Field of the Invention

The invention relates to a method for manufacturing a decorative laminate using UV curable inks in the printing process, and to decorative laminate products having printing that comprises UV cured inks.

Background of the Invention

For the manufacture of decorative laminates, substrates, for example particleboard, fibreboard, OSB, plywood, or impregnated kraft core papers, are laminated with one or more resin impregnated overlaying papers or resin impregnated non-woven materials on one or both sides of the substrate in a hot press. Textured or smooth press tools or textured papers or composite films provide the desired structure and gloss on the finished laminate. The overlaying materials serve as a carrier for the resinous starting material, pigments, additives, print or any subset of those. The overwhelming majority of decor paper today is printed by the rotogravure method. Mainly due to environmental and safety concerns the printing inks are water based and the pigments rarely include heavy metals.

It is known that direct printing onto a woodpanel can substitute the use of printed papers, whether utilizing rotogravure printing cylinders or by inkjet printing, an example is EP1872959. It also known that an inexpensive veneer may be applied to a woodpanel and the veneer printed to give the impression of a more expensive wood species, an example is EP2139696. It is furthermore known that woodpanels may be pretreated and later printed, and the print protected with an overlaying material, example is EP1595718. When ultraviolet (UV) cured inks are used the print is usually lacquered to provide protection of the print. The post printing lacquering process may include application of one or more layers that provide technical attributes to the final surface; for example an abrasive substance such as corundum may be included in a lacquer to provide abrasion resistance. The lacquer may be heat cured, or cured by radiation or electron beam. A hot press is not required for additional curing. With the introduction of inkjet printing using UV cured printing inks, such inks also become an option for the printing of woodpanels and or decorative materials used with woodpanels. UV cured inks may be used for inkjet printing onto decor paper, pre- impregnated papers used to produce finish foils, impregnated decor paper, woodpanels or veneered surfaces. Even in the case of UV cured printing inks the print is usually protected from wear.

Prior art disclosures of the application of a protective coating, for example, to printed pre-impregnated papers have variously entailed use of heat, radiation or electron beam curable lacquers. Pre-impregnated papers once lacquered are known as Finish Foils and are glued to substrates such as particleboard or MDF. While some heat and pressure may be applied in gluing the Finish Foil to the substrate, it is not intended that the resin in the pre-impregnated paper will flow and itself form the bonding layer to the substrate.

For direct printed woodpanels where the lacquer is applied after printing, the lacquer is usually cured using heat or radiation.

It is desirable to be able to use UV cured printing inks in applying a printed design by inkjet printing as this is currently the predominate type of ink supplied with industrial width inkjet printing devices. It is also desirable to be able to use existing hot presses and press tools to cure and apply a texture to the protective surface above the UV printed design. However there exists a high risk of deiamination due to incompatibility between cured UV inks and the amino-formaldehyde resin in the overlaying material. The problem of deiamination caused by the choice of inks already exists in the known laminate manufacturing process and was addressed in international patent publication WO2005/051661 by modifying the ink resin system. However with UV cured ink and the later application of an amino based resin the risk of deiamination between UV cured inks and amino-based resins is exacerbated.

There are economic benefits that would be gained by having a compatible coating, and optionally an amino formaldehyde impregnated protective overlaying material, applied above the UV cured inks that could be pressed and finally cured in existing hot lamination presses. These presses are commonly variously referred to as short cycle presses, continuous presses or multi daylight high pressure presses. These hot presses usually have a textured press tool or textured cornposite to provide the desired surface structure on the finished laminate. It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained, understood, regarded it as relevant or combined it in anyway at the priority date.

It is an object of the invention to at least in part address one or more of the aforesaid difficulties that have been encountered with the use of UV cured inks in the manufacture of decorative laminates.

