GB2063178A - Registration of colour and embossment by an ink-coated release medium - Google Patents

Abstract

There is provided a method of producing a decorative laminate of contrasting colour in response to embossment during the lamination operation wherein its decorative surface protrusions are of a colour different from the background colour of the laminate. To accomplish this result, the release sheet in an otherwise essentially conventional arrangement of superimposed laminae has an ink layer on the surface thereof adjacent to the decor sheet so that during the heat and pressure consolidation of the laminae with an embossing press plate the ink layer is transferred to the adjacent surface of the decor sheet, or of the overlay sheet if such is present. Subsequently, the surface of the resulting laminate is burnished to remove the ink from the high areas of its embossed surface.

Description

SPECIFICATION Registration of color and embossment by an inkcoated release medium Background of the Invention For many years decorative laminates have been used as a surfacing material in residential and commercial structures wherein aesthetic effects, in combination with functional behavior such as wear, heat and stain resistance, are desired. Typical applications of said laminates are surfacing for walls, partitions, table tops, counter tops, furniture, doors and the like. Such decorative laminates are generally produced from a supporting base member, usually either a particleboard product or a plurality of core sheets usually composed of kraft paper which has been impregnated with a thermosetting resin and, more particularly, with a thermosetting, watersoluble orwater-insoluble phenolic resin.After the kraft paper has been impregnated with the thermosetting resin, the sheets are dried and cut to the appropriate size. Thereupon, a plurality of these resin impregnated sheets are stacked in a superimposed relationship. The number of plies or sheets in the stack depend on the ultimate intended use of the laminate. For most purposes, the number of plies of these core sheets will total about six to nine but can total as many as 12-15. When particleboard is used, the material preferred is that produced from thermosetting resin impregnated wood chips which are heat and pressure consolidated into a composite structure. This particleboard is usually also referred to as flakeboard, chipboard, etc. and is weli known in the art.

There is then placed on the stack of core sheets or particleboard, a decorative sheet which is generally an opaque, pigmented sheet of alpha-cellulose paper and is impregnated with a noble thermosetting resin which is not subject to significant darkening upon the application of heat. Suitable resins for the decorative sheets are the aminotriazine resins and more particularly the melamine-formaldehyde resins, the benzoguanamine-formaldehyde resins, the unsaturated polyester resins and the like. Often the decorative sheet may carry a printed pattern design on its surface. It is generally desirable, although not essential, when making printed pattern decorative laminates, to make use of a protective overlay sheet which is placed atop and is similar to the decorative sheet but is devoid of design and in the final laminate is transparent.The superimposed laminate components are then inserted into a laminating press and are heat and pressure consolidated to a unitary structure. During the consoldation step, the thermosetting resins are converted to the thermoset state thereby providing an extremely hard, attractive and permanent laminated product. For obvious economic reasons, it is common practice, when producing the paper supported laminates, to consolidate a plurality of these individual laminating assemblies into one large assembly, or press pack, said stacks being separated from one another by a release sheet, and then to laminate this pack by heat and pressure application.

In consolidating the laminate components according to most widely practiced techniques, an individual assembly is placed with its decorative overlayment surface adjacent to a stainless steel press plate. The function of the press plate is twofold. First, it provides a smooth, defect-free surface to one side of the laminate. Second, in connection with the paper based supported systems, it serves to separate pairs of back-to-back assemblies, thus permitting a plurality of these assemblies to be consolidated into laminates in one operation, usually in back-to-back relationship. In the art, the paper base supported laminates are referred to as "high pressure" laminates while the particleboard based laminates are referred to as "low pressure" laminates, obviously because of the pressure used during the consolidation processes.

In the earliest days of the high pressure laminating art, the smooth, glossy surface produced during the pressing operation was sometimes, upon customer's request, reduced to a matte finish by rubbing the surface with pumice. Subsequently, a slightly textured surface was produced by pressing the laminate surface against an aluminum foil caul stock. Such a surface was described as mini-textured because the hilltop-to-valley bottom depth of such textures was from about 0.5 mil (.0005 inches) to about 1.0 mil (.001 inches). These mini-textured laminates met with immediate success and almost totally replaced the glossy surface market. Somewhat coarsertextures of three dimensional surfaces, sometimes called "low-relief" laminates were then produced, e.g., by a printing process known as the "heavy ink" method, described in U.S. Patent No. 3,373,068.

