France) at 50.degree. to 
60.degree. C. for 2 hours. The norbornene polymer was then kneaded on a 
mixing roll heated at 80.degree. to 90.degree. C. to prepare an 
oil-extended norbornene polymer I. 
A powdered norbornene polymer II was prepared by passing a volcanizate of 
an oil-extended norbornene polymer through the narrow gap of a mixing 
roll. The volcanizate of an oil-extended norbornene polymer was prepared 
by vulcanizing the following polymer composition while pressing at 
145.degree. C. for 10 minutes: Norbornene polymer 100 parts, zinc oxide 3 
parts, stearic acid 1 part, ISAF carbon black 30 parts, silica filler 10 
parts, aromatic process oil 40 parts, sulfur 2 parts, 
H-cyclohexyl-2-benzothiazole sulfenamide 1.5 parts, and triethanolamine 1 
part. 
An oil-extended styrene-butadiene copolymer rubber (SER 1712, containing 
37.5% by weight of a high aromatic oil) and the oil-extended norbornene 
polymer I or the powdered Norbornene polymer II were mixed by a B-type 
Banbury mixer in the proportions shown in Table I. At the same time, 
various compounding agents were added in the amounts shown in Table I. 
Then, the rubber compositions were vulcanized by pressing at 145.degree. 
C. for 45 minutes. The resulting vulcanizates had the properties shown in 
Table I. 
TABLE 1 
______________________________________ 
Sample No. 
Present 
Comparison Invention 
1 2 3 4 
______________________________________ 
Recipe & 
physical properties 
SPE 1712 (parts) 
100 90 80 100 
Oil-extended norbornene 
-- 10 20 -- 
polymer I*.sup.1 (parts) 
Powdered norbornene 
-- -- -- 30 
polymer II*.sup.2 (parts) 
Compounding Agents (parts) 
Zinc oxide 3 
Stearic acid 2 
ISAF carbon black 
60 
Aromatic process oil 
5 
N--Phenyl-N--isopropyl-p- 
1 
phenylenediamine 
Phenyl-.beta.-naphthylamine 
1 
6-Ethoxy-2,2,4-trimethyl-1,2- 
1 
dihydroquinoline 
Sulfur 1.7 
N--Oxydiethylene-2-benzo- 
1.1 
thiazole sulfenamide 
Hardenss (JIS) 66 66 70 64 
Skid resistance on ice*.sup.3 
4 4 3 9 
Occurence of scratch*.sup.4 
NO NO NO NO 
______________________________________ 
Table 1 shows that the rubber material of the present invention gives a 
vulcanizate having an excellent skid resistance on ice and causing no 
damage to an acetate film; in contrast, the comparisons containing the 
same polymer as the powdered polymer of the Example of the present 
invention, but unpowdered, do not have an improved skid resistance on ice. 
EXAMPLE 2 
Synthetic cis-1,4-polyisoprene rubber (NIPOL IR 2200, a trademark for a 
product of Nippon Zeon Co., Ltd.) and the oil-extended norbornene polymer 
I or the powdered norbornene polymer II prepared in Example 1 were mixed 
by a B-type Banbury mixer in the proportions shown in Table 2. At the same 
time, various compounding agents were added in the amounts shown in Table 
2. Cured products obtained by pressing the resulting compositions at 
145.degree. C. for 35 minutes were tested for hardness, skid resistance on 
ice, and occurrence of scratch. The results are shown in Table 2. 
TABLE 2 
______________________________________ 
Sample No. 
Present 
Comparison 
Invention 
1 2 3 
______________________________________ 
Recipe & 
Physical properties 
IR 2200 (parts) 100 80 100 
Oil-extended norbornene 
-- 20 -- 
polymer I (parts) 
Powdered norbornene 
-- -- 30 
polymer II (parts) 
Compounding Agents (parts) 
Zinc oxide 5 
Stearic acid 2 
HAF carbon black 50 
Aromatic oil 5 
Diphenyl guanidine 1 
Sulfur 2.3 
N--Oxydiethylene-2-benzothiazole 
1 
sulfenamide 
Hardness (JIS) 65 73 65 
Skid resistance on ice 
3 3 10 
Occurrence of scratch 
NO NO NO 
______________________________________ 
EXAMPLE 3 
Powdered styrene-butadiene copolymers (size: 25-mesh through) were prepared 
by passing vulcanizates of a styrene-butadiene copolymer through the 
narrow gap of a mixing roll. 
The vulcanizates of a styrene-butdiene copolymer were prepared by mixing 
100 parts of a styrene-butadiene copolymer--which has a styrene-butadiene 
ratio of 55/45, 60/40, 66/34, 71/29, 77/23 or 88/12 by weight--with 3 
parts of zinc oxide, 1 part of stearic acid, 30 parts of ISAF carbon 
black, 10 parts of silica filler, 20 parts of an aromatic oil, 2 parts of 
sulfur, 1.5 parts of N-cyclohexyl-2-benzothiazole sulfenamide and 1.0 part 
of triethanolamine by a mixing roll, and then pressing the mixture at 
145.degree. C. for 10 minutes. 
Thirty parts of the powdered styrene-butadiene copolymer were mixed with 
100 parts of styrene-butadiene copolymer rubber (SBR 1502) and various 
compounding agents in the amounts shown in Table 3 by a B-type Banbury 
mixer. The resulting compositions were heated at 145.degree. C. for 45 
minutes to form vulcanizates. The properties of the vulcanizates are as 
shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Sample No. 
Comparison 
Present Invention 
Comparison 
1 2 3 4 5 6 7 
__________________________________________________________________________ 
Recipe & 
physical properties 
SER 1502 (parts) 100 100 100 100 100 100 100 
Powdered styrene-butadiene copolymer 
30 30 30 30 30 30 -- 
(parts) 
(styrene/butadiene ratio, parts) 
(55/45) 
(60/40) 
(66/34) 
(71/29) 
(77/23) 
(88/12) 
Compounding Agents (parts) 
Zinc oxide 3 
Stearic acid 2 
HAF carbon black 50 
Aromatic oil 5 
N--Phenyl-N--isopropyl-p-phenylene 
1 
diamine 
Phneyl-.beta.-naphthyl amine 
1 
6-Ethoxy-2,2,4-trimethyl-1,2- 
1 
dihydroquinoline 
Sulfur 1.75 
N--Oxydiethylene-2-benzothiazole 
1.1 
sulfenamide 
Temperature for tan .delta. maximum of 
-10 -3 +4 +13 
+22 +45 -- 
powdered styrene-butadiene copolymer 
(.degree.C.) 
Hardness (JIS) 66 66 65 66 
66 70 66 
Skid resistance on ice 
5 10 11 10 
14 11 4 
Occurrence of scratch 
NO NO NO NO 
NO YES NO 
__________________________________________________________________________ 
It is clear from Table 3 that vulcanizates prepared from rubber blend with 
the powdered polymer of the present invention which has a tan .delta. 
maximum at -3.degree. C., +4.degree. C., +13.degree. C. or +22.degree. C. 
have a high skid resistance on ice and cause no damage to the surface of 
an object in contact with the vulcanizates. It is also apparent from the 
table that vulcanizates prepared from rubber blended with a powdered 
polymer which has a tan .delta. maximum at -10.degree. C. have a low skid 
resistance on ice, and vulcanizates prepared from a rubber blended with a 
powdered polymer having a tan .delta. maximum at +45.degree. C. cause 
damage to the surface of an object in contact with them.