Note: Descriptions are shown in the official language in which they were submitted.
1~ 3.~
This inv~ntion relates to tubeless rubber tires
constructed so as to be self-sealing with respect to
small puncture holes. In one embodiment, this invention
relates to a tire sealant composition for use on an
internal surface of an automotive rubber tire whlch is
capable of self-sealing puncture holes in the tread region
when the tire is in use and at a temperature in the range
of about -20F. to 270F. In another embodiment, the com-
position may be used as a sealant for bicycle tires, in
which case it must be capable of operating in a temperature
range of approximately 30F. to 125F.
Considerable effort has been expended to develop
a rubber tire for automotive applications which is capable
of self-healing puncture wounds while in operation. United
States patents 2,756,801, 2,765,018 and 2,782,829 disclose
different approaches to this problem. The development~jof
an effective self-healing tire is very difficult because
the operating tire may experience temperatures over a very
wide range. Tires on vehicles standing outside in the
wintertime may experience temperatures of -20F or lower.
On the other hand, the tires of a vehicle traveling for
prolonged periods in summer weather at highway speeds may
reach temperatures of 220F. or higher. To be effective,
the sealant portion of such a tire must be sufficiently
tacky to stick to a puncturing object, or to itself if
the puncturing object is removed, and have sufficie~t
strength to seal the hole at any temperature in this broad
range. Furthermore, the sealant must resist oxidative or
thermal degradation when subjected to the air, which may
become quite hot, filling the tire. None of the prior art
,; compositions and approaches directed to self-sealing tires,
that we are aware of, are effective under all of these con-
ditions. Furthermore, in our experience, no currently
r ~?
3~8
available sealants effectively perform as a self-healing
composition in vehicle tires under all t~e conditions that
a tire can be expected to encounter.
Accordingly, it is an object of the present inven-
tion to provide a vehicle tire construction incorporating
an inner circumferential layer of sealant composition that
is effective to seal puncture holes up to about one-quarter
inch or so in diameter when the tire is at a temperature in
the range of below zero Fahrenheit to about 270F. The
multicomponent composition of the sealant layer has the
ability to immediately heal a newly formed puncture hole
at a temperature in this wide range and sufficient strength
to prevent significant loss of air pressure.
It is another object of the present invention to
provide a tire sealant composition suitable upon curing for
use in a conventional rubber tire. The composition is a
specific combination of several ingredients which cooperate
to provide the ~elf-healing properties and the strength
properties required for this demanding application.
In accordance with one embodiment of our invention,
these and other objects and advantages are accomplished by
provid~ng a circumferential layer of ~ured sealant composi-
tion on an internal surface of a vehicle tire, particularly
in the region behind the tread stock. The sealant layer
is formed by initially mixing specific quantities of a
relatively high molecular weight curable isobutylene-
i- isoprene copolymer, a relatively low molecular weight cur-
able isobutylene-isoprene copolymer, a liquid polybutylene
tackifier, a partially hydrogenated block copolymer of a mono-
vinyl arene and a conjugated diene, carbon black and a
crosslinker and initiator to cure the butyl rubber compo-
nents. For example, a sealant may be prepared by initially
mixing 15 parts by weight of curable
~! -2-
32138
isobutylene-based copolymer having an average molecular
weight in the range of about 100,000 to 300,000; 10 parts
by weight of a curable isobutylene-based copolymer hav-
ing an average molecular weight in the range of about
10,000 to 30,000; 65 parts by weight of a liquid polybuty-
lene having an average molecular weight of about 500 to
5,000; 10 parts by weight carbon black; and 5 parts by
weight of a partially hydrogenated block copolymer of the
A-B-A configuration wherein prior to hydrogenation each-
A is a polystyrene block and each B is-substant-ially~ a poly-
isoprene block, the total molecular weight of the block
copolymer being about 100,000 and the polyisoprene making
up about two-thirds by weight of the block copolymer.
A suitable solvent, such as toluene, for the
polymeric components may be employed to assist in the mix-
ing and handling of the composition. A small amount of
a crosslinking agent, such as para-quinone dioxime, and a
crosslinking initiator, such as benzoyl peroxide, are em-
- ployed to cure the two isobutylene copolymer components.
Where it is desired to apply a sealant layer of
the subject composition to a preformed tire, a toluene
dispersion of the uncured composition may be sprayed onto
- the inside surface of the tire. For example, about 200
grams (on a solvent-free basis) of the above composition
containing crosslinkers is air sprayed into a steel belted
JR-78-15 tire preheated to 125F. The composition gels in
about two to five minutes. The tire is then allowed to
set at ambient temperature for one-half hour to allow for
: evaporation of excees toluene and then placed in an oven
at 125F. for an additional one-half hour to preheat the
tire for spraying of the second coat of sealant. Thi~
procedure is repeated after the second coat. Upon comple-
tion of the application of the third coat, the tire is
again allowed to stand at room temperature for one-half
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1083~88
hour and then placed in an oven at 125F. for sixteen hours for finai curing.
