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New processing agent in tire compounds.

New processing agent in tire compounds

Beginning in early 1980, the requirements for tire materials were becoming more and more specialized and diversified to achieve a specific dynamic property. One of the most important requirements is the better balance of fuel economy and safety. In the case of tire tread materials, these requirements are good wet traction and low rolling resistance. It is well known that the materials showing good wet traction should have high tangent delta at 0 [degree] C, while the compounds having low rolling resistance should have low tangent delta at 50-100 [degrees] C. These two properties are very critical because of the inherent viscoelastic properties of polymers. In a wet skidding condition, the tread rubber performs at a relatively high frequency deformation at relatively low temperatures. On the other hand, in a rolling condition, the tread rubber experiences a relatively low frequency deformation at relatively high temperatures. A polymer with good wet skid/traction should be designed to have a relatively high glass transition temperature.

Thus, high glass polymer usually shows high hysteresis and hence high fuel consumption. In emulsion SBR or polybutadiene, it has been known that good, wet skid/traction and low rolling resistance are contradictory to each other. For example, low glass transition high Cis polybutadiene rubber has very poor wet skid/traction, while it provides lower rolling resistance and good wear resistance. However, a high styrene content emulsion SBR provides high glass transition temperature resulting in high rolling resistance and good wet skid/traction.

In that same period, Dunlop unveiled its Elite series of tires made from Shell Cariflex solution SBR. Shell-Dunlop claimed that Cariflex solution SBR provided lower rolling resistance and better skid/traction. The solution SBR contains a higher content of vinyl group and fewer branches. The linear and high molecular weight SBR polymer provides lower hysteresis, good flexing and good wear resistance, while its processability is getting more difficult. The higher content of a vinyl group in solution SBR increases its glass transition temperature, which provides improved wet skid/traction.

In industrial products, highly loaded compounds have been a problem for dispersion of fillers. Without a well mixed stock, especially in radiator hose, a crack frequently occurs in the early stages. The power transmission and v-belts have also broken due to poor mixing. Processing agents would assist to mix and process uniformly in industrial rubber products such as hoses, conveyor belts, v-belts, power transmission belts and rubber sheets.

In this article, Processing Agent 1109 has been introduced in lower oil tread, replacing oil with PA 1109, conventional tread and high modulus tread compounds.

Experiments with individual ingredients

PA 1109 consists of organic esters, paraffin wax and calcium carbonate. The conventional tread compound, which contained 75/25 emulsion styrene butadiene rubber (E-SBR)/ high Cis polybutadiene rubber (Cis BR) and 55 phr of N-234 ISAF (intermediate super abrasion resistance furnance) carbon black, was utilized for the evaluation of the individual ingredients, commercial PA 1109 and a lab blend. The PA 1109, a lab blend, organic ester, calcium carbonate and wax were added to the conventional tread compound. A thiocarbamyl sulfenamide/2 (4-morpholinyl-mercapto) benzothiazole/ sulfur system was used to vulcanize the experimental tread compounds. With these experiments, conducted with an experimental passenger tire tread compound, one cure time and temperature was taken, 10 minutes at 177 [degrees] C. This higher temperature was utilized to simulate the currently used curing temperature in the tire industry. The completely mixed compounds were measured for Mooney viscosity at 100 [degrees] C, Mooney scorch at 132 [degrees] C and curemeter at 177 [degrees] C, which had employed identical mixing procedure and cycle. All the cured samples were tested for unaged and aged stress/strain, and viscoelastic properties.

Results and discussion

The evaluation included five compounds. Compound A consisted of 3 phr of PA 1109, compound B contained 3 phr of a lab blend, compound C had 2 phr of organic esters, compound D consisted of 2 phr of calcium carbonate and compound E consisted of 2 phr of paraffin wax, which are shown in table 1. The Mooney viscometer at 100 [degrees] C indicated that compounds A, B, C and E are approximately similar to each other except compound D, whose viscosity was higher than that of the other compounds. The three point rise time of the Mooney scorch at 132 [degrees] C for compound C was shorter than other compounds whose scorch time was not significantly different from each other. The tensile strength at room temperature and at 121 [degrees] C for both compound C and compound D was slightly higher than that of other compounds. The static modulus of compound D was much higher than that of the other compounds, however the static modulus of compound C was the same as compound D, measured at 121 [degrees] C. The static modulus for both compound C and compound D was much higher than that of the other compounds, tested at 121 [degrees] C. All other physical properties including elongation, Shore A hardness and tear strength (Die C) were not significantly different from each other, as shown in table 1.

