METHOD AND UNIT FOR MANUFACTURING A LAMINATED Wrapping MATERIAL COIL

Abstract

A continuous in-line method for producing a web (100) of packaging material, comprising: inkjet printing a plurality of ink droplets (300) on a printing surface (131) on a paperboard layer (130), the ink droplets (300) comprising a colorant and a solvent; drying (S30) the plurality of ink droplets (300) printed onto the cardboard layer (130) such that the colorant is fixed wherein the drying (S30) is performed by evaporating (S31) at least part of the solvent by applying infrared radiation (IR) onto the printing surface (131); and absorbing (S32) the infrared radiation (IR) transmitted through the paperboard layer (130) through an absorbing surface (400) arranged on an opposite side of the paperboard layer (130) with respect to the printing surface (131).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a roll of laminated packaging material for liquid food packaging containers, a converting unit, and a roll of laminated packaging material. Background Art

[0002] Disposable liquid food packaging containers are typically made of laminated packaging material. The laminated packaging material is produced in the form of a continuous roll, which can be used in a reel-fed filling machine or cut into individual blanks for a blank-fed packaging machine.

[0003] The laminated packaging material is produced by a converting process that joins and processes multiple materials into a ready-to-use roll of laminated packaging material.

[0004] During the converting process, the cardboard layer that forms the core layer of the laminated packaging material can be digitally printed, for example by inkjet printing, dried, and creased on the outer side (i.e., the side intended to be the outer side of the laminated packaging material). Optionally, the cardboard layer can also be pre-coated before printing and / or adhered to one or more layers before or after printing.

[0005] Maintaining the required moisture level of the cardboard layer throughout the converting process is crucial; this is not only to ensure the optimal performance of various converting processes but also to control the required performance of the final packaging container.

[0006] After digital printing with a water-based ink (such as a pigmented water-based ink), it is recommended to use an infrared dryer combined with back reflectors located on both sides of the cardboard layer to dry the cardboard layer. The back reflectors are located in a position not in contact with the cardboard layer. Although this technique can dry quickly, it has been observed that it also dries the cardboard layer, i.e., reduces the moisture content of the cardboard layer. A lower cardboard moisture content can have a negative impact on the converting process, such as when the cardboard layer is creased in a subsequent process. If the moisture content of the cardboard layer is reduced to a certain level, the cardboard layer will crack instead of bend, which may reduce the quality of the final roll of laminated packaging material and the packaging containers made from this roll of laminated packaging material. On the other hand, if the printed pattern is not dried sufficiently, defects such as wear or blurring of the printed color pattern may occur. Therefore, there is a need in the art to improve the manufacturing technology of rolls of laminated packaging material, especially in terms of ink drying. Summary of the Invention

[0007] The object of the present invention is to at least partially overcome one or more of the above limitations in the prior art. Specifically, the object of the present invention is to provide a reliable and efficient method for manufacturing a roll of laminated packaging material that can maintain the moisture level of the cardboard layer.

[0008] To achieve these objectives, the present invention provides a continuous on-line method for manufacturing a roll of laminated packaging material. The method includes: inkjet printing a plurality of ink droplets on the printed surface of a cardboard layer, the ink droplets containing a colorant and a solvent; and drying the plurality of ink droplets printed on the cardboard layer to fix the colorant. The drying process is carried out as follows: applying infrared radiation to the printed surface of the cardboard layer to evaporate at least part of the solvent; and absorbing the infrared radiation transmitted through the cardboard layer by an absorption surface arranged on the opposite side of the cardboard layer relative to the printed surface; at the same time, absorbing the infrared radiation directly irradiating the outer absorption surface of the cardboard layer to minimize the secondary reflection on the opposite side of the cardboard layer.

[0009] Most likely, the cardboard layer to be used is for liquid food packaging. In other words, most likely, the roll of laminated packaging material is a roll of laminated liquid food packaging material, or liquid packaging cardboard.

[0010] The advantage of this method is that the moisture content of the cardboard layer remains substantially unchanged. The moisture content of the cardboard layer can be, for example, 4% or higher, between 5% and 10%, or preferably between 5% and 8.5%.

[0011] The method can also include flexographic printing or other printing techniques, so the printed surface can be printed only using inkjet printing, or by a hybrid method combining two or more printing techniques. In other words, the printed surface can use inkjet printing and flexographic printing.

[0012] The method can also include applying a printed substrate layer to the cardboard layer to provide a printed surface before inkjet printing thereon.

