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  Decorative laminate assembly and method of producing sameUSPTO Application #: 20060157195Title: Decorative laminate assembly and method of producing same Abstract: A decorative laminate assembly having a decorative laminate top layer assembly. This top layer assembly includes, in descending superimposed relationship, a decorative layer and a core layer that includes PETG, or other polymeric material. Preferably, the top layer assembly also includes a wear resistant overlay layer on top of the decorative layer, and the core layer's PETG is in a sheet form. The top layer assembly may be directly bonded to a water resistant substrate. The decorative laminate assembly of the present invention can be used for a variety of purposes, including flooring applications. When the present invention is used for flooring applications, it is preferred that the overlay layer has enhanced wear resistant qualities and that the water resistant substrate comprise PVC or cement fiberboard. (end of abstract) Agent: Mayer, Brown, Rowe & Maw LLP - Chicago, IL, US Inventors: Kenneth John Laurence, Terry Paul Drees, Kevin Francis O'Brien, Robert P. Fairbanks USPTO Applicaton #: 20060157195 - Class: 156307100 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060157195. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a divisional of U.S. patent application Ser. No. 09/955,822 filed Sep. 18, 2001, which is a continuation-in-part of application Ser. No. 09/767,556, filed on Jan. 22, 2001, the entire disclosures of which are hereby incorporated by reference herein in their entirety. FIELD OF THE INVENTION [0002] The present invention relates generally to decorative laminate assemblies and methods for producing the same, and more specifically, decorative laminate assemblies with enhanced moisture resistance and dimensional stability, which qualities are particularly useful in flooring applications where there will be repeated or prolonged exposure to moisture or water. BACKGROUND OF THE INVENTION [0003] Decorative laminates have been used as a surfacing material for many years, in both commercial and residential applications, where pleasing aesthetic effects in conjunction with desired functional behavior (such as superior wear, heat and stain resistance, cleanability and cost) are preferred. Typical applications have historically included, while not limited to, furniture, kitchen countertops, table tops, store fixtures, bathroom vanity tops, cabinets, wall paneling, office partitions, and the like. [0004] More recently, the applications for decorative laminates have been expanded to include their use as a flooring material in lieu of more expensive real wood, stone or ceramic tile, less sanitary and rugged carpeting, as well as less aesthetically attractive vinyl tile or linoleum-like products. However, as discussed in more detail below, existing decorative laminates are not particularly suited in applications where there is repeated or prolonged exposure to moisture and/or water due to their intrinsic hydrophilic properties. Such existing laminates have therefore been primarily limited to residential applications having dry conditions. Accordingly, as discussed further below, there is a need for a decorative laminate that can be used where there is repeated or prolonged exposure to moisture and/or water, thereby overcoming the deficiencies present in existing decorative laminates. [0005] In general, decorative laminates can be classified into two broad categories, namely high pressure-decorative laminates (HPDL) and low pressure decorative laminates (LPDL). As defined by the industry's governing body, the National Electrical Manufacturers Association (NEMA) in their Standards Publication LD 3-1995, high pressure decorative laminates are manufactured or "laminated" under heat and a specific pressure of more than 750 psig. Conversely, low pressure decorative laminates are typically manufactured at about 300 to 600 psig specific pressure to avoid excessive crushing of their substrate material. The other broad distinction between high pressure and low pressure decorative laminates is that the former are generally relatively thin, typically comprising a decorative surface and a phenolic resin impregnated kraft paper core, and are not self supporting as manufactured. As such they are normally bonded, with a suitable adhesive or glue, to a rigid substrate such as a particleboard or medium density fiberboard (MDF), as a separate step during final fabrication of the end product. Conversely, low pressure decorative laminates are typically comprised of a similar type of decorative surface, without the supporting core layer, which is bonded to a substrate such as particleboard or MDF in a single laminating or "pressing" operation during its manufacture. [0006] Both high pressure and low pressure decorative laminates have historically been manufactured in heated, flat-bed hydraulic presses. With the exception of some newer types of