Table : Table - 1 unaged physical properties
 A B C D E
E-SBR 1500 75 75 75 75 75
Cis BR 1203 25 25 25 25 25
N-234 black 55 55 55 55 55
Aromatic oil 15 15 15 15 15
PA 1109 3 - - - -
Blends - 3 - - -
Organic ester - - 2 - -
Calcium carbonate - - - 2 -
Paraffin wax - - - - 2
ML 1+4 at 100 [degrees] C 58 56 58 64 56
MS at 132 [degrees] C 28' 32' 24' 27' 31'


3 pt. rise time
Cured at 177 [degrees] C 10' 10' 10' 10' 10'
Tensile at RT 23.8 21.9 25.6 25.5 23.3
% Elongation 530 500 550 520 520
300% Modulus 10.9 10.2 10.7 12.0 10.8
Shore A hardness 68 63 68 69 67
Tear strength (Die C) 56.0 56.0 57.8 59.5 59.5
Tensile at 121 [degrees] C 9.4 8.9 9.9 10.9 9.6
% Elongation, 280 280 300 320 300
200% Modulus 5.2 5.4 6.2 6.0 5.3
Tear strength (Die C) 28.0 29.8 29.8 28.0 29.0


The shear loss modulus (G") and storage modulus (G") were measured by using a viscoelastic tester. Tangent delta (G"/G') and composite modulus [Mathematical Expression Omitted] were computed from loss and storage modulus. The measurements were carried out with 1 through 12 Hertz and at three different temperatures (50 [degrees] C, 75 [degrees] C and 100 [degrees] C. In table 2 and figures 2 and 3, only tangent delta and composite dynamic modulus are shown with 10 Hertz, because the trends are the same with the other frequencies. The dynamic modulus of compound C is significantly higher than that of other compounds. Tangent delta of compound C is slightly higher than that of the others.

All the cured samples were aged in an over for two weeks at 70 [degrees] C. Aged physical properties were measured for tensile strength, elongation, Shore A hardness, tear strength (Die C), modulus at room temperature and at 121 [degrees] C. No significant differences were observed among the five compounds (table 3). [Tabular Data Omitted]

Experiments with lower oil tread

It is well known that higher modulus tread which has a higher cornering coefficient provides a better handling radial ply tire, and lower oil tread has better abrasion resistance or provides a better wear resistant tire. However, it is extremely difficult to mix and process lower oil tread compounds. In this experiment, six batches were mixed in a laboratory internal mixer with varying amounts (0 to 5 phr) of PA 1109. The lower oil tread compound contained 75/25 ESBR/Cis BR with 55 phr of N-234 ISAF carbon black and 10 phr of aromatic oil. The same sulfur system as mentioned earlier was used to cure the lower oil tread compound. One cure time and temperature was taken, 10 minutes at 177 [degrees] C. The Mooney viscosity at 100 [degrees] C from the vulcanized rubber and the unaged vulcanized samples were tested for tensile strength, elongation at break, modulus, tear strength and rheometer measurements.

Results and discussion

The Mooney viscosity at 100 [degrees] C was decreased with linear proportionality as the same amount of PA 1109 was increased, which is shown in figure 1 and table 4.

A three point rise time of the Mooney scorch at 132 [degrees] C was measured by using the Mooney viscometer with a small rotor. No differences in the Mooney scorch were observed among the six compounds. The 300% modulus of compound F, which contained 5 phr of PA 1109, was decreased significantly. The tensile strength, elongation at break, modulus, tear strength (Die C) and Shore A hardness are not significantly different from each other with 0 to 4 phr of PA 1109, which is shown in table 4.

Table : Table 4 - unaged physical properties (lower oil tread
 A B C D E F
E-SBR 1500 75 75 75 75 75 75
Cis BR 1203 25 25 25 25 25 25
N-234 black 55 55 55 55 55 55
Aromatic oil 10 10 10 10 10 10
PA 1109 - 1 2 3 4 5
ML 1+4 at 100 [degrees] C 69 67 66 64 62 60
MS at 132 [degrees] C, 20' 21' 21' 21' 21' 22'


3 pt. rise time
Cured at 177 [degrees] C 10' 10' 10' 10' 10' 10'
Tensile at RT, MPa 24.0 23.3 23.2 23.4 22.5 22.6
% Elongation 450 450 470 450 430 460
300% Modulus, MPa 13.7 13.6 13.2 13.1 13.2 12.1
Shore A hardness 68 65 67 68 68 65


Tear strength

(Die C) KN/m 56.0 59.5 59.5 49.0 56.0 57.8

Tangent delta and composite dynamic modulus were measured with a viscoelastic tester. Tangent delta value was decreased as the PA 1109 was increased. However, with the addition of more than 4 phr of PA 1109, tangent delta began to increase (figure 2). The dynamic modulus for compounds A, B and C, which contained 0, 1 and 2 phr of PA 1109, were similar to each other, tested at 50 [degrees] C, 75 [degrees] C and 100 [degrees] C, respectively. However, with the addition of more than 3 phr of PA 1109, the dynamic modulus was reduced, which is shown in table 5 and figure 3.

