Curable polyurethane polymer

Details Curable polyurethane polymer Curable polyurethane polymer

2000-07-11

2003-03-25

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S096000, C522S090000, C522S174000, C522S084000, C524S507000, C524S589000, C524S590000, C524S591000, C524S839000, C524S840000, C525S123000, C525S455000, C528S044000, C528S060000, C528S059000, C528S061000, C528S065000, C528S066000, C528S067000

Reexamination Certificate

active

06538046

ABSTRACT:

The present invention relates to a curable polyurethane polymer containing in copolymerized form at least one hydroxyl-containing prepolymer having at least one thermally or photochemically free-radically polymerizable &agr;,&bgr;-ethylenically unsaturated double bond. The invention further relates to an aqueous polymer dispersion comprising such a curable polymer in dispersed form and to the use of said polymer or polymer dispersion for coating substrates.
Aqueous polyurethane dispersions comprising components having ethylenically unsaturated groups have found broad application. They are used in particular to produce coatings on inflexible substrates such as wood, for example, and on flexible substrates, such as leather, for example. Their crosslinkability means that films formed from said dispersions generally have good performance properties, such as chemical resistance and increased mechanical stability as compared with uncrosslinkable polyurethane dispersions. To produce coatings on substrates having little or no heat resistance it is usual to use polyurethane dispersions which are radiation curable. An important property of these UV or EB (electron beam) curable dispersions is that as soon as the water they contain has evaporated the resulting films have a highly tack-free surface which may already be capable of withstanding mechanical stresses. This firstly permits the coating, inter alia, of substrates which owing to their external form exhibit radiation shadow regions and thus for technical reasons are not fully accessible to radiation curing. Secondly, the substrates can thus be subjected to mechanical operations even before curing. This is particularly important in the context of the production of coatings on wood, since in this case the surfaces are generally sanded before curing in order, for example, to remove the erect wood fibers and, in a second, coating step, to obtain a smooth surface. A further 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 high gloss coatings on leather. EP-A-0 554 784 describes aqueous dispersions of a radiation-curable polyurethane whose structural components include polyols and polyisocyanates having isocyanurate or biuret groups. Evaporation of the water from the abovementioned polyurethane dispersions produces coatings which before radiation curing are still not able to withstand mechanical stresses and/or which produce tacky surfaces.
EP-A-0 209 684 describes aqueous emulsions based on ionic urethane urea acrylates.
None of the abovementioned publications describes polymer dispersions based on polyurethanes containing 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 used 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, forming a mercapto ether bridge.
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,
b) from 5 to 95% by weight of a prepolymer or prepolymer mixture dispersible with the aid of c), and
c) from 0 to 30% by weight of a protective colloid.
Component a) 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 are not, therefore, attached to the polyurethane component a). 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 radiation-curable polyurethanes formed from
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 from 400 to 6000 g/mol,
c) from 0 to 0.8 gram equivalent of OH of a polyol having a molecular weight of from 62 to 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 equivalents 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 of NH of a compound with ionic groups, or groups which can be converted to ionic groups, having at least one isocyanate-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 from 0.9 to 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 used in amounts of from 0.02 to 0.08 gram equivalent of OH. The amount 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 to 120 mg KOH/g, and p
1
b) from 0.1 to 20% by weight of one or more monofunctional and/or difunctional, isocyanate-reactive compounds containing cationic groups, anionic groups and/or groups which exert a dispersing action by virtue of ether units, with
c) from 10 to 50% by weight of one or more polyisocyanates, and by subsequent reaction with
d) from 0.1 to 10% by weight of one or more diamines and/or polyamines.
The coatings obtained with these dispersions are in need of improvement as regards their performance properties. For instance, the films as yet uncured by radiation have an inadequate pendulum hardness; in other words, under mechanical load, the coated substrates adhere to one another and to other uncoated surfaces, and surface damage may remain when the substrates are subsequently separated. This is a disadvantage in particular if the dispersions as described above are used to coat surfaces with have shadow regions that are difficult to access for radiation curing. The cured films as well are in need of improvement in terms of their mechanical properties, especially in terms of a satisfactory combination of surface hardness with film flexibility.
None of the abovementioned documents describes curable polyurethane polymers where the molar ratio of incorporated isocyanato components to components having isocyanate-reactive groups is chosen such that not more than 90% of the latter are reactive.
It is an object of the present invention to provide a curable polyurethane polymer suitable for preparing aqueous polymer dispersions having good performance properties.
We have found that this object is achieved by a curable polyurethane polymer where the ratio of isocyanate group equivalents of the incorporated isocyanato components to equivalents of isocyanate-reactive groups of the components containing active hydrogen atoms is in a range from about 0.4:1 to 0.9:1.
The present invention therefore provides a curable polyurethane polymer containing in copolymerized form
A) from 10 to 60% by w

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