WO2000000338A1

WO2000000338A1 - Improved polymer glazing system

Info

Publication number: WO2000000338A1
Application number: PCT/GB1999/001792
Authority: WO
Inventors: Kerry Emmett Arthur Kirwan; Gordon Frederick Smith
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 1998-06-26
Filing date: 1999-06-07
Publication date: 2000-01-06
Also published as: AU4277799A

Abstract

A method of producing a component, comprising a scratch resistant coating on a plastics substrate (40), in which a mould (1, 21) is heated, a glass filler material (11, 31) placed in the mould, and a resin material (35) injected into the mould to impregnate the glass filler material, the resin and the glass filler material thereby forming the coating, the mould being heated to a temperature in the region of the melting temperature of the resin and kept at that temperature for a period following injection of the resin, before cooling of the mould and removal of the component from the mould.

Description

Improved Polymer Glazing System

The present invention relates to an improved polymer glazing system, having particular, but not exclusive, use in the production of a translucent automotive glazing component such as a lamp lens or window panel.

It is known to use polycarbonate plastics material as a clear moulding material due to its specific weight advantages. However, polycarbonate is less resistant to scratching than glass.

While a polycarbonate moulding can be provided with a siloxane coating, such a coating involves dip, brush or spray application techniques in a clean environment and also represent a further processing step.

An alternative route is known from GB 2 305 890 A. A method of producing a scratch resistant coating on a plastics substrate comprises providing a resin material such as polycarbonate, mixing the resin with a glass filler material causing the resin and glass mixture to form the coating on the substrate in a mould. Such a technique does not involve the dip, brush or spray coatings of the previously described route.

However, there have been difficulties in repeatedly producing a sufficiently clear component for the technique to enter mass production. One reason for this is that although the resin and the glass filler have a similar or the same refractive index, the final article can appear cloudy. This is believed to be because of incomplete wetting of the glass filler by the resin. In addition the less translucent articles produced by this technique tend to lack the necessary integral strength for use in large size applications.

It is an aim of the present invention to eliminate, or substantially reduce, these problems.

According to a first aspect of the present invention a method of producing a component comprises the steps of providing a mould having a cavity, heating the mould to a predetermined temperature, placing a glass filler material in the cavity, closing the mould, injecting a thermoplastic resin material into the cavity to fill the cavity and to impregnate the glass filler material, then cooling the mould, before opening the mould to remove the component, characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

According to a second aspect of the invention a method of producing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material and a substrate material, providing a glass filler in the form of a fibrous glass mat, placing the mat in a mould, closing the mould and heating the mould to a predetermined temperature, dual injecting the thermoplastic resin and the substrate material into the mould to fill the cavity whereby the thermoplastic resin is injected into the mould 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, cooling the mould, characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

According to a third aspect of the invention, a method of providing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material, mixing the thermoplastic resin with a glass filler material to form a mixture, heating a mould having a mould cavity to a predetermined temperature, dual injecting the mixture and the substrate material into the mould cavity to fill the mould cavity whereby the mixture is injected into the mould ahead of the substrate material in order to form the coating on the substrate, and cooling the mould characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

According to a forth aspect of the invention, a method of providing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material, mixing the thermoplastic resin with a glass filler material to form a mixture, heating a mould having a mould cavity to a predetermined temperature, dual injecting the mixture and the coating material into the mould cavity to fill the mould cavity whereby the coating material is injected into the mould ahead of the mixture in order to form the coating on the substrate, and cooling the mould characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

Preferably, the predetermined temperature is within the melting temperature of the thermoplastic resin. For example if polycarbonate is used as the resin the temperature is in the region of 300 °C. Alternatively, if nylon is used as the resin, the predetermined temperature will be in the region of 270°C. Further alternatively, if acrylic is used as the resin, the predetermined temperature will be in the region of 280°C. It will be understood that the optimum predetermined temperature in any particular case will depend upon the commercial blend of thermoplastic resin used.

Preferably, the resin is a non-pigmented resin.

According to a fifth aspect of the invention a component such as a vehicle component is made by a method according to a previous aspect of the invention.

A component according to the invention advantageously has improved scratch resistance and greater rigidity than a component produced by the route of GB 2 305 890 A.

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

Figure 1 is a diagrammatic cross-section through a two section mould in an open position with a glass filler material in position; and

Figure 2 is a diagrammatic cross-section through a two section mould in a closed position following dual injection. Referring first to Figure 1 , a mould assembly 1 comprises a first mould section 2 and a second mould section 3, the first mould section 2 defining a cavity having a first mould surface 4 complimentary to a second mould surface 5 on the second mould section 3. The first mould section 2 is formed with an injection passage 6 through which plastics material can be injected from an injection moulding machine (not shown). The first mould section is backed with a first insulating plate 7 through which the injection passage 6 also extends.

