New reinforcing materials for rising tire performance demands.

The general phenomenon of reinforcement by carbon black has accompanied the rubber industry and especially the tire industry for more than a century. The most important aspect of the introduction of carbon black was the strong improvement of abrasion resistance. With the development of the furnace process, the flexibility to produce different blacks was enhanced. Nowadays, tailor-made carbon blacks with wide variations in surface area and structure can be produced using the furnace production process. Due to its performance, flexibility and cost, carbon black is the dominating filler in the tire industry, for both passenger and truck tires.

This situation began to change with the market introduction of the green tire concept by a major European tire producer in 1992 (ref. 1). The development of passenger car tire treads based on highly dispersible silica with a CTAB surface area of 150 to 170 [m.sup.2]/g in combination with a bifunctional silane like the TESPT (bis-[triethoxysilylpropyl] tetrasulfide), Si 69 (ref. 2), and a special solution-SBR copolymer, allowed a considerable progress in the performance of passenger car (PC) tires. With this filler system, simultaneous improvements of seemingly contradictory tire properties like rolling resistance and wet traction were now possible, while keeping the treadwear on a high level. This led to a considerable extension of the tire performance and became state-of-the-art for original equipment PC tires in Europe during the last few years. Figure 1 illustrates this improvement in tire performance, which could not be achieved previously by using carbon black alone as the filler. A review on the reinforcement of silica/silane filler systems (refs. 3 and 4), as well as carbon black (ref. 5) has been published recently.

[FIGURE 1 OMITTED]

The enormous performance jump regarding rolling resistance and wet grip by simultaneously good abrasion resistance values brought the silica/silane-filler system a favorable position for car tire tread compounds in Europe. Nowadays, this filler system is also gaining ground in the U.S. market. This is probably due to the rising requirements on tire durability and tire safety. Additionally, the upcoming Y-generation seems to take environmental concerns more seriously, and hence lower fuel consumption is becoming an issue in the U.S., as well. Recently, a major tire producer has launched in the U.S. a new tire series with improved wet traction. Nevertheless, further performance demands from the automotive industry for PC tires require an optimization of this filler system with regard to further reduced rolling resistance and improved grip by maintaining a high mileage level. Therefore, new silicas differing in surface area and their activity towards the silane coupling reaction, as well as new silane coupling agents, are under investigation. But alternative solutions to the silica/silane-filler system were also introduced recently, or are in the course of development.

Besides the use of silica as the main filler in PC-tire tread compounds in Europe, the application of silica in tire body compounds has a potential to further reduce heat build-up accompanied with a reduction in rolling resistance. In truck tire tread compounds, the usage of silica may be extended by using specialized highly dispersible silica in combination with fine particle carbon blacks having a high structure level. With such an optimized filler system, it may be possible to reduce the hysteresis loss, and hence rolling resistance, by maintaining the treadwear, which is the major demand for truck tires.

The competition of the two reinforcing filler systems, silica/silane and carbon black, was the driving force to overcome limitations. The progress in carbon black development could be achieved by specific variations in carbon black surface and structure to adjust the special needs in truck tire tread compounds even at different axle positions of highway trucks. Enhancement of polymer filler interaction was another key to further extend the performance.

Tailor-made blacks with high structure levels find application in truck tire tread compounds to improve the mileage and to ensure a good balance between the heat build-up and the durability. A better cut and chip behavior is also an important issue and is mainly achieved by the usage of carbon blacks with a low structure, but high surface area, like N 115. Another well-known method is the addition of a small amount of silica without silane, which results in a better cut and tear resistance (ref. 6). The drawback of these two possibilities is the higher heat build-up and reduced treadwear, respectively. To improve the hysteresis loss of tire body compounds, new low surface area carbon blacks have been developed and are a solution to further reduce rolling resistance of a tire.

The aim of this article is to highlight the latest developments and market introductions of the above mentioned reinforcing filler systems for tire applications, as well as the different approaches to fulfill the rising performance demands.

Demands for passenger and truck tires

Due to the different needs in the different regions, the requests of the automotive industry and the customers on PC tire performance have evolved in different directions. Figure 2 gives an overview about today's performance requirements of passenger tires in the U.S. and Europe.

[FIGURE 2 OMITTED]

In Europe, the request for high driving safety and environmental requirements (low fuel consumption) at the same time can only be matched by using silica/silane as the main reinforcing filler. With special polymers and the silica/silane system, a high level of wet traction and wet braking could be achieved. The rolling resistance, and therefore the fuel consumption, could be reduced by up to 5%. Carbon black is used in PC tread compounds to positively influence dry grip, as well as dry handling, and finally to balance all properties. The penetration of the silica/silane filler system in car tire tread compounds in Europe has reached more than 80% in the original equipment market (OEM). The performance jump of modern winter tires is mainly related to the use of silica/silane in the tread compound. Therefore, full-silica winter tires are state-of-the-art in central Europe. In contrast to this, carbon black is still the best choice to fulfill the actual demands of the U.S. market, a very high mileage combined with a low rolling resistance and a high driving comfort. But increasing demands of the automotive industry and also the new DOT 139, effective June 2007 (NHTSA/U.S.), requesting a higher endurance and high-speed performance, will result in a higher penetration of the silica tire technology also in the U.S. These increasing demands in the U.S. will also have an impact on the imported tires, especially from Asia, which also have to fulfill the DOT 139.

Further requirements of the European automotive industry for passenger car tires with impact on the filler system are as follows:

* Further reduction of rolling resistance of about 20%;

* improvements in wet grip;

* improved anti-lock braking under dry conditions;

* introduction of run-flat tires; and

* environmentally-friendly products.

