GB1591954A

GB1591954A - Decorative facing sheet for abrasion-resistant laminate

Info

Publication number: GB1591954A
Application number: GB54256/77A
Authority: GB
Original assignee: Nevamar Corp
Current assignee: Nevamar Corp
Priority date: 1977-01-10
Filing date: 1977-12-30
Publication date: 1981-07-01
Also published as: FR2376746B1; IT1091960B; IL53694A; CA1104051A; IL53694A0; BR7800068A; FR2376746A1; DE2800762C2; JPS6240191B2; IT7819087A0; JPS5392875A; FR2530534B1; JPS6335419B2; CA1245965B; FR2530534A1; DE2800762A1; JPS59106961A; DE2858182C2

Abstract

The invention relates to abrasion-resistant laminates. It relates to a decorative laminate which comprises, on support (backing) sheets, a decorative sheet comprising a paper 15 coated with an extremely thin, 0.5 to 7.6 microns, layer of alumina particles 19 which are bound together by particles of microcrystalline cellulose. The laminates formed do not require external protective covering. Application to the production of highly abrasion-resistant decorative laminates. <IMAGE>

Description

(54) DECORATIVE FACING SHEET FOR ABRASION-RESISTANT LAMINATE (71) We, NEVAMAR CORPORATION, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of 8339 Telegraph Road, Odenton, Maryland 21113, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to decorative facing sheets for abrasion resistant laminates and the manufacture of such facing sheets and laminates.

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 backing which generally comprises a plurality, e.g., three to eight, core sheets made from phenolic resin impregnated kraft paper, a pattern or print sheet impregnated with melamine resin and an overlay sheet which, in the laminate, is almost transparent and provides protection for the pattern sheet.

The core sheets of the backing are conventionally made from kraft paper of about 90-125 pound ream weight. Ream weight is the weight per ream (500 sheets) of paper having a sheet size of 24 x 36 inches; thus ream weight is pounds per 3000 sq. ft. of paper.

Prior to stacking, the kraft paper is impregnated with a water-alcohol solution of phenolformaldehyde resole resin, dried and partially cured in a hot air oven, and finally cut into sheets. The print sheet is a high quality, 50-125 lb. 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 or leather.

An overlay sheet is almost invariably used when the 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 backing and print and overlay sheets are stacked in the manner indicated above and, if six sheets of impregnated core paper are used for the backing, there results a finished laminate having a thickness of about 50 mils, it being understood that a different number of core 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 230-340"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. 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 aluminium foil-kraft paper composite sheet inserted between the over-lay and the metal plate, with the aluminium facing the over-lay, in order to 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 particle 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 application 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 the fastest growing materials competing with high-pressure 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 LD31975 which includes standards relating to abrasive wear, stain resistance, heat resistance, impact resistance and dimensional stability. While various other decorative printed, surfacing materials, such as some of the low-pressure 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 LD-3.01. In this test a device known as a Taber abrader is used. A laminate sample is clamped on a rotating disc, over which ride two weighted rubber wheels, faced with calibrated sandpaper strips. As the laminate surface is rotated under the wheels, the abrasive action of the sandpaper 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 250-200 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 not meet the 400 cycle minimum required by the NEMA standard.

Nevertheless, it is desirable to produce a laminate without an overlay sheet which is capable of attaining the performance characteristics of a laminate using an over-lay, and, in particular, one that provides a 400 cycle abrasion resistance. Furthermore, it is desirable to provide a laminate which, in addition to having the 400 cycle abrasion resistance, has an initial wear point at least equal to the initial wear point of a conventional high-pressure laminate having overlay, typically 175-200 cycles. This is desirable because in actual use the laminate appearance becomes unsatisfactory not when 50% of the pattern is destroyed, but when a much lower percentage is destroyed. It is well known from many years of field experience that conventional laminates with overlay. which have 175-200 cycle initial wear point, when used in hard use areas, will have a satisfactory appearance, at least as long as the normal replacement cycle, it being understood that replacement of most laminates in commercial uscs is made for style reasons rather than because of pattern wear. Therefore, a laminate without overlay should meet these same criteria, namely it should have both a NEMA abrasion resistance of at least 400 cycles nnd an initial wear point in the same test of at least 175-200 cycles, even though the latter requirement is not part of the NEMA standard.

It is desirable to be able to provide a laminate having abrasion resistant qualities, but without using an overlay, for several rcasons: 1. Ovcrlay adds substantial raw material costs to the manufacture of laminates, both the cost of the overlay paper itself, the cost of the resin used to impregnate the overlay paper and the in-process and handling losses of these materials.

2. The overlay, by imposing an intermediate layer of substantial thickness between the print sheet and the eyes of the viewer, detracts significantly from the desired visual clarity of the pattern. The cellulose fibers used to make overlay paper have a refractive index close to that of cured melamine-formaldehyde resin. The fibers are therefore almost invisible in the cured laminate, and permit the printed pattern to be seen with very little attenuation.

However, modern printing techniques are making available very accurate reproductions of natural materials, particularly various wood veneer species. As these printed reproductions approach in appearance the natural veneer, even small amounts of haze or blur introduced by the overlay paper are disturbing visually and destroy much of the realism desired by the user.

