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
2002-04-11
2004-09-07
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...
C524S591000, C524S839000, C524S840000, C525S123000, C525S128000, C525S455000
Reexamination Certificate
active
06787596
ABSTRACT:
The present invention relates to a solvent-free polyurethane-polymer hybrid dispersion having a high solids content of polymer or formulation constituents and to its use.
The binder class consisting of the aqueous or water-based polyurethanes has been known for more than 40 years. The property profile of the water-based polyurethanes has been continuously improved in the past decades, which is impressively demonstrated by a large number of patents and publications on this topic area. There are three reasons for the fact that aqueous polyurethanes have acquired increasing commercial importance precisely in recently years:
1. The increasing stringency of the environmental legislation requires the development of ecologically and physiologically compatible products for which the emissions of solvents and other volatile organic compounds (VOC) are minimized.
2. The use of expensive organic solvents in conventional and aqueous polyurethanes is undesired for economic reasons.
3. The performance of aqueous polyurethanes reaches or surpasses that of even the conventional solvent-based polyurethanes.
Water-based polyurethanes are also becoming more and more important as binders in applications involving construction chemistry. In construction chemistry, in particular polyurethane dispersions and polyurethane-polymer hybrid dispersions having a high solids content of polyurethane polymer or formulation constituents are desired, which dispersions can be provided with the aid of efficient and at the same time universal preparation processes. Low-solvent (low VOC) or solvent-free (zero VOC) products are of primary importance.
The chemistry and technology of the water-based polyurethanes has been known for many years and is described in detail in a large number of publications, e.g. D. Dieterich, K. Uhlig in
Ullmann's Encyclopedia of Industrial Chemistry,
Sixth Edition 1999 Electronic Release. Wiley-VCH; D. Dieterich in
Houben
-
Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry
], Vol. E20, H. Bartl, J. Falbe (Editors), Georg Thieme Verlag, Stuttgart 1987, page 1641 et seq.; D. Dieterich, Prog. Org. Coat. 9 (1981) 281-330; J. W. Rosthauser, K. Nachtkamp, Journal of Coated Fabrics 16 (1986) 39-79; R. Arnoldus, Surf. Coat. 3 (Waterborne Coat.) (1990), 179-98.
Aqueous polyurethane dispersions consist of polyurethane polymers or polyurethane-polyurea polymers which contain both urethane groups and urea groups and are obtainable by polyaddition reactions of polyols, polyisocyanates and polyamines. Polyurethane prepolymers are first prepared from the polyols and the polyisocyanates and are then dispersed in the aqueous phase and are subjected to chain extension with polyamines with synthesis of the polyurethane-polyurea polymers. The polyurethane polymers also contain a sufficient amount of hydrophilic groups which ensure stabilization in the aqueous phase. These hydrophilic groups are anionic, cationic or nonionic groups. The charge density of the hydrophilic groups in relation to the polyurethane polymer depends on the characteristics and on the stoichiometry of the structural components used. Polyurethane dispersions are two-phase systems which consist of micelles with polyurethane polymers and an aqueous phase. In the drying of the polyurethane dispersions, coalescence or fusion of the micelles and film formation of the polyurethane polymers take place.
The prepolymer mixing process and the solvent process have become most important for the preparation of polyurethane dispersions in industry.
However, these conventional processes for the preparation of polyurethane dispersions are associated with various problems.
In the prepolymer mixing process, significant amounts of high-boiling and water-soluble solvents, such as, for example, N-methylpyrrolidone, are added in order to reduce the viscosity of the polyurethane prepolymers. These solvents remain in the polyurethane dispersion after the preparation. During drying of the polyurethane dispersions or of the products prepared therefrom, these solvents are released into the environment. In addition to the solvent content present, the low solids contents, the generally moderate material properties and the large amounts of the hydrophilic groups required for stabilizing the polyurethane dispersions are disadvantageous. However, the prepolymer mixing process is a simple and efficient preparation process having a large synthetic range, which is very advantageous in many cases.
In the solvent process or acetone process, the complete synthesis of the polyurethane polymers is carried out in the presence of large amounts of low-boiling and water-soluble solvents, such as, for example, acetone or methyl ethyl ketone. After the preparation of the polyurethane dispersion, the solvents have to be removed again by a complicated redistillation, and the resulting polyurethane dispersions are therefore substantially solvent-free. In addition to the freedom from solvent, the high solids contents, the excellent material properties and the small amounts of the hydrophilic groups required for stabilizing the polyurethane dispersions are advantageous. However, the solvent process is a complicated and economically nonoptimal preparation process having a low space/time yield, which is very disadvantageous particularly with regard to applications involving construction chemistry.
There are also various combinations of prepolymer, mixing process and solvent process, which however have similar problems. Thus, a mixture of low-boiling and high-boiling solvents can be used in the polymer mixing process or the complete synthesis of the polyurethane dispersion can be transferred to the aqueous phase in the solvent process.
Recently, efforts have increasingly been made by the producers of polyurethane dispersions to replace solvents such as N-methylpyrrolidone by ecologically safe glycol ethers, such as, for example, dipropylene glycol dimethyl ether (Proglyde DMM® from Dow), which are not subject to labeling requirements. However, such a changeover leads to an increase in the costs of the prepolymer mixing process.
Polyurethane dispersions and acrylate dispersions are widely used in finishes and coatings, but both binder types have specific advantages and disadvantages. Acrylate dispersions generally have only a moderate property profile but are economical. Polyurethane dispersions on the other hand have excellent performance in combination with significantly higher costs. Simple blends of polyurethane dispersions and acrylate dispersions are therefore frequently used as price/performance compromise, but the material properties of these blends are usually poorer than would be expected from the known “mixing rules”.
In order to achieve a true price/performance advantage, aqueous polyurethane-acrylate hybrid dispersions have therefore increasingly been developed in recent years. The preparation of these polyurethane-polymer hybrid dispersions is carried out by an in situ polymerization. There, the monomers are subjected to a free radical polymerization in the presence of polyurethane base dispersions and suitable initiator systems. Micellar structures which, at the molecular level, consist of physically linked polyurethane chains and polymer chains are present in the resulting hybrid systems. The glass transition temperature, which extends over wide ranges (>50° C.), can be used as an indicator for the formation of these interpenetrating networks. Without corresponding modification of the polyurethane dispersions, there is no additional chemical linkage between the polyurethane chains and polymer chains. The cohesion of the macromolecules is due firstly to the mutual entanglement of the polyurethane chains and polymer chains and secondly to intermolecular interaction forces. However, it is not possible to rule out the fact that grafting of polymer chains onto polyurethane chains takes place to a small extent, which leads to an increase in the stability of the hybrid system. Owing to their particular morphology, polyurethane-polymer hybrid
Bergs Ralph
Ingrisch Stefan
Kern Alfred
Maier Alois
Temme Werner
Fulbright & Jaworski L.L.P.
Niland Patrick D.
SKW Bauchemie GmbH
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