The demands for truck tires are listed in table 1. As can be seen, the environmental requirements, as well as those of the fleet owner and the drivers, differ strongly. Presently, carbon black is the reinforcing material of choice for truck tread compounds. By using different grades having high surface areas and different structure levels, the request of different truck tires for on-, off-the-road and different axle positions can be matched very well. In some cases, the use of small amounts of silica (10-15 phr) in the tread can help to balance the performance of the tread compound. Considering a cap and base construction, the usage of silica/silane in the base compound is the best solution to reduce hysteresis, while maintaining the modulus of the belt package, without a negative impact on the treadwear of the cap. New truck tire concepts like super single tires for the driving axle will result in special demands for the reinforcing filler system. In this respect, heat build-up is a critical factor.

Limitations of the classical filler systems

As shown in figure 1, the tire tread performance is limited by the magic triangle, picturing the contradiction of an overall improvement in rolling resistance wet grip and treadwear. Due to the extension of the magic triangle concerning rolling resistance and wet traction, silica/silane is the benchmark in PC-tire tread compounds. With the rising performance demands discussed above, the other tire properties gain more and more importance and have to be considered more strongly. In the case of PC, further improvements in dry traction and dry braking are needed, whereas for truck tires, improved cut and chip behavior is more serious (figure 4).

[FIGURE 4 OMITTED]

The strong improvement in wet traction of PC tires using silica is commonly sacrificed by a reduced dry traction. To overcome this drawback, high surface area carbon blacks are added to the compound. Maybe improvements regarding dry traction can also be found by a combination of new silicas and silanes. The use of a blend of white and black fillers results in a higher rolling resistance, which may be compensated by an altered tire construction and/or a modified polymer blend. To extend the tire performance the use of the optimal fillers and polymers is needed.

For the requested better treadwear of track tires, fillers with a higher structure are needed, but other properties should not be deteriorated. The better cut and chip behavior demands high surface area low structure blacks, which on the other hand increases rolling resistance. To fulfill these contradictory performance demands, new fillers are also needed for truck tires. These fillers must develop their optimal reinforcement potential with natural rubber, the common basis for truck tire treads.

Experimentals

All rubber stocks presented in this study were prepared in a 1.5 L mixer. For the tread compounds, three-stage mixes, and for the tire body compounds, two-stage mixes, were commonly applied. The exact mixing conditions are given in the corresponding cited references.

Truck tire application

Rolling resistance

As demonstrated in figure 5, all compounds of a track tire contribute significantly to the rolling resistance. Therefore, not only an optimization of the tread, but also of all tire compounds is needed to reduce the hysteresis loss.

To reduce the rolling resistance of a track tire tread, we offer two possible solutions: firstly, the so-called nano-structure blacks (ref. 7) and secondly, highly dispersible high surface area silicas.

The nano-structure blacks are produced by a modified furnace process, which results in a higher surface roughness and higher surface activity in comparison to conventional ASTM blacks. The higher surface activity is mainly related to smaller crystallite sizes linked with a high degree of geometrical disarrangement. Both facts yield a high number of edges, which are the active sites with a particular high surface energy leading to strong mechanical/physicochemical interactions with the polymer (figure 6). Furthermore, simple physical models (refs. 8 and 9) suggest that the number of polymer-surface attachments is strongly enhanced with increasing surface roughness without taking into account any surface activity effects. This enhanced filler-polymer interaction leads to reduced hysteresis loss and heat build-up under dynamic deformation, while all other in-robber properties remain nearly unchanged (ref. 10).

[FIGURE 6 OMITTED]

Table 2 compares the in-rubber data in a NR truck tire tread compound filled with 52 phr of the ASTM black N 356 and a corresponding nano-structure black E-1670 (ref. 11). As can be seen, the nano-structure black results in a significantly reduced hysteresis loss tan [delta] and heat build-up, indicating the reduction in rolling resistance. The slightly lower modulus of 300% is due to the 10 pt. lower DPB number.

Besides the above shown in-rubber data, the abrasion resistance, measured with the labor abrasion tester (LAT) 100 (ref. 12) under high and low severity conditions, was also determined. As shown in figure 7, the abrasion resistance under all severity conditions is superior to the one of the reference compound with N 356 (SBR/1,4-BR compound with 80 phr carbon black) (ref. 13). Therefore, E-1670 is a good choice to reduce rolling resistance with at least an excellent treadwear.

[FIGURE 7 OMITTED]

The second possibility to reduce the rolling resistance of the tread is the use of silica in combination with a high reinforcing black like N 121 (ref. 14). Especially the use of highly dispersible silica with higher surface area (HD-HSA) silica than the common PC the tread silicas may overcome the drawback of a deteriorated treadwear (ref. 15). The higher specific surface area corresponds to smaller primary particle sizes, which should improve the abrasion resistance, as known from carbon black.

Compared to a reference compound with N 220, the black and white filler blend results in a significantly reduced hysteresis loss (tan [delta], ball-rebound, heat build-up), while maintaining the high moduli and good DIN abrasion resistance (table 3). The differences between the compounds A and B with the different silica surface areas are only minor, but as stated above, the treadwear should be better for compound B. Payne effect and dynamic stiffness ale reduced for the carbon black silica blends compared to the reference compound, and hence, the hysteresis loss is lowered too (figure 8, RPA-measurement). These graphs confirm the data measured with the MTS under constant force, shown in table 3.

[FIGURE 8 OMITTED]

As demonstrated in figure 5, a further reduction in rolling resistance is possible through the optimization of the tire body compounds. As for the tread, special carbon blacks and silicas can be used to reduce the hysteresis loss of the different tire parts. The nano-structure black E-1830 (ref. 16) is a good choice for the adhesion compound, as well as breaker cushion, whereas the low surface area blacks with CTAB values of 20 [m.sup.2]/g are most suitable for e.g., the carcass, bead and innerliner compounds.

