Process for the preparation of a multilayer protective and/or de

Details Process for the preparation of a multilayer protective and/or de Process for the preparation of a multilayer protective and/or de

1992-07-21

1994-01-25

Beck, Shrive

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

428204, 428447, 427409, 4274121, 4274197, 4274198, B05D 714

Patent

active

052814688

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the preparation of a multilayer protective and/or decorative coating on a substrate surface.
In particular in automotive coating, but also in other areas in which coatings having a good decorative effect and, at the same time, good corrosion protection are desired, it is known to provide substrates with several coating layers on top of each other.
Multilayer coatings in which the substrate is first coated with a pigmented basecoat and then a clearcoat is applied have achieved great importance. The preferred procedure is a wet-in-wet process in which the basecoat is coated with the clearcoat after a short flashoff time without a baking step and basecoat and clearcoat are then cured together.
U.S. Pat Nos. 4,499,150 and 4,499,151 disclose basecoat/clearcoat systems in which either the basecoat, the clearcoat or both basecoat and clearcoat contain polyaddition products having alkoxy- or acryloxysilane units.
These polymers containing silane groups are prepared by copolymerization of silicon-free monomers having at least one double bond and ethylenically unsaturated monomers containing silane groups. Not only the basecoat but also the clearcoat are conventional coats, i.e. they are formulated on the basis of organic solvents.
The international patent application published under the number WO 88/02,010 discloses basecoat/clearcoat systems in which either the basecoat, clearcoat or both the basecoat and clearcoat contain polyaddition products having alkoxy- or acryloxysilane units. Not only the basecoat but also the clearcoat are conventional coats. The coatings thus obtained are distinguished in particular by very good stability to gasoline and short drying times. However, the disadvantage of these systems is the pollution of the environment by the solvents when the paint films are dried. Moreover, it is desired to further improve the Erichsen indentation and cross hatch values and the stone-chip resistance of the resulting coatings.
Furthermore, economic and ecological reasons have resulted in the attempt to use aqueous basecoat compositions when multilayer coats are prepared. Aqueous basecoat compositions of this type are described, for example, in German Offenlegungsschrift 3,545,618, U.S. Pat. No. 4,558,090, U.S. Pat. No. 4,489,135, EP-A 89,497 and German Offenlegungsschrift 3,739,332. Conventional solvent-containing, water-dilutable coatings or powder clearcoats are used as topcoat. Typical clearcoats are solvent-containing, acid-curing clearcoats based on amino resins and hydroxyl-containing acrylate copolymers or hydroxyl-containing polyester resins. However, clearcoats of this type require increased baking temperatures and are therefore not suitable for the automotive repair coating field. Therefore, in the automotive repair coating field, clearcoats based on hydroxyl-containing acrylates and blocked isocyanates are used in most cases. However, toxicological and allergy-related aspects are shifting the interest to isocyanate-free automotive repair coatings.
Accordingly, the object of the present invention was to provide a process for the preparation of a multilayer coating in which the pollution of the environment by the solvent when the paint films are dried is minimal. Furthermore, the resulting coatings should have in particular good adhesion, i.e. good Erichsen indentation and cross hatch values and good stone-chip resistance. However, the remaining technical properties, such as gloss, overcoating characteristics and the like should be on a very high level, i.e. comparable with the values obtained when conventional solvent-containing basecoat compositions are used. Finally, the process in question should also be suitable for the automotive repair coating field, i.e. not only the basecoat composition but also the topcoat composition used in the process should be curable at fairly low temperatures of in general below 100.degree. C., preferably below 80.degree. C. The process should of course also be usable, for example, for assembly line coating, i.e. curing cond

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