Method and apparatus for printing on paper material

Abstract

Method (100) of printing on containers (1) for food products, said method (100) comprising at least the following steps: preparing (101) a container (1) for food products, said container (1) comprising at least one layer made of paper material, and performing a printing procedure (102) on said container (1) to define a graphic pattern (GP). The printing procedure (102) comprises emitting (103) a laser beam (21) on said container (1) by means of a laser emitter (20), wherein said laser beam (21), during the printing procedure, impinges on said layer in paper material to define said graphic pattern (GP) on said layer in paper material.

Description

[0001] 'Method and apparatus for printing on paper material'

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method of printing by means of a laser beam on paper material, to a respective laser beam printing apparatus and to a container made of paper material for foodstuffs comprising a print made by means of said method and / or said printing apparatus.

[0004] STATE OF THE ART

[0005] Containers made of paper material are known in the food industry to hold food products, e.g. baked goods such as pandoro, panettone, muffins or similar.

[0006] Such containers may comprise one or more layers of foil material so as to be easily recyclable or compostable. State-of-the-art containers may also comprise a plastic coating to make the container substantially impermeable to liquids: this plastic layer may include polyethylene, which is used to create what is known as polyethylene-coated paper. Such a coating offers several advantages, such as impermeability, resistance to grease and consequently a longer life of the container.

[0007] State-of-the-art containers may be used to define a food product mould, especially for baked goods. In such a case, the process of making the food product may involve placing a substantially raw food product in the mould, and then placing the mould in the oven to bake the food product, e.g. for confectionery products such as pandoro, panettone, muffins or the like.

[0008] Containers made of paper material may have graphic prints on their surface. Graphic prints may bear logos, lettering or designs of an aesthetic nature.

[0009] In more detail, the state of the art is to print the paper material inline, in which the paper material is presented in a flat form. The paper material can be wound into large reels and unwound along a feed line along which the printing process takes place: the paper material is then moved from an upstream station, comprising the paper material feed reel, to and through a printing station. The printing stations, in the case of inline printing, can be fixed in position or mobile along a direction transverse to the direction of the paper material feed. Such printing processes are commonly referred to as inline printing processes, in which the paper material in flat form is moved while the printing station is fixed in position.

[0010] The Applicant points out that inline printing techniques offer on the one hand a high printing speed, but on the other hand are extremely rigid, offering a limited ability to customise the print motif. In other words, inline printing performs very well when it is necessary to put identical graphic prints on a large number of products: however, the inline printing technique does not lend itself well to repeatedly varying the logo, lettering or design to be placed on the product in paper material. Furthermore, inkjet and laser printing technologies are mainly used to print on paper or cardboard. Inkjet printers print by spraying ink onto the paper, while laser printers print by letting the surface of the paper absorb the toner ink. Printing inks contain some harmful organic compounds, such as polycyclic aromatic hydrocarbons and dimethylaniline, which are carcinogenic, and studies have shown that particles released from printers during use can irritate the mouth, eyes, nose and throat of the human body, and long-term exposure to large numbers of particles can cause liver and lung damage.

[0011] US20140099267A1 discusses an ink formulation designed for marking substrates like packaging materials. The ink includes reduced indium tin oxide (r-ITO) which serves as a NIR-absorber, enabling markings using a NIR laser. This technology is particularly useful for integrating into existing production lines because of the compact nature of NIR systems compared to mid-IR systems. The ink formulation can be applied to various substrates such as paper, cardboard, and plastic films. When exposed to NIR radiation, the ink enables visible markings, ideal for product coding and labelling, especially in high-speed production environments.

[0012] US2023211624, US2020148907, US2016168407, and US2006090868 primarily discuss various technologies and methods related to marking and printing on materials using specific compounds that react to certain types of light, such as near-infrared (NIR) or ultraviolet (UV) light, to create durable and visible markings.

