Inkjet printing method

Abstract

An inkjet printing method on a continuous substrate web (100) having a pair of edges (1011, 1021), comprising the steps of: a) forming a pair of elongated strips (101, 102) by bending the substrate web (100) along a pair of lines (1010, 1020), wherein each line is parallel to the pair of edges (1011, 1021); and b) supporting the bent substrate web in a support zone (201) of a printer (200), wherein the pair of elongated strips (101, 102) are oriented towards the zone (201); and printing an image (500) on the supported substrate web by an inkjet printhead (202) of the printer (200).

Description

TECHNICAL FIELD

[0001] The present invention is a method of inkjet printing on a continuous substrate web, in particular a lightweight continuous substrate web, having edge waviness. BACKGROUND

[0002] Methods of inkjet printing on a continuous substrate web 100 have been explored for decades, not only by multi-pass printing, but also by single-pass printing, wherein the continuous substrate web 100 is transported through a web-fed roll-to-roll process or a web-fed roll-to-sheet process. The substrate web 100 is transported by unwinding a roll of the substrate web 100 (so-called input roll 111) before it is supported in a support zone 201 of the printing machine. After printing, the substrate web can be cut into sheets or can be rewound on another roll (so-called output roll 112). The continuous substrate web is typically a lightweight material, which can be wound on a roll for printing. It can easily be bent around a core. The printing machine has means for supporting the input roll 111 and optionally the output roll 112, and is configured for transporting the substrate web 100 underneath inkjet printheads 202.

[0003] The method tries to solve the known problems that result in poor print quality when using inkjet printing technology on a continuous substrate web 100:

[0004] - irregular transport speed of the substrate web 100;

[0005] - web swim of the substrate web 100;

[0006] - stretching or shrinking of the substrate web 100 due to changes in internal forces in the substrate web 100 while printing, drying and / or transporting.

[0007] The method is for example applied in the following printing machines:

[0008] - Agfa Dotrix Modular by manufacturer AGFA NV;

[0009] - KBA Rotajet by manufacturer Koenig & Bauer AG;

[0010] - Rho 312R Plus / LED by manufacturer Durst Phototechnik AG;

[0011] - GallusLabelfire 340 by manufacturer Heidelberg Druckmaschinen Aktiengesellschaft.

[0012] Another problem is the unevenness at the edges 1011, 1021 of the continuous substrate web 100 when transporting said substrate web 100 underneath the inkjet print head 202 of the printing press 200. Said unevenness occurs after unwinding the substrate web 100 and transporting towards the support zone 201 and is a result of previous rewinding of the input roll 111, previous cutting of a large roll into smaller rolls, storage conditions of the input roll 111, internal forces in the substrate web 100 that change after unwinding, lower internal forces at the edges than in the middle of the substrate, humidity of the input roll 111 and / or humidity of the printing room. Said unevenness is sometimes referred to as edge waviness.

[0013] US9682573 BB (XEROX CORPORATION) discloses a method wherein said unevenness at the edges 1011, 1021 is first calendered to have a completely flat substrate web before printing. It was found that this is not feasible for all types of material of the substrate web.

[0014] Said unevenness can also result in a non-optimal holddown of the substrate web 100 against the support zone 201 of the printing press 200, which can cause the substrate web 100 to hit the inkjet print head 202 of the printing press 200 and create wrinkles in the substrate web 100 during the transport of said substrate web 100 through the printing press 200. SUMMARY

[0015] It is an object of the present invention to provide a solution for holddown of a substrate web 100 with edge waviness very well, so that no wrinkles in said substrate web 100 occur during the transport underneath the inkjet print head 202 of the printing press.

[0016] This object has been achieved with the inkjet printing method defined below: an inkjet printing method on a continuous substrate web having a pair of edges, comprising the steps of: a) forming a pair of elongated strips by bending the substrate web along a pair of lines, wherein each line is parallel to the pair of edges; b) supporting the bent substrate web in a support zone of a printing press, wherein the pair of elongated strips is oriented towards the support zone; and c) printing an image on the supported substrate web by an inkjet print head of the printing press; wherein the pair of elongated strips is flattened towards the support zone by unfolding the pair of elongated strips with a vacuum applied in the support zone.

[0017] Further objects of the present invention will become apparent from the description hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figures 1 to 5is a cross section of the preferred embodiment of an inkjet printer 200, where at the left side is the entry of the substrate web 100 from the input roll 111.

[0019] Figure 6 is a cross section of the preferred printer 200, which illustrates how the bent substrate web 100 is applied on the support area 201.

[0020] Figures 7 to 9 is a halftone image of the preferred edge bender unit 203. Figure 8 and Figure 9 Also shown is the substrate web 100 being bent by the edge bender unit 203. The bending is illustrated by the small black arrows. At the other edge of the substrate web 100 there is a similar edge bender unit 204 in the printer 200. This is a mirror image. The mirror image is not shown in the image.

[0021] Figure 10 and Figure 11 illustrates Figures 7 to 9 the edge bender unit. Figure 11 is the edge bender unit not assembled.

[0022] Figure 12 and Figure 13 illustrates how the substrate web 100 is bent in a top view of the preferred printer 200, i.e. a single pass inkjet printer with an elongated inkjet print head 202 positioned above the substrate web 100.

