GB2363318A - Windscreen wiper blade with reduced friction - Google Patents

Abstract

A wiper blade for wind screen wipers comprises a synthetic rubber coated, at least on its screen-engaging surfaces, with paraxylene. Suitable rubbers are silicone rubber and the coating may be of 0.4 to 1 microns thickness.

Description

2363318 WIPER BLADE This invention is concerned with a wiper blade

suitable for use in a wind screen wiper, eg of a vehicle.

Wind screen wipers usually operate by sweeping one or more wiper blades back and forth across an area of the surface of a wind screen to sweep water, snow etc away from that area. A typical wiper blade has integral mounting and sweeping portions, the mounting portion being received in a holder for the blade and the sweeping portion engaging the wind screen. The sweeping portion is in the form of a relatively thin strip terminating at an edge. Extending away from the edge are two oppositely- facing screen-engaging surfaces of the sweeping portion of the blade. When the blade is pressed against a wind screen, the sweeping portion of the blade bends bringing one of the screenengaging surfaces into engagement with the wind screen. During a sweep of the wiper blade across a wind screen, the sweeping portion of the blade is bent in such a way that the edge trails and the leading screen-engaging surface engages the screen. When the direction of sweeping reverses, the sweeping portion of the blade bends bringing the other screen-engaging surface (which now becomes the leading surface) into engagement with the screen.

A wiper blade must have a low coefficient of friction between its screenengaging surfaces and the screen, to ensure smooth movement without judder.

This can be achieved by making the blade from natural rubber and lowering the coefricient of friction of its surface by halogenation (chlorine treatment).

However, natural rubber may become set in one bent shape if left stationary in hot conditions. Synthetic rubbers (elastomers) such as silicone rubber can be found which are not subject to becoming set in one bent condition and have other improved properties, such as wear resistance, over natural rubber. However, 2 most synthetic rubbers cannot be halogenated so that their coefficients of friction are unacceptably high unless they are given a low friction coating. Various coatings have been thed but none was entirely satisfactory. For example, a coating of graphite tends to wear off in a relatively short time. EP 0 933 268 A proposes a coating formed from silicone varnish, polyurethane varnish or mixtures thereof but this is only a partial solution.

It is an object of the present invention to provide an improved wiper blade which utilises synthetic rubber.

The invention provides a wiper blade for wind screen wipers comprising a synthetic rubber coated, at least on its screen-engaging surfaces, with paraxylene.

Paraxylene is marketed under the name "Paralene" by Union Carbide. It is used to form rigid coatings for, eg, electrical insulation.

Preferably, the coating of paraxylene is 0.4 to 1 micron in thickness so that, although the material of the coating is relatively rigid, it is thin enough to flex with the blade.

Preferably, the synthetic rubber is a silicone rubber.

The invention also provides a method of manufacturing a wiper blade for wind screen wipers, the method comprising forming a blade from a synthetic rubber and coating it at least on its screen-engaging surfaces with paraxylene.

The method may comprise the steps of vaporisation of di-paraxylene, pyrolysis of the di-paraxylene into monomer of paraxylene, and deposition of polymer paraxylene on to the wiper blade.

There now follows a detailed description of an illustrative method of manufacturing a wiper blade according to the invention.

3 In the illustrative method, the raw material used for the coating was climer di-para-xylene. The wiper blade was formed from silicone rubber. The wiper blade was extruded as two blades joined at the edge of their sweeping portions.

The two blades were extruded to the required cross-section, then coated with para-xylene, and then separated by cutting. Thus, the blades were coated all over, including their screen-engaging surfaces, except that their cut edges were free from the coating.

The blades were coated by first vaporising the raw material in a first chamber at 15011C and a pressure of 1 torr. Next, the vaporised raw material was fed into a second chamber and converted into a monomer by pyrolysis at 6800C and 0.5 torr. Finally in the illustrative method, the two joined wiper blade were placed in a third chamber to which the monomer was fed. The blades were coated by deposition of the polymeric para-xylene at 250C and 0.1 torr. The wiper blade was coated with a coating 0.7 microns in thickness.

Claims (6)

1. A wiper blade for wind screen wipers comprising a synthetic rubber coated, at least on its screen-engaging surfaces, with paraxylene.
2. 2 A wiper blade according to claim 1, wherein the coating of paraxylene is 0.4 to 1 micron in thickness.
3. 3 A wiper blade according to either one of claims 1 and 2, wherein the synthetic rubber is a silicone rubber.
4. 4 A method of manufacturing a wiper blade for wind screen wipers, the method comprising forming a blade from a synthetic rubber and coating it at least on its screen-engaging edge with paraxylene.
5. 5 A method according to claim 4, wherein the method comprises the steps of vaporisation of di-paraxylene, pyrolysis of the di-paraxylene into monomer of paraxylene, and deposition of polymer paraxylene on to the wiper blade.
6. 6 A method of manufacturing a wiper blade substantially as hereinbefore described with reference to the illustrative example.