WO1996007525A1

WO1996007525A1 - A method of producing a scratch resistant coating on a plastics substrate

Info

Publication number: WO1996007525A1
Application number: PCT/GB1995/002083
Authority: WO
Inventors: Gordon Frederick Smith
Original assignee: Rover Group Limited
Priority date: 1994-09-02
Filing date: 1995-09-04
Publication date: 1996-03-14
Also published as: GB9417678D0; AU3394795A

Abstract

A method of producing a scratch resistant coating on a plastics substrate (18) comprising providing a resin material, mixing the resin with a glass filler material causing the resin and glass mixture to form the coating (17) on the substrate (18) in a mould (10), whereby the coating can be produced by an in-mould coating technique which does not involve dip, brush or spray coating of a substrate. Use of the method in the production of translucent 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 polycarbonate 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 scratch resistant coating on a plastics substrate comprising providing a resin

material, mixing the resin with a glass filler material and causing the resin and glass

mixture to form the coatine on the substrate in a mould.

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 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 is

preferably polycarbonate to provide the required degree of translucence and

toughness and the resin is preferably a clear unpigmented powdered plastics paint

material. The resin preferably has a refractive index substantially the same as that

of the glass filler material. The use of the in-mould coating technique enables the method in accordance with

the invention to be carried out in various different wavs.

A first way of performing the method involves initially producing a coating film

from the resin and glass, placing the film in the mould and moulding the substrate

onto the film to produce the coated component.

A second way of performing the method involves providing the glass in the form

of a fibrous mat. placing the mat and a preformed substrate in the mould and

introducing the resin into the mould to so as to impregnate the glass mat and coat

the substrate.

A third way of performing the method involves dual injection moulding and

comprises providing the glass in the form of a fibrous glass mat. placing the mat

in the mould and dual injecting the resin and substrate material 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. With such a method, the resin will normally form a skin over

substantially the whole of the injected substrate material which may be

advantageous in certain cases. However, the scratch resistant coating will be applied only over a specific area.

A fourth way of performing the method involves mixing the resin with glass filler

particles and dual injecting the mixture with the substrate material into the mould

to form the coated component. In such a case, the resin and glass mixture will

normally form the coating over substantially the whole of the injected substrate

material which will be advantageous in certain cases where an all-round scratch

resistant coating is required.

In any of the first second, third or fourth methods, the glass matt can be replaced

or the glass filler can comprise glass beads which can be solid or hollow spheres.

Preferably, the resin material is a thermoserting powdered plastics paint material

or could be a thermoplastic acrylic.

Where a transparent coating is required, the resin is preferably a non-pigmented

polyester resin powder which may have ultra violet protection additives. One

suitable material is Interpon JZ004D available from Courtaulds.

According to another aspect of the invention there is provided an article such as vehicle component made by a method in accordance with the method of the" first

aspect of the invention or any of the consistory clauses related thereto.

According to a further aspect of the invention there is provided a method of

producing a scratch resistant translucent material including providing a glass filler

material, mixing with the glass filler a non-pigmented resin having a refractive

index substantially the same as that of the glass and allowing or causing the resin

to cure.

Preferably, the glass filler material is in the form of a fibrous glass mat and/or glass

beads which can be solid or hollow spheres, and/or glass flakes. Beneficially, the

glass filler provides UV resistance to protect the substrate. In the case of hollow

beads, the transparency of the coating is reduced and therefore such a coating is not

as suitable as others for head lamp applications for example.

The invention also includes a scratch resistant translucent material produced by a

method according to the aforesaid further aspect of the invention.

Methods in accordance with the invention and components made by such methods

will now be described by way of example with reference to the accompanying drawings in which:

Fig 1 is a diagrammatic cross-section through a two-section mould showing a resin

impregnated glass mat in position in the mould.

Fig 2 is a view of the mould sections in Fig 1 in a closed position and after the

injection of a polycarbonate substrate.

Fig 3 is a view of the component formed in the mould shown in Figs 1 and 2.

Fig 4 is a cross-section through a two-section mould showing a pre-formed

polycarbonate moulding and a glass mat in position in the mould.

Fig 5 is a view of the mould sections in Fig 2 in a closed position and after the

injection of resin to impregnate the glass mat.

Fig 6 is a diagrammatic cross-section through a two-section mould with a glass mat

shown in position therein ready for dual injection and

Fig 7 is a view of the mould of Fig 6 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 polycarbonate plastics

material can be injected from an injection moulding machine (not shown).

With the mould sections 12. 13 in the positions shown in Fig 1, a thin flexible film

17 formed from a mixture of resin and glass fibres is then placed against the female

mould surface 14 and the mould halves are closed as shown in Fig 2. The thickness

of the film 17 is shown exaggerated in Figs 1 to 3. Molten polycarbonate P is then

injected through the passage 16 against the film 17. the film and the polycarbonate

bonding together homogenously due to the injection temperature of the

polycarbonate. The poly carbonate is then allowed to cure in the mould 10 until

the mould can be opened to allow the moulding M to be removed as shown in Fig

3. As will be appreciated, the moulding M comprises a polycarbonate substrate 18

having one surface coated bv the film 17.

