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
1996-06-20
2002-11-12
Gorr, Rachel (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...
C548S951000
Reexamination Certificate
active
06479613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel, simple process for the preparation of polyisocyanates containing uretdione groups and to their use in light-stable and weather-stable polyurethane (PUR) coating systems, especially in PUR powder coatings.
2. Discussion of the Background
DE-A 30 30 572 presents a process for the preparation of polyaddition products which contain uretdione groups, and the products prepared accordingly. These are reaction products of the isocyanurate-free uretdione (UD) of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI)—which can be prepared according to DE-A 30 30 513 or DE-A 37 39 549—with diols and, if desired, monoalcohols or monoamines. The reaction can be carried out in bulk or else in the presence of appropriate solvents. However, so far, in practice, this class of crosslinking agent has been produced in economically significant, saleable quantities only in a suitable solvent under mild conditions, at about 60°C., so as to avoid thermal ring cleavage during the synthesis. Preparation in bulk (i.e. in the absence of solvent) has not previously gone beyond the laboratory scale, since the viscosity reaches unmanageable levels during the reaction as a function of the molecular mass of the crosslinking agent. While DE-A 3030572 indicates that increasing the reaction temperature can operate as a means of controlling the reaction viscosity this measure is somewhat limited since higher temperatures can lead to detrimental effects on the reaction products. The industrial implementation of the solvent-free preparation of polyaddition products containing uretdione groups has previously been without success, despite the numerous corresponding attempts to solve this problem. Production in solvent not only has the disadvantage that the solvent(s) must be removed again subsequently, but also that it requires long reaction times and complex, reaction products are freed from the solvent in vacuo at about 120° C. using thin-film evaporators, filmtruders or extruders. This makes the process very costly.
Thus, a method is needed for the bulk preparation of polyisocyanates containing uretdione groups.
SUMMARY OF THE PREFERRED INVENTION
Accordingly, one object of the present invention is to a simple process for the production of polyisocyanates containing uretdione groups, which is solvent free.
A further object of the present invention is to provide a process for the bulk production of polyisocyanate containing uretdione groups which maintains a manageable viscosity throughout the process.
A further object of the present invention is to provide polyurethane coating systems containing bulk prepared polyisocyanates having uretdione groups.
Surprisingly it has been found that the reaction of polyisocyanate-uretdione with diols and, if desired, with monoalcohols or monoamines can be carried out continuously in bulk, in other words without solvent, in an intensive mixer, provided that certain process conditions are observed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention therefore relates to a process for the preparation of polyaddition products containing uretdione groups and based on polyisocyanate-uretdione having at least two free isocyanate groups, on diols and, if desired, on monoalcohols or monoamines, which process is characterized in that the polyaddition products containing uretdione groups are prepared by a solvent-free and continuous procedure.
The present process relies on the ability to continuously heat the reaction products for short periods in an intensive kneading apparatus, such as a single- or multi-screw kneading apparatus, preferably in a twin-screw extruder, at temperatures which are unusually high for polyisocyanates containing uretdione groups, but are necessary for the solvent-free preparation.
These unusually high synthesis temperatures can exceed 120° C., and range up to 190° C. The reason that such temperatures are considered unusually high is that these temperatures are already well within the range in which uretdiones unblock, so that high free isocyanate contents or uncontrolled reaction procedures would be expected. However, this was not the case.
The temperatures in the intensive kneading apparatus or twin-screw extruder must be sufficient to provide reaction between the reactants and to maintain a manageable viscosity, with these temperatures ranging up to 190° C., preferably up to 180° C., most preferably up to 170° C.
In the present process the brief exposure to heat must be sufficient to allow the reactants to be mixed homogeneously and to react to at least near completion (>95%). Controlled cooling is then carried out in accordance with the establishment of equilibrium, and, if desired, conversion is completed.
By appropriate equipping of the mixing chambers and/or the composition of the screw geometry, the intensive kneading apparatus renders possible intensive, rapid mixing and highly viscous product streams coupled with intensive heat exchange. Additionally, uniform flow in the longitudinal direction with a residence time which is as uniform as possible is also obtained. Furthermore, it must be possible to set different temperatures in the individual housings or sections of the device.
The reactants are metered to the intensive kneading apparatus in separate streams and/or as one or more streams containing more than one reactant. One such mixed reactant stream would include a combination of diols, monoalcohols, monoamines, catalysts and/or other conventional coating additives, such as levelling agents and stabilizers. Another example of a mixed stream would include a polyisocyanate-UD and those components which are inert towards isocyanate groups: catalysts and, correspondingly, coating additives as mentioned above.
The input of the product streams into the kneading apparatus can varied in sequence and offset in terms of time. The controlled cooling step which occurs after kneading can be performed using: tube bundles, pipe coils, cooling rolls, air conveyors and, preferably metal conveyor belts. Most preferably, the cooling means should allow for the setting of individual temperature zones. If desired the controlled cooling in the reaction section can be integrated in the form of a multi-housing apparatus, as in the case of extruders or Conterna machines.
The final stages of processing are initiated, depending on the viscosity of the product leaving the screw extruder and/or the post-reaction zone, first by further cooling—using controlled cooling devices as mentioned above—to a temperature which is sufficient for subsequent bagfilling/containment with comminution being carried out before bag-filling. During cooling, at an appropriate point, the product (which is produced preferably in strip form) can be pre-impressed in order to prepare for and facilitate subsequent comminution to the desired particle size or granule form, using roll-type crushers, pin mills, hammer mills or similar apparatus, and to reduce the amount of dust obtained. If a bed of coded rolls is used, this pre-impression can be combined with cooling and the dust collected afterward can be recycled directly and re-incorporated into the product.
Surprisingly, with respect to their physical and chemical characteristics and their technological properties, the crosslinking agents prepared according to the present invention are indistinguishable (within the margin of experimental error) from the same crosslinking agents prepared in conventional solvent based processes under much different conditions.
As starting compounds for use in the process of the present invention, it is possible to use uretdiones of diisocyanates, uretdiones prepared from two different diisocyanates, so-called mixed dimers (uretdiones) of mixtures of uretdiones or mixtures thereof. The diisocyanates suitable for the process of the present invention include aliphatic, (cyclo)aliphatic and araliphatic diisocyanates such as those described in Houben-Weyl, Methoden der Organischen Chemie
Behrendt Klaus
Brandt Siegfried
Gras Rainer
Herda Silvia
Dugussa-Huels Aktiengesellschaft
Gorr Rachel
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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