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
1999-11-15
2002-05-28
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, C524S539000, C524S591000, C524S839000, C524S840000, C525S123000, C525S455000
Reexamination Certificate
active
06395820
ABSTRACT:
BACKGROUND OF THE INVENTION
Waterborne, or water based, polyurethanes have been in existence for a number of years and there has been steady improvement in the performance properties of these materials to fit specific needs. Aqueous polyurethanes have been commercially attractive for a number of reasons, one of the most important of which is the elimination or substantial reduction of solvents and volatile organic compounds (VOC) emissions into the atmosphere. Another important reason relates to the performance of aqueous polyurethane systems which is now comparable to or better than conventional solvent-based polyurethanes for many applications.
Among the important advancements in this area have been water based and substantially solvent free, two component polyurethane-polyurea dispersions, also known simply as two component (2K) aqueous polyurethane dispersions. These dispersions are superior to well known one component aqueous dispersions of polyurethanes in which the polyurethanes are typically first formed in a solvent based system. The two component water based polyurethanes also match or exceed performance of two component solvent based polyurethane coatings while minimizing emission of organic solvents.
Two component waterborne polyurethanes tend to dry more slowly than two component solvent borne polyurethane coatings. This enables the waterborne coating molecules to have more mobility in the coating for longer periods of time, until coalescence can occur. However, this longer open time allows particles of different pigments to segregate causing “flooding”/“floating” at the surface.
Presently, there are aqueous acid functional polyester polyol compositions which can be reacted with conventional isocyanates, such as either hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) trimer. When such two component systems contain two different pigments, they exhibit a flooding and/or floating problem and do not respond to typical approaches in solving flooding/floating behavior such as listed in Clive Hare's book,
Protective Coatings Fundamentals of Chemistry and Composition
. On pages 456-457, the author describes “floating” behavior as mottled or blotchy color variations in the dry coating caused by one or more of the following differences: particle sizes. two types of pigments, extent of pigment flocculation, surface tension, density or temperature gradients formed by currents as the paint dries. On the other hand, “flooding” causes a uniform color on the coating surface but variations in color throughout the coating thickness caused by different rates of pigment settling in the applied film. These various rates can be due to differences in pigment size, density, shape, or degree of flocculation. Flooding can be affected by temperature, and humidity and intensified by low viscosity. slow dry times and thick films. Some traditional solutions for eliminating flooding/floating behavior, as described in Clive Hare's book, are to use low surface energy flow agents or thixotropes, to match pigment sizes used in dispersions, to normalize degree of pigment dispersion, or to decrease dry time.
Unfortunately, with the water based, two component polyurethane-polyurea systems based on aqueous acid functional polyester polyols, these traditional approaches were not successful in eliminating the flooding behavior.
Water based, two component polyurethane-polyurea systems are described in the following patents:
U.S. Pat. No. 5,508,340 discloses a substantially solvent free, aqueous two-component coating composition in which the first component is an aqueous polyol phase containing an acid-containing polyol combined with an amine phase containing one or more amines having active hydrogens that are reactive with isocyanate groups. The second component is one or more polyisocyanates. Example 9 shows a black pigmented solution prepared using 100 wt parts aqueous polyol/amine, 25 parts acid functional acrylic resin, 20 parts water, and 10 wt parts black pigment dispersion. The aqueous polyol/amine comprises an acid-containing polyol, a nonacidic aromatic polyester diol, trimethylol propane and an amine blend. 100 parts of this black pigmented solution is then reacted with 50 parts of HDI trimer at NCO/OH=2/1. Since there is only one type of pigment present in the formulation, no apparent or visual flooding or floating would be evident.
U.S. Pat. No. 5,552,477 discloses a binder for a coating system which consists of a polyol component and a polyisocyanate component. The polyol component consists of a high molecular weight (Mn>500) acid containing polyol which is water dilutable and possesses hydroxyl groups, and a reactive diluent containing a low molecular weight polyol (Mn<500) which has at least one group that is reactive with isocyanates.
U.S. Pat. No. 4,120,841 discloses an acid functional acrylic copolymer for use in aqueous paints as a levelling agent to primarily eliminate craters and improve gloss, but to also prevent or decrease flooding by increasing wettability of the pigments.
J. R. Taylor and H. Foster, “The Pigmentation of Acrylic Resins”, JSDC December 1969, pp 579-588, recommends eliminating flooding and floating in solvent borne acrylic coatings by the addition of small amounts of silicone fluid (M.S. 200) or incorporation of a silicone treated calcium carbonate during the mill charge. The pigment particle size and surface treatment will also greatly affect degree of flocculation, therefore affecting flooding and floating. It is critical in coatings formulated using waterborne acrylic dispersions that the correct surfactants are chosen in the pigment dispersions. To ensure optimum color stability in the paint, surfactants with suitable HLB (hydrophilic lipophilic balance) values for the pigments used must be chosen.
P. Quednau, “How polymeric dispersants can reduce pigment paste stocks”, Paint & Ink International, January/February 1995, p 9 states that a major problem in the coatings industry is the flooding and floating behavior of some pigment dispersions. Pigment concentrates based on high molecular weight polymeric dispersants, either polyurethane or polyacrylate based, are recommended to achieve good pigment stability without flooding and floating. Both types of dispersants contain tertiary amines leading to strong adsorption on the pigment surfaces due to their basic character. These dispersants need to have a high molecular weight of 10,000-25,000 to be effective in steric hindrance and deflocculation of the pigment particles.
U.S. Pat. No. 4,978,708 discloses aqueous-based basecoat compositions comprising an anionic polyurethane principal resin and an anionic acrylic pigment grind resin. The coating compositions are alleged to exhibit good pigment wetting and dispersion characteristics with improved shelf life and color stability.
U.S. Pat. No. 3,578,635 discloses certain halogenated carbon blacks as pigments in the preparation of paint and lacquer compositions which possess excellent non-flooding properties and excellent tinting properties.
SUMMARY OF THE INVENTION
This invention is directed to a blend of an aqueous polymer emulsion with an aqueous pigmented polyol/amine composition and to its use in the production of a substantially solvent free, aqueous, pigmented two component polyurethane-polyurea coating composition. The pigmented polyol/amine composition contains at least one acidic polyol and at least one non-acidic polyol together with one or more amines and two or more different pigments, all in water. One or more reactive polyisocyanates can be combined with the aqueous mixture of the polymer emulsion and the pigmented polyol/amine composition to form a water based, substantially solvent free, pigmented two component polyurethane-polyurea dispersion which is useful in coating systems and exhibits substantially reduced or no pigment flooding or floating.
The polymer emulsion should be compatible with the pigmented polyol/amine composition. The polymer emulsion is used in an amount sufficient to afford a thixotropic mixt
Hegedus Charles Raymond
Lindenmuth Denise Luise
Pepe Frank Ralph
Air Products and Chemicals Inc.
Leach Michael
Niland Patrick D.
LandOfFree
Aqueous polymer emulsion-polyester polyol blend for reducing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous polymer emulsion-polyester polyol blend for reducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous polymer emulsion-polyester polyol blend for reducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2899604