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...
Reexamination Certificate
2001-05-15
2003-01-28
Niland, Patrick D. (Department: 1714)
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...
C524S086000, C524S100000, C524S102000, C524S507000, C524S539000, C524S590000, C524S591000, C524S839000, C524S840000, C525S123000, C525S127000, C525S455000
Reexamination Certificate
active
06512044
ABSTRACT:
The present invention provides a polyurethane coating composition comprising
a) one or more polyester resins (A),
b) one or more polyacrylate resins (B),
c) one or more di- and/or polyisocyanates (C) having free or blocked isocyanate groups,
d) one or more light stabilizers (L1) based on a UV absorber,
e) one or more light stabilizers (L2) based on sterically hindered amines, and
f) one or more organic solvents (D).
The present invention further relates to processes for preparing the coating composition and to the use of the coating composition as a topcoat or clearcoat, especially for coating plastics.
In industry today there is increasing use of shaped components which are based on plastic, are used together with metal components, and require coating. This applies in particular to automotive components, which are being manufactured from plastics parts to an increasing extent: examples are bumper linings, spoilers, sills, wheel-arch linings and side trims or protection strips. For shaped components of this kind use is increasingly being made of plastics comprising polycarbonate and polycarbonate blends, preferably with a polycarbonate content of more than 5% by weight, based on the plastics fraction.
Plastics, however, are generally sensitive to the effects of weathering, such as UV radiation and moisture, and when exposed in this way exhibit a variety of problems, such as yellowing, embrittlement or cracking, for example, unless appropriate precautions are taken. In order to avoid these problems it is known, for example, to provide plastics that are exposed to the effects of weathering as a result of their use, for example, as exterior automotive components with clearcoats or topcoats. It is common to add light stabilizers to the coating materials employed for this purpose, in order to avoid or at least reduce the problems caused by UV radiation.
The requirements made of such light stabilizers are diverse. For instance, these additives should not have an adverse impact on the mechanical and chemical properties of the coating material. In addition, these additives should be chemically stable and stable to UV radiation and should also be light in color, stable in shade, easy to incorporate, and compatible with the other components of the coating material. A large number of different light stabilizers and their use in coating materials are already in fact known.
For example, various benzophenone derivatives, benzotriazole derivatives, triazines, acrylates, salicylates, oxazolines, organic nickel compounds, ferrocene derivatives, sterically hindered amines and the like are used, individually or in combination, as light stabilizers.
Despite the large number of known light stabilizers and known clearcoat systems there are still great problems in the coating of colored thermoplastics as are used in particular for exterior automotive components of large surface area. In addition to the weathering stability already mentioned, the coating materials employed are in fact required at the same time to exhibit good adhesion to the plastics substrates and to result in a hydrolysis-resistant system (i.e., good adhesion after moisture exposure) having good chemical resistance and good strength at room temperature, and exhibiting a ductile fracture behavior even at low temperatures of from −20 to −30° C. In the sector of the coating of plastics, furthermore, there is the additional requirement that the coating compositions used are curable at low temperatures (generally <100° C.) and even when cured at these low temperatures lead to films having the desired properties.
DE-A-43 26 670 discloses a polyurethane coating composition based on a hydroxybutyl (meth)acrylate-containing polyacrylate resin and, if desired, further polyacrylate resins and/or polycondensation resins and polyisocyanates as crosslinkers and also discloses the use thereof as a clearcoat in the field of automotive refinishing and for coating plastics. As light stabilizers, the clearcoat comprises a mixture of benzotriazine as UV absorber and a light stabilizer based on sterically hindered amines (Tinuvin® 292 from Ciba Geigy, light stabilizer based on bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate).
EP-B-0 455 211, finally, discloses an effect basecoat for the direct coating of unprimed plastics substrates consisting of or comprising polypropylene. Said effect basecoat described therein comprises not only physically drying binders but also cellulose acetobutyrate and from 0.5 to 15% by weight of one or more chlorinated polyolefins. Clearcoats and topcoats, however, are not described in EP-B-0 455 211.
U.S. Pat. No. 5,145,839 discloses coating compositions which comprise mixtures of the light stabilizers (L1) and (L2), in an amount of from 0.2 to 20% by weight, based on the film-forming resins. The amounts of the light stabilizer (L1) are not more fully specified; the examples only reveal that less than 2% by weight, based on the total coating composition, is used. Additionally, it is not stated which specific binder combinations are to be used. The coating compositions may be used to coat plastics.
U.S. Pat. No. 5,504,178 or DE-A-31 09 604 describes coating compositions which comprise polyester resins (A) and polyacrylate resins (B) as binders, polyisocyanates as crosslinkers, and light stabilizers (L1). Light stabilizers (L2) are not present therein. These coating compositions may also be used to coat plastics.
EP-A-0 518 779 discloses a coating composition for the coating of plastics which comprises a polyester polyol (A) and/or a polyether polyol as binder(s), triisocyanates as crosslinkers, and a combination of sterically hindered amines (HALS) and light stabilizers (L1).
However, the color stability following radiation exposure of the coatings produced from these known coating compositions still leaves much to be desired, a further difficulty being that the radiation exposure results in the formation of cracks in the coatings.
It is an object of the present invention therefore to provide coating compositions which combine good weathering stability of the resulting coatings with good adhesion to the plastics substrates and which lead to a hydrolysis-resistant system (i.e., good adhesion after moisture exposure) having good chemical resistance and good strength at room temperature, said system also exhibiting a ductile fracture behavior at low temperatures of from −20 to −30° C. Moreover, the ovel coating compositions as clearcoat material should bring about a much higher color stability following radiation exposure in the colored plastics parts or in the basecoats and, viewed per se, should be less susceptible to cracking than the conventional coating compositions.
This object is surprisingly achieved by means of a coating composition, of the type specified at the outset, wherein
1.) the polyester (A) has an OH number of from 80 to 200 mg KOH/g and an acid number <10 mg KOH/g,
2.) the polyacrylate resin (B) has an OH number of from 80 to 200 mg KOH/g and an acid number <20 mg KOH/g,
3.) the light stabilizer (L2) based on sterically hindered amines is amino ether functionalized, and
4.) the light stablizer (L1) is included herein in an amount of at least 3% by weight, based on the coating composition.
The present invention further provides processes for preparing this coating composition and provides for the use of this coating composition as a topcoat or clearcoat, especially for coating plastics.
It is surprising and was not foreseeable that by the use of a specific binder combination and, at the same time, a specific light stabilizer combination it is possible to provide coating compositions which are suitable as protective coating for color-pigmented plastics and meet all of the requirements commonly imposed on such coating compositions. Thus the coatings produced using these coating compositions are notable for good weathering stability coupled with good adhesion to the plastics substrates. In addition, they lead to a hydrolysis-resistant system (i.e., good adhesion after moisture expo
BASF Coatings AG
Niland Patrick D.
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