3. Furthermore, the overlay contributes to the rejection rate of the laminate products produced. The impregnated, dry overlay sheet tends to attract small dirt particles because it develops static electricity charges during drying. This dirt is hard to detect and remove before laminating, and results in spoiled laminate sheets that cannot be reprocessed. In addition, the impregnated dried overlay is brittle and hard to handle without breakage. Broken pieces are accidentally trapped on the surface of the overlay and also result in visually defective sheets.

Additionally, overlay containing laminates, particularly those having a relatively high surface gloss, have a tendency to become dull very quickly when subjected even to only moderate abrasive wear. This is understandably unacceptable where glossy laminates are desired.

The problem of providing improved abrasion resistance has been a long-standing problem in the field. Many solutions to the problem have been suggested and, in fact, some of these have reached commercial development. Nevertheless, it has not heretofore been possible to provide a laminate, not having an overlay sheet, but having a NEMA abrasion resistance of at least 400 cycles and an initial wear point in the same test of at least 175-200 cycles.

It is well known that small, hard mineral particles dispersed in overlay paper, or in resin mixtures to coat the impregnated pattern sheet, can enhance the abrasion resistance of high-pressure laminates (see, for example, the U.S. patents to Michl, 3,135,643; Fuerst 3,373,071 and Fuerst 3,373,070). Techniques such as these do not eliminate the overlay, but either enhance its abrasion resistance, or provide an alternative form of overlay and associated resin.

For example in the Barna U.S. patent 3,123,515, the overlay sheet is impregnated with a finely divided frit. The overlay is used in the normal manner by placing it over the print or pattern sheet.

Another technique is that disclosed in the Lane et al U.S. patent 3,798,111 in which there is disclosed the use of small mineral particles, preferably alumina, which are incorporated within and near the upper layer of the base paper during its manufacture. In tests, it has been shown that laminates made with the print paper of Lane et al, without overlay, had initial wear values of under 100 cycles, some as low as 35 cycles. Furthermore in a rubbing test to determine initial wear, such laminates began to show pattern destruction after only 3,000 rub cycles, far less than necessary.

Other prior art patents of some interest with regard to the background of the present invention are the U.S. patents to Fuerst 3,445,327; Gibbons 3,928,706 and Merriam 3,661,673. Of somewhat less interest are the Battista U.S. patents 3,259,537 and 3,157,518; Ando et al 3,716,440; Power et al 3,946,137 and Boenig 3,318,760.

Even after the considerable activity in the field in order to solve the problems indicated above, these problems have not been solved until the present time.

It is an object of the present invention to provide an improved method of producing an abrasion resistant laminate which has enhanced resistance to abrasion without an overlay sheet and which is capable of producing a laminate which meets the requirements of the NEMA abrasion standard, and of providing an initial wear point of at least 175-200 cycles in this same test.

According to one aspect of the present invention there is provided a method of producing a thermosetting resin impregnated decorative facing sheet for an abrasion resistant decorative laminate which laminate comprises a backing and such a facing sheet and has enhanced abrasion resistance without an overlay layer, the method comprising coating the decorative facing sheet with an abrasion resistant wet mixture and drying the coated mixture at an elevated temperature before impregnating the facing sheet with the thermosetting resin, the mixture comprising an abrasion resistant mineral of particle size 20-50 microns and in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the facing sheet decoration and a binder material for the mineral selected to withstand the subsequent laminating conditions and to be compatible with the thermosetting resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the surface of the decorative facing sheet and the coating in the dry state being permeable to the thermosetting resin.

According to another aspect of the invention there is provided a decorative facing sheet for use in the preparation of abrasion resistant decorative laminates comprising a facing sheet having a decorative design thereon and an abrasion resistant coating thereover of a mixture comprising an abrasion resistant mineral of particle size 20-50 microns in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the decorative design and a binder material for the mineral selected to be compatible with a thermosetting resin selected from the group consisting of melamine formaldehyde resin and polyester resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the substrate and the facing sheet including the coating being impregnable with said thermosetting resin.

The invention also provides an abrasion resistant laminate comprising a backing and a facing sheet according to the immediately preceding paragraph, laminated thereto by said thermosetting resin by the application of heat and pressure.

Embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings.

Fig. lisa flow-diagram showing a method of preparing a print layer in accordance with the present invention; Fig. 2 is a schematic sectional view showing an embodiment of the print sheet in accordance with the present invention; and Fig. 3 is a schematic sectional view showing a laminate in accordance with the present invention.

There has now been discovered a mixture containing abrasion resistant mineral particles of between 20 to 50 microns in size and a binder material which when coated without resin over unimpregnated printed pattern paper provides surprising and unexpected properties by permitting such paper to be used in the preparation of decorative laminates without an overlay sheet and wherein the resultant laminates are abrasion resistant. In its preferred form, the coating mixture is composed of a mixture of particles of alumina and a lesser amount of microcrystalline cellulose particles, both dispersed in a stable, aqueous slurry. The particles of alumina do not interfere with the visual effects in the final product and serve as the abrasion resistant material and the microcrystalline cellulose particles serve as the preferred binder material. It will be understood that the binder must be compatible with the resin system latcr utilized in the laminating procedure, usually a melamine resin or in the case of certain low-pressure laminates a polyester resin system, and the microcrystalline cellulose serves this function as well as stabilizing the small particles of alumina on the surface of the print sheet.

