Transfer coating of abrasion-resistant layers.

The present invention relates to the coating of surfaces and, more particularly, the provision of abrasion-resistant coatings on various types of substrates by means of transfer coating or printing.

U.S. Patents 4,255,480; 4,263,081; 4,305,987; and 4,327,141 disclose embodiments which demonstrate abrasion-resistant enhancement of high and low pressure decorative laminates by providing an ultra-thin coating composed of mineral particles and microcrystalline cellulose on the surface of conventional decor paper, followed by impregnating the paper with melamine or polyester resin, and then using the decor paper in a normal laminating process but without the overlay paper. The resultant laminate exhibits abrasion-resistance qualities much better than those of conventionally produced high or low pressure decorative laminates containing an overlay layer.

However, the embodiments illustrated in these patents are directed to the manufacture of abrasion-resistant high and low pressure laminates containing thermosetting resins, and there is no disclosure of the use of microcrystalline cellulose in combination with mineral particles in other environments, particularly for the protection of thermoplastic substrates. Moreover, the ultra-thin coating is applied to one of the elements, e.g. the decor sheet, which becomes part of the final laminate product.

Transfer coating or printing, on the other hand, is well known. For example, there is a considerable body of prior art which shows coating compositions for use in transfer (hot stamp) applications to provide abrasion resistance to thermoplastic resin surfaces. Such heat transfers can include a layer containing inorganic grit particles to enhance abrasion resistance.

As described in patents such as U.S. 3,666,516; 4,007,067; 3,770,479; 3,953,635; and 4,084,032, hot stamp tapes are often produced with the following layers, noting Fig. 1: <ul id="ul0001" list-style="none"><li>A. Carrier Sheet or Web - such as films of polyester, cellophane, cellulose acetate, or paper.</li><li>B. Primer Coat (optional) - to hold tick coat (see C.) to carrier sheet or web.</li><li>C. Tick Coat (optional) - to impart a texture if desired.</li><li>D. Release Coating (optional) - to enable release of subsequent coating from the above.</li><li>E. Replicating Coat (optional) - to replicate the surface of the carrier sheet or web and surfaces of heretofore coated ticks.</li><li>F. Abrasion Coat - to impart abrasion resistance.</li><li>G. Color Coat - may be one coat or several to decorate the coating.</li><li>H. Adhesion Coat - to enable the transferable portion of the composite to stick to the substrate.</li></ul>

The hot stamp tape produced as described is then applied to a suitable substrate (adhesion coat against the substrate) under heat and pressure, and the carrier sheet or web with primer, tick and release coats, if applicable, are removed leaving the subsequent coats laminated onto the substrate, as shown in Fig. 1.

These hot stamp tapes of the prior art typically do not offer suitable abrasion resistance to be used in environments of high traffic and abrasion. This deficiency has kept hot stamp tapes out of sizable markets.

The present invention is based on the discovery that the ultra-thin abrasion-resistant layers of the type disclosed in the aforementioned U.S. Patents 4,255,480; 4,263,081; 4,305,987; and 4,327,141 provide enhanced abrasion resistance to a wide variety of both thermoplastic and thermosetting resin surfaces, and that coatings of this type can be transferred from one surface to another. It is an important feature of the present invention that when inorganic grit is compounded with a suitable binder material such as microcrystalline cellulose, much greater enhancement of abrasion resistance is obtained than in the prior transfer compositions containing equal amounts of inorganic grit. An ultra-thin layer has a thickness of less than 0.5 mils and preferably in the range of 0.02 to 0.3 mils. One mil equals one thousandth of an inch.

We have discovered that the ultra-thin abrasion-resistant coatings of the aforementioned U.S. Patents 4,255,480; 4,263,081; 4,305,987; and 4,327,141 not only enhance abrasions resistance on thermosetting-type resins such as polyester and melamine-formaldehyde as disclosed in such patents, but also on thermoplastic-type resins such as acrylic and vinyl. We have also discovered that such ultra-thin (less than about 0.5 mils thick and preferably in the range of 0.02 to 0.3 mils thick) abrasion-resistant coating need not be applied onto paper, which is subsequently resin impregnated and used in a laminating process, but that such a layer can be transfer coated in a variety of ways. Furthermore, we have found that enhanced abrasion resistance can be obtained on thermosetting and thermoplastic resins by transferring the dried ultra-thin coating to the plastic surface from a mold surface, or from a separator or release sheet during the molding or laminating process. Enhanced abrasion resistance using such an ultra-thin layer can also be achieved by transferring the layer plus thermosetting and/or thermoplastic resins as a composite from a carrier to a substrate after which the carrier is subsequently discarded. We have also discovered that abrasion-resistance enhancement can be obtained using this coating in press cycles of very low pressure and duration.

