Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1992-10-30
1996-05-07
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524458, 524460, 4273722, 4273855, 4273882, 4273884, C08L 3100
Patent
active
055147461
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of a multicoat protective and/or decorative coating on a substrate surface, in which process polyacrylate resin as binder and an amino resin as crosslinking agent is applied to the basecoat obtained in this way and subsequently
The invention also relates to aqueous coating compositions, to water-thinnable polyacrylate resins and to a process for the preparation of water-thinnable polyacrylate resins.
The process according to the preamble of 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).
For ecological and economic reasons it is desirable to employ aqueous topcoat compositions in stage (3) of the so-called basecoat/clearcoat process described above.
The topcoat compositions must be capable of application by spraying using automatic painting equipment. For this purpose their solids content must, at spray viscosity, be sufficiently high to obtain paint films having adequate film thickness with two passes of the spray gun (cross passes), and they must furnish baked paint films of good appearance (good flow-out, high gloss, good topcoat appearance, etc.).
The aqueous topcoat composition disclosed in Example 2 of EP-A-38,127 does not meet all the above requirements.
The object forming the basis of the present invention consists in providing aqueous topcoat compositions which comply with the above requirements.
Surprisingly, this object is achieved by topcoat compositions containing a water-thinnable polyacrylate resin as binder, which resin can be obtained (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), contains 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), is essentially free from carboxyl groups and is different from (a1) and (a2), or a mixture of such monomers in the presence of at least one polymerization initiator, and and, if appropriate, (a3) has been added, ethylenically unsaturated monomer which contains at least one carboxyl group per molecule and is copolymerizable with (a1), (a2), (a3) and (b2), or a mixture of such monomers, together with from carboxyl groups and is copolymerizable with (a1), (a2), (a3) and (b1), or a mixture of such monomers,
and carrying out further polymerization, and at the end of the polymerization and dispersing it in water, the sum of the proportions by weight of (b1) and (b2) always being 100% by weight and the type and amount of (a1), (a2), (a3), (b1) and (b2) being chosen so 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.
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). Basecoat compositions containing metallic pigments, especially aluminum pigments, are preferably used in stage (1). Metallic finishes are obtained in this way.
A more detailed description of the preparation of the polyacrylate resins to be used according to the invention is preceded by an explanation of two of the terms used: for "methacrylic acid or acrylic acid". indicate that the components (a1), (a2) and (a3) can have a low carboxyl group content (but no higher than would cause the polyacrylate resin prepared from the components (a1), (a2) and (a3) to have an acid value no higher than 10). It is preferred, however, for the carboxyl group content of the components (a1), (a2) and (a3) to be kept as low as possible. Components (a1), (a2) and (a3) which are free from carboxyl groups are particularly preferred.
For the preparation of the polyacrylate resins to be use
REFERENCES:
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patent: 4539363 (1985-09-01), Backhouse
patent: 4677004 (1987-06-01), Das et al.
patent: 4730020 (1988-03-01), Wilfinger et al.
patent: 4798746 (1989-01-01), Claar et al.
patent: 4978708 (1990-12-01), Fowler et al.
Dangschat Manfred
Reimann Manfred
Schwarte Stephan
Westermann Carlos
BASF Lacke & Farben AG
Cain Edward J.
Sabourin Anne Gerry
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