With reference to Fig. 1, in the preferred operation a conventional unimpregnated print or pattern paper is coated with the mixture of hard mineral particles and binder, preferably alumina and microcrystalline cellulose particles in a stable aqueous slurry, and the coating is dried at an elevated temperature, such as in a hot-air oven, to produce a thin coating only 0.02 to 0.3 mils thick. The resultant abrasion resistant coated paper (Fig. 2) is then impregnated with the melamine or polyester resin and dried in a conventional way, at which point it is ready for the laminating procedure such as the high pressure or low pressure laminate producing procedure described above.

With reference to Fig. 3, it is seen that the abrasion resistant resin impregnated print sheet, having an abrasive resistant coating on its upper surface, is assembled with a backing for the laminating step in the conventional way, except that no overlay sheet is used. The laminate is then cured under heat and pressure in the conventional manner.

The conventional laminate assembling step and laminate curing are described above in relation to the production of high pressure laminates and low pressure laminates. In the case of high pressure laminates, the backing comprises a plurality of resin impregnated core sheets and the temperature and pressures employed are respectively from 230-340"F and from 800-1600 p.s.i. In the case of low pressure laminates, the backing preferably comprises a wood particle panel and the temperature and pressures employed are respectively 325-350"F and 175-225 p.s.i.

A surprising characteristic of the coating is that even though it is so thin, i.e., preferably between 0.02 to 0.3 mils thick, it enhances the abrasion resistance in the finished laminate and can not only meet the 400 cycles NEMA Standard, but also provide an initial wear point in excess of 175-200 cycles.

It is also surprising that this coating tightly adheres to the surface of the printed paper when the paper is later impregnated with melamine resin, without significant amounts of the mineral particles either being lost in the impregnating solution or migrating away from the surface of the paper. A further surprising characteristic of this coating is that it does not appear to hinder the penetration of the melamine-formaldehyde resin solution into the interior of the paper, during the impregnation step. Such penetration is essential, or the pattern sheet will be irregularly starved such as at its center, and could possibly de-laminate after pressing. A further desirable characteristic of the coating is that it does not significantly scatter or attenuate light, resulting in very clear, crisp appearance of the pattern in the finished laminate.

Without being bound to the following therory, it is believed that the improved characteristics of the invention can be accounted for as follows: Microcrystalline cellulose particles contain very large external forces that bind to other polar substances, such as cellulose and alumina. Thus an aqueous slurry of microcrystalline cellulose and alumina is stable and does not quickly settle out, even though alumina particles in water are not stable. Furthermore, when this slurry is coated on the paper, the microcrystalline cellulose apparently binds the alumina particles to the surface fibers of the paper, and to the top of the ink pattern, preventing migration of the alumina particles to below the surface. This may account for the good abrasion resistance developed by such small quantities of alumina. Thus, all or substantially all of the alumina particles stay at the surface where they do the most good, rather than becoming dispersed below the surface where they would contribute relatively little initial wear resistance.

As indicated above, the preferred slurry composition contains a mixture of particles of alumina of a size between 20-50 microns and a lesser amount of microcrystalline cellulose particles, both dispersed in water. There must be an amount sufficient of the mineral particles to provide the resultant product with the desired abrasion resistance as discussed above, and there must be an amount sufficient of the binder to retain the mineral particles in place on the surface of the print sheet. In general, it has been found that satisfactory results are attained with about 5 to 10 parts by weight of the microcrystalline cellulose for about 20-120 parts by weight of the alumina; it is possible to work outside this range but there is no advantage doing so and, furthermore, the handling problems become complicated. The quantity of water in the slurry is also dictated by practical considerations, since if there is too little water the slurry becomes so thick that it is hard to apply; similarly, if there is too much water the slurry becomes so thin that it is difficult to maintain a consistent thickness during the coating operation due to running of the slurry. Thus, a slurry containing about 2.0 wt. % microcrystalline cellulose and about 24 wt. % alumina, based on the water, is stable, i.e. the alumina does not settle out; but if more than about 3.5 wt.%micro-crystalline cellulose and about 24 wt.% alumina, based on the water, is used, the slurry becomes very thixotropic and difficult to apply.

The composition also preferably contains a small amount of wetting agent, preferably a non-ionic wetting agent, and a silane. The quantity of wetting agent is not critical, but only a very small amount is desirable and excess quantities provide no advantage. If a silane is used, it acts as a coupling agent which chemically binds alumina particles to the melamine matrix after impregnation and cure, and this provides better initial wear since the alumina particles are chemically bound to the melamine in addition to being mechanically bound there to and therefore stay in place longer under abrasive wear. The silane should be selected from among the group making it compatible with the particular thermosetting laminating resin used; in this regard silanes having an amino group, such as gamma-aminopropyl trimethoxy silane, are particularly effective for use with melamine resins. The quantity of silane used need not be great and, in fact, as little as 0.5% based on the weight of the alumina is effective to enhance the abrasion resistance of the final laminate; a maximum quantity of about 2% by weight based on the weight of the alumina is suggested since greater quantities do not lead to any significantly better results and merely increase the cost of the raw materials.

