Abrasion resistant laminate

Abstract

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.

Description

This is a division of application Ser. No. 879,848, 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 % microcrystalline 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 the alumina or other inorganic 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 thereto 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 enchance the abrasion resistance of the final laminate; a maximum quantity of about 2% by weight based on the weight of the alumina or other hard particles is suggested since greater quantities do not lead to any significantly better results and merely increase the cost of the raw materials. ≠*Silanes as coupling agents in other arts are known, e.g. in the manufacture of fiberglass tires, grinding wheels and fiberglass reinforced polyester bodies. See the 1976-77 Edition of Modern Plastics Encyclopedia, Page 160, which lists some silanes useful with melamine and polyester systems.

It is an important feature of the present invention that the coating using micro-crystalline 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 140° 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 considerably inferior results in the present invention compared with alumina. Other minerals of sufficient hardness such as zirconium oxide, cerium oxide, diamond dust, etc. can work, but are either too expensive for practical usage or under certain circumstances produce excessive color shift. Glass beads have been tried unsuccessfully. Silicon carbide also was tried, and while providing good abrasion resistance, produced excessive color shift. Mixtures of silica and alumina give good results, and in some environments, such as where wear of cutting tools is a significant factor, silica may be the preferred particles.

An important feature is the size of the alumina or other hard particles. Beneath 20 micron particle size, abrasion resistance becomes poor, and the preferred minimum average particle size is about 25 microns. Maximum average particle size is limited by surface roughness in the article and interference with visual effects. The preferred maximum average size of the abrasive resistant particles is about 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 celluose 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, polyvinyl pyrrolidone, etc. 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 trademark "AVICEL", the preparation of which is disclosed in the Battista U.S. Pat. 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.

Features and advantges of the instant invention which are considered to be particularly significant are as follows:

(1) The mixture of mineral particles and microcrystalline cellulose is deposited from a water slurry, rather than used as fillers in a resin solution. The abrasion-resistant mineral particles are thereby highly concentrated in the resultant layer.

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

(3) The coating is dried at an elevated temperature of at least about 140° F.

(4) The coating thickness is 0.02-0.3, preferably 0.02-0.2 mils, rather than 1-2 mils.

(5) After applying the coating and drying it, the pattern sheet is then impregnated with the thermosetting resin, and this conventional impregnation of the pattern sheet is carried out on conventional equipment, rather than special, difficult to control, coating of a thick slurry.

(6) The ultra-thin layer provides unexpectedly high abrasion resistance.

The desirable characteristics of the alumina particle binding agent, which characteristics are all met by microcrystalline 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

A slurry of the ingredients was prepared in a Waring blender. Microcrystalline cellulose (AVICEL RC 581) was added to stirred water. After 2 to 3 minutes in the blender, the AVICEL was completely dispersed and the aluminum oxide (Microgrit WCA) was gently stirred in. At the end, three drops of TRITON X-100 (a non-ionic detergent) was added to promote wetting.

The resultant slurry was applied as a coating to a 65 lb/ream (3000 ft²) unimpregnated pattern sheet having a woodgrain surface print. The coating was dried at 265° F. for 3 minutes. The paper was then saturated in the normal way using melamine formaldehyde resin and was dried in accordance with normal procedures. The resin content was 45-48% and the volatile content was 5-6%. The laminate was made up and pressed using a conventional general purpose cycle, viz. about 300° F., 1000 p.s.i., for about 25 minutes.

Formulations and abrasion results are listed below for a nominal 1.5 mil wet coating which calculates to a 0.11 mil thick dry coat for Trials 3, 4 and 5, and 0.17 mil thick for Trials 6 and 7.

TABLE 1
__________________________________________________________________________
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 100%
100%
20%
5%
2%
95%
0%
Pattern Destruction, %,
at 500 cycles
Coating rate in lbs/ream*
--  --   5   5   5   9    9
__________________________________________________________________________
*In all examples coating weight in pounds/ream is dry coat weight.

In the above Table, MICROGRIT WCA is aluminium oxide lapping powder manufactured by Micro Abrasives Corporation of Westfield, Mass.