[0023] Figure 14 and Figure 15 illustrates how the substrate web 100 is bent in a top view of the preferred printer 200, i.e. a multiple pass inkjet printer with an inkjet print head 202 positioned above the substrate web 100, the inkjet print head being configured to move across the substrate web 100. DETAILED DESCRIPTION

[0024] The invention is an inkjet printing method on a continuous substrate web 100 having a pair of edges 1011, 1021, comprising the steps of:

[0025] a) forming a pair of elongated strips 101, 102 by bending the substrate web 100 along a pair of lines 1010, 1020, wherein each line is parallel to the pair of edges 1011, 1021; and

[0026] b) The bent substrate web is supported in a support area 201 of the printing press 200, wherein the pair of elongated strips 101, 102 are oriented toward the area 201; and an image 500 is printed on the supported substrate web by the inkjet printhead 202 of the printing press 200. Therefore, instead of flattening the pair of edges 1011, 1021 before printing as is known in the prior art, the pair of edges is bent before printing.

[0027] like Figure 6 As shown, a substrate web 100 is applied here onto a support region 201 located on a vacuum belt 250, wherein a vacuum stage 253 is used to provide vacuum power in the support region 201 via a vacuum chamber 255. Before being applied to the support region 201, edges 1011, 1021 are bent toward the support region 201 such that they form elongated strips 101, 102 along lines 1010, 1020 at defined bending angles 2010. These lines are also referred to as bend lines.

[0028] When the substrate web 100 is supported, the elongated strips 101, 102 are preferably not oriented below the substrate web 100 between the strips 101, 102. This can be achieved by bending the substrate web 100 at a bending angle 2010 greater than 90 degrees. Therefore, bending is not folding, and folding would result in a bending angle of 0 degrees.

[0029] The elongated strips 101 and 102 are applied by bending the substrate web 100 through the respective free-edge bending units 203 and 204, and they are further oriented toward the support area 201. This results in a more stable positioning of the substrate web on the area 201. The pair of lines 1010 and 1020 formed after step a) provide greater stiffness in the substrate web, and the elongated strips 101 and 102 behave as a pair of flanges on which the substrate web between the flanges is supported.

[0030] The material of the substrate web 100 should, of course, be flexible; this is mainly for materials with a density below 150 g / m². 2 More preferably below 120 g / m 2 And higher than 10 g / m 2 For lightweight substrate webs, if the material of the substrate web includes fibers such as cellulose fibers, then a pair of lines 1010, 1020 are preferably substantially parallel to the orientation of the fibers in order to facilitate bending and avoid fiber breakage. The substrate web 100 can also be a polymer substrate.

[0031] The material of the substrate web 100 between the elongated strips 101, 102 is preferably hanging towards the support zone 201, whereby more preferably the substrate web between said strips 101, 102 is connected to the support zone 201 in the middle. Thus, the width of the substrate web is preferably larger than 1 m. Said width is measured as the shortest distance between a pair of edges 1011, 1021.

[0032] Preferably, the smallest angle between the support zone 201 and each of the elongated strips 101, 102 of the pair of elongated strips 101, 102 is below 80 degrees when the continuous substrate web 100 is supported in said zone 201. Said smallest angle is more preferably between 0.1 and 70 degrees, and most preferably between 2 and 65 degrees. Said degrees depend on the material of the substrate web 100 and how much stiffness is caused by said downwardly oriented elongated strips 101, 102 on the support zone 201.

[0033] In a preferred embodiment, the width of each of the elongated strips 101, 102 of the pair of elongated strips 101, 102 is below 10 cm. Said width is more preferably between 1 mm and 70 mm, and most preferably between 2 mm and 40 mm. Said width is chosen by the operator of the printing machine 200, but it is mainly chosen depending on the material of the substrate web 100 and / or how much stiffness is caused by said downwardly oriented elongated strips 101, 102 on the support zone 201. Said width is the shortest distance between the line 1010, 1020 of the elongated strips 101, 102 and the edge 1011, 1021 being part of said elongated strips 101, 102.

[0034] In a preferred embodiment, the inkjet printing method is a single pass inkjet printing method Figure 11 , Figure 12 ).

[0035] Figure 11 and Figure 13 Fig. 1 illustrates the bending of the edges 1011, 1021 of the substrate web 100 as a preferred embodiment of the present disclosure, wherein the edges 1011, 1020 are held bent 2000 by the edge bender unit 203, 204, and whereby the lines 1010, 1020 and the elongated strips 101, 102 are formed at printing time, and they 101, 102 can be flattened after printing or can be flattened 1000 before printing, as illustrated in Figure 12 and Figure 14 .

[0036] Polymeric substrate

[0037] Any polymeric substrate having a maximum in Tan delta between 40 °C and 110 °C is suitable as a web-shaped polymeric substrate for use in the present invention. Polyethylene is the most preferred polymeric substrate for use as a web-shaped polymeric substrate in the present invention.

[0038] Polyethylene is produced in various low and high densities. Polyethylene is well known to the skilled person manufacturing polyethylene films and foils under their abbreviations such as UHMWPE, HDPE, PEX, MDPE, LLDPE, LDPE and VLDPE. The last three are most commonly used to make plastic bags.

