Coating apparatus – Gas or vapor deposition – With treating means
Patent
1994-10-14
1996-05-28
Breneman, R. Bruce
Coating apparatus
Gas or vapor deposition
With treating means
118723MR, 118723MA, 118719, 118729, 118728, C23C 1600
Patent
active
055207413
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to an apparatus for producing a plasma polymer protective layer on workpieces, in particular headlamp reflectors, of the generic type of the main claim.
To protect the reflective layer, generally comprising very bright aluminium, on headlamp reflectors against corrosion, a corrosion-protection layer has to be applied over the aluminium layer. To produce such a corrosion-protection layer for headlamp reflectors, the plasma polymerization process has become generally established. An early process variant known from DE-C 26 25 448 depends on a non-self-maintained glow discharge for generating the plasma required for activation of a monomer to be polymerized. A newer process known from DE-A 40 03 904 for producing such a protective layer depends on plasma generation in the microwave region by electron cyclotron resonance (ECR). When the ECR condition is met, a plasma is ignited in the magnetic field of a magnet bank comprising permanent magnets. If a polymerizable monomer, such as hexamethyl-disiloxane, is introduced into the coating chamber, a glow-polymer protective layer can thereby be deposited. This is described in more detail in the cited document.
Both processes are nowadays employed industrially in a batch process, i.e. the production flow in the production of a headlamp is interrupted, and several hundred manually charged reflectors are provided in a coating chamber with the corrosion-protection layer and are then manually returned to the production flow. A problem in both processes is that the coating source is not completely maintenance-free: with the non-self-maintained glow discharge as in the earlier process, the tungsten glow emitters used have to be replaced after a few batches. In the more recent ECR method, the magnets required by the process are likewise coated and therefore, to avoid uncontrolled flake formation, have to be brushed from time to time. However, this means that these processes cannot easily be built into an in-line process. The coating chamber always has to remain under vacuum, and the reflectors are transferred in and out via locks. A maintenance step, for example for cleaning the magnets, would make it necessary to open the coating chamber to the air and therefore mean a halt in production.
ADVANTAGES OF THE INVENTION
The apparatus of the invention having the characterizing features of the main claim has the advantage in comparison with the above that the known ECR coating process can be used in an in-line process without it being necessary to stop production for the purpose of cleaning work. Since the magnets are arranged on the workpiece carriers, these can, by means of vacuum locks, be conveyed through the evacuated coating chamber and conveyed back again outside this chamber. A cleaning chamber can then be arranged without difficulty in the return section outside the coating chamber, in particular to free the magnets of coating material. The coating process can therefore proceed continuously, with the cleaning of the workpiece carriers and thereby the magnets also being carried out continuously.
The measures indicated in the subclaims make possible advantageous embodiments and improvements of the apparatus specified in the main claim.
The transport facility advantageously has a feed velocity corresponding to the production rhythm for the workpieces so that this apparatus can easily be built into an existing production line.
The plasma polymer coating chamber is arranged between vacuum inlet locks and outlet locks. The coating chamber can here preferably be preceded by a metallization chamber and this be preceded by a pre-glow chamber, so that the reflective metal coating can also be produced on the reflector during the same pass shortly before application of the corrosion-protection layer.
To give a high deposition rate and a good constancy of thickness for the protective layer on the optically effective surfaces, the permanent magnets on the workpiece carriers reach into the headlamp reflectors arranged thereon, preferably through the
REFERENCES:
patent: 4842707 (1989-06-01), Kinoshita
patent: 4902934 (1990-02-01), Miyamura
patent: 5021114 (1991-06-01), Saito
patent: 5308417 (1994-05-01), Groechel
patent: 5378284 (1995-01-01), Geisler
patent: 5425611 (1995-06-01), Huges
Benz Gerhard
Hahn Juergen
Schneider Guenter
Breneman R. Bruce
Chang Joni Y.
Robert & Bosch GmbH
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