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 #3. Each was used to coat 3 mils wet at 9.4 lbs/ream onto 65 lb. unimpregnated paper, and dried as in Example I to provide a dry coating thickness of approximately 0.2 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
______________________________________
MICROGRIT Average
Pattern Destruction
Particle Size    at 500 cycles
______________________________________
40μ            1%
30μ           <5%
20μ           20%
9μ           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
Lbs/Ream Wet Coating Thickness
at 500 cycles
______________________________________
9.4      3 mils (0.2 mil dry)
1%
5.8      2 mils (.13 mil dry)
10%
3.6      1 mil (.08 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 mil (7.4 lbs/ream) and 2 mils (10.5 lbs/ream), 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. Coating rates were 11, 15 and 18 lbs/ream, respectively. Abrasion resistance of the final laminate after 500 cycles gave the following results:

TABLE 4
______________________________________
1 mil (.2 mil dry)
10% pattern destruction
1 mil (.27 mil dry)
<1% pattern destruction
1.5 mil (.33 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 resistance    6.5%
Center Swell           8.9%
Impact (unsupported)   36"
Radiant Heat (unsupported)
186 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
______________________________________
% Pattern Destruction at 500 Cycles
Coating      SIC 400      SIC 1000
______________________________________
1/2 (.1 mil dry)
20          85
1 (.14 mil dry)
5           80
1.5 (.17 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

Example IV was again repeated with three compositions, this time substituting 60 gms of glass spheres (-325 screen size), 240 gms of such glass spheres and 60 gms of CABOSIL L-5 (silica aerosil of millimicron particle size), respectively, in place of the alumina particles. Each composition was coated at 1/2, 1 and 1.5 mils wet, at coatings up to 20 lbs/ream. The results for the heaviest coating weights were as follows:

TABLE 7
______________________________________
Type           Silane Worn on Taber
______________________________________
60 g glass    200 cycles
240 g glass    200 cycles
60 g Silica Aerosil
<100 cycles
______________________________________

None of these samples gave satisfactory abrasion resistance.

EXAMPLE VIII

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 from Hercules) 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 milked the laminate slightly, 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 IX

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 (MICROGRIT 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 at 5.0 pounds per ream (0.1 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 X

The present invention was tested to determine its efficacy in upgrading the performance of low pressure board. A slurry was prepared as in Example 1 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 as coated in a 1/2 mil wet layer at 2.5 lbs/ream (0.5 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 p.s.i. at 300° F. 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 XI

The procedure of Example IX was repeated and the coatings were applied at 9 lbs/ream to a thickness of 11/2 mils wet (0.17 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
______________________________________
Quanity of Silane-
gms/100 gms 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 XII

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 XIII

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 5.0 pounds per ream (0.11 mil dry thickness). The print paper was then 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 using a standard 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 NEMA wear value of 1021 cycles. In the sliding can rub test, the comparative results were as follows:

TABLE 12
______________________________________
SURFACE DULLING
Laminate Made
Conventional    with Coated
CYCLES     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).

EXAMPLE XIV

An aqueous slurry of ingredients was prepared as in Example I using the following formula:

300 ml. water

11.2 gms AVICEL RC 581

5.4 gms CMC 7L

125 gms silica crystals having maximum particle size 45 microns

2.5 gms Silane 1100

This slurry was coated at 12.1 lbs/ream, the print sheet was then dried, impregnated with melamine resin and finally laminated to phenolic impregnated core sheets. The resultant laminate had the following wear properties:

______________________________________
Initial wear  225 cycles
Final wear    950 cycles
Wear value    587 cycles
______________________________________

These results are far superior to both bare print sheet, i.e. without overlay, and the use of silica aerogel, i.e. millimicron size (Example VII) which are worn out in less than 100 cycles.

EXAMPLE XV

Example XIV was repeated with part of the silica replaced with 30 micron averge size alumina, i.e. in the formulation of Example XIV the 125 gms of silica were replaced by 94 gms of silica and 31 gms of alumina. The slurry was coated at 8.1 lbs/ream. After drying, melamine impregnation and lamination, test results were as follows:

______________________________________
Initial wear  300 cycles
Final wear    1150 cycles
Wear value    725 cycles
______________________________________

Thus, at a lower coating weight compared with Example XIV, improved wear was obtained.

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.

The closest thing previously available (see FIG. 2) has been the use of print paper made in accordance the Lane et al U.S. Pat. No. 3,798,111. While laminates made using this paper, without an overlay, have excellent abrasion values according to the NEMA Standard, the initial wear point in these products, however, is still very poor. Tests conducted on such laminates show that many have initial wear values of under 100 cycles, some as low as 35 cycles, whereas conventional laminates made with conventional overlay have an initial wear point of 175-200 cycles. In contrast, laminates made in accordance with the present invention have initial wear points of no less than 175 cycles (usually a minimum of 200 cycles) and up to about 500 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.