The second mould section is backed by a heating plate 8, which in turn is backed by a second insulating plate 9. The heating plate may be heated by any convenient means. The second mould section is additionally provided with a number of passages 10 extending through the second mould section.

The operation of the mould assembly will now be described with reference to a first example. The second mould section 3 is heated to the required temperature. A glass filler in the form of a glass weave 11 is placed in the mould assembly. The mould assembly is closed and the mould assembly allowed to heat to the required temperature. A clear resin in the form of a polycarbonate is injected through the injection passage into the mould cavity to impregnate the glass weave. A suitable polycarbonate is MAKROLON (Registered Trade Mark of Bayer AG).

The resin does not solidify because the mould is heated to a temperature within the melting temperature of the resin. In this example, the temperature of the mould is in the region of 300°C. The mould is held at this temperature to allow sufficient time for the resin fully to wet the fibres of the weave. In the present example a time of about 9 minutes was found to be sufficient.

The mould is then cooled. This may conveniently be achieved by passing a coolant through the passages 10 extending through the mould assembly. In the present example it has been found that a cooling period of about 5 minutes is sufficient for the component to have achieved sufficient structural integrity for the mould assembly to be opened to allow the component to be removed from the mould assembly.

It is found that this method allows more complete wetting of the glass filler material than previous methods. This in turn means that the transmission of light through the component is better than previously, giving the component produced a high degree of translucency, and in the case of a non-pigmented resin, a high degree of transparency. It has further been found that a component manufactured according to the invention advantageously has improved structural stiffness in comparison with a similar component produced by the methods described in GB 2 305 890 A.

As an alternative, a nylon material may be used as the resin. In such a case, the mould assembly is preferably heated to a temperature in the region of 270 °C, and is held at this temperature following injection for about 10 minutes. The mould is then cooled for about 5 minutes. A suitable nylon is GRILAMID TR90 (Registered Trade Mark of Ems Grillon).

As a further alternative, an acrylic material may be used as the resin. In such a case, the mould assembly is preferably heated to a temperature in the region of 280°C, and is held at this temperature following injection for about 10 minutes. The mould is then cooled for about 5 minutes. A suitable acrylic material is PLEXIGLAS (Registered Trade Mark of Rohm

& Haas).

Alternatively, OROGLAS an acrylic material obtained from Rohm & Haas may be used. In this case the mould assembly is preferably heated to a temperature in the region of 260°C, and is held at this temperature following injection for about 10 minutes. The mould is then cooled for about 5 minutes.

It will be understood that the optimum temperature in any particular case will depend upon the commercial blend of resin used. In addition, if the glass fibres have been sized to aid wetting of the fibres by the resin, it will be understood that the resin is to be chosen to match the wetting agent of the glass fibres both chemically and optically.

In an alternative embodiment, the glass fibre mat may be hot pressed prior to use to be more accurately shaped to take the form of the mould cavity.

Referring now to Figure 2, a mould assembly 21 comprises a first mould section 22 and a second mould section 23, the first mould section 22 defining a cavity having a first mould surface 24 complimentary to a second mould surface 25 on the second mould section 23. The first mould section 22 is formed with an injection passage 26 through which plastics material can be injected from an injection moulding machine (not shown). The first mould section is backed with a first insulating plate 27 through which the injection passage 26 also extends.

The second mould section is backed by a heating plate 28, which in turn is backed by a second insulating plate 29. The heating plate may be heated by any convenient means. The second mould section is additionally provided with a number of passages 30 extending through the second mould section.

The component is formed by means of dual injection. The mould assembly 20 is mounted on a dual injection machine of a known kind. The machine is adapted to inject a thermoplastic resin 35 slightly ahead of a substrate material 40 such as a polycarbonate. Initially a glass fibre mat 31 is placed in the mould assembly 21 as in the previous example. Again the mould assembly is heated to a temperature in the region of the melting temperature of the resin prior to injection of the resin. Injection of the polycarbonate causes the polycarbonate to spread the resin 35 over the glass mat 31 to cover and impregnate the glass mat 31. Injection is continued until the entire mould cavity is coated with the resin and the resin envelopes the injected polycarbonate. The mould is held at this temperature to allow sufficient time for the resin fully to wet the fibres of the glass mat 31. In the present example a time of about 9 minutes was found to be sufficient.

