WO2004041534A1

WO2004041534A1 - Thermoplastic laminate structure with a wood veneer core

Info

Publication number: WO2004041534A1
Application number: PCT/US2003/028795
Authority: WO
Inventors: Richard C. Wilson
Original assignee: Wilson Richard C
Priority date: 2002-09-12
Filing date: 2003-09-12
Publication date: 2004-05-21
Also published as: AU2003272364A1

Abstract

A thermoplastic laminate includes a top layer or 'cap sheet' of either a first PVC material upon which a thin hardcoat is applied for scratch resistance, or one or more acrylic sheets that are preferably modified to enhance impact strength. Immediately beneath the top layer is a first polycarbonate layer for improved impact strength and high chemical resistivity; and a decorative wood veneer forming an image layer for the laminate. A bottom layer formed of one or more sheets of either a second polycarbonate layer, a second PVC material (which may be the same as the first PVC material), or an ABS material. Adhesive layers are disposed between the first, intermediate, second intermediate, and bottom layers. The bottom layer is preferably formed of multiple plies of like-thickness sheets which are bonded to one another when the stacked layers of the laminate are hot pressed.

Description

THERMOPLASTIC LAMINATE STRUCTURE WITH A WOOD VENEER CORE

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Application No. 60/410,107, filed September 12, 2002, the disclosure of which is hereby expressly incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a thermoplastic-wood laminates, and a method for making such thermoplastic laminates.

BACKGROUND OF THE INVENTION

[0003] Decorative panels, walls, countertops, furniture, and architectural building components that incorporate a real wood veneer remain in great demand. To accommodate the demand for such products that are intended for use relatively less-hospitable service environments, such as the water-laden environment of marine industries, the prior art teaches the use of decorative polymeric veneers applied to wood or medium-density fiberboard (MDF) substrates that simulate the look of real wood. While such polymeric veneers typically perform significantly better in such environments than real wood veneers, a need continues to exist to improve the performance of such veneered products, including the reduction of a "telegraphing" by the veneer of substrate features, including glue lines, dirt, and other substrate surface imperfections.

BRIEF SUMMARY OF THE INVENTION

[0004] In accordance with an aspect of the invention, a thermoplastic laminate includes a top layer selected from the group consisting of at least one sheet of a first acrylic material, and a sheet of a first polyvinyl chloride material having an upper face to which a scratch-resistant coating is applied. The laminate of the invention further includes a first intermediate layer formed of a sheet of a first polycarbonate material, a second intermediate layer formed of a cellulose-based material, such as wood, cloth, or printed paper, and a bottom layer selected from the group consisting of a sheet of a second polycarbonate material, at least one sheet of a second polyvinyl chloride material, and at least one sheet of an acrylonitrile-butadiene- styrene (ABS) material. A layer of a polyurethane adhesive is disposed between both the first intermediate layer and the second intermediate layer, and the second intermediate layer and the bottom layer.

[0005] Upon hot pressing, the top layer bonds to the first intermediate layer while the polyurethane adhesive bonds the remaining lower layers to the top and first intermediate layers. A thermoplastic laminate is thus provided that incorporates a real or simulate wood core (or another image printed on the cellulosed-based material in compatible ink, as desired) while featuring the enhanced impact strength of both the top layer and the upper polycarbonate layer, and either the increased wear resistance of the top layer's hardcoated PVC sheet, or the "repairability" and optical performance of the top layer's acrylic sheet.

[0006] In accordance with another aspect of the invention, the top layer may advantageously include additives that enhance the acrylics performance such as UV inhibitors or colorants, pigments, decorative metal flakes, abrasion resistant additives, or other materials that can alter the appearance of the top acrylic layer and/or provide the laminate's upper surface with a desired set of characteristics, such as impact and wear resistance, opacity, and modification or enhancement of the "image" provided by the second intermediate layer. Similarly, the invention contemplates providing a selected surface finish to the top layer, such as a textured or patterned surface finish, whereby the second intermediate layer's "image" can be similarly modified or enhanced.

[0007] In accordance with another aspect of the invention, in an exemplary embodiment, the bottom layer features at least two sheets of either the PVC or ABS materials, each sheet preferably is of substantially the same thickness. The use of multiple plies in the bottom layer helps reduce "telegraphing" of substrate surface irregularities and imperfections, thereby improving the aesthetic qualities of the resulting veneered product incorporating the thermoplastic laminate of the invention.

