Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1992-09-16
1994-08-02
Marquis, Melvyn L.
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427409, 427412, 4274121, 524521, 525 63, B05D 136, B05D 716, B05D 726
Patent
active
053344200
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process in which and subsequently
The invention also relates to an aqueous paint.
The process for the production of multicoat finishes described above is known and is employed especially for the finishing of automobile bodies.
The result of the process described above crucially depends on the basecoat used. The basecoat has a strong influence on the quality of the overall finish.
No aqueous basecoats have been known up to now which are suitable for production line finishing and for refinishing and which furnish high-quality overall finishes.
The object of the present invention consists in providing novel aqueous paints which are suitable as basecoats for performing the process described above.
This object is achieved by making available aqueous paints which comprise as binder a polymer which can be obtained by polymerizing in an organic solvent or in a mixture of organic solvents unsaturated monomers in the presence of to 30,000, preferably of 1,000 to 5,000 and contains on statistical average 0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.7 polymerizable double bonds per molecule dispersion.
The basecoats according to the invention are distinguished by the fact that they may be recoated after a short time with an aqueous or conventional clearcoat by the "wet-on-wet" process without disturbing the basecoat film, and that they furnish--even at low baking temperatures, for example at 80.degree. C.--finishes with high moisture resistance and good mechanical properties.
EP-A-297,576 discloses basecoats which are suitable for performing the process under discussion. The basecoats described in EP-A-297,576 comprise as binders polymers which can be obtained by polymerizing in water ethylenically unsaturated compounds in the presence of a polyurethane resin which is free from double bonds. This process is costly and gives rise to binder dispersions which often contain a coagulate and are unsuitable for pigment dispersion. In addition, the binders disclosed in EP-A-297,576 differ significantly in their chemical structure from the binders used according to the invention.
For the preparation of the binders used according to the invention a polyurethane resin (B) is prepared in a first step according to well-known methods of polyurethane chemistry. The polyurethane resin is prepared from the following components: molecular weight of 400 to 5,000, or a mixture of such polyester polyols and/or polyether polyols, polymerizable double bond at least one group reactive toward NCO groups, or a mixture of such compounds, group which is reactive toward isocyanate groups and at least one group which is capable of forming anions, or a mixture of such compounds, group which is reactive toward NCO groups and at least one poly(oxyalkylene) group, or a mixture of such compounds and, if appropriate, molecular weight of 60 to 600, or a mixture of such compounds.
The polyurethane resin (B) should have a number average molecular weight of 200 to 30,000, preferably 1,000 to 5,000, and on statistical average 0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.7 polymerizable double bonds per molecule. It is preferred that the polyurethane resin (B) has an acid value of 0 to 2.0. As is known to a person skilled in the art, the molecular weight of the polyurethane resins can be controlled in particular by the quantity ratio and the functionality of the starting compounds (a) to (f) used.
The polyurethane resins may be prepared both in bulk and in organic solvents.
The polyurethane resins may be prepared by simultaneous reaction of all starting compounds. However, in many cases it is expedient to prepare the polyurethane resins in stages. Thus, for example, it is possible to prepare a prepolymer containing isocyanate groups from the components (a) and (b) which is then reacted further with the component (c) . It is further possible to prepare from the components (a), (b), (c) and, if appropriate, (d) and (e) a prepolymer containing isocyanate groups which can subsequently be r
REFERENCES:
patent: 4036800 (1977-07-01), Sekmakas et al.
patent: 5095069 (1992-03-01), Ambrose et al.
Grabbe Michael
Hartung Michael
Mayenfels Peter
Aylward D.
BASF Lacke & Farben Aktiengesellschaft
Marquis Melvyn L.
Sabourin Anne Gerry
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