Summary of the Invention

The invention entails the concept of applying a coating after printing of a substrate with UV curable inks, but preferably before final curing of the inks, that is compatible with the UV curable inks and also preferably compatible with amino based resin impregnating any overlay of paper or non-woven material placed above the coating. Such an overlay is optional. Preferably the coating is finally curable in a hot press.

The invention accordingly provides, in one aspect, a method of manufacturing a decorative laminate, including: applying one or more UV curable printing inks to a substrate; applying over the one or more UV curable printing inks on the substrate a coating that is compatible with the one or more UV curable printing inks; partially curing the compatible coating; and placing the coated substrate in a hot press and completing curing at elevated temperature and pressure. , The method of the invention preferably includes providing over the compatible coating an overlay, e.g. of paper or non-woven, before said placement of the coated substrate in a hot press. This overlay may be impregnated with a resin, preferably a resin with which the coating is compatible. In this case, the overlay material is preferably applied after being fully impregnated. The resin may be, for example, an amino resin, e.g. a melamine and/or urea resin.

In another aspect, the invention provides a decorative laminate, including: a substrate having thereon printing comprising one or more UV cured printing inks; and a coating over the printing on the substrate that is compatible with said one or more UV cured printing inks.

The coating is preferably also compatible with amino based resin impregnating any protective overlay, e.g. of paper or non-woven material, subsequently placed above the coating. The decorative laminate may further include a protective overlay, e.g. of paper or non- woven material, over said compatible coating. This overlay may be impregnated with an amino based resin with which the coating is compatible.

The decorative laminate of the invention may be the product of final or complete curing in a hot press at elevated temperature and pressure, or may be further coated or lacquered on the first mentioned compatible coating, after pressing in a hot press. Thus, the decorative laminate may further include a further coating or lacquering over the coating or the protective overlay material.

By "compatible" in this context is meant that the respective materials have components in their chemical compositions that are compatible and therefore intersperse or intermingle, or even form bonds, at their interface. The substrate may be, without limitation, a paper, non-woven, panel or board or an assembly of papers such as a compact laminate.

The surfaces of the substrate may be pretreated or prepared to enhance the quality of the UV ink printing. The pretreatment may be by application of a primer or an Inkjet receiving layer, or by application of a unicolour base paper. The preparation of a panel may also include lamination of a unicolour base paper. It is known that a smooth surface provides a better print image, therefore preparation of the substrate surface may also include calendering or alternative smoothing processes.

The UV curable ink(s) may, for example, be based on an acrylic or methacrylic resin, and the coating therefore preferably includes an acrylic or methacrylic based constituent.

The compatible coating may be applied before or after partial curing or drying of the UV curable ink(s), though it may be advantageous to apply the coating after such partial curing or drying of the ink(s). Partial curing of the ink(s) and compatible coating may be effected simultaneously.

Preferably, the compatible coating is heat curable, e.g. in a hot press. The coating may be partially cured by UV radiation and finally cured by the application of heat and pressure.

The coating preferably includes respective acrylic and amino constituents that are curable to form acrylic and amino based resins. A suitable composition (crystal clear thick liquid) is prepared from an acrylate (with hydroxyl functional group), an amino powder such as melamine or urea (either or both of these are dissolved in the formulation), a source of formaldehyde, for example paraformaldehyde, and a crosslinking catalyst. The coating, and preferably also the overlay, are advantageously transparent or at least translucent. After application of the print using UV curable inks and application of the coating, and optionally the provision of an amino-resin impregnated protective overlay, the components may be finally cured in a hot press.

It is advantageous that the compatible coating is applied before the UV curable printing inks are fully cured. It is sufficient that the compatible coating is partially cured by known means such as heat or radiation sources before final curing in a hot press. Preferably the coating may be partially cured by application of UV light, which would enable the coating to be incorporated into the printing equipment. Advantageously the UV curable inks are not fully cured before application of the coating and partial curing of the coating also further cures the inks.