processing equipment, high pressure laminates are typically pressed as multiple sheets in press "packs" or "books" in a multi-opening press (which is usually steam or high pressure hot water heated, and water cooled), with a 30 to 60 minute thermal cycle and 130.degree. C. to 150.degree. C. top temperature. On the other hand, low pressure decorative laminates are typically pressed as a single sheet or "board" in a single opening press (which is usually thermoil or electrically heated) using an isothermal,.hot discharge "short cycle" of 20 to 60 seconds with press heating platen temperatures of 170.degree. C. to 220.degree. C. Continuous laminating or "double belt" presses for decorative laminate manufacture blur the above distinctions somewhat, in that their "cycle" times and temperatures are similar to those employed for low pressure decorative laminates. In such a process, pressures are intermediate, typically in the range of 300 to 800 psig, while the continuous laminates themselves are relatively thin, without direct bonding to a substrate material and thus requiring a second fabrication step to do so as is the case with conventional high pressure decorative laminates. The process and product dissimilarities delineated above, as well as more subtle process differences, will be appreciated by those versed in the art. [0007] High pressure decorative laminates are generally comprised of a decorative sheet layer, which is either a solid color or a printed pattern, over which is optionally placed a translucent overlay sheet, typically employed in conjunction with a print sheet to protect the print's ink line and enhance abrasion resistance, although an overlay can be used to improve the abrasion resistance of a solid color as well. A solid color sheet typically consists of alpha cellulose paper containing various pigments, fillers and opacifiers, generally with a basis weight of 50 to 120 pounds per 3000 square foot ream. Similarly, print base papers are also pigmented and otherwise filled alpha cellulose sheets, usually lightly calendered and denser than solid color papers to improve printability, and lower in basis weight at about 40 to 75 pounds per ream, onto which surface is rotogravure or otherwise printed a design using one or more inks. Conversely, overlay papers are typically composed of highly pure alpha cellulose fibers without any pigments or fillers, although they can optionally be slightly dyed or "tinted", and are normally lighter in basis weight than the opaque decorative papers, in the range of 10 to 40 pounds per ream. [0008] For high wear applications (such as flooring), it is often desirable to have a more highly wear resistant top layer. Accordingly, the overlay papers may contain hard, abrasive, mineral particles such as silicon dioxide (silica), and preferably aluminum oxide (alumina), which is included in the paper's furnish during the papermaking process. Alternatively, the abrasive particles can be coated on the surface of the overlay or decorative papers, during the "treating" process described below, prior to the final lamination step. Further, the abrasive particles can be added to the resin which is used to impregnate the overlay or decorative layers, thus causing the abrasive particles to be deposited on, and to a lesser extent, dispersed within such layers. As is known in the art, if the abrasive particles are deposited on the decorative layer, a separate overlay layer may not be necessary. [0009] Typically, these overlay and decorative print and solid color surface papers are treated, or impregnated, with a melamine-formaldehyde thermosetting resin, which is a condensation polymerization reaction product of melamine and formaldehyde, to which can be co-reacted or added a variety of modifiers, including plasticizers, flow promoters, catalysts, surfactants, release agents, or other materials to improve certain desirable properties during processing and after final press curing, as will be understood by those skilled in the art. As with melamine-formaldehyde resin preparation and additives thereto, those versed in the art will also appreciate that other polyfunctional amino and aldehydic compounds can be used to prepare the base resin, and other thermosetting polymers, such as polyesters or acrylics, may be useful as the surface resin for certain applications. It is common practice, particularly in low pressure processes, to treat the decorative paper, and optionally a high wear abrasive loaded overlay, with a coreacted melamine-urea-formaldehyde (MUF) resin, or a blend of a melamine-formaldehyde (MF) resin and urea-formaldehyde (UF) resin, where the urea serves as an inexpensive, low cost resin solids extender. However, in the practice of the present invention, which is directed primarily to moisture resistant flooring applications, inclusion of urea, in any form, in the surface resin should be avoided if the best moisture and water resistance of the decorative laminate assembly is to be achieved. It will be appreciated, however, that