The thus formed sealant layer remains in its place in the tire despite normal
usage thereof. Furthermore, it has the ability to fill and seal a puncture hole
formed in the tire even at high speed and high temperature tire operation.
It is a principal object to provide a sealant compos7tion comprising
a Partially cross-linked matrix, said matrix comprising 10 to 15 parts by
weight of a high average molecular weight butyl rubber having an average
molecular weight in the range of about 100,000 to 300,000, 6 to 10 parts by
weight of a low average molecular weight butyl rubber having an average mole-
10 cular weight in the range of about 10,000 to 30,000, and 5 to 17 parts of
carbon black, in admixture with 60 to 65 parts by weight of a liquid polybutylene
based tackifier.
Other advantages of our invention will become more apparent
from a detailed description thereof which follows. Reference ~iill be made to
the drawings, in which:
FIGURE 1 is a perspective view of a tire broken away to show
the cross-sectional structure thereof and to display one embodiment of the
invention in which the sealant layer is located on the innermost surface of
the tire behind the tread; and
FIGURE 2 is a perspective view of a tire broken away to show
the cross-sectional structure of the tire and depicting another embodiment
of the invention in which the subject sealing layer is located behind the
tread and between an air impervious film conventionally employed in the
tire and the carcass portion of the tire.
In FIGURE 1 is depiected a tubeless tire 10 which comprises
the tread portion 12, carcass 14, and side walls 16. In tubeless tires it is
generally desirable to employ a barrier layer or lining 18 which is imper-
meable to air. The air impermeable lining 18 extends typically over the
entire i-nner surface of the tire from one bead portion to the other bead
30 portion. In accordance with one embod7ment of our invention a sealing layer
20 is placed on the inside of the tire against the air barrier layer 18.
The sealant layer 20 is arranged and constructed to lie principally
behind the tread of the tire because it is contemplated that the sealing
~ayer wilI serve principalIy to seal
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la~32&~
punctures coming through the tread portion of the tire.
FIGURE 2 depicts a tubeless tire 10 having parts
similar to those depicted in FIGURE 1 (and identified by
like numerals), except that in this embodiment of our in-
vention the sealing layer 20 is located between the carcass
14 of the tire and the air impermeable barrier layer 20.
In general, it is preferred that our sealant
layer be formed and cured at the time the tire is being
manufactured. Production economies can be realized, in=
cluding the fact that the subject sealant layer can be
cured at the higher temperatures (about 3504F.) employed
in curing the other tire rubber compositions. When this
is done it is possible to locate the sealant layer either
betweèn the carcass 14 of the tire l~ and the air imperm- ~ -
eable barrier layer 18 as shown in FIGURE 2, or inside the
air imperme~ble layer 18 as shown in FIGURE 1. However,
if the sealant layer is applied after the tire is manufac-
tured, of course, it is only possible to place such layer
inside the air impermeable barrier as shown in ~IGURE 1.
Our sealant layer 20 is a tacky, carbon-filled
rubber material formed by curing a compound mixture of a
high molecular weight and a low molecular weight butyl
- rubber. In~orporated with these rubber materials prior to
curing is a tackifier and, optionally, a thermoplastic
elastomer bLock copolymer, preferably of poly~tyrene and
polyisoprene, which significantly contributes to the high
temperature strength and sealing capability of our sealing
layer.
A better appreciation of our invention will be
i 30 gained through specific examples which illustrate how the
sealing composition is compounded, cured, applied and`
evaluated.
Example 1
The screening of a number of commercial sealants
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had indicated that a curable butyl rubber sealant would
be compatible with the rubber tires and might afford a
good starting place for a self-sealing tire composition.
~owever, the butyl rubber-based sealant by itself did not
have sufficient strength at high temperatures nor sufficient
tack to serve as a tire sealant composition.
A commercially available sealant composition was
obtained having the following compositions.
Ingredients Parts by Weight
High molecular weight,
curable butyl rubber 60
Low molecular weight,
curable butyl rubber 40
HAF carbon black 50
SRF carbon black 25
MT Carbon black 25
Tung oil 5
Toluene 483.5
Para-quinone dioxime 2.5
.~ . ' .
