Three-dimensional surface texturing

Abstract

A method for producing a coating with a surface texture on a substrate is proposed. The method comprises applying an IR- reflective pattern (24) on the substrate (22), covering the IR-reflective pattern and the substrate with an IR-transparent plastisol composition (30), irradiating the substrate across the plastisol composition with IR light so as to selectively heat the substrate in gaps of the IR-reflective pattern, and to induce gelling of the plastisol composition adjacent the gaps of the IR-reflective pattern rather than adjacent the IR- reflective pattern. Ungelled (or less gelled) plastisol composition is then removed, leaving a three-dimensionally textured layer (36) of at least partially gelled plastisol composition. The invention further relates to a method for producing a decorative surface covering, e.g., flooring or wallcovering, which implements the above method.

Description

Three-Dimensional Surface TexturingBackground of the Invention

[0001] The invention generally relates to producing a coating with a surface texture. The expression “surface texture” is used herein to designate a three-dimensional surface topography, such as a relief or an embossing.

[0002] In a more specific aspect, the invention relates to the production of finishing materials for constructions, in particular of decorative surface coverings such as, for instance, floorings, wallcoverings or ceiling coverings, wherein a surface-textured coating is produced.

[0003] Decorative surface coverings such as flooring, wallcovering or ceiling covering, may be of the so-called homogeneous or heterogeneous types. A homogeneous surface covering has essentially the same composition throughout its thickness (except, maybe, for a topcoat and / or a textile backing), whereas a heterogeneous surface covering comprises a stack of layers which differ in their functions and compositions. A typical layer structure of a heterogeneous surface covering comprises a backing layer, one or more core layers, a decor layer, a protective wear layer and a topcoat.

[0004] The decor layer may be a thin layer of a natural material, e.g., cork or wood, but may also comprise a printed decor, imitating or not a natural material. In order to improve the realism of a printed decor imitating a natural material, such as wood, cork, stone, etc., the surface covering may be given a surface texture by embossing. Mechanical embossing involves pressing an embossing plate or cylinder against the surface covering under high temperature so as to transfer the three-dimensional pattern of the embossing plate or cylinder into the surface covering. In high-quality surface coverings, the embossing is carried out in register with the printed decor.

[0005] WO 2017 / 046309 A1 discloses a base panel suitable to be processed into a covering panel, consisting of: (i) a substrate having a top surface, (ii) a resilient layer having a top surface and a bottom surface, the bottom surface being connected to the top surface of the substrate, and (iii) optionally, a contact layer between the bottom surface of the resilient layer and the top surface of the substrate. The covering panel comprises a digitally printed decor on the top surface of the resilient layer of the basepanel. The covering panel may further be provided with an embossing pattern, which may be applied in register with the print, so as to accentuate the appearance of the decor.

[0006] Digitally printed decors are gaining in importance, in particular (but not only) due to the fact that designs can be changed more quickly and at much lower costs than with conventional printing techniques, such as, e.g. heliogravure printing. This allows the industry to react more flexibly to changing market demands and to reduce product development costs. Likewise, digital embossing techniques have been developed to replace the conventional embossing cylinders.

[0007] WO2017067978A1 relates to a method for manufacturing embossed decorative substrates, e.g., panels and boards, in particular based on wood fibers such as MDF (Medium Density Fiberboard) or HDF (High Density Fiberboard) substrates on which a decor is formed by digital printing. The method comprises the steps of: a) mechanical embossing a substrate so as to form an embossed surface; b) applying a primer on the embossed surface of the substrate; c) drying or curing the primer coated on the embossed surface so as to form a base layer; d) digitally printing a decor onto the base layer using a liquid ink; and e) drying or curing the liquid ink forming the digitally printed decor.

[0008] US2020346246A1 relates to a method for manufacturing a structure on the surface of a workpiece. The method comprises the following steps: applying a liquid base layer onto the surface of the workpiece; jetting droplets into the not yet solidified base layer, wherein the droplets at least partially penetrate into the base layer; indurating the base layer; and removing the droplets.

[0009] EP3109056A1 discloses a method for producing a structure on a surface. A liquid layer is applied onto a workpiece. Subsequently, a manipulation medium in the form of droplets is sprayed onto the liquid layer, whereby a displacement of the liquid layer occurs by the droplets so that recesses together forming a structure in the liquid layer are formed therein. Subsequently, this layer is solidified.

[0010] US2020368777A1 discloses a method for producing a decorative surface on a workpiece. The method comprises: feeding of the workpiece coated with a liquid layer to a digital printing station; application of an agent capable of at least partially absorbing electromagnetic radiation, at least on a partial area of the surface of theliquid layer, or which, in contact with the surface, produces a reaction product which is capable of at least partially absorbing electromagnetic radiation; irradiation of the surface of the liquid layer and of the agent with electromagnetic radiation having a wavelength of less than 300 nm. Irradiation of the surface of the liquid layer causes polymerization of the liquid layer and leads to micro-folding, thereby forming a microstructure.

