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United States Patent [i9]
Scher et al.
[ii] 4,255,480  Mar. 10, 1981
 ABRASION-RESISTANT LAMINATE
 Inventors: Herbert I. Scher; Israel S. Ungar,
both of Randallstown, Md.
 Assignee: Nevamar Corporation, Odenton, Md.  Appl. No.: 879,848  Filed: Feb. 22, 1978
Related U.S. Application Data
 Continuation-in-part of Ser. No. 758,265, Jan. 10, 1977, abandoned.
 Int. a.3 B32B5/16
 U.S. a 428/208; 156/222;
156/277; 156/279; 428/164; 428/165; 428/172;
 Field of Search 428/172, 156, 167, 168,
428/164, 165, 204, 206, 207, 309, 324, 208; 156/219, 2 TT, 220, 222, 221; 427/180, 197, 262, 267, 280, 285; 162/134, 135, 130, 132, 128, 275; 264/137, 132
 References Cited
U.S. PATENT DOCUMENTS
2,060,824 11/1936 Rafton 162/128
2,732,325 1/1956 Lindenfelser 156/220
2,739,081 3/1956 Wohnsiedler 428/474
3,067,077 12/1962 Latella et al 156/277
3,223,579 12/1965 Dorland et al 162/225
3,346,443 10/1967 Elmer 428/413
3.373.070 3/1968 Fuerst 428/452
3.373.071 3/1968 Fuerst 428/452
3,525,664 8/1970 Hale et al 156/274
3,669,727 6/1972 Raymond 156/313
3,798,111 3/1974 Lune et al 428/328
3,814,647 6/1974 Scher et al 428/357
3,928,706 12/1975 Gibbons 428/328
3,968,291 7/1976 Chevallier 428/203
3,975,572 8/1976 Power 428/452
4,006,271 2/1977 French et al 428/447
4,024,842 6/1977 Yoshida et al 428/447
FOREIGN PATENT DOCUMENTS
836522 3/1970 Canada .
130162 3/1978 Fed. Rep. of Germany .
Chemical Abstracts, 149425 vol. 83.
Primary Examiner—Stanley S. Silverman
Attorney, Agent, or Firm—Karl W. Flocks
An abrasion-resistant laminate is prepared by providing an ultra thin coating of mineral particles and micro crystalline cellulose on the surface of conventional printed paper, followed by impregnating the paper with a conventional laminating resin, and then using the print paper so obtained in a laminating process without the necessity of using an overlay sheet.
17 Claims, 6 Drawing Figures
U.S. Patent Mar. 10, 1981 Sheet 1 of 2 4,255,480
U.Sc Patent Mar. 10, 1981 Sheet 2 of 2
This is a continuation-in-part of parant copending application Ser. No. 758,265, filed Jan. 10, 1977 now abandoned.
FIELD OF INVENTION
The present invention relates to laminates and, more particularly, decorative laminates of high abrasion resistance.
High pressure decorative laminates are conventionally produced by stacking and curing under heat and pressure a plurality of layers of paper impregnated with various synthetic thermosetting resins. In normal practice the assembly, from the bottom up, consists of a plurality, e.g. three to eight, core sheets made from
obtain a laminate having a lower gloss and a slightly textured surface which is desirable for some products.
At the completion of the laminating operation, the backs of the laminates are sanded to permit gluing to practicle board, plywood or other substrates. The glued, laminate surfaced panel is then fabricated into furniture, kitchen counter tops, table tops, store fixtures and other end-use applications widely accepted for the combination of appearance, durability and economy.
A number of variations of the above-described general process are known, particularly those operations designed to obtain special effects in appearance and texture. Also other curing cycles are possible and, in fact, sometimes other resin systems are used as well.
Besides decorative high-pressure laminates referred to above, there are also a number of low-pressure products which have been developed in recent years, including low-pressure laminates using either saturated polyester resins, or melamine-formaldehyde resin. One of
phenolic resin impregnated kraft paper, above which 20 the fastest growing materials competing with high-pres'
lies a pattern or print sheet impregnated with melamine resin; on top of the print sheet is provided an overlay sheet which, in the laminate, is almost transparent and provides protection for the pattern sheet.
