Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2001-02-23
2002-12-31
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S428000, C428S522000, C427S195000, C427S385500, C524S507000, C524S539000, C525S124000, C525S440030, C525S934000
Reexamination Certificate
active
06500548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to transparent or pigmented powder coating materials with crosslinkers comprising hydroxyalkylamides and blocked nonaromatic polyisocyanates and acidic polymers, said materials possessing reduced susceptibility to pinholing.
2. Discussion of the Background
Powder coating materials based on triglycidyl isocyanurate (TGIC) and acid-functional polyesters produce corrosion-resistant and weather-stable powder coatings. EP 0536 085 describes, however, how expensive processes or a relatively large and thus likewise expensive purification effort are required in order to prepare the TGIC in solid form. Moreover, TGIC is classified by the European Community as a category II mutagen (“is regarded as causing mutations”) and as of May 31, 1998 has required labeling as “toxic”.
Toxicologically unobjectionable and at the same time more reactive as well are &bgr;-hydroxyalkylamide crosslinkers. In U.S. Pat. Nos. 4,076,917 and 4,101,606, &bgr;-hydroxyalkylamides are combined with polymers having at least one carboxyl or anhydride function, in particular with polyacrylates, to form powder coating materials. U.S. Pat. No. 4,988,767 describes powder coating materials based on hydroxyalkylamides and acidic acrylate resins. EP 0 322 834 describes thermosetting powder coating materials composed of &bgr;-hydroxyalkylamides and polyesters containing acid groups. These coatings with &bgr;-hydroxyalkylamide crosslinkers are highly weatherstable, very flexible, hard, and chemical-resistant. Especially at relatively high coat thicknesses, however, the water which is released on crosslinking leads to pinholing.
U.S. Pat. No. 4,889,890 describes hybrid powder coating materials. The acidic polymers they contain are cured with polyepoxides such as, for example, polyglycidyl ethers of aromatic phenols. To increase the crosslinking density, a &bgr;-hydroxyalkylamide is used. These hybrid powder coating materials afford good corrosion protection but are unsuited to use outdoors owing to a lack of weathering stability.
Thometzek et al. in 5th Nuremberg Congress, Congress Papers, Volume 1, 251-273 (1999) describe powder coating materials comprising a hydroxy-functional polyester resin, a hydroxyalkylamide, and a bifunctional crosslinker which in addition to blocked isocyanate groups contains carboxyl groups. These powder coating materials are suitable for obtaining matte rather than glossy coatings.
It is an object of the present invention to provide powder coating materials which give highly glossy, flexible, light-stable and weather-stable coatings of low susceptibility to pinholing.
SUMMARY OF THE INVENTION
It has surprisingly been found that coatings comprising acidic polymers and &bgr;-hydroxyalkylamide crosslinkers, especially at relatively great coat thicknesses, are markedly less susceptible to pinholing if blocked polyisocyanate crosslinkers are added as an additional component. Flexibility, gloss, reactivity, and weather stability remain at the traditional high level of polyester/hydroxyalkylamide or polyurethane powder coating materials.
According to another embodiment of the present invention is a method of coating a surface by applying a powder coating material and curing.
According to another embodiment of the present invention is a coated article obtained by applying a powder coating material and curing.
These and other embodiment of the present invention are made possible by a transparent or pigmented powder coating materials with crosslinkers comprising hydroxyalkylamides and blocked polyisocyanates, comprising:
A) from 20 to 99% by weight of at least one acidic polymer;
B) from 1 to 25% by weight of at least one &bgr;-hydroxyalkylamide;
C) from 0.05 to 10% by weight of at least one blocked nonaromatic polyisocyanate having an NCO functionality≧2;
D) from 0 to 50% by weight of at least one pigment and/or inorganic filler;
E) from 0 to 5% by weight of at least one adjuvant or auxiliary.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable non-limiting examples of acidic polymers A) for preparing the powder coating materials of the invention include polyester resins and acrylate resins.
The acidic polyesters preferably possess a glass transition temperature (Tg) in the range from 30 to 85° C. and an acid number of from 20 to 80 mg KOH/g. They may be prepared in principle by a condensation reaction of aliphatic polyols and/or cycloaliphatic polyols with aliphatic and/or aromatic polycarboxylic acids and anhydrides. Polyesters of this kind are described, for example, in EP 0 322 807, DE 198 50 970 or WO 95/01406.
The acidic acrylate resins possess an acid number in the range from 10 to 250 mg KOH/g and a melting point of from 60 to 160° C. They are prepared in principle by copolymerizing a monomer mixture comprised of
a) from 0 to 70 parts by weight of methyl (meth)acrylate,
b) from 0 to 60 parts by weight of (cyclo)alkyl esters of acrylic acid and/or methacrylic acid having 2 to 18 carbon atoms in the alkyl or cycloalkyl radical,
c) from 0 to 90 parts by weight of vinylaromatic compounds, and
d) from 0 to 60 parts by weight of olefinically unsaturated carboxylic acids, the sum of the parts by weight of components a) to d) being 100.
The monomers b) preferably comprise (cyclo)alkyl esters of acrylic or methacrylic acid having 2 to 18 carbon atoms in the (cyclo)alkyl radical. Non-limiting examples of suitable and, respectively, preferably suitable monomers b) are ethyl (meth)acrylate, n-propyl (meth)acrylate , isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl methacrylate, neopentyl methacrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate and stearyl methacrylate.
Non-limiting examples of suitable monomers c) include styrene, vinyltoluene and ethylstyrene
Non-limiting examples of d) are acrylic and methacrylic acid, which are also used with preference, and also crotonic acid, itaconic acid, fumaric acid, maleic acid and citraconic acid.
The copolymers may be prepared by copolymerizing the exemplified monomers a) to d) in accordance with customary free-radical polymerization processes, such as solution, emulsion, bead or bulk polymerization, for example.
The monomers may be copolymerized at temperatures of from 60 to 160° C., preferably from 80 to 150° C., in the presence of free-radical initiators and, if desired, molecular weight regulators.
The carboxyl-functional acrylate copolymers are preferably prepared in inert solvents. Non-limiting examples of suitable solvents are aromatic compounds, such as benzene, toluene, xylene; esters, such as ethyl acetate, butyl acetate, hexyl acetate, heptyl acetate, methylglycol acetate, ethylglycol acetate, methoxypropyl acetate; ethers, such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether; ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, methyl isoamyl ketone; or any desired mixtures of such solvents.
The copolymers may be prepared continuously or batchwise. A normal procedure is to meter the monomer mixture and the initiator into a polymerization reactor continuously and at a uniform rate and at the same time to draw off continuously the corresponding amount of polymer. In this way it is possible, preferably, to prepare copolymers which are virtually uniform in chemical terms. Chemically near-uniform copolymers may also be prepared by running the reaction mixture at a constant rate into a stirred vessel without taking off the polymer.
Alternatively, a portion of the monomers, by way of example, may be introduced as an initial charge in solvents of the stated type and the remaining monomers and auxiliaries, separately or together, may be introduced into this initial charge at the reaction temperature. In general, the polymerization takes place under atmospheric pressure, but may also be conducted at pressures of up to 25 bar. The initiators are preferably used in amounts of from 0.05 to 15% by weight, based on th
Degussa - AG
Oblon, Spivak, McClelland, Maier & Neustadt PC
Short Patricia A.
LandOfFree
Transparent or pigmented powder coating materials with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transparent or pigmented powder coating materials with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transparent or pigmented powder coating materials with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2942820