Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1995-05-11
1996-10-08
Johnson, Rachel
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524591, 524840, 524873, 524875, 525454, 525456, 528 71, 528 745, 528 75, 528 85, C08G 1862
Patent
active
055632068
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION AND FIELD OF THE INVENTION
This invention relates to aqueous polyurethane dispersions prepared by reaction of diisocyanates and/or polyisocyanates with polyol mixtures containing dimer diol, chain-extending agents and optionally polyols containing at least three hydroxyl groups and subsequent dispersion in water, to a process for their production and to their use in stoving lacquers.
DISCUSSION OF RELATED ART
Aqueous polyurethane dispersions are acquiring increasing technical and economic significance because they are toxicologically and ecologically safer than polyurethanes in organic solvents. In principle, most polyurethanes may be converted into aqueous emulsions and dispersions with the assistance of external emulsifiers and intensive shear forces. Unfortunately, the stability of these systems is extremely poor. For this reason, efforts have been made to develop self-emulsifiable polyurethanes which spontaneously form stable dispersions in water without the assistance of external emulsifiers and intensive shear forces. Self-emulsifying polyurethanes of the type in question contain compounds with an anionic group, a cationic group or groups convertible into anionic and cationic groups incorporated in the polyurethane. One example of such a compound is dimethylol propionic acid which is incorporated in the polyurethane through the hydroxyl groups. After conversion into the carboxylate anion, the carboxyl group effects the dispersion of the polyurethane in water.
For example, EP-A-299 148 describes a self-emulsifying polyester urethane prepared by reaction of a hydroxyl-terminated polyester and dimethylol propionic acid with polyisocyanates. Although polyester urethanes such as these are undoubtedly self-emulsifying, they also show signs of hydrolysis because the incorporated polyester segment is susceptible to hydrolysis, so that the dispersion as a whole is destabilized. Polyether urethanes containing incorporated polyether segments, such as polyethylene glycols, polypropylene glycols, polytetrahydrofurans, etc., are less susceptible to hydrolysis. However, self-emulsifying polyurethanes showing more hydrophobic properties than the polyether urethanes mentioned are required for certain applications. Thus, relatively hydrophobic polyurethanes are required in particular in the field of coatings to ensure that the coatings reliably protect the systems to be coated against water. For this reason, there has been no shortage of attempts to provide polyurethanes containing hydrophobic segments which are self-emulsifiable in water.
Accordingly, it is proposed in DE-A-39 39 566 to terminate polyurethanes with alkoxysilane groups. Thus, according to this document, bricks which have been treated with alkoxysilane-terminated polyurethanes, optionally in the form of aqueous dispersions, show distinctly reduced permeability to water vapor. These alkoxysilane-terminated polyurethanes are obtained by a two-stage reaction. In the first stage, polyisocyanates are reacted with polyethylene glycols, which may be mixed with hydrophobic diols and/or polyols and trimethylol propane, and with dimethylol carboxylic acids to form polyurethane prepolymers still containing free isocyanate groups. The polyurethane prepolymers are then reacted with alkoxysilanes. Dimer diols, ring-opened epoxidized fats and oils, fatty acid ethanolamides, monoglycerides of fatty acids, polypropylene glycols and/or polysiloxanes are mentioned as examples of hydrophobic diols. Unfortunately, these alkoxysilane-terminated polyurethanes can only form stable aqueous dispersions up to a polyurethane solids content of 12% by weight. However, there is an increasing demand in practice for dispersions having higher polyurethane contents.
In addition, it is known from the prior art that polybutadiene polyols can be incorporated in self-emulsifying polyurethanes to obtain relatively hydrophobic polyurethanes. Unfortunately, polybutadiene diols are extremely sensitive to oxidation on account of their high percentage content of un
REFERENCES:
patent: 4066591 (1978-01-01), Scriven et al.
patent: 5312865 (1994-05-01), Hoeffer et al.
DIN 50 017, Oct., 1982; The German Institute for Testing.
DIN 50 021, Jun., 1988; The German Institute for Testing.
DIN 53 240 Dec. 1971; The German Institute for Testing.
Eicken Ulrich
Gruetzmacher Roland
Hoefer Rainer
Westfechtel Alfred
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Johnson Rachel
Ortiz Daniel S.
Wood John Daniel
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