White sidewall tire

White tire sidewall made from a urethane derived from a hydrogenated diphenylmethane diisocyanate terminated apolytetrahydrofuran and pigmented with titanium dioxide has exceptionally good flex resistance and adhesion. High molecular weight triol and a low molecular weight diol are used to chain extend and crosslink the urethane.

The invention relates to a white sidewall tire. 
Evaluation of tires in the run flat mode reveals that blackwall tires 
generally out-performed white sidewall tires of similar construction. 
Failure of the white sidewall tires occurred preferentially around the 
whitewall region. These observations suggest that the present method of 
fabricating a whitewall tire might have to be modified or the white 
sidewall compound be eliminated for improved mileage, especially in the 
run flat condition. 
Painting a blackwall tire would be an attractive alternative for it permits 
one to retain the better performance of the blackwall tire without 
sacrificing the aesthetic look of a whitewall tire. In addition, painting 
could amount to a substantial reduction in the number of steps required to 
build a whitewall tire. U.S. Pat. No. 3,979,547, Roberts (1976) discloses 
a polyurethane-rubber based paint which can be used to paint rubber and 
not "orange peel". 
A suitable paint should adhere effectively to the tire sidewall and be able 
to withstand the repeated flexing of the tire during service. None of the 
commercial paints evaluated to date can meet the above requirements 
satisfactorily. 
A flexible coating which appears to have excellent flex resistance to 
"orange peel" plus ability to adhere to a nonstaining tire sidewall 
substrate is characterized by the presence of two essential ingredients. 
The first ingredient is (1) 100 parts of a prepolymer of a hydrogenated 
diphenylmethane diisocyanate terminated polytetrahydrofuran containing 
from 1 to 10% by weight of isocyanate groups; (2) a chain extending 
organic diol having a 2 to 6 carbon atom chain, and (3) a chain extending 
and cross-linking triol having a molecular weight of from 1,000 to 20,000 
wherein the ratio of NCO groups of (1) to the total OH groups of (2) and 
(3) has a value of from 100:80 to 100:110 and preferably 100:90 to 100:95. 
Preferably the mole ratio of diol to triol has a value of about 30 to 
about 400. 
The second ingredient is a titanium dioxide pigment from 4 to 10 parts of 
the pigment can be present. The pigment preferably has a particle size of 
from 0.1 to 0.5 microns. 
Ingredients which can be used are old and well known and will not be 
described in detail here. Representative examples include: 
______________________________________ 
Ingredients 
Example (mfr) Description 
______________________________________ 
Prepolymer Adiprene LW510 
Polytetrahydrofuran 
(duPont) terminated by hydro- 
genated diphenyl- 
methane diisocyanate 
and containing 
4.25% NCO 
Chain extending 
diol 1,4 Butanediol 
______________________________________ 
Triols 
Triols Equivalent Weight 
Manufacturer 
______________________________________ 
Trimethylol 
propane 44.7 Mobay Chemicals 
Pluracol TP740 
241.0 BASF Wyandotte 
Thanol SF5500 
1675.0 Jefferson's Chemical 
Thanol SF6500 
2244.0 Jefferson's Chemical 
Pigment 
TITANOX.RTM. 
2015 pigment 
______________________________________ 
TITANOX.RTM. 2015 is a low oil absorption rutile pigment designed for 
coatings containing only titanium dioxide. Controlled particle size 
ensures high brightness, high tinting strength, blue tone in white and 
tints and ease of dispersion. 
Physical Properties 
Crystal Structure Rutile 
Specific Gravity 4.1 
One Pound Bulks 0.0293 gallon 
Oil Absorption, .+-. 10% 
19.5 
Retained on 325 Mesh 
0.01% maximum 
Chalk Resistance Moderate 
pH 7.0-8.0 
Composition 
TiO.sub.2 95.0% minimum 
Remainder Principally alumina 
Avg. Wear Particle size 
0.2.mu. 
Specifications 
ASTM D 476-70, Type II 
U.S.A.S. Z66.1 - 1964

A specific formula is disclosed in Table I below. Both the properties of 
the coating and that of a regular white sidewall rubber compound are shown 
for comparison. 
TABLE I 
______________________________________ 
Coating Formulation and Properties 
Parts 
By 
Materials Description Weight 
______________________________________ 
Adiprene Hydrogenated diphenylmethane 
LW 510 diisocyanate-terminated poly- 
tetrahydrofuran, 4.25% NCO; 
duPont Chemicals 100.0 
A1163-96 65/35 ratio by weight of TITANOX.RTM. 
