GB2023516A

GB2023516A - Pneumatic tubes and tyres for vehicles

Info

Publication number: GB2023516A
Application number: GB7830487A
Authority: GB
Original assignee: T I RALEIGH IND Ltd
Current assignee: T I RALEIGH IND Ltd
Priority date: 1979-06-20
Filing date: 1978-07-20
Publication date: 1980-01-03

Abstract

An inner tube or tubeless tyre cover is given enhanced resistance to air diffusion by applying a low permeability coating. Typically, a natural rubber inner tube for a pedal cycle is given a coating on its inner surface with polyvinylidene chloride, or a tubeless tyre cover is chosen to be of a material having a good flexibility and low hysteresis loss with poor resistance to air diffusion but this resistance is made good with a low permeability coating. Alternative coating materials are polyvinyl chloride, nylon and nylon 6.

Description

SPECIFICATION Pneumatic tubes and tyres for vehicles This invention relates to the reduction of air loss from inflated vehicle tubes and tyres.

Since the adoption of butyl rubber which is about ten times better than natural rubber, and of the tubeless tyre, deflation rates of car tyres through diffusion of air through the molecules of rubber have been so small (around 2 p.s.i. per year) that there appears to be no problem in keeping them satisfactorily inflated. Bicycle tyres continue to use inner tubes for a variety of essential reasons, and although these are also made of butyl rubber, the high pressures, thin walls, large wall surface area, and small air volumes of the tubes combine to give much higher rates of pressure loss, of the order of 0.5 p.s.i. per day. It is necessary, therefor, to pump up a bicycle tyre at least once a month if it is to be kept properly inflated.

According to the invention an annular rubber body has a wall having a coating, on at least one surface thereof, of a smaller air permeability than the rubber.

In one arrangement the body is an inner tube for the tyre of a pedal cycle, for example a bicycle or tricycle, in which case the coating is on the whole of the inner or outer surface of the annular tube.

In another arrangement the body is in the form of a vehicle tyre with the coating on its radially inner surface.

The coating is desirably of plastics material, for example polyvinyl chloride (PVC), mylar, nylon 6 or, preferably, polyvinylidene chloride (PVDC).

The air permeability of natural rubber (that is the rate at which air diffuses through the molecules thereof) is about ten times that of butyl rubber, the air permeability of PVC is about one tenth that of butyl rubber, the air permeability of mylar and nylon 6 is about one hundredth that of butyl rubber, and the air permeability of PVDC is about one thousandth that of butyl rubber.

In the case of PVDC, the coating thickness may, for example, be 0.005 mm, which is thinner than a normal coat of paint but equivalent in its resistance to the passage of air to a thickness of 5 mm of butyl rubber or 50 mm of natural rubber. In the case of other coating materials suitable coating thicknesses may be between 0.01 and 0.1 mm.

The invention may be performed in various ways and some specific embodiments will now be described by way of example.

In the application of the invention to an inner tube for a pedal cycle tyre, the rubber inner tube is formed by extrusion in the usual way and during extrusion the inner or outer surface of the tube, as it emerges from the extrusion press, is coated with liquid PVDC in the form of a solution, dispersion or emulsion, for example by spraying. The tube is then heated, causing the PVDC coating to solidify.

The ends of the tube length are then butt welded in the usual way to form the inner tube, a valve for inflation being provided, also in the usual way.

The thickness of the rubber wall of the tube is commonly about 1.0 mm and a PVDC coating of 0.005 mm will therefore substantially increase the resistance to the passage of air, so that it is no longer important to use butyl rubber for the tube.

Thus, with such a coating the tube can be made of natural rubber which, as compared with butyl rubber, gives advantages in the form of easier mending of punctures (at least where the coating is on the inner surface), lower cost, and reduction of rolling resistance due to the lower mechanical hysteresis and better flexibility of natural rubber. In addition natural rubber is easier to butt weld, and the tube can be made with a thinner wall.

In the application of the invention to vehicle tubeless tyres, for example car tyres, coating the inside of the tyre with material providing an air barrier of at least usual effectiveness enables the tyre itself to be made of materials of low air holding ability (that is, materials which allow air to diffuse through them more readily than butyl rubber) but with properties better in other respects than with butyl rubber, for example in mechanical hysteresis loss and in flexibility, so that it should be possible to make tyres with reduced resistance to rolling and reduced noise transmission.

The effective air barrier thickness of a typical car tyre is about 5 mm so that a thickness of 0,005 mm of polyvinylidene chloride coating provides the same effective barrier. The PVDC coating is applied to the inner surface of the tyre, for example by spraying as a solution, dispersion or emulsion, either after completion of the manufacture of the tyre or before vulcanization and moulding of the tyre.

Other plastics materials may be used as the air barrier coating, for example polyvinyl chloride (PVC), mylar, nylon 6, and the thickness of the coating can be varied to suit requirements.

1. An annular rubber body having a wall with a coating, on at least one surface thereof, of a smaller air permeability than the rubber.

