Pneumatic tire having air retention innerliner

A pneumatic rubber tire having an integral innerliner comprising a compounded rubber composition comprised of a sulfur cured blend of a halobutyl rubber and an unsaturated copolymer of propylene oxide and copolymerizable monomer.

FIELD OF THE INVENTION 
This invention relates to a pneumatic tire having an air retention 
innerliner. 
BACKGROUND OF THE INVENTION 
The inner surface of pneumatic rubber tires is typically comprised of a 
rubbery, elastomeric composition designed to prevent or retard the 
permeation of air and moisture into the carcass from the tire's air 
chamber. The portion of the tire containing such inner surface is often 
referred to as an innerliner. Innerliners have also been used for many 
years in tubeless pneumatic vehicle tires to retard or prevent the escape 
of air used to inflate the tire, thereby maintaining tire pressure. 
Rubbers which are relatively impermeable to air are often used as a major 
portion of said innerliners and can include butyl rubber and halobutyl 
rubbers. U.S. Pat. No. 3,808,177 discloses other polymers which may also 
be relatively impermeable. 
The innerliner is normally prepared by conventional calendering or milling 
techniques to form a strip of uncured compounded rubber, which is 
sometimes referred to as a gum strip. Typically, the gum strip is the 
first element of the tire to be applied to a tire building drum, over and 
around which the remainder of the tire is built. When the tire is cured, 
such innerliner becomes an integral, co-cured, part of the tire. 
The preparation of a gum strip composed entirely of compounded chlorobutyl 
or bromobutyl rubber has been observed to have some processing and 
fabrication problems such as sticking to processing equipment during the 
milling and calendering operations. 
Furthermore, it has sometimes been desired to provide a gum strip 
composition for the innerliner which has both an enhanced building tack in 
its uncured state and a good cured adhesion to the tire carcass while also 
having a satisfactory degree of air impermeability. 
Therefore, it is desired to provide a tire innerliner composition having 
enhanced processing characteristics, uncured building tack and cured 
adhesion to a tire carcass. 
STATEMENT AND PRACTICE OF THE INVENTION 
In accordance with this invention, a pneumatic rubber tire is provided 
having an integral innerliner comprising a compounded rubber composition 
comprised of a blend of halobutyl rubber and an unsaturated copolymer of 
at least one alpha-olefin oxide and copolymerizable monomer. Such blend is 
preferably comprised of about 50 to about 98 parts by weight of a 
halobutyl rubber selected from chlorobutyl and bromobutyl rubbers and 
about 50 to about 2 parts by weight, or phr, (parts by weight per 100 
parts by weight halobutyl rubber and copolymer) of at least one 
unsaturated copolymer of an alpha-olefin oxide and copolymerizable 
monomer. 
Therefore, as a particular embodiment of this invention, a pneumatic rubber 
tire is provided having an integral innerliner comprising a compounded 
rubber composition comprised of a sulfur cured blend of about 50 to about 
98, preferably about 80 to about 95, phr of at least one halobutyl rubber 
selected from chlorobutyl rubber and bromobutyl rubber and about 50 to 
about 2, preferably about 20 to about 5, phr of at least one unsaturated 
copolymer of propylene oxide and about 0.5 to about 20, preferably about 2 
to about 10, weight percent based on the propylene oxide of at least one 
copolymerizable monomer selected from butadiene monoxide, isoprene 
monoxide, 1,2-epoxy-3-allyloxypropane (allyl glycidyl ether) and limonene 
monoxide. The preferred copolymerizable monomer is allyl glycidyl ether. 
In practice, the innerliner composition is first prepared as an uncured 
compounded rubber gum strip, constructed as an inner surface (exposed 
inside surface) of an uncured rubber tire structure, (carcass), and sulfur 
co-cured with the tire carcass during the tire curing operation under 
conditions of heat and pressure. Thus, the innerliner becomes an integral 
part of the tire by being co-cured therewith as compared to being a simple 
adherent laminate. 
The innerliner rubbers can be compounded with conventional rubber 
compounding ingredients comprised of carbon black, zinc oxide, stearic 
acid, rubber processing oil, sulfur, accelerator and antidegradant and 
then typically extruded and/or calendered to form the uncured gum strip. 