The compatible coating may also be partially cured after application of a protective overlay which has not been impregnated. A further coating or coatings may be applied to the unimpregnated overlaying material after the unimpregnated overlaying material has been applied to, e.g. embedded into, the first-mentioned coating. The further coating or coatings may be the same as the coating compatible with the UV curable inks, or may be a different coating such as an MF resin coating, however the coatings must be compatible to avoid delamination after the hot press.

It is also practical that a further coating or lacquering of the laminate surface takes place after the hot press, optionally with a preceding application of a primer or adhesion promoter. Curing of the coating after the hot press may be by any known method, for example by UV or alternative radiation curing, by heat, by electron beam or any combination of these.

It is also practical that an overlay of paper or non-woven fully impregnated with an amino resin be positioned above the compatible coating and combined in a hot press. In all cases treatment in a hot press under pressure produces the desired laminate.

The coating may be applied as a single coating or may be applied in several layers. In a particular embodiment of the invention, the coating may be applied to the printed substrate as several layers with a partial curing of each layer.

In another embodiment the compatible coating is applied to an un-impregnated decor paper printed with UV curable inks. The coated decor paper printed with UV curable inks is used in the manufacture of a laminate using the known dry pressing process. A general description of the dry pressing is where the decor paper has not been previously impregnated, the required resin being forced into the decor paper from either a resin impregnated underlay or overlay or an alternative source of resin such as the kraft papers in high pressure laminate manufacture, or a resin coating applied to the surface of a panel.

The one or more UV curable inks and the compatible coating may be on one or both sides of a substrate.

The coating may be applied by any appropriate means, for example but not limited to roller coating, spraying, brushing, curtain coating, vacuum coating, slotted die or jetting. In an embodiment of the invention the coating and or the overlay or overlaying material may contain additives to provide technical or decorative properties, for example but not limited to pigments, dyes, optical brighteners, UV absorbers, impact absorbers, metallic particles, nano-particles, pearlescent effect additives, laser activated particles, antistatic agents, antimicrobial agents, wetting agents, release agents, catalysts, anti-scratch agents, anti-abrasion agents, dispersants, thickeners, gloss or matte effect additives, ^; or additives with self cleaning or stain repellency properties.

The coating weight measured in grams per square metre (gsm) may be . in the range 1gsm to 100gsm, preferably between 2gsm to 60gsm, more preferably between 3gsm to 40gsm, most preferably between 5gsm to 30gsm. The protective overlay may be a paper or non-woven material, or overlapping material such as loose fibres of cellulose, plastic or glass. A suitable grammage per square metre (gsm) is in the range 10gsm to 100gsm, preferably between 14gsm and 60gsm, more preferably between 16gsm and 30gsm, most preferably between 18gsm and 25gsm.

The protective overlay may itself be printed before or after impregnation and prior to application to the UV curable ink printed substrate and the compatible coating. It is practical that the printing of the overlay provides one or more print sections helpful to provide registered embossing or a 3D effect.

The protective overlay may by applied without being impregnated. For example, the substrate may be an unimpregnated d6cor paper and the coated substrate used for dry pressing onto a further substrate. The surface of the laminate may be further coated or lacquered after the hot press.

Said application of the UV curable inks may be by any known method, for example but not limited to gravure printing, screen printing, offset printing, flexo printing or digital inkjet printing. Inkjet printing is the preferred method due to the known economic advantage of being able to print small lot sizes. Partial curing of the coating before or after application of the protection overlay or overlaying material may be by heat or radiation. The choice of method for introducing energy into the coating to dry or advance the cure can be freely selected and adapted to the preferred coating material. Ideally the introduction of energy to the coating takes place as soon as possible after the application of the coating to the substrate. It is also practical to apply energy for advancing the cure of the coating after the application of the overlay to the coating.

In this specification the terms "overlay" and "overlay material" embrace overlaying paper, non-woven materials and overlapping material such as loose fibres of cellulose, plastic or glass. The terms "resins" and "coating" have been used as synonyms for monomers, oligomers and polymers. As used herein, except where the context requires otherwise the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or steps.

