Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1993-01-29
1994-01-04
Beck, Shrive
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427409, 524512, 525301, C08F26502, C08F26702, C08L 6100
Patent
active
052758478
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for the production of a multi-layered protective and/or decorative coating on a substrate surface, in which
(1) a suitable pigmented base coating composition is applied to the substrate surface,
(2) a polymer film is formed from the composition applied in stage (1),
(3) a transparent aqueous top coating composition containing a water-dilutable polyacrylate resin as the binder and an aminoplast resin as the crosslinking agent is applied to the base layer thus obtained, and
(4) the base layer is then stoved together with the top layer.
The invention also relates to aqueous coating compositions, water-dilutable polyacrylate resins and a process for the preparation of water-dilutable polyacrylate resins.
The process for the preparation of a water-dilutable polyacrylate resin is known. It is used in particular for the preparation of automobile metallic effect lacquerings (compare, for example, U.S. Pat. No. 3,639,147, DE-A-33 33 072 and EP-A-38,127).
For economic and ecological reasons, it is desirable to employ aqueous top coating compositions in stage (3) of the so-called "base coat clear coat" process described above.
It must be possible to apply the top coating compositions by spraying with the aid of automatic lacquering lines. For this, they must have such a high solids content at the spraying viscosity that lacquer films of adequate layer thickness are obtained with one to two spray passes (cross passes), and they must produce stoved lacquer films which exhibit a good appearance (good flow, high gloss, good top lacquer status...).
The aqueous top coating composition disclosed in Example 2 of EP-A-38,127 does not meet all the abovementioned requirements.
Summary of the Invention
The object on which the present invention is based consists of providing aqueous top coating compositions which meet the abovementioned requirements.
Surprisingly, this object is achieved by top coating compositions which contain, as the binder, a water-dilutable polyacrylate resin which is obtainable by (b1) and (b2) and is essentially free from carboxyl groups, or a mixture of such (meth)acrylic acid esters and (a1), (a3), (b1) and (b2), carries at least one hydroxyl group per molecule and is essentially free from carboxyl groups, or a mixture of such monomers, and if appropriate (a1), (a2), (b1) and (b2) and is essentially free from carboxyl groups, or a mixture of such monomers, the presence of at least one polymerization initiator, and and if appropriate (a3) has been added, adding carries at least one carboxyl group per molecule and is copolymerizable with (a1), (a2) and (a3), or of a mixture of such monomers, together with free from carboxyl groups and is copolymerizable with (a1), (a2), (a3) and (b1), or of a mixture of such monomers, resulting polyacrylate resin and dispersing it in water, the sum of the amounts by weight of (b1) and (b2) always giving 100% by weight and the nature and amount of (a1), (a2), (a3), (b1) and (b2) being chosen so that the polyacrylate resin has a hydroxyl number of 40 to 200, preferably 60 to 140, an acid number 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.
The pigmented base coating compositions to be applied in stage (1) of the process according to the invention are well-known (compare, for example, U.S. Pat. No. 3,639,147, EP-A-38,127, DE-A-33 33 072 and EP-A-279,813). Base coating compositions preferably containing metal pigments, in particular aluminum pigments, are employed in stage (1). Metallic effect lacquerings are in this way obtained.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a comparison of viscosities of a composition prepared according to the one step polymerization of the invention (V) and a composition prepared by a two step polymerization (P2).
DETAILED DESCRIPTION OF THE INVENTION
Before the preparation of the polyacrylate resins to be employed according to the invention is described in more d
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Poth Ulrich
Schwarte Stephan
BASF Lacke+Farben Aktiengesellschaft
Beck Shrive
Dudash Diana
Sabourin Anne Gerry
Werner Frank G.
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