[0011] US2020346395A1 discloses a method for producing a decorative surface, wherein a manipulation medium (such as that of EP3109056A1 or the agent of US2020368777A1 ) to the surface is removed therefrom in a mechanical and / or contactless manner.

[0012] US2022355335A1 relates to manufacturing areas having different degrees of hardness in a base layer. The method comprises the steps: applying a mask (e.g., in the form of droplets) on a partial area of the surface of the base layer, the mask at least partially absorbing electromagnetic radiation; and irradiating the base layer and the applied mask with electromagnetic radiation, in particular with UV radiation and / or IR radiation, to set different degrees of hardness of the base layer. The mask and the areas of the base layer with a lower degree of hardness may be removed, e.g., physically and / or chemically, so as to create depressions or holes in the base layer.

[0013] WO2010070485A2 relates to manufacturing coated panels comprising at least a substrate and a top layer with a motif. The method for manufacturing of the top layer comprises at least two steps, namely, a first step, in which a synthetic material layer is provided on the substrate, and a second, subsequent step, in which a relief is provided on the surface of the synthetic material layer. The relief comprises a pattern of recesses and / or projections, that is at least partially determined by one or more prints. The same printing technique may be applied both for forming the motif and for forming the one or more prints. For instance, a digital printing technique, such as inkjet printing, may be applied.Summary of the Invention

[0014] According to a first aspect of the invention a method for producing a coating with a surface texture on a substrate is proposed. The method comprises applying an IR-reflective (infra-red reflective) pattern on the substrate, covering the IR-reflective pattern and the substrate with an IR-transparent plastisol composition, irradiating thesubstrate across the plastisol composition (e.g., a PVC plastisol) with IR light so as to selectively heat the substrate in gaps of the IR-reflective pattern, and to induce gelling of the plastisol composition adjacent the gaps of the IR-reflective pattern rather than adjacent the IR-reflective pattern. Ungelled (or less gelled) plastisol composition is then removed, leaving a three-dimensionally textured layer of at least partially gelled plastisol composition.

[0015] The term “plastisol” generally designates a suspension of polymer (resin) particles, e.g., polyvinyl chloride (PVC) particles, in a liquid plasticizer. The expression “plastisol composition” may designate a plastisol as well as the semi-solid or the solid obtained from gelling and / or fusing the plastisol. When a plastisol is heated, plasticizer diffuses into the polymer particles causing the polymer particles to swell. Concurrently, the volume of plasticizer between the particles decreases. This translates into an increase of the viscosity of the plastisol composition up to a certain maximum. When the temperature is further increased, the viscosity then decreases again and the material more and more behaves like a macromolecular liquid, i.e., a monophasic material rather than a biphasic material with a solid phase and a liquid phase. The transition characterized by the (steep) viscosity increase is often referred to as gelation. The plastisol composition may be qualified as “gelled” when the liquid plasticizer phase has (substantially) disappeared. This is the case at maximum viscosity or in vicinity thereof. When the boundaries between individual particles become less and less discernible, the plastisol composition may be qualified as (partially) fused.

[0016] The substrate may consist of IR-absorbing material or comprise IR-absorbing material. The substrate may, e.g., comprise a thermoplastic material with IR-absorbing pigments or particles (e.g., calcium carbonate filler, which absorbs IR light at 7 pm, black pigment, etc.) and / or comprise an IR-absorbing layer (e.g. a decorative motif printed on the substrate base from inks containing IR-absorbing pigments). The IR- absorbing material of the substrate is preferably selected in accordance with the wavelength or, more generally, the spectrum of the IR light employed, so as to ascertain that the substrate is effectively heated (locally) when exposed to the IR light.

[0017] In the method according to the first aspect of the invention, the substrate is locally heated (in the gaps of the IR-reflective pattern), as a consequence of which the plastisol composition in the immediate vicinity is heated by conduction. This initiatesthe gelation process of the plastisol composition. The closer a volume element is located to a heated-up substrate portion, the faster the gelation process of the plastisol composition therein will take place. This leads to a spatially inhomogeneous gelation of the plastisol composition: plastisol composition in volume elements having undergone more heating will be further gelled and will be more coherent than plastisol composition in volume elements less exposed to heating. Less gelled and thus less coherent plastisol composition is more easily removed. It is worthwhile noting that it is not necessary, in the context of the invention, to exactly delimit the more gelled and less gelled states of the plasticiser composition in an absolute sense. What matters is that the localized heating of the substrate leads to gelation gradients in the plastisol composition between zones with more solid character (more gelled) and zones with more liquid character (less gelled). The difference in cohesiveness can then be utilised to remove the less gelled plastisol composition while leaving the more gelled plastisol composition in place. Where the boundary lies between the removed zones and the zones remaining in place depends on the mode(s) of action employed for the removal and, in particular, on the forces acting on the plastisol composition when the removal takes place. For example, the removal of ungelled or less gelled plastisol composition could comprise brushing, blowing (e.g., by using an airknife), centrifugation and / or aspiration. The removal could, e.g., be carried out using one or more brushes or one or more air knives to expel the ungelled or less gelled plastisol composition. One or more suction apparatuses may be used to evacuate the expelled plastisol composition from the production line.

