Tire sealant composition

A tire sealant mixture contains water, mica flakes, hydrated bentonite clay, and a water-miscible carrying agent such as propylene glycol. This sealant mixture is capable of sealing a puncture caused by a 3mm diameter nail without significant pressure loss when the mixture is deployed inside the tire as a prophylactic measure against flat tires.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to materials that may be used to seal 
punctures in pneumatic tires, and, more particularly, to sealant 
compositions that contain a puncture filler material and a liquid carrier 
agent. Still more specifically, the invention pertains to low-viscosity 
sealant compositions that are introduced into inner tubes for rapidly 
sealing punctures as they occur, in order to prevent the occurrence of 
flat tires. 
2. Statement of the Problem 
Automotive tire sealant and/or ballasting compositions typically have a 
high apparent viscosity due to the need to resist escaping air and the 
need to provide a balanced uniform thickness of sealant on the tire wall 
where punctures occur. Kent et al, U.S. Pat. No. 4,101,494, teaches a 
ballasting composition having an apparent viscosity of from 1000 to 2200 
centipoise at 100.degree. F. This ballasting composition contains asbestos 
fibers and a polyvinyl alcohol, as well as an optional ethylene glycol 
antifreeze portion. Tibbals, U.S. Pat. No. 3,747,660, teaches a 
thixotropic tire ballasting composition that consists essentially of a 
gel-forming clay and an alkali metal hexametaphosphate. Kitamura et al, 
U.S. Pat. No. 4,607,065, teaches a sealant composition including butyl 
rubber, a tackifier, an acrylol or methacrylol group-containing a 
polymerization unsaturated compound, a filler, and a photopolymerization 
initiator. The filler may include glass fibers, clay, and silica. These 
high-viscosity compositions are useful in tubeless automotive tires, which 
operate at elevated temperatures resulting from high rpm and frictional 
contact with the pavement. A major problem exists with these compositions 
in that they contain ingredients which are potentially very hazardous to 
human health. Additionally, the butyl rubber-containing sealants are 
typically sprayed into a fixed position on the outer tire wall, but inner 
tubes cannot receive the sealants in this manner. 
Prior tire sealant mixtures of the type that may be applied through a valve 
stem opening have traditionally been used only in Schrader-type valves, 
i.e., those having a spring-biased valve core that may be completely 
removed from the valve air inlet opening by unthreading the core from the 
threaded interior of the valve stem where it is seated. The Schrader 
valves are in widespread use on automobiles and probably a majority of 
bicycles. Even so, many bicycles have a European style Presta-type valve, 
which has a narrower valve stem interior than does the Schrader valve, and 
relies upon air pressure (not spring bias) for sealing. Tire sealant 
mixtures that include a viscous mixture of liquid and fibers typically 
clog Presta valves. 
A commercially available viscous-fiber tire sealant composition, 
SLIME.sup.1 from Access Marketing of Shell Beach, Calif., contains 
propylene glycol, man-made fibers, a corrosion inhibitor, and a biocide. 
These ingredients are typical of most commercially available fibrous 
bicycle tire sealants. This liquid composition is sold as a bicycle tire 
sealant, and is pumped into tires through a Schrader-type valve stem 
opening; however, the composition usually clogs the Presta-type valve 
cores and, as a practical matter, cannot be used to seal inner tubes 
having these types of valve cores. Furthermore, the mixture fails to seal 
many types of punctures in an instantaneous manner, and significant 
pressure drops are often observed after the puncture occurs. While the 
fibrous mixture has a lower apparent viscosity than do the automotive 
sealants and ballasting compositions that are discussed above, the 
apparent viscosity is still relatively high. 
FNT .sup.1. SLIME is a trademark of Access Marketing of Shell Beach Calif. 
There remains a need for an environmentally compatible prophylactic sealant 
composition that is effective for sealing tire and inner tube punctures 
without significant pressure loss. 
