Metal working – Method of mechanical manufacture – Combined manufacture including applying or shaping of fluent...
Patent
1998-09-29
1999-11-23
Cameron, Erma
Metal working
Method of mechanical manufacture
Combined manufacture including applying or shaping of fluent...
294695, 295271, 2952501, 2952504, 2952507, 2952509, 2952512, 2952515, 72 46, 156196, B05D 714, C09D17506
Patent
active
059877278
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the production of automobile parts lacquered with two coats, in which two coating layers are applied on both sides of a coil of sheet metal and are each stoved, and corresponding sheet metal parts are then stamped out of the coil and shaped by the deep-drawing process, which is characterized in that, in each case by the coil coating process, a coating composition (A) which comprises, based on its solid resin composition, 55 to 80 wt. % of one or more polyester-polyols, 2 to 10 wt. % of one or more aromatic epoxy resins and, as crosslinking agents, 5 to 15 wt. % aminoplast resin and 10 to 25 wt. % blocked polyisocyanate is applied to produce the first coating layer, and a coating composition (B) which comprises, based on its solid resin composition, 60 to 80 wt. % of one or more polyester-polyols and, as crosslinking agents, 10 to 20 wt. % aminoplast resin and 10 to 20 wt. % blocked polyisocyanate is applied to produce the second coating layer, the sum of the constituents of the coating compositions in each case giving 100 wt. %, and to a process for the production of automobile bodies.
BACKGROUND OF THE INVENTION
Prior art in the lacquering of motor vehicles or parts thereof is initially the production of the body or the body parts. For this, correspondingly shaped sheet metal parts are first stamped out and shaped by the deep-drawing process using drawing lubricant or oil, and are then in general assembled by welding and subsequently subjected to expensive cleaning. A lacquer coat is then applied by electro-diplacquering and, if desired, one or, in the case of automobile bodies in particular, more further coats of lacquer are applied.
There is the desire to discover a simpler production process which, in particular, avoids the cleaning steps and enables the electro-diplacquering to be replaced.
European Patent Application EP-A-0 603 772 discloses a process for the production of vehicle parts from prelacquered sheets. The sheets, which have been prelacquered with a primer, are cut into sections, and these are deep-drawn and coated with a powder lacquer as the top lacquering. The lacquers used to produce the primer and the top lacquering are not described in more detail.
European Patent Application EP-A-0 438 773 discloses a process for the production of motor vehicle bodies in which sheets which have been precoated with a lacquering of at least two coats are deep-drawn and then assembled. An acrylate lacquer is employed as the primer and a polyurethane lacquer is employed as the top lacquer. The compositions of these lacquers is not explained in more detail.
WO 89/11497 describes a coating composition which can be applied by the coil coating process and is suitable for applying one-coat lacquerings, which can be subjected to deep-drawing, to sheet metal. After correspondingly shaped sheets have been stamped out, the parts lacquered with one coat in this way can be shaped by the deep-drawing process without the lacquer coat showing damage. The coating compositions from WO 89/11497 comprise a polyester-polyol with a controlled degree of branching and a weight-average molecular weight of 4,000 to 40,000 and a hydroxyl number of 10 to 100 mg KOH/g as the binder, which is crosslinked via free or blocked polyisocyanate.
The coatings produced by the coil coating process using the coating compositions from WO 89/11497 are in need of improvement in respect of their deep-drawing properties. This has been found in the case of coil coating application to both sides, where the coating layer applied to the later inside of the shaped part does not withstand the shaping process, which has a particularly extreme effect there. This manifests itself, for example, in the simulation of the deep-drawing operation in which a square dish with rounded corners is produced from a sheet coated on both sides by the coil coating process. The coating in the region of the corners on the inside of the dish shows cracks or even flaking, especially if sheets having a thicknes
REFERENCES:
patent: 4103050 (1978-07-01), Laskin et al.
patent: 4619825 (1979-10-01), Yapp et al.
patent: 4720405 (1988-01-01), Carson et al.
Fritz Pamela
Hanske Silke
Shafik Ahmed
Cameron Erma
Herberts GmbH
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