[0039] LLDPE is defined by a density between 0.915 g / cm 3 and 0.925 g / cm 3 and is a substantially linear polymer with a high level of short chain branching, usually made by copolymerization of ethylene with short chain a-olefins (e.g., 1 -butene, 1 -hexene, and 1 -octene). LLDPE has higher tensile strength than LDPE and exhibits higher impact and puncture resistance than LDPE.

[0040] LDPE is defined by a density between 0.910 g / cm 3 and 0.940 g / cm 3 . LDPE has a high degree of short chain branching and long chain branching, which means that the chains also do not pile up into crystalline structures. As a result, it has less strong intermolecular forces because the instantaneous dipole induced dipole attraction is less. This results in lower tensile strength and increased ductility. LDPE is formed by free radical polymerization. The high degree of long chain branching imparts unique and desirable flow properties to molten LDPE.

[0041] VLDPE is defined by a density between 0.880 g / cm 3 and 0.915 g / cm 3 and is a substantially linear polymer with a high level of short chain branching, usually made by copolymerization of ethylene with short chain a-olefins (e.g., 1 -butene, 1 -hexene, and 1 -octene). VLDPE is most commonly produced using metallocene catalysts because these catalysts exhibit greater comonomer incorporation rates.

[0042] The polymeric substrate for use as a web-shaped polymeric substrate in the present invention is preferably selected from the group consisting of LLDPE, LDPE and VLDPE. Most preferably, the polymeric substrate for use as a web-shaped polymeric substrate in the present invention is LDPE.

[0043] The thickness of the polymer substrate depends on the specific application. For plastic bags, a thickness of preferably between 30 and 200 pm, more preferably between 50 and 100 pm and most preferably between 60 to 80 pm is used.

[0044] Sometimes, a prime layer is applied to the polymer substrate to produce a specific effect, such as a glossy or matte finish. These primes have no influence on the present invention as long as the dry thickness is less than 5 pm, preferably less than 3 pm. The prime can be applied beforehand, for example by coating or flexographic printing as a continuous layer. In a preferred embodiment, the prime is a non-aqueous radiation-curable liquid.

[0045] The present disclosure (printing method) with the polymer substrate as a substrate web 100 can also be part of the manufacturing of decorative plastic bags.

[0046] Edge folding

[0047] In a preferred embodiment, the printing machine 200 comprises a separate edge-bender unit 203, 204 for forming each elongated strip 101, 102.

[0048] Each edge-bender unit 203, 204 is preferably used after unwinding of the substrate web 100 and before applying the substrate web 100 on the support area 201 of the printing machine 200.

[0049] In a preferred embodiment, the inkjet printing method comprises a step for controlling the width of one of the pair of elongated strips 101, 102, for example by:

[0050] - moving an edge-bender unit of the pair of edge-bender units 203, 204 across the continuous substrate web for controlling the width of one of the pair of elongated strips 101, 102. The position of the edge-bender can thus also be adjusted according to the width of the substrate web. The printing machine 200 is configured such that this movement is possible. It can thus be a gantry attached to the printing machine 200, which is positioned across the continuous substrate web, on which the two edge-bender units 203, 204 are moveably attached, for example along a track in the gantry.

[0051] The edge bender unit 203, 204 preferably comprises a staggered pair of slide devices 2031, 2041, 2032, 2042 for bending the continuous substrate web 100 between said staggered pair of slide devices 2031, 2041, 2032, 2042, said staggered pair of slide devices 2031, 2041, 2032, 2042 comprising a support slide device 2031, 2041 for supporting said substrate web 100 and a bending slide device 2032, 2042 for applying pressure along said support slide device 2032, 2042 towards said substrate web 100. The slide devices 2031, 2041, 2032, 2042 in the edge bender unit 203, 204 are preferably rollers, more preferably rotatable rollers, which rotate while the edge of the substrate web 100 is passed through the edge bender unit 203, 204. This minimizes damage to the surface of the substrate web 100.

[0052] Figures 7 through 11 illustrate such preferred edge bender units.

[0053] In a preferred embodiment, the inkjet printing method comprises step(s) for controlling the bending angle at one of the pair of elongated strips 101, 102 by the edge bender unit:

[0054] - moving the bending slide device 2032, 2042 in one direction along the support slide device 2032, 2042 towards the substrate web 100; and / or

[0055] - moving said bending slide device 2032, 2042 in another direction towards said support slide device 2032, 2042.

[0056] With the handle 20321 as shown in Figures 7 through 11, the bending slide device 2023 can be moved towards the substrate web 100. This is shown as a white arrow. Here, the edge bender unit 203 can also be moved along a rail or gantry, as shown by the long black arrow.

[0057] Flattening

[0058] In a preferred embodiment, the inkjet printing method comprises the additional step:

[0059] c) flattening the printed substrate web towards the support area 201 by spreading the pair of elongated strips 101, 102.

[0060] In another preferred embodiment of the inkjet printing method, step b) comprises the steps of:

[0061] - the substrate web to be supported is flattened towards the support zone 201 by spreading the pair of elongated strips 101, 102.