[0013] Applying the printed substrate layer can include, for example: coating a precoat on the cardboard layer, or priming the cardboard layer by plasma treatment to form a printed substrate layer on the surface of the cardboard layer, and / or applying a surface modifier to change its topological structure or electrostatic-related properties. The printed substrate layer can completely cover the cardboard layer, or only cover the area that needs to be covered on the printed surface, or can cover a medium-sized area of the cardboard layer.

[0014] In one embodiment, the present invention may be more beneficial when the cardboard layer needs to be dried as soon as possible. For example, if the cardboard has a printed substrate layer that can prevent the ink solvent (most likely water-based ink) from migrating through the cardboard, it may be more beneficial to dry as quickly as possible without over-drying the packaging material. In other words, if the cardboard has a printed substrate layer that can keep almost all the ink solvent (most likely water-based ink) printed on the printed substrate layer, it may be more beneficial to dry as quickly as possible without over-drying the packaging material.

[0015] In one embodiment, the cardboard layer may include a printable coating, such as a white pigment and clay coating as the printing substrate layer. Such a clay coating will form a waterproof surface on the cardboard layer, meaning that ink solvents cannot migrate and be absorbed into the cardboard fiber layer. This requires increased drying power as it is important to dry the ink quickly before further downstream processes.

[0016] In one embodiment, the printing substrate layer may be a clay coating, which is also primed before inkjet printing.

[0017] In one embodiment, the printing substrate layer may be provided on the cardboard layer before inkjet printing at the same production site; and / or before this, for example, at another production site, i.e., at the site where inkjet printing is implemented, the application of the printing substrate layer is not carried out.

[0018] Preferably, the cardboard layer has a thickness of at least 90 μm and / or a weight of at least 65 g / m².

[0019] Before inkjet printing and / or applying the printing substrate layer, the cardboard layer may be an uncoated cardboard or a cardboard laminated with one or more layers (such as a polymer layer).

[0020] The absorption surface may be black for absorbing infrared radiation. However, it can also be other colors or transparent. The absorption surface can be treated to form a high absorber, such as a blackbody. A high absorption rate means that the surface has a very low reflectivity within the wavelength spectrum of 0.4 μm - 4 μm. Examples of such treatments (as further described in the following detailed description) can provide improved absorption rates.

[0021] The absorption surface may have a topology that makes its reflectivity very low, especially within the wavelength spectrum of 0.4 μm - 4 μm.

[0022] The absorption surface may be supported by a plate on the main side. The plate may be made of a highly thermally conductive material and act as a heat exchanger. The method may also include removing heat from the absorption surface by a cooling medium (such as a gas or liquid), which preferably acts on the opposite side of the plate relative to the absorption surface. The secondary side of the plate may have its surface area increased, for example, by providing fins, thereby improving the heat transfer capacity.

[0023] The method may also include providing a crease line pattern on the cardboard layer. The crease line pattern may be repeated in the machine direction. The cardboard layer may be conveyed in the machine direction at a substantially constant speed, such as at 200 m / min or faster.

[0024] In one possible embodiment, the crease lines may be provided upstream and / or downstream of the inkjet printing.

[0025] The steps of inkjet printing, drying, and providing crease lines can be carried out in sequence.

[0026] The drying step may also include applying hot air to the printed surface. This is beneficial because it helps maintain the moisture content in the shortest drying time.

[0027] Hot air can be applied after infrared radiation. In this way, the method ensures time efficiency while ensuring that the moisture content of the cardboard layer reaches the required level.

[0028] The method may further include: determining an adjusted drying power based on the determined humidity parameter, where the determined moisture parameter indicates the moisture content of the cardboard; then, infrared radiation and / or hot air can be applied at the adjusted drying power. In this way, it can be ensured that the moisture level of the cardboard layer is maintained in an effective manner.

[0029] The adjusted drying power can be determined separately for infrared radiation and hot air, so that infrared radiation and hot air are applied in an appropriate proportion based on the determined humidity parameter. Therefore, the process efficiency can be further improved.

[0030] The spectral emission range of the infrared radiation can be between 0.4μm - 4μm. Therefore, the infrared radiation can be near-infrared radiation, short-wave infrared radiation, mid-wave infrared radiation, or radiation in multiple infrared regions. The absorption surface can be configured to absorb radiation in the same range (0.4μm - 4μm).