SOLUTION TO THE PROBLEM 
The present invention overcomes the problems that are outlined above by 
providing an environmentally compatible tire sealant mixture that is very 
effective in sealing tire and inner tube punctures as they occur. The low 
viscosity mixture contains is rapidly deployed to puncture sites where it 
is needed and, consequently, a lesser volume and weight of the mixture is 
required for effective use. 
Broadly speaking, the tire sealant mixture includes a hydrated clay, solid 
mineral flakes, water, and a water-miscible polyhydric alcohol. These 
ingredients are combined and stirred to substantial homogeneity, but may 
settle out of solution in the absence of agitation. In the proper relative 
proportions, these ingredients are effective for permitting a four ounce 
portion of the mixture to stop air flow through a tire puncture caused by 
a 3mm diameter nail after the nail is removed from the puncture. This 
stoppage is typically effective for retaining at least about 50 psi of 
internal pressure within the tire after sealing of the puncture. 
The polyhydric alcohol is preferably a glycol having a carbon number 
ranging from two to seven, and is most preferably propylene glycol. Other 
glycols, such as ethylene glycol, may be used, but are less preferred due 
to corresponding increases in toxicity and/or viscosity. The mineral 
flakes are preferably mica flakes having an effective diameter up to about 
1 millimeter ("mm"), and having an average effective particle diameter 
from about 0.01 to about 0.5 mm. The glycol is preferably present in a 
volume ranging from about 0.15 to about 0.4 gallons of glycol per gallon 
of the final mixture. 
The hydrated clay is preferably formed from a dry bentonite powder, which 
most preferably has a majority sodium montmorillonite portion. The dry or 
desiccated clay is preferably provided in the form of a very finely 
divided powder, which may be obtained as a variety of commercially 
available drilling mud materials. These muds are designed to disperse 
individual clay platelets in a uniform manner throughout a fresh water 
aqueous system upon hydration of the muds, though, the mud system can 
typically tolerate some salts. The clay powder is hydrated by mixing it 
with water at ambient temperature and pressure prior to introducing the 
clay to the water-miscible polyhydric alcohol. The pre-hydration is 
preformed to avoid the deleterious effects upon viscosity and gel strength 
of direct mixing between the dry clay and the glycol or polyhydric 
alcohol. The weight of dry clay to the volume of the final sealant mixture 
will preferably range from about 0.2 to about 0.4 pounds of clay per 
gallon of the final mixture. 
The final mixture will preferably contain hydrated clay in a minimal amount 
as needed to provide a gel strength sufficient to prevent any substantial 
settling of the mica in the mixture for an interval of approximately ten 
seconds immediately after agitation of the mixture ceases. This agitation, 
for example, may be caused by the rotation of a tire that contains the 
mixture in addition to compressed air. The amount of hydrated clay added 
to the mixture will also preferably provide an apparent viscosity of up to 
about 70 centipoise, more preferably up to about 50 centipoise, and most 
preferably about 30-40 centipoise, as determined at about 70.degree. F. 
using a FANN-VG meter at 300 rpm. 
The mineral flakes are preferably formed of mica, and are present in an 
amount ranging from about 0.5 to about 0.9 pounds of mica per gallon of 
the final mixture. The mica portion has a relatively larger particle size 
distribution than does the clay portion. This size distribution difference 
permits the mica to form a loose bridge over the puncture under the force 
of pressurized air attempting to escape. The hydrated bentonite completes 
the filter cake to completely seals the puncture by filling in the 
remaining voids. A small amount of fluid or sealant filtrate may be 
observed at the external puncture site after sealing, and represents a 
very small quantity of fluid that has been strained substantially free of 
bentonite and mica during the formation of a completely-sealing internal 
filter cake. The addition of polyhydric alcohol to the mixture serves to 
reduce the amount of fluid loss through the puncture, and also prevents 
the clay from completely drying at the site of the puncture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1-3 depict a bicycle inner tube 20 having a conventional Presta-type 
valve 22 as tube 20 is prepared to receive a tire sealant mixture 24 of 
the present invention. As is best depicted in FIG. 1, valve 22 includes a 
valve stem 26 having a threaded upper neck portion 28 and an interior 
core-seating portion 30. Valve stem 26 may optionally be provided with 
exterior threads and a nut to lock stem 26 in place through a 
stem-receiving hole in a conventional bicycle wheel rim (not depicted). 