Table 4 demonstrates the benefits of E- 1830 in a steel cord adhesion compound, with and without additional silica. As can be seen, the moduli are on a comparable level, the pull out forces (POF) measured under static conditions are similar and aging at 70[degrees]C shows no significant decrease. The tan [delta] measured under constant strain (MDR) is reduced by more than 20%. This reduced tan [delta] results in a lower heat generation, which reduces not only the rolling resistance, but should also improve the adhesion during the tire life. In order to simulate the benefit in adhesion under dynamic deformation, an experiment applying the rotation flexometer under constant deformation has been performed with these compounds. Figure 4 depicts the increase in temperature with increasing deformation, as well as the remaining adhesion strength (brass steel cord), after applying the different deformations. Compound A with E-1830 results in a significantly reduced heat generation and better adhesion under dynamic deformation. Such an excellent adhesion is a precondition for tire durability.

For the carcass but also for the bead, the use of the carbon black EB 204 (ref. 17) can be recommended, which has a lower CTAB surface area (20 [m.sup.2]/g) and increased DBP number (140 ml/100 g) compared to the classical N 550. Table 5 demonstrates the possible redaction of hysteresis loss in a carcass formulation with EB 204. As expected by the lowered surface area, the tan [delta] value decreased by more than 20% under the remaining modulus when the filler loading is increased slightly.

The carbon black EB 206 has a lower structure (DBP 80 ml/100 g) than the EB 204, and the same CTAB surface area of 20 [m.sup.2]/g. Despite the lower structure compared to EB 204, this carbon black has excellent behavior regarding dispersion and has to be added at higher loadings than N 772 and N 660, used commonly to obtain comparable moduli 300% values and durometer hardness levels. Therefore, this black is best suited to be used for innerliner compounds to reduce air permeability. Figure 10 demonstrates that the modulus 500% is comparable for the two compounds with 50 phr N 660 and 70 phr EB 206, respectively, but the air permeability is significantly lower for the one with EB 206.

[FIGURE 10 OMITTED]

For the reduction of the hysteresis loss and rolling resistance of tire body compounds, not only special blacks can be used. Part of the carbon black can be advantageously replaced by low surface area silica in combination with moderate amounts of a coupling agent (refs. 18 and 19). As an example, table 6 compares the in-robber data of a model sidewall compound where the carbon black N 375 is partly replaced by a highly dispersible low surface area silica (HD-LSA silica) with a CTAB surface area of 115 [m.sup.2]/g. The hysteresis loss is reduced, while the modulus is nearly unchanged. Therefore, the use of a carbon black/silica blend is a second possibility to reduce the hysteresis loss of tire body compounds without a sacrifice in reinforcement. Of course, the change of carbon black to silica/silane needs an accurate adjustment of the filler loading, amount of silane and curing system to regain the high tensile strength of the black-filled compound.

An additional reduction in rolling resistance can be achieved by the use of a cap and base construction, with the base having a very low hysteresis loss, e.g., by the use of E-1830 or a low surface area silica as filler. Problems can arise with the use of silica as the main filler in tread and body com pounds regarding the reduced electrical conductivity. To guarantee a sufficiently high conductivity, constructions with highly conductive compounds are one solution. Another possibility is the use of small parts of a conductive black like XE 2, which has a high surface area of 600 [m.sup.2]/g in CTAB.

Another approach to reduce the hysteresis loss of carbon black-filled compounds is the use of carbon silica dual-phase fillers produced by a Si-doping of the black in the furnace process. It is reported that such blacks can achieve a remarkable reduction of tan [delta], but a silane-coupling agent is important for good treadwear (refs. 20 and 21). It is reported that the reduction of hysteresis loss is mainly due to a reduced filler-filler network and that the silane-polymer coupling can compensate losses in reinforcement caused by a less active carbon black surface. Other fillers than carbon black and precipitated silica resulting in a reduced hysteresis loss are discussed in the literature, but the reinforcement is lowered, leading to a deteriorated treadwear, as well as to reduced tensile and tear strength.

Abrasion resistance and cut and chip

As discussed above, the most requested property for thick tires is an excellent treadwear, especially for long haul tracks. A better resistance to cutting and chipping, as well as chunking, is of importance lot heavy duty track tires in on/off- and off-the-road service. The concept to apply the nano-structure technology to meet the truck tire performance demands is depicted in figure 11 (ref. 22). The possibilities to improve abrasion resistance as well as cut and chip and chunk behavior, are marked in gray.

[FIGURE 11 OMITTED]

To improve cutting and chipping, high tear and tensile strength, high elongation at break and low heat generation have been observed to be the most important factors. To fulfill these requests, the technology of nano-structured blacks is best suited, because the reduced hysteresis loss of such carbon blacks can be used to increase the surface area to enhance tensile and tear strength, while retaining heat build-up on a low level. Due to the enhanced filler-polymer interaction, the structure level can be reduced without dispersion problems or significant losses in modulus. To achieve the improved balance between heat generation, treadwear; tear resistance and cut and chip properties, the special nano-structure black E-1990 (ref. 23) with a high specific surface area of 135 [m.sup.2]/g in CTAB, a medium to low structure level of 91 ml/100 g in CDBP and a low microporosity, was developed. With this type of carbon black, the abrasion resistance can be maintained, despite the low structure, and the rolling resistance is comparable to a corresponding carbon black with a much lower surface area.