The core sheets are conventionally made from kraft paper of about 90-125 pound ream weight. Prior to stacking, the kraft paper is impregnated with a wateralcohol solution of phenol-formaldehyde resole, dried and partially cured in a hot air oven, and finally cut into sheets. The print sheet is a high quality, 50-125 ream weight, pigment filled, alpha cellulose paper that has been impregnated with a water-alcohol solution of melamine-formaldehyde resin, dried and partially cured, and finally cut into sheets. The print sheet, prior to impregnation with the resin, usually has been printed with a decorative design, or with a photogravure reproduction of natural materials, such as wood, marble, leather, etc.
The overlay sheet is almost invariably used when the 40 print or pattern sheet has a surface printing in order to protect the printing from abrasive wear. The overlay sheet is a high quality alpha cellulose paper of about 20-30 pounds ream weight that is also impregnated with melamine-formaldehyde resin in a manner similar to that used for the print sheet, except that a greater amount of resin per unit weight of paper is used. The individual sheets are stacked in the manner indicated above and, if six sheets of impregnated core paper are used, there results a finished laminate having a thickness of about 50 mils, it being understood that a different number of sheets can be used to provide thicker or thinner laminates.
The stack of sheets as described above is placed between polished steel plates and subjected to about 55 230°-240° F. (e.g. 300° F.) at 800-1600 p.s.i. (e.g. 1000 p.s.i) for a time sufficient to consolidate the laminate and cure the resins (e.g. about twenty-five minutes). This causes the resin in the paper sheets to flow, cure and consolidate the sheets into a unitary laminated mass referred to in the art as a decorative high-pressure laminate. In actual practice, two laminated stacks are pressed back to back, separated by a coated release sheet that allows the two laminates to be peeled apart after separation. Also, a large proportion of the stacks are laminated with an aluminum foil-kraft paper composite sheet inserted between the overlay and the metal plate, with the aluminum facing the overlay, in order to
sure laminates in recent years is a product referred to as low-pressure melamine board which is normally pressed in a short cycle at 175-225 p.s.i at 325°-350° F. These low-pressure products have the advantage of being normally less expensive, but they cannot be given the title of "high pressure laminates" because in order to be entitled to that designation, a product must meet a variety of rigid standards promulgated by the National Electric Manufacturers Association, NEMA LD3-1975 which includes standards relating to abrasive wear, stain resistance, heat resistance, impact resistance, dimensional stability, etc. While various other decorative printed, surfacing materials, such as some of the lowpressure laminates, have certain of the desirable characteristics, no products other than high-pressure laminates currently available have all of these properties.
One of these properties in particular which is very important is abrasion resistance. A high-pressure decorative laminate must have sufficient abrasion resistance to permit use in high exposure areas such as dinette surface tops, check-out counters, etc. The standard NEMA test for abrasion resistance is NEMA test LD3.01. In this test a laminate sample is clamped on a rotating disc, over which ride two weighted rubber wheels, faced with calibrated sand-paper strips. As the laminate surface is rotated under the wheels, the abrasive action of the sand-paper cuts through the surface of the laminate and gradually through the overlay until the printed pattern is exposed and destroyed. The NEMA standard for Class I laminate requires that the laminate, after four hundred rotation cycles, has no more than 50% of its pattern destroyed. The 50% end point is estimated by averaging the number of cycles at which the pattern shows initial wear, and the number of cycles at which the pattern is completely destroyed.
If a high-pressure decorative laminate is prepared in a conventional manner, with a normal 35-40% resin content in the print or pattern sheet, but without an overlay sheet, the abrasion resistance will be only about 50-75 cycles. If specially formulated melamine resins,are used in the pattern sheet with a resin content of 50-55%, abrasion resistance of up to about 150-200 cycles are on occasion obtainable without an overlay sheet, but in this latter case the laminates have a tendency to develop surface craze and, furthermore, they are quite difficult to prepare due to the difficulty of impregnating the print sheet in a uniform manner; additionally, they do