It is an important feature of the present invention that the coating using microcrystalline cellulose as the binder must be dried at an elevated temperature before the print sheet is impregnated with the melamine resin. Thus, a minimum drying temperature is about 180 F.

and the preferred drying temperatures are from 240-270"F.

With regard to the abrasion resistant mineral particles, alumina is the preferred material.

Silica, which has been suggested in certain prior art patents as an abrasion resistant material, provides inferior results in the present invention compared with alumina. Other minerals of sufficient hardness such as zirconium oxide, cerium oxide and diamond dust can work, but are either too expensive for practical usage or can produce a color shift which is not acceptable under certain circumstances tried unsuccessfully. Silicon carbide also was tried, and while providing good abrasion resistance, produced color shift.

An important feature is the size of the abrasion resistant particles. Beneath 20 micron particle size, abrasion resistance becomes poor, and the preferred minimum particle size is about 25 microns. Maximum particle size is limited by surface roughness in the article and interference with visual effects. The maximum size of the abrasion resistant particles is 50 microns.

The nature of the binder for the mineral particles is a very important feature in the present invention. Of all the materials tried, microcrystalline cellulose is by far the most satisfactory material. The binder must serve not only to maintain the mineral particles in position on the surface of the print sheet, but should also act as a suspending agent in the slurry (otherwise, it would be necessary to add an additional suspending agent). The peculiar property of microcrystalline cellulose is that it acts like a typical suspending binding agent and film former, but unlike other agents is not water soluble before or after suspension and forms a highly porous film through which the thermosetting resin can penetrate. In addition, the binder must be compatible with the laminating resin and microcrystalline cellulose is compatible with both melamine resin and polyester resins. Furthermore, it must not scatter or attenuate light in the thicknesses applied in the final laminate, and microcrystalline cellulose is satisfactory in this regard as well.

Other binders which may be used, but which provide inferior results compared with microcrystalline cellulose, are various typical suspending-binding agents including anionic acrylic polymer, carboxy methylcellulose and similar materials such as hydroxypropyl cellulose, methylcellulose, polyvinyl alcohol and polyvinyl pyrrolidone. However, as indicated above, microcrystalline cellulose is by far the preferred binder.

Microcrystalline cellulose is a non-fibrous form of cellulose in which the cell walls of cellulose fibers have been broken into fragments ranging in length from a few microns to a few tenths of a micron. It is not a chemical derivative but a purified alpha cellulose.

Microcrystalline cellulose is available under the the trademark "AVICEL", the preparation of which is disclosed in the Battista patent No. 3,275,580. AVICEL Type RC 581 is a white, odorless hygroscropic powder. It is water dispersible and contains about 11% sodium carboxymethyl cellulose as a protective colloid. Its particle size is less than 0.1 %on a 60 mesh screen.

It will be noted that in carrying out the method of the invention (1) The mixture of alumina particles and micro-crystalline cellulose is deposited from a wet mixture, e.g., a water slurry, rather than being used as a filler in a resin solution. This permits the mineral particles to be concentrated in the form of the thin layer, i.e., without being diluted by resin.

(2) Such wet mixture is coated on an unimpregnated printed pattern sheet, rather than on an impregnated pattern sheet.

3 The coating is dried at an elevated temperature which preferably is at least 1800F.

4 The pattern sheet is subsequently impregnated with the thermosetting resin, and this conventional impregnation of the pattern sheet is carried out on conventional equipment.

(5) The coating thickness is preferably from 0.02-0.2 mils, and the resultant thin layer provides unexpectedly high abrasion resistance.

The desirable characteristics of the alumina particle binding agent, which characteristics are all met by micro-crystalline cellulose, are: It acts as a film former; it acts as a binding agent for the mineral particles; it acts as a suspending agent in the slurry for the mineral particles; it is not washed off during the subsequent thermosetting resin impregnating process; it is compatible with the subsequently applied thermosetting resin, such as melamine resin or polyester resin; it is permeable to the thermosetting impregnating resin (indeed microcrystalline cellulose forms a porous film); it is resistant to the heat generated during the laminating procedure; and it does not scatter or attenuate light in the laminate.

The following examples are offered illustratively: EXAMPLE I Microcrystalline cellulose (AVICEL RC 581) was added to stirred water in a Waring blender. After 2 to 3 minutes in the blender, the AVICEL was completely dispersed and the aluminum oxide (Microgrit WCA) was gently stirr

TABLE I 1 2 3 4 5 6 7 Water (ml) - 250 250 250 250 250 250 AVICEL RC 581 - 6.5 7.5 7.5 7.5 7.5 7.5 (quantity in gms.) MICROGRIT WCA - - 30 30 30 60 60 (quantity in gms) MICROGRIT WCA - - 20 30 40 9 30 (particle size in microns) Abrasion cycles, 25 40 100 400 475 > 75 500 Initial wear Pattern Destruction, % at 500 cycles 100% 100% 20% 5% 2% 95% 0% In the above Table, MICRO GRIT WCA is aluminum oxide lapping powder manufactured by Micro Abrasives Corporation of Westfield, Massachusetts.

