Aqueous polyurethane emulsions

Details Aqueous polyurethane emulsions Aqueous polyurethane emulsions

2000-11-20

2003-02-18

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...

C428S423100, C428S425100, C522S090000, C522S097000, C522S098000, C522S173000, C522S174000, C524S507000, C524S539000, C524S547000, C524S591000, C524S840000, C525S123000, C525S131000, C525S440030, C525S454000, C525S455000, C525S459000, C528S071000, C528S075000

Reexamination Certificate

active

06521702

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aqueous polyurethane emulsions that cure under the influence of high energy radiation and to their use as coating compositions, especially for coating wood and furniture.
2. Description of the Prior Art
EP-A-0 012 339 describes aqueous dispersions based on radiation-curable repolymers which are stabilized by dispersing agents such as polyvinyl pyrrolidone. However, these dispersions have the disadvantage that they are not miscible with other alkaline, radiation-curable dispersions or alkaline polyacrylate dispersions. Furthermore, as a result of the use of the dispersing agents a considerable amount of water is left behind in the film after evaporation, which can result in interference with the optics and hardness of the film in the course of curing by UV light.
Radiation-curable polyurethane dispersions are also described in EP-A-0 704 469, EP-A-0 753 531, EP-A-0 870 788 and EP-A-0 872 502. The polyurethane dispersions described therein already begin to dry physically to a considerable extent after evaporation of the water and prior to UV curing and show only slight penetration when applied to absorbent substrates such as wood. Therefore, they do not accentuate the natural structure or grain of wood, this accentuation is familiar to those skilled in the art. Moreover, the dispersions according to the state of the art that have begun to dry, but have not been cured, can only be inadequately redispersed in water, rendering difficult both the re-use and the cleaning of appliances that are required for application of the dispersions.
An object of the present invention is to provide radiation-curable, aqueous binders that are compatible with other binders and free of dispersing agents, show good penetration into absorbent substrates and accentuate the appearance of wood. Moreover, the binding agents should also be redispersible in water after evaporation of the water. These objects may be achieved with the polyurethane emulsions according to the invention.
SUMMARY OF THE INVENTION
The present invention relates to a radiation-curable, aqueous polyurethane emulsion which is prepared by
I) reacting
A) 40 to 90 wt. % of an isocyanate-reactive component that contains a polyester acrylate containing hydroxyl groups and having an OH content of 40 to 200 mg KOH/g and optionally other isocyanate-reactive compounds other than B) and
B) 0.5 to 20 wt. % of one or more monofunctional and/or difunctional isocyanate-reactive compounds that contain cationic or anionic groups, potential cationic or anionic or hydrophilic ether groups, with
C) 10 to 50 wt. % of one or more diisocyanates and/or polyisocyanates,
II) optionally converting any potential cationic or anionic groups into cationic or anionic groups by salt formation and
III) forming a dispersion of the reaction product of A), B) and C) in water and reacting it with
D) 0.1 to 10 wt. % of one or more diamines and/or polyamines,
wherein the wt. % percentages of (A) to (D) add up to 100%, and the equivalent ratio of the sum of the isocyanate-reactive groups in (A) and (B) to the isocyanate groups in (C) is 0.8:1 to 1.25:1 and the reaction of components (A) and (B) with (C) is carried out such that 65 to 95% of the isocyanate groups in (C) react with the isocyanate-reactive groups of (A) and (B).
The present invention also relates to a process of making these polyurethane emulsions and to substrates coated with the polyurethane emulsions.
DETAILED DESCRIPTION OF THE INVENTION
Suitable polyester acrylates A) include polycondensation products of dicarboxylic or oligocarboxylic acids or the anhydrides thereof (for example, adipic acid, sebacic acid, maleic anhydride, fumaric acid and phthalic acid) and difunctional polyols and/or polyols of higher functionality (e.g. ethylene glycol, propylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, alkoxylated diols or polyols, such as the addition product of ethylene oxide on trimethylolpropane with a hydroxyl value of 550) and acrylic acid and/or methacrylic acid.
Known hydrophilic groups are described, e.g., in Progress in Organic Coatings, 9 (1981), 291-296 and may also be incorporated into these polyester acrylates. Thus polyethylene glycols and/or methoxypolyethylene glycols may be incorporated through the alcohol component. Examples include polyethylene glycols and polypropylene glycols started on alcohols and the block copolymers thereof, as well as the monomethyl ethers of these polyglycols. Particularly suitable are a 1500 molecular weight polyethlylene glycol and/or a 500 molecular weight polyethylene glycol monomethyl ether.
It is also possible to convert a portion of the (excess) carboxyl groups, in particular those of (meth)acrylic acid, with monoepoxides, diepoxides or polyepoxides. This reaction can be used, in particular, for increasing the hydroxyl value of the polyester acrylate, since an OH group is formed in each instance during the epoxide/acid reaction.
The production of polyester acrylates is described in DE-A-4 040 290, DE-A-3 316 592, P.K.T. Oldring (Ed.), Chemistry & Technology of UV & EB Formulations for Coatings, Inks & Paints, Vol. 2, 1991, SITA Technology, London, pp 123-135.
Alternatively, known polyepoxy acrylates containing hydroxyl groups or polyurethane acrylates containing hydroxyl groups (preferably having hydroxyl values of 40 to 200 mg KOH/g) may also be employed, as well as mixtures thereof with one another and with unsaturated and/or saturated polyesters containing hydroxyl groups.
Component A) may also contain diols with short alkyl chains (2 to 10 carbon atoms) in amounts of less than 30 wt. %, preferably less than 10 wt. %, based on the weight of component (A). Examples of such diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,3- or 1,4-butanediol, neopentyl glycol, 1,6-hexanediol or mixtures thereof.
Component A) may also contain hydroxy(C
1
-C
6
alkyl) (meth)acrylates in amounts of less than 30 wt. %, preferably less than 5 wt. %, based on the weight of component (A).
Compounds (B), which contain cationic groups, anionic groups and/or hydrophilic ether groups, include those which contain sulfonium, ammonium, carboxylate, sulfonate groups or groups that can be converted into the these groups by salt formation (potential cationic or anionic groups) and/or polyether groups. These groups can be incorporated into the polyurethane emulsions by isocyanate-reactive groups, such as hydroxyl groups and amine groups. Examples of compounds (B) include bis(hydroxymethyl)propionic acid, bis(hydroxymethyl)butyric acid, hydroxypivalic acid, malic acid, glycolic acid, lactic acid, glycine, alanine, taurine, 2-aminoethylaminoethane sulfonic acid, polyethylene glycols, polypropylene glycols started on alcohols and the block copolymers thereof, as well as the monomethyl ethers of these polyglycols. Preferred are bis(hydroxymethyl)propionic acid and polyethylene glycol monomethyl ethers, especially those having a molecular weight of about 500.
The polyaddition can be performed with aromatic, araliphatic, aliphatic or cycloaliphatic polyisocyanates (C). Mixtures of polyisocyanates (C) may also be used. Suitable polyisocyanates (C) include butylene diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate), the isomeric bis(4,4′-isocyanatocyclohexyl)methanes, isocyanatomethyl-1,8-octane diisocyanate, 1,4-cyclohexylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, 1,5-naphthylene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate, triphenylmethane-4,4′,4″-triisocyanate or the derivatives of these isocyanates containing urethane, isocyanurate, allophanate, biuret, uretdione and/or imino-oxadiazinedione groups and mixtures thereof. Preferred are hexamethylene diisocyanate, isophorone diisocyanate, the isomeric bis(4,4′-isocyanatocyclohexyl)methanes and mixtures thereof.

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