[0018] The IR-reflective pattern may remain on the substrate but, preferably, it is also removed partially or completely. The removal of the IR-reflective pattern may be effected together with the removal of the ungelled or less gelled plastisol composition or in an additional, separate removal step.

[0019] The application of the IR-reflective pattern on the substrate may comprise printing the IR-reflective pattern on the substrate. Different printing technique could be used. However, digital printing of the IR-reflective pattern is preferred because of its versatility and the ease of modifying the IR-reflective pattern.

[0020] The substrate may comprise a decor layer carrying a printed (two-dimensional) decorative motif. The application of the IR-reflective pattern on the substrate may then comprise printing, e.g., digitally printing, the IR-reflective pattern in register with theprinted decorative motif. An IR transparent PVC-based layer may be applied on the decor layer before the IR-reflective pattern is applied thereon.

[0021] The IR-reflective pattern may be cured prior to covering it with the plastisol composition. Preferably, the IR-reflective pattern is obtained from printing a thermosetting ink, a UV-curable ink or an electron-beam-curable ink. The IR-reflective pattern may be obtained by applying a UV-curable ink containing a photoinitiator. Examples of suitable IR-reflective inks include water-based gravure ink with aluminium pigment, water-based gravure ink with silver pigment, water-based inkjet ink with silver pigment, water-based inkjet ink with aluminium pigment, solvent-based inkjet ink with silver pigment, and solvent-based inkjet ink with aluminium pigment. The IR-reflective ink(s) may have a concentration of metallic pigment in the range from 5 to 15 % by weight (with respect to the total weight of the ink).

[0022] Preferably, the method comprises curing (fusing) the three-dimensionally textured layer, e.g., in an oven, e.g., at a temperature between 120°C and 190°C, preferably between 120°C and 160°C for a time duration in the range from 2 to 6 minutes, preferably from 3 to 4 minutes. It is also possible to proceed with the curing (fusing) of the three-dimensionally in an IR oven at a temperature between 120°C and 190°C, preferably between 120°C and 160°C with adapted IR power and belt speed.

[0023] The plastisol composition covering the IR-reflective pattern and the substrate may be applied with a height in the range from 50 pm to 400 pm, preferably in the range from 60 pm to 200 pm and more preferably in the range from 80 pm to 150 pm.

[0024] A topcoat may be applied over the three-dimensionally textured layer, preferably after the latter has been fused. The topcoat is preferably continuous. The topcoat preferably comprises a thermosetting (pre-)polymer resin, or a radiation curable (pre-)polymer resin (e.g., a UV curable or an electron-beam curable crosslinkable polymer composition). The crosslinkable resin composition forming the topcoat may optionally comprise at least one photoinitiator. According to a preferred embodiment, a UV-curable topcoat is applied. Applying such UV-curable topcoat may comprise generating a microfolded skin layer in the topcoat by exposing the UV- curable topcoat to V-UV light (vacuum ultraviolet light, i.e. , UV light with a wavelength in the range from 100 nm to 200 nm) and then curing the topcoat in depth. In-depth curing of the topcoat may include irradiation with UV light of longer wavelengths (> 200 nm), capable of penetrating further into the topcoat layer than the V-UV light,which is quickly absorbed in the superficial skin layer (typically not thicker than 200 nm). The topcoat composition may comprise (poly)urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, amino (meth)acrylate, silicone (meth)acrylate, and / or any mixtures thereof.

[0025] According to a preferred embodiment, the method for producing a coating with a surface texture on a substrate comprises: applying the IR-reflective pattern on the substrate, curing the IR-reflective pattern (e.g., with UV light or another radiation, or by heating), covering the cured IR-reflective pattern and the substrate with a transparent plastisol composition, irradiating the substrate across the plastisol composition with IR light so as to selectively heat the substrate in gaps of the IR-reflective pattern, and to induce gelling of the plastisol composition adjacent the gaps of the IR-reflective pattern rather than adjacent the IR-reflective pattern. Preferably, the plastisol composition covering the IR-reflective pattern and the substrate is applied with a height in the range from 50 pm to 400 pm, more preferably in the range from 60 pm to 200 pm and yet more preferably in the range from 80 pm to 150 pm. The three-dimensionally textured layer is preferably cured after the removal of the ungelled or less gelled plastisol composition. The removal of ungelled or less gelled plastisol composition preferably comprises brushing, blowing, centrifugation and / or aspiration. Preferably, a continuous topcoat is applied over the three-dimensionally textured layer. This is preferably done after the curing (fusing) of the three-dimensionally textured layer. The topcoat is preferably UV-curable and applying the topcoat preferably comprises generating a microfolded skin layer in the topcoat by exposing the UV-curable topcoat to V-UV light and then curing the topcoat in depth.