[0031] In one embodiment, after applying infrared radiation to the printed surface to evaporate at least part of the solvent, the printed packaging material can be wound onto a reel. If a crease line pattern is provided on the cardboard layer, the printed and creased packaging material can be wound onto a reel. Therefore, the wound packaging material reel can be conveyed to the next step in a convenient manner, such as filling the product (possibly a liquid food) into the packaging material reel.

[0032] The present invention places no restrictions on the order of the method steps. Those skilled in the art can use various orders of the above steps as long as the advantage of basically maintaining the moisture content of the cardboard layer can be achieved technically.

[0033] Another aspect of the present invention relates to a converting unit configured to manufacture a laminated packaging material reel. The converting unit can be configured to perform the continuous online method for manufacturing a laminated packaging material reel described herein, and thus covers all the disclosed aspects related to this method.

[0034] The conversion unit includes: a feeding unit configured to continuously convey a cardboard layer; an inkjet printer configured to print a plurality of ink droplets containing colorant and solvent on the printing surface of the cardboard layer; and a drying station configured to dry the ink by exposing the printing surface to infrared radiation, wherein the drying station further includes an absorption surface disposed on the opposite side of the cardboard layer relative to the printing surface, and the absorption surface is configured to absorb at least a portion of the infrared radiation (IR) transmitted through the cardboard layer. The feeding unit can be configured to convey the cardboard layer at a constant speed.

[0035] The conversion unit may further include a sensor unit and a control unit operatively interconnected. The sensor unit can be configured to sense a humidity parameter indicating the moisture content of the cardboard and send a signal related to the humidity parameter to the control unit, and the control unit can be operatively connected to the drying station and configured to adjust the drying power in response to the signal related to the humidity parameter. Thereby, the time efficiency of the method is ensured while minimizing moisture loss in the cardboard layer and / or ensuring the required moisture level in the cardboard layer.

[0036] The drying station may also be configured to dry the plurality of ink droplets by exposing the cardboard layer to hot air. The drying station may include an impingement hot air dryer different from the infrared dryer, and the hot air dryer may be disposed downstream of the infrared dryer. The advantages of combining infrared radiation and hot air have been explained above.

[0037] The conversion unit may further include a cooling unit configured to remove heat from the absorption surface.

[0038] The cooling unit may include a heat exchanger and / or heat dissipation fins.

[0039] The conversion unit may further include a creasing station configured to provide a crease line pattern to the cardboard layer, and / or a laminating station configured to laminate another layer onto the printed cardboard layer.

[0040] The creasing station may be located downstream or upstream of the inkjet printer; alternatively, multiple creasing stations may be located downstream and upstream of the inkjet printer respectively; or, a combined unit of the inkjet printer and the creasing station may perform creasing before and / or after printing.

[0041] The conversion unit may further include a printing substrate station configured to apply a printing substrate layer to prepare the cardboard layer before printing by the inkjet printer. As described above, applying the printing substrate layer may include coating the cardboard layer with a pre - coating (such as a clay coating or a primed clay coating), or priming the cardboard layer by plasma treatment to form a printing substrate layer on the surface of the cardboard layer, or applying a surface conditioner or otherwise changing the surface characteristics of the cardboard layer. The conversion unit may further include a second drying station for drying the printing substrate layer.

[0042] The order of steps at each station can be unrestricted for the present invention. Those skilled in the art can use various orders of the above stations as long as the advantage of substantially maintaining the moisture content of the cardboard layer can be achieved technically.

[0043] In one embodiment, after at least part of the solvent is evaporated by applying infrared radiation to the printing surface, a winding unit can be provided for winding the printed packaging material onto a reel. If a crease line pattern has been provided on the cardboard layer, the printed and creased packaging material can be wound onto the reel. Thus, the wound packaging material web can be conveyed to the next step in a convenient manner, such as filling the product (which may be a liquid food) into the packaging material web.

[0044] Another aspect of the present invention relates to a laminated packaging material web. The laminated packaging material web can be obtained by a converting unit and / or the method steps described herein. The laminated packaging material web includes an inkjet-printed cardboard layer. The moisture content of the cardboard layer is 4% or higher. The moisture content of the cardboard layer can be between 5% and 10%. More preferably, the moisture content can be between 5% and 8.5%.

[0045] For example, after inkjet printing on the printing surface, the moisture content of the cardboard layer can be between 6% and 8.5%, while in the final laminated packaging material web, the moisture content of the cardboard layer may be substantially the same or slightly lower. This means that the cardboard layer does not suffer any significant moisture loss, at least to an extent that does not cause any major defects in the laminated packaging material web.