These surfaces had hili-to-valley depths of about 3 to 5 mils.

Finally, very deep, three dimensional textured or embossed laminates were offered commercially.

These laminates may be produced by e.g., the methods of U. S. Patent No. 3,860,470, Jaisle et al., 3,718,496, Willard. Here the hill-to-valley depth in the surface is of the order of about 20 mils.

The techniques used to produce these deep textured surfaces encompass a design latitude heretofore not achieved by producing simulated patterns such as those occurring in natural materials like sandstone, brick, slate, mosaic, marble, leather, rough or weathered timber; even material like rough woven goods such as jute, hemp.

As demands for these new laminates grew, many new designs, such as those simulating tiles or heavy woven cloth, evolved. These designs must have appropriate color contrast and registry with the surface hill-to-valley configuration. Unfortunately, the problem of registration of color and embossing has proven very difficult to solve. The problem has plagued the industry, not only from the standpoint of the appearance of the finished laminate but from the standpoint of the cost of the production of laminates having a substantially perfect registry of color and embossment, since their inception. Embossed laminates have been successfully produced, however, see U.S. Patent No. 3,373,068, and laminates of substantially registered color and embossment have also been prepared, see U. S. Patent Nos. 3,732,137 and 3,814,647.

The use of an encapsulated ink, as taught by U. S.

3,732,137, results in fine laminates of good colorembossment register. The method disclosed therein, however, is very expensive and requires extreme care in its use. The use of a sheet containing encapsulated ink, of necessity, requires the concern of the manufacturer with ink coverage i.e., varying degrees of ink coverage across a specific laminate sheet and ink capsule depth, pressure distribution of the texturing plate, penetrability of the encapsulated ink through the overlay sheets of the laminate and accidental rupturing of the capsules during storage and transportation of prepared sheets before lamination. Control of the flow of the inkfrom the ruptured capsules and difficulty in utilizing opaque white and metallic inks are two more problems which plague the use of this system.

U. S. Patent No. 3,661,672 teaches a method of forming a B-staged overlay transfer laminate from an embossing die, subsequently coating the embossed surface of the transfer laminate with color and then employing the temporary transfer laminate on a separator which transfers embossing, and color to the high pressure laminate during its production.

This process is complex, at least two consolidation steps and the handling of many sheets during laminate production.

The method taught in U. S. Patent 3,814,647 obviates some of those difficulties mentioned above.

This system consists of the application of a thermosetting ink to an embossed press plate die in registry with the embossing of the die. Subsequently, the ink press plate is impressed into a laminate assembly wherein the ink is transferred to the surface of the laminate in registry with the embossment. The patentee has formulated his ink so that it will release from the press plate die and transfer to the surface of the laminate without running or migrating sideways during the laminating step.

This process is difficult to conduct because it is very difficult to administerthe inktothe press plate only in those areas where it is wanted on the ultimate laminate. That is to say, if only the highest protuberances of the ultimate laminate are to be colored by the ink, only the valley areas of the press plate are ink treated. This is usually accomplished by coating the entire embossing surface of the press plate with the ink and then removing the ink from the highest protuberances. If only the valleys of the laminate are to be colored by the ink, only the highest protuberances of the press plate embossing surface are ink treated.The treatment of the press plate is usually accomplished in this instance by roller coating or brushing, etc. only the high areas thereof, however, such a treatment is difficult unless all the high areas are equal in height.

Summary A novel process for obtaining an exact registry of color and embossment in high and low pressure laminate production has now been discovered. This method is very economical and obviates many of the disadvantages of the prior procedures. When utilizing the novel process, there is no limit to dimension, design, depth of embossment or color which can be achieved. It avoids the mechanical registration of the embossing media with decorative sheets in the laminates before or after pressing and the bothersome application of materials e.g., ink, at press time.

According to the novel process, one may produce a decorative laminate having on its decorative surface, protrusions and valleys of any selected design, which protrusions are of a different color from the valleys of the laminate.