[0026] In a second aspect, the invention relates to a method for producing a decorative surface covering, e.g., flooring or wallcovering, wherein the method according to the first aspect is implemented. In this case, the substrate may comprise one or more structural layers (so-called core layers) of the decorative surface covering. The substrate preferably comprises a decor layer, preferably protected by a first layer of IR transparent PVC based composition (plastisol or film), on which the IR-reflective pattern is applied. The decorative surface covering produced according to the method may be a resilient floor covering compliant with the standard ISO 10582:2017.

[0027] The abbreviation “IR” stands for infrared (light). As used herein, “infrared light” (or IR light) designates electromagnetic radiation with wavelengths from 750 nm to15 pm, i.e., belonging to the near-infrared (0.75 pm - 1.4 pm), the short-wavelength infrared (1 .4 pm - 3 pm), the mid-wavelength infrared (3 pm - 8 pm) and / or the long- wavelength infrared (8 pm - 15 pm) ranges. Preferably, the IR light comprises wavelengths from 1 pm to 8 pm.

[0028] The reflectance of the IR-reflective pattern (the IR-reflective zones thereof, not including the gaps of the pattern) is selected such that a significant portion of the IR light used to irradiate and heat up the substrate across the plastisol is reflected when it hits the IR-reflective pattern. The expression “reflectance” herein designates the ratio of reflected optical power to the incident optical power over the spectrum (wavelength range) of the IR light source used to irradiate and heat up the substrate. Preferably, the reflectance of the IR-reflective pattern (after application on the substrate) at a wavelength of 850 nm amounts to at least 50%, more preferably to at least 60%, still more preferably to at least 70%, even more preferably to at least 75% and yet even more preferably to at least 80% (measured in accordance with ASTM E1331 -15). More preferably, the reflectance of the IR-reflective pattern (after application on the substrate) in the wavelength range from 850 nm to 1 .4 pm amounts to at least 50%, more preferably to at least 60%, still more preferably to at least 70%, even more preferably to at least 75% and yet even more preferably to at least 80%. Preferably, the reflectance of the IR-reflective pattern (after application on the substrate) in the wavelength range from 1 .4 pm to 3 pm amounts to at least 50%, more preferably to at least 60%, still more preferably to at least 70%, even more preferably to at least 75% and yet even more preferably to at least 80%. Preferably, the reflectance of the IR- reflective pattern (after application on the substrate) in the wavelength range from 3 pm to 8 pm amounts to at least 50%, more preferably to at least 60%, still more preferably to at least 70%, even more preferably to at least 75% and yet even more preferably to at least 80%.

[0029] The expressions “decor” and “decorative” are used herein to indicate that the corresponding item, layer or surface remains visible in the final product when in use as intended and contributes to the outer appearance of the surface covering.

[0030] Various layers of the substrate or its coating may involve the use of one or more photoinitiators. E.g., the ink(s) used in the printing of the decorative motif, the ink used in the printing of the IR-reflective pattern, or the topcoat may include a photoinitiator. Examples of photoinitiators include: a-hydroxyketones, a-aminoketones,benzildimethyl-ketals, acyl phosphines, benzophenone derivatives, thioxanthones and blends of these.

[0031] The substrate or the decorative surface covering may comprise additional layers not specifically mentioned above. For instance, they may comprise one or more reinforcing layers, such as, e.g., a fibre veil, a glass veil, a fibre mesh, etc. The substrate or the decorative surface covering may also comprise a backing layer on the rear surface, e.g., a fibre backing, a foam underlay (e.g., a Pll foam underlay like in EP 3 228 448) and / or an acoustic foam.

[0032] In the present document, the verb “to comprise” and the expression “to be comprised of’ are used as open transitional phrases meaning “to include” or “to consist at least of’. Unless otherwise implied by context, the use of singular word form is intended to encompass the plural, except when the cardinal number “one” is used: “one” herein means “exactly one”. Ordinal numbers (“first”, “second”, etc.) are used herein to differentiate between different instances of a generic object; no particular order, importance or hierarchy is intended to be implied by the use of these expressions. Furthermore, when plural instances of an object are referred to by ordinal numbers, this does not necessarily mean that no other instances of that object are present (unless this follows clearly from context). When this description refers to “an embodiment”, “one embodiment”, “embodiments”, etc., this means that the features of those embodiments can be used in the combination explicitly presented but also that the features can be combined across embodiments without departing from the invention, unless it follows from context that features cannot be combined.Brief Description of the Drawings

[0033] By way of example, preferred, non-limiting embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:Fig. 1 : is a schematic illustration of the manufacturing of a decorative surface covering according to a first preferred embodiment of the invention;Fig. 2: is schematic illustration of the manufacturing of a decorative surface covering according to a second preferred embodiment of the invention;Fig. 3: is a picture of a surface texture obtained by a method in accordance with an embodiment of the invention;Fig. 4: is an elevation profile of a valley in a surface texture obtained by a method in accordance with an embodiment of the invention.

