Home Education Fillers for Polymer Applications
Tires are the main user of elastomers and also of the reinforcing fillers such as carbon blacks, which have always played a key role in them. Indeed, it is very unlikely that a useful tire could be made without them. As a result of this, and with the dominance of this market, these fillers have evolved in parallel with tire developments and continue to do so.
Tires are very complex items with the elastomeric components being required to fulfill a number of demanding roles. As a result, one has to consider a number of properties not well known outside of this technology. In the early days, the main concern was with tire life and the use of fillers to reduce tread wear and for some tires (truck and especially off-road ones) to also reduce cutting and chunking. Heat buildup in use was another important consideration and is still a significant factor in failure of truck tires. Grip (also known as traction) is a further important criterion which has to be maintained under a wide range of road, driving, and climatic conditions. Over time, the contribution of the filler to grip began to be understood and developed. Precipitated silica, in particular, was noted for good grip, especially in the wet and under cold, winter conditions. More recently, attention has shifted to minimizing fuel consumption by reducing rolling resistance, while maintaining adequate tire life and grip. This has led to the emergence of what is known as the green or energy tire. Again the filler choice has proved to be a key factor in optimizing this type of tire.
The service conditions and hence requirements of a tire also vary according to the type of vehicle, automotive, van, truck, off-road, etc.
Tires are made up of several parts in order to maximize performance, each optimized for the role that it has to play. The main parts of the tire that can be recognized are tread, side wall, beading, and inner liner. These use different types of elastomer and impose different requirements on the filler. Most interest today is focused on the tread, which is responsible for the grip and for most of the wear issues and requires the highest filler performance. In automotive tires, it is also responsible for most of the rolling resistance. While carbon black has been, and remains, the principal filler used, different grades have evolved to suit the different tire parts. Precipitated silica has long been recognized as giving better tear and chunking resistance and has found a niche in tires requiring this. It has also been recognized that precipitated silicas offer the possibility of achieving lower rolling resistance and they have made great strides in penetrating parts of the tire market over the last 20 years or so. So much so that virtually all new cars in Europe now feature silica- based tread formulations. These tires are often called green or energy tires.
Currently, there is considerable interest in the inner liner. This replaces the inner tube found in old tires, and its primary function is to retain the air added to obtain the desired tire pressure. Thus, gas impermeability is a key requirement. Currently, the impermeability is achieved by using specialized elastomers such as bromobutyl for this purpose. These are much less permeable than more conventional elastomers, but tires still lose pressure at a measurable rate. There are two factors focusing attention on upgrading current inner liners; both are related to the need to reduce fuel consumption. Firstly, the elastomers used are significantly denser than more conventional ones, making the weight of the inner liner a significant factor in the overall weight of the tire. Secondly, running with underinflated tires increases the rolling resistance. Much of the upgrading effort is focused on the filler. All fillers reduce permeability to some degree, but platy ones, such as some clays, can significantly increase this effect. Much of the work is proprietary, but it is confidently expected that significant progress will be made.
|< Prev||CONTENTS||Next >|