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
2001-03-22
2003-05-20
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...
C524S589000, C524S590000, C524S591000, C524S839000, C524S840000, C525S123000, C525S128000, C525S455000
Reexamination Certificate
active
06566438
ABSTRACT:
The present invention relates to an aqueous polyurethane/polymer hybrid dispersion with high film hardness and a low minimum film formation temperature (MFFT), to a process for preparing it and to its use as a binder for one- or two-component coating materials, seals, adhesive bonds, and coatings.
Coating systems based on aqueous polyurethane dispersions and polyurethane/polymer hybrid dispersions have gained increasingly in importance in recent years owing to their good properties such as adhesion to different substrates, abrasion resistance, and also flexibility and touchness. The preparation of aqueous polyurethanes has been known for many years and is described in detail in a great number of publications, e.g., Houben-Weyl, Methoden der organischen Chemie, volume E 20, part I, pp. 1659-1681; D. Dieterich, Prog. Org. Coat. 1981, 9, 281-330; J. W. Rosthauser, K. Nachtkamp, Journal of Coated Fabrics 1986, 16, 39-79; R. Arnoldus, Surf. Coat. 1990, 3 (Waterborne Coat.), 179-98.
The polyurethane/polymer hybrid dispersions, which are more favorable in cost terms than polyurethane dispersions, are particularly suitable for the coating, sealing and adhesive bonding of the surfaces of metallic and mineral substrates and also of woodbase materials and plastics.
The polyurethane/polymer hybrid dispersions represent synergistic combinations of straight polyurethane dispersions and straight polymer dispersions, whose profile of properties cannot be achieved by a simple blending of the two types of dispersion. Polyurethane/polymer hybrid dispersions are based on inter-penetrating networks of polyurethane polymers and acrylic polymers, which may be linked with one another both physically and chemically. This type of dispersion requires specific synthesis methods. Straight polyurethane dispersions are too expensive for numerous building applications. In the polyurethane/polymer hybrid dispersions, therefore, the advantageous properties of the straight polyurethane dispersions are united with the cost advantage of the straight polymer dispersions. For these reasons, the more cost-effective polyurethane/polymer hybrid dispersions are gaining more and more in importance relative to conventional polyurethane dispersions in building applications.
With a view, too, to adherence to existing and future emissions guidelines, considerable efforts have been undertaken in recent years to develop water-based polyurethane/polymer hybrid dispersions containing a very small amount of volatile organic solvents (VOCs, volatile organic compounds). These low-solvent (low-VOC) or solvent-free (zero-VOC) products offer both environmental and economic advantages and already correspond substantially in terms of their performance and materials properties to conventional polyurethane systems.
In chemicals for the building industry, there is a desire—on cost grounds—in particular for polyurethane/polymer hybrid dispersions with high film hardness and good chemical resistance which can be made accessible with the aid of rational and at the same time universal preparation processes.
The hybrid systems known from the relevant patent literature still have a number of disadvantages, which restrict their replacement of polyurethane dispersions in certain applications.
For instance, known preparation processes of polyurethane/polymer hybrid dispersions as described, for example, in the documents EP 0 649 865 A1, EP 0 657 483 A1, EP 0 742 239 A1, and U.S. Pat. No. 5,521,246, are highly complicated with regard to the synthesis procedure.
The patent application EP 0 649 865 A1 discloses a process in which a portion of the acrylate component is added to the prepolymer solution during the polyol/isocyanate reaction. The second portion of the acrylate component is metered in at a later point in time, and the final portion is added to the prepolymer solution prior to dispersion.
In accordance with the patent application EP 0 657 483 A1, the acrylate component is metered in during the actual synthesis of the polyurethane prepolymer at 70° C. in a number of steps. Then, before the polyurethane acrylate prepolymer is dispersed in water, a further portion of the acrylate component is added and the initiator component is added subsequently at 80° C. as it is or in solution in organic solvent.
The U.S. Pat. No. 5,521,246 describes a similar process, in which the acrylate component is again added in steps at 75° C. during the polyurethane prepolymer synthesis. Following neutralization at 25° C. and dispersion in water, the initiator component, dissolved in N-methylpyrrolidone, is supplied. Only then is chain extension carried out with ethylenediamine, and the final portion of the acrylate component is added to the dispersion. The polymerization is conducted for 2 to 3 hours at a temperature of 65° C. Publications on the polymerization of acrylates with 2,2′-azoisobutyro-nitrile are evidence that these conditions are inadequate for complete monomer conversion.
As disclosed in EP 0 742 239 A1 and EP 0 668 300 A1, additional emulsifiers (surfactants) are often necessary in order to ensure sufficient stability of the polyurethane micelles during the polymerization.
High film hardnesses of polyurethane/polymer hybrid dispersions as described in the patent applications EP 0 657 483 A1 and EP 0 668 300 A1 have to date been achieved by means of complicated synthesis processes, by chemical postcrosslinking of the dispersions with corresponding reagents, or, as described in WO 93/24551, by means of polyesterpolyols modified with fatty acid. EP 0 745 625 A1 discloses, for example, a polyurethane dispersion where bisaldimines, which are in equilibrium with the corresponding bisenamines, are incorporated into polyurethane prepolymers by way of amino groups and, as a result, the film hardness of the resulting polyurethane dispersions is increased. In the aforementioned documents, moreover, high film hardnesses are often achieved only with hybrid dispersions, which because of their complicated synthesis contain relatively large amounts of organic solvents (≧10% by weight) and have a minimum film formation temperature of ≧20° C.
It was an aim of the present invention to develop a low-solvent polyurethane/polymer hybrid dispersion with high film hardness, good chemical resistance and low minimum film formation temperature, said dispersion not having the aforementioned disadvantages of the prior art and at the same time being preparable cost-effectively by a simple synthesis route.
This object has been achieved in accordance with the invention by the provision of an aqueous polyurethane/polymer hybrid dispersion with high film hardness, obtainable by reacting the reaction components (A) to (G) specified below. The dispersion accordingly comprises as reaction components
(A) from 3 to 25% by weight of a polyol component consisting of
(i) from 2 to 20% by weight of a high molecular mass polyol having two or more polyisocyanate-reactive hydroxyl groups and a molar mass of from 500 to 4000 daltons,
(ii) from 0.5 to 5% by weight of a low molecular mass polyol having two or more polyisocyanate-reactive hydroxyl groups and a molar mass of from 50 to 500 daltons,
(iii) from 0.5 to 3% by weight of a low molecular mass, anionically modifiable polyol having two or more polyisocyanate-reactive hydroxyl groups and also one or more polyisocyanate-inert carboxyl groups and a molar mass of from 100 to 200 daltons,
(B) from 2 to 20% by weight of a polyisocyanate component consisting of one or more polyisocyanates, polyisocyanate homologs or polyisocyanate derivatives having two or more aliphatic and/or aromatic Isocyanate groups,
(C) if desired, from 0 to 6% by weight of a solvent component consisting of
(i) at least one polyisocyanate-inert organic solvent which following the preparation of the polyurethane/polymer hybrid dispersion may remain therein or may be removed in part or in whole by distillation, and/or
(ii) at least one polyisocyanate-inert reactive diluent consisting of at least one polyisocyanate-inert organic compound having one or more free-rad
Ingrisch Stefan
Kern Alfred
Maier Alois
Weichmann Josef
Winkelmann Herbert
Fulbright & Jaworski L.L.P.
Niland Patrick D.
SKW Bauchemie GmbH
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