Polyurethane dispersions

Details Polyurethane dispersions Polyurethane dispersions

2002-02-27

2003-05-06

Gorr, Rachel (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...

C524S840000, C428S423100, C528S074500

Reexamination Certificate

active

06559225

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to binders for aqueous coatings, to a process for the production thereof and to the use thereof for lacquers and coatings.
Aqueous coating compositions are increasingly being used instead of systems containing solvent with the objective of reducing emissions of organic solvents. Polyurethane dispersions comprise one important class of aqueous lacquer binders. D. Dieterich provides an overview in
Prog. Org. Coatings
9, 281 (1981). Polyurethane dispersions combine the important properties of resistance to chemicals and mechanical stress. It is thus advantageous to use polyurethane dispersions, especially for coating surfaces exposed to severe mechanical stress.
Resistance to the damage caused by shoe heels on floor coatings (heel marking resistance) is of particular interest. Especially in the case of markedly thermoplastic coatings, such heel marks give rise to permanent damage. Resistance to such damage may be improved by crosslinking the floor coating.
One method of achieving such an improvement to the range of properties is to use hydrophilised polyisocyanates, as are described for example in EP-B-0 540 985. Aqueous, two-component polyurethane lacquers achieve a very high level of properties. However, due to the comparatively complex application process for coating systems which are to be applied as two components, the range of applications thereof is limited, especially in the case of manual application.
One simple, previously described way of obtaining crosslinked coatings from polyurethane dispersions is to incorporate unsaturated units into the binder (
Advances in Urethane Science
&
Technology
, K. C. Frisch, D. Klempner (eds.), vol. 10, pp. 121-162 (1987)). Coatings prepared from such binders crosslink by reaction with atmospheric oxygen (autooxidative crosslinking). In comparison with combining a polyurethane dispersion with a hydrophilised polyisocyanate, this binder which is applied as a single component is in particular simpler to apply.
Such dispersions containing urethane groups and air-drying structural units are also described in EP-A-0 017 199, EP-B-0 379 007, WO97/19120, DE-A-4 004 651, DE-A-4 416 336, U.S. Pat. No. 5,039,732 and JP-A-6 340 842. One disadvantage of hitherto known autooxidatively crosslinkable polyurethane dispersions is, however, that the mechanical properties of the lacquer film do not achieve the high level achieved by purely physically drying polyurethane dispersions. This is manifested, for example, by poorer abrasion resistance.
Another possible process for the production of polyurethane dispersions containing unsaturated units is described in EP-A-0 709 414. Products having a defined content of C═C double bonds are obtained by using dehydrated castor oil as the OH component in the production of a polyurethane dispersion.
When dehydrating castor oil (c.f. for example K. T. Achaya,
J. Am. Oil Chem. Soc
. 48, p. 758 [1971]), a single C═C double bond is produced for each molecule of water which is eliminated. The process described in EP-A-0 709 414 is thus limited by the fact that, by dehydrating castor oil having a certain content of OH groups and double bonds, the products obtained always have the same total number of hydroxyl groups and double bonds. Using this process, it is thus not possible to produce products having an elevated content of double bonds and simultaneously an elevated content of OH groups.
The object of the present invention was to provide polyurethane dispersions obtainable in simple manner which may be applied to yield coatings having excellent heel marking resistance simultaneously combined with excellent abrasion resistance.
This object is achieved according to the invention by polyurethane dispersions in which the polyurethanes contain certain unsaturated polyester oligomers and are obtainable using a simple production process by transesterification from castor oil. The dispersions may be applied to yield particularly high grade floor coatings. In addition to elevated resistance to water/ethanol mixtures and to abrasion, these coating are distinguished by heel marking resistance.
SUMMARY OF THE INVENTION
The present invention provides polyurethane dispersions, characterised in that 5 to 50% of a polyurethane oligomer (A) are used as one of the structural components, which oligomer is obtainable from
AI) 30-85%, preferably 50-70%, of castor oil fatty acid,
AII) 10-60%, preferably 25-35%, of one or more carboxylic acids having 8 to 30 C atoms and 0 to 4 C═C double bonds and
AIII) 3-20%, preferably 5-15%, of one or more alcohols with an average functionality of 2.5 to 3.5
wherein the percentages are by weight and add up to 100%.
The further constituents which are required for synthesis of the PU dispersions according to the invention are known and frequently described in the literature. These constituents comprise
B) 5-60% of polyisocyanates,
C) 0.5-40% of polymeric polyols having average molecular weights of 500 to 6000,
D) 0-10% of monoalcohols and/or monoamines,
E) 0.5-15% of polyols, aminopolyols and/or polyamines having a molecular weight of below 500, wherein one of these polyols or polyamines preferably contains an ionic group or should be capable of forming an ionic group, which may be cationic or anionic, and
F) 0-10% of OH— and/or NH-functional, nonionic, hydrophilic polyoxyalkylene ethers,
wherein the percentages are by weight and add up to 100%.
DETAILED DESCRIPTION OF THE INVENTION
The carboxylic acids (AII) are preferably aliphatic and cycloaliphatic monocarboxylic acids such as for example 2-ethylhexanoic acid, lauric acid, stearic acid, oleic acid, linoleic acid or linolenic acid. The acids particularly preferably comprise fatty acid mixtures as may be obtained from natural vegetable or animal oils, such as for example soya oil, peanut oil, tall oil, linseed oil, wood oil, sunflower oil or castor oil, optionally with further chemical and/or physical modification.
Alcohols (AIII) are difuncional alcohols such as ethylenglycol, diethylenglycol, 1,4-butanediol, neopentyl glycol, 1,2-propanediol, 1,3-propanediol or 2-ethylhexanediol, trifunctional alcohols such as glycerol or trimethylolpropane, or higher functional alcohols such as pentaerythrol. Preferred alcohol (AIII) is glycerol. The average functionality (i.e. the arithmetical average based on molar concentration of alcohols (AIII)) is between 2.5 and 3.5, preferred 3.0.
Suitable polyisocyanates (B) are preferably diisocyanates of the formula R
1
(NCO)
2
, wherein R
1
means an aliphatic hydrocarbon residue having 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon residue having 6 to 15 carbon atoms, an aromatic hydrocarbon residue having 6 to 15 carbon atoms or an araliphatic hydrocarbon residue having 7 to 15 carbon atoms. Examples of such preferably used diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanatodiphenylmethane, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene or &agr;,&agr;,&agr;′,&agr;′-tetramethyl-m- or -p-xylylene diisocyanate, together with mixtures of the stated diisocyanates. Particularly preferred diisocyanates are 1-diisocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate) and 4,4′-diisocyanatodicyclohexylmethane.
Those polyisocyanates having isocyanurate, biuret, allophanate, uretidione or carbodiimide groups are furthermore suitable as the polyisocyanates (B). Such polyisocyanates may have elevated functionalities, for example of greater than 3. Further polyisocyanates suitable for the production of the polyurethane dispersions suitable according to the invention are those having nonionic or ionic, hydrophilic structural components and are conventionally used as crosslinking agents in aqueous two-component PU lacquers.
The polymeric polyols (C) within the molecular weight range from 500-6000 are those which have long conventionally been used for the production of polyurethanes. They have an OH functionality of at leas

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