GB1570531A - Method of manufacturing lamp reflectors - Google Patents

Description

(54) A METHOD OF MANUFACTURING LAMP REFLECTORS (71) We, LUCAS INDUSTRIES LIMITED, a British Company, of Great King Street, Birmingharn, B19 2XF, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of manufacturing lamp reflectors for headlamps, fog lamps or spot lamps of road vehicles.

A method, according to the invention, comprises the steps of: (a) starting with a hollow body formed to the shape of the required reflector and, with said body received in a first mould part defining a recess complementary with the external shape of the body, introducing into the interior of the body an unreinforced, unfilled, thermosetting glazing composition, (b) causing said first mould part and a second mould part complementary with the internal shape of the body to move towards each other so that said glazing composition is urged to flow by said second mould part over the internal surface of said body, then (c) curing said glazing composition to produce a glazed layer over said internal surface, and then (d) applying a coating of a reflective material direotly over said glazed layer.

Conveniently, said body is formed from metal and preferably is pressed from steel sheet.

More preferably, said body is produced from a cured, thermosetting, low profile polyester moulding composition containing glass fibres.

Most preferably, said moulding composition contains between 12% and 18% of glass fibres by weight of the composition.

Preferably, said first and second mould parts are used to mould said moulding com- position into said body and, after moulding of the body and prior to step (b), the second mould part is separated from said first mould part and said body to allow introduction of said glazing composition.

Conveniently, said body is produced by compression moulding, or more preferably by injection moulding.

Preferably, said moulding composition contains an internal mould release agent compatible with the moulding composition.

Preferably, said glazing composition is a polyester con:positioa and most preferably the polyester is an isopbthalate resin.

Preferably, where the glazing composition is an isophthalate resin composition, the glazing composition also contains between 11.5% by weight of a thutyl peroctoate catalyst.

Preferably, said reflective material is aluminium.

Conveniently, a protective top coat is provided over the reflective material.

The 'accompanying drawing is a sectional view of a lamp reflector, acording to one example of the present invention, for a road vehicle headlamp.

Referring to the drawling, the reflector is defined by a moulded, substantially cup shsped body 11 which is generally rectangular in transverse cross Section and which has an aperture 12 in its base so that when the reflector is in use in a vehicle headlamp, a bulb holder (not shown) can be received in the aperture 12. In one practical embodiment, the body 11 was llem deep and had rectangular dimensions of 25cm by 15cm.

The body 11 is produced by introducing a low profile thermosetting moulding composition containing between 12% and 18% by weight of glass fibre into a suitably shaped die cavity defined between a recess in a first mould part, and a complementary projection in a second mould part. In said one practical embodiment, a suitable moulding composition was produced by mixing 1 part by weight of benroyl peroxide paste, 25 parts by weight of a styrene solution of an unsaturated polyester, 15 parts by weight of 0.25 inch length chopped glass fibres, 50 parts by weight of a carbonate filler, with 7 parts by weight of polypropylene adipate, 1-2 parts by weight of a zinc stearate internal mould release agent and 1.5 parts by weight of finely divided polyvinyl chloride to make up the remainder of the composition.

After mixing to thoroughly disperse the glass fibres, the moulding composition is introduced into said mould cavity by an injection process. Preferably, the injection process is arranged so as to remove any entrapped air from the moulding composition prior to injection, since in this way it is found that the surface finish of the final body 11 is improved. This is conveniently achieved by arranging that the moulding composition is fed to the injection device by a hopper which is connected to a vacuum source so that any entrapped air is drawn out of the moulding composition before injection. A suitable machine for performing such an injection process is that manufactured by Georg Seidle K.G. Munich as type F.P.A. 1 BX-A. When injection is complete, the moulding composition received in the mould cavity is cured by heating the mould parts to between 1300C and 170"C. The actual time of curing depends upon the thickness of the body to be produced and varies between about 20 secs. and 3 minutes. During curing, the shrinkage of the moulding composition is found to be insignificant and, after curing, the body 11 is found to have a surface substantially free from distortion and with high gloss.

In said one practical embodiment, injection moulding of the body 11 was effected with an injection pressure of 9000 p.s.i. and with the mould parts being held at between 145-150 C. The pressure was held at 9000 p.s.i. for 3 seconds and was then allowed to fall to a "reduced" or "hold" pressure of 4000 p.s.i. which was then maintained for the remaining 12 seconds of a 15 second mould cycle. Then with the mould parts remaining at 145--150"C, the pressure was fully released and the moulding composition was retained in the mould cavity for a further 27 seconds to effect curing.

When moulding and curing of the body 11 is complete, the second mould part is separated from the first mould part, while the body 11 is retained in the recess in the latter. Thereafter with the mould parts maintained at a temperature between 145-150 C, a predetermined amount of an unfiled, unreinforced glazing composition is applied to the exposed internal surface of the body 11, the glazing composition conveniently being an isophthalate polyester resin containing between 11.5% by weight of a t-butyl octoate catalyst An example of such a glazing composition, is that supplied by B.I.P.

