Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
1999-03-02
2001-05-15
Meeks, Timothy (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S512000, C427S358000, C427S393000
Reexamination Certificate
active
06231931
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of coating a wooden substrate. More particularly, the present invention relates to a method of coating a wooden substrate with an energy curable polymer. Even more particularly, the present invention relates to a method of coating a wooden substrate with a structural polymer having a substantially 100% solids content which is ultraviolet light curable.
Wood is used as a durable and inexpensive building material in numerous items including doors in houses and trucks, decks, ramps, buildings, roofs, etc. An even less expensive alternative to solid wood boards is plywood or fiberboard. Wood by its very nature is a porous material and tends to decay when exposed to the elements such as rain, snow, ice, wind, sun, etc. To preserve wood, numerous types of treatments and coatings have been developed. For example, wood can be treated with chemicals such as a copper solution or alternatively be painted. When wood is painted, the surface is typically primed with a solvent-based primer to prepare the porous surface for a finishing coat of paint. The primer is necessary due to the surface characteristics of the wood. The primer and paint work to seal the wood surface from exposure to the elements and additionally work to fill various fissures and crevices in the surface. Typical paints contain about 20% solids and 80% solvent. When paint is applied to a wooden surface, the solvent evaporates away to leave the solid behind. Solids typically are the paint pigment and a polymer material such as latex. Problems with paints result in adhesion and shrinkage. Because the typical paint contains only about 20% solids, the paint tends to shrink upon application and drying. A porous surface such as wood is especially difficult to seal. Thus, numerous coats of paint along with the associated prolonged drying times are required to effectively seal and fill the porous surface. The multiple step processes associated with multiple coats of paints are undesirable, especially in a manufacturing setting, and are therefore to be avoided were possible.
Plywood or fiberboard offers additional problems over solid wood products. Plywood is typically made of pressed wood particles held together with glue or adhesives. Solvents used in the production of plywood often linger in the pressed wood long after the plywood is manufactured. These solvents tend to leach from the plywood and can create bubbling and blistering in a painted surface. For example, plywood or fiberboard is often used in the manufacture of truck doors that roll up when opened. The doors are formed with a plurality of wood slats individually hinged together and roll upwards upon a track connected to a door frame. It was discovered early on that fiberboard used to make these slats could not be economically painted due to the porosity of the surface and incompatibility of paint with glues and solvents present in the plywood. The roll-up truck door industry responded to the problem by covering the plywood slats with a veneer or cardstock paper covering. The covered slates or medium density overlay (MDO) could then be more effectively painted. It has been discovered that the present day technique of covering the plywood or fiberboard slats with a paper covering glued to the surface and then painting the surface does not adequately seal the door from exposure to the elements. It has also been discovered that the use of a veneer or paper covering of the slates adds a needless step in the production process of manufacturing overhead roll-up truck doors.
The present invention overcomes the above mentioned problems and others. As noted hereinabove, the present invention provides a method of coating a substrate with an ultraviolet (UV) light curable polymer or polymeric coating. The present method is particularly adapted for coating a “wooden” substrate and, in particular, the panels or slats comprising a vehicular wooden roll-up overhead door. The present invention enables the coating of such a wooden substrate with a structural polymer overlay having a substantially 100% solids content, in an ultraviolet light curable formulation, to create a waterproof, weatherproof, pore-bridging, grainfilling, surface strengthening member. The coating may be used as a single coat or as a layer suitable for receiving topcoats without primers. As noted, the present invention is particularly adapted for manufacturing vehicular overhead roll-up wooden doors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In a first aspect of the present invention, there is provided a method for applying the coating to a wooden substrate which, generally, comprises the steps of:
(a) applying a first layer of a structural polymer, in an uncured form, to at least one surface of the substrate, the polymer being an ultraviolet light curable filler polymer; and
(b) curing the polymer of the first layer.
Additionally, after curing the polymer of the first layer, the layer may be scuffed to allow application of subsequent layers of the polymer to the resulting surface of the substrate, which additionally may be cured, and scuffed in repeated fashion to provide as many layers as desired.
The method of the present invention eliminates the need for paper overlays normally applied on exterior paint grade plywood and similar substrates. In addition to eliminating the need for paper overlays, such polymer coating provides protection to the underlying substrate from moisture and extreme weather conditions, and, thus, seals the substrate. The provided protection more adequately prevents undesired warping and degradation of the substrates.
According to the method hereof, the first layer of the polymer, in an uncured form, is applied, at ambient temperature and pressure, to at least one surface of the substrate to a depth of about 0.2 to 60 mils and, preferably, to a depth of about 1.0 to 2.0 mils. The polymer is applied to the at least one surface of the substrate by any suitable method known to those skilled in the art to which the present invention pertains. Ordinarily, the methods used include, but are not limited to, spraying, immersion or dipping, roll coating (reverse fill, direct roll, etc.), and curtain coating.
The reverse fill roll coating method is the method that is preferably used. The reverse fill roll coating method is a method where the uncured polymer is applied across the surface of the substrate by direct rolling, either by hand or mechanically, and is followed by a reverse direction rolling, leaving the surface adequately filled with polymer.
Once the first layer has been applied onto a surface of the substrate, the first layer of the polymer is cured by exposure to an energy source, preferably UV light. As further detailed hereinbelow, the step of curing is a chemical reaction, which causes the liquid resins to solidify by way of a free radical or cationic polymerization reaction. The mode by which curing the polymer is achieved is dependent on the particular polymer used.
As stated hereinabove, after the application of polymer is complete, the polymer is cured. The polymer is cured by exposure to an energy source, preferably a dose of UV radiation, in a dosage which, generally, ranges from between about 0.005 joules/cm
2
to about 15 joules/cm
2
. Preferably, the radiation dose ranges from between about 1 joules/cm
2
to about 9 joules/cm
2
or about 300 to 400 wpi at about 20 to 80 fps. Typically, curing is done with a UV lamp within the focal point of one or more focused lamps, in order to reduce the likelihood of elevated heat levels. Elevated heat levels may cause the cured polymer to shrink. Elevated heat levels may also cause the cured polymer to crack. The curing of the UV curable polymer is effected by a rapid polymerization reaction which is initiated by a photoinitiator component of the composition, as detailed below, when it is exposed to UV light. Substantially the entire composition remains in place on the substrate during and after curing.
The first layer is a complete coating in and of itself. In a
Blazey John S.
Robertson Gary
Sgro Joseph C.
Chen Bret
Meeks Timothy
Plunkett & Cooney PC
Weintraub Arnold S.
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