It is, accordingly, an object of the invention to overcome deficiencies in the prior art, such as pointed out and/or suggested above.

It is another object of the invention to provide for the transfer coating of ultra-thin abrasion-resistant layers.

It is another object of the invention to provide improved products of a great variety of materials, having improved abrasion-resistant surfaces.

These and other objects and the nature and advantages of the.instant invention will be more apparent from the following detailed description of specific embodiments, taken in conjunction with the drawing wherein:

Brief Description of the Drawing

<ul id="ul0002" list-style="none"><li>Fig. 1 is a typical prior art hot stamp tape, which may be modified to incorporate an ultra-thin abrasion-resistant layer in accordance with the instant invention;</li><li>Fig. 2. is a schematic view showing a method for incorporating a grit coating into the surface of a substrate using a mold, according to a control process;</li><li>Fig. 3 is a schematic view similar to Fig. 2, showing the transfer of an ultra-thin abrasion-resistant coating according to the invention from a mold surface into the upper surface of a substrate;</li><li>Fig. 4 schematically shows a process similar to Fig. 2, except using a separator instead of a mold;</li><li>Fig. 5 shows a process similar to Fig. 3 using an abrasion-resistant coating applied to a separator instead of to a mold, for transfer to a substrate;</li><li>Fig. 6 is a schematic view of a hot stamp tape of simplified construction compared to that of Fig. 1, used for control comparisons in some of the following examples;</li><li>Fig. 7 is a hot stamp tape of similar construction to the control tape of Fig. 6, but made in accordance with the present invention, Fig. 7 also schematically showing the transfer operation in process;</li><li>Fig. 8, similar to Fig. 3, shows application of the invention to continuous lamination; and</li><li>Fig. 9, similar to Fig. 3, shows application of the invention to another form of continuous lamination.</li></ul>

Detailed Description of Embodiments

The present invention is operable in a great variety of embodiments, and using a great variety of substrates, and the term "substrate" is used in a broad sense to mean any kind of body capable of receiving a transfer layer, whether the substrate be fibrous, thermoplastic, thermoset or thermosettable, wood, metal, particleboard, etc., it being understood that the transfer layer must bond to the substrate. The following examples are intended to illustrate, but not to limit, the various possibilities.

I - HOT STAMP TAPE (HEAT TRANSFERABLE COATINGS)

Hot stamp tape is a web of indeterminate length that carries thermally transferable material that is structured to provide an improved appearance, such as a woodgrain pattern, on a suitable substrate after transfer to the substrate, such as particleboard or the like, of transferable layers from the heat stamp web. Of course, the web can also be provided in sheet form. Inexpensive furniture is now made in this way. However, the surface of the product, which involves merely a particleboard backing with a thin woodgrain printed coating thereon, is not very durable and is easily abraded.

Typically, a carrier web such as Mylar film is coated with a protective coating, then printed with woodgrain reproduction (normally three prints), and is then coated with an adhesive layer for bonding to the substrate. The construction is typically even considerably more complex, such as illustrated in Fig. 1.

The so constructed heat transfer web or hot stamp tape is wound into rolls and sold to furniture companies who heat transfer the composite to particleboard or other substrate, the carrier sheet or web being discardedThe particleboard is thus decorated with a high quality woodgrain reproduction superior to direct wet printing on the particleboard. It eliminates a fairly involved process at the furniture manufacturer level, as well as solving fume problems which are becoming increasingly more difficult as environmental concerns become more predominate, and it also eliminates the need for highly skilled personnel. However, as noted above, the resultant product is not very abrasion-resistant as the top coating provides a NEMA (LD3.1980) abrasion resistance of only about twenty cycles. In addition, most applications require that the furniture manufacturer run the product through an additional coating and drying line.