Chemicals Limited as Beetle Resin L3686.

After application of the glazing composition, the mould parts are returned to their original closed position, whereby the glazing composition is caused to flow by said second mould part to cover the internal surface of the body 11. The assembly is then left for 15-20 seconds at said temperature of 145-150 C, to allow the glazing composition to cure, whereafter the mould parts are again opened and the glazed body 11 is separated from the first mould part.

In said one practical embodiment, a 5-ggm sample of the Beetle Resin L3686 composition mentioned above was used for the glazing operation and after application of the glazing composition the mould parts were moved together at a final closing speed of 4 inches/ second. The mould parts were then damped together with a force of 100 tons and, after the curing operation, the body 11 was found to have a glazed layer of surface density 0.75 gm/square inch.

It is to be appreciated that the glazing operation described above need not be performed immediately after moulding of the body 11 in which case, before application of the glazing composition, the mould parts and the body must be heated to the required glazing temperature of 145150 C before the mould is closed.

The glazed layer is supplied to the internal surface of the body 11 so a, to provide a suitable base for subsequent application of a reflective coating, it L being appreciated that, in conventional techn7ques, this base is normally produced tby the application of one or more lacquer layers. However, as will readily by mslerstoosl5 application of a lacquer layer to a reflects body necessitates movement of the body to spread the lacquer layer, which not only requires relatively expensive equipment, but also tends to result in rippling of the lacquer layer. The latter can of course result in iridescense when the reflector is in use. By way of contrast, application of the glazed layer described above requires no additional equipment, but rather uses the mould employed to produce the reflector body.

In addition, it is found that the glazed layer conforms accurately to the second mould part and hence can be produced substantially free of surface blemishes and ripples. In fact, in view of the surface accuracy of the glazed layer, the method described above can be employed with moulding compositions containing in excess of 18% by weight of glass fibres, it being understood that the high fibre content of such compositions tends to result in irregularities in the surface of the body 11.

These irregularities are, however masked by the glazed layer.

After application of the glazed layer, the reflector is completed by vacuum depositing an aluminium film over the top of the glazed layer so as to render reflective the internal surface of the body 11. Finally, a protective top coat may be provided over the aluminium film.

In a modification of the above example, the same process is repeated but with the moulding composition being formed into the required body 11 by compression moulding. Using this process, the internal surface of the body 11 is found to exhibit some degree of distortion but any adverse effect of this distortion is eliminated by the overlying glazed layer.

In a further modification, the body 11 is formed by stamping a mild steel sheet.

Claims (16)

WHAT WE CLAIM IS:

1. A method a manufacturing a lamp reflector comprising the steps of: - (a) starting with a hollow body formed to the shape of the required reflector and, with said body received in a first mould part defining a recess complementary with the external shape of the body, introducing into the interior of the body an unreinforced, un filled, thermosetting glazing composition, (b) causing said first mould part and a second mould part complementary with the internal shape of the body to move towards each other so that said glazing composition is urged to flow by said second mould part over the internal surface of said body, the (c) curing said glazing composition to pro duce a glazed lyer over said internal surface, and then Xd) applying a coating of a reflective material directly over said glazed layer.

2. A method as claimed in Claim 1, wherein said body is formed from methal and preferably is pressed from steel sheet.

3. A method as claimed in Claim 1, where in said body is produced from a cured, thermo setting, low profile polyester moulding com position containing glass fibres.

4. A method as claimed in Claim 3, wherein said moulding composition contains between 12% and 18% of glass fibres by weight of the composition.

5. A method as claimed in Clam 3 or Claim 4, wherein said moulding composition contains an internal mould release agent com patible with the moulding composition.

6. A method as claimed in any one of Claims 3 to 5, wherein said first and second mould parts are used to mould said moulding composition into said body and, after mould ing of the body and prior to step (b), the second mould part is separated from said first mould part and said body to allow introduction of said glazing composition.

7. A method as claimed in any one of Claims 3 to 6, wherein said body is produced by comprression moulding.

8. A method as claimed in any one of Claims 3 to 6, wherein said body is produced by injection moulding.

9. A method as claimed in any one of the preceding claims, wherein said glazing composition is a polyester composition.

10. A method as claimed in any one of the preceding claims, wherein said glazing composition is an isophthalate resin.

11. A method as claimed in Claim 10, wherein the glazing composition is an isophthalate resin composition, the glazing com position also contains between 1-15% by weight of a t-butyl peroctoate catalyst.

12. A method as claimed in any preceding Claim, wherein Caid reflective material is aluminium.

13. A method as claimed in any preceding Claim, wherein a laquer coating is provided over the reflective material.

14. A method of manufacturing a reflector substantially as hereinbefore described.

15. A reflector manufactured by a method as claimed in any one of the preceding Claims.

16. A road vehicle fog, spot or headlamp including a reflector as claimed in Claim 15.