Coating processes – Solid particles or fibers applied – Uniting particles to form continuous coating with...
Reexamination Certificate
2001-07-27
2003-04-15
Parker, Fred J. (Department: 1762)
Coating processes
Solid particles or fibers applied
Uniting particles to form continuous coating with...
C427S470000, C427S485000, C427S202000, C427S393000, C428S413000, C428S423100, C428S537100
Reexamination Certificate
active
06548109
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to a method of reinforcing wood substrate with a substantially solvent-free treating composition. The invention is also directed to a method of powder coating wood substrate including pre-treating the substrate surface(s) with a substantially solvent-free treating composition prior to powder coating.
BACKGROUND OF THE INVENTION
Powder coated composite wood such as powder coated medium density fiberboard (MDF) is often used in the office furniture industry for desktops, drawers, kitchen cabinet doors, etc., as it provides a decorative appearance as well as performance advantages such as toughness and hardness. However, it has been a challenge to coat wood substrate by means of conventional electrostatic application of powder coatings. A wood substrate has very low electrical conductivity, which comes from its moisture content. Without sufficient conductivity, wood substrate can not attract enough powder to its surface(s) to form a uniform coating. To obtain a uniform coating, conventional processes have tried to pre-heat the substrate. Pre-heating the substrate dries off surface moisture, which helps to reduce outgassing during the cure cycle. Pre-heating the substrate, however, tends to drive more moisture out of round edges and/or routed areas of the substrate. As the drying of the surface(s) of the substrate reduces the electrical conductivity of the surface(s), especially at round edges and/or routed areas, it is even more difficult to coat powder on sharp edges and corners to obtain a uniform coating using traditional electrostatic technique.
Other proposals for obtaining a uniform coating include pre-coating substrate with aqueous and/or organic solvent-based primers prior to the application of the powder coatings. While helping to provide electrical charge for roughened edges or difficult to coat areas, the aqueous primer systems tend to warp the surface(s) of the substrate and to raise the grain of the surface(s); and the organic solvent-based primer systems bring various undesirable volatile components into the environment.
It is desirable to obtain a uniform powder coating on wood substrate, especially around sharp edges, corners and routed areas of the substrate. It is also desirable to obtain a smooth powder coating on wood substrate, which minimizes pinholes and other surface defects. It is also desirable to obtain a high performance powder coating on wood substrate as defined by hardness, toughness, and impact resistance, etc.
SUMMARY OF THE INVENTION
In one aspect, the invention features a method of reinforcing wood substrate. The method includes (a) applying a substantially solvent-free treating composition on at least one surface of the substrate, and (b) optionally curing said treating composition. The treating composition includes at least one thermoset material and has a viscosity sufficiently low to allow the treating composition to wet out the surface(s) of the substrate and penetrate into the surface fiber structure of the substrate.
In another aspect, the invention features a method of powder coating wood substrate. The method includes (a) pre-treating at least one surface of the substrate with a substantially solvent-free treating composition, (b) applying a powder coating composition on the pre-treated surface, and (c) curing the powder coating composition. The treating composition includes at least one thermoset material and has a viscosity sufficiently low to allow the treating composition to wet out the surface(s) of the substrate and penetrate into the fiber structure of the substrate.
In one embodiment, the treating composition is preferably a substantially solvent-free liquid. In other embodiments, the treating composition is preferably a 100% solids liquid at ambient conditions.
In yet another aspect, the invention features an article manufactured by the reinforcing method. The article includes a wood substrate having at least one surface treated by a treating composition that is optionally cured. The article exhibits improved electrical conductivity and toughness.
In yet another aspect, the invention features an article manufactured by the powder coating method. The article includes a wood substrate having at least one surface treated by a treating composition, and a continuous uniform powder coating deposited thereon. The treating composition is integrally cured into the surface fiber structure. The powder coating is either crosslinked with or adhered to the treating composition upon final cure, depending on the specific formulations, to form an integrated composite.
In one embodiment, the wood substrate has round edges and corners, and/or routed areas.
The methods of the invention are particularly advantageous with respect to wood substrate. The substrate may preferably be pre-treated at ambient temperature without the need to pre-heat it. Pre-treating the substrate with a substantially solvent free, liquid treating composition would slow down the moisture evolution from the substrate, especially from the round edges and/or routed areas so that these areas would not be dried out as they would by the conventional pre-heating. The reduced moisture evolution helps to maintain the capability of the overall substrate to carry sufficient electrical charge for efficient electrostatic application of the powder coating to the substrate since the substrate will not dry out as quickly during heating. Hence, a continuous uniform coating on the substrate including even difficult to coat areas such as sharp edges and corners can be obtained even if the substrate may not be pre-heated and the powder coating may be applied at ambient temperature. By the pre-treatment, pinholes and other defects on the powder-coated surface(s) can also be minimized and even eliminated. In addition, curing the treating composition prior to the application of the powder coating composition is optional.
The methods of the invention can minimize, and preferably, eliminate the emission of volatile organic component (VOC) associated with the use of conventional solvent-based primer systems.
The treated substrate exhibits improved electrical conductivity, especially at sharp edges, comers and routed areas. The treated substrate also exhibits reinforced surface quality including e.g., stronger surface fiber bond strength and increased impact resistance relative to the untreated substrate. In one embodiment, the treated substrate exhibits good adhesive bondability to the powder coating such that the substrate does not flake apart when a crosshatch adhesion test is performed.
DETAILED DESCRIPTION OF THE INVENTION
The treating composition is substantially solvent-free, i.e., it does not contain water and it does not contain any substantially amount e.g., greater than 10 wt %, and in some cases, greater than 5 wt %, based on the total weight of the treating composition, of organic solvent(s). The treating composition is preferably free of volatile organic solvent(s). More preferably tie treating composition is a substantially solvent-free liquid, and most preferably a 100% solids liquid, i.e., a liquid thermoset free of volatile components and aqueous and/or organic solvent(s).
The treating composition is formulated to have a viscosity such that it can effectively wet out the surface(s) of the substrate and preferably penetrate into the surface fiber structure of the substrate. Preferably, the viscosity of the treating composition is such that the treating composition does not form an appreciable coating film on the surface(s) of the substrate to achieve the desirable binding and/or reinforcing effect to the surface fiber. The treating composition preferably has a viscosity of no greater than about 5,000 cps, more preferably no greater than about 1,000 cps, and even more preferably no greater than about 100 cps at 77° F.
The treating composition is formulated to be preferably compatible with powder coatings or other topcoats. The treating composition is also formulated to be preferably electrically conductive.
The treating composition inc
Blatter Walter J.
Hagquist James A. E.
H.B. Fuller Licensing & Financing Inc.
Parker Fred J.
Su Bin
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