The present invention deals with a method for manufacturing a floor plank planks with a substrate, notably panels and boards, in particular wood based or thermoplastic based substrates on which a decor is formed by digital printing.

The invention also deals with a floor plank with a wood based substrate, obtainable using such a method.

Digital printing refers to methods of printing from a digital based image directly to the substrate. It usually refers to professional printing where small run jobs from desktop publishing and other digital sources are printed using large format and/or high volume laser or inkjet printers. Digital printing has a higher cost per printed object than traditional offset printing methods but this price is usually offset by the cost saving achieved by avoiding all the technical steps in between needed to make printing plates.

In order to obtain high quality, the decor may be printed on a separate support of paper or fleece which is applied onto the substrate. Indeed, while a basic layer may be applied in order to ensure sufficient adherence of the applied inks, such basic layers may affect the printing quality. Indeed, a porous layer may absorb the ink leading to insufficient covering while a non-porous basic layer may lead to their coalescence and affect color quality. The use of a separate support for printing however makes the process more costly and complex.

Usually the substrate comprises a core layer made preferably from wood or thermoplastic material and an upper layer which is made of wood or derived from wood. When the upper layer thickness is relatively small and lies for example between 0.5 and 2.5 mm, it is usually referred to as “veneer”, and when the thickness is larger, for example between 2.5 and 4 mm it is usually referred to as ‘wooden lamellas’. This upper layer is selected for having a nice aspect, devoid of any visible imperfections.

In a known solution, a single piece of veneer or wooden lamella covers the core layer of the plank. In this case, the dimensions of the veneer are those of the plank, typically 2 m x 18-22 cm with a thickness of 0.5-2.5 mm (veneer) or 2.5-4.0 mm .

As a consequence, the upper layer, and consequently the plank, are rather expensive. In order to obtain planks at a more competitive cost, several pieces of veneer or wooden lamellas are used for covering the core layer. In this solution, each single piece has a smaller surface than the plank. For a same quality, these smaller pieces cost less than the large ones, so that production costs are decreased. However, the visual aspect of the plank is less qualitative, since the junctions between the pieces of veneer or wooden lamellas tend to remain visible, which gives the user an impression of lower quality.

A technique consisting in applying a fist layer containing a hardener and a second layer containing a filler on the pieces of veneer or the wooden lamellas has been used for efficiently hiding the junctions and obtaining planks with a smooth surface. However, the obtained planks still lack realism compared with real wood.

Embossing and brushing are techniques known for providing surfaces with reliefs. However, they are also known, when applied on several adjacent pieces of veneer or wooden lamellas, for making the junctions more visible.

An aim of the invention is to provide a floor plank at a competitive cost and having an improved wooden aspect to the user.

To this end, the invention proposes a method for the manufacture of a floor plank, comprising at least the following successive steps:

- obtaining a substrate comprising a core layer and a wood based upper layer formed with several pieces of veneer or wooden lamellas paving the core layer;

- optionally sanding an upper surface defined by the upper layer;

- embossing, or embossing and brushing the optionally sanded upper surface of the upper layer;

- applying a coating on the substrate, wherein the coating contains a hardener;

- optionally applying a primer layer on an upper surface of the coating;

- digitally printing a decor on the primer layer or the coating; and

- applying a top coat on the decor.

In other embodiments, the method may comprise one or several of the following features, taken in isolation or any technically feasible combination:

- the core layer comprises a material chosen from the group consisting of HDF, MDF, soft wood ribs, cardboards, a thermoplastic materials, and composite materials;

- the hardener comprises an isocyanate;

- the hardener comprises a mix of hexane, 1 ,6-diisocyanato-homopolymer and hexamethylene-di-isocyanate;

- the step of digitally printing includes a multipass digital printing;

- the upper layer has a thickness comprised between 0.5 and 4 mm;

- the coating has a specific weight comprised between 10 and 50 g/m ² ;

- the coating has a thickness comprised between 5 and 10 pm;

- the primer layer is white;

- the step of digitally printing includes a multipass digital printing; and

- the step of digitally printing is carried out using UV ink or water-based ink. The invention also relates to a floor plank successively comprising:

- a substrate comprising a core layer, and a wood based upper layer formed with several pieces of veneer paving the core layer, the upper layer defining an upper surface being optionally sanded and being embossed, brushed, or embossed and brushed;

- a coating located on the upper surface of the upper layer and containing a hardener, the coating defining an upper surface optionally sanded,

- optionally a primer layer located on the upper surface of the coating;

- a decor digitally printed on the primer layer or on the coating; and

- a top coat located on the decor.