Valve 22 also includes a valve core 32 having a stem-seating portion 34, a 
threaded rod 36, and a threaded cap 38. When tube 20 is filled with 
compressed air, the internal air forces stem-seating portion 34 into 
sealing engagement against core-seating portion 30, as assisted by tension 
in rod 36 derived from tightening cap 38. 
Tube 20 is prepared for receiving sealant mixture 24 by cutting rod 36 at a 
position remote from stem-seating portion 34 and unscrewing cap 38 to drop 
core 32 into the position depicted in FIG. 2. As depicted in FIG. 2, 
bottle 40, which has a neck opening complementary to neck portion 28 for 
receipt thereover, is inserted over neck 28 and squeezed to force the 
sealant mixture 24 into tube 20. FIG. 3 depicts tube 20 being inverted to 
reinstall core 32 in a conventional manner after the addition of sealant 
mixture to the confines of tube 20. In contrast to prior fibrous filler 
materials, the present invention will not typically render valve 22 
inoperable by clogging the area of seating elements 30 and 32. 
The following non-limiting examples set forth preferred materials and 
methods for practicing the present invention. 
EXAMPLE 1 
THE PREFERRED SEALANT COMPOSITION FORMULATION 
An approximate five gallon mixture of tire sealant was prepared by mixing 
the ingredients of Table 1. 
TABLE 1 
______________________________________ 
Ingredient Quantity 
______________________________________ 
propylene glycol* 1.5 gallons 
water* 1.5 gallons 
dipotassium orthophosphate* &lt;0.8 pounds 
hydrated bentonite gel 2 gallons 
mica 3.5 pounds 
______________________________________ 
*Purchased together as AMBITROL.sup.2 NTF 50 Coolant from Dow Chemical 
Company of Midland, Michigan 
FNT .sup.2. AMBITROL is a trademark of Dow Chemical Company of Midland, Mich. 
The bentonite gel was prepared by mixing as a homogenous slurry 2.5 gallons 
of water with 2.25 pounds of dry, finely divided drilling mud powder 
(AQUAGEL.sup.3 from Baroid Drilling Fluids, Inc., of Houston, Tex.) 
containing bentonitic clay of the sodium montmorillonite variety. The 
resultant slurry was allowed to stand for about 12 hours to form a final 
hydrated gel having an approximate three gallon volume from which two 
gallons were used to mix the sealant composition. The mica was purchased 
as MICATEX.sup.4 from Baroid Drilling Fluids, Inc., and included small 
mica flakes having effective particle diameters ranging up to about 1 mm. 
FNT .sup.3. AQUAGEL is a trademark of Baroid Drilling Fluids, Inc. of Houston, 
Tex. 
FNT .sup.4. MICATEX is a trademark of Baroid Drilling Fluids, Inc. of Houston, 
Tex. 
The propylene glycol, free water, and potassium orthophosphate were 
purchased together as a commercially available mixture that is formed of 
50% propylene glycol, about 47% water, and less than about 3% dipotassium 
orthophosphate by weight as a buffering agent. The glycol mixture was 
combined to substantial homogeneity with the prehydrated bentonite gel at 
an ambient temperature of about 75.degree. F. and atmospheric pressure. 
The gel was first hydrated prior to being mixed with the propylene glycol, 
as is most preferable, because the addition of propylene glycol prior to 
hydration of the bentonite clay would impair the sealing performance of 
the final mixture by increasing viscosity, reducing gel strength, and 
reducing the level of clay platelet dispersion. 