The high molecular weight butyl rubber was a copolymer of
96% isobutylene and 4% isoprene. The average molecular
weight of the polymer was in the range of 100,000 to
300,000. The low molecular weight butyl rubber was like-
wise a copolymer of 96~ isobutylene and 4% isoprene. How-
ever, the molecular weight of this butyl rubber was in the
range of 10,000 to 30,000. These two butyl rubber compon-
ents are curable because of the residual unsaturation pro-
vided by the small isoprene content. The carbon black
filler contributes strength to the sealant. The tung oil
component is a processing additive. Toluene i9 a solvent
for the uncured butyl rubber components. The para-quinone
dioxime is a crosslinking agent which has to be oxidized
to para-dinitroso benzene with a suitable oxidant, such as
'; -6-
'1083'~f~
lcad dioxide or benzoyl peroxide, to initiate curing.
In making up the subject sealant, 35 parts by
weight of the above com~ercial composition (on a solvent-
free basis) was mixed with 60 parts by weight of a liquid
polybutylene-ba~ed tackifi~r and 5 parts by weight of a
partially hydrogenated block copolymer of styrene and
isoprene, and the para-quinone dioxime was added. In this
case an additiona~ 1.5 parts of para-quinone dioxime per
100 parts of butyl rubber constituents were added. This
made a total of 4 parts of the dioxime per 100 parts
curable rubber. The additional dioxime crosslinker wa~
employed to increase the crosslink density of the cured -
ru~ber and provide greater strength. These constituents
were all dissolved or suspended in the toluene solvent.
The liquid tackifier was actually a copolymer
of 98% butylene and 2% isobutylene. It had an average
molecular weight in the range of 500 to 5,000. It was a
commercial product available under the trade name "Indopol
~ H-300" .
The block copolymer employed was of the A-B-A
type wherein the A blocks were formed of polystyrene, the
B blocks were polymeric segments of isoprene and some higher
carbon chain length conjugated dienes. The block copolymer
employed in the sealant of this example had an avérage
molecular weight of about 100,000 and was made up of about
68% by weight polyisoprene. The block copolymer had been
hydrogenated so that the polyisoprene segments were almost
completely saturated. However, the polystyrene segments
were not hydrogenated to any significant extent. The
specific material used in this example was obtained under
the trade designation "Kraton G-6500". ~lock copolymèrs
of this type are described in United States patent 3,595,942.
New Uniroyal JR-78-15 steel belted radial tires
* l~ k
~ ' .
3~3
were obtained to evaluate the subject sealant composition.
It was noted that the tires had residual mold release
agent on their internal surfaces. To remove the mold re-
lease agent, the tires were first mounted on a rotator and
then one-half gallon of a soap solution containing a 50
milliliter cup of Amway SA-8 soap powder was added to a
tire. A steel rotary brush on a flexible cable was then
used to brush the tire with the soap solution while the
tire was rotating. The tire was then thoroughly rinsed
out with tap water. The rinse water was then removed,
followed by a vacuuming step to remove the remaining water.
The tire was then dried at ambient prior to coating.
A tire was then preheated to 125F. A ~uantity
of the subject sealant composition prepared as described
above was provided. Ten parts of benzoyl peroxide per 100
parts of total curable butyl rubber constituents present
were added to the mixture and thoroughly mixed therewith.
The sealant composition dispersed in toluene was then
sprayed onto the inner surface of a cleaned and preheated
tire employing commercial air paint spray equipment. A
pressure feed was employed and the sealant was sprayed using
50 psig compressed air. However, an airless spray system
could also be used. The tire was rotated as the sealant
was sprayed onto the internal surface and directed to the
region behind the tread, as indicated at 20 in FIGURE 1.
Two hundred grams (on a solvent-free basis) of the sub-ject
sealant composition were applied. Some of the solvent
evaporated during spraying and the applied composition gelled
in the tire in about five minutes. The tire was then left
at ambient temperature for a minimum of one-half hour to
evaporate excess solVent and cure the sealant layer. One-
half hour prior to the second coating the tire was placed
in an oven at 125F.
lQ~33~3~
The tire was remove~ from the oven and, while
still warm, a second 200 gram layer (on a solvent-free
basi~) of sealant composition i~entical to that described
was applied. Much of the toluene solvent evaporated upon
spraying and the second layer was observed to quickly gel.
The tire was set asi~e for one-half hour to allow much of
the toluene to evaporate and returned to the oven for an
additional one-half hour. The tire was then removed from
the oven and a third 200 gram coating ~solvent-free basi~)
was applied. The tire was returned to the oven as before
and the third sealant layer cured at 125F. overnight.