Conventional high pressure laminates (see FIG. 1) with initial wear values of 175-200 are known to be satisfactory in commercial or institutional service, and show perhaps 10-20% pattern loss in 3-5 years on checkout counters. To determine a predicted wear-out time for laminate (FIG. 2) without overlay made using the print paper of the Lane et al U.S. Pat. No. 3,798,111, such laminates along with conventional laminates and those made in accordance with the present invention were subjected to an abrasive rub test consisting of sliding a simulated fiberglass tray surface back-and-forth over the test laminate, the simulated fiberglass tray surface being bonded to the botto of a No. 10 can carrying 5 lbs. of weight, and flexibly clamped in a cam driven jig that provided about 5 inches of oscillatory motion. In this test, the laminate according to U.S. Pat. No. 3,798,111 began to show pattern distruction after about 3000 rub cycles. Conventional laminate with overlay and laminate prepared in accordance with the present invention without overlay did not show any pattern destruction after 30,000 cycles.

In addition to providing poorer initial wear values, the laminates made without overlay using the print paper of the Lane et al U.S. Pat. No. 3,798,111 provide other disadvantages as well. In the Lane et al patent, the alumina particles are introduced during the period making process and this results in a special grade paper for each base paper color required, greatly increasing inventory requirements; in contrast, in the present invention in which the coating is applied after printing, use is made of all existing stocks of conventional print paper. Furthermore, the present invention is more flexible than the Lane et al process in that it permits tailoring of the abrasion resistance to specific needs, without the cumbersome redevelopment of a paper base on a paper machine.

As pointed out in Example XIII above, the "rub test" or "sliding can test" was also used to compare the present invention with conventional mirror-surfaced laminates having overlay. As previously noted, both start initial pattern destruction at about 30,000 rub cycles. The conventional laminate shows gradual surface dulling beginning almost with the first few hundred rub cycles, and is completely dulled well before initial pattern destruction. The laminate made with the abrasion-resistant print in accordance with the present invention, however, showed negligible surface dulling almost up to the point of pattern destruction. These results suggest not only an important advantage of the instant invention compared with conventional laminates including overlay, but also similar advantages compared with laminates produced by the casing of the overlay in situ on the print sheet, e.g. the Fuerst U.S. Pat. No. 3,373,071.

The present invention is also believed to constitute other important improvements over the casting of an overlay sheet (Michl U.S. Pat. No. 3,135,643 and Fuerst U.S. Pat. No. 3,373,071; and other patents). Such patents show the coating of a resin containing layer onto resin impregnated pattern sheet, in which the upper resin layer contains abrasion resistant mineral particles (see FIG. 3). In these techniques, the base paper already contains the melamine resin and the thick coating applied also contains melamine resin. The coating is applied in a thickness of, at the very least, 0.022 lbs. per sq. ft. which is a quantity at least 8 times as great as that used in the present invention. The thickness of the dry layer runs at least 1 mil and preferably more compared with calculated dry coatings in the present invention running from 0.02 to 0.3 mils, preferably maximum of 0.2 mils.

The Michl patent essentially discloses how to deposit an overlay layer onto the impregnated pattern sheet, rather than how to eliminate the overlay. The finished laminate (FIG. 3) is essentially the same as that of a conventional laminate, containing cellulose fibers, resin, and differs only by the mineral particles dispersed in this layer. The Fuerst U.S. Pat. No. 3,373,071 states that the process taught by Michl results in laminates that are blotchy when satinized. A significant percentage of laminates are satinized with pumice and rotating brushes to reduce their surface gloss. The Fuerst patent replaces the cellulose fiber of the Michl process with microcrystalline cellulose in order to provide blotch-free surfaces after satinizing. Thus, the basic process of Fuerst is the same as that of Michl, i.e. depositing a resin containing overlay layer onto the wet, impregnated pattern sheet, the thickness of the Fuerst coating being between 8 and 100 times thicker than those found useful in the present invention, and offering no significant savings of raw material compared with conventional, overlay containing laminate.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification. For example, it will be understood that certain additional variations in processing will, in certain instances, give somewhat different results. For example, results are generally better when the laminates in accordance with the present invention are formed against a hard surface. Thus, plate produced finishes, such as mirror and satin, provide better initial wear under given coating conditions then do foil (or other soft-backed pressing surfaces) produced finishes. Accordingly, in some instances it is advantageous to calendar the dried, coated pattern sheet prior to impregnation with the thermosetting resin.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the engineering concept and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purposes of description and not of limitation.

