Patent Application
20180257106
This invention relates to an improved apparatus for infrared heating and curing powder coatings on porous wood products, such as medium density fiberboard (MDF). More specifically, the invention relates to a novel arrangement of infrared heaters for efficiently heating and curing powdered coatings on MDF board.
For the past twenty-five years powder coating of metal parts has become a popular method of finishing. There are numerous suppliers of the powder coating catering to all segments of the metal industry, ranging from automotive to architectural to marine applications. Powder on metal has become a mature industry. The principle method of applying powder to metal parts charges the powder particles via a powder spray gun. The charged particles are then attracted to metal parts that are earthed via a grounded hanging device on a conveying system.
Wood, or engineered wood products (EWP), such as medium density fiberboard (MDF) are not naturally as conductive as typical metal parts. MDF is made to become conductive by preheating the MDF to a range that is between about 150 and 250 degrees Fahrenheit. Preheating the MDF activates the moisture content of the MDF (typically about 5-10%) causing it to become conductive. Thus, charged powder will attach to a properly grounded MDF board.
Once the powder is attached to the board, the method of curing has been by either heating the powder in a convection oven for a certain period of time or by infrared heat for a period of time that is less than that of a convection oven. The infrared heat source has been either electric resistance heaters or catalytic heaters. In recent years, catalytic heaters have attracted considerable attention as the preferred choice of infrared heat sources.
Curing powder coatings on medium density fiberboard (MDF) using an infrared heat source has given rise to certain difficult problems. MDF board is available in various thicknesses ranging from one-quarter (¼) inch through to two inches, for example. With all thicknesses, the face surfaces of the MDF board are of a considerable higher density than the core of the board. The greater the thickness of the MDF board, the greater the difference is between the core density and the face surface density. MDF board has a certain amount of naturally occurring porosity within the board structure and hence a characteristic moisture content. The greater the thickness, the greater the porosity due to the lower core density.
When heating powder coated. MDF board to cause the powder or liquid to cure, the board is typically hanging in a vertical position. As the board heats, the entrapped moisture expands and out-gases through the edges of the board, typically from the center of the core in the area of lowest density. During the curing process using a conventional catalytic heating oven, the face surfaces of the board are easily heated, while the edges, especially the vertical edges, do not receive a full direct line of site of infrared energy. As a result, the edges of the board are the last to cure as compared to the face surfaces. This leads to an occurrence where the expanding moisture, which is out-gassing from inside the board, bubbles and forms blisters along the side edges of the board. These blisters occur because the powder at the edges has not reached a degree of cure, as compared to the face of the board, which would prevent the blisters from forming.
Furthermore, powder coatings, going through the curing process, first turn to liquid and then a gel stage followed by a curing stage where the powder reaches its full cured properties. However, the liquefied powder will be drawn into the edges of the MDF in a similar manner to a wood edge grain absorbing liquids. The result is an undesirable different look and feel to that of the coated and cured face sides of the MDF board and EWP's. In general the edges will display pitting and/or protruding fibers.
Depending on the method of cutting and sanding, of the edges of the MDF board the fibers will protrude in varying degrees. The degree of this protrusion is dependent on the density across the board thickness and a number of other factors to do with the physical properties of the board—fiber type and length, percentage and type of glue used and the MDF board and/or the EWP's manufacturing process in general.
Thus, the manufacturing and pre-finishing processes for the MDF board, along with the precise application of the powder thickness on the edges, contribute too many variables that may produce sub-standard edge finishes, resulting in waste and low yields.
To compensate for the issues associated with powder coating the edges of MDF boards the present state of the art employs a two coat process. First a powder prime coat is applied to the edges and faces of the MDF, partially cured, followed by a powder top coat and then the two coats are co-cured together. The end result provides an acceptable edge finish that mitigates, but doesn't eliminate the undesirable variables mentioned above.
It will be appreciated, that while it is only the edges of the MDF board that require the prime coat, the entire board is primed as part of the overall process; resulting in an unnecessary expenses since the primer coat adds no extra cosmetic benefit to the face sides of the MDF board. Additionally, there is the extra capital equipment cost of the primer powder application station and associated primer curing oven.
Thus, there exists a need for a system and method for the edge treatment of MDF boards and EWPs to maintain a high quality powder or liquid coated MDF board while reducing associated manufacturing expenses.
The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings
The invention is directed towards an efficient production line for curing an epoxy powder or liquid primer. The production line includes an edge sealing oven vestibule or booth having at least one focused infrared (IR) emitter assembly. The focused IR emitter assembly is adaptable to emit IR energy field or pattern substantially matched to a predetermined absorption characteristic of the epoxy powder or liquid primer, The focused IR emitter assembly is adaptable to emit the focused IR energy field comprising substantially a 60 degree arc.
A focused infrared apparatus for curing a primer coated edge is provided. The apparatus includes at least one focused infrared (IR) emitter assembly adaptable to emit IR energy substantially matched to a predetermined absorption characteristic of the primer and is adaptable to emit a focused IR energy pattern substantially focused on the primer coated edge.
