GB2041244A - Method of providing surface coverings with a nubbly textured wear layer - Google Patents

Abstract

A method for manufacturing a nubbly textured, decorative vinyl composition surface covering having a high performance, clear, glossy, radiation-cured wear layer overlying a decorative printed vinyl composition substrate. The nubble textured wear layer is achieved by first overprinting the decorative substrate 20, 21 with nubs 22 of a clear, radiation-curable coating, after which an overall clear, radiation-curable wear layer 23 is applied with the coated, printed substrate being radiation cured to yield a high performance wear layer having a nubbly texture. <IMAGE>

Description

SPECIFICATION Method of providing surface coverings with a nub bly textured wear layer This invention relates to surface coverings, especially decorative vinyl composition surface coverings, having wear layers, especially clear, glossy, radiation-cured wear layers.

In recent years, there have been developed in the resilient flooring industry high gloss coatings which are designedto give the consumer a resilient flooring product which does not require the conventional wax treatments heretofore commonly associated with resilient flooring products of a vinyl composition. Some of the products have clear, tough, glossy coatings formed with heat and moisture curable urethane based coating compositions. More recently, particularly for vinyl asbestos tile products, but also for sheet vinyl surface coverings, radiationcurable coatings have been developed which also yield tough, glossy, high performace, wear resistant coatings when applied as wear layers. In order to minimize any scratching which would take place and thus retain the high degree of gloss, these products are generally provided with an overall nubbly texture.Such nubs are normally, and desirably, applied without regard to, i.e., not in registry with, any decorative pattern on the surface covering. Two previously proposed methods of achieving this overall nubblytexture have been either to post-emboss the wear layers with a nubbly textured roll or embossing plate orto pre-emboss the vinyl composition substrate with a nubblytextured embossing roll or plate prior to applying the generally viscous, radiationcurable wear coating. Because of the viscous nature of these coatings and because they are usually applied in an on-line process with at least partial curing being almost immediately achieved after application, the wear layers generally conform to the nubbly texture of the substrate.

It has been found, however, that embossing of the substrate or the post-embossing of the wear layer causes some distortion of the decorative substrate.

Where, for example, a relatively smooth substrate is first printed with a desired visual design and it is desirable not to disturb or distort the printed design by using the above-described embossing techniques, a need remains for a suitable process.

The present invention provides a decorative substrate with a nubblytextured, at least partially radiation-cured wear layer by first overprinting the decorative vinyl composition substrate with nubs (which, as indicated above, are desirably not in registry with the decorative pattern) of a clear, at least partially radiation-curable coating, after which an overall clear, at least partially radiation-curable wear layer composition is applied to form an overall nubbly coating, this subsequently being cured to form a nubbly wear layer.

The invention will for simplicity be described with reference to the production of so-called "no-wax" vinyl asbestos tile products, but it will be obvious to those skilled in the art that the invention is equally applicable to the production of printed decorative vinyl composition tile and sheet goods wherein at least a portion of the printing is applied to a smooth planar surface of the vinyl composition substrate and it is desired not to distort the printing through an embossing step.

Similarly, for the purpose of illustrating the invention, the use of a photopolymerizable coating curable by a ultraviolet radiation will be described, although it will be evident to those skilled in the art that the invention may be carried out using any radiation-curable coating utilizing radiation sources such as electron beams. The application of photocurable coatings to printed surfaces such as floor coverings, for example, is described in U.S. Patent 3,840,448, and the application of photopolymerizable coatings to tile is described in U.S. Patent 3,717,558. Earlier prior art has described the cure by ionizing radiation or light of ethylenically unsaturated coatings and such coatings are used for protectively coating impervious articles such as linoleum (see, for example, U.S. Patent 3,056,760) Boranian et al., U.S.Patent 3,924,023, describes a process wherein, for example, printed tile products having high performance, wear resistant coatings may be formed. Ultimately, the performace of the wear coat will depend upon the formulation of the UV curable coating. In their process, it is recommended that an on-line process be used wherein a tile-forming blanket is calendered from the usual vinyl asbestos tile-forming composition, the blanket then printed with the desired design, and coated with a UV cu-rable coating composition which is then cured after which the individual tiles are cut from the cured coated blanket. Since the high performance coatings which form the clear wear layer are neces warily extremely expensive compared with the vinyl asbestos composition substrates, any scrap losses can be extremely costly.Accordingly, the specific embodiment described in this invention uses a process wherein preformed vinyl asbestos tiles are printed and coated.