2015 (N&L Ind.) in dioctyl 
phthalate 9.6 
Ionol 2,6 di-t-butyl-4-methyl phenol, 
antioxidant; Harwick Chem. 
0.5 
T-12 Dibutyltin dilaurate solution, 
catalyst, M&T Chemicals 
0.01 
1,4 Butanediol 
Chain extender 4.13 
Thanol SF6500 
Trifunctional polyether polyol of 
molecular weight 6500; chain ex- 
tender and cross-linker; 
Jefferson's Chemicals 0.73 
______________________________________ 
.sup.1 Adiprene LW 510 is a polyetherbased casting urethane polymer which 
is readily processable by conventional hand and machine mixing techniques 
Adiprene LW 510 produces high quality elastomers in the 90A durometer 
hardness range when cured with MDA. 
Product Description 
Physical Form Viscous liquid 
Color Honey colored 
Specific Gravity at 25.degree. C./4.degree. C. 
1.03 
Flash Point, .degree.F. 
Above 450.degree. F. 
Storage Stability Excellent in absence 
of moisture 
Viscosity, Brookfield 
cps at 212.degree. F. 
1800-2000 
Available Isocyanate 
Content, % 4.1-4.4 
Solubility Soluble in aromatic 
hydrocarbons, 
ketones, esters 
and chlorinated 
hydrocarbons 
The diol and triol were mixed prior to addition to the polymerization 
mixture. Curing conditions: 250.degree. F. (121.degree. C.) for 30 
minutes, followed by 122.degree. F. (50.degree. C.) for one week post 
cure. 
______________________________________ 
Commercial 
Coating White Sidewall 
Properties Formulation Rubber Compound 
______________________________________ 
Shore A Hardness 
80 -- 
100% Modulus, MPa 
(ASTM D 412) 1.66 0.34 
Tensile, MPa 
(ASTM D 412) 28.95 11.6 
Elongation % 
(ASTM D 412) 850 675 
Trouser tear, kN/m 
(ASTM D 470) 18.5 3.4 
Flex Life 
Monsanto, flexes to 
failure (60% exten- 
sion).sup.2 473,500 295,000 
DeMattia pierced 
(ASTM D 813) 10.sup.5 flexes to 0.76 cm 
10.sup.5 flexes to 
0.64 cm 
______________________________________ 
.sup.2 Monsanto Fatigue or Flex Life Testing Dumbbell shaped tensile 
specimens are cyclically strained at a fixed frequency and a series of 
fixed maximum extension ratios such that little or no temperature rise is 
induced. As a result of flexing, cracks usually initiated by a flaw, 
ultimately grow and cause failure. The number of cycles to failure 
(fatigue life) recorded. 
As shown, relative to the control, the flex life elongation of the coating 
and the tensile strength and the tear resistance is superior to the 
commercial white sidewall rubber compound. The in-situ formation of 
domains which are essential for reinforcing most polyurethanes available 
today, is apparently absent in the coating. The nature of the chain 
extenders used results in a soft coating which is essential for this 
application. The presence of hard domains would tend to make the coating 
overly stiff. The combination of a diol and a triol, when used with the 
proper stoichiometry, provides a network having the desired crosslink 
density for good tear and flex properties. 
This particular method of chain extension plus using the proper type and 
level of pigmentation leads to the unexpected improvement in flex life. 
The properties of the coating formulation minus the pigment are shown in 
Table II below. 
TABLE II 
______________________________________ 
Properties of Coating Formulation Without Pigment 
______________________________________ 
10% Modulus, MPa 1.48 
Tensile, MPa 31.7 
Elongation, % 725 
Trouser tear, kN/m 8.62 
DeMattia, flexes to 0.5" 
.about.500 
______________________________________ 
The remarkable difference in resistance to both tear and crack growth 
between a pigmented (Table I) and non-pigmented coating is demonstrated. 
The adhesion of the pigmented coating to a non-staining sidewall compound, 
with and without surface modification, is also excellent. Adhesion 
(.pi.-peel) test results are shown in Table III. 