The mould is then cooled. This may conveniently be achieved by passing a coolant through the passages 30 extending through the mould assembly. In the present example it has been found that a cooling period of about 5 minutes is sufficient for the component to have achieved sufficient structural integrity for the mould assembly to be opened to allow the component to be removed from the mould assembly.

In a further embodiment of the invention, instead of positioning a glass mat 30 in the mould assembly 20 as shown in Figure 2, the thermoplastic resin 35 is mixed with glass fibres or other glass particles prior to injection.

In a still further embodiment of the invention, the dual injection machine is adapted to inject a coating material such as a polycarbonate slightly ahead of a mixture of thermoplastic resin and glass fibres or other glass particles. The mixture is again formed prior to injection. The mould assembly is heated to a temperature in the region of the melting temperature of the resin prior to injection of the resin. Injection of the mixture causes the mixture to spread the coating over the mould cavity. Injection is continued until the entire mould cavity is coated and the coating envelopes the injected mixture. The mould is held at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

As in the first example, these methods can be used with a variety of different resins.

In a further embodiment (not shown) a film may be provided to line one of the mould surfaces. The mould is then used following the steps of one of the methods described above. The film may be used to stop the glass fibres from sticking to the mould surface. The film may also be used to improve the surface finish of the component. The film, for example an aluminium sheet, can be removed from the component, for example by peeling, after removal of the component from the mould assembly. Alternatively, the film, for example a plastics material such as a polyester or a polycarbonate sheet, can be incorporated into the component. Preferably, the film can be provided with a chemical hard coat further to improve the scratch resistance of the component.

Such in-mould coating of components enables components to be made easily in the required shape with a high quality surface finish. If tinting of the components is required, the resin, or indeed the substrate where appropriate, can be combined with suitable tinting additives.

Claims

1. A method of producing a component comprises the steps of providing a mould having a cavity, heating the mould to a predetermined temperature, placing a glass filler material in the cavity, closing the mould, injecting a thermoplastic resin material into the cavity to fill the cavity and to impregnate the glass filler material, then cooling the mould, before opening the mould to remove the component, characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

2. A method according to claim 1, characterised in that the glass filler material is a fibrous glass mat.

3. A method of producing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material and a substrate material, providing a glass filler in the form of a fibrous glass mat, placing the mat in a mould, closing the mould and heating the mould to a predetermined temperature, dual injecting the thermoplastic resin and the substrate material into the mould to fill the cavity whereby the thermoplastic resin is injected into the mould 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, cooling the mould, characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

4. A method of providing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material, mixing the thermoplastic resin with a glass filler material to form a mixture, heating a mould having a mould cavity to a predetermined temperature, dual injecting the mixture and the substrate material into the mould cavity to fill the mould cavity whereby the mixture is injected into the mould ahead of the substrate material in order to form the coating on the substrate, and cooling the mould characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

5. A method of providing a coating on a plastic substrate, the coating and the substrate being formed by dual injection, comprises the steps of providing a thermoplastic resin material, mixing the thermoplastic resin with a glass filler material to form a mixture, heating a mould having a mould cavity to a predetermined temperature, dual injecting the mixture and the coating material into the mould cavity to fill the mould cavity whereby the coating material is injected into the mould ahead of the mixture in order to form the coating on the substrate, and cooling the mould characterised in that prior to cooling the mould is maintained at the predetermined temperature for a time beyond that required to allow the cavity to be filled.

6. A method according to any previous claim, characterised in that the predetermined temperature is in the region of the melting temperature of the resin.

7. A method according to claim 6, characterised in that the resin is a polycarbonate and the predetermined temperature is in the region of 300┬░C.

8. A method according to claim 6, characterised in that the resin is a nylon and the predetermined temperature is in the region of 270 ┬░C.

9. A method according to claim 6, characterised in that the resin is an acrylic and the predetermined temperature is in the region of 260-280┬░C.

10. A method according to any previous claim, characterised in that the resin is a non- pigmented resin.

11. A method according to any previous claim, characterised in that the mould is provided on a least one surface with a film.

12. A method according to claim 11, characterised in that the film is incorporated into the component.

13. A method according to claim 11, characterised in that the film is removed from the component after the component has been removed from the mould.

14. A method according to claim 12 or claim 13, characterised in that the film comprises a plastics sheet.

15. A method according to claim 12 or claim 13, characterised in that the film comprises a metal sheet.

16. A component manufactured according to a method according to any preceding claim.

17. Use of the method of any of claims 1 to 15 in the manufacture of a component.