Vinyl-asbestos tile formulations are well known in the art, as are the processing conditions for tile formation (see, for example, U.S. Patent 2,773,851 and the above-discussed U.S. Patent 3,924,023).

One method of carrying out the invention will now be described by way of example only with reference to the accompanying drawings, in which, Figure lisa schematic diagram showing a process wherein smooth vinyl asbestos tile substrates are first printed using aflexographic printerto achieve the desired visual image on the smooth surface, after which print-on nubs are applied and the tile curtain coated and cured, and Figure 2 is a cross-sectional view of a printed decorative tile having a textured glossy wear layer formed by the process of Fig. 1.

With reference more especially to Fig. 1 of the drawings, a flexographic printer of a commerically available design (Apex Machine Co.) is shown schematically at 5, the unit consisting of three independent printing heads 6,7, and 8, one for each of three colors, arranged around a single, rubbercovered offset cylinder 9, which transfers all three colors to the file 2. The pattern or plate cylinder roll 9 carries conventional molded rubber or photo polymerflexographic plates. The back-up roll 10 is steel. As shown in the drawing, the printer 5 and slice feeder 11 which is utilized for feeding the tile beneath into the printer, share a common support frame and drive. In this embodiment, the three inks are all UV curable, although heat curable inks could equally well be used.After the inks have been transferred in the desired design to the tile substrate, they are then preferably cured to minimize smearing in subsequent operations, this being accomplished, when using UV curable inks, by placing medium pressure mercury arc lamps at 12. Atypical UV exposure requirement at 180 ft./min. (55 m/min.) conveyor speed is about 600 watts/inch (236 watts'cm) of line width.

After passing beneath the UV lamps, pnrit-on nubs are applied to the tile surface to impart the surface texture which plays as important role in gloss retention in the finished product.

The printer 13 for printing on the nubs comprises a magnesium roll 14 which is chemically engraved with the desired nub pattern and used as the top roll in a two-roll printer assembly. The other roll 15 is a rubber-covered back-up roll which forces the tile being processed into intimate contact with the engraved roll. A rubber doctor blade 16 is used to apply a partially radiation-, partially moisturecurable printing composition to the engraved roll and to doctor it evenly into the engraved cells as the roll turns. As tile passes between the two rolls, the nubbly pattern is transferred to the flexographic printed tile. Adjustments in the engraved roll can be made and, generally speaking, the nubs produced will range in height from about 2.5 to 5.0 mils, (0.064 to 0.127 mm), in this example, an average of about 3.5 mils (0.09 mm).

The actual patterns etched into the magnesium roll have a fine, straight line Ben Day superimposed at 45Q to the roll axis which result in ribs formed within the etched areas. The preferred rib geometry is about 20/inch (0.8 per mm), each rib being 4 mils (0.10 mm) wide at the roll face. The ribs help prevent the doctor blades from scooping coating out of the relatively large nubbly patterned areas. After a tile has been printed, the coating flows out enough to wash out the rib image. In addition, the pattern is etched in two steps, the second step in register with the first, but smaller in etched area. This provides a nub pattern cell which is deeper in the center and which produces a nub having a more rounded top than is produced by a single-step etch.

The nub printing unit 13 operates at about 200 ft./min. (61 metres/minute). To control foaming within the coating pool behind the doctor blades, excess coating is allowed to run off the edges of the print roll to be collected, defoamed, and returned to the printing unit.

The tile, after being printed with the nubs, is then conveyed directly beneath a curtain coater 17 which applies an overall coating to the nubbled surface of the tile of approximately 3 mils (0.8 mm) in thickness. In this embodiment, the coating material used forth nubs, is also used in the curtain coater.

Generally speaking, the viscosity of the print-on nub coating and of the coating applied by the curtain coater is sufficiently high that a nubbly texture is formed. However, depending upon the viscosity of the print-on nub composition, it may be desirable to subject the nubs to at least a partial UV cure by interposing UV lamps 18 between the print-on nub printer 13 and the curtain coater 17. The texture may be varied by the shape of the cavities in the nub printer and by adjustments in coating viscosities.