Table : Table 5 - rheometer measurement
 A B C D E F
E-SBR 1500 75 75 75 75 75 75
Cis BR 1203 25 25 25 25 25 25
N-234 black 55 55 55 55 55 55
Aromatic oil 10 10 10 10 10 10
PA 1109 - 1 2 3 4 5
 10Hz 10Hz 10Hz 10Hz 10Hz 10Hz


Tan [delta] (G"/G')

at 50 [degrees] C .192 .182 .178 .193 .169 .181

G(*) (dyne/[cm.sub.2])

x 10.sub.7 6.17 6.15 6.12 5.64 4.81 5.39

Tan [delta] (G"/G')

at 75 [degrees] C .172 .159 .159 .164 .144 .158

G(*) (dyne/[cm.sub.2])

x 10.sub.7 4.90 5.06 4.78 4.45 4.402 4.52

Tan [delta] (G"/G')

at 100 [degrees] C .158 .145 .139 .144 .127 .149

G(*) (dyne/[cm.sub.2])

x 10.sub.7 4.33 4.55 4.06 3.90 3.49 3.97

Experiments with replacing oil with PA 1109

In this experiment, the lower oil tread compound was utilized by replacing oil with PA 1109 from 1 to 5 phr. Also, the lower oil tread compound contained 75/25 ESBR/Cis BR with 55 phr of N-234 ISAF carbon black. The same sulfur system was used. The cure time and temperature was also the same. The completely mixed five compounds were tested for viscosity at 100 [degrees] C, and the tensile strength, elongation at break, modulus, tear strength (Die C), and rheometer measurements were measured from the cured samples.

Results and discussions

The Mooney viscosity at 100 [degrees] C varied from 69 to 75 among all five batches. Due to different mixes, experimental errors have occurred. The physical properties showed no differences among them (table 6). However, in rheometer measurements, tangent delta (G"/G') with PA 1109 was much lower than that without PA 1109, except compound J, which might cause experimental errors (table 7 and figure 4). No significant differences in composite dynamic modulus were measured among all six batches, which are shown in table 7 and figure 5.

Table : Table 6 - unaged physical properties (replacing oil with PA 1109)
 G H I J K
E-SBR 1500 75 75 75 75 75
Cis BR 1203 25 25 25 25 25
N-234 black 55 55 55 55 55
Aromatic oil 9 8 7 6 5
PA 1109 1 2 3 4 5
ML 1+4 at 100 [degrees] C 73 67 75 68 70
MS at 132 [degrees] C 21' 21' 22' 23' 22'


3 pt. rise time
Cured at 177 [degrees] C 10' 10' 10' 10' 10'
Tensile at RT 25.1 24.0 25.2 22.6 24.6
% Elongation 430 450 430 430 440
300% Modulus 14.8 13.1 15.1 13.0 14.4
Shore A hardness 69 68 71 70 69
Tear strength (Die C) 56.0 54.3 63.0 56.0 52.5


Table : Table 7 - rheometer measurement
 (*)A G H I J K
E-SBR 1500 75 75 75 75 75 75
Cis BR 1203 25 25 25 25 25 25
N-234 black 55 55 55 55 55 55
Aromatic oil 10 9 8 7 6 5
PA 1109 - 1 2 3 4 5
 10Hz 10Hz 10Hz 10Hz 10Hz 10Hz


