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
1998-08-17
1999-11-02
Niland, Patrick D.
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...
4273722, 4273855, 4284231, 524539, 528 44, 528 60, 528 61, 528 62, 528 64, 528 65, 528 66, 528 73, 528 80, 528 81, 528 83, 528 84, 528 85, C08J 300, C08K 320, C08L 7500, C08G 1800
Patent
active
059772468
DESCRIPTION:
BRIEF SUMMARY
This invention relates to polyurethane coating compositions, their preparation and use.
Coatings for the original painting of motor vehicles and for their repair are required to have very good physical properties such as hardness and resistance to water and solvents. The coating compositions are also required to have good application and appearance properties so that they are easy to apply to a substrate using spray application and result in final films having a good gloss.
One class of coating compositions commonly used for these applications comprises a hydroxyl functional polymer, such as a polyester or acrylic polymer, and a polyisocyanate. These two components react together after application to a substrate to form a polyurethane coating.
Due to environmental considerations there is a general trend in the coatings industry towards coating compositions with reduced solvent content. One way to achieve a lower solvent content is to use so-called high solids compositions. High-solids compositions are solventborne compositions which contain a relatively high level of non-volatile materials such as film-forming polymer, pigments and fillers, and a relatively low level of organic solvent.
A problem with formulating high solids coating compositions suitable for use in painting motor vehicles is that the compositions can have an unacceptably high viscosity. This is because the film forming polymers traditionally used in this field have a high solution viscosity in high solids solutions. The high viscosity gives rise to problems in spray application with poor paint atomization, and poor flow out and consequent low gloss levels and poor appearance. In practice, these types of composition are formulated so as to have a predetermined viscosity to enable consistent spraying and this puts a limit on the solids content.
One way around the viscosity problem is to use lower molecular weight polymers which generally have a lower solution viscosity. However this route has limitations and disadvantages. To produce low molecular weight acrylic polymers requires the use of high levels of initiators and chain transfer agents. These initiators and chain transfer agents become less efficient at high levels and lead to the presence of high levels of recombination products which cause toxicological and film performance problems. To produce polyesters of low molecular weight, conditions must be used under which a high level of residual polyol monomer remains which can cause film performance problems.
A better approach to very high solids compositions is to use a compound known as a reactive diluent as a partial or full replacement for the polyol. These reactive diluents reduce the viscosity of the polymer solution. Particularly useful reactive diluents are blocked or hindered amines such as aspartic esters, aldimines or ketimines. Compositions containing these types of viscosity modifier together with a hydroxyl functional acrylic or polyester polymer and a polyisocyanate are disclosed, for example, in EP-A-0 531 249.
Aldimines, ketimines and aspartic esters can be used to make compositions having a good balance of viscosity and solids content. However, partial replacement of the polyol by reactive diluents leads to compositions having a very short pot-life, probably because the diluent catalyses the reaction between the polyol and the polyisocyanate. Replacement of all of the polyol by diluent improves on the pot-life problems but the compositions form brittle films with poor adhesion to a substrate, and are expensive due to the high cost of the diluents.
We have now discovered compositions which contain a polyisocyanate, an aldimine or a ketimine viscosity modifier and a particular hydroxyl containing component which have both a good viscosity/solids balance and a good pot-life and which also give films having good early properties such as hardness and drying.
According to the present invention there is provided a coating composition comprising a solution in a volatile organic solvent of; hydroxyl groups.
The volatile organic s
REFERENCES:
patent: 5214086 (1993-05-01), Mormile et al.
patent: 5856420 (1999-01-01), Tucker et al.
Imperial Chemical Industries plc
Niland Patrick D.
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