The coated tile was passed under four, in line, 200 watt per inch (78 watt per cm), medium pressure mercury lamps, indicated at 19, art a speed of about 16 feet per minute (4.8 m/minute) to partially polymerize the coating by photopolymerizing the ethylenically unsaturated components of the coating formulation. Surprisingly, there was no necessity to use an inerting blanket during the ultraviolet light cure. The coating on the tile, which is tack-free at this point, although not tough and mar-resistant, is then given a final moisture cure by allowing the coating to age at room conditions whereby the unreacted isocyanate end groups in the coating react with moisture and chain extend and cross-linkto form the final durable, tough, glossy clear coat. At average room conditions, the coating develops its final properties within about 3 weeks.

It will be obvious to those skilled in the art that the formulations for the printing inks, print-on nubs, and wear coating may be the same or different (e.g., the nubs may be partially radiation-curable only) and that adjustments within given compositions may be made to achieve the desired viscosity required by the process conditions.

In the embodiment described, the coatings are cured by both a UV cure mechanism and also through chain extension of the isocyanic terminated prepolymer by the formation of urea linkages on moisture cure. The latter chain extension results in a somewhat tougher, more scratch resistant coating than is usually achievable with a completely 100% UV curable coating.

The decorative tile thus formed is illustrated in cross-section in Fig. 2. The vinyl-asbestos tile base is represented by numeral 20 with the decorative print 21, nubs 22, and wear coat 23 positioned as shown.

It will be clear to those skilled in the art that electron beam curing or radiation sources other than UV light may be used to cure the inks, nubs, and wear coatings, although UV cure is at present preferred since it does not require elaborate shielding as is required when using some other radiation sources.

As stated above, it is also possible to use a heat cured ink formulation, substituting a heat source for the UV source just afterthe printing station. Other modifications will become apparent to those skilled in the art.

Although the invention has been described with specific reference to the printing and coating of tile to form a nubbly coated product, the on-line printing and coating of a tile blanket is readily achieved with suitable modifications in equipment required for printing and coating wider goods. Also, although the invention has been described with respect to the production of a decorative vinyl tile product, decorative vinyl sheet goods may also be produced in accordance with the invention. The invention is of particular utility wherever at least a portion of a flat substrate is printed and wherein it is desired not to distort the printed image by embossing when forming a nubbly texture.For example, if a vinyl asbestos tile substrate is under consideration, the tile may first be valley printed with a conventional valley printing roll to yield an embossed colored pattern over a portion of the surface of the tile product, after which the flat areas are subjected to flexographic printing, for example. Where valley printing is utilized for producing at least a portion of the image, prime coating in accordance with Bagley et al., U.S.

Application Serial No. 864,464, filed December 27, 1977: has been found desirable, such prime coating preferably being applied after the flexographic printing step and afterthe curing of the ink and priorto the print-on nub printing step.

It will likewise be obvious that other methods of printing or other wise forming a decorative vinyl composition substrate, such as rotogravure printing a vinyl composition sheet, may be employed in this invention.

The following Example illustrates the invention: UV Curable Flexographic Inks The photopolymerizable oligomerforming the basis for a flexographic ink is formed from the following reactants: Ingredients Grams 4,4'-diisocyanato dicyclohexylmethane 29.41 Diol (Union Carbide PCP0200) A polycaprolactone diol having a MW of 540 and a Hydroxyl No. of 207 32.47 2-Hydroxyethyl acrylate 17.87 2-Ethylhexyl acrylate 13.15 Trimethylolpropane triacrylate 7.03 Dibutyl tin dilaurate 0.02 2,6 Ditertbutyl-4-methylphenol 0.05 In forming the oligomer, the diol, 2-ethylhexyl acrylate and trimethylolpropane triacrylate are first charged into a reaction vessel.The diisocyanate and dibutyl tin dilaurate catalyst are then added and the mixture reacted at 45" to 50"C. After the reaction has proceeded for approximately 45 minutes, the hydroxyethylaciylate is added, continuing the stirring and heating for an additional two hours at which point the isocyanate functionality is constant.