The tire was then mounted on a wheei and inflated
with air to 30 psig. The wheel was rotated and the tire
was punctured with 0.200 and 0.250 inch diameter spikes at
temperatures of -20F., ambient, and 270F., and the spikes
were removed. After puncturing at each temperature, each
puncture was squirted with a commercial soapy leak detector
called "Snoop" to observe if any leakage took place. In
each instance the tire sealed itself without any significant
leakage of air.
~ , ' ' .
A second sealant composition was prepared. It
was made up by mixing together 14.25 parts by weight of a
curable high molecular weight butyl rubber having an average
molecular weight in the range of 100,000 to 300,000, 9~5
parts by weight of a curable butyl rubber having a molecular
weight in the range of 10,000 to 30,000, 62 parts by weight
of the polybutylene liquid tackifier, 9.5 parts by weight
of an industrial carbon black, a furnace black with a surface
area of 235 sq. meters/gm and a pH of 9.0, 4.75 parts by
partially hydrogenated block copolymer of polystyrene and
polyisoprene, and 2.5 parts by weight para-quinone dioxime
_g_
:1~83~A8
per 100 parts total curable butyl rubber constituent~.
This mixture was dissolved in and suspended in 90 part~
by weight of toluene. Just prior to usage, 10 parts by
weight of benzoyl peroxide per 100 parts of butyl rubber
components were dissolved in 60 parts of toluene and added
to the curable rubber composition.
A number of Uniroyal JR-78-15 tires were cleaned
with a soap-sodium metasilicate cleaning solution as des-
cribed in Example 1. The tires were preheated to 125F.
and each coated with three 20D gram layers (solvent-free
basis) of the subject composition. Each layer was observed
to gel within a period of minutes. After the application
of the third layer the tire was then set aside for one
hour to allow for st of the toluene to evaporate at
ambient and then placed in the oven at 125F., wherein
solvent was evaporated and the sealing composition was
cured over a sixtesn hour period. The tires were then
mounted on wheels and tested with nail punctures through
the tread at temperatures from -20F., ambient, and 270F.
as described in Example 1. In each instance the sealant
healed the puncture hole without significant loss of air.
It has been noted that the healing occurs in the following
manner. The sealant adheres to the nail when the nail is
in the tire, and this sealant adhering to the nail i8
pulled into the puncture hold if the nail is removed. Air
pressure helps to force sealant to the nail and also into
the puncture hole. When a tire has been punctured and
; self-healed in accordance with the subject invention and
then removed from its wheel and examined from the inside,
it is usually very different to locate the puncture. The
sealant is drawn or forced into the hole to very effectively
; heal it.
It has been found that the subject sealant
composition must be formulated to contain certain specific
., ~
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iQ~
constituents witllin narrow and definite composition
ranges. In the automobile tire embodiment, the diffi-
culty lies in providing a composition which has the ability
to both re-heal any cut in the sealant caused by a puncture
and seal a puncture hole at a temperature anywhere in the
range from a~out -20F. to 270F. Once the hole has been
filled (which must occur very rapidly), it is then necessary
for the sealant to have sufficient strength to maintain air
under pressures up to 30 to 40 psig and higher while the
tire is continually being flexed and stressed as it is in
normal vehicie use. While the automobile tire sealant has
been tested and found effective at temperatures up to 270F.
it is usually felt automotive tires in normal usage will not
experience temperatures above about 220F.
The automobile sealant embodiment is made up
according to the following specification. Two curable
butyl rubber components -- one a relatively high molecular
weight constituent and the other a relatively high molecular
weight constituent -- are employed in combination. Ten
to fifteen parts of an isobutylene-based copolymer
(preferably about 96% isobutylene - 4% isoprene) having
an average molecular weight in the range of about 100,000
to 300,000 is employed in combination with 6 to 10 parts
of a copolymer of 96% isobutylene and 4% isoprene, having
an average molecular weight in the range of about 10,000
to 30,000. Mixed with the curable butyl rubber constitu-
ents are 60 to 65 parts by weight of a liquid polybutylene
(e.g., 98% butylene - 2% isobutylene) tackifier having an
average molecular weight in the range of 500 to S,000.
This liquid saturated C4 polymer represents a major part
of the total composition. It possesses excellent thermal
stability, stickiness and flowability over the wide temp-
erature range in which the subject sealant must serve.
