Coating processes – Optical element produced – Polarizer – windshield – optical fiber – projection screen – or...
Patent
1991-09-12
1993-10-26
Beck, Shrive
Coating processes
Optical element produced
Polarizer, windshield, optical fiber, projection screen, or...
522121, 428461, 428483, 4274071, B05D 506, B32B 1508, B32B 1520, C08J 328
Patent
active
052564460
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the manufacture of reflectors, in particular reflectors for automotive vehicle headlamps, wherein base and is cured by Uv or electron beams, and
The present invention furthermore relates to the radiation-curable coating compositions used in the process and to the use thereof for coating smooth surfaces.
If reflectors are to reflect incident light as fully as possible and in the correct direction, the reflecting surface must have a high gloss and its shape must be very accurately designed. This requirement is true in particular for the parabolic reflectors of automotive vehicle headlamps. Automotive vehicle headlamps should on the one hand deliver high-intensity light despite the very limited available output and on the other hand their light, especially that of the dipped beam, must be directed as accurately as possible in order not to dazzle oncoming traffic.
The accuracy of the shape of the reflecting surface is determined in the known process for the manufacture of parabolic reflectors by the parabolic bases made mostly of metal or plastic. For this reason severe demands are made in the manufacture of those bases on the accuracy of their shape.
In the known process for achieving a high-gloss reflective coating, the reflector base is first coated with a paint film and to this paint film is then applied a metallic film by vacuum or electrolytic deposition (cf. for example DE-OS 1,772,120). However, very severe demands are made on the paint film in order that the applied metallic film acquires superior, optically flawless reflecting characteristics without, as far as possible, having to be polished.
An important task of the paint film is to provide a smooth surface for the subsequent metallization without costly grinding and polishing operations having to be performed on the paint film, i.e. the paint film must provide a well-levelled substrate. Important criteria for a suitable coating composition are therefore good flowout and absence of stresses.
Furthermore, it is important to avoid the so-called irisization in the metallization process, for example by avoiding microfine gas emissions from the paint film. Adhesion is also extremely important. On the one hand the paint film must adhere well to the reflector base and on the other the metallic film must also adhere well to the paint film.
Finally, the coating composition must be readily applied by conventional application techniques (for example dipping, f low-coating, spraying) and they must be rapidly curable; the paint film must also be readily coated with metal in most cases by vapor metallization.
However, the use of radiation-curable coating compositions as priming coats for reflector bases creates considerable problems, especially as regards adhesion. The typically used reflector bases represent very smooth and partially non-homogeneous substrate surfaces consisting in general of various metals or thermosetting plastics, for example those based on low-profile (LP) polyester thermosets (i.e. polyester-thermoset moldings with a slight volume shrinkage incurred in hot press molding) or those based on fiber-reinforced plastic components derived from bulk-molding compounds (BMC). Reliable adhesion of the radiation-curable coating compositions on these surfaces can only be achieved by costly pretreatment of the surfaces (for example flame treatment, preliminary irradiation, corona discharge, introduction of an adhesion promoting layer) and/or aftertreatment of the coating (for example by heat).
It is true that JP-A 61/181871 discloses radiationcurable coating materials based on acrylate copolymers containing ethylenically unsaturated side chains which furnish coatings with improved adhesion, but this prior art does not come close to the invention, since it does not suggest using these known radiation-curable coating materials as primers in the manufacture of headlamp reflectors.
In an effort to improve adhesion, the crucial part of the invention disclosed in JP-A 61/181871 for synthesizing the acrylate copol
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BASF Lacke + Farben Aktiengesellschaft[DE/DE]
Beck Shrive
Dudash Diana
Sabourin Anne Gerry
Werner Frank G.
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