Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-07-18
2004-01-20
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S440030, C525S443000, C528S045000, C528S080000, C528S081000, C528S230000, C428S482000
Reexamination Certificate
active
06680358
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a new liquid, storage-stable coating composition, which is suitable for the production of coatings which have an outstanding resistance to external weathering, and binders thereof which are composed of a hardener component comprising an aminoplast resin and/or a blocked polyisocyanate and a specific polyol component of selected units, and to its use for the production of weathering-resistant coatings on any desired heat-resistant substrates.
One-component stoving lacquers based on polyisocyanates with blocked isocyanate groups and their use in polyurethane lacquers are known (cf. e.g. Kunststoff-Handbuch [Plastics Handbook], volume VII, Polyurethane [Polyurethanes], Carl Hanser-Verlag Munich (1966), pages 11-13, 21 et seq.).
For the use of such blocked polyisocyanates in combination with hydroxy-polyesters, there are the following main requirements:
1) Low splitting-off temperatures with the shortest possible stoving time.
2) No or only slight yellowing on stoving and brief over-stoving.
3) Adequate storage stability of the one-component lacquers.
4) No splitting off of toxicologically unacceptable cleavage products.
These requirements can be fulfilled by specific stoving binders based on hydroxy-polyesters and blocked polyisocyanates, such as are described in DE-A 2 550 156. It can be seen from DE-A 3 046 409 that the stoving binders of DE-A 2 550 156 cannot be used for the production of coatings which are exposed to shock and impact stresses in the surface region during protection of industrial goods, such as e.g. machine components, vehicle bodies or transportation containers.
Although the stoving binders of DE-A 3 046 409 give shock-and impact-resistant coatings, they cannot meet the normal demands of stability to weather. They are therefore unsuitable for coating surfaces which are exposed to extreme weathering influences, such as e.g. car bodies, facade elements etc., and for which high requirements are imposed on the mechanical properties and capacity for exposure to solvents, such as e.g. petrol.
One-component stoving binders based on hydroxy-polyesters and aminoplast resins also meet the requirements imposed after the stoving process only inadequately in respect of resistance to solvents and weathering, but lead to lacquer films which are distinguished by a favourable hardness/elasticity ratio and good adhesion. Such binder combinations are described in DE-A 2 621 657 and can be applied by the technique of automatic coil coating.
It can be seen from EP-A 494 442 that the stoving binders to date described above are unsuitable as stoving lacquers for intended uses where coatings are required of which the weathering properties must be so extremely high that in the pigmented state the lacquer films must also withstand short wavelength UV light for a relatively long time without yellowing and cracking and with high degrees of gloss of the lacquer film surfaces. Significant improvements in the UV resistance are shown by stoving lacquerings according to EP-A 494 442, where lacquer films are obtained which not only have a high level of hardness and elasticity with good adhesion to metal and good abrasion resistance but moreover withstand exposure to short wavelength UV light over a relatively long period of time without cracking and yellowing and without the addition of light stabilizers.
It is generally known in the lacquer branch that tests on lacquerings by means of intensive exposure to short wavelength UV light are not necessarily suitable for making exact predictions in respect of the resistance of lacquers to weathering in practice. Such accelerated laboratory tests with UV apparatuses sometimes do not correlate with long-term tests under realistic conditions in practice (e.g. in Florida), so that it may be that lacquers which show good weathering results in such laboratory tests give a poorer result in practice, thus also lacquers according to EP-A 494 442.
However, the use of metal sheets lacquered by means of automatic coil coating in areas where, in addition to a good resistance to solvents and chemicals, an excellent resistance to light and weather over a period of several years is required, e.g. on facades, is of increasing importance. Here also, a high level of properties is required in respect of the mechanical properties, such as e.g. hardness, elasticity and abrasion resistance.
Surprisingly, it has now been found that the coating compositions described below in more detail, based on a hardener component of the type known per se and a specific polyester component, give lacquer films which not only have a balanced hardness and elasticity ratio with good adhesion to metal and good abrasion resistance, but moreover show an exceptionally high, hitherto unknown resistance of such lacquer systems to external weathering in a test in practice lasting several years, in the form of an extremely high gloss retention, although accelerated weathering tests on these lacquers with exposure to UV light predict poor weathering properties.
SUMMARY OF THE INVENTION
The invention provides a liquid coating composition which is stable to storage at room temperature and comprises a binder mixture, organic solvents and optionally the conventional auxiliary substances and additives known from lacquer technology, where the binder is a mixture of
A) 2.0 to 30 wt. %, based on the sum of components A) and B), of a crosslinking component comprising at least one aminoplast resin and/or at least one blocked polyisocyanate
and
B) 98 to 70 wt. %, based on the sum of components A) and B), of a polyester component comprising at least one polyester containing hydroxyl-and carboxyl groups, characterized in that
component B) has an average number-average molecular weight Mn of 500 to 10,000 g/mol, a hydroxyl number of 20 to 50 mg KOH/g and an acid number of 0.5 to 30 mg KOH/g and has been prepared by polycondensation of
a) 50.5 to 53 mol % of a polyol component comprising
a1) 60 to 80 mol % neopentylglycol and/or 1,4-cyclohexanedimethanol,
a2) 20 to 30 mol % ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol and/or 1,6-hexanediol,
a3) 0.1 to 5 mol % trimethylolpropane, glycerol and/or pentaerythritol,
a4) 0 to 19.9 mol % of other alcohols which differ from a1) to a3) with
b) 47 to 49.5 mol % of a polycarboxylic acid component comprising
b1) 55 to 75 mol % isophthalic acid,
b2) 10 to 40 mol % terephthalic acid and/or phthalic acid or the anhydride thereof,
b3) 0.1 to 20 mol % adipic acid and
b4) 0 to 34.9 mol % of other carboxylic acids which differ from b1) to b3).
The invention also provides the use of this coating composition for the production of coatings which can be cured under the influence of heat on any desired heat-resistant substrates.
DETAILED DESCRIPTION OF THE INVENTION
The binders of the coating composition according to the invention comprise 2 to 30, preferably 3 to 25 wt. % of a crosslinking component A) and 98 to 70, preferably 97 to 75 wt. % of a polyester component B), the percentages stated adding up to 100.
Crosslinking component A) comprises at least one aminoplast resin and/or at least one blocked polyisocyanate.
Melamine-formaldehyde or urea-formaldehyde condensation products, for example, are to be regarded as aminoplast resins. Suitable melamine resins are all the conventional melamine-formaldehyde condensates which are not etherified, partially etherified or completely etherified with saturated monoalcohols having 1 to 4 C atoms, such as are described e.g. in FR-A 943 411 or by D. H. Solomon, The Chemistry of Organic Film Formers, 235-240, John Wiley & Sons, Inc., New York, 1967. However, some or all of the melamine resins can also be replaced by other crosslinking aminoplasts, such as are described e.g. in “Methoden der Organischen Chemie [Methods of Organic Chemistry]” (Houben-Weyl), vol. 14/2, part 2, 4th ed. Georg Thieme Verlag, Stuttgart, 1963, 319 et seq.
Those blocked polyisocyanates which are based on aromatic polyisocyanates are less suitable as the blocke
Füssel Christian
Noble Karl-Ludwig
Wamprecht Christian
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
Short Patricia A.
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