urea can be used in the practice of the present invention. [0010] Optionally, an untreated decorative paper can be used in conjunction with a treated overlay, provided the overlay contains sufficient resin to flow into and contribute to the adjacent decorative layer during the laminating process heat and pressure consolidation so as to effect sufficient interlaminar bonding of the two, as well as bonding of the decorative layer to the core. The equipment used to treat these various surface papers is commercially available and well known to those skilled in the art. The papers are normally treated to controlled, predetermined resin contents and volatile contents for optimum performance as will be well understood by those versed in the art, with typical resin contents in the ranges of 64-80%, 45-55% and 35-45% for overlay, solid color and print (unless used untreated) papers respectively, and all with volatile contents of about 5-10%. Overlay and decorative surface papers used with a low pressure process usually employ higher resin contents and catalyst concentrations (and/or stronger catalysts) to compensate for the lower pressure and resultant poorer resin flow, and the short thermal cure cycle, during the pressing operation. [0011] The surface papers (i.e., the overlay and decorative layers) of a high pressure decorative laminate are simultaneously bonded to the core during the pressing operation. The core of a conventional high pressure decorative laminate is typically comprised of a plurality of saturating grade kraft paper "filler" sheets, which have been treated or impregnated with a phenol-formaldehyde resin, which also simultaneously fuse and bond together during the laminating process, forming a consolidated, multi-lamina unified composite or laminate. Phenol-formaldehyde resins are condensation polymerization reaction products of phenol and formaldehyde. Again, those versed in the art will appreciate that a variety of modifiers such as plasticizers, extenders and flow promoters can be co-reacted with, or added to, the phenol-formaldehyde resin, that other phenolic and aldehydic compounds can be used to prepare the base resin, or that other types of thermosetting resins such as epoxies or polyesters may be used. A phenol-formaldehyde resin, however, is generally preferred in the manufacture of conventional high pressure decorative laminates, as is the use of a saturating grade kraft paper, generally with a basis weight of 70-150 pounds per ream, although other materials such as linerboard kraft paper, natural fabrics, or woven or nonwoven glass, carbon or polymeric fiber clothes or mats may also be used as the core layer, either by themselves or in combination with kraft paper. In any case, these core layers must either be treated with a resin that is chemically compatible with the "primary" filler resin (and surface resin if used adjacent to it), or if used untreated, sufficient resin must be made available from adjacent filler plies to contribute to it and insure adequate interlaminar bonding. The filler resin preparation procedures, and filler treating equipment and methodologies, are also well known to those skilled in the art. With a conventional low pressure process, typically a core layer is not used, and the decorative surface components are bonded directly to a substrate material rather than to an intermediate core layer. [0012] During the HPDL laminating or pressing operation, the various surface and filler sheets or laminae are cured under heat and pressure, fusing and bonding them together into a consolidated, unitary laminate mass, albeit asymmetric in composition throughout its thickness. As mentioned previously, typically this process is accomplished in a multi-opening, flat bed hydraulic press between essentially inflexible, channeled platens capable of being heated and subsequently cooled while under an applied pressure. [0013] Typically in such a press, back-to-back pairs of collated laminate assemblies (with means of separation as described below), each consisting of a plurality of filler sheets and one or more surface sheets, are stacked in superimposed relationship between rigid press plates or "cauls", with the surfaces adjacent to the press plates. As is known in the art, such press plates are typically fashioned from a heat-treatable, martensitic stainless steel alloy such as AISI 410, and can have a variety of surface finishes which they impart directly to the laminate surface during the pressing operation, or they can be used in conjunction with a non-adhering texturing/release sheet positioned between the laminate surface components and the press plate, which will impart a selected finish to the laminate surface during pressing as well (and is later stripped off and discarded). [0014] While martensitic stainless steel press plates are most commonly used in the manufacture of high pressure decorative laminate, optionally chrome plated to enhance their wear resistance and releasibility, austenitic stainless