Blend of polychloroprene and epoxidized natural rubber

The present invention relates to an elastomeric composition comprising a blend of from about 25 to about 75 percent by weight of polychloroprene and from about 75 to about 25 percent by weight of epoxidized natural rubber having a level of epoxide modification in the range of from about 15 to 85 mole percent. These blends may be incorporated along with conventional sulfur-vulcanized elastomers to provide new and improved compounded rubbers particularly suited for use in tire tread applications.

BACKGROUND OF THE INVENTION 
A pneumatic tire is a polymeric composite and is a complex system of 
interacting components, each with specific properties for maximum 
effectiveness. One of the more important components of a tire is the 
tread. Since the tread of a tire comes into contact with the road, it is 
particularly compounded for traction and low rolling resistance. To 
achieve these various properties, blends of rubbers are conventionally 
used in the tread rubber. The tread of a passenger tire is generally 
composed of a blend of styrene butadiene rubber and polybutadiene rubber. 
The tread for truck and aircraft tires are normally composed of natural 
rubber or isoprene rubber in blends with other synthetic elastomers such 
as styrene butadiene rubber, polybutadiene rubber, etc. In order to 
improve the performance characteristics of tires, tire manufacturers look 
to the viscoelastic properties of the tread rubber. For low rolling 
resistance of the tire, a tan. delta optimization at about 60.degree. C. 
is desired. For good traction, a tan. delta optimization at about 
0.degree. C. is desired. Unfortunately, it is difficult to adjust a rubber 
blend for a tan. delta optimization at both temperature ranges and thus, 
achieve good rolling resistance and traction. Therefore, there exists a 
need for a rubber composition which optimizes the tan. delta values for 
both temperatures. 
SUMMARY OF THE INVENTION 
The present invention relates to an elastomeric composition which contains 
a blend of from about 25 to about 75 percent by weight polychloroprene and 
75 to 25 percent by weight epoxidized natural rubber The elastomeric 
composition is particularly suited for use in the tread of a tire. 
DETAILED DESCRIPTION OF THE INVENTION 
There is disclosed an elastomeric composition comprising a blend of from 
about 25 to about 75 percent by weight of polychloroprene rubber and from 
about 75 to about 25 percent by weight of epoxidized natural rubber having 
a level of epoxidized modification in the range of 15 to 85 mole percent. 
There is also disclosed a pneumatic tire having an outer circumferential 
tread adapted to be ground contacting, where said tread is prepared from a 
sulfur curable elastomeric composition comprised of, based on 100 parts by 
weight rubber (phr), (A) from about 60 to about 95 phr of at least one 
rubber selected from the group consisting of medium vinyl polybutadiene, 
SBR, synthetic polyisoprene, natural rubber, cis-polybutadiene, 
styrene-isoprene-butadiene rubber and NBR, and (B) from about 5 to about 
40 phr of a blend of (1) from about 75 to about 25 percent by weight of 
polychloroprene rubber and (2) from about 25 to about 75 percent by weight 
of epoxidized natural rubber having a level of epoxidized modification in 
the range of 15 to 85 mole percent. 
In accordance with the present invention, the blends will comprise from 
about 25 to about 75 percent by weight of polychloroprene and from about 
75 to about 25 percent by weight of epoxidized natural rubber. Preferably, 
the blends comprise from about 40 to about 60 percent by weight of 
polychloroprene and from about 60 to about 40 percent by weight of 
epoxidized natural rubber. A particularly preferred blend comprises 50 
percent by weight of polychloroprene and 50 percent by weight of 
epoxidized natural rubber. 
As known to those skilled in the art, epoxidized natural rubber is a 
modified form of natural rubber in which some of the unsaturation is 
replaced by epoxide groups. Epoxidized natural rubber which may be used in 
the present invention may have a level of epoxide modification ranging 
from about 15 to 85 mole percent. Preferably, the epoxide level will be in 
the range of from about 20 to about 30 percent. A particularly preferred 
epoxide level is 25 percent. Representative of a epoxidized natural rubber 
which may be used is commercially available from The Malaysian Rubber 
Producers' Research Association under the designation ENR.TM.-25. 
