Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-07-20
2001-09-11
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S330000, C428S331000, C428S402000, C428S403000, C428S404000, C428S407000, C442S294000, C442S417000
Reexamination Certificate
active
06287681
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wear resistant overlay for use in a decorative laminate and flooring and to laminates and flooring prepared therefrom. Decorative laminates have been conventionally made by stacking a plurality of layers of paper impregnated with synthetic thermosetting resins. Normally, the assembly consists of a plurality (for example, three to eight) core sheets made from phenolic resin impregnated Kraft paper, above which lies a decor sheet, usually a print or solid color, impregnated with melamine resin. An overlay sheet is often provided on top of the decor sheet which, in the laminate, is made to be as transparent as possible and which provides protection for the decor sheet.
The overlay sheet can be formed in a number of different ways. In one, the overlay is a sheet of cellulose fibers having a very low basis weight which carries therein and thereon abrasion resistant particles. Conventionally, the cellulose fibers are deposited on the papermachine wire from a first headbox and overcoated with a slurry of mineral particles which are deposited from a secondary headbox. The slurry of mineral particles cascades over and through the cellulose fibers and causes many of the mineral particles to become embedded in the overlay where they are not as effective in preventing abrasion. Also much of the mineral particles is washed to the floor of the papermachine. Thus, the conventional practice of depositing mineral particles from a secondary headbox is terribly inefficient in terms of the usage of the mineral particles.
One method for more efficiently depositing the mineral particles involves use of a slot orifice coater such as a curtain coater instead of a secondary headbox as described in U.S. Pat. No. 5,820,937.
SUMMARY OF THE INVENTION
In accordance with the present invention, abrasion resistant mineral pigment particles are incorporated into a suitable carrier material to produce mineral pigment composites. These composites can be coated on the overlay from a secondary headbox or any other coating device. Because the mineral pigment particles are embedded in a carrier material as part of a larger mineral pigment composite particle, the particles tend to be retained at the surface of the overlay where they are more effective in preventing abrasion. Additionally, the carrier material encompassing the mineral particles functions as a protective barrier between the abrasive mineral particles and scratch sensitive surfaces, such as highly polished caul plates. Such overlays can be used for manufacture of decorative laminates, furniture components, flooring laminates and other surfaces where wear protection is needed.
DETAILED DESCRIPTION
Except for the transparent protective layer overlaying the decor sheet, the laminate of the present invention is suitably made according to standard practice and suitably has a conventional construction, e.g., it can comprise 2 to 8 core sheets formed of phenolic impregnated Kraft paper with a melamine resin impregnated decor sheet thereover, plus the protective layer of the present invention over the decor layer pressed by a mirror plate to a high gloss finish. The final laminate is made in the typical way such as by stacking the core layers on a suitable press or pressing plate die with the protective layer-coated decor sheet thereover, and subjecting the assembly to sufficient heat and pressure between the bottom pressing plate die and the highly polished upper pressing plate die for a time sufficient to produce the desired decorative laminate. The conditions of pressing for both high pressure laminate and low-pressure laminate are standard and well known.
One of the key features of the present invention is the utilization of a suitable carrier material into which the mineral particles can be dispersed to form a composite capable of being cured, solidified or otherwise hardened and individuated into discrete composite particles containing abrasion resistant particles. The abrasion resistant mineral pigment particles are dispersed or otherwise introduced into a molten, uncrosslinked, uncured or dissolved form of a suitable carrier material to produce a mineral pigment composite slurry. The mineral pigment composite slurry is solidified, cured or otherwise hardened and processed to produce mineral pigment composite particles at a desired particle size. Each mineral pigment composite particle preferably contains one or more abrasion resistant particles encased in a cured carrier material. The term “cured” as used herein is not limited to materials which are cross-linked, but is open to materials which set, harden or solidify by any known means such as polymerization, removal of solvent, freezing, chemical reaction, etc.
The mineral pigment composite particles are coated on the overlay from a secondary headbox or any other coating device. Although the composite particles are typically applied to the sheet in place of the regular abrasion resistant particles, in some applications it may be advantageous to use both types of particles. If both the abrasion resistant particles and the mineral pigment composite particles are used they can either be admixed and applied as a single coating or applied separately from two different units. When used in combination with the regular abrasion resistant particles, the mineral pigment composites function as spacers and separators which prevent the abrasive grit particles from coming into contact with and damaging the caul plates during the lamination process.
The mineral pigment composite particles are larger than the abrasion resistant particles alone and, therefore, are less likely to be carried through the web with the white water being drained from the web. The carrier material surrounding the abrasion resistant particles also improves the retention of the particles on the sheet by acting as a coupling agent to improve adhesion between the composite particles and the laminating resin. In a preferred embodiment of the invention, the mineral pigment composites are extruded in the form of filaments. The filamentous form of the composite particle further enhances particle retention by spanning pores in the paper structure and increasing the degree of intermeshing with the mat of cellulosic fibers. Whereas conventional grit tends to become embedded in the sheet to different degrees or falls through the sheet with the white water, the mineral pigment composites of the present invention remain essentially on the surface of the sheet where they are most needed for abrasion resistance. Furthermore, the larger composite particles are easier to process during the coating operation. Since the particles remain on the surface of the sheet and are easier to process, less grit can be used and yet still provide acceptable levels of abrasion resistance.
The carrier material also functions as a protective barrier between the abrasive mineral particles embedded in the composite and scratch sensitive surfaces, such as caul plates. Abrasive mineral particles added to wear resistant sheets to impart wear resistance to the laminates produced therefrom can cause excessive incidental wear to various components on the paper machine and auxiliary finishing and handling equipment. The highly polished caul plates used during the high pressure laminating process are particularly susceptible to incurring damage as a result of coming in contact with the sharp exposed edges of the mineral pigments. In accordance with the present invention, the abrasive mineral pigments are embedded in a curable carrier material to form mineral pigment composites. The cured carrier material protects scratch sensitive components by covering and rounding off the sharp edged surface features of the abrasive mineral pigments. Therefore, overall production costs are reduced because repair and replacement costs for the paper machine, secondary equipment and caul plates are minimized.
In a preferred embodiment of the invention, the carrier material is a thermoset resin which, in its pre-cured state, has the same or su
Das Amitabh
Mehta Mahendra
Rourke John
Morris Terrel
Ruddock Ula C.
The Mead Corporation
Thompson Hine LLP
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