[0013] AIM OF THE INVENTION

[0014] The aim of the present invention is therefore to solve at least one of the drawbacks and / or limitations of the previous solutions. A first objective is to make printing operations on paper material more flexible. A further object is to make it possible to print on a container made of preformed paper material, i.e. on a three-dimensional container having the shape of a mould for food use. A further objective is to allow each pre-formed container to be customised with a different graphic print. A further objective is to provide a printing method and apparatus compatible with the food sector, in particular compatible with regulations to prevent contamination of the food product to be inserted or already contained in the container to be printed. Furthermore, it is an objective to avoid the use of inks by eliminating associated health and environmental problems, offering a cleaner and more sustainable solution than traditional ink-based printing. A further goal is to provide a printing method and apparatus that enables fast and cost-effective printing. A further aim is to provide a printing method and apparatus that allows the structural characteristics of the container to be maintained. These purposes and others, which will be more apparent from the following description, are substantially achieved by a printing method and apparatus in accordance with one or more of the following claims and / or aspects. SUMMARY

[0015] In a first aspect, a method (100) of printing on containers (1) for foodstuffs is provided for, comprising at least the following steps:

[0016] • provide (101 ) a container (1 ) for foodstuffs;

[0017] • perform a printing procedure (102) on said container (1) to define a graphic pattern (GP), said printing procedure (102) comprising emitting (103) a laser beam (21) on said container (1) by means of a laser emitter (20).

[0018] In a 2nd aspect, a method (100) of printing on a layer of paper material is provided, said method (100) comprising at least the following steps:

[0019] • provide (101 ) a layer of paper material;

[0020] • perform a printing procedure (102) on said layer to define a graphic pattern (GP), said printing procedure (102) comprising emitting (103) a laser beam (21) on said layer in paper material by means of a laser emitter (20).

[0021] Containers (1) are baking (oven) moulds made of paper material for food products.

[0022] In a 3rd aspect according to any of the above aspects, the printing procedure is an inkless printing procedure.

[0023] In a 3bis aspect according to any of the preceding aspects, an energy of the laser beam is absorbed by the paper-material layer in the form of excitation of atomic electron vibrations or and at least in part the energy of the laser beam is converted into thermal energy, in particular the absorption of an increasing amount of energy, increases a local temperature of the paper-material layer and causes a carbonisation reaction to fade the surface, thus resulting in an ink-free print.

[0024] In a 3rd aspect according to any of the preceding aspects, said container (1) comprises at least one layer of paper material.

[0025] In a 4th aspect according to any of the preceding aspects, said laser beam (21), during the printing process, impinges on said paper material layer to define said graphic pattern (GP) on said paper material layer.

[0026] In a 5th aspect according to any of the above aspects, said container (1) is made of paper material.

[0027] In a 5A aspect according to any of the above aspects, the paper material is resistant up to a maximum temperature of 300°, optionally up to 250°.

[0028] In aspect 5B according to any of the above aspects, the paper material is suitable for contact with foodstuffs during their cooking, e.g. baking.

[0029] In a 6th aspect according to any one of the preceding aspects, at least 85% by weight, and optionally at least 88% by weight, of the container (1) is of paper material. In a 7th aspect according to any of the previous aspects, said paper material is suitable for contact, optionally direct contact, with foodstuffs.

[0030] In an 8th aspect according to any of the previous aspects, said paper material comprises cellulose fibres in a concentration of between 75% and 95% by weight.

[0031] In a 9th aspect according to any of the previous aspects, said paper material comprises cellulose fibres in a concentration between 85% and 90%.

[0032] In a 10th aspect according to any of the above aspects, said paper material contains cellulose fibres at a concentration of approximately 88%.

[0033] In an 11th aspect according to any of the preceding aspects, said paper material comprises filler material in a concentration of less than 3% by weight, optionally less than 1 % by weight.

[0034] In a 12th aspect according to any of the preceding aspects, said paper material does not include filler material.

[0035] In a 13th aspect according to any one of the two preceding aspects, said filler material comprises at least one among:

[0036] - calcium carbonate;

[0037] - starch optionally including amylose and amylopectin;

[0038] - talc;

[0039] - kaolinite or Kaolin, chemical composition Al2Si2Os(OH)4).

[0040] In a 14th aspect according to the previous aspect, calcium carbonate has the chemical composition CaCOs.

[0041] In a 15th aspect according to any of the two previous aspects, starch has the chemical composition CeHioOsJn where 'n' represents the number of glucose units repeated in the polymer chain.

[0042] In a 16th aspect according to any of the three previous aspects, talc has the chemical composition Mg3Si 0io(OH)2.

