Polyurethane-polyurea dispersions

Details Polyurethane-polyurea dispersions Polyurethane-polyurea dispersions

2003-06-10

2004-08-31

Sergent, Rabon (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...

C008S115600, C428S375000, C428S378000, C428S423100, C428S425600, C524S839000, C524S840000, C528S045000, C528S071000

Reexamination Certificate

active

06784243

ABSTRACT:

CROSS REFERENCE TO RELATED PATENT APPLICATIONS
The present patent application claims the right of priority under 35 U.S.C. §119 (a)-(d) of German Patent Applications No. 10226931.9, filed Aug. 14, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polyurethane-polyurea dispersions, referred to below as PU dispersion, which contain aralkylamine-blocked isocyanate groups, and to their preparation and use.
2. Description of the Related Art
In the coating of substrates, solvent-containing binders are increasingly being replaced by aqueous, environmentally friendly systems. An increasing role has been played in particular by binders based on polyurethane-polyurea dispersions, owing to their excellent properties. Many areas of application are using 2K (2-component) systems, which are generally composed of an OH-functional binder and a polyisocyanate (blocked or not blocked). Furthermore, 1K (1-component) self-crosslinking PU dispersions, which, as described for example in U.S. Pat. No. 4,387,181, possess blocked isocyanate groups and isocyanate-reactive groups, are of great interest for many areas. The thermal treatment of the systems following application produces highly crosslinked coatings which, however, exhibit little or no chemical crosslinking with the coated substrate. PU dispersions which, in contrast to this, possess blocked isocyanate groups and no significant amounts of isocyanate-reactive groups may be crosslinked, under thermal loading, with the substrate to which they have been applied or into which they have been incorporated. This type of what are referred to as post-crosslinkable PU dispersions is described in, for example, DE-A 195 48 030.
The principal compounds used for blocking isocyanates and polyisocyanates are &egr;-caprolactam, butanone oxime, malonates, secondary amines, and triazole derivatives and pyrazolee derivatives, as described in, for example, EP-A 0 576 952, EP-A 0 566 953, EP-A 159 117, U.S. Pat. No. 4,482,721, WO 97/12924 or EP-A 0 744 423 and also DE-A 195 48 030.
Secondary amine blocking agents, including aralkyl-substituted amines, are known from, for example, EP-A 0 096 210. The use of such amines in aqueous systems, particularly in post-crosslinkable PU dispersions, however, is not known from EP-A 0 096 210.
The preparation of aqueous post-crosslinkable PU dispersions normally involves using prior art blocking agents such as, for example, &egr;-caprolactam, and butanone oxime.
Whereas for post-crosslinkable PU dispersions possesssing &egr;-caprolactam-blocked isocyanate groups it is normal to employ baking temperatures around 160° C., post-crosslinkable PU dispersions for which butanone oxime has been used as the blocking agent can be deblocked at temperatures lower by 10-20° C. At these temperatures, however, the desired properties are no longer achieved in many coatings. Furthermore, high deblocking temperatures or drying temperatures often cause unwanted thermal yellowing of the binders or coating. Moreover, these deblocking temperatures are now considered too high, for reasons of cost, so that a demand has developed for post-crosslinkable PU dispersions containing blocked isocyanate groups which crosslink with a corresponding substrate at temperatures lower than in the case of butanone oxime.
A further disadvantage of prior art post-crosslinkable PU dispersions is the low hydrolysis stability in films and coatings.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide post-crosslinkable PU dispersions containing isocyanate groups blocked with a blocking agent which has a significantly lower deblocking temperature as compared with the prior art and, furthermore, where coatings resulting from this coating composition have high hydrolysis resistances.
It is now been found that PU dispersions possesssing aralkylamine-blocked isocyanate groups meet the abovementioned profile of requirements.
The present invention provides post-crosslinkable aqueous PU dispersions containing aralkylamine-blocked isocyanate groups composed of the following components:
A1) polyisocyanates,
A2) polymeric polyols having average molar weights of 400 to 6 000,
A3) optionally mono- or polyalcohols or mono- or polyamines having average molar weights of up to 400,
A4) at least one blocking agent, of which at least 20% by weight is composed of aralkylamines,
and at least one compound selected from
A5) compounds which have at least one ionic or potentially ionic group and/or
A6) nonionically hydrophilicizing compounds, plus, where appropriate, diluents, solvents and adjuvants.
The dispersed polymer obtained from components A1) to A6) essentially no longer contains any isocyanate-reactive groups.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials, times and temperatures of reaction, ratios of amounts, values for molecular weight, and others in the following portion of the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount or range.
The solids content of the post-crosslinkable PU dispersions of the invention can be varied within limits of from 10 to 70% by weight. The post-crosslinkable PU dispersions of the invention preferably contain a solids content of from 20 to 60% by weight and with particular preference from 25 to 50% by weight. As a proportion of the overall composition, the fraction of organic solvents is preferably less than 15% by weight, with particular preference less than 10% by weight and with very particular preference less than 5% by weight.
In the context of the invention, a potentially ionic group is a group which is capable of forming an ionic group.
Preferably, the PU dispersions according to the invention contain 10 to 40% by weight of A1), 30 to 90% by weight of A2), 0 to 30% by weight of A3) 1 to 20% by weight of A4), 0 to 15% by weight of ionic or potentially ionic compounds A5) and 0 to 40% by weight of compounds A6), the sum of the components being 100% by weight.
More preferably, the PU dispersions according to the invention contain 10 to 30% by weight of A1), 30 to 80% by weight of A2), 0 to 20% by weight of A3), 1 to 15% by weight of A4), 0 to 8% by weight of ionic or potentially ionic compounds A5) and 0 to 35% by weight of compounds A6), the sum of the components being 100% by weight.
Most preferably, the PU dispersions contain 15 to 30% by weight of A1), 30 to 70% by weight of A2), 0 to 10% by weight of A3), 1 to 10% by weight of A4) 0 to 8% by weight of ionic or potentially ionic compounds A5) and 5 to 30% by weight of compounds A6), the sum of the components being 100% by weight.
Suitable diisocyanates (A1) are in principle those of the molecular weight range 140 to 400, having aliphatically, cycloaliphatically, araliphatically and/or aromatically bonded isocyanate groups, such as, for example, 1,4-diisocyanatobutane, 1,6-diisocyanatohexane (HDI), 2-methyl-1,5-diisocyanatopentane, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- and 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- and 1,4-diisocyanatocyclohexane, 1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4,4′-diisocyanato-dicyclohexylmethane, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, bis-(isocyanatomethyl)-norbornane, 1,3- and 1,4-bis-(2-isocyanato-prop-2-yl)-benzene (TMXDI), 2,4- and 2,6-diisocyanatotoluene (TDI), 2,4′- and 4,4′-diisocyanatodiphenylmethane, 1,5-diisocyanatonaphthalene or any desired mixtures of such diisocyanates.
They are preferably polyisocyanates or polyisocyanate mixtures of said type having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups. Very particularly preferred starting components (A1) are polyisocyanates and polyisocyanate mixtures based on HDI, IPDI and/or 4,4′-diisocyanato-dicyclohexylmet

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