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
2001-02-15
2002-05-07
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...
C544S222000, C252S182200, C252S182220
Reexamination Certificate
active
06384175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to water-dispersible polyisocyanate mixtures containing acylurea groups, a process for their preparation, and their use as a starting component in the preparation of polyurethane plastics, in particular as crosslinking agents for water-soluble or -dispersible binders or binder components with isocyanate-reactive groups.
2. Description of the Prior Art
Water-dispersible polyisocyanates have gained importance in recent years for various fields of use and play a particular role today as crosslinking components for water-dilutable two-component polyurethane (2K PU) coating compositions. In combination with aqueous polyol dispersions, they allow the formulation of solvent-free coating systems which already cure to high-quality coatings at room temperature and are equivalent to conventional coatings in respect of resistance to solvents and chemicals or capacity for exposure to mechanical stresses. This is described for example in EP-A 358 979, EP-A 469 389, EP-A 496 210, EP-A 542 105, EP-A 543 228, EP-A 562 282, EP-A 562 436, EP-A 583 728, DE-A 41 29 951, DE-A 42 26 242, DE-A 42 26 243 or DE-A 42 26 270.
Water-dispersible polyisocyanate formulations are also important as additives for aqueous dispersion adhesives. With their aid, for example, the heat stability and water resistance of bonds between different materials can be improved considerably as explained in EP-A 61 628 and EP-A 206 059.
Water-dispersible polyisocyanates are also used as crosslinking components for aqueous dispersions in textile finishing (EP-A 560 161 or WO 95/30045), in formaldehyde-free textile printing inks (EP-A 571 867 or DE-A 195 33 218), and as auxiliary substances for wet strength treatment of paper (EP-A 564 912, EP-A 582 166, EP-A 707 113, WO 96/20309 and WO 97/04169).
Nonionic polyisocyanates, hydrophilically modified with polyethers, have also found acceptance in all these fields of use. The preparation of such water-dispersible polyisocyanates is described in a number of publications.
According to DE-A 24 15 435, for example, urethanes of organic, in particular aromatic, polyisocyanates and polyethylene glycol monoalkyl ethers containing at least 5 ethylene oxide units are surface-active substances. GB-A 1 444 933 and DE-A 29 08 844 describe their use in the preparation of stable aqueous emulsions of aromatic polyisocyanates.
Aromatic polyisocyanates hydrophilically modified by reaction with alkylene oxide polyethers are also known from EP-A 61 628 and EP-A 95 594. These products are used in the form of aqueous emulsions particularly in the adhesives sector.
EP-A 206 059 describes water-dispersible formulations of (cyclo)aliphatic polyisocyanates, specifically reaction products of polyisocyanates with mono- or polyfunctional polyalkylene oxide alcohols consisting of at least one polyether chain containing at least 10 ethylene oxide units, which are used as emulsifiers and additives for aqueous adhesives.
EP-A 516 277 describes the hydrophilic modification of specific polyisocyanates containing tertiary isocyanate groups by reaction with monofunctional polyalkylene oxide polyethers and the use of these products as a crosslinking component for aqueous coating compositions.
The polyisocyanate mixtures described in EP-B 540 985 and US-A 5 200 489, which are obtainable by urethanization of aliphatic and/or cycloaliphatic lacquer polyisocyanates with short-chain polyethylene oxide polyether alcohols having a statistical average of less than 10 ethylene oxide units, are suitable for high-quality light-fast lacquer applications.
The water-dispersible polyisocyanates based on 2,4(6)-diisocyanatotoluene (TDI) or mixtures of TDI and 1,6-diisocyanatohexane (HDI), described in EP-A 645 410 and EP-A 680 983 as crosslinking agents for aqueous wood and furniture lacquers, also contain urethanes of polyisocyanates and mono functional polyethylene oxide polyether alcohols as hydrophilic constituents.
In addition to these purely nonionically hydrophilically modified polyisocyanates containing polyether-urethanes, polyether-modified water-dispersible polyisocyanates have also been described, which additionally also contain ionic groups, for example sulfonate groups (cf. e.g. EP 703 255) or amino or ammonium groups (cf. e.g.
EP-A 582 166 and EP-A 707 113) for improving the emulsifiability or to achieve special effects. Such ionically
onionically modified polyisocyanates are generally less suitable for coating applications. They are preferably employed in environment-friendly textile finishing or as we t strength agents for paper.
In spite of their broad acceptance on the market for the most widely varying applications, the water-dispersible polyisocyanates of the prior art modified with polyetherurethanes have a number of main disadvantages.
Some water-dispersible polyisocyanates have a very high viscosity which has to be overcome during the dispersing operation, especially those that have been prepared using higher molecular weight polyether alcohols. In the case of pure polyethylene oxide polyethers with a number average molecular weight of approx. 700 or more, considerable shear forces (e g. high-speed stirrers) have to be applied to produce homogeneous aqueous dispersions. Furthermore such products, in particular at high emulsifier contents (necessary to achieve particularly finely divided dispersions which are stable to sedimentation), often tend to crystallize.
Water-dispersible polyisocyanates which can be stirred manually very easily into water to give stable dispersion and show no tendency at all towards crystallization even at high degrees of hydrophilic modification, i.e. at high contents of ethylene oxide units, can be obtained using shorter polyether chains. However, because of the relatively low molecular weight of the polyalkylene oxide polyethers both the content of isocyanate groups and the average isocyanate functionality decrease constantly with increasing degree of hydrophilic modification. For the majority of the abovementioned fields of use, for example, as crosslinking components for lacquers and coatings, highly hydrophilically modified polyisocyanates are desired that have high NCO contents and the highest possible functionality and are emulsified in a particularly finely divided form.
Furthermore, films of aqueous 2K PU coating compositions based on water-dispersible polyisocyanates modified with polyether-urethanes have poor surface-drying, detectable from a slow development of hardness, and are therefore not suitable for all applications.
An object of the present invention is to provide new water-dispersible polyisocyanate mixtures which are suitable for use in all the abovementioned fields of use of hydrophilic polyisocyanates, in particular as starting components for the preparation of polyurethane plastics, and above all as crosslinking agents for aqueous binders or binder components in coating systems, without having the disadvantages mentioned for the water-dispersible polyisocyanates of the prior art.
This object may be achieved with the polyisocyanate mixtures according to the invention which are described below in more detail and the process for their preparation. The invention is based on the surprising observation that the reaction of polyisocyanate molecules consisting of at least two diisocyanate molecules with polyalkylene oxide polyethers containing acid groups results, after elimination of CO
2
, in water-dispersible polyisocyanate mixtures which, at significantly lower degrees of hydrophilic modification, can be stirred considerably more easily and in a more finely divided form into aqueous systems than water-dispersible polyisocyanates of the prior art in which the polyether chains are linked to the polyisocyanate via urethane bonds. The process according to the invention allows the preparation of hydrophilic polyisocyanates which are stable towards crystallization and, compared with the known polyisocyanate mixtures, which contain polyether chains, are distinguished by a higher content of isocyana
Blümel Burkhard
Brahm Martin
Danielmeier Karsten
Lass Hans-Josef
Noble Karl-Ludwig
Bayer Aktiengesellschaft
Gil Joseph C.
Gorr Rachel
Roy Thomas W.
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