TABLE III 
______________________________________ 
Adhesion of Coating 
to Sidewall (.pi.-peel) 
Substrate Surface 
Average Peel Peak Force, 
Treatment Technique 
Force/meter, kN 
kN 
______________________________________ 
Surface wiped with MEK 
4.17 0.205 
Chlorination (3 minutes) 
6.77 0.207 
Benzophenone activation 
followed by 5' exposure 
to UV -- 0.203 
Chlorination (3 minutes) 
plus surface priming with 
Thixon's CB3/AB936-66 
5.47 0.18 
______________________________________ 
In all cases, peeling occurred by either fracturing the coating itself or 
the rubber substrate. The peak force shown represents the maximum force 
measured when the peeling test was stopped. It is actually the force 
required to deform the rubber until failure occurred without effecting 
peeling and is therefore related to the strength of the rubber. A 
comparison between the peak force and the average peel force provides an 
appreciation of the peel force involved. Treatment of the substrates 
surface prior to coating definitely improves adhesion but the level of 
adhesion achieved without any treatment may be adequate for the subject 
application. What causes the coating to adhere so well to the substrate 
even without treatment may be related partly to the reaction 
stoichiometry. The combined levels of the chain extenders used represents 
only 90% of the theoretically calculated stoichiometry (OH/NCO), hence, 
leaving an excess of 10% unreacted isocyanate. Some of these isocyanates 
would undergo further reaction within the urethane network to form 
intermolecular linkages either in the form of biuret or allophonate 
branch. Others may actually serve as adhesion promotor across the 
coating/substrate interface. 
The solventless nature of the coating is another desirable feature for 
obvious reasons. Solvent(s) may be used, however, if the coating were to 
be applied by spraying or by other means where viscosity becomes 
important. 
The following two Tables IV and V show the effect of the different 
molecular weight triols on the properties of the coating at OH/NCO ratios 
of 0.975 and 1.025, respectively. At the ratios of OH/NCO examined, there 
appears to be an increase in DeMattia flex life with increasing triol 
molecular weight. The DeMattia flex results represent the average of at 
least five specimens per sample. In the case when the variance is 
exceedingly large, the lower and upper values are reported. The poor flex 
life of sample below may be due to defects observed in the samples. 
TABLE IV 
______________________________________ 
Effect of Triol Molecular Weight 
On Coating, OH/NCO = 0.975 
A B C D E 
______________________________________ 
Materials 
Adiprene LW 510 
100 100 100 100 100 
A1163-96 (65% 
TITANOX.RTM. 2015 
in DOP) 6.85 6.85 6.85 6.85 6.85 
Ionol 0.5 0.5 0.5 0.5 0.5 
Dibutyltin di- 
laurate T-12 0.025 0.025 0.0125 0.01 0.025 
1,4 Butanediol 
4.3 4.3 4.3 4.3 4.4 
Trimethylol propane 
0.22 -- -- -- -- 
Pluracol TP740.sup.3 
-- 1.2 -- -- -- 
Thanol SF5503.sup.4 
-- -- 8.3 -- -- 
Thanol SF6500.sup.4 
-- -- -- 11.1 -- 
GT10650 Triol.sup.5 
-- -- -- -- 7.0 
Properties 
Shore A 81 80 79 79 80 
10% modulus, MPa 
1.4 1.3 1.2 0.9 1.2 
100% modulus, MPa 
4.3 4.1 3.9 3.9 3.8 
300% modulus, MPa 
5.7 5.6 5.2 5.7 5.2 
Tensile, MPa 12.4 19.5 19.7 18.2 13.5 
Elongation, % 
735 1010 1085 740 740 
Trouser, tear, kN/m 
14.0 14.4 13.5 13.1 15.1 
DeMattia, pierced 
flexes to 0.5" 
&lt;1000 2500 7500 1500 10,000- 
75,000 
______________________________________ 
.sup.3 The Pluracol TP740 trifunctional polyols were developed for use in 
flexible and rigid urethane foams, coatings and elastomers. Various 
members may be used in the preparation of prepolymers, as crosslinking 
agents or as polyol reactants in oneshot systems. 
TP-740 
Approximate weight per gallon, lbs. 
8.5 
Viscosity at 77.degree. F., cps. 
300 
Specific gravity 25/25.degree. C. 
1.02 
Molecular weight 730 
Hydroxyl number 232 
pH, apparent 6.5 
Water, % by weight, max. 0.10 
Color, APHA, max. 40 
__________________________________________________________________________ 
pH, 
Color, 
Flash- 10:6 iso- 
Potas- Water at 
Acid number, 
Pt-CO 
point 
Hydroxyl 
propanol 
sium, 
Specific 
Unsatura- shipment 
mg. KOH/g., 
scale, 
COC, 
number, water 
ppm, gravity 
tion, meq/ 
Viscosity, 
wt. %, 
Max. Max. 
.degree.F. 
mg. KOH/g. 
solvent 
Max. 20/20.degree. C. 
g. Max. 
cP, 75.degree. 