From the above comparative trials, it is seen that the microcrystalline cellulose by itself was not satisfactory (trial 2) and that the use of alumina having a particle size less than 20 microns did not give good results (trial 6). It is seen that MICROGRIT alumina above 20 micron average particle size provided both satisfactory initial wear, and NEMA wear resistance. In addition, the resulting laminates had clearer pattern appearance than conventional laminates having overlay sheets, and such laminates also passed the other NEMA durability tests.

EXAMPLE II Four slurries were prepared as in Example I, trial &num;3. Each was used to coat 3 mils wet onto 65 lb. unimpregnated paper, and dried as in Example I to provide a dry coating thickness of approximately 0.3 mil. The dried paper was impregnated with melamine resin and assembled in a laminate stack as shown in Fig. 2. Lamination was carried out as described in Example I.

The only variation in the four trials was the average particle size of the alumina. Results were as follows: TABLE 2 MICRO GRIT Average Particle Pattern Destruction at 500 Size cycles 40,u 1% 30,a < 5% 20,a 20% 98x 70% EXAMPLE III Example II was repeated in three trials, in each case using alumina particles having an average particle size of 40 microns. The only variation was in the wet coating thickness.

Laminates were compared as in Example II. The results were: TABLE 3 Pattern Destruction Wet Coating Thickness at 500 cycles 3 mils (0.3 mil dry) 1% 2 mils (0.2 mil dry) 10% 1 mil (0.1 mil dry) 30% EXAMPLE IV The procedure of Example I was repeated using as a coating slurry for the print sheet the following composition: 250 ml. water; 7.5 gms. microcrystalline cellulose; 60 gms. of alumina of average particle size 40 microns; and 1 drop of TRITON X-100.

Two trials were carried out providing wet thicknesses of 1 and 2 mils, respectively. After lamination, abrasion testing produced no initial pattern destruction at 500 cycles.

EXAMPLE V The procedure of Example IV was repeated using the same coating composition, except that 120 gms. of alumina having an average particle size of 30 microns was used. Three trials were run with wet coatings of 1/2, 1 and 1.5 mils, respectively. Abrasion resistance of the final laminate after 500 cycles gave the following results: TABLE 4 1/2 mil (.05 mil dry) 10% pattern destruction 1 mil (.1 mil dry) < 1% pattern destruction 1.5 mil (.15 mil dry) < 1% pattern destruction The three laminates were highly satisfactory in all other respects. Machineability was good with no chipping.

The physical properties of the third sample (prepared with 0.1 mil coated paper) tested in accordance with NEMA Standard LD3-1975, after impregnation and pressing, were as follows: TABLE 5 Wear resistance > 500 cycles Stain resistance No effect Moisture absorption 6.5% Center Swell 8.9% Impact (unsupported) 36" Radiant Heat (unsupported) 185 seconds Hot Water No effect Hot wax No effect Dimensional stability M.D. 0.24% C.D. 0.56% These are all satisfactory or superior values.

EXAMPLE VI Example IV was repeated in two trials using the same composition, except that in the first trial 60 gms. of MICROGRIT SIC 400 (27 micron silicon carbide) was substituted for the alumina and in the second trial 60 gms. of MICROGRIT SIC 1000 (10 micron silicon carbide) was substituted for the alumina. For each composition, coatings were deposited at 1/2, 1 and 1.5 mils wet. The print sheet had a generally "gray" color due to the color of the silicon carbide. Results were as follows: TABLE 6 Coating % Pattern Destruction at 500 Cycles SIC 400 SIC 1000 1/2 (.05 mil dry) 20 85 1 .1 mil dry) 5 80 1.5 (.15 mil dry) < 5 70 As can be seen, while abrasion resistance was satisfactory, the 10 micron silicon carbide gave poorer results than the 27 micron silicon carbide. The poor color can be tolerated in only certain colors of print paper.

EXAMPLE VII The procedure of Example IV was again repeated except that this time the coating composition was modified in one sample by the substitution of 6 gms. of an anionic acrylic polymer (RETENE 420 - Hercules Powder Company) in place of the microcrystalline cellulose, and in a second sample by 9 gms. of carboxy methyl cellulose in place of the microcrystalline cellulose. For both samples, the Taber abrasion test showed about 5 % wear at 500 cycles, a satisfactory performance. However, the anionic acrylic polymer caused a slight milkiness in the laminate indicating that the use of this material would be satisfactory for only certain colors. The laminate in which carboxyl methyl cellulose had been used as the binding agent for the alumina had a poor boiling water resistance and could not meet the NEMA Standard in this regard; this material could only be used on certain lower grade low pressure laminates.