The invention is also directed towards an apparatus for edge curing engineered wood products (EWP) with trailing and leading edges and supported by a conveyor track. The apparatus includes a first infrared (IR) emitter assembly having a plurality of infrared emitters for emitting IR energy; and, a first reflector adaptable to reflect the IR energy emitted by the first plurality of IR emitters. The apparatus also includes a second infrared emitter assembly having a second plurality of infrared emitters for emitting IR energy; and, a second reflector adaptable to reflect the IR energy emitted by the second plurality of IR emitters. The first IR emitter assembly and the second IR emitter assembly are disposed on opposite sides of the conveyor track and offset from a common axis by a predetermined amount, and are adaptable to overlap respective IR energy fields onto the trailing edge of the EWP.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The following brief definition of terms shall apply throughout the application:
The term “outer” or “outside” refers to a direction away from a user, while the term “inner” or “inside” refers to a direction towards a user;
The term “comprising” means including but not limited to, and should be interpreted in the manner it is typically used in the patent context;
The phrases “in one embodiment,” “according to one embodiment,” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention (importantly, such phrases do not necessarily refer to the same embodiment);
If the specification describes something as “exemplary” or an “example,” it should be understood that refers to a non-exclusive example; and
If the specification states a component or feature “may,” “can,” “could,” “should,” “preferably,” “possibly,” “typically,” “optionally,” “for example,” or “might” (or other such language) be included or have a characteristic, that particular component or feature is not required to be included or to have the characteristic.
The term “cure”, “cured” or “curing” shall be understood to mean the hardening of a suitable edge covering material. Further, curing may be brought about by chemical additives, ultraviolet radiation (UV), or applied heat.
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Air knife 214 and air knife 215 provide gas flows 214A and 215A, respectively. Gas flows 214A, 214B may be any suitable gas flow, such as, for example, high pressure air.
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Fixture 41 may be any suitable fixture for holding infrared assembly 42 and adaptable to rotating within respective housing (see
Focused infrared assembly 42 includes infrared emitter 5A1, transmission medium 5A2, and reflector 5A3. Infrared assembly 42 is adapted to emit a focused infrared energy pattern comprising a 60 degree arc.
Infrared emitter 5A1 may be any suitable IR emitter for heating MDF boards 33. For example, infrared emitter 5A1 may be any suitable short wave, medium wave, or long wave IR emitter. For example, the IR emitter 5A1 may be a resistive element, a chromium alloy filament, or a tungsten filament, In alternate embodiments, IR emitter may include single or a pair of heating filaments.
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It will also be appreciated that the transmission medium 5A2 and/or the reflector 5A3 may be suitably shaped or formed to direct, focus, or concentrate the IR energy onto a particular area of an MDF board. For example, the, transmission medium 5A2 may contain characteristics of a Fresnel lens.
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Preheated MDF board 11B exiting preheat oven 12 at point A is at approximately 200 degrees Fahrenheit and thus conductive which allows powder to electrostatically adhere to the board. Conveyor track 13 moves preheated board 11B from point A to point B in about 2 minutes where the preheated MDF board 11B enters primer booth 14 at approximately 100 degrees Fahrenheit.
Primer booth or vestibule 14 electrostatically epoxy powder coats, the face and edges of MDF board 11B in approximately 1.5 minutes. Exiting primer booth 14 the primed MDF board 11C is conveyed by conveyor track 13 from point C to point D in approximately 2 minutes where the primed MDF board 11C enters a hybrid multi-section infrared gel oven 16. The infrared catalytic heater portion of the hybrid multi-section infrared gel oven is described in U.S. Pat. No. 7,159,535 and incorporated herein. In general, heat is produced when a gaseous fuel is brought into contact with a catalyst in the presence of air containing a normal level of oxygen. Typically, the fuels are natural gas, propane and butane, for example.
Generally, the gaseous fuel is fed through a bottom of the catalytic heater and is dispersed at atmospheric pressure into contact with a porous active layer. This active layer contains a catalyst which may be platinum, for example. Oxygen from the atmosphere enters the porous catalytic layer and reacts with the gaseous fuel, promoted by the catalyst.
This reaction releases the BTU content in the fuel in the form of infrared heat. The chemical reaction that occurs during the oxidation reduction process produces temperatures within the catalyst of from about 500 to 1000 degrees Fahrenheit (F.). The by-products of the reaction include carbon dioxide and water vapor.
In approximately 3 minutes the 3-section infrared gel oven 16 heats the primed MDF board 11C to approximately 300 degrees Fahrenheit causing the epoxy powder on the MDF board 11C to gel or partially liquefy.
Exiting the gel oven 16, the gelled MDF board 11D is conveyed from point E to point F by conveyor track 13 in approximately 8 minutes where the gelled MDF board 11D enters the top coat booth 18 at approximately 130 degrees Fahrenheit. The top coat booth 18 top coats the gelled MDF board 11D with another powder layer on all faces and edges of the gelled MDF board 11D in approximately 1.5 minutes.
