Silica-filled tires

Used for sulfur-cure, mineral-filled rubber applications. Silica-filled tires with lower rolling resistance, longer lasting, heat resistant belts or hoses, and light weight shoe soles are some of the typical uses. 

Amorphous high vinyl polybutadienes (>70% vinyl) have glass-transition temperatures higher than -40°C (349). These materials are t5 ically made with lithium initiators combined with a muted alkali metal alkoxide and/or polar modifier system. As a result, commercial high vinyl polybutadienes are t5 ically quite branched but display excellent traction properties. These materials are most often used in silica-filled tire applications. 

Therefore, it might be possible to formulate a compound which both conducts and has all the other advantages of the green tire by the incorporation of relatively small amounts of carbon nanotubes into the silica-filled compound. 

The Payne effect of carbon black reinforced rubbers has also been investigated intensively by a number of different researchers [36-39]. In most cases, standard diene rubbers widely used in the tire industry, bke SBR, NR, and BR, have been appbed, but also carbon black filled bromobutyl rubbers [40-42] or functional rubbers containing tin end-modified polymers [43] were used. The Payne effect was described in the framework of various experimental procedures, including pre-conditioning-, recovery- and dynamic stress-softening studies [44]. The typically almost reversible, non-linear response found for carbon black composites has also been observed for silica filled rubbers [44-46]. 

Silica-filled tread compounds for passenger car tires have become state-of-the-art and have taken a significant share from conventional carbon black-filled systems. In addition to the well-known benefits of fillers such as reinforcement (Fig. 11) and increased cut resistance, silica-based compounds are mainly successful because they provide improved rolling resistance (leading to lower fuel consumption), better wet and snow track resistance, and thermal stability. 

There is much interest in using silica fillers in tires, because it is possible to obtain abrasion-resistant treads of lower hysteresis (thus better fuel economy) than that of carbon-black-filled treads. However, there have been problems with the processing of the silica-filled compounds. Also silica, being nonelectrically conductive, gives vulcanizates that can hold static electrical charges due to rolling on the road. Efforts to get around these and other problems have led to the introduction of hybrid silica-carbon fillers. 

With the advent of HDS, the ability to disperse silica to levels equal to that of carbon black is now possible for the creation of highly silica-filled rubber compounds. Thus, there has been a revolution in growing use of silica in place of carbon black in tires since the early 1990s, requiring growing use of specific coupling agents, whose number and chemistries have also expanded in this time period. A description of this class of rubber chemicals follows. 

Silane adhesion promoters are manufactured globally. They have traditionally been manufactured in the United States, Europe, and Japan, but manufacturing facilities in China and Korea are supplementing the supply with high-quality products. The emergence of large-volume applications for silanes, especially in silica-filled rubber tires, has substantially increased the number of global suppliers. 

Rubber Chemistry and Technology 73, No.2, May-June 2000, p.240-52 THE EFFECTS OF CERTAEV RECIPE INGREDIENTS AND MIXING SEQUENCE ON THE RHEOLOGY AND PROCESSABILITY OF SILICA- AND CARBON BLACK-FILLED TIRE COMPOUNDS... 

Any silica-filled rubber formulahon may benefit from in situ silanization during the compounding operations and, in the tire industry, it is now well established that partial or total substitution of carbon black by silanated... 

FIGURE 29.6 Temperature profile of the phase angle tan 8 for a 75 phr N234 carbon black-filled versus a 75 phr silica/silane-reinforced green-tire compound. (From Wang, M.-J., Rubber Chem. Technol., 71, 520, 1998.)... 

The PVD process by means of electric arc evaporation has attained a high degree of importance in deposition of hard layers on an industrial scale. The hardness achieved is a minimum of 2100 HV. Compare this to the standard nitriting process which provides a hardness of about 900 HV or the stelliting process which offers about 500-600 HV. Extmsion screws treaded with this special process in the tire industry have seen a much improved wear life when processing highly filled silica compounds or very hard apex compounds. 

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