EXAMPLE Vlll In order to investigate the effects of silanes, the following procedure was carried out. One gram of gamma-amino propyltrimethoxy silane was mixed with a 10% water-90% methanol solution until dispersed; a minimum quantity of liquid is used sufficient to wet the alumina powder. This dispersion was then added to 100 gms. of alumina of 30 micron size (MIC ROGRIT WCA 30) and the alumina was mixed with the solution until thoroughly wetted.

The alumina was then dried. Example IV was repeated except that the coating was applied to the print sheet in a 1/4 mil thick wet coating (0.025 mils dried). The resultant laminate was compared to laminates prepared in accordance with Example IV (without the silane) also applied at a thickness of 1/4 mil wet. All laminates were pressed to a mirror finish. The results of the abrasion resistant tests are set forth in Table 8 below: TABLE 8 No Silane Silane Initial Wear (cycles) 300 525 Final Wear (cycles 1075 1250 Wear Value 687 887 It is seen from the above results that the silane improved the efficiency of the abrasion resistant coating.

EXAMPLE IX The present invention was tested to determine its efficacy in upgrading the performance of low pressure board. A slurry was prepared as in Example I with 250 gms water, 6.5 gms. of microcrystalline cellulose, 30 gms of alumina of 30 micron size and 2 drops of TRITON X-100. The slurry was coated in a 1/2 mil wet layer (.05 mil dry) onto unimpregnated printed pattern paper, and dried for 3 minutes at 260"F. The sheet was then impregnated and dried twice to ensure complete impregnation. The impregnated sheet was then placed over a wood particle panel and was pressed at 200 psi at 3000F. for 6 minutes. As a comparison, an otherwise identical low pressure laminate was made without providing the abrasion resistant coating on the top surface of the print sheet. Both samples were subjected to the NEMA Abrasion Test and the results were as follows: TABLE 9 Abrasion Resistant Coating No Coating Initial Wear 200 cycles nil NEMA Abrasion 1050 cycles 150-200 cycles From the above tests as tabulated in Table 9, it is seen that the present invention vastly improves the abrasion resistance of low pressure laminates as well.

EXAMPLE X The procedure of Example IX was repeated and the coatings were applied at a thickness of 1-1/2 mils wet (0.15 mil dry). Four trials were run with the quantity of silane being varied, and the resultant laminate subjected to the NEMA Abrasion Test. The initial wear was recorded, results being given in Table 10 below.

TABLE 10 Quantity of Silane gms /1 O0gms alumina Initial Wear, Cycles 0 175 2 475 3 510 6 400 The above tests show the effect of the silane is not substantially enhanced after reaching a quantity of about 2 wt. % based on the weight of the alumina; and, in fact, in this particular test at 6% silane, the results were poorer than at 2%, although significantly better than the layer containing no silane at all.

EXAMPLE XI The procedure of Example IX was repeated to determine initial wear resistance of the final laminate as a function of the temperature used to dry the coating applied over the print sheet.

Thus, the pattern sheet was coated with the coating composition of Example IV at a rate of 8-10 pounds per ream (0.2 mils dry), except that the coating composition contained silane in accordance with Example IX. The coating was dried for 3 minutes in each sample at the various temperatures given in Table 11 below. After drying the coated sheets were allowed to come to moisture equilibrium with room air at 50%relative humidity at 70"F; the sheets were then impregnated as usual with melamine formaldehyde resin, and were then laminated in the usual way against a satin finished plate. The results were as follows: TABLE 11 Oven Temperature, "F Initial Wear, Cycles 160 225 180 550 200 550 240 575 265 575 EXAMPLE XII A slurry of ingredients was prepared as disclosed in Example I using 6.5 parts by weight of AVICEL microcrystalline cellulose, 2 parts by weight of carboxymethyl cellulose, 30 parts of 30-micron alumina, and 250 parts by weight of water. A trace quantity of TRITON X-100 was added.

The resultant slurry was applied to print sheet using a Meyer rod coating machine at the rate of 5.5 pounds per ream (0.15 mil dry thickness). After drying, the print paper was impregnated with melamine formaldehyde resin to provide a resin content of 41.7%, and drying was effected to provide a volatile content of 4.2%. A laminate was then pressed with the coated print paper applied to a backing using a standard high pressure laminating cycle and a mirror-finished laminating plate so that the final laminate had a gloss surface.

The laminate so produced was compared with another mirror-finished laminate made in a conventional way using a 20-pound overlay, both laminates being subjected to the "sliding can test", described infra. The laminate in accordance with the present invention had an initial wear of 325 cycles and a NWMA wear value of 1021 cycles. In the sliding can rub test, the comparative results were as follows: TABLE 12 SURFACE DULLING Laminate Made CYCLES Conventional with Coated Overlay Laminate Print Sheet 1500 slight no effect 3000 slight no effect 6000 (gradually worse) no effect 12000 slight 18000 24000 extreme wear slight wear Pattern destruction began at about 30,000 cycles on both samples, but it is seen that the conventional laminate shows gradual surface dulling even at only 1500 rub cycles and, in fact, gradual surface dulling began almost with the first few hundred rub cycles. Furthermore, the conventional laminate is completely dulled well before initial pattern destruction (30,000 rub cycles).