About seven billion square feet of wood veneer and wood reproductions are used by the furniture industry per year, and if a sufficiently abrasion-resistant product could be provided by transfer printing at a reasonable cost, it is estimated that a large fraction of this market could benefit from such a product.

As is evidenced in Table 1, even the addition of aluminum oxide in relatively large quantity to resins typically used in the abrasion coat F (as mentioned in Dunning, U. S. 4,007,067) does not significantly increase the abrasion resistance of the product. Surprisingly though, with the use of the abrasion-resistant composition of U. S. Patents 4,255,480; 4,263,081, and 4,305,987, and 4,327,141, the abrasion resistance of the hot stamp tape material is dramatically improved.

Referring to Table 1, a series of trials were run to compare the relative abrasion resistances (as measured by the initial point of wear, NEIIA LD3-3.01) of hot stamp tapes of various compositions. Each hot stamp tape composition differed in one way or another from all of the others. Different classes of resins were employed, i.e. thermosetting and thermoplastic types. Two types of thermoplastic resins were used, i.e. vinyl and.acrylic. Two types of acrylic were used, i.e. Acrysol WS68 (Acrylic A)* and Rhoplex AC-61 ^* Acrysol WS68 is said to be a thermosetting acrylic polymer which, when formulated with monomeric melamine resins, produces industrial baking enamels. However, it is based on or incorporates a thermoplastic, has thermoplastic characteristics, and was used to simulate a thermoplastic. (Acrylic B). One type of thermosetting resin was used, i.e. a butylated melamine-formaldehyde resin.

The tapes used were basically of the construction shown in Figs. 6 and 7. In each case a polyester carrier web was coated first with an aqueous top coat composition as set forth in Table 1, after which the top coat was dried at 250⁰F, the drying being carried out for periods of from 30 seconds to 90 seconds until the coating was dry to the touch. An aqueous base coat composition was then applied to the top coat and was dried under the same conditions. In Examples 3-10 and 12-14, the base coat also served as an adhesive layer. Fig. 6 shows control Examples 3-10, and Fig. 7 shows Examples 12-14. In Examples 11, 15 and 16 an additional coating was applied as an aqueous emulsion over the base coat, which additional coating after drying served as an adhesive coat; in Examples 11 and 16, this adhesive coat was Acrylic A, and in Example 15 it was Acrylic B as shown in Table 1., Consistent with USP's 4,255,480; 4,263,081; 4,305,987 and 4,327,141, the ultra-thin top coat in Examples 12-14 must be dried at a temperature of at least 140°F.

All hot stamps were transferred from the polyester film carrier (Melinex 377) onto mirror finish, high pressure decorative laminates used as substrates. So initial wear could be easily determined, the mirror surface of the laminates were decorated with a grid pattern before the transfer process. All thermoplastic transfers were made at pressing conditions of 325⁰F, 50 psi for 30 seconds and cooled to 90OF while maintaining pressure. The butylated melamine transfers were made at 375⁰F, 750 psi for 3 minutes and cooled at 90°F while maintaining pressure. The aluminum oxide used in all examples was the same.

Control Examples 1-4 illustrate the initial wear values where only resins are used. Control Examples 5-11 show how the addition of aluminum oxide (44-50% by dry coat weight) into the top coat, exposed after transfer, affects abrasion resistance of the hot stamp tapes. The hot stamp tapes of Examples 12-15 were made with approximately the same amount of resin and aluminum oxide as each of the preceding examples, but the abrasion-resistant deposit (ARD) of the invention was the exposed coating after transfer.

The Taber test was used to measure initial wear value. As can be seen from Table 1, the results are dramatic. Control Examples 1, 5 and 6 using Acrylic A gave an initial wear of only 75 cycles, even though control Examples 5 and 6 had a top coat containing, respectively 2.9 and 4.0 pounds per 3000 ft² of aluminum oxide. When the quantity of aluminum oxide was raised to 5.1 pounds per 3000 ft² in the top coat as shown in control Example 7, the initial wear doubled to 150 cycles. These poor values should be compared to Examples 12 and 13 according to the invention wherein initial wear values of more than 500 cycles and 450 cycles were obtained with only 4.6 pounds per 3000 ft² and 2.5 pounds per 3000 ft² aluminum oxide, respectively.