[0008] When the top or bottom layers are formed of one or more PVC sheets, the sheet material is preferably characterized by a relatively-low loading of plasticizers to thereby reduce gas-off during heat-and-pressure lamination. Additives such as UV inhibitors may be included to improve or otherwise alter the performance of the PVC material, and each such PVC sheet is preferably provided with a matte finish to prevent bubble formation by trapped gases during hot pressing.

[0009] In accordance with another feature of the invention, a method of making a substantially-rigid composite laminate includes stacking or "booking" several layers of selected thermoplastic polymers between a designated pair of press plates, and urging the layers together under suitable heat and pressure, for example, by hot pressing between the heated platens of a hot press, at a selected platen temperature, for a period of time sufficient to achieve cross-linking of the polymers of the several contiguous layers and their constituent sheets, and the curing of the layers of polyurethane adhesive.

[0010] Other benefits, features, and advantages of the invention will appear from the following description of several exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a sectional view of first exemplary thermoplastic laminate in accordance with the invention;

[0012] Figure 2 is a sectional view of second exemplary thermoplastic laminate in accordance with the invention;

[0013] Figure 3 is a sectional view of third exemplary thermoplastic laminate in accordance with the invention; [0014] Figure 4 is a sectional view of several "books" stacked within a hot press during an exemplary method of making several of the first exemplary thermoplastic laminates; and

[0015] Figure 5 is an enlarged sectional view showing one of the "books" of

Figure 4, as stacked in the hot press.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Three exemplary thermoplastic laminates 10,12,14 incorporating either a wood or other cellulose-based intermediate "image" layer are illustrated in partial section in Figures 1 -3. Each of the exemplary thermoplastic laminates in accordance with the invention includes a thermoplastic top layer 16, a thermoplastic first intermediate layer 18, the cellulose-based image layer 20, and a thermoplastic bottom layer 22.

[0017] As illustrated in Figures 1 and 2, the first and second laminates 10,12 each has a top layer 16 formed of one or more sheets of a polymethylmethacrylate (PMMA) material that, depending upon the desired characteristics of the upper surface 26 of the laminate 10,12, may be a modified acrylic, or impact acrylic. By way of example, in the first and second laminates 10,12, the top layer's acrylic material is modified with dibutyl rubber (DR) to thereby improve the layer's impact strength. The top layer's acrylic material may also be modified, as desired, with additives that enhance other of the layer's performance characteristics, such as UV inhibitors, and/or colorants, pigments, decorative metallic flakes or particles, or other materials that can alter the appearance of the resulting laminate's upper surface 26. The acrylic top layer 16 advantageously features a "repairable" upper surface, inasmuch as the nominally glossy surface finish may be restored as by polishing. An abrasion-resistant coating (not shown) may alternatively be applied to the upper surface 26 of the acrylic sheet.

[0018] While the desired thickness of each laminate 10,12 necessarily plays a role in selecting appropriate layer thicknesses, in the first and second laminates 10,12, the acrylic top layer 16 preferably has a thickness greater than about 0.005 inches, and less than about 0.025 inches. By way of example, in the first and second laminates 10,12, the top layer's acrylic sheet is perhaps about 0.015 inches thick. In accordance with an aspect of the invention, the minimum thickness of the acrylic top layer 16 is preferably selected to achieve a desired optical characteristic, for example, depth or "wetness" of image, as when viewing the resulting laminate's upper surface 26.

[0019] The next layer 18 of the first and second laminates 10,12 of Figures 1 and 2 is formed of a polycarbonate material. The polycarbonate first intermediate layer 18 may have additives such as UV inhibitors that can improve or otherwise alter the performance of the polycarbonate, and a matte finish is preferred. By way of example, the polycarbonate first intermediate sheet can have a thickness greater than about 0.001 inches, up to about 0.020 inches. In the first laminate 10, the polycarbonate first intermediate layer 18 is perhaps about 0.010 inches thick.