Description of the Invention Including Preferred Embodiments The novel invention constitutes a method for producing a decorative laminate which comprises: A. assembling, in superimposed relationships, a laminate assembly comprising: (i) a rigidity imparting substrate, (ii) a fibrous decor sheet impregnated with a thermosetting resin, (iii) a release sheet having an ink layer on the surface thereof adjacent to said decor sheet and (iv) an embossing press plate having a surface with protuberant and valley areas capable of being impressed into at least said release sheet, B. heat and pressure consolidating said assembly so as to transfer said ink layer to the supermost surface of said decor sheet, C. removing said release sheet and said embossing press plate from the resultant ink-surfaced embossed laminate, D. burnishing the surface of said laminate to remove said ink from the highest areas of the embossed surface thereof and E. recovering the resultant laminate.

Fibrous core sheets are used as the rigidity imparting substrate in the method of preparing high pressure laminates in accordance with the present invention. They are usually paper sheets and, more preferably, kraft paper sheets. When such kraft paper sheets are used, it is preferred that they have a basis weight of between 40 Ibs. (per 3000 sq. ft. ream) and 140 Ibs. and more preferably about 90 Ibs. per ream.

The thermosetting resin used to impregnate such core sheets may be any suitable resin known for such use but phenol/formaldehyde resin is preferred. When using such a resin, it is preferred to impregnate and dry the impregnated sheets, by methods known in the art, to a resin content of from about 25% to 45%, and more preferably to a resin content of about 30%, based on the weight of resin solids in the impregnated sheets. The volatile content of the dried impregnated sheet is preferably between 5% to 10%, more preferably about 8%, based on the total weight of the sheet.

The decorative sheets are also fibrous sheets which are thermosetting resin impregnated and, more preferably, are opaque, pigmented alphacellulose of a solid color and may carry a printed design.

Any suitable basis weight paper may be used to advantage to form the decor sheet, but papers of from 40 Ibs. (per 3000 sq. ft. ream) to 120 Ibs. (per 3000 sq. ft. ream) are generally preferred.

An alpha-cellulose paper is generally used in the preparation of the laminate when a thermosetting resin-impregnated overlay is included, if desired.

The overlay is positioned above the decor sheet in forming the laminate assembly and it may constitute any paper known for such use in the production of conventional decorative plastic laminates. Preferably, it is a wet strength aipha-cellulose paper having a basis weight of between 10 Ibs. (per 3000 sq. ft. ream) and 40 Ibs. and, more preferably, 25 Ibs.

(per 3000 sq. ft. ream). In its impregnated and cured condition in the ultimate laminate, the overlay is substantially transparent. When an overlay is employed, the ink layer which is transferred from the release sheet is imparted to its upper surface and not that of the decor sheet.

When a low pressure decorative laminate is being produced, the decor sheet may also constitute any of the above-described decor sheets. The substrate, however, as mentioned above, comprises a particleboard ranging in thickness from about 1/8" to 1" which is produced in a manner known in the art.

Medium density, mat formed, wood particleboard and medium density, wood fiberboard substrates are preferred. An overlay sheet may or may not be employed, however, aesthetically a finer laminate is produced when an overlay is employed.

The thermosetting resins used to impregnate the decorative paper sheet, in the low or high pressure laminate production, and the overlay if used in the high pressure laminates, may be the same or different and may be any thermosetting resin suitable for such purpose. For example, melamineformaldehyde resins, melamine-urea-formaldehyde resins, unsaturated polyester resins and the like may be employed. If different resins are used to impregnate the different layers, care should be taken to ensure that the resins are compatible, that is, the resins must be capable of forming strong coherent bonds with each other under the conditions used for consolidation and no deleterious reactions between the resins should occur. It is preferred to use only one type of resin for the purposes mentioned, and more preferably, to use a melamine-formaldehyde resin for these purposes.

Various plasticizers and/or other modifiers may be incorporated into the impregnating resins in order to obtain improved properties during the curing of the material. Other modifiers may also be employed to improve release from press plates, workability and other properties of the amino plastic resins, as is known in the art.

The embossing press plates used in the novel process of the instant invention can be prepared by etching or machining a design on a metal plate.

Alternatively, and more preferably, the plate can be prepared as disclosed in U. S. Patent No.3,718,496, which patent is hereby incorporated by reference.

Still further the raised printed design technique, as taught by Grosheim in U.S. 3,373,068, will also work well as an embossing medium in the instant invention.