Compared with the prior attempts, the present invention provides vastly improved results such that the present invention can be truly considered to be a revolutionary development in the field of decorative laminates. Insofar as is known, the present invention provides the first time a laminate without an overlay sheet has been made which is capable of meeting both the NEMA Abrasion Resistance Standard of at least 400 cycles, and an initial wear point in this same test of at least 175-200 cycles.

There are many uses of laminates in which initial pattern wear rather than NEMA wear value determine the acceptable life of the surface. For example, supermarket check-out counters, food service counters, cafeteria tables, and other commercial surfaces are exposed to abrasive rubbing and sliding of unglazed dinnerwear, canned goods, fiberglass trays, etc. If small areas of the pattern begin to disappear after a relatively short period of use, particularly in an irregular pattern, the surface will be unacceptable to the owner and will result in an expensive replacement. If the surface wears gradually and evenly over a long period of time, the wear out time exceeds the normal replacement cycle due to style changes, approximately 3-5 years.

WHAT WE CLAIM IS: 1. A method of producing a thermosetting resin impregnated decorative facing sheet for an abrasion resistant decorative laminate which laminate comprises a backing and such a facing sheet and has enhanced abrasion resistance without an overlay layer, the method comprising coating the decorative facing sheet with an abrasion resistant wet mixture and drying the coated mixture at an elevated temperature before impregnating the facing sheet with the thermosetting resin, the mixture comprising an abrasion resistant mineral of particle size 20-50 microns and in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the facing sheet decoration and a binder material for the mineral selected to withstand the subsequent laminating conditions and to be compatible with the thermosetting resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the surface of the decorative facing sheet and the coating in the dry state being permeable to the thermosetting resin.

2. A method according to Claim 1 in which the thermosetting resin is selected from the group consisting of melamine formaldehyde and polyester resin.

3. A method according to Claim 1 or 2 in which the binder material is microcrystalline cellulose.

4. A method according to Claim 1 or 2 in which the binder material comprises a mixture of microcrystalline cellulose and carboxymethyl cellulose.

5. A method according to any one of the preceding claims in which the abrasion resistant mineral is alumina.

6. A method according to Claim 5 in which the mixture comprises 5-10 parts by weight of microcrystalline cellulose for 20-120 parts by weight of alumina with sufficient water to facilitate the coating step.

7. A method according to any one of the preceding claims in which the mixture includes a silane compatible with the thermosetting resin, the silane being present in an amount sufficient chemically to bond the mineral to the thermosetting resin.

8. A method according to Claims 6 and 7 in which the silane is an amino silane included in the proportion of 0.5% to 2% by weight based on the weight of alumina.

9. A method according to any one of the preceding claims in which the mixture includes a non-ionic wetting agent.

10. A method according to any one of the preceding claims in which the thickness of the coating, after drying is from 0.02 to 0.3 mils.

11. A method according to any one of the preceding claims in which the coating is dried at a temperature of at least 1800F.

12. A method according to Claim 11 in which the drying is carried out at a temperature of 240-270"F.

13. A method of producing an abrasion resistant laminate which comprises assembling over a backing comprising a plurality of phenolic resin impregnated kraft paper sheets a coated decorative facing sheet impregnated with melamine formaldehyde thermosetting resin and produced by the method according to any one of the preceding claims, and subjecting the assembly to heat and pressure at a temperature of from 230-340"F and a pressure of from 800-1600 psi.

14. A method of producing an abrasion resistant laminate which comprises assembling over a backing comprising a wood particle panel a coated decorative facing sheet impregnated with melamine formaldehyde thermosetting resin and produced by the method according to any one of Claims 1 to 12, and laminating the facing sheet to the backing by the application of heat and pressure at a temperature of from 325"-350"F and a pressure of from 175-225 psi.

15. A method of producing an abrasion resistant laminate substantially as herein described with reference to any one of Examples 1 to 6 or any one of Examples 8 to 12.

16. A product produced by the process according to any one of the preceding claims.

17. A decorative facing sheet for use in the preparation of abrasion resistant decorative laminates comprising a facing sheet having a decorative design thereon and an abrasion resistant coating thereover of a mixture comprising an abrasion resistant mineral of particle size 20-50 microns in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the decorative design and a binder material for the mineral selected to be compatible with a thermosetting resin selected from the group consisting of melamine formaldehyde resin and polyester resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the substrate and the facing sheet including the coating being impregnable with said thermosetting resin.

18. A sheet according to Claim 17 in which the facing sheet is a paper sheet substrate with a print design thereon.

19. A sheet according to Claim 17 or 18 impregnated with said thermosetting resin.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

3-5 years.

