Chemistry: electrical and wave energy – Processes and products – Vacuum arc discharge coating
Patent
1983-02-25
1984-12-25
Demers, Arthur P.
Chemistry: electrical and wave energy
Processes and products
Vacuum arc discharge coating
350600, 427123, 427124, 427125, 428469, C23C 1500
Patent
active
044902280
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of manufacturing a reflecting metal surface which can especially be used in order to form a reflector, in particular for the headlight of a motor vehicle.
It is known that for certain metal parts for industrial use surfaces with a very great reflective power are sought; this is in particular the case for parts which reflect light or heat waves, for example reflectors intended for headlights for motor vehicles. In order to achieve this a coating of aluminium is applied by metallization under vacuum to the surface of the part previously treated. In a traditional method the metal surface which is to be aluminized is polished, then in several layers a sufficient thickness of varnish is applied to the polished surface with a view to obtaining a satisfactory surface state. This technique has the main disadvantage of being difficult, slow and troublesome. Thus there has already been proposed in the French Pat. No. 2 304 690 an improvement of this prior art in which firstly a layer of powdered resin is applied to the unpolished metal surface; in which secondly the resin layer is melted and hardened on its base; and in which thirdly a coating of bright aluminium is applied to the surface thus pretreated. If the resin is sufficiently polymerized on its base before the application of aluminium this technique is satisfactory for surfaces which do not undergo any subequent relatively great heating; but if there is subsequent great heating, either when using the part or during a subsequent finishing operation, it has been ascertained that the layer of bright aluminium tended to tarnish.
In the case of reflectors for car headlights it is evident that the reflector always undergoes a considerable increase in temperature during operation, in the vicinity of the lighting lamp. It was thus necessary in the case of reflectors for motor vehicles to remedy this risk of deterioration of the optical qualities of the reflective surface. In the above mentioned French Pat. No. 2 304 690 the application on the resin layer of a layer of phenolic or water-soluble varnish compatible with the resin layer has already been disclosed; this layer of varnish improves the adhesion of the aluminium coating on the resin and it has been noted that its presence eliminates any risk of the reflective surface tarnishing if the temperature rises subsequently. It is thought, although this explanation is in no way limiting, that tarnishing is due to the difference of the expansion coefficients existing between the resin and the layer of bright aluminium, and that the interposition of varnish avoids the disadvantages which could arise if the elastic limit of aluminium is exceeded owing to the great expansion of the resin which forms its base.
The use of such a varnish between the resin layer and the layer of bright aluminium is thus entirely satisfactory for the manufacture of reflectors of headlights of motor vehicles but it has several disadvantages: firstly, the varnish used is a relatively expensive product, secondly the application of the varnish forms an additional stage in the manufacture of headlights and thus increases manufacturing time and costs; thirdly, the varnish requires a drying force. It can thus be seen that, although the application of a varnish is satisfactory from a practical point of view, it entails disadvantages from a financial point of view.
The object of the present invention is to propose an improvement for this type of manufacture of reflecting metal surfaces. According to this improvement the application of a varnish between the resin layer and the bright metal film of the reflector is omitted but any risk of tarnishing in the case of a subsequent rise in temperature of the part after manufacture is avoided. Such a part may thus be used without difficulty in order to form a reflector for a headlight.
According to the invention it has been ascertained that if a layer composed, in a form combined or not with another element such as oxygen, of silicon, nickel or a nickel-chrome alloy,
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Bodin Claude
Gouin Alain
Demers Arthur P.
Equipements Automobiles Marchal
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