The invention and its advantages will be better understood upon reading the following description, given solely by way of example and with reference to the appended drawing, in which the Figure is a schematic cross sectional view of a floor plank according to the invention.

With reference to the Figure, a floor plank 1 according to the invention is described. The floor plank 1 has a thickness E along a direction N perpendicular to the floor plank. The floor plank 1 , in view along the direction N, may have any shape allowing paving a floor (not represented): rectangular, square, triangular, hexagonal... etc. The floor plank 1 is intended to be applied on a floor adjacent to other planks (not represented) having the same shape or composition, or different ones.

Advantageously the floor plank 1 includes locking tabs (knows in themselves and not represented) enabling to connect it to adjacent planks.

Successively in the direction N, the floor plank 1 comprises a substrate 2, a coating 5, optionally a primer layer 7 located on the coated substrate, a decor 9 digitally printed on the primer layer, and a top coat 11 located on the decor.

The substrate 2 comprises a core layer 3 (partially represented), and an upper layer 4 applied on the core layer. The thickness of the substrate 2 for example ranges from 6 to 20 mm and is preferably around 15 mm. For example, the thickness of the substrate 2 is 14.8 mm.

The substrate 2 has an upper surface 13 which has advantageously been sanded, in order to promote the adherence between the substrate and the coating 5.

The core layer 3 is made from a material that may be chosen from the group consisting of wood (FIDF, MDF, soft wood ribs), cardboards, thermoplastic (PVC based, polyolefin based) material, and composite materials (WPC Wood Plastic Composite). In a preferred embodiment, the core layer 3 is obtained from panels or boards, in particular wood based boards, for example of the type used to form engineered wood as described in WO 2018/077636.

The upper layer 4 is for example formed by several pieces of veneer or wooden lamellas paving the core layer 2, of which two pieces 4A, 4B are represented on the Figure. However, the floor plank 1 may have more than two pieces of veneer or wooden lamellas.

The upper layer 4 is for example made of wood, or derived from wood. The veneer or wooden lamellas are selected for having a nice aspect, normally devoid of any visible imperfections.

The upper layer 4 for example has a thickness comprised between 0.5 and 4 mm.

The pieces forming the upper layer 4 are adjacent to each other perpendicularly to the direction N in order to cover the core layer 3.

The two pieces 4A, 4B defines a junction 4C between themselves.

Preferentially, the pieces 4A, 4B are attached to the core layer 3 by an adhesive.

In a most preferred embodiment the pieces 4A, 4B are additionally glued the one with the other by their edges.

The upper surface is embossed, or embossed and brushed. This aims at providing the upper surface 13 with reliefs 15 simulating the depressions located at the surface of a natural wood plank.

The brushing, if any, is performed after the embossing and allows to open the pores of the wood with very low pressure and results in smoothening the surface 13 that has been embossed. The brushing also helps for adhesion of the top surface (lacquer).

The embossments 15 advantageously have a depth between 20 pm and 1 mm in the upper layer 4.

The coating 5 is located on the upper surface 13. The coating 5 has an upper surface 19 which has advantageously been sanded. The coating 5 for example has thickness between 5 and 10 pm, and advantageously a specific weight comprised between 10 and 50 g/m ² .

The coating 5 contains a hardener and has been cured by UV rays.

In a particular embodiment, the coating 5 only contains the hardener.

The hardener is for example an additive, preferably an isocyanate which advantageously reacts with the moisture of wood fibers of the core layer 3.

The hardener promotes the bound between wood fibers and the coating 15. The hardener may contain a mix of hexane, 1 ,6-diisocyanato-homopolymer and/or hexamethylene-di-isocyanate. According to a particular embodiment, the hardener is made of said mix.

The primer 7 is optional and is advantageously white.