[0046] The laminated packaging material can have a crease line pattern. For example, the crease line pattern can be cyclically repeated in the machine direction.

[0047] As long as all the above possible features are within the scope of the claims, they should be regarded as valid for all aspects of the present invention.

[0048] Other objects, features, aspects and advantages of the present invention will become apparent in the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0050] Figure 1 is a flowchart of a method for manufacturing a laminated packaging material web according to an embodiment.

[0051] Figure 2 is a cross-sectional view of a laminated packaging material web and an absorbent surface during manufacturing according to an embodiment.

[0052] Figure 3Schematic diagram of a conversion unit according to an embodiment. Detailed implementation

[0053] Reference Figure 1 , which shows an embodiment of a continuous on-line method 1 for manufacturing a web 100 of laminated packaging material. The method 1 includes: inkjet printing S10 a plurality of ink droplets 300 on the printing surface 131 of the cardboard layer 130, the ink droplets 300 containing a colorant and a solvent. The cardboard layer 130 may include paper, cardboard, or other cellulose-based materials. Inkjet printing is a type of digital printing or computer printing. During inkjet printing, a digital image is reconstructed by ejecting a plurality of ink droplets 300 onto a substrate (such as the cardboard layer 130 or the printed substrate layer 140, which will be further discussed herein). The plurality of ink droplets may contain a solvent and a colorant or dye. The solvent may include water, non-volatile organic compounds, and / or volatile organic compounds, such as high-boiling alcohols. The method may also include other printing techniques, such as flexographic printing, so that the printing surface 131 may be printed only by inkjet printing S10 or by a hybrid method combining two or more printing techniques. In other words, the cardboard layer 130 may be inkjet printed and flexographically printed. The ink used for inkjet printing S10 may contain a higher ratio of solvent to colorant than the ink used for flexographic printing. For example, the solvent content of inkjet ink may be about 4 times higher than that of flexographic printing ink. In addition, compared with flexographic printing, the total amount of ink deposited on the cardboard layer 130 by inkjet printing is usually several times more. Therefore, for inkjet printing, it is even more crucial to provide a rapid drying process without reducing the moisture content of the cardboard layer 130. As described above, the method may also include applying S5 the printed substrate layer 140 to the cardboard layer before inkjet printing the printing surface.

[0054] The method further includes drying S30 a plurality of ink droplets 300 printed on the printing surface 131 to fix the colorant. The drying S30 is carried out by: applying infrared radiation IR to the printing surface 131 on the cardboard layer 130, evaporating S31 at least part of the solvent, and absorbing S32 the infrared radiation IR transmitted through the cardboard layer 130 by an absorption surface 400 arranged on the opposite side of the cardboard layer 130 relative to the printing surface 131. During the infrared drying process, the infrared radiation (hereinafter referred to as IR) irradiates the printing surface 131, where it will be absorbed to a certain extent by the molecules in the plurality of ink droplets 300, resulting in the evaporation of the solvent in the ink droplets 300 from the cardboard layer 130. The intensity of the IR affects the transmission level through the cardboard layer 130 and can be adjusted. By including the drying S30 step of evaporation S31 by IR, a more reliable process is ensured and is not affected by the air boundary layer. Due to the very efficient spectral energy transfer process, infrared drying further improves the process time efficiency. The rapid removal of the solvent in the plurality of ink droplets can further form a brighter and more vivid printing effect on the printing surface 131.

[0055] The drying process can be controlled by selecting the wavelength, intensity, and exposure time of the IR radiation. Ideally, the IR radiation should be selected such that the energy transmitted to the cardboard layer 130 and absorbed by its water molecules is minimized, thereby reducing the moisture loss of the cardboard layer 130.

[0056] In addition, hot air HA can be applied to the printing surface 131 before, during, or preferably after the infrared radiation IR. Applying the hot air HA means heating the ambient air and transferring heat from the hot air stream to the printing surface 131 by convection, and the evaporated solvent in the plurality of ink droplets is also conveyed to the air by convection. The temperature and flow rate of the hot air HA can be controlled. A drying process based only on hot air will be inefficient and time-consuming, so a longer installation length is required to achieve the desired drying time and significantly reduce the yield of the manufacturing process. In the drying S30 step, it is preferable to use IR and hot air HA in combination.

