GB2329183A

GB2329183A - Improvements to tyres

Info

Publication number: GB2329183A
Application number: GB9719438A
Authority: GB
Inventors: Peter Raymond Appleton
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1997-09-13
Filing date: 1997-09-13
Publication date: 1999-03-17
Also published as: GB9719438D0

Abstract

The invention provides a tyre comprising a tyre carcass extending between two wheelrim-contacting bead regions, each of the bead regions being provided with a chafer in at least the region contacted by the wheelrim flange, wherein the chafer comprises a compound of a rubber elastomer and between 2 and 20 phr by weight of discontinuous discrete fibrillated aramid fibres. Preferably the chafer comprises natural rubber and the fibrillated aramid fibres are orientated in the same direction.

Description

IMPROVEMENTS TO TYRES This invention relates to improvements to vehicle tyres and in particular but not exclusively to improvements in pneumatic radial tyres.

The wheelrim contacting bead regions of such tyres are commonly provided with a component, termed a chafer', comprising a relatively hard rubber compound. The term chafer' is somewhat of a misnomer since the rubber compound is normally formulated to specifically resist chafing against the flange of the wheelrim. Such rubber chafers may comprise only a relatively thin rubber layer disposed on the outer surface of the tyre bead regions or they may comprise a large proportion of the material of the bead.

A problem which exists with chafers of all forms however relates to stretching and distortion of the component during assembly of the uncured tyre carcass and undesirable flow or smearing of the rubber under the influence of heat and pressure in the final moulding and vulcanisation operation.

Accordingly it is an objective of the present invention to provide a tyre having a chafer improved in hardness and resistance to deformation and flow.

US 4 871 004 discloses rubber compounds reinforced with aramid pulp in the form of short fibrillated fibres orientated in a substantially parallel 1 unidirectional configuration. For tyres it is disclosed to use such compounds for the reinforcement of cured bead apexes and the supplementary reinforcement of belt overlay and carcass plies.

However it has been discovered unexpectedly that such short fibrillated fibres can remarkably improve the properties of uncured rubber compounds used in the chafers of tyres.

According to the present invention a tyre comprises a tyre carcass extending between two wheelrimcontacting bead regions, each of the bead regions being provided with a chafer in at least the region contacted by the wheelrim flange wherein the rubber chafer comprises compound of a rubber elastomer and between 2 and 20 phr by weight of discontinuous discrete fibrillated aramid fibres.

More preferably the chafer comprises natural rubber and between 5 and 10 phr, most preferably 10 phr, of discontinuous discrete fibrillated aramid fibres.

The discontinuous discrete fibrillated aramid fibres may advantageously be orientated substantially in the same direction.

Further aspects of the invention will become apparent from the following description by way of example only of one embodiment of the invention in conjunction with the following drawings in which: Figure 1 shows a schematic cross-section of a motorcycle tyre according to the invention.

Shown in Figure 1 is a radial motorcycle tyre having a highly curved tread region 1 extending between tread edge 3,4 and having a camber value C/L in the range of 0.5 to 0.75, and specifically 0.73 in this embodiment. By camber value is meant the ratio of the radial and axial distances C and L between the tread edge 3 and tread centre on the tyre circumferential centreline C'-C'.

A carcass ply 14 comprising twin plies extends between bead regions 10,11, through sidewall regions 8,9 and the tread region 2. In each bead region the carcass ply is anchored by being turned axially outwardly around a circumferentially extending inextensible bead core 12,13 to form ply turn-up portions 15,16. Extending radially outwardly of the bead core 12,13 a tapering apex 17,18 is disposed between the carcass ply 14 and the ply turn-up portion 15,16.

In the tread region 1, radially outward of the carcass ply 14 and inward of the tread rubber is a reinforcing belt comprising two breaker plies 6 and 7 and an overlay ply 5.

Disposed on the outer surface of each of the bead regions of the tyre is a rubber chafer 21,22, having a relatively thin cross-section. In this embodiment the chafer extends fully around the bead region on both the axially inner surface and bead base in addition to the axially outer surface where the bead contacts the rim flange.

The material of the rubber chafer comprises a sulphur cured compound of natural rubber containing per hundred parts of rubber 40 parts by weight of carbon black N326 and 10 parts by weight of discontinuous discrete fibrillated aramid fibres.

To facilitate preparation of the chafer compound the aramid fibres are used in the commercially available form of a predispersion of 23% by weight of fibres in natural rubber which is marketed by E I Du Pont de Nemours as one of the KEVLARs "M/B" elastomer masterbatch range of materials.

The cured chafer compound has a modulus at 50% extension of 2.5 MPa and a Shore A hardness at 210C of 81, which level of properties represent an increase of the order of 80% and 20% respectively due to the incorporation of the aramid fibres.

Whilst the aramid fibres may be dispersed randomly within the chafer compound to provide improved hardness and resistance to flow and deformation they may also be orientated in a particular direction to provide further advantages in the tyre.

Orientation of the aramid fibres in a particular direction may be achieved in compounding by for example processes such as calandering or extrusion which will align the aramid fibres in the direction of flow of the compound.

Thus for example the fibres may be orientated radially of the tyre to increase radial stiffness without increasing lateral stiffness or vice-versa they may be orientated circumferentially to increase lateral stiffness without affecting radial stiffness. Alternatively they may be orientated at a bias angle dependent on the balance of radial and lateral stiffening desired.

Claims

1. A tyre comprising a tyre carcass extending between two wheelrim-contacting bead regions, each of the bead regions being provided with a chafer in at least the region contacted by the wheelrim flange, wherein the chafer comprises a compound of a rubber elastomer and between 2 and 20 phr by weight of discontinuous discrete fibrillated aramid fibres.

2. A tyre according to claim 1, wherein the chafer comprises between 5 and 15 phr by weight of discontinuous discrete fibrillated aramid fibres.

3. A tyre according to claim 1, wherein the chafer comprises 10 phr by weight of discontinuous discrete fibrillated aramid fibres.

4. A tyre according to any of claims 1 to 3, wherein the chafer comprises natural rubber elastomer.

5. A tyre according to any of claims 1 to 4, wherein the discontinuous discrete fibrillated aramid fibres are orientated in substantially the same direction.