Max. 
__________________________________________________________________________ 
Thanol SF5503 
0.1 50 460 31-36 7.0-9.5 
-- 1.022 
0.09 900 0.1 
Thanol SF6500 
0.1 50 440 24-26 4.0-7.0 
5 1.036 
0.11 1220 0.1 
__________________________________________________________________________ 
.sup.4 Thanol polyols 
.sup.5 A triol having a molecular weight of 10,650 produced by the method 
disclosed in U.S. Pat. Nos. 3,278,459, Herold (1966); 3,829,505, Herold 
(1972) and 3,941,849 Herold (1974). 
TABLE V 
______________________________________ 
Effect of Triol Molecular Weight 
On Coating, OH/NCO = 1.025 
A B C D 
______________________________________ 
Materials 
Adiprene LW 410 
100 100 100 100 
A1163-96 6.85 6.85 6.85 6.85 
Ionol 0.5 0.5 0.5 0.5 
T-12 0.0125 0.0125 0.0125 0.003 
1,4 Butanediol 
4.5 4.5 4.5 4.5 
Trimethylol propane 
0.24 -- -- -- 
Pluracol TP740 
-- 1.23 -- -- 
Thanol SF5503 -- -- 8.7 -- 
Thanol SF6500 -- -- -- 11.7 
Properties 
Shore A 83 80 77 83 
10% Modulus, MPa 
1.9 1.3 1.2 1.3 
100% Modulus, MPa 
4.5 4.1 3.8 3.5 
300% Modulus, MPa 
5.3 4.8 5.05 4.3 
Tensile, MPa 15.2 12.3 16.8 6.8 
Elongation, % 1115 1030 1050 640 
Trouser tear, 
kN/m 16.5 16.3 14.4 11.7 
DeMattia, pierced 
flexes to 0.5" 
2,500- 5000 5000 40,000- 
15,000 75,000 
______________________________________ 
The coatings shown in the above two Tables have working life of only about 
five minutes. This is probably a bit short to be used for coating a tire 
manually. Reducing the amount of the catalyst from 0.0125 to 0.003 part 
extended the workable life to about 30 minutes. In order to accurately 
weigh the 0.003 part of catalyst, a 0.1% solution of dibutyltin dilaurate 
(T-12) in dioctyl phthalate was prepared. The presence of DOP, however, 
had an adverse effect on the tensile strength and tear property of the 
unaged coating, as shown in the Table below. After heat aging for one week 
at 50.degree. C. (122.degree. F.), significant improvements of the above 
properties, including the DeMattia flex life, were obtained. 
TABLE VI 
______________________________________ 
Effect of Catalyst Dilution and of Aging 
A B C 
______________________________________ 
Materials 
Adiprene LW 510 
100 100 100 
A1163-96 6.85 6.85 6.85 
Ionol 0.5 0.5 0.5 
T-12 0.0125 3.0* 3.0* 
1,4 Butanediol 4.3 4.3 4.3 
Thanol SF5500 8.3 8.3 8.3 
Properties** 
Shore A 79 84 82 
10% Modulus, MPa 
1.2 1.5 1.4 
100% Modulus, MPa 
3.9 3.6 3.9 
300% Modulus, MPa 
5.2 -- 5.4 
Tensile, MPa 19.7 4.1 8.9 
Elongation, % 1085 232.5 750 
Trouser tear, kN/m 
13.5 9.9 12.2 
DeMattia, pierced, 
cycles to 0.5" 7500 8000 20,000- 
40,000 
______________________________________ 
*0.1% by weight of T12 solution in DOP 
**Samples aged for one week at 50.degree. C. after curing 
Experimental JR70-15 Dual 90 radial tires which contained a buffed-in 
groove around the sidewall region was coated with the following paint and 
tested. The groove measures about 2.85 cm (11/8 inch) wide.times.0.16 cm 
(1/16 inch) deep. As mentioned earlier, half of the tire sidewall compound 
is staining and half is not. 
______________________________________ 
Materials phr 
______________________________________ 
Adiprene LW 510 100 
DC 203 0.2 
T-12 0.015 
A1163-69 (65% Titanox 2071 in DOP) 
6.85 
DOP 3.2 
Ionol 0.5 
90:10 by weight (44:1 molar ratio) 
1,4 Butanediol/Pluracol TP440 
5.13 
______________________________________ 
The formulation was derived from a series of designed experiments. It has a 
DeMattia flex life of about 27,500 cycles. 
Tire No. 1 
The tire's sidewall groove was first cleaned with MEK then dried in air. 
