GB2319744A

GB2319744A - Moulding a component having a scratch resistant coating and a plastics base

Info

Publication number: GB2319744A
Application number: GB9801857A
Authority: GB
Inventors: Gordon Frederick Smith
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1994-09-02
Filing date: 1995-09-04
Publication date: 1998-06-03
Anticipated expiration: 2015-09-04
Also published as: GB9801857D0; GB2305890B; GB2305890A; GB2319744B; GB9703688D0

Abstract

A method of forming a translucent scratch resistant coating on a plastics substrate comprises mixing a clear resin together with a glass filler material (eg. glass beads) and dual injecting the mixture and the substrate into a mould so that the mixture forms a coating on the substrate Preferably the resin is a thermosetting polyester provided in the form of a powdered paint containing u-v protection additives and the substrate is a polycarbonate material. The method is particularly suitable for producing components such as vehicle headlamp lenses and windows.

Description

A METHOD OF PRODUCING A SCRATCH RESISTANT COATING ON A PLASTICS SUBSTRATE The invention relates to a method of producing a scratch resistant coating on a plastics substrate and is particularly, but not exclusively, concerned with the production of a translucent component such as a lamp lens or window for use on a motor vehicle.

For some time. polycarbonate plastics material as a clear moulding has been applied as a replacement for windows and lenses as it has specific weight advantages. Polycarbonate lenses and glass have substantially equal transparency but polycarbonate is less resistant to scratching than glass. In order to improve scratch resistance special siloxane coatings have been produced for coating the moulded poivcarbonate for protection. Such siloxane coating involves dip, brush or spray application techniques in a clean environment and subsequent curing.

An object of the present invention is to provide an improved scratch-resistant coating suitable for use with polycarbonates or other substrates of plastic material where a scratch resistant coating is required.

According to one aspect of the invention there is provided a method of producing a translucent scratch resistant coating on a plastic substrate comprising providing a non-pigmented resin material, mixing the resin with a glass filler material and causing the resin and glass mixture to form the coating on a substrate in a mould, wherein the coating and the substrate are formed by dual injection in which the resin is mixed with glass filler particles and the mixture is dual injected with the substrate material into the mould to form the coated component.

By using a method in accordance with the invention, the coating can be produced by an in-mould coating technique which does not involve dip, brush or spray coating of a substrate. The in-mould method also enables such components to be produced accurately with a surface finish dictated by the mould surface without the need for special clean environments.

Moreover, the use of the glass filler material provides an extremely hard coating for the substrate which is highly resistant to scratching.

The resin and glass mixture may form the coating over substantially the whole of the injected substrate material.

The resin is preferably a clear thermoset resin, such as a polyester resin powder having ultra violet protection additives. One suitable material is Interpon (R.T.M.) JZ004D available from Courtaulds.

A preferred use of the method is in the production of translucent components such as vehicle headlamp lenses and windows. In such a case the substrate preferably comprises polycarbonate material to provide the required degree of translucence and toughness. The resin preferably has a refractive index substantially the same as that of the glass filler material.

The materials produced by the methods referred to above are novel.

Hence, according to a second aspect of the invention there is provided a scratch resistant translucent material produced by a method according to said first aspect and , according to a third aspect of the invention there is provided an article such as vehicle component made by a method in accordance with said first aspect.

Similarly, it is novel to use the methods described above in the production of translucent components such as vehicle headlamp lenses and windows. Hence, according to a fourth aspect, the invention also provides use of the method according to said first aspect in the production of translucent components such as vehicle headlamp lenses and windows.

The present application is divided from application no. 9703688.3 (published as GB-A- 2 305 890) which describes and claims a method of producing a translucent scratch resistant coating on a plastic substrate comprising providing a non-pigmented resin material, mixing the resin with a glass filler material and causing the resin and glass mixture to form the coating on a substrate in a mould, wherein the coating and the substrate are formed by dual injection in which the glass is provided in the form of a fibrous glass mat by placing the mat in the mould and the resin and the substrate material are dual injected into the mould whereby the resin is injected ahead of the substrate material in order to impregnate the glass mat so that the resin impregnated glass mat forms the coating on the substrate.

In essence the present invention differs from that described and claimed in application no. 9703688.3 in that the fibrous glass mat is replaced by glass fibres or particles. Hence a method in accordance with the present invention and components made by such a method will now be described by way of example as a modification to the method and components described in application no. 9703688.3 and with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic cross-section through a two-section mould with a glass mat shown in position therein ready for dual injection in accordance with the method claimed in application no. 9703688.3; and Fig.2 is a view of the mould of Fig.1 in a closed position following dual injection.

