Latent cross-linking aqueous dispersions comprising a...

Details Latent cross-linking aqueous dispersions comprising a... Latent cross-linking aqueous dispersions comprising a...

2000-05-01

2003-07-29

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...

C427S372200, C427S385500, C428S423100, C524S507000, C524S839000, C524S840000, C525S123000, C525S127000, C525S130000, C525S455000

Reexamination Certificate

active

06599975

ABSTRACT:

1. The present invention related to latent-crosslinking aqueous polyurethane dispersions comprising
I) a disperse phase (P.I) comprising
Ia) a polyurethane (Ia) which carries carbodiimide groups in addition to hydrophilic groups which make it dispersible in water but carries essentially no carboxyl groups or
Ib) a physical mixture of
Ibi) a polyurethane (Ibi) which carries hydrophilic groups which make it dispersible in water but carries essentially no carbodiimide or carboxyl groups and
Ibii) a carbodiimide (Ibii) which carries essentially no hydrophilic groups which make it dispersible in water, and
II) a disperse phase (P.II) comprising another polymer (II) which carries carboxyl groups and essentially no carbodiimide groups.
The invention also 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 disperse form are common knowledge. In order that coatings prepared from the polyurethane have particularly good mechanical properties, a crosslinking component is added to these dispersions. It is particularly desirable here for the crosslinker to bring about the buildup in molecular weight of the polyurethane only after the polyurethane dispersion, following application to the substrate workpiece, has already formed a film. If this is the case, the resulting films are of particularly high cohesion, since the polymer molecules of a dispersion particle can then be linked to another, adjacent dispersion particle by a covalent bond.
Especially good film cohesion is required in the adhesives sector, for example, when the adhesive bond is subjected simultaneously to heat and mechanical loading.
To obtain adhesive bonds of sufficient strength even under these conditions it has been recommended, for example, in EP-A-206059, to add a water-emulsifiable polyisocyanate as crosslinker to the dispersions shortly before they are processed as adhesives.
The disadvantage of these two-component systems, however, is that the potlife—that is, the period within which these systems can be processed after mixing—is very short. Since the two-component system cannot be stored for prolonged periods and the processor has to prepare an extra amount of adhesive to be processed within one operating cycle, the effort required by the adhesives processor is greater for two-component systems than for one-component systems.
U.S. Pat. Nos. 4,977,219 and 5,117,059 disclose mixtures of an aqueous dispersion of a carbodiimide and of an aqueous dispersion of an emulsion polymer having carboxylate groups, the first-mentioned 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 which is stabilized by hydrophilic polyalkylene oxide radicals carried by the carbodiimides. These dispersions are blended with aqueous dispersions of an emulsion polymer having carboxylate groups.
EP-A-792 908 discloses mixtures of an aqueous dispersion of a carboxyl-containing polyurethane and an aqueous dispersion of a carbodiimide, the dispersion being stabilized with the aid of customary surface-active substances.
According to 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 bonds produced with these dispersions, however, especially under hot conditions, still leaves something to be desired. In addition, the potlife of such mixtures is limited.
German Patent Application 19733044.4, unpublished at the priority date of the present specification, relates to aqueous dispersions of a polyurethane which carries carbodiimide groups.
It is an object of the present invention to provide a further one-component polyurethane dispersion devoid of the disadvantages of the prior art. In particular, it should have good storage stability and should permit the production of heat-resistant 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 Ibi and Ibii.
Examples of suitable polyurethanes (Ia) are described in EP-A-792908.
Suitable polyurethanes (Ia) are, in principle, all hydrophilic polyurethanes synthesized using monomers having carbodiimide structural units. The carbodiimide structural units are incorporated into the polyurethane (Ia) preferably by way of polyisocyanates (Ia1.1), containing one or more of the carbodiimide structural units. Polyisocyanates (Ia1.1) of this kind are preferably of the 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 contains urethane groups and possibly ether or ester groups and which is terminated by isocyanate groups; if there are two or more radicals R
c
in the same molecule, then different radicals R
c
conforming to the given definition may 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 formula Ia1.1.2
O═C═N—R
a
(—R
b
—)
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
Ia1.1) comprise carbodiimide structural units, with or without those which
Ia1.2) are free of carbodiimide structural units,
Ia2) diols of which
Ia2.1) from 10 to 100 mol %, based on the overall amount of the diols (b), have a molecular weight of 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 of from 60 to 500 g/mol,
Ia3) monomers other than the monomers (Ia1) and (Ia2), which have at least one isocyanate group or at least one isocyanate-reactive group and also carry at least one hydrophilic group or one potentially hydrophilic group which makes the polyurethanes dispersible in water,
Ia4) if desired, further, polyfunctional compounds which are different from the monomers (Ia1) to (Ia3) and have reactive groups which are alcoholic hydroxyl, primary or secondary amino or isocyanate groups, and
Ia5) if desired, monofunctional comounds which are different from the monomers (Ia1) to (Ia4) and have a reactive group which is an alcoholic hydroxyl, primary or secondary amino or isocyanate group.
Particularly suitable diisocyanatocarbodiimides (Ia1.1) are those of the 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 employed in polyurethane chemistry.
Monomers (Ia1.2) are, in particular, diisocyanates X(NCO)
2
, where X is an aliphatic hydrocarbon radical of 4 to 12 carbons, a cycloalphiphatic or aromatic hydrocarbon radical of 6 to 15 carbons or an araliphatic hydrocarbon radical of 7 to 15 carbons. Examples of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,2-bis-(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate, 1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyan

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