Using a different resin system, namely Acrylic B, similar results were achieved. In control Example 2, without alumina, the initial wear was only 50 cycles. In Examples 8 and 9, having a top coat containing 3.5 and 5.6 pounds per 3000 ft², respectively, of aluminum oxide, the initial wear increase to 100 and 200 cycles, respectively, still relatively poor performance. On the other hand, when using transfer ARD according to the invention as shown in Example 14 and using only 2.5 pounds per 3000 ft² of aluminum oxide, the initial wear value was 500 cycles.

Using still a different resin, namely vinyl resin, again the results were similar. In control Example 3 using no alumina, the initial wear was only 50 cycles. In control Example 10, having a top coat containing 3.6 pounds per 3000 ft² of alumina, the initial wear value was 125 cycles. In Example 15 according to the invention, using an ARD top coat containing 4.6 pounds per 3000 ft² of alumina, the initial wear was 475 cycles; because the vinyl did not act as a good adhesio layer, the vinyl layer in Example 15 (and Example 16 as well as discussed below) was backed by an acrylic adhesion layer.

The results with thermosetting resin were essentially the same. In control Example 4 the initial wear value was only 100 cycles. In control Example 11, having a top coat containing 3.7 pounds per 3000 ft² of alumina, the initial wear was 225 cycles. But in Example 16, in accordance with the invention, and using approximately 30% less alumina, i.e. 2.5 pounds per 3000 ft² in an ARD layer, the initial wear was 650 cycles.

Hot stamp tapes are often transferred using heated nip rolls rather than the conventional pressing scheme used above. To simulate a heated nip roll operation, additional ARD coatings were transferred with heat and pressure application for 1 to 3 seconds and no cooling under pressure. Initial wear values comparable to those in Table 1 were achieved using this transfer method. <tables id="tabl0001" num="0001"><img file="EP0109313A2_D0001.tif" /></tables>

II - TRANSFER ARD FORMULATIONS

Table 2 below shows under the heading "ARD A" the basic ARD formula used in Example 12, above. This formulation is essentially the same as those disclosed in U. S. Patents 4,255,480; 4,263,081; 4,305,9087; and 4,327,141. Details regarding the ARD composition are to be found in these patents, and such details are incorporated by reference. As can be seen from the initial wear value in Table 1, Example 12, above, abrasion resistance is excellent.

However, due to handling techniques which are used in transfer coating, it has been found that handling is improved if a sticking aid or film forming binder is incorporated into the transfer ARD formulation. Any sticking agent that helps the ARD layer adhere to the carrier, such as a thermoplastic, a thermosetting resin, a gum, a colloid, etc., can be used. The quantity of the sticking agent is not critical at the lower end, but at the upper end one must be careful not to use so much sticking agent that the density of the alumina particles in the transfer ARD layer become so low that the abrasion-resistant properties of the ARD layer becomes significantly reduced, i.e. the ARD composition should not be diluted to the point where it is no longer effective. In general, one should use a minimum quantity of sticking agent or film forming binder sufficient to make the process work better; in general, this quantity, measured as solids, should not exceed about 10-35% by weight of the total quantity of solids in the ARD layer, although larger quantities may sometimes be desirable.

Noting Table 2 below, it is seen that the other ARD examples contained as such sticking agent a small quantity of partially advanced melamine-formaldehyde resin or vinyl chloride which enabled better coating adhesion to the polyester film during the coating process. ARD F contains a larger than usual quantity of CMC which in this case serves as a film former. Use of such a sticking agent or film former reduces processing problems of flaking, insufficient wetting, and overcoating all relative to the carrier web. <tables id="tabl0002" num="0002"><img file="EP0109313A2_D0002.tif" /></tables>

The ARD composition may also desirably include a small amount of finely divided solid lubricant, such as micronized polyethylene wax, in accordance with copending U.S. application S.N. 508,629, filed June 28, 1983, in the name of O'Dell et al, hereby incorporated by reference, the solid lubricant being one which desirably melts during the transfer process. Such solid lubricant imparts scuff resistance to the final product and may be present in an amount of 2-30% by weight or more of the composition although the preferred range is 3-10%.