While the above tire sealant mixture can tolerate some ionic salts, e.g., 
the potassium orthophosphate, the addition of ionic salts to the mixture 
is undesirable due to flocculation of the clay platelets. Flocculation 
results in increased fluid loss through punctures and increased viscosity 
in the final mixture. While flocculated sealant mixtures will still 
function as tire sealants, these mixtures will not function in an optimal 
manner. Accordingly, it is preferred to maintain the total salt 
concentration in the final mixture at a minimal level. This minimal level 
is preferably less than about a 80,000 ppm sodium chloride equivalent, 
more preferably less than about 50,000 ppm, and most preferably less than 
about 30,000 ppm. The potassium orthophosphate is beneficial for its 
mixture buffering effect, but may optionally be eliminated from the 
preferred mixture. A dye or colorant may be added as an optional 
ingredient, and is preferably any water-soluble coloring agent, such as 
food coloring, and may be added in an effective amount for achieving a 
desired color. 
The mica was stirred into the glycol and bentonite gel mixture. Settling of 
the mica and clay components was observed during storage of the mixture, 
but these were easily mixed again to a homogenized distribution throughout 
the composition by shaking of the mixture. The homogenized solution had an 
apparent viscosity of about 38 cp determined at 70.degree. F. on a FANN VG 
meter at 300 rpm. 
The mica and bentonite clay of Table 1 were added as filler materials to 
form a filter cake that serves to seal the flow of air upon puncturing of 
a pneumatic tire. This mixture of filler materials provided a combination 
of particle size distributions that produced particularly advantageous 
effects in the sealing of pneumatic tire punctures. The relative amounts 
of these ingredients may be varied up to about .+-.25% for purposes of 
producing effective sealant mixtures. 
EXAMPLE 2 
TIRE PUNCTURE TESTING 
A mountain bicycle tire having a 5 cm width, a 26 inch diameter, and an 
approximate 270 cubic inch internal volume was selected for testing. A 
four ounce portion of the homogenous tire sealant mixture from Example 1 
was introduced to the confines of the tire inner tube, in the manner 
depicted in FIGS. 1-3. After the valve core was replaced, the tire was 
repressurized to 50 psi. A nail having a 3mm diameter was driven flush 
into a one-inch thick board with a pointed two inch segment of the nail 
protruding through the board on the opposite side of the board from the 
flush nail head. The tire was positioned above the pointed nail segment 
for puncturing of the lowermost tire portion, and the nail was withdrawn 
from the punctured tire. No air leakage was observed, but a small 2mm 
diameter bead of liquid, which comprised sealant filtrate having most of 
the filler materials removed, could be observed at the exterior side of 
the puncture. The filtrate bead stopped growing at the approximate 2mm 
diameter size. 
The pointed nail segment was used to puncture the tire a second time, 
except that the side of the tire was punctured while holding the board at 
a right angle with respect to the ground to puncture the tire at a nine 
o'clock position. In this case, the tire leaked while held in the original 
position, but sealed substantially instantaneously when the puncture was 
rotated downwardly towards the ground. The term "substantially 
instantaneously" is used here because a mist exited the puncture very 
briefly for a period of about a tenth of a second just prior to complete 
sealing of the puncture as the puncture rotated downward. Accordingly, in 
the sense of an observed internal tire pressure, no appreciable quantity 
of air escaped the tire. 
These puncture tests were repeated ten times on the same tire, with the 
same sealing result in each case. At the end of the puncture testing, the 
tire with ten sealed holes was placed upon a bicycle and performed well on 
a five mile ride, i.e., the tire functioned without deflating or loosing 
an appreciable amount of internal tire pressure. The bicycle was parked, 
and the tire maintained a useful internal pressure for a period of about 
three months with no appreciable leakoff of pressure for an initial period 
of about two weeks. The gradual decline in sealant effectiveness derives 
from slow drying of the puncture-sealing filter cake, which may be 
restored by rotating the tire to redistribute the remaining internal tire 
moisture. 