Tan [delta] (G"/G')

at 50 [degrees] C .192 .191 .177 .155 .188 .161

G(*) (dyne/[cm.sub.2])

x 10.sup.7 6.17 6.09 5.73 5.84 6.16 6.02

Tan [delta] (G"/G')

at 75 [degrees] C .172 .172 .163 .137 .168 .142

G(*) (dyne/[cm.sup.2])

x [10.sup.7] 4.90 5.11 4.74 4.80 4.83 5.00

Tan [delta] (G"/G')

at 100 [degrees] C .158 .156 .147 .131 .155 .140

G(*) (dyne/[cm.sup.2])

x [10.sup.7] 4.33 4.51 4.14 4.14 4.08 4.25 (*) A from table 5

Experiments with conventional tread compound

Studies were conducted with the basic recipe from a passenger tire tread compound. The conventional tread compound contained 75/25 E-SBR/Cis BR with 55 phr of N-234 ISAF carbon black and 20 phr of aromatic oil. Three different compounds were mixed in a laboratory size internal mixer and two cycle mixing procedures (masterbatch and final batch) were employed in preparing three compounds. Compound A does not contain a processing agent, compound B consists of 2 phr of PA 1109, compound C contains 3 phr of PA 1109 (table 8). The same vulcanization system was used, along with the same cure time and temperature. The Mooney sorch at 132 [degrees] C was measured from the completely mixed compounds. The cured samples were tested for unaged and aged physical properties, and rheometer measurements.

Table : Table 8 - conventional tread compound
 A B C
E-SBR 75 75 75
Cis BR 25 25 25
N-234 black 55 55 55
Oil 20 20 20
PA 1109 - 2 3
ML 1+4 at 100 [degrees] C 56 54 52
MS at 132 [degrees] C, 25' 25' 22'


3 pt. rise time
Cure rate (min.) 4.6 4.5 4.4
Cured at 177 [degrees] C 10' 10' 10'
Tensile, MPa at RT 23.4 23.2 23.1
Elongation, % 570 560 590
300% Modulus, MPa 9.4 9.1 8.7
Shore A hardness 61 65 65
Tear strength, KN/m 52.5 52.5 52.5


(Die C)
Tensile, MPa at 121 [degrees] C 9.6 8.5 7.1
% Elongation 340 330 290
200% Modulus, MPa 4.3 3.9 4.3
Tear strength, KN/m 25.9 25.7 30.6


(Die C)

Results and discussions

The Mooney viscosity at 100 [degrees] C was decreased linearly as the amount of PA 1109 was increased in the conventional tread compound. The Mooney sorch and the cure rate at 132 [degrees] C were not significantly different from each other. Compound C, which contained 3 phr of processing agent, reduced 300% modulus at room temperature. Tensile strength and elongation at 121 [degrees] C was reduced slightly, however, the tear strength at 121 [degrees] C was increased slightly in compound C, compared with compound A and compound B, which are shown in table 8. The cured samples were aged in an oven for two weeks at 70 [degrees] C. Percent retention were not different from each other, measured at room temperature. Percent retention in tensile strength and elongation for compound C was better than that of compound A and compound B tested at 121 [degrees] C. Lower initial physical properties might contribute to these results for compound C, which are shown in table 9. The shear loss modulus and storage modulus were measured by rheometer.

Table : Table - 9 conventional tread compound

(% retention, aged two weeks at 70 [degrees] C
 A B C
E-SBR 1500 75 75 75
Cis BR 25 25 25
N-234 black 55 55 55
Oil 20 20 20
PA 1109 - 2 3
Tensile, psi at RT 94.1 97.0 93.7
Elongation, % 77.2 80.4 78.0
300% Modulus 137.5 144.7 141.3
Shore A hardness 116.4 110.7 112.3
Tear strength (Die C) 103.3 96.7 91.0
Tensile at 121 [degrees] C 104.3 95.1 118.4
% Elongation, 82.3 78.8 96.6
200% Modulus 149.2 156.1 132.2
Tear strength (Die C) 87.8 81.6 74.3


Tangent delta and composite dynamic modulus were computed from loss and storage modulus. In compound B, tangent delta value was decreased significantly and a slight decrease in tangent delta for compound C was observed, compared with that of compound A which did not contain PA 1109, while composite dynamic modulus for both compound C and compound B was significantly increased. Good dispersion of polymers and blacks with PA 1109 will result. These results are shown in table 10 and figures 6 and 7.

Table : Table 10 - conventional tread rheometer test results - frequency 10 Hz
 A B C
E-SBR 1500 75 75 75
Cis BR 1203 25 25 25
N-234 black 55 55 55
Aromatic oil 20 20 20
PA 1109 - 2 3
Tan [delta] (G"/G') at RT .221 .185 .207
G(*) (dyne/[cm.sup.2]) x [10.sup.7] 7.22 7.68 8.82
Tan [delta] (G"/G') at 50 [degrees] C .204 .156 .175
G(*) (dyne/[cm.sup.2]) x [10.sup.7] 5.41 5.60 6.13
Tan [delta] (G"/G') at 75 [degrees] C .193 1.30 1.50
G(*) (dyne/[cm.sup.2]) x [10.sup.7] 4.40 4.61 5.02
Tan [delta] (G"/G') at 100 [degrees] C .176 .120 .134
G(*) (dyne/[cm.sup.2]) x [10.sup.7] 3.85 4.10 4.34