As a test compound, a 100% natural robber compound was chosen, widely used in on/off-the-road truck services. Table 7 indicates the in-rubber properties of an N 220-filled com pound as reference, a compound consisting of a blend of N 115 and unmodified silica, a common way to improve the cut and chip behavior, and the E-1990-filled compound with adjusted filler loading. As can be seen, the hysteresis loss, tensile and tear resistance are improved for compound A, regarding the reference. To test the propagation of a cut, the Graves test was applied because the test specimen is performed with incision. Due to the reduced DBP number, a lower modulus of 300% is observed, but through the high surface activity, the reinforcing index 300%/100% is the highest one. The DIN abrasion resistance is on a good level, indicating a high severity treadwear comparable to the reference, whereas the low severity treadwear could be expected to be on a higher level compared to N 220 and N 115, due to the increased surface area. In the case of compound B with the added silica, improvements in tear resistance are obvious, but tensile strength, moduli and DIN abrasion resistance are deteriorated compared to the full black reference. The unique performance of the black E-1990 makes it an ideal candidate to improve the balance between cut and chip, treadwear and hysteresis.

To improve treadwear and to maintain the rolling resistance, the high structure, high surface area carbon black E-1720 may substitute standard ASTM blacks offering lower surface areas. This application possibility is also depicted in figure 11. To demonstrate this effect, the ASTM black N 339 is substituted by E-1720 (table 8). With this black having a higher specific surface area of about 30 [m.sup.2]/g in comparison to N 339, the mileage is by all expectations improved, but due to the higher filler-polymer interaction, the hysteresis loss, indicated by tan [delta] 60[degrees]C tested under constant strain and force, is comparable. Additionally, the black N 234, which has a similar surface area as the E-1720, is included in this series. As expected, the tan 15 is much higher for this compound.

Product and application overview

The family of the various nano-structure blacks available at Degussa, coveting different specific surface areas and structure levels to offer solutions for different applications, is pictured in figure 12. The U performance silica grades and two experimental products are also added. In this respect, it is important to mention that the DBP and CDBP numbers correlate rather well with the reinforcing in-rubber structure of carbon blacks, whereas in the case of silicas, the DBP gives an indication about the interagglomerate structure, which is important for the incorporation and dispersion of the silica.

[FIGURE 12 OMITTED]

Taking the above mentioned possibilities into account to reduce rolling resistance and heat build-up, respectively, to improve treadwear or the cut and chip behavior, figure 13 gives an overview of the possible fillers for the different truck tire parts.

[FIGURE 13 OMITTED]

Passenger tire applications

For European PC tires, which already contain high amounts of the silica/silane-reinforcing system in the tread, a further compound optimization essentially depends on the increase of the polymer-filler interaction, respectively, on the decrease of the filler-filler network. This will lead to a further reduction of rolling resistance and improved treadwear. The improvement of traction and braking performance requires a hysteresis behavior most capable of dissipating, the energy, which could be achieved by a change of the filler system and/or filler blend in combination with the optimal polymer basis. For example, the addition of butyl rubber to silica-filled SBR compounds or the use of tricopolymers is discussed in literature.

With a view to the contributions of the different the parts to the rolling resistance, it is obvious that a low-hysteresis loss tread compound reduces the rolling resistance of the tire most, btu an optimized carcass also contributes to a certain extent (figure 14). A cap-base construction, which reduces the hysteresis loss, is also a good possibility to further lower rolling resistance. The beneficial use of low hysteresis blacks and low surface area silicas for tire body compounds has been discussed in the previous section. A specialty that will most probably gain more importance in the future is the construction of run-flat tires, which have a special sidewall to carry the load under low and zero pressure. The compounds for such a sidewall, respectively carcass construction, must have a high stiffness combined with a very low hysteresis loss. To meet these requirements, highly crosslinked NR/BR compounds filled with low surface area blacks having a relatively high structure are optimal, e.g., N 550 or EB 204.

The following will focus on the possibilities of further optimization of the tread compound in order to meet the increasing performance demands.

The decrease of hysteresis loss with an increasing ratio of silica versus carbon black in an S-SBR/1,4-BR compound is well known. As an example, figure 15 pictures the improvements in tan [delta] 60[degrees]C and heat build-up by the partial replacement of 80 pin- N 234 by the silica/silane-filler system (ref. 24). To achieve a further decrease of the hysteresis loss of the tread compound, several approaches are possible.

[FIGURE 15 OMITTED]

Besides the change of the polymer blend or the use of chain-end modified rubbers, the filler network can be decreased by the use of a silica with a lower surface area (LSA) (ref. 25) or the addition of an additional alkylalkoxysilane to make the surface more hydrophobic and hence reduce the silica-silica interaction (ref. 26). In order to keep the treadwear on a good level, a reduction of the silica surface area should not be followed by a reduced amount of coupling agent, which leads to less filler-rubber-crosslinks, which are essential for the good treadwear (ref. 27).

Table 9 demonstrates the influence of a reduced silica surface area on the in-rubber properties in a model passenger car tire tread compound. The reinforcement remains on the level of the reference compound A, while tan [delta] 60[degrees]C of the compound B is reduced by about 10%. The slightly higher moduli are mainly due to a higher crosslink density caused by less accelerator adsorption on the surface of LSA silica. Due to the lower dynamic stiffness, especially at low temperatures, such LSA silicas may also suitable for winter tire treads.

Other concepts to reduce rolling resistance consist of using fillers that form a less strong network and hence contribute to a much smaller extent to the hysteresis loss. Those can be low surface area natural fillers and organic substances like modified starch (ref. 28), cellulose (ref. 29) or microgels (ref. 30). The idea is to add a second or even third filler, which forms an independent and/or less developed network than the main filler, and hence reduces the hysteresis loss. Several publications and patents deal with such alternative fliers, but the problem with each of these fillers is the lower reinforcement, due to a less active surface and/or a less rigid structure compared to silica and carbon black. To overcome problems with treadwear, the loading is limited to 5-15%, and most often a coupling agent has to be used.