III - MOLD TRANSFER

Dramatically enhanced abrasion resistance can also be obtained on molded thermoplastic and thermosetting parts and products by transferring the abrasion-resistant coating from a mold to the plastic part surface during the molding process such as shown in Fig. 3. This process has wide utility in forming a great variety of products, and can be applied easily in any molding or laminating process wherein a mold or die surface is brought into contact under pressure against the plastic (thermoplastic or thermosetting resin) to be shaped or pressed. Thermoset products made in this way include laminates of various kinds, dinnerware, fiberglass impregnated products, automative and aircraft parts, housings, trays, boxes, helmets, etc. Thermoplastic products include, for example, vinyl floor tile, seat covers, wallpaper, shoes, transparent (e.g. acrylic) products, etc.

Thermosetting Resin

To illustrate that the above-mentioned approach yields unexpected results on melamine-formaldehyde resin, ARD C from Table 2 was coated at a rate of 8.7 lb/3000 ft² (,u2.8 lb/3000 ft² of grit) onto a mirror finish, chrome plated, stainless steel press plate, and dried at 250^oF. This composite was pressed against a substrate of melamine-formaldehyde impregnated decor sheet (dry resin to decor paper ratio = 0.5 to 1) backed by four phenol-formaldehyde impregnated kraft sheets. The press cycle was typical for high pressure decorative laminates. Bonding occurred during the flowing and curing of the melamine resin. As illustrated in Table 3, the abrasion resistance initial wear value was dramatically improved over the control (which had no abrasion-resistant coating). <tables id="tabl0003" num="0003"><img file="EP0109313A2_D0003.tif" /></tables>

These results enable the production of overlay free, enhanced abrasion resistant laminate on continuous laminating equipment such as the Siempelkamp equipment, modified as generally shown in Fig. 8, and on single opening semi-continuou apparatus which is currently under development. Also, low pressure laminate with an ARD surface can be continuously made using the Hymenn equipment modified as shown in Fig.'9.

Thermoplastic Resin

Table 4 illustrates how ARD layers result in dramatic abrasion-resistance incrreases when transferred from mold surfaces onto thermoplastic type resins. Again, one vinyl and two different acrylic resins were used as examples. While Acrylic A is technically a product which sets upon application of heat, it is derived from or incorporates a thermoplastic and has many characteristics of thermoplastic resins and thus was used to simulate thermoplastics; the other two resins may also be curable upon the application of heat, but are believed to remain thermofusible, i.e. thermoplastic.

Examples 1, 2, and 3 are controls for the invention and were produced by coating Lhe base coat, then top coat, onto textured finish high pressure decorative laminates, noting Fig. 2. The top coat contained resin/grit ratios of either 1.0 to 0.8 (both acrylic resins) or 1.0 to 1.0 (vinyl). These composites were then pressed against mirror finish chrome plated stainless steel molds under the same conditions that ARD was transferred onto corresponding composites in Examples 4-6.

Examples 4, 5 and 6 were produced by coating the ARD onto the same mold used in Examples 1, 2 and 3, noting Fig. 3, an external mold release agent having first been coated onto the mold. The ARD was dried and then transferred from the mold to the respective thermoplastic resin which was previously coated onto textured, high pressure decorative laminates. Bonding resulted during the fusion and then solidification of the thermoplastic coating serving as the substrate.

Note the grit weights for the controls (Examples 1, 2 and 3) are always greater than their ARD transfer equivalents (Examples 4, 5 and 6). Note also that in Examples 3 and 6, a pure vinyl coating was not used, i.e. we used acrylic as the coating against the laminate because the vinyl would not adhere well to the laminate surface.