[0062] The spreading of the elongated strips 101, 102 means in the present invention that the angle of the bend is enlarged back to substantially 180 degrees.

[0063] Thus, after the bending of the substrate web, the substrate web is flattened again. Step c) can be performed by (hot) rubbing the elongated strips 101, 102, especially at the pair of lines 1010, 1020 and / or by (hot) pressing the elongated strips 101, 102. For the flattening step in step b), the pair of lines 1010, 1020 must still be present in order to give said higher stiffness in the substrate web 100, for example by a gentle touch, rubbing or pressing, so that the elongated strips 101, 102 still behave like a pair of flanges on which the substrate web is supported.

[0064] Preferably, in order to spread the pair of elongated strips 101, 102 towards the support zone 201, a vacuum is applied. It was found that the elongated strips 101, 102 behave like a seal, whereby the vacuum applied on the support zone 201, also called vacuum zone, is more effective, especially when said applied vacuum is also used to press the supported flattened substrate web towards said zone 201 during the step of printing. Most preferably, said support zone 201 is a vacuum zone of a vacuum belt of the printing machine 200 for transporting the substrate web 100 underneath the inkjet print head 202 of said printing machine 200. Then the vacuum is applied from said vacuum zone. It was found that by applying said elongated strips 101, 102; supporting the substrate web 100 on a vacuum zone, whereby the elongated strips 101, 102 are directed towards said zone; and applying a vacuum to press the entire medium including the elongated strips, whereby the elongated strips spread, the substrate medium 100 is pressed better against the substrate web 100 than without said elongated strips 101, 102, especially when the substrate web 100 has edge waviness. In addition, no wrinkles occur during the transport of the substrate web 100. The elongated strips 101, 102 can also be printed as control strips, for example for controlling the color and alignment of information to print the printed image. However, due to said flattening, a part of the image can also be printed on said elongated strips 101, 102 if applied before printing.

[0065] In a less preferred embodiment, the support zone 201 is a vacuum zone of a vacuum table 253 of the printing machine 200. Thus, said vacuum belt 250 or vacuum table 253 is a support device of the printing machine 200 on which the support zone 201 is located.

[0066] Printing press

[0067] The printing press 100 of the present disclosure is a digital printing press, wherein a non-contact printing technique is used with inkjet printheads 202. The printing press is also referred to as an inkjet printing press.

[0068] In order to have a good image quality, a constant height is required between the inkjet printheads 202 and the ink-receiving article, here the continuous substrate web 100. In the present disclosure, the inkjet printing press can be a multi-pass inkjet printing press Figure 13 and Figure 14 ), but a single-pass inkjet printing press is preferred Figure 11 and Figure 12 One of the big problems in inkjet printing is that the ink-receiving article can touch the inkjet printheads 202, whereby the inkjet printheads are damaged or have non- ejecting nozzles that have to be repaired. If the height between the inkjet printing, the inkjet printheads and the ink-receiving article needs to be constant, the ink-receiving article has to be flat, or cannot be warped, or cannot be moved upwards from the support area 201.

[0069] Figures 1 to 5 Several configurations of the preferred printing press are illustrated, wherein the substrate web 100 is applied on a support area of the printing press, and wherein the edges 1011 are bent towards the support area by an edge bender unit 203. Thereby, an elongated strip 101 is formed along the line 1010. The substrate web 100 is unwound from an input roll 111 and after printing the image by the inkjet printheads 202 is wound on an output roll 112 or cut into sheets as shown in Figure 2 wherein the substrate web 100 is cut by a cutter 285 and the sheets are collected in an output tray 290.

[0070] Figure 1 and Figure 2 Each illustrates a printing press 200 with a vacuum belt 250 that wraps around two pulleys 270. The support area has a vacuum area that is formed via a vacuum table 253 by a vacuum power from a vacuum chamber 255. The vacuum power flattens the bent substrate web 100 towards the support area, as shown by the vertical black arrow. The curved black arrows show the movement of the different rolls in the printing press 200.

[0071] Figure 3 A conveyor belt printing press is illustrated, wherein the bent substrate web 100 is flattened by a flattener 280 before the image 500 is printed.

[0072] Figure 4 A web printing press is illustrated, wherein the substrate web 100 is conveyed on a vacuum table 253 that forms the support area with a vacuum power from a vacuum chamber 255. The vacuum power flattens the bent substrate web 100 before printing.

[0073] The image is preferably printed with one or more pigmented inkjet inks, which can be selected from the group consisting of aqueous pigmented inkjet inks, solvent-based pigmented inkjet inks and radiation-curable pigmented inkjet inks.

[0074] The one or more pigmented inkjet inks preferably comprise organic color pigments, as they allow to obtain a high color gamut on the substrate web 100. Carbon black and titanium dioxide are inorganic pigments, which can advantageously be used in the present disclosure to constitute black and white pigmented inkjet inks, respectively.

[0075] In a preferred embodiment, the one or more pigmented inkjet inks form a CMYK(W) or CRYK(W) inkjet ink set. The last inkjet ink set is suitable for printing wood colors, especially when manufacturing decorative surfaces.

