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...
Reexamination Certificate
1999-12-17
2002-05-28
Wu, David W. (Department: 1713)
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...
C524S555000, C524S556000, C524S813000, C526S219000, C526S318430, C428S423300, C428S001400
Reexamination Certificate
active
06395822
ABSTRACT:
TECHNICAL FIELD
This invention relates to coating compositions. More particularly, this invention relates to liquid coating compositions that are thermally curable in the presence of oxygen and are comprised of a multifunctional (meth)acrylate monomer or oligomer, an azo initiator and oxygen.
BACKGROUND OF THE INVENTION
The coatings industry is constantly searching for new technologies that will reduce or eliminate the amount of volatile organic compounds (VOCs) in industrial paints and coatings. High solids solvent borne coatings, water based coatings, powder coatings and radiation cured (ultraviolet and electron beam) coatings are technologies that significantly reduce the amount of VOCs relative to traditional solvent borne coatings. Each of the aforementioned technologies has limitations. Thermally cured solvent borne coatings still dominate the industry because suitable substitutes for many coatings have not been found.
With the exception of ultraviolet and electron beam cured coatings and coatings comprising polyallyl glycidyl ethers, (meth)acrylate functional resins and coatings are not used in industrial coating applications. A primary reason for this is that atmospheric oxygen inhibits the curing process. Oxygen inhibited coatings cure at a low rate, often remain tacky, and exhibit poor tensile strength and durability, resulting in film properties that are unsuitable for industrial paints and coatings.
Ultraviolet curing of acrylate films in air is practical because the high density of initiating radicals generated during irradiation consumes dissolved oxygen faster than oxygen can diffuse back into the film. During irradiation, polymerization proceeds in a quasi-anaerobic environment.
Attempts to derive the benefits of free radical chemistry by thermally curing thin, high solids acrylate coatings similar to those used in ultraviolet and electron beam cured coatings have produced under-cured films with marginal solvent resistance. This is true even under practical anaerobic conditions. In practice, the total exclusion of oxygen is difficult in commercial coating operations.
Polyallyl glycidyl ether resins have been used in two-component, high-solids, thermally cured coatings that comprise (meth)acrylate monomers and oligomers. These coatings are two component systems with limited pot life and are expensive due to the high cost of the polyallyl glycidyl ether component. Additionally, they require oxygen and drier compounds such as cobalt carboxylates, and require solvent for spray application. Polyallyl glycidyl ether resins have been commercially available since the early 1990's, but have only achieved very limited use in industrial paints and coatings due to their limitations.
The present invention provides a replacement for many traditional thermally cured solvent borne coatings. In one embodiment of this invention, a solventless coating is provided that can be applied via traditional/existing spray application equipment, and cured in traditional existing cure ovens at traditional cure temperatures and bake times. This embodiment can be characterized as a one-component, storage-stable, solventless, thermally curable, (meth)acrylate functional, clear or highly pigmented paint or coating with a VOC content lower than solvent or water borne coatings and equal to or less than powder coatings. These (meth)acrylate functional coatings can be cured in the presence of atmospheric oxygen. This embodiment is cost competitive with traditional general industrial coatings and is expected to result in a significant reduction in VOC emmisions introduced into the atmosphere.
SUMMARY OF THE INVENTION
This invention relates to a liquid coating composition that is thermally-curable in the presence of oxygen, comprising: a monomer or oligomer containing two or more acrylate and/or methacrylate functional groups; an azo initiator; and oxygen. This invention also relates to a process for coating a substrate comprising the steps of applying a thin film of the foregoing coating composition to said substrate; and heating said coating composition at an effective temperature for an effective period of time to cure said coating composition, said applying and heating steps being conducted in the presence of oxygen.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The monomers or oligomers containing two or more acrylate and/or methacrylate functional groups that are useful with this invention can be any such monomers or oligomers known in the art. These are sometimes referred to as multifunctional (meth)acrylate monomers or oligomers. These multifunctional (meth)acrylate monomers or oligomers include difunctional, trifunctional, tetrafunctional, pentafunctional and hexafunctional monomers and oligomers. The difunctional and trifunctional monomers and oligomers are especially useful. These monomers and oligomers may include other functional groups other than the acrylate and/or methacrylate functional groups. These other functional groups include epoxy, hydroxyl, carboxyl, sulfonic, phosphonic, isocyanate, vinyl, allyl, halide (e.g., fluoride, iodide, bromide), amine, sulfonamide, carbamide, carbodilmide, cyano, acetylenic, aldehyde, peroxy, hydroperoxy, azo, peroxyester, and combinations of two or more of the foregoing. The monomers and oligomers that are useful typically have molecular weights in the range of about 200 to about 5000, and in one embodiment about 200 to about 3000, and in one embodiment about 300 to about 1000.
In one embodiment, the multifunctional (meth)acrylate monomer or oligomer is a compound represented by the formula
wherein in formula (I):
R is a hydrocarbon group, a siloxane group, a partially fluorinated hydrocarbon group or a perfluorocarbon group;
each A is independently a divalent group derived from an epoxide, a mixture of diol and dicarboxylic acid, a lactone, a lactarn, an amino acid, a hydroxy acid or lactide;
each B is independently hydrogen, a hydrocarbon group, a siloxane group, a partially fluorinated hydrocarbon group or a perfluorocarbon group, or a group represented by the formula
wherein in formula (II) R
1
is hydrogen, a hydrocarbon group, a siloxane group, a partially fluorinated hydrocarbon group, or a perfluorocarbon group;
x is a number in the range from zero to about 50, and in one embodiment about zero to about 15; and
y is a number in the range from 2 to about 10, and in one embodiment 2 to about 6.
R in formula (I) a hydrocarbon group, a siloxane group, a partially fluorinated hydrocarbon group or a perfluorocarbon group containing up to about 50 carbon atoms, and in one embodiment about 5 to about 20 carbon atoms. R can be a straight chain or branched chain hydrocarbon group. The group R may also contain one or more oxygen, nitrogen, sulfur and/or halide atoms (e.g., fluoride, bromide, iodide). The group R can contain one or more hydroxyl, carboxyl and/or amine groups.
The group A in formula (I) contains 1 to about 25 carbon atoms, and in one embodiment about 2 to about 12 carbon atoms. The epoxides which A is derived from include ethylene oxide, propylene oxide, glycidyl methacrylate, and the like. The diols from which A is derived include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,2-, 1,3- and 1,4-butanediols, hexane diol, caprolactone diol, caprolactone triol, and the like. The dicarboxylic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and the like. The lactones include propiolactone, butyrolactone, valerolactone, caprolactone, and the like. The lactams incldde propiolactam, butyrolactam, valerolactam, caprolactam, and the like. The amino acids include 3-amino propionic acid, 4-amino butyric acid, 5-amino valeric acid, 6-amino caproic acid, 7-amino heptanoic acid, 8-amino octanic acid, and the like. The hydroxy acids include lactic acid, 4-hydroxy butyric acid, 5-hydroxy valeric acid, 6-hydroxy caproic acid, 7-hydroxy heptanoic acid, 8-hydroxy octanoic acid, and the like. Mixtures of the foregoing may be used.
The hydro
Renner , Otto, Boisselle & Sklar, LLP
Wu David W.
Zalukaeva Tanya
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