The resultant initial wear values presented in Table 4_'show ARD increased the abrasion resistance of thermoplastic coatings by mold transfer. <tables id="tabl0004" num="0004"><img file="EP0109313A2_D0004.tif" /></tables>

IV - SURFACE SEPARATOR TRANSFER

ARD can also be transferred onto thermosetting and thermoplastic resins from a surface separator or release sheet. ARD is coated onto the surface separator or release sheet, dried and then transferred to the resin as shown in Fig. 5. As in the other transfer procedures described above using ARD in accordance with the instant invention, the surface onto which the ARD layer is transferred must become receptive, e.g. melted, during the transfer operation, for the ARD to adhere thereto, or there must be present a suitable adhesive layer by which the transfer ARD becomes adhered to the substrate.

Thermosetting Resin

To show how abrasion resistance of melamine resin is enhanced by ARD transfer from several types of surface separators during the molding operation, a set of runs were conducted (See Table 5). Different coats weights of ARD C formulation were applied to several types of surface separators and dried at 250⁰F to touch. The surface separators used were: <ul id="ul0003" list-style="none"><li>(1) Polypropylene film</li><li>(2) Release agent coated glassine paper</li><li>(3) Release agent coated foil-paper lamination (release coat on foil side).</li></ul>

These surface separators with the dried ARD coatings thereon were then pressed against substrates of melamine resin impregnated decor papers of varying resin contents as shown in Column 2 of Table 5, it being understood that the ratio of 0.5-1.0 is the normal industrial resin/paper ratio for making high pressure laminate. The decor papers were reinforced by 4 sheets of phenolic impregnated kraft paper. Press cycles were varied in duration as shown in Table 5. Upon completion of the press cycles, the surface separators were removed from the composites. From Column 4 in Table 5, it is readily apparent that ARD dramatically increased the abrasion resistance of each composite. <tables id="tabl0005" num="0005"><img file="EP0109313A2_D0005.tif" /></tables>

Use of ARD transferred from surface separator for some applications of use is an improvement over the process shown in U. S. Patent 4,255,480 because the coating does not have to be applied directly to the decor sheet, which is more expensive than the release sheets, resulting in lower cost from handling losses during the coating process.

Scuff resistant products can also be made by this procedure using compositions as disclosed in the O'Dell et_al copending U.S.application Serial No. 508,629, filed June 28, 1983. Thus, an aqueous mixture is made up of 100 parts (dry weight) of ARD F and six parts by weight of Shamrock 394 micronized polyethylene wax. The mixture is coated on _al_u- minum foil/pnper parting sheet on the aluminum side, and also on parchment paper at the rate of 8.5 pounds/3000 ft² (dry solids weight), and the composition is dried at a temperature between 18Q^OF and the melting point of the polyethylene wax. After drying, both types of coated release paper are pressed in a normal cycle laminating procedure down on top of a solid color decor sheet saturated with melamine resin, beneath which is located a normal phenolic core. Standard press cycles of 800-1200 psi and 260-300^oF are used. After cooling, the release paper is removed, and it is found that the coating has transferred to the melamine impregnated decor paper, and the resultant laminates are slippery and scuff resistant, as well as being abrasion resistant.

The procedure described immediately above can also be carried out to produce a scuff-resistant product without enhanced abrasion resistance using a mixture of microcrystalline cellulose and hydroxymethyl cellulose as binder material for finely divided solid lubricant. Or other binder material such as sodium alginate (Kengin LV) may be used in place of the microcrystalline cellulose. Thus, an aqueous emulsion of 6 parts by weight Kelgin and 6 parts by weight Shamrock 394 in 300 parts of water is coated on the aluminum side of aluminum/foil paper parting sheet on parchment paper at the rate of 1.5-2 lbs./3000 ft² (dry weight) and processed as described above. The resultant laminates are slippery and scuff-resistant.

Thermoplastic Resins

ARD also can be transferred from surface separators (e.g. foil/paper laminate) onto thermoplastic resins, e.g. vinyl coated wallpaper. Fig. 5 shows this process using low transfer pressure. The only difference between this and the mold transfer process described earlier is the substitution of a surface separator for the mold. The results of the experiments with surface separators are set forth in Table 6.

Again, while one or more of the products used are technically heatsetting, they are derived from thermoplastics and have many thermoplastic properties and were used for sake of convenience. <tables id="tabl0006" num="0006"><img file="EP0109313A2_D0006.tif" /></tables>

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 drawing and described in the specification.