The quantity of primer 7 used is between 10 and 100 g/m ² , preferably between 30 and 50 g/m ² , and more preferably between 35 and 40 g/m ² .

The decor 9 comprises one or several UV inks. The used inks may comprise cyan, magenta, yellow and black inks, but advantageously no white ink. The quantity of inks used is in total between 1 and 30 g/m ² , preferably between 2 and 20 g/m ² , and more preferably between 5 and 15 g/m ² . The thickness of the primer 7 and the decor 9, taken altogether, is between 25 and 30 pm.

If the primer layer 7 is absent, the decor 9 is directly printed on the coating 5.

The topcoat 11 is for example as described in WO 2017/067978.

A method for producing floor planks such as the floor plank 1 will now be described.

First the wood based substrate 2 is obtained. Ways to obtain such a substrate are known to the skilled person (for example described in WO 2018/077636) and will not be described.

Then the upper surface 13 of the substrate 2 is optionally sanded.

The upper layer 4 is embossed, brushed, or embossed and brushed. In a preferred embodiment, the surface 13 of the upper layer 4 is embossed with an embossing cylinder (not represented) or a short cycle press (not represented) equipped with an embossing plate.

The coating 5 is then applied on the upper surface 13, and cured using UV rays (not represented). Curing is performed in a manner known in itself. Preferably, the applied amount of dry film is between 10 and 50 g/m ² .

Thanks to the coating, the junction 4C or the imperfections of the veneer will not be perceived one the plank 1 is finished.

The primer layer 7 is optionally applied on the upper surface 19. Preferably, the applied amount of dry film is between 10 and 60 g/m ² . The primer layer 7 facilitates future application of the inks.

The decor 9 is then printed on the primer layer 7 or on the coating 5 in case there is no primer layer 7. This is advantageously carried out using a Drop-on-Demand inkjet system, for example using UV ink. Advantageously, only cyan, magenta, yellow or black inks are used, but no white ink. The printer can be a multipass or single pass printer.

The top coat 11 is finally applied on the decor 9. Preferably, the applied amount of top coat, once dry, is between 5 and 12 g/m ² . The thickness of the top coat 11 is between 40 and 50 microns. In particular embodiments, the obtained panel is cut into smaller pieces forming the planks.

Thanks to the above features, imperfections due to the junction between the pieces 4A, 4B of veneer or wooden lamellas, or due to a lower quality of the veneer or wooden lamellas are still masked by the coating 5, despite the embossing or the embossing and brushing. Thanks to the embossing, or the embossing and brushing, the visual aspect and the realism of the floor plank 1 is improved. Surprisingly, the embossing, or the embossing and brushing, improve(s) the aspect of the floor plank 1 without making the junction 4C between the pieces 4A, 4B more visible.

Hence the floor plank 1 provides the user with an impression of better quality at a very competitive cost. In addition, the obtained parquet looks very natural. It also allows a variety of design effects thanks to the combination of digital printing and embossing.

The obtained floor planks are cheaper compared to corresponding standard wood products, and have an equal durability, thanks to the top coat 11.

Environmental aspect of the obtained floor planks is also really positive, since about twice less veneer raw material or wooden lamellas is used in order to produce high quality planks with several pieces of veneer or wooden lamellas in each plank. Indeed, pieces of veneer or a wooden lamellas containing a defect and having to be discarded are much smaller. This explains why less raw material is used.

Example(s)

As an example, the first layer of coating 15 may by a mixture of the UV SEALER 583 and the HARDENER 896 from AkzoNobel.

The primer 7 may be the UK1373-9001 from Sherwin-Williams.

The top coat 11 may be a lacquer from AkzoNobel, such as UV TOP COAT NATURA, UV TOP COAT PROTECO or UV TOP HIGH GLOSS.

Protocole:

Obtain the substrate 2,

Emboss, or emboss and brush, the upper layer 4 with standard equipment usually used in the flooring industry, such as cylinders or an SC press plate,

Apply the coating 5 with hardener and then cure the coating,

Change of line for performing digital printing of the white primer 7 and then curing of the UV inks, Go back to the first line and print the decor 9 using UV inks and then cure the UV inks,

Apply the top coat 11 and then cure it.