Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-26
2003-04-01
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S409000, C523S412000, C525S107000, C525S111000, C525S119000
Reexamination Certificate
active
06541544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to new thermosetting powder coating materials. More particularly, the invention relates to new textured and weatherable powder coating compositions providing a textured surface to mask defects in the surface of an underlying substrate without using a texturing agent, and to the articles containing the same. The powder coating compositions are provided as powdered material, and are adaptable to electrostatic application to conventional substrates and substrates intolerant of high cure temperatures.
2. Description of the Related Art
The preparation and application of powder coating compositions is known in the surface coating art. Powder coatings are considered desirable because they contain little or no organic solvent. They consequently release minimal amounts of volatile organic compounds during storage, application, or cure of the materials. Accordingly concerns related to worker safety, as well as deleterious environmental effects, are minimized.
Historically powder coatings have been used primarily on metal substrates because of the tolerance of such substrates for relatively high cure temperatures and because of the ease with which metal objects may be grounded to provide a target of uniform electrical potential for electrostatic application. More recently, powder coatings have been applied to non-metallic substrates such as plastic and wood, more specifically, medium density fiberboard (MDF). Although some success has been achieved in coating such non-metallic substrates, problems remain. Wood and MDF release water and other compounds as gasses during the high temperature cure associated with traditional powder coatings. This outgassing disrupts the surface of the coating material during flow and cure, resulting in pinholes and other defects in the coating surface. Also, non-metallic substrates often present less uniform substrate surfaces for coating. A smooth coating applied over such a surface may display aesthetically undesirable variations.
One way to effect pleasing coverage of a non-uniform substrate is to provide a coating having a texture that masks the underlying non-uniformity of the substrate. Previously, textured coatings have been prepared by adding inorganic or rubber texturing material to existing powder coatings. However, such efforts have resulted in coatings of relatively poor weatherability.
Various powder coating compositions are described in the patent literature such as EP-A2-911 709 and the following United States patents. U.S. Pat. No. 4,341,819 describes a powder applied in a fusion coating process that yields a low gloss, wrinkled finish of heat reactive epoxy resulting from the use of methylene disalicyclic acid as the curing agent for the epoxy resin; U.S. Pat. No. 5,721,052 describes thermosetting powder coating compositions adapted to form a grainy textured finish on heat sensitive substrates, especially wood products such a particleboard, based on bisphenol A type epoxy resin and a texturing agent. U.S. Pat. No. 5,212,263 describes a powder coating composition forming a textured finish comprising epoxy resin, methylene disalicyclic acid and an imidazole Bisphenol A epoxy resin. U.S. Pat. No. 5,494,994 describes the production of a matt epoxy hybrid powder coating using salts of pyromellitic acid and various amines. U.S. Pat. No. 5,714,206 describes wood electrostatically coated with a thermosetting powder coating system in which a mixture of self-curing epoxy resin and catalyst is made to cure at low temperatures by the addition of a curing agent. The coatings disclosed, however, do not provide the advantageous combination of textures, low cure temperatures, and weatherability of the present invention without using a texturing agent.
SUMMARY OF THE INVENTION
The invention is directed to a textured and weatherable powder coating composition comprising a mixture of a hardener or curing agent with a functionality of 2 or greater capable of reacting with an acid or anhydride functional group, a polymeric coreactant with a functionality of 2 or greater capable of reacting with the hardener, a carboxylic acid functional polyester, and optionally, a catalyst. The polymeric coreactant is made by polymerizing ethylenically unsaturated monomers such as carboxylic acid functional ethylenically unsaturated monomers or anhydride functional ethylenically unsaturated monomers. The powder coating composition can provide a textured and weatherable finish without including a texturing agent.
The invention also includes a robust weatherable coating having a desired textured surface formed by applying the composition to at least one surface of a substrate and curing the same thereon. The invention provides the weatherable textured coating to cover the surface nonuniformities found, such as in wood, MDF and other substrates. Moreover, the invention also includes textured and weatherable coatings having a low-temperature cure characteristic that minimizes the volatilization of compounds within the substrate during cure and thus minimizes disruption of the coating surface.
The composition of the invention is readily applied using conventional means, including electrostatic spray and fluidized bed methods, to various substrates, such as metal and heat sensitive substrates, e.g., plastic and wood substrates, more specifically, medium density fiberboard (MDF). In some embodiments, the composition exhibits a reduced cure temperature, as compared to other embodiments of the invention or conventional textured coating compositions. Among other advantages, such reduced cure temperatures tend to diminish outgassing from some substrates. A reduction in outgassing is associated with reduced disruption of the coating surface during flow, and consequently improved ultimate coating quality.
In a further aspect, the composition and coating of the invention exhibits weatherability, including resistance to ultra-violet light, that is superior to other known textured coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
These favorable physical characteristics result from a composition comprising, a hardener with a functionality of at least 2 that is reactive with an acid or anhyride functional group, a polymeric coreactant that has a functionality of at least 2. The polymeric coreactant is reactive with the aforementioned hardener and includes a substantially ethylenically saturated polymer made by polymerizing ethylenically unsaturated monomers, in which at least one monomer is a carboxylic acid functional ethylenically unsaturated monomer, or an anhydride functional ethylenically unsaturated monomer. The composition does not include a texturing agent. In some embodiments, the composition may also include a catalyst. In addition, The composition may also include a variety of other components such as fillers, pigments, flow control agents and stabilizers, and the like, as would be clear to one of skilled in the art.
The hardeners useful in the invention include glycidyl functional compounds and betahydroxyalkylamides, which react with the carboxylic acid functional group. Examples of glycidyl functional hardeners for weatherable coatings include hydrogenated bisphenol A and bisphenol F epoxy resins, 1,3,5-tris(2,3-glycidyl- propyl) 1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, 1,3,5-tris(2,3-glycidyl-2methyl propyl) 1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, the diglycidyl ester of terephthalic acid and the triglycidyl ester of trimellitic acid. The 1,3,5-tris(2,3-glycidyl- propyl) 1,3,5-triazine-2,4,6-(1H,3H,5H)-trione is known by those skilled in the art as triglycidyl isocyanurate (TGIC), and is sold under the tradename of PT-810 from Ciba Specialty Chemicals Brewster, N.Y. The 1,3,5-tris(2,3-glycidyl-2methyl propyl) 1,3,5-triazine-2,4,6-(1H,3H,5H)-trione is sold under the tradename MT-239 and is available from Nissan Chemical. The mixture of the diglycidyl ester of terephthalic acid and the triglycidyl ester of trimellitic acid is sold under the tradename of PT-910 by Ciba Specialty Chemicals, Brewster
Carlson Brian W.
Hart Stephen C.
Schmierer Jeffrey G.
H. B. Fuller Licensing & Financing Inc.
Su Bin
Woodward Ana
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