[0043] In a 17th aspect according to any of the four previous aspects, kaolinite or kaolin has the chemical composition Al2Si2Os(OH)4.

[0044] In an 18th aspect according to any of the above aspects, said paper material comprises an additive concentration of less than 10% by weight, optionally less than 8% by weight.

[0045] In a 19th aspect according to the previous aspect, said concentration of additives is between 5% and 7% by weight.

[0046] In a 20th aspect according to any of the aspects above, said paper material comprises a concentration of additives substantially equal to 6%.

[0047] In a 21st aspect according to any of the three previous aspects, these additives include at least one of retention agents, dyes, and materials for surface treatment of the paper material. In a 22nd aspect according to the previous aspect, said additives comprise retention agents comprising at least one of polyacrylamides, polyacrylates, starch and alum.

[0048] In a 23rd aspect according to any of the two preceding aspects, said additives comprise materials for surface treatment of the paper material, said materials for surface treatment comprising at least one of paraffin, natural wax, polyethylene layer, PLA (polylactic acid) layer, silicone, water-based resins.

[0049] In a 24th aspect according to any one of the three preceding aspects, said additives comprise at least one of a colouring agent (10), said at least one of a natural colouring agent (10), an organic colouring agent (10), a direct colouring agent (10) comprising azo dyes, vegetable carbon, mineral pigments optionally comprising iron oxide.

[0050] In a 25th aspect according to the previous aspect, said paper material comprises a concentration of said dyes between 1% and 3% by weight.

[0051] In a 26th aspect according to the previous aspect, said dye concentration is essentially 2% by weight.

[0052] In a 27th aspect according to any of the above aspects, said paper material comprises water in a concentration of between 4% and 8% by weight, optionally between 5% and 7%.

[0053] In a 28th aspect according to any of the above aspects, said paper material comprises water in a concentration of essentially 6%.

[0054] In a 29th aspect according to any of the above aspects, the paper material is a supercalendered paper.

[0055] In a 30th aspect according to the previous aspect, said supercalendered paper is made by a respective mechanical calendering process comprising a step in which the paper passes through calendered cylinders or rollers configured to apply pressure and heat to the surface of the paper material.

[0056] In a 31st aspect according to any of the above aspects, the paper material has a grammage between 60 g / m2and 95 g / m2.

[0057] In a 32nd aspect according to any of the previous aspects, the paper material is produced without the use of post-consumer recycled paper material.

[0058] In a 33rd aspect according to any of the preceding aspects, said container (1) comprises at least one dye (10) defining a respective colour of the container (1).

[0059] In a 34th aspect according to the preceding aspect and / or according to aspect 24, said laser beam (21), during the printing procedure, impinging on said dye (10) of the container (1).

[0060] In a 35th aspect according to any one of the two preceding aspects, said paper material comprises a concentration of said at least one dye (10) between 1 % and 3% by weight, optionally said concentration being substantially 2% by weight.

[0061] In a 36th aspect according to any one of the three preceding aspects, said dye (10) comprises at least one of a natural dye (10), an organic dye (10), a direct dye (10) comprising azo dyes, vegetable charcoal, mineral pigments optionally comprising iron oxide. In a 37th aspect according to any of the four previous aspects, said dye (10) comprises an azo dye (10).

[0062] In a 38th aspect according to any of the previous five aspects, said dye (10) comprises an organic dye (10).

[0063] In a 39th aspect according to any of the previous six aspects, said dye (10) comprises a natural dye (10). In a 40th aspect according to any of the seven aspects above, said at least one dye (10) includes direct dyes including azo dyes.

[0064] In a 41st aspect according to any of the preceding aspects, said at least one dye (10) has a brown colour.

[0065] In an aspect 41 A according to any of the three aspects above, the paper material layer has a wavy surface including valleys and ridges, said paper material layer defining a corrugated paper material layer.

[0066] In an aspect 41 B according to the preceding aspect, the printing procedure (102) involves emitting (103) the laser beam (21) on said corrugated surface to define the graphic pattern (GP) on said corrugated surface.

[0067] In a 41 C aspect according to any of the two previous aspects, the wavy surface comprises the dye (10).