One-half of the groove was chlorinated, rinsed and further dried. The 
coating was applied with the aid of a Teflon blade. Curing of the tire was 
done in an oven for 30 minutes at 215.degree. F. (102.degree. C.), 
followed by two days of room temperature aging. The tire was then tested 
on a pulley wheel with the following applied conditions: 
TABLE VII 
______________________________________ 
Speed = 50 mph 
Inflation Pressure = 24 psi 
Approximate Load Time of Cumulative 
on Tire % Rated Test Time 
(lbs.) (Kg) Load (hrs.) (hrs.) 
______________________________________ 
1180 536 100 2 2 
1320 600 119 4 6 
1530 695 1130 10 16 
1860 845 160 6.5 22.5 
______________________________________ 
Pronounced discoloration was observed on the paint which was applied on the 
staining half of the sidewall prior to the test. At the end of the test, 
some of the paints were peeled off all over the tire. Very large size 
cracks in the paint were observed which extended from either edge of the 
groove to the near center. It is obvious that improvement in both fatigue 
life and adhesion of the coating was necessary. 
Tire No. 2 
The second tire was coated with the following formulation: 
______________________________________ 
Materials phr 
______________________________________ 
Adiprene LW 510 100 
A1163-96 (65% TITANOX.RTM. 2015 in DOP) 
6.85 
Ionol 0.5 
Dibutyltin dilaurate, T-12 
0.0125 
1,4 Butanediol 4.3 
Thanol SF5503 8.3 
______________________________________ 
About 40 grams of the paint were needed to fill the sidewall groove to 
about 1/32" (0.08 cm) thick using a brush. The coated tire was cured for 
45 minutes at 225.degree. F. (107.2.degree. C.). It took about 15 minutes 
for the tire to reach the required temperature. The tire was then run on a 
pulley wheel at 100% rated load for two hours followed by another four 
hours at about 120% of rated load. The paint started to peel off after two 
hours of test. This might have been caused by the presence of masking tape 
placed around the two edges of the groove. The masking tape was used so 
that no coating was applied on the grooves' vertical edges. Cracking 
appeared to propagate from flaws generated at the outer groove edges, 
based on the results of the first tire test. The use of the masking tape 
did prevent cracks from occurring on the paint but the test was 
discontinued due to extensive adhesive failure. 
The same tire was rebuffed and recoated with formulation C as described in 
Table VI. The coated tire was cured at the same conditions as before. 
After it had been aged for one week at room temperature, the tire was 
further postcured for one week at 122.degree. F. (50.degree. C.) before 
testing on the pulley wheel. No sign of peeling or cracking of the paint 
was observed after 21/2 hours of test at 100% rated load (1180 lbs.) at 50 
mph. Continued testing of the tire at 120% rated load (1320 lbs.) for five 
hours resulted in peeling of some portions of the paint, notably at the 
staining sidewall half. Only a few cracks were observed but these were 
rather large in size (up to 0.5" in length). The test was stopped 
overnight but resumed the following day at 120% rated load for four hours. 
Finally the load was increased to 130% of rated load (1530 lbs.) and the 
test continued for another three hours. 
At the end of this period, practically all the paint around the staining 
sidewall half was peeled off while that on the nonstaining side still 
remained. A large number of discrete cracks extending radially toward the 
center from the outer edge were observed in the paint remaining around the 
nonstaining half of the sidewall. The debonding of the paint appeared to 
be both cohesive (in the coating phase) and adhesive. The staining 
sidewall section was covered with a noticeable layer of the white coating. 
The underside of the peeled coating and the remaining white film on the 
sidewall groove both assumed an orange peel look. This probably resulted 
from the entrapment of volatile material coming out of the tire during the 
application and curing of the paint. The discoloration of the paint on the 
staining sidewall section is an indication of the migration of foreign 
volatile matter from the tire. This probably caused a weakening of the 
interfacial bond strength and also deleteriously affected the flex and 
tear resistances of the applied coating. 
The results gathered in this application suggest that a high molecular 
weight triol, preferably no less than 6000MW, be used with the 1,4 
butanediol for chain extending and crosslinking the Adiprene LW510 based 
coating. Although the flex life of the best coating formulation described 
is approaching that of a rubber white sidewall compound, it is felt that 
improvement can still be achieved by reducing its modulus. Paint adhesion 
looks good but apparently not yet adequate. A staining rubber sidewall is 
not suitable for painting but it affects the integrity of the applied 
paint, causes interfacial debonding and discoloration.