Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-05-14
2003-09-16
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S099000, C524S102000, C524S507000, C524S590000
Reexamination Certificate
active
06620868
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 (Ll) based on a UV absorber,
e) one or more light stabilizers (L2) based on sterically hindered amines,
f) one or more pigments (P), and
g) 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 land 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 la 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). It is not stated which specific binder combinations are to be used. The coating compositions may be used to coat plastics and they may comprise pigments in a hiding concentration.
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 may result in the formation of cracks in the coatings.
In recent years, the effect coating of substrates, especially of automobile bodies, has undergone dramatic progress. Numerous effect pigments which bring about new kinds of esthetic effects are nowadays available. Owing to the increased use of effect coatings in automobile construction, it is also necessary to an increased extent to provide plastics moldings with coatings of this kind. However, the customary and known two-coat systems composed of an effect basecoat and a clearcoat cannot readily be used to paint plastics moldings. Apart from problems of adhesion, the different substrate may bring about a shift in color, which is particularly noticeable when metal parts and plastics moldings painted in the same way adjoin one another directly.
Attempts have therefore been made to pigment the plastics moldings with effect pigments. Apart from the excessive consumption of comparatively expensive effect pigments, it is not possible to achieve the optical effects of conventional two-coat systems.
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 novel 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. Not least, the novel coating compositions should provide coatings which on colored or uncolored substrates, especially colored substrates, give the visual impression of an effect and/or metallic finish.
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
BASF Coatings AG
Sanders Kriellion A.
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