2. A rubber inner tube for the tyre of a pedal cycle, having a coating, on at least one of the inner or outer surface thereof, of a smaller air permeability than the rubber.

3. A rubber vehicle tyre having.a coating on the inner surface thereof, of a smaller air permeability than the rubber.

4. A body, tube or tyre as claimed in any one of claims 1 to 3 in which the coating is a plastics material of the group comprising polyvinyl chloride, mylar, or nylon 6.

5. A body, tube or tyre as claimed in any one of claims 1 to 3 in which the coating is polyvinylidene chloride.

6. A tube as claimed in claim 5 when appendant to claim 2 in which the coating is on the outside of the tube and the tube is made of natural rubber.

7. A tyre as claimed in claim 3 in which the material of the tyre has greater flexibility and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Pneumatic tubes and tyres for vehicles This invention relates to the reduction of air loss from inflated vehicle tubes and tyres. Since the adoption of butyl rubber which is about ten times better than natural rubber, and of the tubeless tyre, deflation rates of car tyres through diffusion of air through the molecules of rubber have been so small (around 2 p.s.i. per year) that there appears to be no problem in keeping them satisfactorily inflated. Bicycle tyres continue to use inner tubes for a variety of essential reasons, and although these are also made of butyl rubber, the high pressures, thin walls, large wall surface area, and small air volumes of the tubes combine to give much higher rates of pressure loss, of the order of 0.5 p.s.i. per day. It is necessary, therefor, to pump up a bicycle tyre at least once a month if it is to be kept properly inflated. According to the invention an annular rubber body has a wall having a coating, on at least one surface thereof, of a smaller air permeability than the rubber. In one arrangement the body is an inner tube for the tyre of a pedal cycle, for example a bicycle or tricycle, in which case the coating is on the whole of the inner or outer surface of the annular tube. In another arrangement the body is in the form of a vehicle tyre with the coating on its radially inner surface. The coating is desirably of plastics material, for example polyvinyl chloride (PVC), mylar, nylon 6 or, preferably, polyvinylidene chloride (PVDC). The air permeability of natural rubber (that is the rate at which air diffuses through the molecules thereof) is about ten times that of butyl rubber, the air permeability of PVC is about one tenth that of butyl rubber, the air permeability of mylar and nylon 6 is about one hundredth that of butyl rubber, and the air permeability of PVDC is about one thousandth that of butyl rubber. In the case of PVDC, the coating thickness may, for example, be 0.005 mm, which is thinner than a normal coat of paint but equivalent in its resistance to the passage of air to a thickness of 5 mm of butyl rubber or 50 mm of natural rubber. In the case of other coating materials suitable coating thicknesses may be between 0.01 and 0.1 mm. The invention may be performed in various ways and some specific embodiments will now be described by way of example. In the application of the invention to an inner tube for a pedal cycle tyre, the rubber inner tube is formed by extrusion in the usual way and during extrusion the inner or outer surface of the tube, as it emerges from the extrusion press, is coated with liquid PVDC in the form of a solution, dispersion or emulsion, for example by spraying. The tube is then heated, causing the PVDC coating to solidify. The ends of the tube length are then butt welded in the usual way to form the inner tube, a valve for inflation being provided, also in the usual way. The thickness of the rubber wall of the tube is commonly about 1.0 mm and a PVDC coating of 0.005 mm will therefore substantially increase the resistance to the passage of air, so that it is no longer important to use butyl rubber for the tube. Thus, with such a coating the tube can be made of natural rubber which, as compared with butyl rubber, gives advantages in the form of easier mending of punctures (at least where the coating is on the inner surface), lower cost, and reduction of rolling resistance due to the lower mechanical hysteresis and better flexibility of natural rubber. In addition natural rubber is easier to butt weld, and the tube can be made with a thinner wall. In the application of the invention to vehicle tubeless tyres, for example car tyres, coating the inside of the tyre with material providing an air barrier of at least usual effectiveness enables the tyre itself to be made of materials of low air holding ability (that is, materials which allow air to diffuse through them more readily than butyl rubber) but with properties better in other respects than with butyl rubber, for example in mechanical hysteresis loss and in flexibility, so that it should be possible to make tyres with reduced resistance to rolling and reduced noise transmission. The effective air barrier thickness of a typical car tyre is about 5 mm so that a thickness of 0,005 mm of polyvinylidene chloride coating provides the same effective barrier. The PVDC coating is applied to the inner surface of the tyre, for example by spraying as a solution, dispersion or emulsion, either after completion of the manufacture of the tyre or before vulcanization and moulding of the tyre. Other plastics materials may be used as the air barrier coating, for example polyvinyl chloride (PVC), mylar, nylon 6, and the thickness of the coating can be varied to suit requirements. CLAIMS

7. A tyre as claimed in claim 3 in which the material of the tyre has greater flexibility and lower hysteresis loss than butyl rubber.

8. A method of making a rubber inner tube comprising extruding a length of rubber tube, coating the tube as it is extruded with PVDC in solution, drying the coated tube and forming the length of tube into an endless tube.