[0076] The pigment particles in the inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the nozzles. It is also desirable to use small particles to obtain maximum color strength and to slow down sedimentation. The digital average pigment particle size of the organic color pigments and the inorganic black pigment is preferably between 0.050 pm and 1 pm, more preferably between 0.070 pm and 0.300 pm, and most preferably between 0.080 pm and 0.200 pm.

[0077] In a preferred embodiment, the image is dried after or simultaneously with printing the image on the continuous substrate web 100, said image being dried by a radiation device. The radiation can be performed by using a UV bulb lamp or a plurality of UV light emitting diodes or any type of IR dryer.

[0078] The printing machine can perform the inkjet printing method on more than one continuous substrate web 100. An example of such a printing machine is disclosed in WO2019 / 170456 (AGFA NV), which can be part of a production line for manufacturing decorative surfaces.

[0079] A preferred inkjet printhead 202 for the printing machine 200 is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied to it. The application of the voltage changes the shape of the piezoelectric ceramic transducer in the inkjet printhead 202, creating a void, which is then filled with inkjet ink or liquid. When the voltage is removed again, the ceramic expands to its original shape, ejecting a drop of ink from the inkjet printhead.

[0080] A preferred piezoelectric printhead is a so-called push-mode type piezoelectric printhead, which has a rather large piezoelectric element that is also capable of ejecting drops of inkjet ink of high viscosity. Such an inkjet printhead is available as GEN5s printhead from RICOH TM .

[0081] A preferred piezoelectric print head is a so-called through-flow piezoelectric drop-on-demand inkjet print head. Such inkjet print heads are available as CF1ou print heads from TOSHIBA TEC TM and also from TOSHIBA TEC TM and XAAR TM Through-flow print heads are preferred in the present invention because they enhance the reliability of inkjet printing.

[0082] When using water-based or solvent-based inkjet inks, the printing machine 200 comprises drying equipment to evaporate water and solvent from the ink jetted on the packaging material. Suitable dryers include equipment that circulates hot air, ovens and equipment that uses air suction.

[0083] The drying equipment can comprise an infrared radiation source. An effective infrared radiation source has an emission maximum between 0.8 pm and 1.5 pm. Such infrared radiation sources are sometimes referred to as NIR radiation sources or NIR dryers. NIR radiation energy quickly penetrates into the depth of the inkjet ink layer and removes water and solvent from the entire layer thickness, whereas conventional infrared and hot air energy is mainly absorbed at the surface and slowly conducts into the ink layer, which often results in a slower removal of water and solvent.

[0084] In a preferred embodiment, the NIR radiation source is in the form of a NIR LED, which can easily be mounted on the shuttle system of a plurality of inkjet print heads in a multi-pass inkjet printing machine. Another preferred drying equipment uses carbon infrared radiation (CIR).

[0085] When using UV-curable colored inkjet inks, the printing machine 200 comprises a UV curing equipment. The UV curing equipment emits UV radiation, which is absorbed by the photoinitiator or photoinitiating system of the polymerizable compounds used for the polymeric core.

[0086] The UV curing equipment can comprise a high- or low-pressure mercury lamp, but preferably comprises or consists of UV LEDs.

[0087] The UV curing equipment can be arranged in combination with the inkjet print heads 202 of the printing machine 200, traveling therewith, so that the curing radiation is applied a short time after jetting. Preferably, such curing device consists of one or more UV LEDs, because in such an arrangement it can be difficult to provide other types of curing devices that are small enough to be connected to and travel with the inkjet print heads 202. Alternatively, a static fixed radiation source, e.g. a source of curing UV light, can be employed, which is connected to the radiation source by means of a flexible radiation conducting device, such as a bundle of optical fibers or an internally reflective flexible tube, or by a mirror arrangement, which preferably comprises a mirror on the inkjet print heads 202.

[0088] However, it is not necessary to connect the UV light source to the inkjet print head 202. The UV radiation source can also be, for example, an elongated radiation source extending transversely across the ink to be cured on the packaging material. It can be adjacent to the transverse path of the inkjet print head 202, such that subsequent rows of the decorative image formed by the inkjet print head 202 are passed stepwise or continuously underneath the radiation source.

[0089] Any ultraviolet light (UV) source (as long as a part of the emitted light can be absorbed by the photoinitiator or photoinitiator system) can be used as the radiation source, such as high- or low-pressure mercury lamps, cold cathode tubes, black light, UV LEDs, UV lasers, and flash lamps. Among these, the preferred light source is one that exhibits a relatively long-wavelength UV contribution, with a dominant wavelength of 300-400 nm, more preferably 360 nm to 400 nm. In particular, UV-A light sources are preferred because of the reduced light scattering that accompanies them, resulting in a more efficient internal curing.

[0090] UV radiation is generally classified as UV-A, UV-B, and UV-C, as follows:

[0091] • UV-A: 400 nm to 320 nm

[0092] • UV-B: 320 nm to 290 nm

[0093] • UV-C: 290 nm to 100 nm.

[0094] In a preferred embodiment, the inkjet printing apparatus comprises one or more UV LEDs having a wavelength of greater than 360 nm, preferably one or more UV LEDs having a wavelength of greater than 380 nm, and most preferably UV LEDs having a wavelength of about 395 nm.