The film 17 can be made by method of hot impregnation with resin of glass fibre

mat in a continuous process. The glass mat can be in roll or sheet form and the

resin is cured in the process. A suitable resin is Interpon JZ004D mentioned hereinbefore which is a non-pigmented polyester resin having ultraviolet protection

additives. In another method of making the film 17. glass fibre particles or glass

platelets can be dispersed in the resin prior to extruding the resin to produce the

film. The thickness of the film 17 may be in the range 10 microns - 20 microns so

that the film is sufficiently flexible to enable it to conform to the shape of the

mould cavity as the polycarbonate is injected into the mould. The film 17 of glass

fibre and resin forms a transparent, durable coating over the polycarbonate

substrate 18 to produce a transparent component having a surface shape and finish

dictated by the mould 10. If desired, the film 17 could be pre-formed. eg by

vacuum forming to match the shape of the mould surface 14.

Looking at Figs 4 and 5, a pre-formed polycarbonate component 20 can be

positioned in the mould 10 together with a glass fibre mat 22. The mould 10 can

then be closed as shown in Fig 5 and resin R injected through a passageway 23 in

mould section 12 which impregnates the glass mat 22 and adheres to the pre¬

formed polycarbonate 20 to form a coated component. Again, the resin can be a

non-pigmented polyester resin such as Interpon JZ004D to form a transparent

component. The thickness of the impregnated glass mat 22 in Fig 5 is shown

exaggerated. In Figs 6 and 7, the component is formed by means of dual injection. In that

respect, a mould 10 is mounted on a dual-injection moulding machine of known

kind which is arranged to inject a resin R slightly ahead of the polycarbonate

substrate material P. Initially, a glass fibre mat 22 is placed in the mould 10 as

shown in Fig 6. 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 7 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.

Instead of positioning a glass fibre mat 22 in the mould 10 as shown in Fig 6. the

resin R may be 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 6 and 7. The entire substrate will then be enveloped in a scratch-

resistant 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.

In any of the preceeding techniques the glass matt can be replaced or 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.

Preferably, the resin is a clear thermo-set resin.

Claims

1. A method of producing a scratch resistant coating on a plastic substrate comprising

providing a 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.

2. A method in accordance with claim 1 wherein the coating is produced by an in-mould

coating technique which does not involve dip. brush or spray coating of a substrate.

3. The method of claim 1 or 2 comprising the steps of initially producing a coating film

from the resin and glass, placing the film in the mould and moulding the substrate onto

the film to produce the coated component.

4. The method of claim 1 or 2 comprising the steps of providing the glass in the form of

a fibrous mat placing the mat and a preformed substrate in the mould and introducing the

resin into the mould so as to impregnate the glass mat and coat the substrate.

5. The method of claim 1 or 2 involving dual injection moulding and comprising

providing the glass in the form of a fibrous glass mat. placing the mat in the mould and

dual injecting the resin and substrate material 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.

6. The method of claim 5 wherein the resin forms a skin over substantially the whole of

the injected substrate material.

7. The method of claim 6 wherein the scratch resistant coating is applied only over a

specific area.

8. The method of claim 1 or 2 involving mixing the resin with glass filler particles and

dual injecting the mixture with the substrate material into the mould to form the coated

component.

9. The method of claim 8 wherein the resin and glass mixture form the coating over

substantially the whole of the injected substrate material.

10. The method of any of claims 1 to 9 wherein the resin material is a thermosetting

powdered plastics paint material.

11. The method of any of claims 1 to 10 wherein the resin is a non-pigmented polyester

resin powder which may have ultra violet protection additives.

12. The method of any of claims 1 to 11 wherein the substrate comprises polycarbonate

material.

13. The method of any of claims 1 to 12 wherein the resin has a refractive index

substantially the same as that of the glass filler material.

14. A method of producing a scratch resistant translucent material including providing

a glass filler material, mixing with the glass filler a non-pigmented resin having a

refractive index substantially the same as that of the glass and allowing or causing the

resin to cure.

15. The method of claim 14, wherein the glass filler material is in the form of a fibrous

glass mat.

16. The method of any one of claims 1 to 14 wherein the glass filler material

comprises glass beads.

17. The method according to claim 16 wherein the glass beads are solid or hollow

spheres.

18. The method according to claim 16 or 17. wherein the volume fraction of glass

beads to resin material is greater than 27% and more preferably in the order of 50%.

19. The method according to claim 16. 17 or 18 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.

20. A scratch resistant translucent material produced by a method according to any one

of claims 14 or 19.

21. An article such as vehicle component made by a method in accordance with the

method of anv of claims 1 to 20.

22. Use of the method according to any one of claims 1 to 13 in the production of

translucent components such as vehicle headlamp lenses and windows.