In order to improve further wet and dry traction, different approaches are discussed in the literature. The use of higher silica/silane-filler loading is one possibility, but also the use of another filler or optimized polymer blend may improve traction (ref. 24). Besides the use of higher amounts of silica for better wet traction, the combination of a high performance black with, e.g., a surface area of 180 [m.sup.2]/g and a DBP-value of 125 ml/100 g with silica may be a suitable way to improve the dry traction. While the silica filler is responsible for good wet grip, the HP-carbon black is needed to gain a good dry grip under severe driving conditions.

Table 10 compares the in-rubber data of a model PC tire tread compound C with the above mentioned blend of HP-carbon black and silica to the full black compounds A with N 339 and B with N 234. As can be seen, the hardness values and reinforcement with respect to tensile strength and modulus 300%/100% are comparable (a better match of the moduli should be possible by an increase of the crosslink density or a higher filler loading and a higher oil content would reduce hardness). Heat build-up and tan [delta] 60[degrees]C measured under constant torsion is best for compound C, while the tan [delta] measured under constant strain is comparable to compound B filled with N 234. This indicates a similar rolling resistance as for compound B, despite the use of the high surface area black. The silica in compound C is not only responsible for the reduction of the hysteresis loss on the level of the N 234, but also for a good wet grip. From all expectations, the HP-carbon black should improve dry grip of the compound.

It is also reported that the use of aluminum oxide and -hydroxide with a surface area higher than 100 [m.sup.2]/g in combination with a silane-coupling agent improves wet traction without drawbacks in treadwear. But the high density of [approximately equal to] 3 kg/l is one of the main obstacles for this filler (ref. 31). The change of the polymer system using more high Tg-rubbers or a blend with butyl rubber (ref. 32) is also possible. In both cases, the traction is improved, but the maintenance of rolling resistance and treadwear is a problem. To overcome this, the filler must guarantee the lowest possible rolling resistance in combination with optimal treadwear. To meet this requirement, silicas with a surface area of 120 to 140 [m.sup.2]/g in combination with high amounts of silane coupling agents are an adequate choice.

Conclusion

PC tire tread

The market introduction of the green tire concept brought the carbon black in direct competition with the silica/silane filler system. Due to the outstanding performance regarding wet traction and rolling resistance, the silica/silane system is the best solution to improve rolling resistance and wet grip at the same time. Further improvement in wet grip could be expected by an increasing amount of the silica filler, while a lower rolling resistance seems possible by the use of highly reinforcing silicas with a surface area of 120 to 140 [m.sup.2]/g; probably a combination of both is advantageous. The ongoing demands of the automotive industry for improvements in wet traction and rolling resistance are the driving forces for the development of a next generation of highly dispersible silica and improved coupling agents. Carbon black has lost the dominant position in car tire tread compounds in Europe, but is still the main filler in the U.S.

Truck tire compounds

The increasing demands for truck tires to improve the tread-wear, rolling resistance and the resistance to cut and chip can be met by the use of nano-structure blacks, which show improvements in hysteresis loss while maintaining or even improving the high level of abrasion resistance of improved grades. Due to the requested high severity abrasion resistance of truck tires, the silica/silane-reinforcing system can only penetrate into tread compounds in combination with high reinforcing carbon blacks. Therefore, highly dispersible high surface area silicas have been developed. Special low surface area blacks and silicas also offer the possibility to reduce the heat build-up in body compounds, which would not only reduce the rolling resistance, but also improve the durability of the carcass.

Table 1--truck tire performance demands

Fleet owner         Operator             Environment

Excellent           Low interior noise   Low pass-by
  treadwear         High ride              noise
Low fuel              comfort            Low fuel
  consumption       Good                   consumption
High cut and chip     handling           High
  resistance        Good traction          retreadability
Good casing         No blow-out and
  durability and      high puncture
  retreadability      resistance

Table 2--NR truck tire compound with N 356 vs.
E-1670

                                                  Ref.    Exp.

SMR 10; ML = 60-70                                 100     100
N 356                                               52      --
E 1670                                              --      52
Other chemicals: ZnO 3;
  stearic acid 3; 6PPD 1; TMQ 1;
  wax 1; TBBS 1.2, PVI 0.15;
  sulfur 1.5
CTAB, [m.sup.2]/g                                   91      95
DBP, ml/100g                                       152     139
ML (1+4)                                            64      64
t 95%, 150[degrees]C, min.                        12.8    12.7
Tensile strength, MPa                             24.7    25.0
Modulus 100%, MPa                                  3.5     2.9
Modulus 300%, MPa                                 16.8    15.6
Elongation at break, %                             430     440
Durometer A hardness                                72      70
Goodrich flexometer 0.200 inch/2h
Contact temperature, [degrees]C                     58      53
Center temperature, [degrees]C                     101      90
Ball rebound 60[degrees]C, %                      60.6    63.9
[E.sup.*] 60[degrees]C, 50 [+ or -] 25N, , MPa     9.9     8.7
tan [delta] 60[degrees]C, 50 [+ or -] 25N        0.145   0.129
Dispersion (Phillips)                                8       8

