Latent cross-linking aqueous dispersions containing...

Details Latent cross-linking aqueous dispersions containing... Latent cross-linking aqueous dispersions containing...

2001-02-15

2003-04-22

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...

C524S507000, C524S591000, C524S839000, C524S840000

Reexamination Certificate

active

06552119

ABSTRACT:

Latent-crosslinking aqueous polyurethane dispersions comprising
I) a disperse phase (P.I) including
Ia) a polyurethane (Ia) which has hydrophilic groups which make it dispersible in water and also has carbodiimide groups but essentially no carboxyl groups or
Ib) a physical mixture of
Ibi) a polyurethane (Ibi) which has hydrophilic groups which make it dispersible in water but has essentially no carbodiimide or carboxyl groups and
Ibii) a carbodiimide (Ibii) which has essentially no hydrophilic groups which make it dispersible in water and
II) a coherent aqueous phase (P.II) including in dissolved form a polycarboxylic acid which has no carbodiimide groups but has a solubility of at least 1 g/l at 25° C. in the coherent aqueous phase P.II.
The invention additionally relates to the use of the aqueous dispersions of the invention as impregnants, coating compositions or adhesives and to the impregnated, coated or adhesively bonded articles produced using these dispersions.
Aqueous dispersions comprising a polyurethane in dispersed form are widely known. In order that coatings produced from the polyurethane have particularly good mechanical properties, a crosslinking component is added to these dispersions. What is desired in particular here is for the crosslinker to bring about the build up in the molecular weight of the polyurethane only once the polyurethane dispersion has, following its application to the workpiece to be coated, already formed a film. Under these circumstances, films are obtained whose cohesion is particularly high, since in this case the polymer molecules of one dispersion particle can also be linked by a covalent bond to the polymer molecules of another, adjacent dispersion particle.
In the field of adhesives, for example, particularly good film cohesion is necessary in particular when the adhesive bond is subjected to mechanical loading accompanied by the action of heat.
To obtain adhesive bonds of sufficient strength even under such conditions, it has been recommended, in EP-A-206059, for example, to add a water-emulsifiable polyisocyanate as a crosslinker to the dispersions a short time before their processing as an adhesive.
The disadvantage of these two-component or two-pack systems, however, is that the pot life—that is the period within which these systems can be processed after they have been mixed—is severely restricted. Since, moreover, the two-component system cannot be stored for a long period and the processor has to carry out the extra step of preparing a defined quantity of adhesive which can be processed in the course of one working cycle, the effort which needs to be made by the adhesives processor in the case of two-component systems is higher than in the case of one-component systems.
U.S. Pat. Nos. 4,977,219 and 5,117,059 disclose mixtures of an aqueous dispersion of a carbodiimide and an aqueous dispersion of an emulsion polymer having carboxylate groups, the former dispersion being stabilized with the aid of customary surface-active substances.
U.S. Pat. No. 5,574,083 relates to a mixture of an aqueous dispersion of carbodiimides, said dispersion being stabilized by means of hydrophilic polyalkylene oxide radicals carried by the carbodiimides. These dispersions are blended with aqueous dispersions of an emulsion polymer having carboxylate groups.
EP-A-792908 discloses mixtures of an aqueous dispersion of a carboxyl-carrying polyurethane and an aqueous dispersion of a carbodiimide, the dispersion being stabilized with the aid of customary surface-active substances.
According to the teaching of the 4 abovementioned documents, the carbodiimides bring about an increase in the molecular weight of the carboxyl-containing polymers with which they are blended. The strength of adhesive bonds produced using these dispersions, especially under hot conditions, however, leaves much to be desired. Furthermore, the pot life of such mixtures is limited.
German Patent Application 19733044.4, unpublished at the priority date of the present invention, relates to aqueous dispersions of a polyurethane which carries carbodiimide groups.
German Patent Application 19828251.6, unpublished at the priority date of the present invention, relates to aqueous dispersions comprising 1. a disperse phase which comprises a polyurethane having carbodiimide groups or comprises a mixture of polyurethane and another polymer having carbodiimide groups, and 2. a further disperse phase which comprises a polymer having carboxyl groups.
It is therefore an object of the present invention to provide a further one-component polyurethane dispersion which does not have the disadvantages of the prior art. In particular, such dispersions should have good storage stability and should allow the production of heat-resistant adhesive bonds.
We have found that this object is achieved by the aqueous dispersions defined at the outset.
The disperse phase P.I generally contains from 0.01 to 1, preferably from 0.1 to 0.5, and, with particular preference, from 0.15 to 0.4 mol of carbodiimide groups per kg of monomers employed for the synthesis of the polyurethanes Ia or, respectively, Ibi and Ibii.
Suitable polyurethanes (Ia) are described, for example, in EP-A-792908.
In principle, suitable polyurethanes (Ia) are all hydrophilic polyurethanes whose synthesis involves the use of monomers having carbodiimide structural units. The carbodiimide structural units are introduced into the polyurethane (Ia) preferably by way of polyisocyanates (Ia1.1) comprising one or more of the carbodiimide structural units. Such polyisocyanates (Ia1.1) conform preferably to the general formula Ia1.1.1
OCN—(R
c
—N═C═N)
n
—R
c
—NCO  (Ia1.1.1)
where
R
c
is a divalent hydrocarbon radical with or without urea, urethane, ester, and/or ether groups, as is obtained by removing the isocyanate groups from a simple organic isocyanate or from a prepolymer which carries terminal isocyanate groups and has urethane groups with or without ether or ester groups and where, if there are two or more radicals R
c
in the same molecule, it is also possible for different radicals R
c
meeting said definition to be present simultaneously, and
n is an integral or (on average) fractional number from 1 to 20, preferably from 2 to 10.
The carbodiimide structural units are introduced into the polyurethane (Ia) with particular preference by way of polyisocyanates of the general formula Ia1.1.2
O═C═N—R
a
&Parenopenst;R
b
&Parenclosest;
m
N═C═O  Ia1.1.2
where
R
a
is a group of the formula Ia1.1.2.1
R
b
is a group of the formula Ia1.1.2.2
 and
m is a number from 1 to 20.
In general, the polyurethanes (Ia) are otherwise built up from
Ia1) diisocyanates which comprise
Ia1.1) carbodiimide structural units and, if desired, those which
Ia1.2) are free from carbodiimide structural units,
Ia2) diols of which
Ia2.1) from 10 to 100 mol-%, based on the overall amount of the diols (Ia2), have a molecular weight from 500 to 5000 and
Ia2.2) from 0 to 90 mol-%, based on the overall amount of the diols (Ia2), have a molecular weight from 60 to 500 g/mol,
Ia3) monomers which are different from the monomers (Ia1) and (Ia2) and have at least one isocyanate group or at least one isocyanate-reactive group and also at least one hydrophilic group or a potentially hydrophilic group which makes the polyurethanes dispersible in water,
Ia4) if desired, other polyfunctional compounds, different from the monomers (Ia1) to (Ia3), having reactive groups which are alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups, and
Ia5) if desired, monofunctional compounds, different from the monomers (Ia1) to (Ia4), having a reactive group which is an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group.
Suitable diisocyanatocarbodiimides (Ia1.1) are, in particular, those of the general formula Ia1.1.1 or Ia1.1.2.
The radicals R
c
in formula Ia1.1.1 are preferably derived by abstracting the isocyanate groups from monomers (Ia1.2), which are the diisocyanates commonly empl

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