[0057] The drying S30 of the plurality of ink droplets 300 can be carried out by exposing a certain area of the printing surface 131 to the infrared radiation IR and then exposing the same area of the printing surface 131 to the hot air HA stream. Alternatively, the first area of the printing surface 131 can be exposed to IR first, and then the second area of the printing surface 131 (which is larger than the first area and at least partially includes the first area) can be exposed to the hot air HA stream. This means that the IR radiation can only be provided locally to certain areas of the cardboard layer 130.

[0058] Before performing subsequent method steps for manufacturing the laminated packaging material web 100, it is essential to dry the printed surface 131, which particularly helps to avoid defects caused by abrasion or soiling. The traditional method is to use a back reflector that is located on the opposite side of the cardboard layer 130 relative to the surface 131 to which IR is applied. In this case, the back reflector will reflect most of the incident IR, which will then radiate back through the cardboard layer 130 and evaporate more solvent S31. However, the drying process using the back reflector to reflect IR may have defects related to the reduction of the moisture content in the printed cardboard layer 130. The high radiation intensity passing through the cardboard layer 130 will not only remove the moisture in various inks on the printed surface 131 but also the moisture in the cellulose-based cardboard layer 130, which may lead to various problems related to the performance of the laminated packaging material web 100. The laminated packaging material web 100 containing the cardboard layer 130 with reduced moisture content may have problems related to cracks (especially in the areas where multiple crease lines intersect) and delamination of the laminated packaging material 100, as well as problems related to the integrity of the final packaging container.

[0059] As Figure 2 shown, the method according to the present invention instead includes absorbing IR by an absorption surface 400. Thus, instead of being reflected back through the cardboard layer 130, most of the transmitted radiation is absorbed by the absorption surface 400. It has been proven that providing the absorption surface 400 is a simple and economical way to protect the cardboard layer 130 from significant moisture loss.

[0060] The spectral emission range of the IR can be between 0.4 μm and 4 μm, and the absorption surface 400 can be configured to absorb radiation in the same range. For example, less than 1% of the reflected light in a specific range. Preferably, less than 0.5% of the radiation in the wavelength range of 0.4 μm to 4 μm is reflected by the absorption surface 400. The absorption surface 400 can be black, other colors, or transparent. The absorption surface 400 can also have a topology with extremely low reflectivity in the wavelength spectrum of 0.4 μm - 4 μm.

[0061] The absorption surface 400 can be treated to form a high absorber. The treatment can include chemically modifying the absorption surface 400 and / or depositing titanium nitride or oxides (such as tungsten oxide, indium tin oxide, or antimony tin oxide). The oxides can be doped or undoped. The treatment can additionally or alternatively include coating, glazing, painting, or applying a film, polymer sheet, and / or metal layer. Such treatment can include using particles, powders, nanoparticles, or other nanoscale structures, such as carbon nanotubes. Multiple surface layers can be stacked on the absorption surface 400.

[0062] As Figure 2Further shown, the absorption surface 400 can be supported by the plate 410, which means that the plate 410 can be coated, treated, painted, etc., and the absorption surface 400 can be defined as the coated or treated / painted surface of the plate. The plate 410 can comprise a material with high thermal conductivity, such as bauxite. The plate 410 can be used as a heat exchanger.

[0063] Figure 1 The method shown can also include removing heat S33 from the absorption surface. The step of removing heat S33 can be carried out by a cooling medium (such as a gas or a liquid), which preferably acts on the opposite side of the plate relative to the absorption surface. The plate 410 can include an increased surface area by, for example, including fins 420, thereby improving the heat transfer capacity. The plate 410 can be arranged near the cooling unit 270 or at least partially corresponding thereto, as further described below.

[0064] The method can also include: determining S20 an adjusted drying power based on the determined humidity parameter that indicates the moisture content of the cardboard 130; and the infrared radiation IR can be applied alone at the adjusted drying power, or the infrared radiation IR and the hot air HA can be applied simultaneously. The humidity parameter can be obtained by a sensor close to the cardboard layer 130. The sensor can be a thermal sensor, such as a pyrometer, and the humidity parameter can indicate the moisture content of the cardboard 130 by being associated with the temperature of the cardboard layer 130. The temperature can be obtained from the printing surface 131, the opposite side of the cardboard layer 130, or the area therebetween. Preferably, the temperature is obtained from an area of the cardboard layer 130 that is not directly exposed to IR or hot air HA during the measurement process. The adjusted drying power can be determined to keep the desired temperature of the cardboard layer 130 within a certain range. For example, the required cardboard temperature can be below 65 °C, below 60 °C, or preferably around 55 °C to 56 °C.