steels such as AISI 304, or other metal alloys such as brass, either with optional chrome plating, can also be employed, as can heat treatable wrought aluminum alloys, for example 6061 T6 temper, which surface may be anodized to increase its hardness and wear resistance. In addition, nonmetallic press plates or cauls may also be used advantageously. Such plates can be comprised of fully cured materials such as phenolic resin treated kraft paper, epoxy resin treated woven glass cloth, epoxy resin treated carbon fiber mat, or the like compositions. These plates can be optionally clad- with a stainless steel or aluminum foil, which further optionally can be respectively chrome plated or anodized for improved wear resistance. Metallic press plates are typically manufactured by buffing and polishing, chemical etching, mechanical embossing, machining, shot peening, or combinations thereof, depending on the texture and surface finish desired, while the composite press plates are typically produced by a heat and pressure consolidation, i.e. lamination, and embossing process such as that described in U.S. Pat. No. 3,718,496 Willard. Release/texturing papers can be, or may have to be, used in conjunction with a particular type of press plate depending on its intrinsic self-release characteristics as well as the final laminate finish desired. [0015] Typically, several pairs of laminate assemblies or "doublets" are interleaved between several press plates, supported by a carrier tray, to form a press pack or "book". The laminate pairs between the press plates are usually separated from each other by means of a non-adhering material such as a wax or silicone coated paper, or biaxially oriented polypropylene (BOPP) film, which are commercially available. Alternatively, the backmost face of one or both of the laminates' opposed filler sheets in contact with each other is coated with a release material such as a wax or fatty acid salt. Each press pack, so constructed, is then inserted, by means of its carrier tray, into an opening or "daylight" between two of the heating/cooling platens of the multi-opening, high pressure flat bed press. The press platens are typically heated by direct steam, or by high pressure hot water, the latter usually in a closed-loop system, and are water cooled. [0016] A typical press cycle, once the press is loaded with one or more packs containing the laminate assemblies and press plates, entails closing the press to develop a specific pressure of about 1000-1500 psig, heating the packs at a predetermined rate to about 130-150.degree. C., holding at that cure temperature for a predetermined time, then cooling the packs to or near room temperature, and finally relieving the pressure before unloading the packs on their carrier trays from the press. Those skilled in the art will have a detailed understanding of the overall pressing operations, and will recognize that careful control of the laminate's cure temperature and its degree of cure are critical in achieving the desired laminate properties (as are the proper selection of the resin formulations and papers used in the process). [0017] After the pressing operation has been completed, and the press packs discharged from the press, the press plates are removed sequentially from the press pack build-up for reuse, and the resultant laminate doublets separated into individual laminate sheets. In a separate operation, these must then be trimmed to the desired size, and the back sides sanded so as to improve adhesion during subsequent bonding to a substrate. With a continuous laminating process, the trimming and sanding operations, and sheeting if desired, are usually done in-line directly after heat and pressure consolidation and curing between the rotating double belts. Conversely, with a conventional low pressure pressing operation, usually removal of unpressed surface paper edge "flash" is the only finishing step required. [0018] As noted above, a relatively recent development in the building and design industries has been the growing widespread acceptance of using decorative laminates in flooring applications. Such flooring products, simulating stone or ceramic tiles, or wood planks, are most commonly produced either by adhering a conventional high pressure decorative laminate surfaced with a wear resistant overlay, as described in detail above, to a medium density fiberboard (MDF) or a premium grade high density fiberboard (HDF) substrate. Alternatively, the flooring composite material is pressed directly using a one-step low pressure process, again with an abrasive overlay protecting the decorative surface sheet and using MDF or HDF as the substrate. The fiberboard substrates are used in lieu of particleboard or other coarser, less expensive substrates due to the exacting machining requirements for the flooring product's tongue and groove or integral "snap lock" edge treatment joining systems that are most commonly used with these products. However, even with the more expensive HPDL