The second component in the blends of the present invention is a 
polychloroprene, more commonly known as neoprene. Neoprene is the generic 
name for polymers of chloroprene (2-chloro-1,3-butadiene). Neoprenes are 
classified as general purpose or adhesive types. General purpose types are 
commonly used in a variety of elastomeric applications, particularly 
molded in extruded goods, hoses, belts, wire and cable, heels and soles, 
tires, coated fabrics and gaskets. The general purpose types are 
contemplated for use in the present invention. Representative of the 
general purpose neoprenes which are contemplated for use in the blends of 
the present invention are neoprene GN, neoprene GNA, neoprene GRT, 
neoprene GT, neoprene FB, neoprene W, neoprene WHV, neoprene WRT, neoprene 
WD, neoprene WB, neoprene WK, neoprene TW, neoprene TW-100, neoprene GW, 
neoprene W-Ml and neoprene TRT. Preferred polychloroprenes for use in the 
present invention are commercially available from E I Dupont de Nemours & 
Company under the designation neoprene GW and neoprene W-Ml. 
The vulcanization of the blends of the present invention is dependent upon 
the presence of a curing agent. As known to those skilled in the art, 
polychloroprene requires the presence of a metallic oxide. Representative 
of metallic oxides which may be used include zinc oxide and magnesium 
oxide or mixtures thereof. Generally speaking, the metallic oxide is 
present in an amount ranging from about 2 phr to 8 phr (based on the 
polychloroprene), with a range of from about 3 to 6 phr being preferred. A 
particularly preferred range includes a mixture of zinc oxide and 
magnesium oxide. 
The blend of polychloroprene and epoxidized rubber is prepared by blending 
the mixture and masticating the blend at conventional temperatures. For 
example, the temperature of the composition during mixing may range from 
about 110.degree. C. to about 170.degree. C. Conventional masticating 
equipment include Banbury mixers or extruders may be used. 
The blend of polychloroprene and epoxidized natural rubber is compounded 
with conventional rubbers to form new and improved tread stocks. The tread 
stock is prepared from a sulfur curable elastomeric composition comprised 
of, based on 100 parts by weight rubber (phr), (A) from about 60 to about 
95 phr of at least one rubber selected from the group consisting of medium 
vinyl polybutadiene, styrene-butadiene rubber, synthetic polyisoprene, 
natural rubber, cis-polybutadiene, styrene-isoprene-butadiene rubber and 
NBR: and (B) from about 40 to about 5 phr of a blend of (1) from about 25 
to about 75 percent by weight of polychloroprene and (2) from about 75 to 
about 25 percent by weight of epoxidized natural rubber having a level of 
epoxidized modification in the range of 15 to 85 mole percent. Preferably, 
the total amount of the blend of polychloroprene and epoxidized rubber in 
the rubber stock ranges from about 20 to about 30 phr. 
The rubber stock to which the blend is added is conventional to tread 
rubber. Some representative examples of rubbers that can be used include 
medium vinyl polybutadiene, styrene-butadiene rubber (SBR), synthetic 
polyisoprene, natural rubber, styrene-isoprene-butadiene rubber and NBR. 
Preferred rubbers for use in combination with the blend of the present 
invention are SBR, cis-polybutadiene, cis-polyisoprene, natural rubber, or 
mixtures thereof. The most preferred rubbers are styrene/butadiene rubber, 
cis-polyisoprene, cis-polybutadiene or mixtures thereof. The 
styrene/butadiene copolymer rubber is conventionally composed of a 
styrene/butadiene ratio in the range of about 10/90 to about 40/60. 
Although the copolymer is conventionally prepared by aqueous emulsion 
copolymerization, for some purposes a styrene/butadiene copolymer rubber 
prepared by organic solution polymerization is preferred because it 
typically has a narrower molecular weight range and typically a higher 
average molecular weight which affect its physical properties. Both 
emulsion and solution polymerization methods are relatively well known to 
those having skill in such art. 
In addition to the diene rubber, the rubber stock may contain conventional 
additives including reinforcing agents, fillers, peptizing agent, 
pigments, stearic acid, accelerators, sulfur vulcanizing agents, 
antiozonants, antioxidants, processing oils, activators, initiator, 
plasticizers, waxes, prevulcanization inhibitors, extender oils and the 
like. Representative of reinforcing agents include carbon black, which is 
typically added in amounts ranging from about 20 to about 100 phr. 