[0034] It should be noted that the drawings are strictly schematic and not to scale. This holds, in particular, for the inserts showing the cross-sections of the decorative surface covering in the making. In particular, it should be noted that these inserts do not necessarily show the thicknesses of the different layers in the actual proportions.Detailed Description of Preferred Embodiments

[0035] It will be understood that the following description and the drawings to which it refers describe, by way of example, different embodiments of the proposed invention for illustration purposes. This description of preferred embodiments shall not limit the scope, nature or spirit of the claimed subject matter. The skilled person will appreciate that features of the different embodiments may be combined into further embodiments without departing from the scope of the present invention.

[0036] Fig. 1 illustrates a first embodiment of the proposed method for producing a decorative surface covering, e.g., a floor covering.

[0037] A surface covering substructure (also: core structure) 10 is provided as a printing substrate in a digital printing stage 12. The surface covering substructure may be of a monolayer or multilayer configuration. Fig. 1 shows a multilayer core structure comprising a backing layer and two structural core layers.

[0038] An industrial digital printer 14 prints a decorative motif 18 onto the surface covering substructure 10. The printed decorative motif 18 may be considered as two- dimensional to the extent that any height variations in the layer of ink(s) may be regarded as insignificant. The surface covering substructure 10 may comprise a primer layer or base coat for printing thereon or it may comprise a printable layer that is part of the structural layers. The layer that receives the ink directly thereon may be referred to as the decor-carrying layer 16. The digital printer 14 may comprise printheads that project ink droplets onto the decor-carrying layer 14 in a very precise manner, in terms of position and volume of the droplets. The digital printer 14 may comprise a singlepass industrial printer, which uses several printheads aligned side by side in several rows that cover the entire width of the multilayer surface covering substructure. Each row of printheads may print one or more colours. During the printing process, the surface covering substructure 10 advances in the machine direction under theprintheads. The digital printer 14 may be custom-made for the application in accordance with the requirements in terms of capacity and print quality. The digital printer 14 could use thermal printhead technology, wherein a current pulse passing through a heating element vaporizes a tiny quantity of ink in a chamber so as to form a bubble, and this bubble propels an ink droplet through the printhead nozzle onto the printing substrate. Additionally, or alternatively, the digital printer 14 could also use piezoelectric printheads, wherein a piezoelectric element, on application of a voltage, generates a pressure pulse that drives an ink droplet through the nozzle. The ink is chosen in accordance with the printhead technology, the decor-carrying layer, the subsequent processing steps as well as quality and price constraints.

[0039] Various types of ink could be used in implementations of the method. Inks typically comprise one or more colorants, a binder that bonds the colorants to the surface and a carrier liquid. Colorants comprise dyes or pigments or a combination of both. Pigments are solid colorant particles that are suspended or dispersed throughout the carrier liquid. Pigment-based inks may be more light-stable and more fade-resistant than dye-based inks. Furthermore, dye-based inks often comprise organic solvents which may lead to higher VOC emissions than pigment-based inks, especially when water is the carrier liquid of the latter. Carrier liquids may include solvents, oil(s), water and polymeric resins. For certain surface coverings, radiation-curable inks may be considered as particularly advantageous. The digital printing stage 12 may include one or more drying or curing devices (not shown in the drawing), wherein the printed decorative motif 18 is solidified and bonded to the decor-carrying layer 16. Such drying or curing devices could comprise one or more heaters and / or one or more blowers and / or one or more radiation sources, depending on the type of ink used in the printing of the decorative motif.

[0040] After application of the printed decorative motif 18, a wear layer 20 transparent or at least translucent in the visible electromagnetic spectrum, e.g., a PVC wear layer, may be applied. Application of the wear layer 20 may be effected by calendaring. (The calendaring process is not shown realistically in Fig. 1 .) The thickness of the wear layer 20 may lie in the range from 100 pm to 800 pm, more preferably in the range from 150 pm to 770 pm, and still more preferably in the range from 200 pm to 600 pm.

[0041] The assembly of the substructure 10, the printed decorative motif 18 and the wear layer 20 serves as the substrate 22, on which a IR-reflective pattern 24 is applied.The application of the IR-reflective pattern 24 may be effected by digitally printing an IR-reflective ink on the on the substrate 22. In the embodiment illustrated in Fig. 1 , a digital printer 26 is used to apply the IR-reflective pattern 24. However, other printing techniques, although less preferred, could be used as well. Various types of IR- reflective inks could be used in implementations of the method. IR-reflective inks preferably comprise one or more IR-reflectants, a binder and a carrier liquid. IR- reflectants may comprise IR-reflective dyes or IR-reflective pigments or a combination of both. A UV-curable IR-reflective ink may be considered as particularly advantageous, in which case the IR-reflective ink may comprise a photoinitiator. In the embodiment illustrated in Fig. 1 , the IR-reflective ink is UV-cured into the IR-reflective pattern 24 with a UV light source 28.