Table 3--NR truck tire compound with N 220
vs. N 121/HD-HSA silica

                                                 Ref.       A       B

SMR 10; ML = 60-70                                100     100     100
N220                                               52
N121                                                       33      33
HD silica; CTAB = 160 [m.sup.2]/g                          20
HD-HSA silica, CTAB = 200 [m.sup.2]/g                              20
TESPT                                                     2.5     2.5
Other chemicals; ZnO 4; stearic
  acid 3; TMQ 0.75; 6PPD 2;
  PVI 0.2; sulfur 1.4
DPG                                                       0.3     0.3
TBBS                                               12     1.7     1.7
ML (1+4)                                           55      52      54
Delta torque, 150[degrees]C, dNm                 16.6    17.0    16.1
t 90%, min.                                      14.5    12.6    12.2
Tensile strength, MPa                            22.8    23.4    23.3
Modulus 100%, MPa                                 2.5     2.9     2.7
Modulus 300%, MPa                                13.7    14.8    13.5
Elongation at break, %                            460     440     460
Durometer A hardness                               67      66      66
DIN abrasion, [mm.sup.3]                           88      88      88
Dispersion coefficient, %                          97      95      98
Ball-rebound, 60[degrees]C, %                    57.5    67.7    66.8
Heat build-up, ([degrees]C)                       105      81      79
[E.sup.*], 60[degrees]C, 50 [+ or -] 25N, MPa     8.8     8.2     8.0
[E.sup.*], 60[degrees]C, 50 [+ or -] 25N, MPa     1.4     0.8     0.8
tan [delta], 60[degrees]C, 50 [+ or -] 25N      0.155   0.095   0.100

Table 4--steel cord adhesion compound with
N 326 vs. E-1830

                                                   Ref.      A        B

SMR 10; ML = 60-70                                  100     100     100
N 326                                                50
E-1830                                                       50      60
Silica VN2 GR                                        15      15
Hexa K (50%)                                          5       5       5
Other chemicals: ZnO 8;
  stearic acid 1; 6PPD 0.5;
  TMQ 0.8; oil 3 TBBS 0.8;
  resin 1.5; sulfur 5
CTAB, [m.sup.2]/g                                    81              77
DBP, ml/100g                                         72              89
ML(1+4)                                              72      72      80
t 95%, 150[degrees]C, min.                         20.9    20.1    22.5
Tensile strength, MPa                              14.3    15.0    18.0
Modulus 100%, MPa                                   4.7     4.6     4.7
Modulus 200%, MPa                                  10.8    11.1    11.0
Elongation at break, %                              250     250     310
Durometer A hardness                                 80      78      82
POF RT, N/cm                                        390     360     300
POF 3d/70[degrees]C, N/cm                           390     330     330
POF 7d/70[degrees]C, N/cm                           360     350     320
tan [delta], 60[degrees]C, 0.5[degrees] torsion   0.201   0.156   0.150
Dispersion (Phillips)                                 8       8       8

Table 5--carcass compound with N 550
vs. EB 204

                                      Ref.       A       B

SM10; ML = 60-70                        60      60      60
SBR 1712                                55      55      55
N550                                    50
EB 204                                          50      55
Other chemicals:
  stearic acid 1; paraf. oil 6;
  ZnO 3; resin 4; DPG 1.5;
  CBS 1.5; sulfur 2.2
CTAB, [m.sup.2]/g                       39      21      21
DBP, ml/100g                           122     143     143
CDBP, ml/100g                           87      76      76
ML(1+4)                                 31      31      33
Delta torque, 150[degrees]C, dNm      13.5    13.5    14.3
t 95%, min.                            9.4    10.1     9.8
Tensile strength, MPa                 14.6    13.9    13.5
Modulus 100%, MPa                      2.6     2.5     2.8
Modulus 200%, MPa                     10.3     9.1     9.5
Elongation at break, %                 410     440     420
Durometer A hardness                    58      58      59

Goodrich flexometer 0.250 inch/2h
Contact temperature                     52      48      53
Center temperature                      84      76      84
Ball rebound 60[degrees]C             72.1      78      76
E*60[degrees]C, 50+/-25N               6.0     5.7     6.1
tan [delta] 60[degrees]C, 50+/-25N   0.088   0.064   0.068
Dispersion (Phillips)                    8       8       8

Table 6--sidewall compound with N 375, and
partly replacedby an HD-LSA silica

                                                Ref      A       B

SMR 10: ML = 60-70                                50      50      50
1,4 BR                                            50      50      50
N 375                                             50      30      20
HD-LSA silica; CTAB 115 [m.sup.2]/g                       20      30
TESPT                                                    1.6     2.4
Other chemicals:
  ZnO 4; stearic acid 1; oil 6;
  anti-aging 3; wax 2; resin 5;
  CBS 1; sulfur 1.3
DPG                                                      0.7     1.0
ML(1+4)                                           72      71      64
Delta torque, 150[degrees]C, dNm                 6.9     6.7     6.7
t 90%, min.                                     13.0     9.9    11.0
Tensile strength, MPa                           19.1    17.5    16.9
Modulus 100%, MPa                                1.5     1.3     1.3
Modulus 500%, MPa                               14.3    13.6    12.3
Elongation at break, %                           600     600     620
Durometer A hardness                              58      55      55
DIN abrasion resistance                           48      52      56
Ball rebound 60[degrees]C, %                    53.9    59.1    60.6
[E.sup.*] 60[degrees]C, 50 [+ or -] 25N, Mpa     9.0     7.6     7.0
tan [delta] 60[degrees]C, 50 [+ or -] 25N      0.144   0.115   0.105