Figures 1 to 5 are exploded not-to-scale diagrams of altemative embodiments of decorative laminate according to preferred practices of the invention, while Figures 6 to 8 are schematic representations of three processes according to respective embodiments of the invention.

Example 1

A high density fibreboard (HDF) woodpanel was printed with UV curable inks. Coating (A), compatible with the inks, was applied to the printed panel and partially cured with UV light. The printed and coated HDF panel was placed in a hot press. The press operated at 180°C platen temperature and at 25 bar pressure and remained under pressure for 25 seconds. The press opened and the assembly was removed. The elements of the resultant assembly are depicted in Figure 1 , in which the woodpanel is depicted at 11 , the UV curable printing at 12, and the compatible coating A at 13. After allowing the laminate to cool down, the surface of the panel was tested for delamination by cross-hatching a section of the printed area. No delamination was evident.

Coating (A) here and in subsequent examples was a polymeric coating made from a mixture of hydroxyethylacrylate, paraformaldehyde, melamine and a crosslink catalyst.

Example 2.

A high density fibreboard (HDF) woodpanel was printed with UV curable inks. A coating (A) was applied to the printed panel and partially cured with UV light. A melamine formaldehyde (MF) impregnated overlay paper was placed above the coating and the assembly placed in a hot press. The MF impregnated overlay paper had a coating of MF and corundum on the side facing the functional coating A. The hot press operated at 200°C platen temperature and at 35 bar pressure and remained under pressure for 25 seconds. The press opened and the panel was removed. The resultant assembly is depicted schematically in Figure 2, in which the MF impregnated overlay paper is indicated at 14. After allowing the laminate to cool down the surface of the panel was tested for delamination by cross-hatching a section of the printed area. No delamination was evident.

Example 3.

A high density fibreboard (HDF) woodpanel was printed with UV curable inks. Coating (A) was applied to the printed panel and partially cured with UV light. A second coating (A2) containing corundum was applied over the first coating followed by placement of an unimpregnated overlay paper onto the second coating. The combination of the first coating, second coating and the unimpregnated overlay paper was partially cured using UV light. Subsequently a coating of MF resin was applied to the unimpregnated overlay paper and partially dried. The printed and multiple coated HDF panel Was placed in a hot press. The press operated at 180°C platen temperature and at 30 bar pressure and remained under pressure for 30 seconds. The press opened and the panel was removed. The resultant assembly is depicted schematically in Figure 3, in which the unimpregnated overlay paper is indicated as 14'. After allowing the laminate to cool down the surface of the panel was tested for delamination by cross-hatching a section of the printed area. No delamination was evident. Figure 4 and 5 depict respective modifications in which the assembly of Figure 3 retrieved from the hot press is provided with an outer lacquering 15a or a further MF resin coating 15b applied over the overlay.

Example 4.

A white decor paper 80gsm was impregnated with MF resin and partially cured to so- called b-stage. As depicted in Figure 6, the impregnated and partially cured decor paper 111 was inkjet printed at 112 with UV curable inks at inkjet printer 24. Coating 113 (A) was applied to the printed paper from an applicator 26 and partially cured with UV light from a UV curing unit 28. The impregnated and printed decor paper was placed on a piece of particleboard and placed in a hot press. The press operated at 180°C platen temperature and at 25 bar pressure and remains under pressure for 25 seconds. The press opened and the panel was removed. After allowing the laminate to cool down the surface of the panel was tested for delamination by cross-hatching a section of the printed area. No delamination was evident.

In a variation, depicted in Figure 7, coatings 116 of melamine formaldehyde (MF) resin may be applied to both sides of the assembly downstream of UV curing unit 20. In another variation, depicted in Figure 8, overlaying material 114 may be applied over the coating 113 downstream of the UV curing unit.