The preferred unsaturated polymer of alpha-olefin oxide is a copolymer of 
propylene oxide and allyl glycidyl ether. Such copolymer and a method for 
its preparation is disclosed in U.S. Pat. No. 3,509,068. The disclosure 
and description contained in such patent is hereby incorporated into this 
specification by reference. 
An important feature of this invention is the discovery that the halobutyl 
rubber/alpha-olefin oxide copolymer blend provides a sulfur curable tire 
innerliner composition which has been observed to provide an improvement 
in its rubber compound processability and uncured building tack and also 
its cured adhesion to a rubber tire carcass compound as compared to a tire 
innerliner composition composed only of the halobutyl rubber as its 
polymer component. Although the innerliner rubber blend composition has 
been observed to exhibit an increase in air permeability as compared to 
the halobutyl rubber innerliner composition, it is considered that the 
resultant air permeability of the polymer blend is satisfactory, 
particularly in view of its observed enhanced processability. 
The uncured tire carcass rubber interface with which the innerliner is 
sulfur co-cured can be of various sulfur curable rubber and rubber blends 
such as, for example, polybutadiene, polyisoprene and styrene/butadiene 
copolymer rubbers. 
Typically the innerliner has an uncured gum thickness in the range of about 
0.03 to about 0.08 inch (0.08-0.2 cm), depending somewhat on the tire 
size, its intended use and degree of air retention desired. 
The pneumatic tire with the integral innerliner composition may be 
constructed in the form of a passenger tire, truck tire, or other type of 
bias or radial pneumatic tire.

The practice of this invention is further illustrated by reference to the 
following example which is intended to be representative rather than 
restrictive of the scope of the invention. Unless otherwise indicated, all 
parts and percentages are by weight. 
EXAMPLE 1 
Several blend compositions of chlorobutyl rubber and copolymer of propylene 
oxide and allyl glycidyl ether were prepared as a compounded rubber 
composition by mixing in a size BR Banbury blender the chlorobutyl rubber 
and the copolymer as shown in the following Table 1. Additional 
compounding ingredients comprised of carbon black, zinc oxide, stearic 
acid, sulfur and accelerators were mixed with the blend as a two step 
mixing process in which all of the ingredients were mixed in the first 
step except for sulfur and accelerators which were added and mixed in the 
second step. The control compound A is based on the chlorobutyl rubber and 
experimental compounds B-E are based on the blend. 
TABLE 1 
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INNERLINER COMPOSITION 
Control Experimental 
Compound (phr) 
Compounds (phr) 
Components A B C D E 
______________________________________ 
Chlorobutyl 
100 95 90 85 80 
Rubber.sup.1 
Propylene Oxide/ 
0 5 10 15 20 
allyl glycidyl 
ether copolymer.sup.2 
______________________________________ 
.sup.1 Chlorobutyl rubber obtained as HT10-66 from Exxon. 
.sup.2 Copolymer obtained as Parel 58 from Hercules Inc. 
Properties of the cured innerliner composition are shown in Table 2 with 
Composition A being a control as a chlorobutyl rubber and Compositions B-E 
being the experimental compositions as the rubber blends. The compositions 
had been cured for about 36 minutes at about 150.degree. C. 
TABLE 2 
______________________________________ 
INNERLINER COMPOSITION PROPERTIES 
Con- 
trol 
Com- Experimental 
pound Compounds 
Properties A B C D E 
______________________________________ 
Rheometer 
Max Torque 22.6 24.0 24.4 24.9 25.2 
300.degree. F. 
Min Torque 11.6 11.0 10.7 10.9 10.8 
(150.degree. C.) 