[0042] The IR-reflective pattern 24 and the substrate 22 are then coated with an IR- transparent plastisol composition 30. The coating process is represented schematically. Preferably, the IR-transparent plastisol composition 30 is applied by knife-coating, roll-coating, reverse-roll-coating, or spray-coating. The thickness (height) of the transparent plastisol composition 30 preferably amounts to between 50 pm and 400 pm, e.g., to between 60 pm and 200 pm and more preferably to between 80 pm and 150 pm.

[0043] The substrate 22 is then passed under one or more IR lamps 34 which irradiate it across the plastisol composition with IR light so as to selectively heat the substrate in the gaps 32 of the IR-reflective pattern 24. This locally heats up the substrate 22 in the gaps of the pattern 24 to a temperature sufficient to gel the adjacent plastisol composition. The IR-reflective pattern itself reflects a significant portion of the incident IR light so that the regions covered with IR-reflective ink initially remain cooler than the gaps 32. As thermal conduction sets in, gelation of the plastisol composition 30 takes place farther away from the gaps 32. As long as the substrate 22 is exposed to IR light, the gaps 32 remain hotter than the regions covered with IR-reflective ink and provide the heat necessary for the localised gelation of the plastisol composition. It should be noted that thermal conduction also takes place in the substrate 22 and tends to equalize the temperature across it. Exposure to the IR light is kept relatively short, such that gelation stops while it is still inhomogeneous across the plastisol composition 30: more gelled (maybe completely gelled) in the regions next to the gaps and less gelled (maybe ungelled) in the regions next to the IR-reflective pattern 24.

[0044] Ungelled (or less gelled) plastisol composition is then removed, leaving a three-dimensionally textured layer 36 of at least partially gelled plastisol composition. The removal may be effected by mechanical action, e.g., by blowing, brushing, centrifugation and / or aspiration. In the embodiment of Fig. 1 , the removal is carried out using one of more brushes 38 which chase ungelled or less gelled plastisol composition from the substrate by mechanical friction. Preferably, the IR-reflective pattern 24 is also removed. One or more suction apparatuses 40 may be used to evacuate the ungelled or less gelled plastisol composition and, possibly, also the debris of the IR-reflective pattern. As an alternative to, or in addition to the one or more brushes 38, one or more blowers (e.g., air knives) could be used. The removal of less gelled or ungelled plastisol composition leaves a negative of the IR-reflective pattern in the form of elevations (ridges, islands, etc.) on the substrate 22 which form a three- dimensional surface relief.

[0045] After the removal of the ungelled or less gelled plastisol composition, the remaining three-dimensionally textured layer 36 may have (inner) zones that are completely gelled or even fused after the passage at the one or more IR lamps 34. Nevertheless, the outer zones may have remained incompletely gelled. Therefore, the unfinished decorative surface covering is preferably passed through an oven 42 or along one or more further IR lamps so as to completely fuse the three-dimensionally textured layer 36.

[0046] The three-dimensionally textured layer 36 may thereafter be coated with a topcoat 44. The topcoat 44 may comprise a radiation curable crosslinkable composition, e.g., a radiation-curable crosslinkable (pre-)polymer resin, preferably a (poly)urethane acrylate. The coating may be effected by any suitable technique, e.g., by roller-coating (as illustrated in Fig. 1 ) or printing (e.g., digital printing), etc. The topcoat 44 may comprise a UV-curable topcoat. In this case, the topcoat 44 may be cured (crosslinked) by exposing it to an appropriate dose of UV light provided by UV light source 46. A matte surface finish may be obtained by generating a microfolded skin layer in the topcoat by first exposing the topcoat to V-UV light (from a V-UV light source) and then curing the topcoat in depth. In-depth curing of the topcoat may include irradiation with UV light of longer wavelengths (> 200 nm), capable of penetrating further into the topcoat layer than the V-UV light, which is quickly absorbed in the superficial skin layer. The UV light of longer wavelengths may be provided by one or more UV lamps. Thetopcoat is preferably comprised of one or more continuous layers, so as to completely seal off the underlying three-dimensionally textured layer 36.

[0047] The three-dimensional texturing is preferably carried out in register with the decorative motif 18. This may be achieved by printing the IR-reflective pattern in register with the decorative motif 18.

[0048] Fig. 2 illustrates a second embodiment of the proposed method for producing a decorative surface covering, e.g., a floor covering.