Table 7--comparison of E-1990 vs. N 220 and
N 220/silica in NR

                                                 Ref.      A       B

SMR 10; ML = 60-70                                 100     100     100
N 220                                               55
E-1990                                                      52
N 115                                                               55
Silica VN3; CTAB 160 [m.sup.2]/g                                    10
Other chemicals: ZnO 5,
  stearic acid 2; oil 5; resin 3;
  6PPD 3; wax 1.5;
  TBBS-80 1.5; sulfur 1.5
ML(1.4)                                             51      44      61
Delta torque, 150[degrees]C, dNm                  15.8    14.6    13.9
t 95%, 150[degrees]C, min.                        12.5    12.0    12.6
Tensile strength, MPa                             25.3    25.9    22.6
Modulus 100%, MPa                                  2.6     2.0     2.1
Modulus 300%, MPa                                 12.5    10.5    10.1
Modulus 300%/100%                                  4.8     5.2     4.8
Elongation at break, %                             530     550     570
Durometer A hardness                                65      62      64
DIN abrasion 10N, [mm.sup.3]                        84      91     121
Tear properties
Graves, 23[degrees]C, N/mm                          76      74      93
Graves, 120[degrees]C, N/mm                         50      58      69
Goodrich flexometer, 0.175"/2h
  Contact temp., [degrees]C                         60      48      96
  Center temp., [degrees]C                         103      86     151
Ball rebound 60[degrees]C, %                      56.4    56.6    49.4
[E.sup.*] 70[degrees]C, 50 [+ or -] 50N, MPa       7.3     6.3     7.3
tan [delta] 70[degrees]C, 50 [+ or -] 50N        0.143   0.120   0.187
tan [delta] 60[degrees]C, 0.5[degrees] torsion   0.204   0.181   0.248

Table 8--comparison between N 339, N 234
and E-1720 in NR

                                                 Ref.      A       B

SMR 10; ML = 60-70                                 100     100     100
N339                                                52
N234                                                        52
E1720                                                               52
Other chemicals: ZnO 3;
  stearic acid 3; 6PPD 1;
  TMQ 1; wax 1; TBBS 1.2;
  PVL 0.15; sulfur 1.5
CTAB [m.sup.2]/g                                    88     119     119
DBP, ml/100g                                       120     124     137
ML(1+4)                                             53      59      59
Delta torque, 150[degrees]C, dNm                  16.8    16.3    17.3
t 95%, min.                                       10.7    11.1    12.4
Tensile strength, MPa                             23.7    23.4    22.9
Modulus 100%, MPa                                  2.6     2.4     2.6
Modulus 300%, MPa                                 14.8    13.2    13.9
Elongation at break, %                             440     460     410
Durometer A hardness                                67      67      67
DIN abrasion resistance [mm.sup.3]                  91      89      78
Ball rebound 60[degrees]C, %                      64.2    60.0    63.6
[E.sup.*] 60[degrees]C, 50 [+ or -] 25N, Mpa       8.6     9.1     8.9
tan [delta] 60[degrees]C, 50 [+ or -] 25N        0.115   0.133   0.125
tan [delta] 60[degrees]C, 0.5[degrees] torsion   0.170   0.191   0.167

Table 9--influence of the silica surface area on
the in-rubber performance in a model PC-tire
formulation

                                                          A       B

S-SBR, 25% styrene, 37.5 phr oil                           96      96
cis 1,4-BR                                                 30      30
Silica, CTAB = 160 [m.sup.2]/g                             80
Silica, CTAB = 125 [m.sup.2]/g                                     80
TESPT                                                     6.4     6.4
Other chemicals: ZnO 3; stearic acid 2;
  oil 10; 6PPD 1.5; wax 1; DPG 2;
  CBS 1.5; TBZTD 0.5; sulfur 1.5
ML(1+4)                                                    72      61
Delta torque 165[degrees]C, dNm                           7.3     7.8
t 90%, min.                                               9.4     8.8
Tensile strength, MPa                                    13.5    12.6
Modulus 100%, MPa                                         2.4     2.5
Modulus 300%, MPa                                        11.6    12.6
Elongation at break, %                                    330     320
Durometer A hardness                                       69      67
DIN abrasion [mm.sup.3]                                    76      67
Ball rebound 23[degrees]C, %                             29.7    30.0
[E.sup.*] 0[degrees]C, 50 [+ or -] 25N, MPa              25.2    19.6
[E.sup.*] 60[degrees]C, 50 [+ or -] 25N, MPa              8.7     7.7
tan [delta] 0[degrees]C, 0[degrees]C 50 [+ or -] 25N    0.521   0.513
tan [delta] 60[degrees]C, 0[degrees]C 50 [+ or -] 25N   0.149   0.135

Table 10--comparison of N 339 and N 234 vs.
HP 180/silica in model PC tire tread
compound

                                                   A       B       C

E-SBR 1721                                          96      96      96
cis 1,4-BR                                          30      30      30
N339                                                90
N234                                                        90
HP 180, CTAB = 180 [m.sup.2]/g                                      45
Silica, CTAB = 160 [m.sup.2]/g                                      50
TESPT                                                                5
Other chemicals: ZnO 3; stearic acid 1;
  oil 10; resin 4; 6PPD 2; wax 1.5;
  CBS 2.0; sulfur 2
DPG                                                                1.4
ML(1+4)                                             59      65      61
Delta torque 165[degrees]C, dNm                   16.7    17.3    18.8
t 90%, min.                                        6.6     6.2     6.5
Tensile strength, MPa                             16.3    16.6    18.0
Modulus 100%, MPa                                  3.2     3.0     2.6
Modulus 300%, MPa                                 15.8    15.0    12.1
Elongation at break, %                             310     330     420
Durometer A hardness                                72      74      72
DIN abrasion, [mm.sup.3]                            87      90     101
Ball rebound 23[degrees]C, %                      42.2    38.1    41.1
Goodrich flexometer, 0.175inch, 25 min.
Contact temperature, [degrees]C                     76      74      67
Center temperature, [degrees]C                     128     128     119
[E.sup.*] 0[degrees]C, 50 [+ or -] 25N, MPa       72.6   105.8   119.3
[E.sup.*] 60[degrees]C, 50 [+ or -] 25N, MPa      10.5    11.3    10.9
tan [delta] 0[degrees]C, 0[degrees]C 50
  [+ or -] 25N                                   0.486   0.364   0.315
tan [delta] 60[degrees]C, 0[degrees]C 50
  [+ or -] 25N                                   0.229   0.253   0.256
E"/[E.sup.*2] 60[degrees]C, 50 [+ or -] 25N      0.021   0.022   0.021
tan [delta] 60[degrees]C, 0.5[degrees] torsion   0.267   0.295   0.257

Figure 5--contribution of the different parts of a truck
tire to the rolling resistance

Casing     24%
Belt       20%
Thread     30%
Bead       16%
Sidewall   10%

Note: table made from pie graph.