[0065] The adjusted drying power can be determined separately for the infrared radiation IR and the hot air HA such that the application ratio of the infrared radiation IR and the hot air HA is based on the determined humidity parameter. For example, the ratio between IR and hot air HA can be determined by minimizing the amount of infrared radiation IR while still ensuring complete drying within the required drying time and maintaining the required humidity parameter, thereby maintaining the moisture content of the cardboard 130. The required drying time can be defined as the total time that the cardboard layer 130 is arranged at a specific part of the production line (such as the drying station 230 or the extended section between the inkjet printing position and other processing equipment arranged downstream of the drying station).

[0066] As Figure 1As shown, the method may further include: providing a crease line pattern on the cardboard layer 130, preferably after the printing S10 and drying S30 steps. The crease line pattern facilitates the formation of a packaging container from the laminated packaging material web 100 (not shown in the figure). The crease line pattern may be repeated in the machine direction. The machine direction may be defined as the direction parallel to the movement direction of the cardboard layer 130 through the manufacturing equipment (such as the converting unit 200), or as the circumferential direction of the paper roll for providing the cardboard layer 130. The laminated packaging material web 100 may have a machine direction and a cross direction, and the cross direction is defined as the direction perpendicular to the machine direction. The dimension of the laminated packaging material web in the machine direction may be significantly larger than the dimension in the cross direction. In this method, the cardboard layer 130 may be conveyed at a substantially constant speed along the machine direction defined above. Figure 3 An example path of the cardboard layer 130 passing through the converting unit 200 is shown by a solid line, where the arrow points to the machine direction.

[0067] Although not shown in the figure, the method may further include laminating at least another layer to the printed and creased cardboard layer 130. The laminated packaging material web 100 may include, for example, two sealable layers, one on the outer side of the laminated packaging material web 100, corresponding to the printed surface 131 on the cardboard layer 130, to form the outer or outer layer of the packaging container formed by the laminated packaging material web 100; the other on the inner side of the laminated packaging material web 100 to be in direct contact with the filled food in the packaging container. The sealable layer is preferably liquid-tight. The sealable layer may be heat-sealed or may contain a thermoplastic material. In addition, a barrier layer may be laminated to the cardboard layer 130, preferably on the opposite side of the printed surface 131. The barrier layer may be composed of any barrier material suitable for maintaining a food safety environment for the liquid food in the package. This includes metals (such as aluminum foil), polymer materials (such as ethylene-vinyl alcohol copolymer (EVOH) or polyamide (PA)), polysaccharides (such as starch or fibrous or crystalline cellulose), and polymer-based film substrates with barrier coatings; the barrier coatings are selected from metals, metal oxides, inorganic oxides, other inorganic compounds, or carbon-based coatings (such as amorphous diamond-like carbon (DLC) coatings). The barrier layer may be a cellulose-based material and / or a composite material or a multi-layer coating material, such as including a non-metallic material (such as plastic, paper, or cellulose-based material) and a metallic material (such as including aluminum).

[0068] As described above, before the inkjet printing step S10, the printing substrate layer 140 can be arranged S5 between the cardboard layer 130 and the printing surface 131 on the cardboard layer 130. Applying the printing substrate layer 140 can include, for example: coating a pre - coating on the cardboard layer 130; priming the cardboard layer 130 by plasma treatment, flame treatment, corona treatment; or applying a surface conditioner to adjust the surface, for example, changing the topology, surface tension, wettability, electrostatic - related properties or other surface properties. In a specific embodiment, the printing substrate layer can be a clay coating or a primer clay coating, for example, for changing the surface properties of the cardboard. Generally, the clay coating forms a waterproof surface on the printing surface 131, which means that the solvent in the plurality of ink droplets cannot migrate into the cardboard layer 130. This requires higher drying power because it is crucial to quickly dry the ink droplets 300 before subsequent downstream processes. The printing substrate layer can comprise a polymer film or a metallized polymer film. These alternatives also form a waterproof surface on the cardboard layer, which means that the solvent in the ink cannot migrate into the cardboard layer. This requires higher drying power because it is crucial to quickly dry the ink before subsequent downstream processes. The printing substrate layer can completely cover the cardboard layer 130, or can only cover the area to be covered by the plurality of ink droplets 300, or can cover a medium - sized area of the cardboard layer 130. If necessary, the method can also include drying the printing substrate layer before the printing surface 131. Specifically, if the printing substrate layer comprises a certain coating, this drying can include exposing the printing substrate layer to IR.