[0095] Furthermore, it is possible to use two light sources of different wavelengths or illuminations to cure the image, either consecutively or simultaneously. For example, a first UV source can be chosen to be rich in UV-C, particularly in the range of 260 nm-200 nm. Then, a second UV source can be rich in UV-A, for example a gallium-doped lamp, or a different lamp that is high in both UV-A and UV-B. It has been found that using two UV sources has the advantage of, for example, fast curing speed and high degree of curing.

[0096] To facilitate curing, the inkjet printing apparatus typically includes one or more oxygen depletion units. The oxygen depletion units place a cushion of nitrogen or other relatively inert gas (e.g., N2or CO2) that has an adjustable location and an adjustable inert gas concentration in order to reduce the oxygen concentration in the curing environment. The residual oxygen level is typically maintained as low as 200 ppm, but is generally in the range of 200 ppm to 1200 ppm.

[0097] The support zone 201 is part of a support device of the printing press 200, which is preferably a vacuum table, and more preferably a vacuum belt. On said table or belt, a vacuum zone is applied as support zone 201 for vacuum pressing the ink-receiver with vacuum from the vacuum chamber 255 of the printing press 200. For example, WO2016 / 071122 (AGFA GRAPHICS NV) discloses details of a printing press having a vacuum belt 250.

[0098] The support zone 201 can also be formed by a plurality of rollers on which the substrate web 100 is transported for printing, as for example can be found in the Agfa Dotrix Modular and possibly other single pass inkjet printing presses produced by the manufacturer AGFA NV. In Figure 5 An embodiment of a preferred printing press having said plurality of rollers 256) is shown in Fig. 1.

[0099] Manufacturing a decorative surface

[0100] The inkjet printing method of the present disclosure and all its preferred embodiments are preferably used for manufacturing decorative surfaces

[0101] - wherein the continuous substrate web 100 is a paper substrate having a weight of less than 150 g / m 2 and the image is printed with one or more water-based pigmented inkjet inks; or

[0102] - wherein the continuous substrate web 100 is a thermoplastic substrate having a weight of less than 150 g / m 2 and based on a material selected from the group consisting of polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU) and combinations thereof, and the image is printed with one or more UV curable inkjet inks.

[0103] Said latest type of continuous substrate web is for example ideal for manufacturing high-end vinyl floor tiles (LVT). WO2018060189 (AGFA NV) discloses said manufacturing method.

[0104] Furthermore, said one or more water-based pigmented inkjet inks are preferably jetted before or after impregnation of the substrate web 100 with a thermosetting resin.

[0105] The printing press 200 of the present disclosure is therefore preferably part of a production line for manufacturing decorative surfaces.

[0106] The inkjet printing method preferably comprises the following steps:

[0107] - before step a), applying on the paper substrate at least one ink-receiving layer comprising a polyvinyl alcohol polymer and inorganic pigments, wherein, more preferably, the outermost ink-receiving layer does not comprise inorganic pigments or comprises a smaller content of inorganic pigments than the ink-receiving layers between the paper substrate and the outermost ink-receiving layer.

[0108] It is also an embodiment of the present disclosure to use edge benders 203, 204 in a production line for manufacturing decorative surfaces, in particular edge benders having a staggered pair of sliding devices 2031, 2041, 2032, 2042, as described in the section "Edge bending".

[0109] Manufacturing a decorative panel

[0110] The printed paper substrate in the manufacturing of decorative surfaces is preferably turned into a decorative layer of a decorative panel as a decorative surface, which is more preferably selected from the group consisting of floor, kitchen, furniture and wall panels. Herein, the printed continuous substrate web, whether or not cut into sheets, is applied on a core layer such as a MDF board, and optionally other layers such as a balancing layer, a protective layer or a sound absorbing layer, after which the overall assembly of the substrate web and the one or more layers are hot pressed together.

[0111] For example, the DPL process (direct pressure lamination) is a known method for manufacturing decorative panels.

[0112] According to the Gurley method (DIN 53120), the paper substrate has a porosity preferably between 8 and 20 seconds.

[0113] It was found that the pair of lines 1010, 1020 is no longer visible in the manufactured decorative panel. Therefore, the elongated strips 101, 102 can also be inkjet printed with a part of the image, which makes that there is no waste of material of the substrate web 100.

[0114] In a preferred embodiment, the elongated strips 101, 102 become part of a tongue and / or groove applied in the decorative panel, which tongue and / or groove allow the decorative panels to snap into each other. The advantage is easy assembly, no glue is needed. The shape of the tongue and groove needed to obtain a good mechanical connection is well known in the field of laminate flooring, as also exemplified in EP 2280130 A (FLOORING IND), WO 2004 / 053258 (FLOORING IND), US 2008010937 (VALINGE) and US6418683 (PERSTORP FLOORING).

[0115] The tongue and groove profiles are especially preferred for floor panels and wall panels, but in the case of furniture panels, such tongue and groove profiles are preferably absent for aesthetic reasons of furniture doors and drawer fronts. However, the tongue and groove profiles can be used to snap other panels of the furniture together, as illustrated by US 2013071172 (UNILIN).