Any release sheet or separator sheet known in the art to be useful in the production of decorative laminates to prevent the adherence of the press plate to the uppermost surface of the laminate may be used herein. Any non-adherable paper or nonadherable aluminum or other metal foil may be used. These materials are all commercially available and include papers coated, treated or impregnated with polypropylene, fluorocarbon resins and the like.

Films of polypropylene may also be used. Papers coated with sodium alginate or other salts of alginic acid, silicone resin treated papers, silicone oil treated papers, "Quillon" treated papers, wax coated papers, glassine, aluminum coated paper and the like may also be used. Other useful release sheets include those disclosed and claimed as U.S. Patent Nos. 4,117,198 and 4,118,541 which comprise paper sheets coated with a mixture of, or separate individual coatings of, (1) an oil-modified alkyd resin cross-linked with a polyalkylether of a polymethol melamine and (2) a copolymer of a maleic acid, ester or anhydride with a vinyl ether or unsaturated alkyl comonomer, said patents hereby being incorporated herein by reference.

The inks used in the method of the present invention are generally those which are capable of being not only easily applied to the surface of the release sheet but capable of transferring from the release sheet to the surface of the decor sheet or overlay sheet of the resultant laminate. Inks which, after being transferred to the laminate surface, are resistant to removal by wear and abrasion, etc. are particularly advantageous. Useful inks include gravure inks, etc. Those inks based on amino resins, preferably melamine/formaldehyde resin are particularly preferred. These inks are described, for example, in U.S. Patent No.3,814,647 at Column 4, lines 30-75, which patent is hereby incorporated herein by reference.

The ink layer or coating may be applied to the surface of the release sheet in a uniform and controlled manner by any suitable method known in the art. Reverse roll coating, gravure cylinder printing, air knife coating, spraying or applying by brush all contribute satisfactory means for applying the ink.

The ink layer may be of the same color or a different color than that of the decor sheet per se or the design or pattern printed on the decor sheet or both. Normally, the entire surface of the release sheet is coated with the ink layer, however, it is also within the scope of the present invention to apply the ink layer to the release sheet surface in any pattern, design, configuration, etc. desired.

Burnishing of the laminate after it is removed from the laminating press can be accomplished by the use of methods known in the art for dulling laminate surfaces. Burnishing machines wherein the laminate surface is softly contacted with such abrasive materials as steelwool, pumice, etc. may be used. The burnishing step removes the ink from the highest portions of the embossed laminate surface revealing the color and pattern of the decor sheet while the ink remains on the lower areas of the embossed laminate surface thereby obscuring the color and pattern of the decor sheet.

The result is an aesthetically pleasing laminate surface of registered color and embossment. The embossments the in the laminate surface should preferably be at least about .007 inch in depth although depths of less than .007 inch also result in attractive laminates.

The following examples are set forth for purposes of illustration only and are not to be construed as limitations on the present invention, except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

Example A To 92.5 parts of an alkyd resin solution produced from 39.7 parts of soya oil, 41.3 parts of isophthalic acid and 19.0 parts of glycerol and having a solids content of about 62%, a viscosity of 23-29 secs. No. 2 Zohn cap 77.0 F. and a density of 8.4-8.7 Ibs/gal. in a 67/33 isopropanol/xylene solvent and containing 50% of hexakismethoxymethylmelamine are added 7.5 parts of a catalyst solution comprising 50% p-toluene sulfonic acid and 50% isopropanol and 5.0 parts of a 40% solution in toluene of an alkyl vinyl ether/maleic anhydride copolymer in which the alkyl vinyl ether mixture (96% C18 alkyl, 2% C16 alkyl and 2% C10.14 alkyl vinyl ethers) is copolymerized with an equimolar amount of maleic anhydride.The complete solution is applied to a 35 lb/300 ft2 ream, blocked Kraft grease-proof paper of 0.2 mil thickness by means of a gravure printing cylinder. The coated paper is then dried and cross-linked in a hot air oven for 30 seconds at 280"F.

The resultant, dried, release sheeting is then contacted on its coated surface with a black gravure ink using a 150 line printing cylinder, dried and cut into four foot by eight foot sections.