[0020] The second intermediate layer 20 of the first and second laminates

10,12 is the cellulose-based image layer formed, for example, of a wood veneer, cloth, or paper. The second intermediate layer 20 forms the primary "image" layer of the laminate 10,12. Where a printed ink is used, the ink is preferably compatible with the layer of polyurethane adhesive 24 used to bond the polycarbonate first intermediate layer 18 to the second intermediate "image" layer 20.

[0021] As for the bottom layer 22, in the first laminate 10, the bottom layer 20 is formed of a single sheet of polycarbonate material, in a thickness ranging from between about 0.001 inches to about 0.250 inches, and preferably between about 0.025 and about 0.250. In the second laminate 12, the bottom layer 20 is formed of one or more sheets or films of a high-impact PVC material (hereafter collectively referred to as "sheets 28" for clarity), in roughly the same thickness at the polycarbonate bottom layer 20 of the first laminate 10. The multiple plies of PVC material are simply stacked, one atop another. The PVC material forming the second laminate's bottom layer 22 can be either rigid or flexible; however, it is preferable to limit the amount of plasticizers used in material compounding prior to extrusion, to thereby reduce gas-off during heat-and-pressure lamination. The PVC bottom layer 22 may likewise include additives such as UV inheritors that can improve or otherwise alter the performance of the layer's PVC material. The PVC bottom layer 22 preferably has a matte finish to prevent bubble formation by trapped gases.

[0022] Turning to Figure 3, while the first and second intermediate layers

18,20 of the third laminate 14 are identical to those of the first and second laminates 10,12 described above, the third laminate 14 includes a top layer 16 formed of a single sheet 30 of a PVC material, in a thickness of perhaps about 0.005 inches, as a carrier for the sheet's abrasion-resistant coating 32, such as a glass hardcoat having a nominal thickness of perhaps about 0.001 inches, that is applied to the sheet's upper surface 34. The third laminate's bottom layer 22 is formed of multiple sheets 36 of a high-impact ABS material, preferably of like nominal thickness. Once again, the multiple plies of the ABS material are simply stacked, one atop another, to define the bottom layer 22 of the third laminate 14. The ABS material may be modified with additives to enhance performance, e.g., a flame retardant.

[0023] In order to facilitate bonding and gas-off (as well as to facilitate adhesion of the resulting thermoplastic laminate to a structural substrate, when the thermoplastic laminate is acting as a "veneer"), the surfaces of the constituent layers and sheets are preferably provided with a desired surface finish. It will be appreciated, however, that the invention contemplates use, for example, of textured pinch rollers or transfer sheets (not shown) during constituent sheet manufacture/preparation to thereby impart a desired surface finish to the face of a given acrylic, PCV, PC, or ABS constituent sheet, as necessary, thereby obviating any further surface preparation prior to lay up. Other methods for preparing the sheet surfaces prior to booking are also contemplated, including etching and laser scoring, and/or applying a surface charge to the constituent sheets to thereby cause the laid-up sheets to draw closer to one another.

[0024] Referring to Figures 4 and 5, in an exemplary method for making a thermoformable thermoplastic laminate, the constituent layers 16,18,20,22 are stacked between a pair of polished steel press plates 38 to form a "book 40," whereupon one or more such books 40 are placed/stacked between the platens 42 of a hot press 44. Preferably, when multiple books 40 are stacked between the platens 42 of a given hot press 44, like layer/book thickness should be used to achieve greater yield uniformity.

[0025] The stacked books 40 are then hot pressed at a suitable combination of temperatures, preferably ranging from about 240°F to about 330°F, and pressures, preferably ranging from about 50 psi to about 260 psi (or even as high as about 300 psi for particularly thick books 40, or for large stacks of books 40), to cause the constituent layers and sheets of each book 40 to laminate together, i.e, to achieve a cross-linking of their polymers, while the polyurethane adhesive 24 is cured. The time sequence and overall time of a given book 40 in the hot press 44 is dependent upon how fast the combination of temperatures and pressures can be applied and the overall thickness of the book 40 to be laminated.

[0026] In accordance with another aspect of the invention, during hot pressing, the top layer's upper surface 26 may advantageously be imparted with a desired textured or glossy surface finish, depending upon press plate selection. Alternatively, the invention contemplates use of a suitable release sheet (not shown) may be used to provide the desired surface texture and gloss. Still further, the upper press plate 38 used with a given book 40 may itself define a mold so that, during hot pressing, the top layer 16 would assume the design of the mold surface. In this manner, desired surface characteristics and features are readily imparted to the resulting laminate 10,12,14.