[0049] A surface covering substructure (also: core structure) 110 is provided as a printing substrate in a digital printing stage 112. An industrial digital printer 114 prints a decorative motif 118 onto the surface covering substructure 110. Parts of the decorative motif are printed with IR-reflective ink(s), such that an IR-reflective pattern is formed as part of the decorative motif. The digital printer 126 for the IR-reflective pattern may be separate from or integrated with the digital printer 114. UV curable inks may be used for printing the decorative motif and the IR-reflective pattern. In the embodiment illustrated in Fig. 2, the decorative motif including the IR-reflective pattern are cured with a UV light source 128.

[0050] The decorative motif 118 including the IR-reflective pattern and the substrate 110 are then coated with an IR-transparent plastisol composition 130. The coating process is represented schematically. The IR-transparent plastisol composition may be applied by knife-coating, roll-coating, reverse-roll-coating, spray-coating, or any other suitable coating technique. The thickness (height) of the transparent plastisol composition 30 preferably amounts to between 50 pm and 400 pm, e.g., to between 60 pm and 200 pm and more preferably to between 80 pm and 150 pm.

[0051] The substrate 110 is then passed under one or more IR lamps 134 which irradiate it across the plastisol composition 130 with IR light so as to selectively heat the substrate in the gaps 132 of the IR-reflective pattern. This locally heats up the substrate 110 in the gaps of the pattern to a temperature sufficient to gel the adjacent plastisol composition. The IR-reflective pattern itself reflects a significant portion of the incident IR light so that the regions covered with IR-reflective ink initially remain cooler than the gaps 132. As thermal conduction sets in, gelation of the plastisol composition 130 takes place farther away from the gaps 132. As long as the substrate 110 is exposed to IR light, the gaps 132 remain hotter than the regions covered with IR-reflective ink and provide the heat necessary for the localised gelation of the plastisol composition. Exposure to the IR light is kept relatively short, such that gelation stops while it is still inhomogeneous across the plastisol composition 130: more gelled (maybe completely gelled) in the regions next to the gaps and less gelled (maybe ungelled) in the regions next to the IR-reflective pattern.

[0052] Ungelled (or less gelled) plastisol composition is then removed, leaving a three-dimensionally textured layer 136 of at least partially gelled plastisol composition. The removal may be effected by mechanical action, e.g., by blowing, brushing, centrifugation and / or aspiration. In the embodiment of Fig. 2, the removal is carried out using one of more brushes 138 which chase ungelled or less gelled plastisol composition from the substrate by mechanical friction. The IR-reflective pattern being part of the decorative motif 118, it may be preferred that it remains in place on the substrate 110. One or more suction apparatuses 140 may be used to evacuate the ungelled or less gelled plastisol composition. As an alternative to, or in addition to the one or more brushes 138, one or more blowers (e.g., air knives) could be used. The removal of less gelled or ungelled plastisol composition leaves a negative of the IR- reflective pattern in the form of elevations (ridges, islands, etc.) on the substrate 110 which form a three-dimensional surface relief.

[0053] After the removal of the ungelled or less gelled plastisol composition, the remaining three-dimensionally textured layer 136 may have (inner) zones that are completely gelled or even fused after the passage at the one or more IR lamps 134. Nevertheless, the outer zones may have remained incompletely gelled. Therefore, the unfinished decorative surface covering is preferably passed through an oven 142 or along one or more further IR lamps so as to completely fuse the three-dimensionally textured layer 136.

[0054] The three-dimensionally textured layer 136 may thereafter be coated with a top-coat 144. The topcoat 144 may comprise a radiation curable crosslinkable composition, e.g., a radiation-curable crosslinkable (pre-)polymer resin, preferably a (poly)urethane acrylate. The coating may be effected by any suitable technique, e.g., by roller-coating (as illustrated in Fig. 2) or printing (e.g., digital printing), etc. The topcoat 144 may comprise a UV-curable topcoat. In this case, the topcoat 144 may be cured (crosslinked) by exposing it to an appropriate dose of UV light provided by UV light source 146. A matte surface finish may be obtained by generating a microfoldedskin layer in the topcoat by first exposing the topcoat to V-lIV light (from a V-lIV light source) and then curing the topcoat in depth. In-depth curing of the topcoat may include irradiation with UV light of longer wavelengths (> 200 nm), capable of penetrating further into the topcoat layer than the V-LIV light, which is quickly absorbed in the superficial skin layer. The UV light of longer wavelengths may be provided by one or more UV lamps. The topcoat is preferably comprised of one or more continuous layers, so as to completely seal off the underlying three-dimensionally textured layer 136.

[0055] As the IR-reflective pattern is applied as part of the decorative motif, it is in register with the decorative motif 118. Examples

[0056] Embodiments of the method were tested using the two plastisol compositions detailed in Table 1. The amounts of the ingredients are indicated in parts per weight.