Preferably, carbon black is used in amounts ranging from about 45 to about 
85 phr. Typical carbon blacks that are used include N-220, N-330, N-347, 
N-110, N-300, N-550, N-234 and N-339. Representative of conventional 
accelerators are amines, guanidines, thioureas, thiols, thiurams, 
sulfenamides, dithiocarbamates and xanthates which are typically added in 
amounts of from about 0.2 to about 5 phr. Representative of sulfur 
vulcanizing agents include elemental sulfur (free sulfur) or sulfur 
donating vulcanizing agents, for example, an amine disulfide, polymeric 
polysulfide or sulfur olefin adducts. The amount of the sulfur vulcanizing 
agent will vary depending on the type of rubber and particular type of 
sulfur vulcanizing agent but generally range from about 0.1 phr to about 5 
phr with a range of from about 0.5 phr to about 2 phr being preferred. 
Representative of the antidegradants which may be in the rubber stock 
include microcrystalline was, monophenols, bisphenols, thiobisphenols, 
polyphenols, hydroquinone derivatives, phosphites, phosphate blends, 
thioesters, napthylamines, diphenylamines as well as other diarylamine 
derivatives, para-phenylenediamines, quinolines and blended amines. 
Representative of a peptizing agent that may be used is pentachlorophenol 
which may be used in an amount ranging from about 0.1 to 0.4 with a range 
of from about 0.2 to 0.3 being preferred. Antidegradants are generally 
used in an amount ranging from about 0.10 phr to about 10 phr with a range 
of from about 4 to 6 phr being preferred. Representative of processing 
oils which may be used in the rubber stock include activated 
dithio-bisbenzanilide, poly-para-dinitrosobenzene, xylyl mercaptans, 
aliphatic-naphthenic aromatic resins, polyethylene glycol, petroleum oils, 
ester plasticizers, vulcanized vegetable oils, pine tar, phenolic resins, 
petroleum resins, polymeric esters and rosins. These processing oils may 
be used in conventional amounts ranging from about 0 to about 10 phr with 
a range of from about 5 to 10 phr being preferred. Representative of an 
initiator that may be used is stearic acid. Initiators are generally used 
in a conventional amount ranging from about 1 to 4 phr with a range of 
from about 2 to 3 phr being preferred. 
Accelerators may be used in conventional amounts. In cases where only 
primary accelerator is used, the amounts range from about 0.5 to 2.5 phr. 
In cases where combinations of two or more accelerators are used, the 
primary accelerator is generally used in amounts ranging from about 0.5 to 
2.0 phr and a secondary accelerator is used in amounts ranging from about 
0.1 to 0.5 phr. Combinations of accelerators have been known to produce a 
synergistic effect. Suitable types of conventional accelerators are 
amines, disulfides, guanidines, thioureas, thiazoles, thiurams, 
sulfenamides, dithiocarbamates and xanthates. Preferably, the primary 
accelerator is a sulfenamide. If a secondary accelerator is used, it is 
preferably a guanidine, dithiocarbamate or thiuram compound. 
Pneumatic tires are conventionally comprised of a generally toroidal shaped 
carcass with an outer circumferential tread adapted to be ground 
contacting, spaced beads and sidewalls extending radially from and 
connecting said tread to said beads. The tire can be built, shaped, molded 
and cured by various methods which will be readily apparent to those 
having skill in the art. 
In the practice of this invention, the polymer blend tread can be integral 
with and adhered to various tire carcass substrate rubber compositions. 
Typically, such a rubber composition is at least one of a 
butadiene/styrene copolymer rubber, cis 1,4-polyisoprene (natural or 
synthetic rubber) and cis 1,4-polybutadiene. Optionally, such a blend, 
particularly where the tread is in the region of the sidewall area of the 
tire may contain one or more of butyl rubber, halobutyl rubber, such as 
chlorobutyl or bromobutyl rubber, and ethylene/propylene/conjugated diene 
terpolymer rubber, polyisoprene and polybutadiene rubber. 
A rubber composition containing a blend of the present invention may be 
used to form a tread rubber which can then be applied in the building of a 
green tire in which the uncured, shaped tread is built onto the carcass 
following which the green tire is shaped and cured. Alternatively, the 
tread can be applied to a cured tire carcass from which the previous tread 
has been buffed or abraded away and the tread cured thereon as a retread.