Delta Torque 
11.0 13.0 13.7 14.0 14.4 
T.sub.90 (minutes) 
16.25 48.0 48.5 49.5 49.5 
T.sub.2 (minutes) 
7.25 11.5 11.75 
13.25 
14.5 
Ultimate Tensile MPa 
8.0 9.0 8.5 8.4 8.6 
Ultimate Elongation % 
930 935 910 910 910 
100% Modulus MPa 0.6 0.7 0.8 0.8 0.8 
300% Modulus MPa 1.9 2.1 2.2 2.3 2.2 
Shore A Hardness 50 51 52 52 50 
Ketjen Tack 
To: Itself 27 30 28 29 24 
Newtons Carcass Stock.sup.1 
8 10 11 11 12 
Chafer Stock.sup.2 
4 4 4 4 4 
Apex Stock.sup.3 
6 7 8 10 17 
Peel (180.degree.) 
To: Itself 90* 102* 102* 102* 115* 
Adhesion Carcass Stock.sup.1 
41 43 66* 68* 67* 
93.degree. C.; 
Chafer Stock.sup. 2 
72* 72* 66* 78* 74* 
Newtons Apex Stock.sup.3 
76* 79* 77* 77* 87* 
Air Permeability Ratio of 
1.0 1.10 1.14 1.54 1.70 
Experimental Compound to 
Chlorobutyl Control 
Compound (ASTM D1434) 
______________________________________ 
*Sample failure at fabric backing rather than at stock innerface. 
.sup.1 Blend of natural (polyisoprene) and styrene/butadiene copolymer 
rubbers. 
.sup.2 Styrene/butadiene copolymer rubber. 
.sup.3 Blend of natural (polyisoprene) and polybutadiene rubbers. 
The compounded rubber compositions were calendered into strips with fabric 
backing having a thickness of 0.055 inches and 8 inches wide for 
preparation of Ketjen tack and peel adhesion test samples and calendered 
into strips having a thickness of 0.022 inch and 8 inches wide for air 
permeability test samples prior to curing. 
A comparison of cure behavior, stress strain properties (tensile and 
elongation), tack and cured adhesion to other tire components, and air 
permeability has been shown in Table 2. 
Although the experimental blend compositions B-E exhibited a slower rate of 
cure when compared to the control A, the stress strain properties of 
tensile and elongation were observed to be comparable. The slower rate of 
cure of the blend compositions B-E was not considered to be a serious 
consideration since the innerliner is in direct contact with the hot cure 
bladder during the tire cure cycle. 
All of the tested compounds were observed to exhibit excellent tack to 
themselves and poorer tack to the representative chafer stock, whereas the 
experimental blend compositions were observed to show improved tack to 
representative apex and carcass stocks when compared to the control. 
The cured adhesion of the test compounds to themselves or to representative 
apex or chafer stocks cannot be directly or easily compared on a numerical 
basis since the failures occurred at the fabric backing instead of the 
stock interface. These results indicate, however, that adequate adhesion 
should exist between these rubber compounds. In the case of cured adhesion 
to the representative carcass stock, the control test sample A exhibited 
adhesive failure at the interface between the cured rubber compounds. In 
contrast, the blends containing 10 to 20 phr of the copolymer exhibited 
higher values of cured adhesion, which were actually failures at the 
fabric backing, and are therefore considered to have higher adhesion to 
the representative carcass stock. 
Although the experimental blends exhibited a steady increase of air 
permeability relative to the control (1.1/.sub.1 to 1.7/.sub.1) as the 
level of the copolymer in the blend is increased from 5 to 20 phr, it is 
considered that the air permeability is within satisfactory limits. 
Indeed, a natural rubber sample of the same thickness would be expected to 
demonstrate an air permeability ratio of about 10/1 as compared to control 
sample A. Thus, even in the worst case, the air permeability of sample E 
would be about 6 times less than a comparable sample of natural rubber 
compound. 
The processing of the samples B-E was noticeably improved over control 
sample A. During the milling and calendering operation prior to testing, 
the blend compositions, particularly at the 10 to 20 phr level of the 
copolymer in the blend, were observed to be easier to process as a result 
of less sticking to a two roll breakdown mill and the calender used to 
prepare the test samples. In particular, the control composition A was 
found to be more difficult to remove from the roll mill (because of its 
sticking to a roll) and also more difficult to calender as a gum strip 
(because of sticking to a calender roll) than the experimental 
compositions B-E. 
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.