Figure 14--contribution of the different parts of
a PC tire to the rolling resistance

Tread        50%
Belt         20%
Casing       10%
Sidewall     10%
Innerliner    5%
Bead          5%

Note: Table made from pie chart.

References

(1.) R. Rauline, EP 0501227, US 5.227.425, Compagnie Generale des Establissements Michelin.

(2.) Degussa AG, Applied Technology Advanced Fillers, Product Information Si 69, PI 320.

(3.) a) H.-D. Luginsland, "Chemistry and physics of network formation in silica-silane-filled rubber compounds," paper presented at the ACS meeting, April, 2002; b) "A review on the chemistry and the reinforcement of the silica-silane filler system for rubber applications," Shaker Verlag, Aachen 2002.

(4.) H.-D. Luginsland, "A review on the chemistry and the reinforcement of the silica-silane filler system for rubber applications," Shaker Verlag GmbH (2002).

(5.) M.-J. Wang, "Effect of polymer-filler and filler-filler interaction on dynamic properties of filled vulcanizates," Rubber Chem. Technol. 71, 520 (1998).

(6.) T.A. Okel and W.H. Waddell, Rubber Chem. Techn. 67, 217 (1994).

(7.) a) W. Niedermeier, "Ecorax--the concept to extend the magic triangle," presented at the IRC 2000; b) Applied Technology Advanced Fillers, Technical Report TR 814.

(8.) G. Heinrich and T.A. Vilgis, Rubber Chem. Technol 68, 26 (1995).

(9.) W. Niedermeier and B. Freund, "Nano-structure blacks: A new carbon black family designed to meet truck tire performance demands," Kautsch. Gummi, Kunstst. 52, 670 (1999).

(10.) W. Niedermeier, Applied Technology Advanced Fillers, "Inversion blacks," technical report TR 801.

(11.) Ecorax 1670 available from Degussa AG, Advanced Filler's and Pigments Division.

(12.) K.A. Grosch and M. Heinz, "Proposal for a general laboratory test procedure to evaluate abrasion resistance and traction performance of tire tread compounds," presented at the IRC 2000.

(13.) W. Niedermeier, Applied Technology Advanced Fillers, "Inversion blacks," technical report TR 801.

(14.) Y. Bomal, Ph. Cochet, B. Dejean, I. Gelling and R. Newell, "Influence of precipitated silica characteristics on the properties of a truck tire tread, II," Kautsch. Gummi Kunstst. 51, 259 (1998).

(15.) H.-D. Luginsland, O. Stenzel, S. Uhrlandt and A. Wehmeier, "Use of highly dispersible high surface area silica in truck tire treads," presented at the ITEC conference 2002.

(16.) Ecorax 1830 available from Degussa AG, Advanced Fillers and Pigments Division.

(17.) EB 204 Experimental carbon black available from Degussa AG, Advanced Fillers and Pigments Division.

(18.) Ph. Cochet, D. Butcher and Y. Bomal, "Formula optimization for a steel belt cord insulation compound," Kautsch. Gummi Kunstst. 48, 353 (1995).

(19.) B. Schwaiger and A. Blume, "Silica/silane--a winning formula in reinforcement," Rubber World 222, 32 (2000).

(20.) M.-J. Wang, Y. Kutsovsky, P. Zhang, G. Mehos, L.J. Murphy and K. Mahmud, "Using carbon-silica dual phase filler," Kautsch. Gummi Kunstst. 55, 33 (2002).

(21.) M.-J. Wang, Y. Kutsovsky, P. Zhang, L.J. Murphy, S. Laube and K. Mahmud, "New generation carbon-silica dual phase filler: Part I. Characterization and application to passenger tire," Rubber Chem. Technol. 75, 247, (2002).

(22.) H.D. Luginsland, "Competition between precipitated silica and carbon black for tire applications," presented at the Functional Effect Filler's 2000.

(23.) Ecorax 1990 available from Degussa AG, Advanced Fillers and Pigments Division.

(24.) H.D. Luginsland, "Competition between precipitated silica and carbon black for tire applications," presented at the Functional Effect Fillers 2000.

(25.) A. Blume, H.-D. Luginsland, S. Uhrlandt and A. Wehmeier, "Influence of analytical properties of low surface area silicas on tire performance," presented at Silica 2001.

(26.) A. Hasse and H.-D. Luginsland, "Influence of alkylsilanes on the properties of silica-filled rubber compounds," presented at the RubberChem '01 Conference.

(27.) Andre Hasse, Oliver Klockmann, Andre Wehmeier and H.-.D. Luginsland, "Influence of the amount of TESPT and sulfur on the reinforcement of silica-filled rubber compounds," presented at the ACS Meeting 2001.

(28.) T.F.E. Materne and F.G. Corvasce, U.S. patent 6,273,163, The Goodyear Tire & Rubber Company.

(29.) D. Lucas, G. Agostini, F.G. Corvasce, J.O. Hunt and O. Louis, U.S. patent 5,967,211, The Goodyear Tire & Rubber Co.

(30.) W. Obrecht and W. Jeske, EP 1063259, Bayer AG.

(31.) N. Ezawa, K. Yagawa and N. Sasaka, U.S. patent 6,242,522, Bridgestone Corporation.

(32.) W. Hopkins, W. von Hellens, A. Koski and J. Rausa, "Reinforcement of BIIR with silica," Rubber World 226, 37 (2002).