Example 1 An assembly is prepared preparatory to insertion into a laminating press of the following components, reading top to bottom; 1. A sawn wood embossed press plate with its embossing surface facing downwardly, 2. A section of the ink-coated release sheet prepared in Example A above, with its ink-coated surface facing downwardly, 3. A melamine-formaldehyde resin impregnated, a-cellulose overlay sheet, 4. A melamine-formaldehyde resin impregnated a-cellulose tan decor sheet having a wood grain pattern printed thereon with its printed surface facing upwardly.

5. Eight sheets of phenolic resin impregnated Kraft sheets and 6. A pressing plate die.

The assembly is placed in a laminating press and, after the pressing cycle is complete, it is removed and separated at the junction of the release sheet and overlay sheet. A decorative laminate is recovered having a solid black surface on the overlay surface. The laminate is then passed through a burnishing machine equipped with a burnishing surface of steel wool. The laminate exits from the machine with the ink removed from the highest areas of the surface embossment but remaining in the valley areas. The laminate has a very pleasing, aesthetic appearance of sawn wood.

Example 2 The procedure of Example 1 is again followed except that the overlay sheet is omitted from the laminate assembly. Again an attractive laminate is produced having a sawn wood appearance.

Example 8 The procedure of Example 1 is again followed except that the black gravure ink is coated onto the metal side of an aluminum caul sheet (aluminum foil coated paper) and the ink is thickened by adding lecithin. Again, the black ink transfers to the laminate surface and, upon burnishing, results in a fine decorative laminate.

Example 4 The procedure of Example 1 is again carried out except that wax-coated paper is used as the release sheet which is coated with the black gravure ink. A laminate substantially identical to that of Example 1 is recovered.

Example 5 The procedure of Example 1 is again followed except that the black gravure ink is replaced by a dark brown ink composed of 73% of a 50% solid solution of a methylol melamine resin, 23% of pigment, 3.6% of silica and 0.4% of non-ionic surfactant. Similar results are obtained.

Example 6 Again the procedure of Example 1 is employed except that the ink is composed of 67% of methylol melamine resin solution (50% solids), 29% TiO2, 0.5% carbon pigment, 3% silica and 0.5% non-ionic surfactant. Again, a laminate having an excellent aesthetic appearance is produced.

Example 7 Following the procedure of Example 2 except that the ink formulation comprises an aqueous isopropyl alcohol solution containing 25% polyvinyl alcohol to which is added carbon black. A laminate having an aesthetically pleasing surface results.

Example 8 Again following the procedure of Example 1 except that the ink is a 10% dioxane solution of ethyl cellulose (48% ethoxy) containing blue pigment and the release sheet upon which the ink is printed is a 'Quillon" treated paper, excellent results are achieved.

Example 9 The procedure of Example 2 is followed except that the eight sheets of resin impregnated Kraft paper are replaced by a section of 3/8" thick particle board and the pressing plate die is removed. A sawn wood laminate is produced upon pressing at 1550C at 250-350 psi for 2-3 minutes.

Claims (6)

1. A method of producing a decorative laminate having registered color and embossment com prising: A. Assembling, in superimposed relationship, a laminate assembly comprising, (I) a rigidity-imparting substrate, (II) A melamine-formaldehyde resin impregnated fibrous decor sheet, (III) a release sheet having an ink layer on the surface thereof adjacent to said decor sheet and (IV) an embossing press plate having a surface with protuberant and valley areas capable of being impressed into at least said release sheet, B. heat and pressure consolidating said assembly so as to transfer said ink layer to the adjacent surface of said decor sheet, C. removing said release sheet and said embossing press plate from the resultant ink-surfaced, embossed laminate, D. burnishing the surface of said laminate to remove said ink from the high areas of the embossed surface thereof and E. recovering the resultant laminate.

2. A method according to Claim 1, wherein said substrate comprises a plurality of phenol/formaldehyde resin impregnated cellulosic sheets.

3. A method according to Claim 1, wherein said rigidity-imparting substrate is particleboard.

4. A modification of the method defined in any preceding claim, wherein there is positioned between said decor sheet and said release sheet, a resin-impregnated overlay sheet and said ink is transferred in step (B) to the adjacent surface of said overlay sheet.

5. A method of producing a decorative laminate according to Claim 1 or Claim 4 and substantially as described in any one of the Examples herein.

6. A decorative laminate whenever produced by a process according to any preceding claim.