[0027] Following hot pressing, the laminate 10,12,14 is then cooled to an intermediate temperature that facilitates handling, for example, about 110F°. When this intermediate temperature is achieved, the pressure is released and the laminate removed. Alternately, the laminate 10,12,14 while still hot can be transferred to another press, and a secondary pressure, sufficient to maintain the several constituent layers together, such as 100 psi in the exemplary method, reapplied. The laminate 10,12,14 is then cooled, or permitted to cool, at that second pressure until the temperature of the laminate 10,12,14 falls to the intermediate temperature, at which time the secondary pressure is released.

[0028] The resulting laminate 10,12,14 can be bent to conform to a variety of shapes. For relatively-thin laminates, cold bending can be used to achieve gentle bend radii. For sharp bends, the invention contemplates the application of heat prior to bending to thereby achieve a secondary forming temperature of perhaps about 160°F to about 180°F, using a line bender or other suitable equipment will permit the localized bending of the laminate without delamination of the constituent layers. Preferably, after bending, the bent laminate is annealed, for example, using a blanket or warming room, to reduce spring-back due to memory effect.

[0029] The resulting thermoplastic laminates 10,12,14 can be further vacuum thermoformed or pressure thermoformed onto a variety of pre-formed substrates. The thermoplastic laminates 10,12,14 of the invention can also be sawn, routed, drilled, and otherwise machined in order to shape the laminate for the intended use.

[0030] Significantly, as illustrated in the sectional views of Figures 1-3, the interfaces between the several constituent sheets of a given layer continue to define an interface between these bonded sheets after hot pressing. These interfaces cause discontinuities that advantageously serve to bridge surface imperfections to thereby significantly reduce "telegraphing" of substrate surface imperfections when the resulting laminate is applied as a veneer to a pre-formed substrate.

[0031] From the foregoing, it will be appreciated that the thermoplastic laminates of the invention are suitable for a wide variety of applications and uses, including without limitation, as a covering over wood or other material to provide a functional and or decorative cover or stand alone decorative panel or partition, or be installed in a frame. The thermoplastic laminates of the invention can be attached to wood, MDF, or other suitable substrates using a suitable adhesive. The thermoplastic laminates of the invention can also be used in the furniture industry where the flexible laminate will be used to cover and provide a pleasing exterior to cabinet bases, doors, drawers, tables, other articles of furniture. [0032] While the above description discloses several preferred embodiments, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims. For example, while a disclosed exemplary method simultaneously hot presses multiple books at one time, it will be appreciated that the invention contemplates hot pressing one book at a time, for example, on an automated line.

Claims

What is claimed is:

1. A thermoplastic laminate comprising: a top layer selected from the group consisting of at least one sheet of a first acrylic material, and a sheet of a first polyvinyl chloride material having an upper face to which a scratch-resistant coating is applied; a first intermediate layer formed of a sheet of a first polycarbonate material; a second intermediate layer formed of a cellulose-based material; a bottom layer selected from the group consisting of a sheet of a second polycarbonate material, at least one sheet of a second polyvinyl chloride material, and at least one sheet of an acrylonitrile-butadiene-styrene material; a first layer of a polyurethane adhesive disposed between the first intermediate layer and the second intermediate layer; and a second layer of a polyurethane adhesive disposed between the second intermediate layer and the bottom layer.

2. The laminate of claim 1 , wherein the cellulose-based material is a wood veneer.

3. The laminate of claim 1 , wherein the cellulose-based material is a cloth.

4. The laminate of claim 1 , wherein the cellulose-based material is a printed paper.

5. The laminate of claim 1 , wherein the top layer includes one or more selected from the group consisting of colorants, pigments, and decorative metallic flakes.

6. The laminate of claim 1 , wherein an upper surface of the top layer includes a textured surface finish.

7. The laminate of claim 1 , wherein the bottom layer includes at least two sheets of the acrylonitrile-butadiene-styrene material, and wherein each of the at least two sheets of the acrylonitrile-butadiene-styrene material have substantially the same thickness.