Exiting the topcoat booth 18 at point G the top coated MDF board 11E is conveyed to point H where the board 11E enters the multi-section hybrid cure oven 19 (see also
Exiting the multi-section hybrid cure oven 19 at point I the cured MDF board 11F is conveyed to point J in approximately 20 minutes allowing for the cured MDF board 11F exiting the cure oven 19 at approximately 300 degrees Fahrenheit to air cool. At point J the cooled and cured MDF board 11F is removed from, conveyor track 13.
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Different heating zones and/or different pluralities of infrared sources may share all, some or no heating parameters. For example, different pluralities of infrared sources may operate at different peak spectrums, and may have different spectral spreads (see
Yet further variation is possible by selecting or controlling the power output of individual infrared sources. For example, a first plurality of infrared sources may operate predominately in the mid infrared region, while a second plurality of infrared sources may operate in the near infrared portion of the spectrum. The plurality of mid infrared sources may be operated at a first wattage, while the plurality of near infrared sources may be operated at a second wattage. Similarly, the plurality of mid infrared sources may be positioned at a first distance from an MDF board to be cured with a first linear distance between individual sources of the plurality of infrared sources of the mid infrared plurality, while the plurality of near infrared sources may be positioned at a second distance from an MDF board to be cured with a second linear spacing.
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Other types of materials, such as polyethylene, may preferentially absorb mid infrared radiation, thereby enabling such materials to be rapidly heated using mid infrared sources. Other types of materials may preferentially absorb other wavelengths, and infrared sources strongly emitting at those wavelengths may be selected to heat such materials. Based upon the heating to be performed, energy restrictions, time limitations, materials used, etc., different types of sources in different arrangements and numbers/densities may be used at various stages of an oven in accordance with the present invention.
In alternate embodiments MDF board edges 33B may be pre-primed by a liquid primer. It will be understood that the liquid primer may be cured by any suitable method, such as heat curing (e.g., infrared absorption), for example; or, by chemical reaction from catalyst curing and accelerators. It will be also be understood that the liquid primer may be any suitable liquid primer such as PVA glue or other solvent based liquid such as, for example, a lacquer or enamel based primer. It will also be understood that the liquid primer may be a suitable water based primer.
Property characteristics of a suitable primer, water based or solvent based, include, but are not limited to, the capacity to be cured prior to any liquid induced deformation of the MDF board; and, after curing, sufficient mechanical strength (which may be measured by hardness, toughness, stiffness and/or creep, or strength) to resist any deformation of the cured primer due to out-gassing or water vaporization discussed earlier.
Suitable primers, water or solvent based, may also include particulate matter such as resins, polymerized synthetics or chemically modified natural resins including thermoplastic and/or thermosetting polymers. Suitable primers may also include amorphous solid particulate matter, such as, for example, glass or nanostructured materials, which may or may not, exhibit glass-liquid transition.
It should be understood that the foregoing description is only illustrative of the invention. Thus, various alternatives and modifications can be devised by those skilled in the art without departing from the invention. For example, the EWP boards are often flat, however the same application technique applies to molded EWP components as in the case of molded plywood seats that are also stacked to expose the multiple layers of edges in a similar uniform fashion. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims. For example, any engineered wood product (EWP) having non-uniform densities may be edge coated as described herein.
Additionally, the section headings used herein are provided for consistency with the suggestions under 37 C.F.R. 1,77 or to otherwise provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings might refer to a “Field,” the claims should not, be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the “Background” is not to be construed as an admission that certain technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a limiting characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.
Finally, it will be understood that use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of Use of the term “optionally,” “may,” “might,” “possibly,” and the like with respect to any element of an embodiment means that the element is not required, or alternatively, the element is required, both alternatives being within the scope of the embodiment(s). Also, references to examples are merely provided for illustrative purposes, and are not intended to be exclusive.
The present application is related to, claims the earliest available effective filing date(s) from (e.g., claims earliest available priority dates for other than provisional patent applications; claims benefits under 35 USC § 119(e) for provisional patent applications), and incorporates by reference in its entirety all subject matter of the following listed application(s) (the “Related Applications”) to the extent such subject matter is not, inconsistent herewith; the present application also claims the earliest available effective filing date(s) from, and also incorporates by reference in its entirety all subject matter of any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s) to the extent such subject matter is not inconsistent herewith: This application is a continuation-in-part patent application of pending Application No. 15/382686, filed 18 Dec. 2016 entitled “Efficient Infrared Absorption Systems and Methods for Edge Sealing Medium Density Fiberboard (MDF) and Other Engineered Wood Laminates Using Powder and Liquid Coatings naming Michael J. Chapman as inventor, which is a divisional patent application of now abandoned application Ser. No. 14/855,234, filed 15 Sep. 2015 entitled “Efficient Infrared Absorption Systems and Methods for Edge Sealing Medium Density Fiberboard (MDF) and Other Engineered Wood Laminates Using Powder and Liquid Coatings naming Michael J. Chapman as inventor.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14855234 | Sep 2015 | US |
| Child | 15382686 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15382686 | Dec 2016 | US |
| Child | 15978144 | US |