[0116] The image printed on the continuous substrate web 100 is preferably a wood pattern with veins. In a preferred embodiment, the veins of the printed wood pattern are oriented substantially parallel to the pair of lines 1010, 1020.

[0117] Core layer

[0118] The core layer is preferably made of a wood-based material such as chipboard, MDF or HDF (medium or high density fiberboard), oriented strand board (OSB), etc. A board of synthetic material or made by means of a hydraulic setting such as a cement board can also be used. In a particularly preferred embodiment, the core layer is a MDF or HDF board.

[0119] The core layer can also be assembled at least from a plurality of paper sheets or other carrier sheets impregnated with a thermosetting resin, as disclosed by WO 2013 / 050910 (UNILIN). Preferred paper sheets include so-called kraft paper obtained by a chemical pulping process, also known as the Kraft process, for example as described in US 4952277 (BET PAPER CHEM).

[0120] In another preferred embodiment, the core layer is a board material consisting essentially of wood fibers bound by means of a polycondensation glue, wherein the polycondensation glue represents 5 to 20 wt.% of the board material and at least 40 wt.% of the wood fibers are obtained from recycled wood. A suitable example is disclosed by EP 2374588 A (UNILIN).

[0121] Instead of a wood-based core layer, a synthetic core layer can also be used, such as disclosed by US 2013062006 (FLOORING IND). In a preferred embodiment, the core layer comprises a foamed synthetic material such as foamed polyethylene or foamed polyvinyl chloride.

[0122] Other preferred core layers and their manufacture are disclosed by US 2011311806 (UNILIN) and US 6773799 (DECORATIVE SURFACES).

[0123] The thickness of the core layer is preferably between 2 mm and 12 mm, more preferably between 5 mm and 10 mm.

[0124] Embodiments of the present disclosure are methods of manufacturing decorative panels, comprising the steps of:

[0125] - printing a wood pattern on a paper substrate according to the inkjet printing method of the present disclosure and its preferred embodiments;

[0126] - impregnating the printed paper substrate with a thermosetting resin;

[0127] - hot pressing the thermosetting resin impregnated printed paper substrate between a core layer and a protective layer, and cutting into decorative panels selected from the group consisting of floor, kitchen, furniture and wall panels.

[0128] Thermosetting resin

[0129] The thermosetting resin is preferably selected from the group consisting of melamine-formaldehyde based resins, urea-formaldehyde based resins and phenol-formaldehyde based resins.

[0130] Other suitable resins for impregnating paper are listed in

[0028] of EP 2274485 A (HUELSTA).

[0131] Most preferably, the thermosetting resin is a melamine-formaldehyde based resin, commonly referred to in the art as "melamine (based) resin" for short.

[0132] Manufacturing a decorative corrugated cardboard

[0133] The printed paper substrate in the manufacture of decorative surfaces is preferably a decor paper for the linerboard of a decorative corrugated cardboard, as a decorative surface.

[0134] In the manufacture of decorative corrugated cardboard, the printed continuous substrate web, whether or not cut into sheets, is glued on one or more fluted sheets (corrugated medium) of paperboard.

[0135] Corrugated cardboard is the preferred packaging material because it is low cost and lightweight, and has the advantage that corrugated cardboard boxes can be stacked, making them easy to store and transport. Corrugated cardboard is a packaging material formed by gluing one or more fluted sheets (corrugated medium) to one or more flat sheets (called linerboard) of boxboard. It has four common types: (a) Single-faced: one fluted sheet glued to one linerboard (two sheets total). (b) Single-wall: one fluted sheet sandwiched between two linerboards (three sheets total); also called double-faced or single-ply. (c) Double-wall: one single-faced glued to one single-wall, so that two fluted sheets are alternately sandwiched between three flat sheets (five sheets total); also called double-ply or double-ply. (d) Triple-wall: two single-faced glued to one single-wall, so that three fluted sheets are alternately sandwiched between four flat sheets (seven sheets total); also called triple-ply.

[0136] The preferred corrugated cardboard in the present invention is single-wall or double-wall, more preferably single-wall corrugated cardboard, because such cardboard is strong enough and easy to crease. Single-faced corrugated cardboard is generally not strong enough to contain merchandise, while triple-wall cardboard is generally more difficult to crease into a packaging box.

[0137] The paper used in corrugated cardboard, such as Kraft paper, generally has a brown color. In the preferred embodiment of manufacturing decorative corrugated cardboard, the paper substrate as the continuous substrate web 100 has a white color for enhancing the color vibrancy of the inkjet ink printed thereon. The white background helps the customer experience as the customer perceives it as a more premium product. Alternatively, the white background can be applied as a layer by coating or printing prior to the inkjet printed image.

[0138] An embodiment of the present invention is a method of manufacturing decorative corrugated cardboard, wherein the continuous substrate web 100 is a paper substrate; and

[0139] wherein the method of manufacturing has the additional step of gluing the printed paper substrate on a fluted sheet of paperboard for forming the decorative corrugated cardboard.

[0140] After printing the image 500 and before gluing on the fluted sheet of paperboard, the elongated strips 101, 102 can be unrolled again or even more unrolled (if already unrolled). More preferably, after printing the image 500 and before gluing on the fluted sheet of paperboard, the elongated strips 101, 102 are flattened.