Experiments with high modulus tread

In order to obtain a higher modulus tread compound, a tri-blend of solution styrene butadiene rubber, high vinyl content butadiene rubber and natural rubber was used with 55 phr of N-234 ISAF black, 20 phr of naphthenic oil and 0.5 phr of 4,4' dithiodimorpholine. The same system was used to vulcanize the high modulus tread compound. Compound A did not have either PA 1109 or 4,4' dithiodimorpholine, compound B consists of 4,4' dithiodimorpholine only and compound C contained both PA 1109 and 4,4' dithiodimorpholine. One cure time and temperature was taken, namely, 10 minutes at 177 [degrees] C. The Mooney viscosity at 100 [degrees] C and the Mooney scorch at 132 [degrees] C were measured from the uncured compounds, and other physical properties and rheometer measurements were made with the cured samples.

Results and discussion

Previously, in the introduction, it was mentioned that linear high molecular weight polymers, namely narrow distributed high molecular weight styrene butadiene rubber, provides lower hysteresis, which has resulted in lower rolling resistance. Also, high vinyl content in either styrene butadiene rubber or polybutadiene rubber increases the glass transition temperature as wet traction can be improved. The combination of these two polymers is very difficult in processing (mixing and extruding). Therefore, it is essential to have natural rubber for improving the process.

The Mooney viscosity at 100 [degrees] C for compound C, which contained 3 phr of PA 1109, was reduced from 72 to 64. The Mooney scorch values at 132 [degrees] C were not significantly different from each other. However, the cure rate without 0.5 phr of 4,4' dithiodimorpholine is much faster than that with it. The 300% modulus significantly increased and the elongation at break was reduced because of the tight cure with 4,4' dithiodimorpholine. All other physical properties, including tensile strength and tear strength, were similar to each other. The cured ASTM slabs were aged in an oven for two weeks at 70 [degrees] C. Percent retention in tensile strength for compound C is much higher than that of compound A and compound B. This result might come from PA 1109, which contains paraffin wax.

In the rheometer measurements, tangent delta for compound C was much lower than that of compound A and compound B. Also, tangent delta value in compound B was lower than that of compound A because of the tight cure with 4,4' dithiodimorpholine. The dynamic modulus for compound C and compound B was much higher than that for compound A, as expected.

Conclusion

The combination of linear solution SBR and high vinyl content in either BR or SBR provides not only lower rolling resistance tread, but also improves wet skid/traction. These linear high molecular weight polymers would need a processing agent or blend with a highly branched polymer such as natural rubber to improve milling, mixing and extruding. The PA 1109, which consists of organic ester, paraffin wax and calcium carbonate, lowers the Mooney viscosity for improved processing, lowers hysteresis for lower rolling resistance tread, increases the dynamic modulus for improved handling tread and aids dispersion of carbon black for improved physical properties.

References

[1.] W.W. Klingbeil, S.W. Hong, R.N. Kienle and H.H. Witt, "Theoretical and experimental analysis of dual compound tread designs for reduced rolling resistance," presented at a meeting of the Rubber Division, ACS, Chicago, IL, October 5-7, 1982. [2.] John D. Ferry, "Viscoelastic properties of polymers," John Wiley & Sons, Inc., New York, 1960. [3.] Bill Kern and Shingo Futamura, "Solution SBR as tread rubber," presented at a meeting of the Rubber Division, ACS, Montreal, Quebec, May 26-29, 1987. [4.] Klaus Morche and H. Ehrend, "Tire compounds and process aids," presented at a meeting of the Rubber Division, ACS, Cleveland, Ohio, October 6-9, 1987.

PHOTO : Figure 1 - Mooney viscosity vs. PA 1109

PHOTO : Figure 2 - lower oil tread hysteresis vs. PA 1109

PHOTO : Figure 3 - lower oil tread composite dynamic modulus

PHOTO : Figure 4 - replacing oil with PA 1109 - hysteresis vs. PA 1109

PHOTO : Figure 5 - replacing oil with PA 1109 - composite dynamic modulus

PHOTO : Figure 6 - conventional tread hysteresis vs. PA 1109

PHOTO : Figure 7 - conventional tread - composite dynamic modulus
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Author:Hong, S.W.
Publication:Rubber World
Date:Aug 1, 1990
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