Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1991-05-03
1993-11-30
Schofer, Joseph L.
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427409, 524512, B05D 136
Patent
active
052663612
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the preparation of a multicoat protective and/or decorative coating on a substrate surface, in which process surface, polyacrylate resin as binder and an aminoplast resin as crosslinking agent is applied to the basecoat obtained in this manner, and subsequently
The invention also relates to aqueous coating compositions, water-thinnable polyacrylate resins and a process for the preparation of water-thinnable polyacrylate resins.
BACKGROUND ART
The process in accordance with the preamble of patent claim 1 is known. It is used especially for the production of automotive metallic finishes (cf. for example U.S. Pat. No. 3,639,147, DE-A-3,333,072 and EP-A-38,127).
On economic and ecological grounds it is desirable to employ aqueous topcoat compositions in stage (3) of the basecoat-clearcoat process described above.
The topcoat compositions must be sprayable with the aid of automatic painting equipment. For this purpose their solids content must be high enough at spraying viscosity to furnish paint films of adequate film thickness with one to two cross-passes of the spray-gun and they must furnish baked paint films of good appearance (good flow-out, high gloss, good topcoat condition . . . ).
The aqueous topcoat composition disclosed in Example 2 of EP-A-38,127 does not meet all of the above requirements.
The object forming the basis of the present invention consists in the preparation of aqueous topcoat compositions which meet the above requirements.
SUMMARY OF THE INVENTION
Surprisingly, this object is achieved using topcoat compositions which comprise a water-thinnable polyacrylate resin as binder, which resin can be obtained presence of at least one polymerization initiator, a mixture of monomer which contains at least one carboxyl group per molecule and is copolymerizable with (b1), (b2) and (b3), or a mixture of such monomers, together with from carboxyl groups and is copolymerizable with (b1), (b2), (b3) and (a1), or a mixture of such monomers, consisting of is copolymerizable with (b2), (b3), (a1) and (a2) and is essentially free from carboxyl groups, or a mixture of such (meth)acrylic esters, and monomer which is copolymerizable with (b1), (b3), (a1) and (a2), contains at least one hydroxyl group per molecule and is essentially free from carboxyl groups, or a mixture of such monomers, and monomer, different from (a2), which is copolymerizable with (b1), (b2), (a1) and (a2) and is essentially free from carboxyl groups, or a mixture of such monomers, and the termination of the polymerization and dispersing it in water, the total of the weight proportions of (a1), (a2), (b1), (b2), and (b3) being always 100% by weight and the type and amount of (b1), (b2), (b3), (a1) and (a2) being chosen such that the polyacrylate resin has a hydroxyl value of 40 to 200, preferably 60 to 140, an acid value of 20 to 100, preferably 25 to 50, and a glass transition temperature (T.sub.G) of -40.degree. C. to +60.degree. C., preferably -20.degree. C. to +40.degree. C.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying FIGURE is a plot of viscosity as a function of solids content for several of the compositions prepared in the Examples herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The pigmented basecoat compositions to be applied in stage (1) of the process according to the invention are well known (cf. for example U.S. Pat. No. 3,639,147, EP-A-38,127, DE-A-3,333,072 and EP-A-279,813). The basecoat compositions used in stage (1) preferably comprise metal pigments, especially aluminum pigments, metallic finishes being obtained in this manner.
Before the preparation of the polyacrylate resins to be used according to the invention is described in detail, two terms will be clarified first: for "methacrylic or acrylic acid". that the components (b1), (b2) and (b3) may possess a low content of carboxyl groups (not more, however, than would impart to a polyacrylate resin prepared from the components (b1), (b2) and (b3) an acid value greater than 10). It is pr
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Poth Ulrich
Schwarte Stephan
BASK Lacke + Farben Aktiengesellschaft DE/DE
Delmendo R. H.
Marshall Paul L.
Schofer Joseph L.
Werner Frank G.
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