A sealant-containing tire was punctured for sealing in a manner identical 
to that described above. The tire was deflated for removal of the inner 
tube, which was then cut open in the vicinity of a puncture site. As 
depicted in FIG. 4, an analysis of the puncture revealed the formation of 
a filter cake 42 proximal to puncture 44 in tube 20. The mica flakes 46 
formed a large matrix over the interior of puncture 44, and the clay 
platelets 48 filled the voids in the matrix to completely seal puncture 
44. 
EXAMPLE 3 
COMATIVE TESTING AGAINST OTHER SEALANT COMPOSITIONS 
As previously indicated, a leading commercially available viscous fiber 
bicycle tire sealant has ingredients including propylene glycol, man-made 
fiber, 1% corrosion inhibitor, and 1% biocide. The commercial product was 
tested against the mixture derived from Example 1 by using the puncture 
test methods of Example 2. Table 2 serves to provide the comparative 
results, which demonstrate a clear superiority in the mixture from Example 
1. The results were obtained over at least ten trials for each item on a 
given tire. 
TABLE 2 
______________________________________ 
COMATIVE TEST DATA 
Example 1 Commercial 
Test Results Mixture Mixture 
______________________________________ 
Recommended effective 
2-4 ounces 4 ounces 
amount 
Time to Seal 
Pinhole Instant 2 minutes or lon- 
ger 
3mm Nail 2/3 revolution FLAT - Ineffective 
Pressure Loss 
Pinhole Negligible Greater than 20 
psi 
3mm Nail 0-4 lbs @ 50 lbs FLAT - Ineffective 
Effective Pressure Range up to 100 psi 10-20 psi 
Flexible Seal Yes Yes 
Apparent Viscosity; FANN- 38 cp .+-. 10 cp 70 cp .+-. 10 cp 
VG meter @ 300 rpm, 70.degree. F. 
Valve Types Useful Presta/Schrader Schrader 
Environmentally Harmful No No 
______________________________________ 
The pinhole punctures were obtained by using a conventional sewing pin to 
puncture the tire at the 9 o'clock position, removing the pin, and 
rotating the puncture downwardly for sealing. Similarly, the 3mm nail 
punctures were obtained using the nail and board from Example 2 to 
puncture the tire at the 9 o'clock position, and rotating the puncture 
downwardly to seal the puncture. 
These comparative results demonstrate that the mixture of Example 1 has a 
significantly enhanced level of utility as compared to the commercially 
available product. It is significant that the higher viscosity commercial 
mixture permitted air to escape until the internal tire pressure fell to 
about 20 psi. In contrast, the Example 1 mixture was effective at sealing 
punctures even in the presence of up to 100 psi of internal tire pressure. 
Another significant aspect of these results is the fact that the 
commercial mixture typically clogged Presta valves and, therefore, is not 
a useful sealant in these types of tires. In contrast, the Example 1 
mixture did not clog Presta valves. Furthermore, the Example 1 mixture 
served to seal the larger 3mm punctures with very little pressure loss, 
while the commercial mixture was ineffective against these large 
punctures. In terms of the effective volume of sealant mixture, it is 
further significant that a two ounce portion (0.007 ounces per cubic inch 
of tire space) of the Example 1 mixture served to seal punctures in an 
effective manner, whereas the four ounce recommended portion (0.015 ounces 
per cubic inch of tire space) of the commercial sealant was much less 
effective in terms of retaining pressurized air within the punctured tire. 
The correspondingly lesser required volume and weight of the sealant 
mixture from Example 1 is a significant reduction to bicycle racing 
enthusiasts who choose to utilize sealant compositions. 
Those skilled in the art will understand that the preferred embodiments, as 
described hereinabove, may be subjected to apparent modifications without 
departing from the true scope and spirit of the present invention. 
Accordingly, the inventors hereby state their intention to rely upon the 
Doctrine of Equivalents to protect their full rights in the invention.