Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-06-04
2003-01-07
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S085000, C525S131000, C427S388400, C428S425800, C428S423100, C524S839000, C524S840000, C252S182260
Reexamination Certificate
active
06503999
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to liquid film-forming compositions having isocyanate crosslinking agents, polyols having groups that are reactive with isocyanates, and beta-hydroxyalkylamide. The present invention further relates to methods for coating substrates using the present compositions, and substrates coated therewith.
BACKGROUND INFORMATION
Isocyanate crosslinked systems have been used in coating compositions. Because isocyanates are reactive with active hydrogen-containing compounds such as water, one component systems historically have been formulated using organic solvents. Alternatively, waterborne systems have been formulated by using blocked isocyanate groups. The switch from organic solvents to water is neither simple nor straightforward, particularly since many isocyanate crosslinkers are not only reactive with water but are also hydrophobic and non-dispersible.
SUMMARY OF THE INVENTION
The present invention is directed to waterborne coating compositions comprising an active hydrogen-containing polymer, an isocyanate, and beta-hydroxyalkylamide. The present invention is further directed to methods for coating a substrate comprising applying the present coating compositions to the substrate. The compositions and methods find particular application in coating light industrial equipment.
It has been discovered that the use of isocyanate in conjunction with beta-hydroxyalkylamide (“HAA”) can result in a coating with improved hardness and chemical resistance, and increased viscosity when cured at either ambient or low bake temperatures. These improvements are achieved without any reduction in humidity or salt spray resistance. The use of HAA in conjunction with an isocyanate in systems curable at ambient or low-bake temperatures is not believed to have been previously reported. By “low bake” is meant about 60° C. or less. Thus, the present compositions and methods are particularly applicable in the refinish area, where equipment cannot be subjected to the high cure temperature requirements of many coating compositions.
It is a feature of this invention that the present coating compositions have decreased hardening time; that is, the present compositions achieve a desired level of hardness in a shorter amount of time than compositions that lack the HM additive. Such a characteristic is of particular interest to many markets in which the ability to rapidly finish and ship equipment and/or parts is desired. In addition to decreasing the time in which the present coatings achieve the desired hardness, several of the systems described herein have improved hardness as compared with compositions that do not use the HAA additive.
The present compositions also provide resistance to various chemicals; this resistance is particularly apparent when using the polyester polyol systems described herein.
As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. Also, as used herein, the term “polymer” is meant to refer to oligomers and both homopolymers and copolymers.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to an aqueous composition comprising an active hydrogen-containing polymer; an isocyanate compound; and beta-hydroxyalkylamide (“HAA”). An active hydrogen-containing polymer, as that term is used herein, refers to polymers that contain active hydrogens, such as those provided by hydroxyl, primary amino, secondary amino and/or thiol groups. The active hydrogens are reactive with the isocyanate groups; this reaction results in the curing of the material at either ambient or low bake temperatures. Thus, any polymer containing one or more active hydrogens is an active hydrogen-containing polymer suitable for use in the present invention. Examples include acrylic polymers, polyester polymers, polyurethane polymers and polymers derived from epoxy compounds. In one embodiment, the active hydrogens are provided by hydroxyl groups and the hydroxy-containing polymer is an acrylic polyol, a polyester polyol, or mixtures thereof.
The acrylic polyol component of the present invention contains both (i) hydroxyl functionality capable of reacting with isocyanate groups (“hydroxyl-reactive”) and (ii) hydrophilic functionality capable of rendering the surface active isocyanate-reactive material water dispersible. Hydrophilic functionality is well known to those skilled in the coatings art and includes, most commonly, anion generating, cation generating and hydrophilic non-ionic functional groups. By “anion generating” and “cation generating” are meant functionalities such as carboxyl (anion generating) or amino (cation generating) which, when appropriately neutralized, become hydrophilic in nature. Hydrophilic non-ionic functionality is itself hydrophilic in nature, and includes, for example, alkylene oxide units. The amount of hydrophilizing functionality present in the acrylic polyol should, upon at least partial neutralization of the anion generating or cation generating groups (if present), be sufficient to render the polyol water-dispersible.
In some embodiments the acrylic polyol is an acrylic copolymer having the hydrophilic functionality and hydroxyl-reactive functionality incorporated into the polymer via appropriate monomer selection or subsequent modification. Examples of monomers that may be utilized to synthesize the acrylic polyol include carboxyl group-containing ethylenically unsaturated monomers and hydroxyl group-containing ethylenically unsaturated monomers.
The acrylic polyol described in U.S. Pat. No. 6,005,045 is particularly suitable for use in the present invention. There, the active hydrogen-containing acrylic copolymers have a glass transition temperature (T
g
) greater than about 0° C. T
g
is described in
PRINCIPLES OF POLYMER CHEMISTRY,
Flory, Cornell University Press, Ithaca, N.Y., 1953, at pages 52-57. T
g
can be calculated as described by Fox in
Bull. Amer. Physic. Society,
1,3, page 123 (1956). T
g
can be measured experimentally by using a penetrometer such as a Du Pont 940 Thermomedian Analyzer. T
g
of the polymers as used herein refers to the calculated values unless otherwise indicated.
Suitable acrylic polyols are copolymers of one or more polymerizable acrylic monomers, at least some of which include hydrophilic functionality such as acid functional acrylic monomers, amine functional acrylic monomers, and hydroxyl functional acrylic monomers. The copolymers may also be made with additional polymerizable unsaturated monomers such as vinyl monomers. The copolymers may be prepared in organic solvent using conventional free radical polymerization techniques. The copolymers of the U.S. Pat. No. 6,005,045 contain about 5 to about 80, such as about 10 to about 40 percent by weight, of a polymerizable ethylenically unsaturated aromatic monomer; about 5 to about 80, such as from about 10 to 40 percent by weight, of an ethylenically unsaturated hydroxyl functional acrylic monomer; and about 20 to about 95, such as about 30 to about 70 percent by weight, of at least one ethylenically unsaturated monomer different from the other two named above. Weight percents are based on the total solid weight of monomers used to prepare the acrylic polyol.
The ethylenically unsaturated aromatic monomer used to synthesize the acrylic polyol may be selected from monomers such as styrene and alpha-methyl styrene, including substituted styrene or substituted alpha-methyl styrene where substitution is in the para position and is a linear or branched alkyl group having from about 1 to about 20 carbon atoms; examples include but are not limited to vinyl toluene, 4-vinylanisole, and 4-vinylbenzoic acid. The ethylenically unsaturated aromatic monomer may also contain fused aryl rings. Examples include 9-vinylanthracene and 9-vinylcarbazole. Mixtures of monomers may also be used. By “monomer” is meant true monomer; that is, it is not intended to include dimers
Gorr Rachel
Meyers Diane R.
PPG Industries Ohio Inc.
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