Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-03-27
2003-04-01
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S086000, C428S423100, C428S425100
Reexamination Certificate
active
06541536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aqueous polyurethane dispersions which cure under the action of high-energy radiation and coated substrates prepared with these dispersions, especially wood and furniture.
2. Description of the Prior Art
Radiation curable polyurethane dispersions are described in EP-A 0 704 469, EP-A 0 753 531, EP-A 0 870 788, EP-A 0 872 502 and EP-A 0 942 022. The polyurethane dispersions described therein exhibit good physical surface-drying once the water has evaporated, even before UV curing, and only slightly penetrate absorbent substrates such as wood. Thus, these coatings only inadequately emphasize the natural structure of the wood, a phenomenon known in the art as “grain enhancement” (
Römpp Lexikon der Lacke
&
Druckfarben
, Ulrich Zorl (ed.), Stuttgart, New York, Thieme 1998, “wood lacquers” entry, page 289).
EP-A-0 012 339 discloses aqueous dispersions based on radiation curable prepolymers, which are stabilized by dispersion additives such as polyvinylpyrrolidones. While these dispersions exhibit good grain enhancement on wood, they hardly surface-dry at all by releasing water, which is extremely unfavorable in an industrial coating process. This is because uncured lacquer surfaces are sensitive to dust and other disturbances which may occur during handling or movement. Also, the use of the dispersion additives means that some water remains in the film after the majority of water has evaporated, and this residual water may cause problems with the optical properties and hardness of the film on curing by UV light.
Therefore, the prior art systems either surface-dry physically, but exhibit inadequate grain enhancement, or they exhibit good grain enhancement, but insufficient surface drying.
An object of the present invention is to provide radiation curable aqueous polyurethane dispersions that exhibit both good physical surface drying before radiation curing and good grain enhancement on wood.
This object may be achieved in accordance with the invention by incorporating small quantities of 2,2-dimethyl-3-hydroxypropionic acid (2,2-dimethyl-3-hydroxypropyl ester) in radiation curable aqueous polyurethane dispersions. The presence of this compound surprisingly gives rise to greatly improved grain enhancement on wood in physically surface-drying, radiation curable aqueous polyurethane dispersions.
SUMMARY OF THE INVENTION
The present invention relates to radiation curable aqueous polyurethane dispersions containing 0.05 to 20 wt. %, based on the weight of the non-aqueous constituents of the aqueous polyurethane dispersions, of 2,2-dimethyl-3-hydroxypropionic acid-(2,2-dimethyl-3-hydroxypropyl ester) HPSNPG, calculated as MW 204.3.
The invention also relates to substrates coated with these polyurethane dispersions, in particular to coated wood substrates with good grain enhancing properties.
DETAILED DESCRIPTION OF THE INVENTION
The production of polyurethane dispersions is known and described, for example, in
Methoden der organischen Chemie
(Houben-Weyl, supplemental and additional volumes to the 4
th
edition, volume E20, H. Bartl and J. Falbe (eds.), Stuttgart, New York, Thieme 1987, pp. 1659-1693). Polyurethane dispersions are produced by polyaddition of di- or polyisocyanates (component A) with di- or polyfunctional isocyanate-reactive compounds (component B). The reaction may be performed in one or more stages in the homogeneous phase or, in the case of a multistage reaction, in part in the aqueous phase. Once polyaddition has been performed completely or partially, a dispersion step is performed. Further polyaddition or modification in the disperse phase may optionally be performed.
Isocyanate-reactive component B) contains at least one hydrophilizing compound B1. Compounds having a dispersant action, which may be cationic, anionic and/or nonionic, hydrophilic ether groups. Examples of compounds B1 are those containing isocyanate-reactive groups and also containing sulfonium, ammonium, carboxylate or sulfonate groups, groups which may be converted into ionic groups by salt formation and/or containing polyether groups. Preferred isocyanate-reactive groups are hydroxyl and amino groups. Examples of compounds B1 are bis(hydroxymethyl)propionic acid, bis(hydroxymethyl)butyric acid, hydroxypivalic acid, malic acid, glycolic acid, lactic acid, glycine, alanine, taurine and 2-aminoethylaminoethanesulfonic acid. Also suitable are polyethylene glycols, polypropylene glycols, the block copolymers thereof started on alcohols and monomethyl ethers of these polyglycols. Bis(hydroxymethyl)propionic acid is particularly suitable.
Isocyanate-reactive component B) also contains at least one compound B2, which also contains free-radically polymerizable double bonds, preferably acrylates or methacrylates. Examples of these compounds include the mono (meth)acrylates of dihydric alcohols such as ethanediol, the isomeric propanediols and butanediols, or (meth)acrylates of polyhydric alcohols, such as trimethylolpropane, glycerol and pentaerythritol, which contain free hydroxyl groups. Polyester acrylates containing hydroxyl groups and having an OH content of 30 to 300 mg KOH/g may also be used.
Suitable monomer constituents that may be used during the production of the hydroxy-functional polyester acrylates include:
1. (Cyclo)alkanediols (i.e. dihydric alcohols with (cyclo)aliphatically bound hydroxyl groups) having a molecular weight of 62 to 286, such as ethanediol, 1,2- and 1,3-propanediol, 1,2-, 1,3- and 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,2- and 1,4-cyclohexanediol and 2-ethyl-2-butylpropanediol. Also suitable are diols containing ether groups such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, and polyethylene glycols, polypropylene glycols or polybutylene glycols having a maximum molecular weight of about 2000, preferably about 1000 and more preferably about 500. Reaction products of these diols with &egr;-caprolactone or other lactones may also be used as diols.
2. Trihydric and higher functional alcohols having a molecular weight of 92 to 254, such as glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol and sorbitol or polyethers started on these alcohols, for example, the reaction product of 1 mole of trimethylolpropane with 4 moles of ethylene oxide.
3. Monoalcohols such as ethanol, 1- and 2-propanol, 1- and 2-butanol, 1-hexanol, 2-ethylhexanol, cyclohexanol and benzyl alcohol.
4. Dicarboxylic acids having a molecular weight of 104 to about 600 and/or the anhydrides thereof, such as phthalic acid, phthalic anhydride, isophthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, cyclohexanedicarboxylic acid, maleic anhydride, fumaric acid, malonic acid, succinic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid and hydrogenated dimer fatty acids.
5. Higher functional carboxylic acids or the anhydrides thereof, such as trimellitic acid and trimellitic anhydride.
6. Monocarboxylic acids, such as benzoic acid, cyclohexanecarboxylic acid, 2-ethylhexanoic acid, caproic acid, caprylic acid, capric acid, lauric acid, natural and synthetic fatty acids.
7. Acrylic acid, methacrylic acid or dimeric acrylic acid.
Preferred polyester acrylates containing hydroxyl groups are the reaction product of at least one compound from group 1 or 2 with at least one compound from group 4 or 5 and at least one compound from group 7.
Groups with a dispersing action generally known from the prior art, such as those described for example in
Progress in Organic Coatings,
9 (1981), 291-296 may also be incorporated into these polyester acrylates. A portion of polyethylene glycols and/or methoxypolyethylene glycols may thus be incorporated as the alcohol component. Other examples include polyethylene glycols, polypropylene glycols and the block copolymers thereof started on alco
Kremer Wolfgang
Lühmann Erhard
Meixner Jürgen
Weikard Jan
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
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