Coating compositions for transparent topcoat lacquer layers and

Details Coating compositions for transparent topcoat lacquer layers and Coating compositions for transparent topcoat lacquer layers and

1996-01-22

1997-12-16

Short, Patricia A.

Stock material or miscellaneous articles

Composite

Of polyamidoester

4284233, 4284237, 4284244, 4273855, 4273882, 4273883, 4274071, 427409, 525124, 525127, B32B 1508, B32B 2708, C08F21604, C08F22026

Patent

active

056983301

DESCRIPTION:

BRIEF SUMMARY
This invention relates to coating compositions which are suitable, in particular, for transparent as well as pigmented stoved multi-layer coatings, for example in automotive original lacquer coating, which coating compositions are distinguished by elevated "acid rain" resistance and an elevated application solids content.
Japanese patent Kokai no. 1(1989)-158079 describes coating compositions based on caprolactone-modified polyacrylate resins optionally additionally containing hydroxyalkyl (meth)acrylates, alkylated melamine resins and optionally blocked polyisocyanates. While high-solids automotive lacquer coatings may indeed be produced with such coating compositions, industrially required levels of acid rain resistance are not achieved. The clear lacquers tend to yellow and have low initial gloss.
DE-A-42 04 518 describes non-aqueous transparent topcoat lacquers based on synthetic resins containing hydroxyl groups, amino resins and blocked polyisocyanates, wherein the latter are blocked both with dialkyl malonates and with blocking agents containing methylene groups or oximes. In this case, too, the acid resistance of the resultant lacquer coatings is not entirely satisfactory.
The object of the present invention was to provide coating compositions for stoved multi-layer coatings, in particular for automotive original lacquer coating, which compositions both have an elevated application solids content (high solids) and result in coatings with elevated acid resistance, in particular improved resistance to sulphuric acid.
It has been found that the requirement for sulphuric acid resistant and simultaneously high-solids coating formulations may be satisfied by coating compositions which contain one or more hydroxy-functional (meth) acrylic copolymers, carboxy-functional, blocked urethane prepolymers, crosslinking agents and optionally hydroxy-functional polyester resins, conventional lacquer additives and solvents. The coating compositions are characterised in that they contain binders based on with a hydroxyl value of 0 to 80, an acid value of 5 to 50 and a weight average molecular weight (M.sub.w) of 500 to 5000, which are obtainable by reacting thereof, molecule, hydroxyl group and at least one carboxyl group per molecule, araliphatic di- and/or polyisocyanates and NCO groups, case, hydroxyl groups with a weight average molecular mass (M.sub.w) of 2000 to 20000, an acid value of 1 to 50 mg KOH/g and an OH value of 30 to 200, value of 40 to 200 and differing from component A), each case.
The carboxy-functional and optionally also hydroxy-functional, blocked urethane prepolymers (component A) which are contained in the coating compositions according to the invention may be produced in various manners from components a1) to a6). Production may proceed using a single-vessel method or, preferably, in stages. They may be produced in stages, for example, by esterification of alkanediols with polycarboxylic acids or the anhydrides thereof, optionally using polyols and/or hydroxycarboxylic acids with at least one hydroxyl group and at least one carboxyl group per molecule, to yield oligomeric OH- and COOH-functional polycondensation products. The reactants may be reacted at elevated temperature, for example at temperatures of 120.degree. to 240.degree. C., until the desired degree of polycondensation is achieved.
The polycondensation intermediate obtained in this manner may then be reacted with aliphatic, cycloaliphatic and/or araliphatic di- and/or polyisocyanates at elevated temperature, for example at 40.degree. to 100.degree. C.
The excess NCO groups remaining from urethanisation are completely reacted with conventional blocking agents, for example CH-acidic, NH- and/or OH-functional compounds. Examples of CH-acidic compounds are acetoacetic ester, acetylacetone, dialkyl malonate, such as diethyl malonate; examples of OH-functional compounds-are alkanone oximes, alkanols and phenols; examples of NH compounds are lactams, such as caprolactam, NH-functional heterocyclics, such as imidazole and pyrazole derivat

REFERENCES:
Database WPI, week 8931, Derwent Publications Ltd., London, GB; AN 223234 Thermosetting Clear Coating Composition.

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