[0068] In a 42nd aspect according to any of the preceding aspects, the paper material of said container (1) comprises:

[0069] • a first layer (5) intended for food contact, and

[0070] • a second layer (4) attached to and facing the first layer (5), said second layer (4) defining at least part of an outer surface of the container (1 ).

[0071] In a 43rd aspect according to the previous aspect, said second layer (4) includes said colouring agent (10).

[0072] In a 44th aspect according to any of the two previous aspects, the first layer (5) has a substantially smooth surface.

[0073] In a 45th aspect according to any of the three previous aspects, the second layer (4) presents an undulating surface comprising valleys and ridges, in which each valley contacts said first layer (5) and each ridge rises away from said first layer (5).

[0074] In a 46th aspect according to the previous aspect, said laser beam (21), during the printing procedure, is directed at said corrugated surface.

[0075] In a 47th aspect according to any of the previous five aspects, said second layer (4) defines a corrugated paper layer.

[0076] In a 48th aspect according to any one of the preceding aspects 42 to 47, the container (1) comprises a waterproof and / or non-stick coating applied to said first layer (5), wherein said first layer (5) is interposed between said coating and said second layer (4).

[0077] In a 49th aspect according to the previous aspect, said coating comprises one of a polyethylene film, a wax layer or a paraffin layer. In a 50th aspect according to any of the two preceding aspects and in combination with aspect 23, said coating comprises said surface treatment material.

[0078] In a 51st aspect according to any of the preceding aspects 42 to 50, the first layer (5) faces the container containment volume (1).

[0079] In a 52nd aspect according to any one of aspects 42 to 51 above, the second layer (4) comprises a paper material in accordance with any one of aspects 1 to 41 .

[0080] In a 53rd aspect according to any one of aspects 42 to 51 above aspects, the second layer (4) comprises a dye (10) according to any one of aspects 24 to 26 and / or 33 to 41 above.

[0081] In a 54th aspect according to any one of aspects 42 to 53 above aspects, the first layer (5) comprises cellulose fibres in a concentration of between 80% and 97% by weight, optionally between 89% and 95%. In a 55th aspect according to the previous aspect, the first layer (5) comprises cellulose fibres in a concentration of essentially 91 %.

[0082] In a 56th aspect according to any one of aspects 42 to 55 above aspects, the first layer (5) of paper material comprises filler material in a concentration of less than 3% by weight, optionally less than 1 % by weight.

[0083] In a 57th aspect according to any of the preceding aspects 42 to 56, said first layer (5) of the paper material does not include filler material.

[0084] In a 58th aspect according to any one of the two preceding aspects, said filler material comprises at least one among:

[0085] - calcium carbonate;

[0086] - starch optionally including amylose and amylopectin;

[0087] - talc;

[0088] - kaolinite or Kaolin.

[0089] In a 59th aspect according to any one of the preceding aspects 42 to 58, said first layer (5) comprises a lower additive concentration than an additive concentration of the second layer (4).

[0090] In a 60th aspect according to any of the preceding aspects 42 to 59, said first layer (5) comprises an additive concentration of less than 6% by weight, optionally less than 4% by weight.

[0091] In a 61st aspect according to the previous aspect, said concentration of additives in the first layer (5) is between 1 % and 4% by weight.

[0092] In a 62nd aspect according to any of the two previous aspects, said concentration of additives is essentially 3%.

[0093] In a 63rd aspect according to any one of the preceding aspects 59 to 62, said additives comprise at least one of retention agents, dyes, materials for surface treatment of the first layer (5) of paper material. In a 64th aspect according to the previous aspect, said first-layer additives (5) comprise retention agents comprising at least one of polyacrylamides, polyacrylates, starch and alum.

[0094] In a 65th aspect according to any of the two preceding aspects, said additives of the first layer (5) comprise materials for the surface treatment of the paper material, said surface treatment materials comprising at least one of paraffin, natural wax, polyethylene layer, PLA (polylactic acid) layer, silicone, water-based resins.

[0095] In a 66th aspect according to any of the preceding aspects 63 to 65, said additives of the first layer (5) comprise at least one dye (10) in a concentration lower than a concentration of the dye (10) in the second layer (4).