clad flooring products, and using the best grades of "moisture resistant" HDF substrate (in which the board is produced at higher resin content with more moisture resistant resins), and even sized with wax and other "repellents", serious application restrictions and problems persist with the current generation of these most widely used flooring products when exposed to repeated or prolonged contact with moisture or water. These deficiencies are due to their intrinsic hydrophilic, in fact hygroscopic, characteristics, as such products are comprised for the most part of cellulosic wood fibers. These deficiencies are compounded by the non-isomorphic, directional orientation of these fibers inherent to the papermaking and fiberboard manufacturing processes. [0019] Indeed, even the best moisture resistant HDF grades will expand an average of about 0.075% along its machine direction ("MD") and cross-machine direction ("CD") for each 1% increase in its equilibrium moisture content. HDF in its original state, as produced by a mill and used by a flooring manufacturer, has an average moisture content of about 6%. With a non-moisture contributing subfloor, such as lauan plywood, under the best conditions of low relative humidity "RH" (.about.10% RH) and high ambient temperature, the flooring HDF substrate moisture content will increase to about 7% (a+1% increase). On the other extreme, with the same type of subfloor and conditions of high humidity (.about.90% RH) and low ambient temperature, the HDF substrate moisture content will increase to about 9% (a+3% increase). Typically, more moderate temperature and humidity conditions will result in an increase in the floor's HDF substrate moisture content to about 8% (a+2% increase). The practical consequences of this increase in the floor's HDF substrate moisture content, and resultant increase in its overall dimensions, are summarized in Table I below. The expansion figures shown below are an average of the expansion changes in both the MD and CD directions. TABLE-US-00001 TABLE I Expansion With Moisture In- Room Dimension Subfloor RH Temp. Content crease 10 ft. 20 ft. 30 ft. HDF -- -- 6% -- -- -- -- (from Mill) HDF Low High 7% 1% 0.09'' 0.18'' 0.27'' HDF Mod. Mod. 8% 2% 0.18'' 0.36'' 0.54'' HDF High Low 9% 3% 0.27'' 0.54'' 0.81'' [0020] On the other hand, a traditional high pressure decorative laminate used as cladding (i.e., the laminated overlay, decorative and core layers) will lose moisture under low humidity conditions and shrink in both its MD and CD, and absorb moisture under high humidity conditions and grow in both its MD and CD dimensions. The NEMA specification LD 3-3.11 for dimensional change for VGS grade laminate (nominal thickness 0.028 inch "vertical grade standard"), which would typically be used to clad HDF for flooring applications, is 0.7% maximum in the machine direction and 1.2% maximum in the cross-machine direction in terms of total dimensional movement from low humidity conditions (less than 10% relative humidity at 70.degree. C.) to high humidity conditions (90% relative humidity at 40.degree. C.). Assuming equilibrium at ambient conditions of 50% relative humidity (midway for the test method), the laminate under high humidity conditions can grow 0.35% in the machine direction, and 0.60% in the cross-machine direction, with the consequences illustrated in Table II below: TABLE-US-00002 TABLE II Expansion With Relative Direc- % Room Dimensions Humidity tion Change 10 ft. 20 ft. 30 ft. 10% MD -0.35 -0.42'' -0.84'' -1.26'' % CD -0.60 -0.72'' -1.44'' -2.16'' 50% MD 0 -- -- -- 50% CD 0 -- -- -- 90% MD +0.35 +0.42'' +0.84'' +1.26'' 90% CD +0.60 +0.72'' +1.44'' +2.16'' [0021] The relatively poor moisture resistance of the high pressure decorative laminate is primarily related to the phenol-formaldehyde ("phenolic") resin impregnated core layer, in part because it comprises the majority of the laminate bulk and normally has a greater cellulose fiber to resin ratio than the surface components, and partly because of the more hydrophilic nature of "modern" water-solvated phenolic resin systems. Simply increasing the phenolic resin content in the core sufficiently to significantly improve moisture resistance is not practical since it would result in increased resin flow and bleed-out during pressing, as well as possible resin bleed-through into the laminate surface. Conversion to a more hydrophobic, organic solvent based modified phenolic resin is prohibited because of environmental considerations, and both alternatives are precluded because of their increased cost. [0022] Thus, while the dimensional movement of the total floor assembly will be governed predominantly by the much greater mass of the HDF substrate, under high humidity and moisture, and in particularly wet, conditions, the greater movement of the flooring's HPDL cladding could warp convex and buckle the individual floor tiles or planks, lifting them off the subfloor. Continue reading... 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