Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-03-06
1996-11-12
Sellers, Robert E.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525449, 525934, C08L 3314, C08L 6302
Patent
active
055741126
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the preparation of powder coatings, in which a mixture of mixture of epoxide group-containing synthetic resins, and average at least two carboxyl groups and at least one acid anhydride group per molecule, or a mixture of such compounds, after having cooled and solidified, is pulverized.
The invention also relates to powder coatings prepared by this process.
The process described above is known (cf. e.g. U.S. Pat. No. 4,091,048, DE-A-2 214 650 and EP-A-299 420.
EP-A-299 420 discloses a process for the preparation of powder coatings of the type described above, which is intended to enable the preparation of powder coatings which are stable on storage and give coating films having good properties. The process described in EP-A-299 420 is distinguished in that the compound employed as component B) has been modified by reaction with a polyol and contains on statistical average at least two carboxyl groups and at least two acid anhydride groups per molecule. The powder coatings prepared by this process give coating films whose properties, in particular for application in automotive finishing, are in need of improvement.
The object of the present invention consists in the provision of a process for the preparation of powder coatings of the type described at the beginning which enables the preparation of powder coatings which, in comparison with the powder coatings of the prior art, give coating films having improved properties. This object is surprisingly achieved by a process of the type described at the beginning which is characterized in that the mixture of A) and B) is admixed before or during the melt homogenization process with preferably from 0.3 to 0.6, hydroxyl groups of component C) are present per acid anhydride group of component B).
The powder coatings prepared by the process according to the invention are distinguished from powder coatings of the prior art in that they give coating films having improved adhesion (especially when used as clear coats for two-coat automotive finishes) and improved resistance to premium-grade gasoline and methyl ethyl ketone.
Powder coatings are conventionally prepared by homogenizing a mixture of components A) and B) in the molten state and powdering the thus resulting homogenized melt after it has cooled and solidified. The process of melting and homogenizing the mixture of components A) and B) is termed the melt homogenization process. It is usually carried out by extruding the mixture. Depending on the desired powder coating formulation, the mixture of components A) and B) can be admixed before or during the melt homogenization process with further conventional powder coating constituents, such as, for example, one or more crosslinking catalysts (for example quaternary ammonium salts, quaternary phosphonium salts, phosphines, imidazolines and metal salts, cf. also EP-A-299 420, page 4, line 51 and line 52), one or more pigments, one or more light stabilizers, one or more degassing agents (for example benzoin), one or more leveling assistants (cf. e.g. EP-A-299 420, page 5, line 7 to 14), one or more additional binders, one or more additional crosslinking agents etc. The melt obtained at the end of the melt homogenization process is powdered after it has cooled and solidified.
The process described above for the preparation of powder coatings is well known and requires no further discussion (cf. e.g. also H. Kittel, Lehrbuch der Lacke und Beschichtungen [Textbook of Paints and Coatings], Volume VIII, Part 2, Verlag W. A. Colomb in Heenemann Verlagsgesellschaft mbH, Berlin and Oberschwandorf, 1980).
It is essential to the invention that the mixture of components A) and B) is admixed before or during the melt homogenization process with C) a polyol or a mixture of polyols in an amount such that from 0.1 to 0.9, preferably from 0.3 to 0.6, hydroxyl groups of component C) are present per acid anhydride group of component B). Component C) is preferably added to the mixture of components A) and B) before the beginning of the melt homo
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Cibura Klaus
Hilger Christopher
Kranig Wolfgang
Woltering Joachim
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