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
1999-03-11
2001-03-27
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, C525S455000
Reexamination Certificate
active
06207744
ABSTRACT:
The present invention relates to a curable polyurethane polymer which comprises in copolymerized form at least one hydroxyl-containing prepolymer having at least one &agr;,&bgr;-ethylenically unsaturated double bond that can be free-radically polymerized by thermal or photochemical means. The invention additionally relates to an aqueous polymer dispersion which comprises such a curable polymer in dispersed form, to processes for preparing the dispersion, and to its use for producing coatings.
Aqueous polyurethane dispersions comprising components having ethylenically unsaturated groups have found broad application. They are used in particular to produce coatings on nonflexible substrates, such as wood, and on flexible substrates, such as leather. Owing to their capacity to crosslink, the films obtained from these dispersions have good performance properties, such as chemical resistance and enhanced mechanical stability, as compared with noncrosslinkable polyurethane dispersions. In addition, in order to produce coatings on substrates which have little or no ability to withstand thermal stress, it is common to employ polyurethane dispersions which are radiation curable. An important property of these dispersions which can be cured by UV radiation or by means of electron beams is that as soon as the water present has evaporated they produce films which give a highly tack-free surface which may already be able to withstand mechanical stress. On the one hand, this allows the coating even of those substrates whose exterior form means that they exhibit radiation shadow regions and hence for technical reasons are not entirely accessible to radiation curing. On the other hand, it means that the substrates can be worked on mechanically even prior to curing. This is particularly important in connection with the production of coatings on wood, since in this case the surfaces prior to curing are generally sanded in order, for example, to remove the erect wood fibers and, in a second, coating step, to obtain a smooth surface. Another advantage of these coatings is their freedom from tack, with the consequence that the surfaces do not stick to one another, for example, when the substrates are stacked.
DE-A-34 37 918 describes aqueous oligourethane dispersions with incorporated unsaturated groups and their use for producing highly lustrous coatings on leather. They are prepared by reacting an isocyanate-functional oligourethane prepolymer with a hydroxyl-containing ester of acrylic acid and/or methacrylic acid with at least dihydric aliphatic alcohols, such as hydroxyalkyl (meth)acrylates or di(meth)acrylic esters of 1,1,1-trimethylolpropane or glycerol.
EP-A-0 554 784 describes aqueous dispersions of a radiation-curable polyurethane whose structural components comprise isocyanurate- or biuret-functional polyisocyanates and polyols.
Evaporation of the water from these polyurethane dispersions produces coatings which before radiation curing are still not able to withstand mechanical stress and/or which produce tacky surfaces.
EP-A-0 209 684 describes storage-stable, radiation-curable, aqueous emulsions which are free from isocyanate groups and are based on ionic urethane urea acrylates. In order to prepare them, a cycloaliphatic polyisocyanate in an organic solvent is reacted first with a hydroxyalkyl acrylate and a polyhydroxy compound and then with sodium salts of aminocarboxylic acids and/or with aliphatic diamines, the product then being emulsified by adding water and removing the solvent by distillation. The mechanical properties of the films obtained from these dispersions are in need of improvement, especially as regards their sandability.
None of the abovementioned publications describes polymer dispersions based on polyurethanes which comprise in copolymerized form hydroxyl-containing prepolymers having &agr;,&bgr;-ethylenically unsaturated double bonds.
U.S. Pat. No. 4,357,221 describes a process for coating electroconductive parts in which an anionic polyurethane adduct is employed that has &agr;,&bgr;-ethylenically unsaturated, radiation-curable double bonds. This product is prepared by reacting a solution of a polyurethane based on an acrylic ester diol, a low- or high-molecular mass chain extender and a polyisocyanate with a salt of a mercaptocarboxylic acid. The carboxylate group is introduced into the polyurethane here by addition of the mercapto group not onto an isocyanate group but instead onto one of the double bonds in the polyurethane, so as to form a mercapto ether bridge. The resulting anionic polyurethanes have a higher content of ionic groups than is generally the case for film-forming binders, being at least 4%. The double bond values of the polyurethanes are stated with a theoretically possible range from 0.3 to 3 mol per 1000 g of polyurethane, although the specific working examples only embrace polyurethanes having double bond values of at most 0.96 mol per 1000 g.
DE-A-40 31 732 describes radiation-curable aqueous binder dispersions which feature
A) from 5 to 95% by weight of a self-dispersible polyurethane containing not more than 2 mol of polymerizable ethylenically unsaturated groups per kg of polyurethane,
B) from 5 to 95% by weight of a prepolymer or prepolymer mixture dispersible with the aid of C), containing from 1 to 10 mol of polymerizable ethylenically unsaturated groups per kg of prepolymer or prepolymer mixture, and
C) from 0 to 30% by weight of a protective colloid.
Component A) per se is not an acrylate-containing prepolymer. The prepolymers B) can be polyesters, polyethers, polyepoxides or polyurethanes, which are added separately to the aqueous dispersions, and which therefore are not attached to the polyurethane component A). The content of polymerizable ethylenically unsaturated groups employed in the working examples for dispersion A) is not more than 0.32 mol/kg of the mixture of A), B) and C). In the working examples, the presence of a protective colloid is mandatory. The coatings obtained with the dispersions based on a mixture of A) and B) are in need of improvement as regards their performance properties. For instance, the pendulum hardness of the radiation-cured films of the working examples is at most 115 s.
EP-A-0 392 352 describes aqueous dispersions of polyurethanes which can be crosslinked by the action of high-energy radiation, comprising
a) 1 gram equivalent of NCO of a polyisocyanate,
b) from 0.1 to 0.8 gram equivalent of OH of a polyol having a molecular weight of between 400 and 6000 g/mol,
c) from 0 to 0.8 gram equivalent of OH of a polyol having a molecular weight of between 62 and 399 g/mol,
d) from 0 to 0.4 gram equivalent of NH of a polyamine having at least two isocyanate-reactive amino groups,
e) from 0 to 0.4 gram equivalent of OH of an amino alcohol having at least one isocyanate-reactive amino group,
f) from 0.05 to 0.5 gram equivalent of OH or NH of a compound with ionic groups, or groups which can be converted into ionic groups, having at least one iosocyanate-reactive hydroxyl or amino group,
g) from 0 to 0.2 gram equivalent of OH of a monofunctional polyetherol, and
h) a compound having at least one ethylenically unsaturated group and at least one hydroxyl group, with the provisos that (i) the sum of the OH and NH gram equivalents is between 0.9 and 1.2, (ii) the components under a) to h) can be in the form of individual components or mixtures, and (iii) the ethylenically unsaturated component h) is employed in amounts of from 0.02 to 0.08 gram equivalent of OH. The content of polymerizable ethylenically unsaturated groups per 1000 g of polyurethane is therefore very low and is not more than 0.166 mol/kg.
DE-A-195 25 489 describes polyester acrylate urethane dispersions based on hydroxyl-containing polyester acrylate prepolymers. These dispersions are prepared by polyaddition of
A) from 40 to 90% by weight of one or more hydroxyl-containing polyester acrylate prepolymers having an OH content of from 40 to 120 mg of KOH/g and
B) from 0.1 to 20% by weight of one or more mono- and/or difunctional, isocyanate-reacti
Koniger Rainer
Lebkücher Werner
Paulus Wolfgang
Reich Wolfgang
BASF - Aktiengesellschaft
Niland Patrick D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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