FI59221B - DAECKVULST - Google Patents

Description

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Patent and Registration Office . ,,, _, (44) Date of issue and date. - ratent- ocn registerstyrelsen Amökan utiaid oeh uti. Dunlop Limited, Dunlop House, Ryder Street, St. James's, London SWI, England-England (GB) (72) Norman Albert Jones, Streetly, Staffordshire, Robert John Blythe,

This invention relates to bellows for pneumatic tires and in particular to belt tires.

The ring comprises a plurality of circumferentially spaced reinforcing filaments, each located in the radial plane of the ring between two axially spaced ribs around which they are wound.

In the manufacture of a ring, the reinforcing filaments are positioned so as to define a substantially cylindrical structure, the ends of the filaments being located in the longitudinal direction of the structure and wrapped around the ribs located at each end of the filament bundle. When forming a finished tire, the assembled tire parts are reshaped to change the essential cylindrical shape to the desired shape, and this causes the reinforcing filaments to shift so that their axial position becomes substantially radial when viewed in the cross-sectional plane of the finished tire.

The beads generally comprise bale yarns embedded in rubber, and the aforementioned displacement of the reinforcing filaments tends to cause distortion of the cross-sectional shape of the 2,592,21 beads. This distortion, which makes it difficult to produce unchanged quality products, can be substantially avoided by pre-vulcanizing the pallet rubber. However, the use of pre-vulcanized beads makes further preparations necessary to provide good adhesion between the bead and the associated rubber material when vulcanizing the tire; these additional preparations know the additional costs.

GB Patent Publication No. 1,163,108 discloses a means of overcoming the problem of slip resistance of a bobbin in the manufacture of a ring due to the rectangular cross-section of the bale wire winding. This is done by means of a circular rubber sheath surrounding the bale yarns, which minimizes unwanted layer head stresses during shaping, eliminating the need for a complicated and expensive method to achieve a circular cross section of the bobbin yarns themselves.

According to FR-A-2 137 810, bale yarns are coated with unvulcanized high-plastic rubber which is cold-pressed without vulcanization to the desired cross-section. This allows the tire to be manufactured effortlessly without the problems encountered when using a pre-vulcanized bead.

The present invention provides an alternative solution to these known problems associated with bead distortion and / or undesired layer head stresses in the manufacture of a tire using a bead yarn coating consisting of a blend of a natural rubber and a styrene-butadiene copolymer. This coating prevents deformation of the bead during tire manufacture while having good bonding properties to rubber compounds adjacent to the tire and suitable mechanical properties at the various temperatures that occur during tire manufacture.

59221 According to the present invention, a bead of bead comprises bead yarns embedded in a rubber composition consisting of a mixture of natural rubber and a styrene-butadiene copolymer having a copolymer bound styrene content of at least 32% by weight. The styrene content can be determined, for example, according to the method described in British Standard No. BS 1673, Part 5.1, which is suitable for use up to about 40% by weight.

The bellows yarns and the surrounding mixture may be coated with a covering layer, which may also be the same mixture as that used for the rubber surrounding the beads, so that the resulting bead has an external cross-sectional shape that allows relative movement of the bead and other parts of the ring, such as between the reinforcing filaments, the ends of which are wrapped around the bead.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, in which Figure 1 shows a cross-section of beads embedded in a rubber composition according to the present invention, and Figures 2-7 show cross-sections of a bead structure of Figure 1 with different cross-sections to provide bellows combinations with varying overall cross-sectional shapes.

In a suitable embodiment of the invention and shown in Figure 1, the polymer part 10 in which the bale yarns 11 are embedded comprises a polymer part with equal parts of natural rubber and a styrene-butadiene copolymer with a high styrene content. The mixture preferably also contains a resin precursor such as phenol-formaldehyde and HMT (hexamethylenetetramine). The resin precursor prevents the vulcanized mixture from softening at the temperatures generated under the conditions of use of the product.

* Λ 4 59221

Suitable bond examples with or without the use of a resin precursor include:

Without resin precursor

Natural rubber 50 50

Styrene-butadiene copolymer (87.5% bound styrene) 50 50

Carbon black (ASTM standard N 375) 55 55

Insoluble sulfur

Sulfenamide accelerator (e.g. Monsanto Santocure) 1.00 1.00

Zinc oxide 5.00 5.00

Stearic acid 2.00 2.00

Paraffin oil (eg Dutrex RT)

Precondensed phenol-formaldehyde resin (e.g. Schenactady Midland CRJ 448) - 6.00

Hexamethylenetetramine (HMT) - 0.50

Hydrocarbon resin (e.g. Esso, Escorez resin) 6.00

When shaping the assembled parts into the desired shape required by the finished tire, the mixture surrounding the yarns resists distortion of the bead cross-sectional pattern, which is rigid enough to substantially resist the forces generated by the reinforcing filaments and other ring parts around the bead assembly.

The high styrene-containing styrene-butadiene copolymer in the blend facilitates handling at manufacturing temperatures while providing plastic deformation at ambient temperature, allowing the bead shape to be maintained during ring shaping.

When a ring having such a bead is vulcanized, the high styrene butadiene units of the styrene-butadiene copolymer are crosslinked with natural rubber, whereby the ring bead mixture adheres to the rubber compounds adjacent to the ring. The styrene units are not cross-connectable and therefore remain in "moving" groups, i. they move more freely. They develop a thermoplastic phase in the mixture that is dominant at lower temperatures, stiffening the mixture. At higher temperatures, cross-linked units of natural rubber and butadiene dominate, providing a flexible phase.

Surprisingly, it has been found that it is precisely the combination of natural rubber and high styrene-containing styrene-butadiene copolymer 5 59221 that provides the above-mentioned advantageous properties. Examining this phenomenon, it has been found that it is due to the fact that the mixture behaves like a plastic at ambient temperature.

Figure 2 shows a bead structure similar to Figure 1 but coated with a uniform thickness of cover layer 12 which is a mixture of the same material as the yarns.

Figure 3 shows a bellows structure in which the bundle yarn assembly 13 embedded in the mixture 10 has a hexagonal cross-section and is enclosed in a cover layer 14, the cross-sectional thickness of which varies in the circumferential direction so that the cross-sectional dimension of the final bellows is circular.

Figure 4 shows an assembly of bobbin yarns with an irregular cross-sectional dimension and enclosed in a cover layer 15 of varying thickness so that the cross-sectional shape of the final bellows is elliptical.

Figures 5 and 6 show modifications of Figs. 4, wherein one of the surfaces 16, 17 of the hexagonal wire bundle forms an angle with the direction A perpendicular to the plane containing the bead so that the wire assembly is evenly supported when the tire is mounted on a wheel having a corresponding angle in the rim. The angle may preferably be of the order of 15 °.

Fig. 7 shows a bundle of yarn assemblies having an irregular cross-sectional dimension and enclosed in a cover layer 18 of varying thickness so as to provide a further variation of the structure of Fig. 4.

Although there has been particular talk of a blend of an equal weight of natural rubber and a high styrene-styrene-copolymer copolymer, a natural rubber and a high-styrene-styrene-butadiene copolymer may be included in the mixture in proportions ranging from 10/90 to 70/30 parts by weight, whether or not a resin precursor is used.

It is thus obvious that the present invention eliminates the need to use pre-vulcanized beads and thus provides significant savings in production costs.