Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-11-03
2001-09-04
Sergent, Rabon (Department: 1711)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S388100, C427S388200, C427S389700, C427S389900, C427S391000, C427S393000, C427S393500, C427S493000, C427S508000, C427S520000, C522S090000, C522S093000, C522S098000, C522S174000, C525S123000, C525S126000, C525S131000, C525S440030, C525S920000, C528S049000, C528S075000, C528S080000, C528S083000
Reexamination Certificate
active
06284321
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to binders for powder coatings, and to processing powder coatings that contain the binders.
EP 410 242 discloses polyurethanes containing (meth)acryloyl groups, which are prepared by reacting
(A) from 40 to 80 parts of an organic polyisocyanate with
(B) from 15 to 50 parts of a (meth)acryloyl-containing monohydric alcohol and
(C) from 2 to 20 parts of a further structural component consisting of at least one (meth)acryloyl-free compound containing groups which are reactive toward isocyanate groups.
These polyurethanes are used as binders in powder coatings. The blocking stability of these coating materials, however, is in many cases inadequate. EP 0 585 742 discloses that the blocking stability of coating materials based on these polyurethanes can be improved by blending them with solid, unsaturated polyesters. These polyesters are cheaper than the polyurethanes mentioned. By replacing a portion of the polyurethanes with the unsaturated polyesters, there is an overall reduction in cost for the powder coatings. With these powder coatings it is possible to coat even temperature-sensitive substrates, such as wood, wood materials and plastics, since they can be cured even at low temperatures by UV irradiation or by the addition of peroxides.
It is desirable for these powder coatings to flow just as well and to give surfaces that are just as smooth at this reduced baking temperature as conventional powder coatings. The binders must therefore exhibit good flow even at minimal processing temperatures. For this purpose, it is common to add flow additives, which markedly reduce the melt viscosity of the binder. However, these products do not take part in the curing reaction. This impairs the resistance of the coating to chemicals.
In a simultaneously filed U.S. patent application corresponding to German priority application P 44 32 645.9, this object is achieved by the addition of reactive, solid flow agents.
In powder coatings, it is not possible to reduce the melt viscosity to any desired extent, since in many cases the melting temperature decreases at the same time. During storage, the powder coatings thus formulated begin to agglomerate. The powder coating can then no longer be processed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide powder coating binders which can be cured by UV irradiation or by addition of peroxides and which, additionally, have improved flow properties, without the powder coatings formulated from these binders losing their stability during storage.
The invention provides binders for powder coatings, comprising solid, unsaturated polyesterurethane acrylates, having a melting temperature of from 35 to 180° C., which are obtained by reacting an unsaturated, hydroxyl-containing polyester A which is solid at room temperature with a polyisocyanate B and with a hydroxyalkyl (meth)acrylate C.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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Brindoepke Gerhard
Fink Dietmar
Foley & Lardner
Sergent Rabon
Solutia Germany GmbH & Co. KG
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