[0141] List of reference signs

[0142] 100 Substrate web 101 Elongated strip 102 Elongated strip 1010 Wire 1020 Wire 1011 Edge of the substrate web 1021 Edge of the substrate web 200 Printing press 201 Support zone 2011 Edge of the support zone 2012 Edge of the support zone 202 Inkjet print head 2031 Support slide 2041 Support slide 2032 Folding slide 2042 Folding slide 203 Edge folder unit 204 Edge folder unit 500 Image

Claims

1. An inkjet printing method on a continuous substrate web (100) having a pair of edges (1011, 1021), comprising the following steps: a) A pair of elongated strips (101, 102) are formed by bending the continuous substrate web (100) along a pair of lines (1010, 1020), wherein each line is parallel to the pair of edges (1011, 1021); b) The bent continuous substrate web is supported in a support area (201) of a printing press (200), wherein the pair of elongated strips (101, 102) are oriented toward the support area (201); and c) Printing an image (500) on the supported continuous substrate web via the inkjet printhead (202) of the printing press (200); The pair of elongated strips (101, 102) are flattened toward the support area (201) by unfolding the pair of elongated strips (101, 102) using a vacuum applied in the support area (201).

2. The inkjet printing method according to claim 1, wherein, The pair of elongated strips (101, 102) are formed by a pair of edge bending units (203, 204) of the printing press (200), each having an interlaced pair of sliding devices (2031, 2041, 2032, 2042), wherein the continuous substrate web (100) is bent between the interlaced pair of sliding devices (2031, 2041, 2032, 2042), the interlaced pair of sliding devices (2031, 2041, 2032, 2042) being a support sliding device for supporting the continuous substrate web (100) and a bending sliding device for applying pressure toward the continuous substrate web (100) along the support sliding device.

3. The inkjet printing method according to claim 2, further comprising the step of controlling the width of one of the pair of elongated strips (101, 102): - Move one of the edge bending units (203, 204) across the continuous substrate web to control the width of one of the strips (101, 102).

4. The inkjet printing method according to claim 3, further comprising the step of controlling the bending angle at one of the pair of elongated strips (101, 102) by means of the edge bending unit: - Move the bending sliding device in one direction along the supporting sliding device toward the continuous substrate web (100); and / or - Move the bending sliding device toward the supporting sliding device in another direction.

5. The inkjet printing method according to claim 1, wherein, When the continuous substrate web (100) is supported in the support area (201), the minimum angle between the support area (201) and each of the pair of elongated strips (101, 102) is less than 80 degrees.

6. The inkjet printing method according to claim 5, wherein, Each of the pair of slender strips (101, 102) has a width of less than 10 cm.

7. The inkjet printing method according to claim 6, wherein, The support area (201) is formed on the vacuum belt of the printing press (200).

8. The inkjet printing method according to claim 1, used for manufacturing decorative surfaces, wherein, The continuous substrate web (100) has a content of less than 150 g / m 2 The image is printed using one or more water-based coloring inkjet inks on a paper substrate of a certain weight.

9. The inkjet printing method according to claim 1, used for manufacturing decorative surfaces, wherein, The continuous substrate web (100) is a thermoplastic substrate, and the thermoplastic substrate has a density of less than 150 g / m². 2 The image is printed using one or more UV-curable inkjet inks. The image is of a weight thereof and the thermoplastic substrate is based on a material selected from the group consisting of polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and thermoplastic polyurethane (TPU), and combinations thereof.

10. The inkjet printing method according to claim 8, wherein, The paper substrate has a porosity between 8 seconds and 20 seconds according to the Gree method (DIN 53120); including the following steps: - Prior to step a), at least one ink receiving layer comprising a polyvinyl alcohol polymer and an inorganic pigment is applied to the paper substrate; Furthermore, the image is printed using one or more water-based coloring inkjet inks before or after impregnation with a thermosetting resin.

11. The inkjet printing method according to claim 8, wherein, The printing process is a single-pass printing method.

12. The inkjet printing method according to claim 9, wherein, The printing process is a single-pass printing method.

13. A method for manufacturing a decorative panel, comprising the following steps: - Print a wood pattern on the paper substrate using the inkjet printing method according to claim 8; - The printed paper substrate is impregnated with a thermosetting resin; - The printed paper substrate, impregnated with thermosetting resin and hot-pressed between a core layer and a protective layer, is cut into decorative panels selected from a group consisting of flooring, kitchen, furniture, and wall panels.

14. A method for manufacturing a decorative panel, comprising the following steps: - Print a wood pattern on the thermoplastic substrate using the inkjet printing method according to claim 9; - The printed thermoplastic substrate is impregnated with a thermosetting resin; - The printed thermoplastic substrate, impregnated with thermosetting resin and hot-pressed between a core layer and a protective layer, is cut into decorative panels selected from a group consisting of flooring, kitchen, furniture, and wall panels.

15. A method for manufacturing decorative corrugated cardboard, comprising the inkjet printing method according to claim 8; and in, The manufacturing method includes additional steps for forming decorative corrugated cardboard: - The printed paper substrate is glued onto a grooved sheet of cardboard.

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