Solid, oxazoline-terminated, urethane-functional...

Details Solid, oxazoline-terminated, urethane-functional... Solid, oxazoline-terminated, urethane-functional...

1999-09-13

2001-10-23

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...

C525S329900, C525S437000, C525S440030, C525S934000, C528S073000, C528S076000, C528S080000, C528S083000, C548S238000

Reexamination Certificate

active

06306967

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solid, oxazoline-terminated, urethane-functional polyaddition compounds, to a process for preparing them and to their use for preparing plastics, especially powder coating materials, which crosslink to give high-gloss coating films which are stable to light and weathering.
2. Description of the Background
Externally or internally blocked polyisocyanates, which are solid at room temperature, are valuable crosslinking agents for thermally crosslinkable polyurethane (PU) powder coating materials. For example, DE-A 27 35 497 describes PU powder coating materials having excellent weathering and thermal stability. In another disclosure, which is DE 27 12 931, the crosslinking agents, whose preparation is described therein, consist of &egr;-caprolactam-blocked, isocyanate-functional isophorone diisocyanate. Also known are urethane-, biuret- and urea-functional polyisocyanates, whose isocyanate groups are likewise blocked.
The disadvantage of these systems lies in the elimination of the blocking agent during the thermal crosslinking reaction. Since the blocking agent can, therefore, be discharged into the environment, it is necessary on ecological and occupational-hygiene grounds to take special precautions to remove cleanse the atmosphere discharged from the process and to recover the blocking agent. In addition, the crosslinking agents normally employed have low reactivity, i.e., curing temperatures of more than 170° C. are required.
DE 30 30 539 and DE 30 30 572 describe processes for preparing urethane-functional polyaddition compounds whose terminal isocyanate groups are capped irreversibly with monoalcohols or monoamines. The chain-terminating constituents of the crosslinking agents are particularly disadvantageous, since they lead to low network densities in the PUR powder coatings and thus to moderate solvent resistances.
Hydroxyl-terminated, uretdione-functional polyaddition compounds are the subject of EP 0 669 353. Their functionality of two accordingly constitutes an enhanced resistance to solvents. A feature common to the powder coating materials, based on these uretdione functional polyisocyanates, is that they emit no volatile compounds in the course of the curing reaction. However, at a minimum of 180° C., the stoving temperatures are high.
Publications JP 51 125 116, JP 49 124 130, JP 51 054 626, DE 25 05 862 and U.S. Pat. No. 4,245,063 describe powder coating materials whose oxazoline-functional acrylate copolymers are cured with polycarboxylic acids. The oxazoline groups are incorporated into the resin by copolymerizing 2-isopropenyl-2-oxazoline with unsaturated monomers.
Powder coating materials based on acid polyesters or acrylates and polyoxazoline curing agents are described, for example, in DE 23 28 012, DE 23 28 013, JP 51-136727, JP 50-037832, JP 56-036551, JP 51-134 727 and JP 51-089534. The polyoxazoline curing agents contain no additional functional groups, and so the flexibility of the powder coatings and their adhesion to the substrate are in need of improvement.
DE 44 42 908 describes the use of oxazoline-terminated polyurethanes. These compounds, however, are liquid and are, therefore, unsuitable for use as powder coating hardeners (curing agents). Moreover, in this case curing is initiated by cationic polymerization, which is known to be highly susceptible to disruption because of the presence of impurities. Moreover, such polymerization conditions rule out the use of basic pigments and auxiliaries.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide highly reactive crosslinking agents, which are free from elimination products, for preparing plastics, especially ecologically valuable powder coating materials, with the powder coating materials prepared therefrom no longer showing the above-mentioned disadvantages of powder coating materials of the prior art.
Briefly, this object and other objects of the invention as hereinafter will become more readily apparent can be attained by a solid, oxazoline-terminated, urethane-functional polyaddition compound having a melting point ranging from 40-130° C. and a free NCO content of less than 3% by weight, consisting essentially of a reaction product of a) at least one difunctional polyisocyanate and b) at least one hydroxy- or amino-functional oxazoline derivative, the ratio of NCO to OH equivalents ranging from 0.8:1.2 to 1.2:0.8
In an embodiment of the invention, the ratio of NCO to OH equivalents preferably ranges from 1:1.
In still another embodiment the composition further contains a component c) which is a chain extender.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides for the use of oxazoline-terminated, urethane-functional polyaddition compounds for the preparation of plastics, especially in combination with carboxyl-containing polymers, and with the additives customary in paint chemistry such as pigments, fillers leveling agents, degassing agents, catalysts and other additives, for the preparation of transparent and pigmented powder coating materials which are free from elimination products and are of high reactivity and excellent gloss.
The invention also provides transparent and pigmented powder coating materials, free from elimination products, which comprise the oxazoline-terminated urethane-functional polyaddition compounds of the invention.
Polyisocyanates which are specified, for example, in Houben-Weyl, Methoden der Organischen Chemie, Volume 14/2, page 61 ff. and J. Liebigs Annalen der Chemie, Volume 562, pages 75-136 are employed in the polyaddition compounds of the invention. The polyisocyanate can be any organic polyisocyanate suitable for crosslinking compounds containing active hydrogen; in other words, (cyclo)aliphatic, aromatic and heterocyclic polyisocyanates having at least two isocyanate groups, and mixtures thereof Representative examples of the polyisocyanates include aliphatic isocyanates such as akylene isocyanates, embodiments of which are ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene 1,6-diisocyanate, especially the 2,2,4 and the 2,4,4 isomers and technical-grade mixtures of both isomers, decamethylene diisocyanate and dodecamethylene diisocyanate, and also cycloalkylene isocyanates, embodiments of which are 1,3-cyclopentyldiisocyanate, 1,2-cyclohexyldiisocyanate, 1,4-cyclohexyldiisocyanate,&ohgr;,&ohgr;′-diisocyanato-1,4-methylcyclohexane, &ohgr;,&ohgr;′-diisocyanato-1,3-dimethylcyclo-hexane, 1-methyl-2,4-diisocyanatocyclohexane, 4,4′-methylene-bis(cyclohexyl isocyanate) and 3,3,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane. Representative examples of polyisocyanates include aromatic isocyanates such as aryl isocyanates, embodiments of which are m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-biphenyl diisocyanate, 1,4-naphthalene diisocyanate and 1,5-naphthalene diisocyanate, and also alkaryl isocyanates, an example being diisocyanatodiphenylmethane, especially the 4,4′ isomer, and also technical-grade mixtures of various isomers, for example, the 4,4′ and 2,4′ isomers, diisocyanatomethylbenzene, especially the 2,4 and the 2,6 isomers, and technical-grade mixtures of both isomers, 4,4′-toluidine diisocyanate, 1,3-bis(isocyanatomethyl)benzene and polymethylenepolyphenyl isocyanate, and ring-substituted aromatic isocyanates, embodiments of which are dianisidine diisocyanate, 4,4′-diphenyl ether diisocyanate and chlorodiphenyl diisocyanate. Also highly suitable are polyisocyanates which may be prepared by reacting polyisocyanates with themselves by way of the isocyanate groups, such as isocyanurates formed by reaction of three isocyanate groups. The polyisocyanates may likewise include biuret groups or allophanate groups.
As the oxazoline component it is possible to use all hydroxy- or amino alkyl-&Dgr;
2
-oxazoli

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