[0057] The composition of example 2 has been formulated in such a way as to lower the gelation temperature compared to the composition of example 1 . The composition of example 2 does not contain the extender resin Vinnolit EXT, which takes the formof relatively large particles. These differences may render the composition of example 2 more adapted to the step of removal of ungelled or less gelled plastisol composition.

[0058] The compositions of examples 1 and 2 were spread on a substrate on which an IR-reflective ink pattern based on a UV-curable Al ink had been applied previously, in register with a decorative layer representing a wood decor. The thickness of the plastisol layer was approximately 150 pm. The substrate was then passed under an IR lamp. Ungelled or less gelled plastisol composition was thereafter removed by brushing. The resulting surface textures were analysed with a 3D surface profiler (Keyence VK-X3000). Both compositions were found to give acceptable results. Nevertheless, the composition according to example 2 was found to allow the formation of somewhat deeper grooves than the composition of example 1 in the same production conditions.

[0059] Fig. 3 is a picture of a three-dimensionally textured decorative floor covering obtained with the plastisol composition of example 2. Fig. 4 shows an elevation profile across a valley in three-dimensionally textured layer obtained with the plastisol composition of example 2.

[0060] Test samples according to examples 1 and 2 were irradiated with IR light having approximately a black-body spectrum with the spectral radiance maximum at a wavelength above 2.5 pm (corresponding to a black-body temperature below about 900°C). The power density of the IR light source was selected in the range from 40% to 50% of its maximum power of 40 kW / m2, so as to shift the spectral radiance peak to the wavelength range above 2.5 pm. The length of the IR light source in the machine direction was 0.5 m and the samples were passed at a speed of 1.8 m / min. Accordingly, the IR irradiation energy was between about 266 kJ / m2and about 333 kJ / m2.

[0061] While specific embodiments have been described herein in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

Claims1. A method for producing a coating with a surface texture on a substrate, the method comprising: applying an IR-reflective pattern on the substrate; covering the IR-reflective pattern and the substrate with an IR-transparent plastisol composition; selectively heating the substrate in gaps of the IR-reflective pattern by irradiating the substrate across the plastisol composition with IR light and thereby inducing gelling of the plastisol composition adjacent the gaps of the IR-reflective pattern rather than adjacent the IR-reflective pattern; and removing ungelled (or less gelled) plastisol composition, leaving a three- dimensionally textured layer of at least partially gelled plastisol composition.

2. The method as claimed in claim 1 , wherein the IR-reflective pattern is also removed at least partially.

3. The method as claimed in claim 1 or 2, wherein the application of the IR-reflective pattern on the substrate comprises printing.

4. The method as claimed in any one of claims 1 to 3, wherein the application of the IR-reflective pattern on the substrate comprises digital printing.

5. The method as claimed in any one of claims 1 to 4, wherein the substrate comprises a decor layer carrying a printed decorative motif.

6. The method as claimed in claim 5, wherein the application of the IR-reflective pattern on the substrate comprises printing the IR-reflective pattern in register with the printed decorative motif.

7. The method as claimed in claim 6, wherein the IR-reflective pattern is digitally printed in register with the printed decorative motif.

8. The method as claimed in any one of claims 1 to 7, wherein the IR-reflective pattern is cured prior to covering the IR-reflective pattern with the plastisol composition.

9. The method as claimed in any one of claims 1 to 8, wherein the plastisol composition comprises a PVC plastisol.

10. The method as claimed in any one of claims 1 to 9, comprising curing the three- dimensionally textured layer.

11. The method as claimed in any one of claims 1 to 10, wherein the plastisol composition covering the IR-reflective pattern and the substrate has a height in the range from 50 pm to 400 pm, preferably in the range from 60 pm to 200 pm and more preferably in the range from 80 pm to 150 pm.

12. The method as claimed in any one of claims 1 to 11 , wherein the removal of ungelled or less gelled plastisol composition comprises brushing, blowing, centrifugation and / or aspiration.

13. The method as claimed in any one of claims 1 to 12, comprising applying a continuous topcoat over the three-dimensionally textured layer.

14. The method as claimed in claim 13, wherein the topcoat is UV-curable and wherein applying the continuous topcoat comprises generating a microfolded skin layer in the topcoat by exposing the UV-curable topcoat to V-UV light and then curing the topcoat in depth.

15. The method as claimed in claim 5, optionally in combination with any one of claims 2 to 4 and / or any one of claims 6 to 14, comprising applying a IR transparent PVC-based layer between the decor layer and the IR-reflective pattern.

16. The method as claimed in claims 4 and 8 taken in combination.

17. The method as claimed in claims 16, 10, 11 and 12 taken in combination.

18. The method as claimed in claim 17 taken in combination with claim 13 or 14.

19. A method for producing a decorative surface covering, e.g., flooring or wallcovering, including the method as claimed in any one of claims 1 to 18, wherein the substrate comprises one or more structural layers of the decorative surface covering.

20. A decorative surface covering, e.g., flooring or wallcovering, obtained by the method as claimed in claim 19.

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