WHAT WE CLAIM IS: 1. A method of producing a thermosetting resin impregnated decorative facing sheet for an abrasion resistant decorative laminate which laminate comprises a backing and such a facing sheet and has enhanced abrasion resistance without an overlay layer, the method comprising coating the decorative facing sheet with an abrasion resistant wet mixture and drying the coated mixture at an elevated temperature before impregnating the facing sheet with the thermosetting resin, the mixture comprising an abrasion resistant mineral of particle size 20-50 microns and in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the facing sheet decoration and a binder material for the mineral selected to withstand the subsequent laminating conditions and to be compatible with the thermosetting resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the surface of the decorative facing sheet and the coating in the dry state being permeable to the thermosetting resin.
2. A method according to Claim 1 in which the thermosetting resin is selected from the group consisting of melamine formaldehyde and polyester resin.
3. A method according to Claim 1 or 2 in which the binder material is microcrystalline cellulose.
4. A method according to Claim 1 or 2 in which the binder material comprises a mixture of microcrystalline cellulose and carboxymethyl cellulose.
5. A method according to any one of the preceding claims in which the abrasion resistant mineral is alumina.
6. A method according to Claim 5 in which the mixture comprises 5-10 parts by weight of microcrystalline cellulose for 20-120 parts by weight of alumina with sufficient water to facilitate the coating step.
7. A method according to any one of the preceding claims in which the mixture includes a silane compatible with the thermosetting resin, the silane being present in an amount sufficient chemically to bond the mineral to the thermosetting resin.
8. A method according to Claims 6 and 7 in which the silane is an amino silane included in the proportion of 0.5% to 2% by weight based on the weight of alumina.
9. A method according to any one of the preceding claims in which the mixture includes a non-ionic wetting agent.
10. A method according to any one of the preceding claims in which the thickness of the coating, after drying is from 0.02 to 0.3 mils.
11. A method according to any one of the preceding claims in which the coating is dried at a temperature of at least 1800F.
12. A method according to Claim 11 in which the drying is carried out at a temperature of 240-270"F.
13. A method of producing an abrasion resistant laminate which comprises assembling over a backing comprising a plurality of phenolic resin impregnated kraft paper sheets a coated decorative facing sheet impregnated with melamine formaldehyde thermosetting resin and produced by the method according to any one of the preceding claims, and subjecting the assembly to heat and pressure at a temperature of from 230-340"F and a pressure of from 800-1600 psi.
14. A method of producing an abrasion resistant laminate which comprises assembling over a backing comprising a wood particle panel a coated decorative facing sheet impregnated with melamine formaldehyde thermosetting resin and produced by the method according to any one of Claims 1 to 12, and laminating the facing sheet to the backing by the application of heat and pressure at a temperature of from 325"-350"F and a pressure of from 175-225 psi.
15. A method of producing an abrasion resistant laminate substantially as herein described with reference to any one of Examples 1 to 6 or any one of Examples 8 to 12.
16. A product produced by the process according to any one of the preceding claims.
17. A decorative facing sheet for use in the preparation of abrasion resistant decorative laminates comprising a facing sheet having a decorative design thereon and an abrasion resistant coating thereover of a mixture comprising an abrasion resistant mineral of particle size 20-50 microns in an amount sufficient to provide an abrasion resistant layer without interfering with visibility of the decorative design and a binder material for the mineral selected to be compatible with a thermosetting resin selected from the group consisting of melamine formaldehyde resin and polyester resin, the binder material being present in an amount sufficient to bind the abrasion resistant mineral to the substrate and the facing sheet including the coating being impregnable with said thermosetting resin.
18. A sheet according to Claim 17 in which the facing sheet is a paper sheet substrate with a print design thereon.
19. A sheet according to Claim 17 or 18 impregnated with said thermosetting resin.
20. A sheet according to Claim 17, 18 or 19 in which the binder material is microcrystal

line cellulose.
21. A print sheet according to Claim 17,18 or 19 in which the binder material is a mixture of microcrystalline cellulose and carboxymethyl cellulose.
22. A print sheet according to any one of Claims 17 to 20 in which the abrasion resistant mineral is alumina.
23. A print sheet according to Claim 22 in which the mixture comprises 5-10 parts by weight of microcrystalline cellulose for 20-120 parts by weight of alumina.
24. A print sheet according to any one of Claims 17 to 23 in which the mixture includes a silane compatible with the thermosetting resin and the silane is present in an amount sufficient chemically to bond the mineral to the thermosetting resin.
25. A print sheet according to Claims 23 and 24 in which the silane is an amino silane included in the proportion of 0.5% to 2% by weight based on the weight of alumina.
26. A print sheet according to any one of Claims 17 to 25 in which the thickness of the coating, after drying, is from 0.02 to 0.3 mils.
27. A print sheet for use in the preparation of abrasion decorative laminates substantially as herein described with reference to any one of Examples 1 to 6 or nay one of Examples 8 to 12.
28. An abrasion resistant decorative laminate comprising a backing and a facing sheet according to any one of Claims 17 to 27 laminated thereto by said thermosetting resin and the application of heat and pressure.
29. An abrasion resistant decorative laminate according to Claim 28 in which the backing comprises a plurality of phenolic resin impregnated paper sheets.
30. An abrasion resistant decorative laminate according to Claim 28 in which the backing comprises a wood particle panel.
31. An abrasion resistant decorative layer produced and arranged substantially as herein described with reference to the accompanying drawings.