Aqueous barrier layer based on polyurethane dispersions

Details Aqueous barrier layer based on polyurethane dispersions Aqueous barrier layer based on polyurethane dispersions

2001-08-24

2003-08-26

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...

C524S590000, C524S591000, C524S839000, C524S840000

Reexamination Certificate

active

06610779

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to novel polyurethane dispersions, a process for their production and their use in aqueous binders for rapidly drying coatings in automotive painting.
In automotive production-line painting a multi-coat construction, which is obtained on an increasing scale by means of aqueous coating compounds, has become standard. Aqueous coatings frequently exhibit the problem, because of the particular problems of water as the dispersant or solvent, that in order to achieve optimum coating properties the drying has to take place at relatively high temperatures and/or for relatively long periods. Modem coatings, however, also increasingly have to meet requirements connected with a high cost-effectiveness. An important aim is e.g. to apply the coating construction in the initial automotive painting stage in individual steps that are as few and as cheap as possible, that is to say above all follow each other in quick succession. High drying temperatures, long solvent evaporation times and long drying times frustrate this requirement.
For the conventional painting construction at the initial automotive painting stage there is first of all applied to a metal surface primed by cathodic electrophoretic coating (CEC) a coat to protect against impact from flying stones and a filler coat or a combination of both (“filler protecting against impact from flying stones”). There is then applied to these coats a pigmented base coat, then a clear lacquer or alternatively a pigmented top coat.
The filler coat protecting against impact from flying stones serves to smooth out unevenness in the surface and produces through a high elasticity and deformability a good resistance to impact from flying stones. Polyesters and polyurethanes as well as polyisocyanate or melamine crosslinking agents have therefore been used to date for this coat. The filler protecting against impact from flying stones is stoved prior to the application of the base coat and the clear lacquer or top coat. This is necessary in order to improve the “take” of the top coat and to seal any defects still present in the filler coat. Further stoving then takes place after the application of the clear lacquer or top coat. This process has the disadvantage that two expensive stoving operations are required. Paints that dry rapidly naturally, i.e. without a stoving operation, such as can be formulated for example from polyacrylates, do not exhibit the required resistance to impact from flying stones, since on curing they lead to films with inadequate mechanical film properties.
The object of the present invention is to provide a binder for a barrier coat with a protective function against impact from flying stones, which ensures in addition to a good resistance to impact from flying stones in particular, a very rapid natural drying and wherein the coating obtained after the rapid natural drying possesses a very good water resistance and is resistant to incipient dissolution by the subsequently applied base or top coat. In addition the adhesion or inter-layer adhesion must also be exceptional, in order to ensure an optimum paint construction. As well as this the binder must be light-fast, in order to produce a weather-resistant coating also in the case of moderately opaque top or base coats or at points at which a pigmented top or base coat is completely dispensed with. Also required is an outstanding stability, in particular viscosity stability, of suitably formulated paints and a practical repair capability for essential repairs directly on the line.
A proposed solution for coatings resistant to impact from flying stones and/or filler coats based on aqueous binders is described e.g. in EP-A-0 330 139. As is known, the claimed dispersions of acid-functional polyesters have only a limited shelf life, as they are subject to a rapid chemical deposition by the splitting of ester bonds (e.g. Jones, T. E.; McCarthy, J. M., J. Coatings Technol. 76 (844), p. 57 (1995)).
In EP-A-0 498 156 polyester dispersions containing urethane groups are described, which are very suitable for producing intermediate primer coats protecting against impact from flying stones or stoving fillers with high resistance to impact from flying stones. In order to achieve these superior properties, however, high curing temperatures or long stoving times are required.
DE-A-3 936 794 describes polyurethane dispersions containing carbonate groups and their use in automotive painting, e.g. for base coats, namely both under stoving conditions at approx. 140° C. and in cases of repair on the line at approx. 80° C. Important requirements which these dispersions must fulfil are e.g. adhesion, weathering resistance and resistance to condensation also at 80° C. drying.
DE-A-4 438 504 describes paint layer formulations based on water-thinnable polyurethane resins with an average molecular weight Mn of 4000 to 25000 g/mole, with which the thinnest possible paint films for filler and intermediate prime coats resisting impact from flying stones can be produced.
There is nevertheless still a need for additionally improved products which are capable of meeting continually increasing requirements and which permit varied applications. In addition, a very rapid natural drying, a rapidly achievable, very good water resistance and a very high hardness-elasticity level are particularly required, something which cannot always be achieved with the products according to the prior art.
Surprisingly it has now been found that particular high molecular-weight, solvent-free polyurethane dispersions of reaction products consisting of at least one polyol component, at least one at least dihydroxy-functional low molecular-weight component, at least one hydrophilic component and at least one at least difunctional isocyanurate, wherein said polyurethane dispersions have a relatively high content of carboxylate groups and comprise isolated urea groups, are particularly well suited to meeting the requirements made of a barrier coat with a protective function against impact from flying stones. It was also found that such products can be manufactured by a very simple, and hence in particular low-cost process, consisting of a single-stage, rapidly proceeding urethanization reaction, dispersion, chain extension reaction and subsequent solvent distillation. It is possible in this way to produce high-quality, environmentally friendly products at low cost.
SUMMARY OF THE INVENTION
The invention therefore provides aqueous polyurethane dispersions from reaction products of
A) at least one at least difunctional polyol of the molecular weight range 500-6000,
B) at least one at least difunctional low-molecular weight alcohol,
C) at least one di- and/or trifunctional isocyanate and
D) at least one compound with an acid group and one or two hydroxy- and/or primary or secondary amino groups in an amount such as ensures an acid number referred to solids content of <25 mg KO/g of substance, wherein the whole amount of neutralizing agent is added prior to the chain extension reaction,
wherein the degree of neutralization comes to at least 40, but not more than 105% referred to the amount of acid groups,
wherein there are contained in the starting components of the polyols A) or in the low molecular-weight component B) tri- or higher-functional constituents in an amount of at least 1 wt. %, referred to the total solids amount of A) to D), and wherein a content of isolated urea groups (in the brackets of formula I) of 1 to 4 wt. % is contained.
The invention also provides a process for producing polyurethane dispersions according to the invention, characterised in that there is first of all produced from the above-mentioned components A), B), C) and D) in organic solution an isocyanate-and acid-functional polyurethane prepolymer, thereafter neutralizing agent is added for at least 40, but at most 105%, of the acid groups and the prepolymer so obtained is dispersed in or with water, then optionally neutralizing agent is further added up to the maximum amount of the degree of neutraliz

Affiliated with

Also associated with

Rating

Aqueous barrier layer based on polyurethane dispersions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Aqueous barrier layer based on polyurethane dispersions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous barrier layer based on polyurethane dispersions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3079100