Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-07-06
2002-09-10
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C252S182200, C252S182210, C525S124000, C525S440030, C544S222000, C564S032000, C528S073000
Reexamination Certificate
active
06448363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing highly reactive mixtures of (semi)crystalline and amorphous blocked polyisocyanates.
2. Discussion of the Background
Owing to their environmental compatibility, economics and very good coating properties, powder coatings are increasingly displacing conventional solvent-based coating systems. Polyurethane (PU) powder coatings are known for their outstanding coating qualities. The PU powder coatings based on partially or totally blocked polyisocyanates and hydroxyl-containing polymers are heat-curable. These PU powder coatings are widely described in the literature. Examples that may be mentioned include DE-As 21 05 777, 25 42 191, 27 35 497, 28 42 641, 30 04 876, 30 39 824, and 31 28 743. From the large number of blocking agents, described in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/2, 4th Edition, Georg Thieme Verlag, Stuttgart, 1963, pages 61-70, &egr;-caprolactam has become established for PU powder coatings. However, PU powder coatings based on &egr;-caprolactam-blocked polyisocyanates require curing temperatures above 170° C. to crosslink the coating.
In order to open up the powder technology to temperature-sensitive workplaces or to reduce energy costs, blocking agents have been sought which are eliminated at lower temperatures than &egr;-caprolactam. Using oxime-blocked polyisocyanates it is possible to prepare PU powder coatings whose curing temperatures are at a low level. They are described, for example, in DE-A 22 00 342, EP-A 0 432 257, and U.S. 3,857,818. The big disadvantage of these compounds, however, is their thermal instability and pinholing tendency.
Pyrazoles and triazoles are likewise suitable as blocking agents for highly reactive polyisocyanates, but without exhibiting the disadvantages of oximes.
For instance, EP 0 159 117 describes polyisocyanates blocked with pyrazoles. The reaction is conducted batchwise in a solvent. The pyrazole-blocked polyisocyanates may be used as crosslinkers for solvent-based PU powder coatings which may be cured at temperatures around 120° C. The use of these polyisocyanates as powder coating crosslinkers is not described.
U.S. Pat. No. 5,804,646 claims a powder coating containing a hydroxyl-containing polymer and an isocyanate crosslinker. The crosslinker contains a mixture of a (semi)crystalline, aliphatic, (cyclo)aliphatic or cycloaliphatic triazole-blocked isocyanate component and an amorphous aliphatic, (cyclo)aliphatic or cycloaliphatic triazole-blocked isocyanate component.
Such triazole-blocked polyisocyanates are suitable as low-viscosity crosslinkers for outdoor-resistant powder coatings even in automotive finishing, where the quality requirements are extremely exacting. The powder coating composition may be cured at temperatures of 130° C. and above. The crosslinkers of U.S. Pat. No. 5,804,646 are prepared without solvent in a batch process. This process is hampered by great difficulties since the temperature range is very small. On the one hand, high temperatures—generally greater than 120° C.—are required so that the solid obtained during the preparation is present as a melt and can still be discharged from the vessel. On the other hand, the temperature must not rise above 125° C., since otherwise the blocking agent is eliminated.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention to provide a less complicated, simple, continuous process for preparing the highly reactive pyrazole- and triazole-blocked polyisocyanates which does not have the aforementioned disadvantages of conventional systems.
This and other objects of the invention have been achieved by the present invention, the first embodiment of which provides a solventless, continuous process, which includes:
in at least one extruder, intensive compounder, intensive mixer or static mixer,
mixing and heating a reaction mixture including the following (A), (B), and one or both of (C) and (D):
(A) at least one aliphatic, (cyclo)aliphatic and/or cycloaliphatic C
3
-C
50
diisocyanate compound;
(B) at least one aliphatic, (cyclo)aliphatic and/or cycloaliphatic C
3
-C
50
polyisocyanate compound containing one or more isocyanurate groups;
(C) 1,2,4-triazole;
(D) one or more pyrazole having the formula:
where R
1
, R
2
and R
3
simultaneously or independently of one another are hydrogen or alkyl, alkenyl, aralkyl, aryl or N-substituted carbamoyl groups, halogen or —C(═O)—O—R
4
, where R
4
is a C
1
-C
12
alkyl group;
to obtain a product mixture including at least one (semi)crystalline, blocked C
3
-C
50
isocyanate compound and at least one amorphous, blocked C
3
-C
50
isocyanate compound.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.
Surprisingly it has been found that the reaction of aliphatic, (cyclo)aliphatic or cycloaliphatic polyisocyanates with pyrazoles or triazoles to give a mixture of amorphous and (semi)crystalline crosslinkers for PU powder coatings may be conducted in bulk, i.e., without solvent, and continuously in an extruder, intensive compounder or intensive mixer in accordance with the present invention.
Preferably, the present invention includes a process for the solventless continuous preparation of a mixture of a (semi)crystalline and an amorphous aliphatic, (cyclo)aliphatic or cycloaliphatic, triazole- or pyrazole-blocked C
3
-C
50
isocyanate compound by reacting
(A) an aliphatic, (cyclo)aliphatic and/or cycloaliphatic C
3
-C
50
diisocyanate compound
and
(B) an aliphatic, (cyclo)aliphatic and/or cycloaliphatic C
3
-C
50
polyisocyanate compound containing isocyanurate groups
with
(C) 1,2,4-triazole
and/or
(D) pyrazoles of the formula:
where R
1
, R
2
and R
3
simultaneously or independently of one another are hydrogen or alkyl, alkenyl, aralkyl, aryl or N-substituted carbamoyl groups, halogen or —C(═O)—O—R
4
, where R
4
is a C
1
-C
12
alkyl group,
in an extruder, intensive compounder, intensive mixer or static mixer by intensive commixing and short-term reaction with supply of heat and subsequent isolation of the end product by rapid cooling.
Preferably, the reaction takes place solventlessly and continuously in one or more an extruder, intensive compounder, intensive mixer or static mixer by intensive commixing and short-term reaction with supply of heat. The end product is then successfully obtained by subsequent rapid cooling.
Preferable apparatus for the process of the invention include extruders such as single-screw or multi-screw extruders, especially twin-screw extruders or planetary roll extruders, intensive compounders, intensive mixers such as thorax mixers, or static mixers.
It was surprising that in the abovementioned apparatus the reaction, which in the batchwise process requires several hours, proceeds to completion within a few seconds. Prior to the present invention, it has not been possible to obtain a product which can be simply processed further. In conventional systems, the reaction product crystallizes rapidly in the reactor and thereafter can only be removed from the system with difficulty, mechanically.
By the present invention, it is possible to completely or very substantially convert the reactants with short-term thermal loading in conjunction with the mixing action. By appropriately charging the mixing chambers and/or composition of the screw geometries, the apparatus permits intensive rapid commixing with simultaneous intensive heat exchange. It also ensures uniform flow passage in the lengthwise direction with a highly uniform residence time. A further advantage is that it is possible to set different temperatures in the individual barrels or sections of the apparatus.
The reaction products are preferably supplied to the apparatus in separate product streams; in the case of more than two product streams, these streams may also
Weihrauch Thomas
Wenning Andreas
Degussa - AG
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sergent Rabon
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