The following inks were then formulated as follows: Parts by Weight Ink Ink Ink Formulation Formulation Formulation Ingredients I II lil Photopolymerizableoligomer 29.57 5.10 33.58 Monomer diluent (trimethylolpropane triacrylate) 31.00 60.00 40.00 Cellulose acetate butyrate 11.00 11.00 Parts by Weight Ink Ink Ink Fomrulation Formulation Formulation Ingredients I 11 lil Pigments White 20.00 Yellow 25.00 Green 10.00 10.00 Photoinitiators Chlorothioxanthone 0.81 1.30 1.47 Methyldiethanolamine 1.62 2.60 2.95 Silicone flow control agent (Dow Corning DC-57) 1.00 1.00 1.00 The three inks were applied by the printing heads 6, 7, 8 of a flexographic printer and cured as described above with reference to the drawings.

A coating formulation for the print-on inks and the wear layer was prepared as follows: * British Patent Application No. 49720/78 Formulation IV Ingredients Grams Triol (Hooker F-1017-180) Reaction product of 1 mole glycerol, 3 moles of a 7/3 mixture of adipic acid and isophthalic acid, and 3 moles 1,6 hexanediol MW 960; Hydroxyl No. 175 93 Diol (Union Carbide PCP0200) A polycaprolactone diol having a MW of 540 and a Hydroxyl No. of 207 58 2-ethylhexylacrylate 94 Hexanediol diacrylate 62 132.3 Grams of 4,4'-diisocyanato dicyclohexylmethane and 0.4 grams of dibutyltin dilaurate catalyst were then added and the mixture reacted at 45"C.

to 50"C. After the reaction has proceeded for approximately 45 minutes, 5.8 grams of 2-hydroxyethylacrylate were added continuing the stirring and heating for an additional two hours at which point the isocyanate functionality is constant.

Based on 100 parts by weight of the reaction mixture which is a mixture of the partially capped isocyanate terminated urethane prepolymer and the acrylate diluent mixture, 2.0% by weight of benzophenone photoinitiator is added together with 0.1% by weight of polyethylene glycol siloxane (Dow Corning DC472) and 0.5% by weight of dibutyltin dilaurate catalyst.

At this point, the coating thus formed has a viscosity of approximately 9,000 centipoises at room temperature and comprises 35% reactive diluents and 65% partially acrylate capped urethane pre polymer.

The nubs and wear layer were applied and cured as described above with reference to the drawings, to provide a tile product having a nubbly wear layer providing a glossy, tough, clear protective coat over a decorative patterned tile.

Claims (13)

1. A method for forming a decorative vinyl composition surface covering wherein a clear wear layer overlies the decorative substrate, which includes the steps of (a) overprinting the decorative substrate with nubs of clear, at least partially radiation-curable coating; (b) applying an overall clear, at least partially radiation-curable coating composition to form a nubbly textured clear coating on the decorative vinyl composition substrate; and curing (c) the coating.

2. A method as claimed in claim 1, wherein the nubs are subjected to a radiation cur prior to coating with a clear wear layer.

3. A method as claimed in claim 1 or claim 2, wherein the decorative substrate is a printed vinyl asbestos tile.

4. A method as claimed in claim 3, wherein the tile substrate is valley printed prior to being printed with a design on the remaining planar surface thereof.

5. A method as claimed in claim 1 or claim 2, wherein the nubs are printed onto a tile-forming blanket after consolidating the tile-forming composition and a clear coat after applied.

6. A method as claimed in claim 1 or claim 2, wherein the decorative vinyl composition surface covering is a printed vinyl sheet.

7. A method as claimed in claim 1 or claim 2, wherein the decorative vinyl composition surface covering is a rotogravure printed vinyl composition tile.

8. In a method for forming a decorative, printed, vinyl composition surface covering having a high gloss textured wear layer of a photopolymerized clear coating overlying a decorative, printed, vinyl composition substrate, the improvement comprising: (a) overprinting the printed substrate with nubs of a clear photopolymerizable coating; (b) applying an overall clear photopolymerizable coating to the printed substrate to form a nubbly textured clear coating; and (c) subjecting the textured clear coating to a photopolymerization source to set the texture and cure the coating.

9. A method as claimed in claim 8, in which a photoinitiator is present in the clear coating and in which the photopolymerization source is a UV light source.

10. A method as claimed in claim 8 or claim 9 in which the nubs are photopolymerized prior to the application of the overall clear wear layer coating.

11. A method as claimed in claim 1, carried out substantially as described in the Example herein.

12. A method as claimed in claim 1, carried out substantially as described with reference to, and as illustrated by, the accompanying drawings.

13. Asurface covering, whenever prepared by a method as claimed in any one of claims 1 to 12.