--1 1--
33~8~
An optional polymeric constituent of the subject
sealant composition is a thermoplastic, elastomeric, hydro-
genated block copolymer having the general configuration
A-(B-A)l 5. Four to ten parts of this hydrogenated block
copolymer are employed in combination with the other con-
stituents. If more than about 10% of the block copolymer
is employed in the subject sealant (solvent-free and
curing agent-free basis) the composition will not adequately
self-heal. If the block copolymer content is less than
4% (on the same basis) the sealant does not have adequate
strength temperatures above about 220F. Compositions
which include no block copolymers whatsoever are neverthe-
less useful as bic~cle tire sealants, since operating
temperatures within a bicycle tire will normally not range
above 125F.
Prior to hydrogenation each A (of the A-(B-A)1_5
- block copolymer) is a thermoplastic monovinyl arene polymer
block and each B is a conjugated diene polymer block. In
accordance with our invention the monovinyl arene i8
preferably styrene, but may also be alpha methyl styrene,
ring alkylated styrenes and the like as well as mixtures
thereof. Furthermore, in accordance with our invention the
B block(s) may be prepared from conjugated dienes having
from 4 to 10 carbon atoms, but preferably 4, 5 or more
carbon atoms per monomer molecule, including specifically
isoprene. The elastomeric polymerized conjugated diene
component of the block copolymer typically makes up in
total about two-thirds or more of the block copolymer with
the thermoplastic polymer constituent making up the end
groups and the balance of the copolymer. In accordance
! with our invention the average molecular weight of this
block copolymer is suitably in the range of about 60,000
to 400,000 and preferably in the range of about 70,000 to
150,000. The composition is partially hydrogenated so that
~ I ,
-12-
lQ~3~
the conjugated diene block segment(s) are substantially
fully saturated. ~lowever, the polystyrene segm~nts are
not appreciably hydrogenated. Copolymers which are not
hydrogenated in this fashion are not suitably resistant
to oxidation and degradation at the high temperature end
of the operating environment of the tire, particularly
considering that there is considerable oxygen in the tire.
Carbon black filler in the amount of 5 to 17
parts by weight is also incorporated into the composition.
A furnace black having a high surface area and a basic pH
- is preferred.
A solvent, such as toluene, for the polymeric
components may be employed in the preparation and applica-
tion of the sealant composition.
Also incorporated in the composition is a suit-
able crosslinker for the butyl rubber constituents. The
preferred corsslinker for the butyl rubber constituents is
para-quinone dioxime. However, other well known bu~yl rub-
ber curing agents may be employed. At the time the curing
is to take place it is also necessary to incorporate an
oxidative initiator, such as benzoyl peroxide, to convert
para-quinone dioxime to its crosslinking form, para-
dinitroso benzene. Para-quinone dioxime and benzoyl perox-
ide are preferred for use in combination in the practice
of our invention because they promote rapid gel times.
The embodiments of the invention described in
the specific examples involved spraying the subject sealing
composition into tires that had already been manufactured.
In another embodiment, particularly suitable for applica-
tions to bicycle tires, the sealant composition is formed
; and cured in the form of sheets and applied to the inside
of the tire, as desired, employing a suitable adhesive.
However, in many instances it will be preferred to form
-13-
and cure the sealant layer at the same time the tire is
~eing manufactl~red, One practice would be to first lay
up the butyl rubber-based inner liner. An uncured seal-
ing layer of the subject composition would then be placed
on the inner liner member. Then the uncured carcass por-
1:ion of the tire, including its layers of reinforcing
belting and the like, would be formed after the sealing
layer had been laid up. Subsequently, the treat stock
would be laid on the uncured carcass. The whole tire would
then be cured at normal curing temperatures of the orde~
of 350F., at which temperature the curing of the subject
sealing composition would be greatly accelerated and
comparable in time to the curing of the other portions of
the tire. When the butyl rubber portion of the subject
sealant layer is cured at this high temperat`ure, some
modifications may be required in the type and amount of
crosslinker and initiator employed as compared with the
above examples.
Prior to the discovery of the subject composition
a number of other known sealant and elastomeric materials
were tested and evaluated as self-healing tire sealants.
For example, other butyl rubber-containing compositions
were tried but failed to be self-sealing over the wide
temperature ranges involved. Also, ethylene-~inyl acetate
copolymers were tested and found lacking. Urethane rubbers
were also evaluated and it was found that they would not
satisfactorily seal puncture holes over the wide temperature
ranges involved. We have also found, as indicated above,
that even when employing the specific constituents described
as elements fo the subject composition, a wide variation
in their compositional ranges cannot be toierated and still
obtain the benefits of the subject invention.
While our invention has been described in terms
~' l0~32a~
of a few specific embodiments thereof, it will be appreci-
ated that other fonns could be adapted by one skilled in
the art and, accordingly, our invention is to be considered
limited only by the scope of the following claims.
,
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