Claims

1. An abrasion resistant decorative laminate meeting NEMA abrasion resistance standards and also capable of withstanding 175-200 cycles of initial wear in the same test comprising:

a backing layer and laminated thereto a thermoset laminating resin impregnated decorative facing sheet, said decorative facing sheet having a print design thereon and an ultra-thin abrasion resistant coating over said print design, said ultra-thin abrasion resistant coating having a thickness of up to about 0.3 mils comprising a mixture of (1) an abrasion resistant hard mineral particle size 20-50 microns in high concentration sufficient to provide for abrasion resistance without interfering with visibility and (2) stabilizing binder material for said mineral, said thermoset resin being impregnated throughout said print sheet and said coating, said binder material not interfering with visibility, and with said ultra-thin abrasion resistant coating forming the uppermost layer of said laminate.

2. A decorative laminate in accordance with claim 1 wherein said thermoset resin is melamineformaldehyde resin.

3. A laminate in accordance with claim 2 wherein said binder comprises predominantly microcrystalline cellulose.

4. A laminate in accordance with claim 3 wherein said abrasion resistant mineral particles constitute alumina, silica or mixtures thereof.

5. A laminate in accordance with claim 2 wherein said abrasion resistant mineral is alumina, and wherein said alumina is chemically bound to said melamine resin with a silane.

6. A laminate in accordance with claim 1 wherein said ultra-thin abrasion resistant coating is directly over said print design and has a thickness of 0.02-0.2 mils.

7. A decorative, high-pressure laminate in accordance with claim 1 wherein said backing comprises a plurality of phenolic impregnated paper sheets and said facing sheet comprises a paper sheet impregnated with melamine resin, said abrasion resistant particles comprising alumina particles, said binder material comprising microcrystalline cellulose, said abrasion resistant coating comprising about 5-10 parts by weight of said microcrystalline cellulose for about 20-120 parts by weight of said alumina, the thickness of said coating being about 0.02-0.2 mils.

8. A laminate in accordance with claim 7 wherein said alumina is bonded to said melamine resin with a silane.

9. A laminate in accordance with claim 1, wherein said ultra-thin abrasion resistant coating has a thickness no greater than 0.3 mils.

10. A laminate in accordance with claim 1 wherein the quantity by weight of said binder material in said abrasion resistant coating is no greater than the quantity by weight of said mineral therein, and said binder material constitutes a mixture.

11. An abrasion resistant decoration laminate having superior NEMA abrasion resistance, superior initial wear resistance in the same test, and superior wear resistance in the Sliding Can Test comprising:

a backing layer and laminated thereto a thermoset laminating resin impregnated decorative facing sheet, said decorative facing sheet having an ultra-thin abrasion resistant coating thereover, said ultra-thin abrasion resistant coating having a thickness of up to about 0.3 mils comprising a mixture of (1) an abrasion resistant hard mineral of fine particle size sufficiently great such that said decretive laminate meets NEMA abrasion resistance standards and withstands 175-200 cycles of initial wear in the same test, in high concentration sufficient to provide for abrasion resistance without interfering with visibility, and (2) stabilizing binder material for said mineral, said thermoset resin being impregnated throughout said decorative sheet and said coating, said binder material not interfering with visibility, and with said ultra-thin abrasion resistant coating forming the uppermost layer of said laminate. 12. A laminate in accordance with claim 11 wherein said ultra-thin abrasion resistant coating has a thickness of 0.02-0.2 mils. 13. A laminate in accordance with claim 11 wherein the quantity by weight of said binder material in said abrasion resistant coating is no greater than the quantity by weight of said mineral therein, and said binder material constitutes a mixture. 14. A laminate in accordance with claim 11 wherein said ultra-thin abrasion resistant coating has a thickness no greater than 0.3 mils, and said abrasion resistant hard mineral particles have a size of 20-50 microns.

15. A decorative, high-pressure laminate in accordance with claim 11 wherein said backing comprises a plurality of phenolic impregnated paper sheets and said facing sheet comprises a paper sheet impregnated with melamine resin, said abrasion resistant particles comprising alumina particles of 20-50 microns, said binder material comprising microcrystalline cellulose, the thickness of said coating being about 0.02-0.2 mils. 16. A laminate in accordance with claim 15 wherein said alumina is bonded to said melamine resin with a silane. 17. A decorative laminate in accordance with claim 11 wherein said thermoset resin is melamineformaldehyde resin, and the minimum particle size of said abrasion resistant hard material is about 20 microns. 18. A laminate in accordance with claim 17 wherein said abrasion resistant mineral is alumina, and wherein said alumina is chemically bound to said melamine resin with a silane. 19. A laminate in accordance with claim 17 wherein said binder comprises predominantly microcrystalline cellulose, and the minimum particle size of said abrasion resistant hard mineral is about 20 microns. 20. A laminate in accordance with claim 19 wherein said abrasion resistant mineral particles constitute alumina, silica or mixtures thereof.