[0069] Although Figure 2 not explicitly shown in Figure 1 After the method shown, the moisture content of the cardboard layer 130 of the laminated packaging material web 100 should be 4% or higher, between 5% and 10%, or preferably between 5% and 8.5%. After the above - mentioned method, the moisture content of the cardboard layer 130 may not be significantly lower than the moisture content provided before performing the steps of the method. For example, before the drying step S30 of the printing surface 131, the moisture content provided by the cardboard layer 130 can be between 6% and 8.5%. This means that the degree of moisture loss of the cardboard layer 130 of the laminated packaging material web 100 does not reach the level that causes any defects in the cardboard layer 130, thus ensuring the quality of the final product.

[0070] Now turning to Figure 3 , a converting unit 200 for manufacturing the laminated packaging material web 100 is shown schematically in the figure. The converting unit 200 can be configured to perform the above - mentioned reference Figure 1The described method 1, and all aspects disclosed with respect to method 1 are also applicable to the conversion unit 200, and vice versa. The conversion unit 200 includes a feeding unit 210 configured to continuously convey the cardboard layer 130, preferably at a constant speed and / or in the machine direction as defined above. The conversion unit 200 further includes an inkjet printer 220 configured to print a plurality of ink droplets 300 containing colorant and solvent on the printing surface 131 of the cardboard layer 130. The inkjet printer 220 is shown in the figure as a support roller and a plurality of print heads for cyan C, magenta M, yellow Y, and black K. It should be noted that the specific configuration of the inkjet printer 220 may vary depending on the specific application; for example, the inkjet printer 220 may include a plurality of print heads arranged in the machine direction and / or the cross direction to cover the entire width of the cardboard layer 130. The conversion unit 200 may also include a printing substrate station (not shown) located before the inkjet printer 220, and the specific location can be referred to method 1 explained above.

[0071] The conversion unit 200 further includes a drying station 230 configured to dry the ink 300 by exposing the printing surface 131 on the cardboard layer 130 to infrared radiation IR. The drying station 230 may also be configured to dry the plurality of ink droplets 300 by exposing the cardboard layer 130 to hot air HA. The drying station 230 may include a hot air dryer 232 different from the infrared dryer 231, and the hot air dryer 232 may be arranged downstream of the infrared dryer 231.

[0072] The infrared dryer 231 may be arranged to extend in the cross direction and span the cardboard layer 130. The infrared dryer 231 may include a plurality of dryers. The control unit 260 may be programmed to control the operation of each dryer.

[0073] The drying station 230 further includes an absorption surface 400 arranged on the opposite side of the cardboard layer 130 relative to the printing surface 131. The absorption surface 400 is configured to absorb at least a portion of the infrared radiation IR transmitted through the cardboard layer 130, and as Figure 2 visible, also absorb the IR directly irradiating the outer absorption surface 400 of the cardboard layer 130 to minimize the secondary reflection to the opposite side of the cardboard layer 130 relative to the printing surface 131. The drying station 230 may also include an emission reflector located on the opposite side of the infrared dryer 231 relative to the cardboard layer 130.

[0074] The conversion unit 200 may further include a cooling unit 270 for removing heat from the absorption surface 400. The cooling unit 270 may include a heat exchanger and / or heat dissipation fins 420 (see Figure 2 ). The cooling unit 270 may be associated with Figure 2The shown board 410 is connected to, includes, or is synonymous with the board. The cooling unit 270 may include, for example, a coated ore on bauxite or any other highly thermally conductive material, which may act as a heat exchanger, and heat may be dissipated from the absorption surface 400 using air or other media (such as gases or liquids). The cooling unit 270 may include heat dissipation fins 420, that is, to increase the absorption surface area into another material (such as the board 410), thereby improving the heat transfer capacity.

[0075] The conversion unit 200 may further include: a creasing station 240 configured to provide a crease line pattern to the cardboard layer 130; and / or at least one laminating station configured to laminate at least one other layer onto the cardboard layer 130.

[0076] The conversion unit 200 may further include: a sensor unit 250 operatively connected to the control unit 260, and the sensor unit 250 may be configured to sense a humidity parameter indicating the moisture content of the cardboard 130 and send a signal related to the humidity parameter to the control unit 260. The control unit 260 is operatively connected to the drying station 230 and may be configured to adjust the drying power in response to the signal related to the humidity parameter. In particular, the control unit 260 is configured to control the power of the infrared dryer 231 based on the output from the sensor 250.

