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
2001-08-28
2004-07-20
Gorr, Rachel (Department: 1711)
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...
C525S127000, C522S096000
Reexamination Certificate
active
06765057
ABSTRACT:
The present invention relates to a process to prepare aqueous dispersions of anionic polyurethanes and polyurethane-polyacrylate hybrids containing tertiary amino functional acrylic oligomers, polymers or copolymers as acid-neutralizing agents, in the absence of volatile tertiary amines.
INTRODUCTION
Aqueous dispersions of polyurethanes or polyurethane-polyacrylate hybrids are well known as basis for the production of coating compositions. They may be used for protective or decorative coating, optionally in combination with additives like coloring agents, pigments, matting agents, and the like. Polyurethanes can possess many desirable properties such as good chemical resistance, water resistance, solvent resistance, toughness, abrasion resistance, durality. Thermoplastic polyurethane-polyacrylate hybrid dispersions became of interest regarding to polyurethanes because of their lower raw material costs and they became of interest regarding to polyacrylates because of their better performance.
As is by now well known in the art, aqueous polyurethane dispersions are particularly advantageously prepared by dispersing an isocyanate-terminated polyurethane prepolymer bearing ionic and/or non-ionic dispersing groups into an aqueous medium and than reacting the prepolymer with an active hydrogen containing chain extender while dispersed in the aqueous medium. See e.g. UK-patents 1549458 and 1549459.
Generally polyurethane-polyacrylate hybrids are prepared by an addition polymerisation of acrylic monomers in a polyurethane dispersion. The acrylic monomers can be added to the polyurethane dispersion, which is described in for example DE 1953348, EP643734 but they can also be added during the preparation of the polyurethane dispersion at several stages, which is described in for example U.S. Pat. No. 4,644,030, EP742239. The vinylic monomers can be added during or after the polyurethane prepolymer formation and in these cases they function as viscosity reducing solvents. The advantage is that no or less other organic solvents have to be used, and a better homogeneity is obtained. The addition polymerisation is executed after the formation of the aqueous polyurethane. Moreover, further vinylic monomers may be added during the polymerisation as described in for example EP 308115.
Dispersibility of the polyurethanes or polyurethane-polyacrylate hybrids in water can be achieved by incorporation of appropriate chain pendant ionic groups, chain pendant non-ionic hydrophilic groups, or in-chain non-ionic hydrophilic groups in the structure of the polyurethane polymer. If suitable, external surfactants can be applied in addition. Preferably anionic groups are incorporated into the polyurethane backbone, such as carboxylic, sulfonic, sulfate or phosphate groups, by reaction of an isocyanate reactive compound having at least one acid group with a polyisocyanate. Most common is the incorporation of a carboxylic acid functional compound.
The carboxylic acid functions are generally neutralized before or during dispersion of the polyurethane prepolymer or prepolymer-vinylic monomer solution in water with a volatile tertiary amine. Anorganic bases are less convenient, since the polyurethane will coagulate when they are applied or it will provide highly water sensitive films or coatings. To prevent coagulation it is suitable to incorporate a great number of hydrophilic polyethoxy chains into the polymer system.
A disadvantage of the application of volatile tertiary amines as neutralizing agent is that they evaporate during the film formation, and therefore will cause environmental pollution,
The present invention offers a process to prepare aqueous dispersions of anionic polyurethanes or of polyurethane-polyacrylate hybrids containing no volatile tertiairy amines.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a process to prepare a dispersion of a polyurethane or a polyurethane-polyacrylate hybride which contains no volatile tertiary amines as neutralizing agents for carboxylic acid groups.
Accordingly the present invention relates to a process for the preparation of an aqueous dispersion of an anionic polyurethane in which initially a tertiary amino-functional acrylic monomer of formula I
wherein,
R, R
1
, R
2
, R
3
, R
4
and R
5
are organic groups which have no reactivity towards the double bond or the tertiary amine function, is used as neutralizing agent for pendant carboxylic acid groups in dispersions of a polyurethane or a polyurethane/polyacrylate, whereafter the unsaturated monomers undergo in situ an addition polymerisation, optionally together with other unsaturated monomers,
characterized in that the aqueous dispersion of the anionic polyurethane is prepared by the steps of
preparation of an isocyanate functional anionic polyurethane prepolymer, optionally in the presence of vinylic monomers
mixing of the isocyanate terminated anionic polyurethane prepolymer with a tertiary-amino functional unsaturated monomer and optionally other vinylic monomers
followed by dispersion of the obtained mixture into water, and chain extension of the polyurethane prepolymer with an active hydrogen compound during or after the dispersion in water,
initiating radical polymerisation of the vinylic monomers, including the tertiary amino functional unsaturated monomers.
Advantage of this process is that after the polymerisation of the unsaturated monomers containing a tertiary amine the dispersions contain no volatile amines and therefore environmental problems will be eliminated. Another advantage of the process is that the unsaturated monomers containing a tertiairy amine function act as viscosity reducing solvents during the formation of the aqueous polyurethane. This effect is improved when other unsaturated monomers are present as well and an aqueous dispersion of a polyurethane-polyacrylate hybride is formed. In both situations less or sometimes even no other organic solvents have to be be used, and a better homogeneity is obtained.
A further part of the invention is a process in which the isocyanate terminated prepolymer is reacted with 0-100% of a stoichiometric amount of a hydroxy functional unsaturated monomer before the dispersion in water.
As a result the polyurethane prepolymer is completely or partially functionalized with acrylic double bonds by complete or partial reaction of the isocyanate functions of the prepolymer with a hydroxy functional unsaturated monomer. As a result the polyurethane polymer system will contain double bonds and will contribute to the addition polymerisation.
The acid groups in the prepolymer are initially neutralized by a tertiary amine functional unsaturated monomer. In the process of the invention a tertiary amine functional acrylic polymer is formed during the process by radical polymerisation of the tertiary-amino functional unsaturated monomers. When other unsaturated monomers are present a copolymer will be formed during the process including the tertiary amine functional unsaturated monomers and the other unsaturated monomers. The other vinylic monomers which may be present are selected from acrylic alkyl esters, methacrylic alkyl esters, styrene esters or ethers of vinyl alcohol. The other vinylic monomers are present in an amount of 0 to 90%.
The present invention further comprises the dispersions prepared by the process and coatings or films derived from dispersions prepared by the process.
At low levels of other vinylic monomers or, without the presence of vinylic monomers, the performance of the films or coatings of the dispersions will be comparable with the performance of the films or coatings of polyurethane dispersions. At higher levels of other vinylic monomers the performance of the films or coatings of the dispersions will be comparable with the performance of the films or coatings of polyurethane-polyacrylate hybride dispersions.
Both the polyurethane and the acrylic monomers may contain additional functional groups with the objective to improve the waterdispersibility, to improve adhesion to substrates at application
Brutau Montserrat Pous
Chirivella Josep Oller
Martinez Mario Jimenez
Gorr Rachel
Myers Jeffrey D.
Peacock, Myers & Adams P.A.
Stahl International B.V.
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