Self-crosslinking polyurethane polymer hybrid dispersion

Details Self-crosslinking polyurethane polymer hybrid dispersion Self-crosslinking polyurethane polymer hybrid dispersion

2001-01-05

2002-10-08

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, C525S127000, C525S455000

Reexamination Certificate

active

06462127

ABSTRACT:

The present invention relates to an aqueous self-crosslinking polyurethane polymer hybrid dispersion based on oxidatively drying polyols having a very high degree of film hardness and good resistance to chemicals, a process for its preparation and its use as a binder for one- or two-component finishes, seals, adhesive bonds and coatings.
Owing to their good properties, such as adhesion to various substrates, abrasion resistance and flexibility and toughness, coating systems based on aqueous polyurethane dispersions and polyurethane polymer hybrid dispersions have become increasingly important in recent years.
For numerous applications in construction chemistry, where good resistance to chemicals in addition to a high degree of hardness is desired, a combination of physical and chemical drying is of interest. Such properties are possessed by, for example, alkyd resins. Alkyd resins are oil- or fatty acid-modified polycondensates or polyesters of polycarboxylic acids or polycarboxylic anhydrides and polyalcohols. Owing to their wide possibility for variation with respect to structure and composition, but also with regard to their universal applicability, they constitute an important group of synthetic surface coating binders.
The raw materials used are natural triglycerides (oils, fats) or defined synthetic fatty acids. The property profile of the alkyd resins may be varied through the type and amount of the long-chain fatty acids or oils present. Depending on the degree of unsaturation, a distinction is made between drying, semidrying and nondrying fatty acids or oils. Depending on the content of oils, a distinction is made between short-oil, medium-oil and long-oil alkyd resins.
The curing of drying alkyd resins is based on intermolecular crosslinking of double bonds of the unsaturated fatty acids. This polymerization is initiated by autoxidation processes (so-called autoxypolymerization). For the catalytic acceleration of the autoxidative drying and film formation, active and auxiliary drying agents or siccatives, which are generally metal salts of organic acids, may be added to the alkyd resins.
Alkyd resins can be reacted with other components, such as polyisocyanates, polyols, phenolic resins, epoxides, etc., to give polyurethane alkyd resins. In this reaction, long-oil alkyd resins containing hydroxyl groups are reacted with polyisocyanates in suitable organic solvents until free isocyanate groups are no longer present. These solvent-containing urethane alkyds are suitable in particular for high-quality coatings, primers, finishes and seals and are distinguished by rapid drying, a high degree of hardness, excellent mechanical stability, very good abrasion resistance, high water resistance and improved resistance to chemicals.
Fatty acid-modified, oxidatively drying polyurethane dispersions are synergistic combinations of alkyd resins and polyurethane resins, which combine the excellent property profile of both types of polymers. These self-crosslinking aqueous polyurethane dispersions can be prepared in the absence of a solvent (zero VOC) or in the presence of little solvent (low VOC) and are accordingly substantially more environmentally friendly than conventional solvent-containing urethane alkyds.
The preparation of aqueous polyurethanes has been known for-many years and is described in detail in many publications, e.g. Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Volume E 20, Part I, pages 1659-81; 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 economical compared with polyurethane dispersions, are suitable in particular for finishing, coating, sealing and adhesive bonding of the surfaces of metallic and mineral substrates and of wood-based materials and plastics.
The polyurethane polymer hybrid dispersions are synergistic combinations of pure polyurethane dispersions and pure plastics dispersions, whose property profile cannot be achieved by simply mixing the two types of dispersions. Polyurethane polymer hybrid dispersions are based on interpenetrating networks of polyurethane polymers and acrylate polymers, which may be linked to one another both physically and chemically. This type of dispersion requires special synthetic methods.
Fatty acid-modified, oxidatively drying polyurethane polymer hybrid dispersions are modified in a polyurethane dispersion as matrix by a type of emulsion polymerization of acrylate and styrene derivatives. This makes it possible for the excellent properties of an oxidatively drying polyurethane dispersion to be combined synergistically with the cost benefit of a plastics dispersion.
Pure polyurethane dispersions are too expensive for a large number of applications in construction chemistry. In the polyurethane polymer hybrid dispersions, the advantageous properties of the pure polyurethane dispersions are therefore combined with the cost benefit of the pure plastics dispersions. For these reasons, the more economical polyurethane polymer hybrid dispersions are becoming increasingly important compared with conventional polyurethane dispersions in application in construction chemistry.
With regard to compliance with existing and future emission directives, too, considerable efforts have been made in recent years to develop water-based polyurethane polymer hybrid dispersions having as low a content as possible of volatile organic compounds (VOC). These low-solvent (low VOC) or solvent-free (zero VOC) products offer both ecological and economic advantages and correspond in their performance and their material properties substantially to conventional polyurethane systems.
In construction chemistry, in particular self-crosslinking polyurethane polymer hybrid dispersions having a very high degree of hardness and good resistance to chemicals are desirable for cost reasons, said dispersions being obtainable with the aid of efficient and simultaneously universal preparation processes.
The hybrid systems known from the relevant patent literature still have a number of disadvantages which limit replacement of polyurethane dispersions in specific fields of use.
Thus, known preparation processes for polyurethane polymer hybrid dispersions, as described, for example, in the publications EP 0 649 865 A1, EP 0 657 483 A1, EP 0 742 239 A1 and U.S. Pat. No. 5,521,246, are very expensive with respect to the synthetic procedure.
The patent application EP 0 649 865 A1 discloses a process in which a part of the acrylate component is added to the prepolymer solution during the polyol-isocyanate reaction. The second part of the acrylate component is metered in at a later time and the last part is added to the prepolymer solution before the dispersing.
According to the patent application EP 0 657 483 A1, the acrylate component is metered in in a plurality of steps during the polyurethane prepolymer synthesis itself at 70° C. Before the dispersing in water, a further part of the acrylate component is then added to the polyurethane-acrylate prepolymer, and the initiator component, dissolved in an organic solvent or as such, is then added at 80° C.
U.S. Pat. No. 5,521,246 describes a similar process in which the acrylate component is likewise added stepwise during the polyurethane prepolymer synthesis at 75° C. After the neutralization at 25° C. and the dispersing in water, the initiator component, dissolved in N-methylpyrrolidone, is added. Only thereafter is the chain extension with ethylenediamine effected and the last part of the acrylate component added to the dispersion. Polymerization is carried out for 2 to 3 hours at a temperature of 65° C. However, publications on the polymerization of acrylates with 2,2′-azobisisobutyronitrile demonstrates that these conditions are insufficient for complete monomer conversion.
As disclosed in EP 0 742 239 A1 and EP 0 668 300 A1, additional emulsifiers (surfactants) are often nece

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