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...
Reexamination Certificate
1995-05-01
2002-04-23
Niland, Patrick D. (Department: 1714)
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...
C524S507000, C524S839000, C524S840000, C525S123000, C525S127000, C525S455000
Reexamination Certificate
active
06376602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new water-borne, two-component polyurethane coating compositions based on selected polyhydroxyl compounds dispersed in aqueous medium and polyisocyanates emulsified in these dispersions, to a process for the production of these coating compositions by emulsification of the polyisocyanate component in the dispersion and to the use of the coating compositions for the production of coatings on water-resistant substrates.
2. Description of the Prior Art
Ecological factors play an important part in surface technology. A particularly urgent problem is reducing the quantities of organic solvents used in coating compositions.
Until recently it had not been possible to dispense with organic solvents in chemically crosslinking polyurethane coating compositions, which have acquired considerable significance in the coating field due to their outstanding properties. The use of water instead of organic solvents in these two-component polyurethane coating compositions wherein the polyisocyanate component contained free isocyanate groups did not appear possible because it is known that isocyanate groups react not only with alcoholic hydroxyl groups, but also with water. Because the concentration of active hydrogen atoms emanating from water in these systems is substantially greater than the concentration of hydroxyl groups from the organic NCO-reactive component, it had to be assumed that in the ternary polyisocyanate/organic polyhydroxyl compound/water system a reaction would take place between the isocyanate groups and water to form urea and carbon dioxide. Instead of the desired crosslinking reaction between the polyisocyanate and the organic polyhydroxyl compounds, it was expected that the isocyanate groups would react with water resulting in foam formation through the generation of carbon dioxide.
It is already known from DE-OS 2,708,442 and from DE-OS 3,529,249 that organic polyisocyanates may be added to aqueous polymer dispersions to improve their property spectrum. However, the polymers disclosed therein are not the organic polyhydroxyl compounds typically used as reactants for polyisocyanates. In addition, the effect of adding polyisocyanates to aqueous polymer dispersions described in these prior publications is presumably attributable to coating the dispersed polymer with the urea formed from the reaction between the polyisocyanate and water.
It was only from European Patent Application EP-A-0,358,979 that it became known that selected polyhydroxyl compounds based on vinyl polymers could be used as reactants for organic polyisocyanates containing free isocyanate groups for the production of water-borne, two-component polyurethane systems by emulsification of the polyisocyanates containing free isocyanate groups in the aqueous polymer solution or dispersion.
The polyhydroxyl compounds described in EP-A-0,358,979 are preferably prepared by free radical polymerization and have an acid value (based on the non-neutralized sulfonic acid and/or carboxyl groups) of 0 to 150, preferably 0 to 100 mg KOH/g solid resin; and a content of sulfonate and/or carboxylate groups of 5 to 417, preferably 24 to 278 milliequivalents per 100 g solids.
It has now been surprisingly found that even when vinyl polymer polyols containing less than 5 milliequivalents of sulfonate and/or carboxylate groups per 100 g of solid resin are used, it is possible to obtain two-component polyurethane coating compositions having very good properties, including long pot lives and high solvent resistance.
SUMMARY OF THE INVENTION
The present invention relates to water-borne coating compositions wherein the binder contains a mixture of
a) a polyol component dispersed in water or a water/solvent mixture which contains at least one polymer prepared from olefinically unsaturated monomers and having a molecular weight (M
n
) of at least 500, at least two alcoholic hydroxyl groups per molecule, a hydroxyl value of 15 to 250 mg KOH/g, an acid value of 0 to 7 mg KOH/g and a total content of sulfonate and carboxylate groups of 0 to 4.5 milliquivalents per 100 g of solid resin and
b) a polyisocyanate component which is emulsified in the dispersion of polyol component a), has a viscosity at 23° C. of 50 to 10,000 mPa.s and an average NCO functionality of 1.8 to 4.2, and contains 12.0 to 21.5% by weight of (cyclo)aliphatically bound isocyanate groups and, optionally, 2 to 20% by weight of ethylene oxide units present within polyether chains, the polyether chains containing a statistical average of 5 to 70 ethylene oxide units,
wherein the components are present in quantities corresponding to an equivalent ratio of isocyanate groups of component b) to alcoholic hydroxyl groups of component a) of 0.2:1 to 5:1.
The present invention also relates to a process for the production of these coating compositions by emulsifying the polyisocyanate component in an aqueous or aqueous/organic dispersion of the polyol component in amounts corresponding to an equivalent ratio of isocyanate groups to alcoholic hydroxyl groups of 0.2:1 to 5:1 and, prior to the addition of the polyisocyanate, incorporating any auxiliaries and additives into the polyol component.
Finally, the present invention relates to coated water-resistant substrates prepared from these coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
The polyol component is selected from polymer resins prepared from olefinically unsaturated monomers which have a molecular weight (M
n
, as determined by gel permeation chromatography) of at least 500, preferably 500 to 100,000 and more preferably 1000 to 50,000; an average of at least two alcoholic hydroxyl groups per molecule; a hydroxyl value of 15 to 250, preferably 30 to 150, mg KOH/g solids; an acid value (based on unneutralized sulfonic acid and carboxyl groups) of 0 to 7, preferably 0, mg KOH/g solid resin; and a total content of sulfonate and carboxylate groups of 0 to 4.5, preferably 0, milliequivalents per 100 g of solid resin.
The dispersions a) generally contain 10 to 50% by weight, preferably 20 to 40% by weight, of the polyol component as the dispersed phase. The continuous aqueous phase may contain up to 20% by weight, based on the weight of the continuous phase, of the organic solvents to be described hereinafter. Accordingly, the continuous phase of the dispersions is primarily water. The dispersions generally have a viscosity at 23° C. of 10 to 10,000, preferably 100 to 10,000 mPa.s; and a pH of 5 to 10, preferably 6 to 9.
The dispersibility of the polymer resins is based on the presence of the emulsifiers to be described hereinafter. In addition, in a less preferred embodiment, component a) may contain up to 10% by weight, based on the weight of the polyol component, of water-soluble polyhydric alcohols having a molecular weight of 62 to 499, preferably 62 to 200, which are different from the solvents to be described hereinafter. Examples of these alcohols include ethylene glycol, propylene glycol, glycerol, trimethylol propane and the low molecular weight, water-soluble alkoxylation products of these polyhydric alcohols.
The polyol component is produced by known radical polymerization methods, for example, solution polymerization, emulsion polymerization and suspension polymerization. They are preferably produced by radical emulsion polymerization in aqueous medium.
Continuous or discontinuous polymerization processes may be applied. Of the discontinuous processes, the batch process and the inflow process may be used; the inflow process is preferred. In the inflow process, water is initially introduced either alone or with a portion of the anionic emulsifier, an optional nonionic emulsifier and a portion of the monomer mixture, and heated to the polymerization temperature. After introduction of a portion of the monomers the polymerization reaction is radically initiated. The remainder of the monomer mixture is added together with the remainder of the initiator mixture and the emulsifier over a period of 1 to 10 hours, preferably 3 to
Kubitza Werner
Laas Hans Josef
Probst Joachim
Roschu Rolf
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
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