In Figs.1 and 2, a mould 10 comprises first and second sections 12, 13 the first section 12 defining a cavity 11 having a female mould surface 14 complementary to a male mould surface 15 on the second mould section 13.

The mould section 13 is formed with an injection passage 16 through which plastics material can be injected from an injection moulding machine (not shown).

The component is formed by means of dual injection. In that respect the mould 10 is mounted on a dual-injection moulding machine of known kind which is arranged to inject a resin R slightly ahead of a polycarbonate substrate material P. Initially, a glass fibre mat 22 is placed in the mould 10 as shown in Fig.1. Injection of the polycarbonate P causes the polycarbonate to spread the resin R over and impregnate the glass mat 22.

Injection is continued until the entire mould cavity 11 is coated with the resin R as in Fig.2 and the resin envelopes the injected polycarbonate P.

After curing, the formed component is removed from the mould. It will be appreciated that the dual injection method provides an all-round coating which may be advantageous in certain applications. However, the scratch resistant coating formed by the resin impregnated glass mat 22 is applied only to a given area of the moulding.

A suitable resin R is Interpon (RTM) J2004D mentioned above which is a non-pigmented polyester resin having ultraviolet protection properties.

In accordance with the present invention, instead of positioning a glass fibre mat 22 in the mould 10 as shown in Fig.1, the resin R is mixed with glass fibres or other glass particles prior to injection. For example, if glass flakes are used it is possible to achieve substantial alignment of the flakes with the surface of the coating during the injection stage such as shown in figures 1 and 2. The entire substrate will then be enveloped in a scratchresistant coating.

It has been found that the glass/resin mixture adheres well to a polycarbonate substrate and provides excellent resistance to scratching making it possible to produce components such as vehicle lamp lenses and windows having a polycarbonate substrate with a scratch resistant surface.

Ideally, the resin and the glass filler will have the same refractive index whereby the finished component with the polycarbonate substrate will have a high degree of transparency.

In-mould coating of components such as vehicle headlamps and windows will enable such components to be made easily in the desired shape with a highly polished external finish without having to provide any especially clean environment. Moreover, if tinting of the components is required, the resin used to impregnate the glass mat or indeed, the substrate itself, can be combined with suitable tinting pigments.

The glass filler can comprise glass beads. The glass beads should have a refractive index substantially similar to that of the resin in which they are to be incorporated. In forming the scratch resistant coating, the resin and glass beads are preferably thoroughly mixed and a volume fraction of greater than 27% glass beads is preferably used. The volume fraction of beads to resin is more preferably in the order of 50% since this is bound to provide strongest hardness and scratch resistance.

The glass beads are preferably in the form of solid or hollow spheres having a diameter less than 100 microns. More preferably, the diameter of the spheres is less than 36 microns and more preferably still between 2.8 and 4.5 microns. Preferably the powdered resin and glass beads are hot pressed at about 180 C for 10 minutes at a low pressure between copper plates coated with release agent.

Claims

1. A method of producing a translucent scratch resistant coating on a plastic substrate comprising providing a non-pigmented resin material, mixing the resin with a glass filler material and causing the resin and glass mixture to form the coating on a substrate in a mould, wherein the coating and the substrate are formed by dual injection in which the resin is mixed with glass filler particles and the mixture is dual injected with the substrate material into the mould to form the coated component.

2. A method according to Claim 1 wherein the resin and glass mixture form the coating over substantially the whole of the injected substrate material.

3. A method according to any preceding claim wherein the resin material is a thermosetting powdered plastics paint material.

4. A method according to Claim 3 wherein the resin is a polyester resin powder having ultra violet protection additives.

5. A method according to any preceding claim wherein the substrate comprises polycarbonate material.

6. A method according to any preceding claim wherein the resin has a refractive index substantially the same as that of the glass filler material.

7. A method according to any preceding claim wherein the glass filler material comprises glass beads.

8. A method according to Claim 8 wherein the glass beads are solid or hollow spheres.

9. A method according to Claim 7 or 8, wherein the volume fraction of glass beads to resin material is greater than 27% and more preferably in the order of 50%.

10. A method according to Claim 7, 8 or 9 wherein the diameter of the glass beads is less than 100 microns, more preferably less than 36 microns and more preferably still between 2.8 and 4.5 microns.

11. A scratch resistant translucent material produced by a method according to any preceding claim.

12. An article such as vehicle component made by a method in accordance with the method of any of Claims 1 to 10.

13. Use of the method according to any one of Claims 1 to 10 in the production of translucent components such as vehicle headlamp lenses and windows.