[0077] In one embodiment, the sensor unit 250 is configured to measure the surface temperature of the cardboard 130 (preferably at the printing surface 131). Then, the surface temperature is controlled by the control unit 260 not to exceed a predetermined threshold, thereby also indirectly controlling the moisture content of the cardboard 130.

[0078] From the above description, it can be seen that although various embodiments of the present invention have been described and shown, the present invention is not limited thereto and can also be implemented in other ways within the scope of the subject matter defined by the claims.

Claims

1. A continuous on-line method for producing a web of packaging material (100), which comprises: inkjet printing (S10) a plurality of ink droplets (300) containing a colorant and a solvent onto a printing surface (131) of a cardboard layer (130); drying (S30) the plurality of ink droplets (300) printed onto the cardboard layer (130) such that the colorant is fixed, wherein the drying (S30) is carried out by: evaporating (S31) at least part of the solvent by applying infrared radiation (IR) to the printing surface (131); and absorbing (S32) the infrared radiation (IR) transmitted through the cardboard layer (130) by an absorption surface (400) disposed on the opposite side of the cardboard layer (130) relative to the printing surface (131).

2. The method according to claim 1, wherein, the absorption surface (400) is treated to form a high absorber.

3. The method according to any one of the preceding claims, the method further comprises: providing (S40) a crease line pattern to the cardboard layer (130).

4. The method according to claim 3, wherein, the steps of inkjet printing (S10), drying (S30) and providing (S40) the crease line are continuous and carried out in that order.

5. The method according to any one of the preceding claims, wherein, drying (S30) further comprises: applying hot air (HA) to the printing surface (131).

6. The method according to claim 5, wherein, the hot air (HA) is applied after the infrared radiation (IR).

7. The method according to any one of the preceding claims, which further comprises: determining (S20) an adjusted drying power based on a determined humidity parameter indicating the moisture content of the cardboard (130), and wherein the infrared radiation (IR) and / or hot air (HA) is applied at the adjusted drying power.

8. The method according to claim 7 when dependent on claim 5 or 6, wherein, the adjusted drying power is determined separately for the infrared radiation (IR) and the hot air (HA) such that the infrared radiation (IR) and hot air (HA) are applied at a ratio based on the determined humidity parameter.

9. The method according to any one of the preceding claims, wherein, the spectral emission range of the infrared radiation (IR) is between 0.4 μm - 4 μm, and wherein the absorption surface (400) is configured to absorb radiation in the same range.

10. The method according to any one of the preceding claims, which further comprises: removing heat (S33) from the absorption surface (400).

11. A converting unit (200) configured to continuously produce a web of laminated packaging material (100), which comprises: a feeding unit (210) configured to continuously convey a cardboard layer (130); An inkjet printing press (220) configured to print a plurality of ink droplets (300) containing a colorant and a solvent on a printing surface (131) of the cardboard layer (130); and a drying station (230) configured to dry the ink (300) by exposing the printing surface (131) to infrared radiation (IR), wherein the drying station (230) further includes an absorption surface (400) disposed on an opposite side of the cardboard layer (130) relative to the printing surface (131), the absorption surface (400) being configured to absorb at least a portion of the infrared radiation (IR) transmitted through the cardboard layer (130).

12. The conversion unit (200) according to claim 11, further comprising a sensor unit (250) and a control unit (260) operatively interconnected. wherein the sensor unit (250) is configured to sense a humidity parameter indicative of the moisture content of the cardboard (130) and send a signal related to the humidity parameter to the control unit (260), and wherein the control unit (260) is operatively connected to the drying station (230) and is configured to adjust the drying power in response to the signal related to the humidity parameter.

13. The conversion unit (200) according to claim 11 or 12 wherein the drying station (230) is further configured to dry the plurality of ink droplets (300) by exposing the cardboard layer (130) to hot air (HA).

14. The conversion unit (200) according to any one of claims 11-13, further comprising a cooling unit (270) configured to remove heat from the absorption surface (400).

15. The conversion unit (200) according to claim 14 wherein the cooling unit (270) includes a heat exchanger and / or a plurality of heat dissipation fins.

16. The conversion unit (200) according to any one of claims 11-15, further comprising a creasing station (240) configured to provide a crease line pattern to the cardboard layer (130).

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