[0096] In a 67th aspect according to the previous aspect, the concentration of dye (10) in the first layer (5) is less than half the concentration of dye (10) in the second layer (4).

[0097] In a 68th aspect according to any one of aspects 42 to 67 above, said first layer (5) of paper material comprises a concentration of said dyes of less than 1 % by weight.

[0098] In a 69th aspect according to any one of the preceding aspects 42 to 68, said dye (10) of the first layer (5) comprises at least one of a natural dye (10), an organic dye (10), a direct dye (10) comprising azo dyes, vegetable carbon, mineral pigments optionally comprising iron oxide.

[0099] In a 70th aspect according to any of the preceding aspects 42 to 69, said first layer (5) of paper material does not include dye (10).

[0100] In a 71st aspect according to any one of aspects 42 to 70 above, said paper material of the first layer comprises water in a concentration of between 4% and 8% by weight, optionally between 5% and 7%.

[0101] In a 72nd aspect according to the previous aspect, said paper material of the first layer comprises water in a concentration of essentially 6%.

[0102] In a 73rd aspect according to any one of the preceding aspects 42 to 72, the paper material of the first layer (5) is a supercalendered paper, said supercalendered paper being made by a respective mechanical calendering process comprising a step in which the paper passes through calendered cylinders or calendered rollers that apply pressure and heat to the surface of the paper material of the first layer (5).

[0103] In any of aspects 42 to 73 above, the paper material of the first layer (5) has a grammage between 60 g / m2and 95 g / m2.

[0104] In a 75th aspect according to any of aspects 42 to 74 above, the paper material of the first layer (5) is produced without use of post-consumer recycled paper material.

[0105] In a 76th aspect according to any of the preceding aspects 42 to 75, said laser beam (21), at least during the printing procedure, is directed towards the second layer. In a 77th aspect according to any one of the preceding aspects, said laser beam (21), at least during the printing procedure, is directed towards an outer surface of the container (1), optionally towards an outer surface of the second layer (4) of the container (1).

[0106] In an aspect 77bis according to any one of the preceding aspects, the paper material comprises cellulose, said laser beam (21), during the printing process, modifying or being configured to modify the cellulose, in particular to partially carbonise the cellulose by means of localised temperature increase. This partial carbonisation alters the colour of the cellulose and thus of portions of the paper material where the laser beam operated.

[0107] In a 77ter aspect according to any of the preceding aspects, said laser beam (21), during the printing process, does not modify or is not configured to modify chromatically said dye (10).

[0108] In a 77quater aspect according to any of the above aspects, the printing procedure is an inkless laser ablation printing technology acting through a thermal process.

[0109] In a 77quinques aspect according to any of the above aspects, the laser beam (21) irradiates the paper material layer, carbonising it by photothermal radiation in localised areas where the graphic pattern (GP) will be defined.

[0110] In an aspect 77sexties according to any one of the preceding aspects, wherein the laser beam (21), during the printing procedure, modifies or is configured to carbonise the irradiated paper-material layer due to photothermal radiation of the laser beam, leaving graphitised carbon on the paper-material layer, wherein the graphic pattern (GP) is formed on the paper-material layer due to thermal energy of the laser beam.

[0111] In an aspect 77octies according to any of the preceding aspects, wherein an analysis by Fourier transform infrared spectroscopy (FTIR) shows a characteristic absorption peak corresponding a stretching of the groups -OH, increased and in particular shifted from 3282 cm-1to 3334 cm-1for a layer in smooth paper material and from 3334 cm-1to 3346 cm-1for a layer in corrugated paper material.

[0112] In a 77novies aspect according to any of the above aspects, in which the layer of paper material in which the graphic pattern (GP) is made shows gaps and holes when characterised by scanning electron microscopy (SEM).

[0113] In a 78th aspect according to any of the preceding aspects, said laser beam (21), during the printing process, modifies or is configured to modify chromatically said dye (10).

[0114] In a 79th aspect according to any one of the preceding aspects, said laser beam (21), during the printing process, degrades or is configured to at least partially degrade said dye (10) from the container (1).

[0115] In an 80th aspect according to any one of the preceding aspects, said printing procedure results in a chromatic contrast on said container (1) between regions comprising said dye (10) subjected to the laser beam (21) and regions comprising said dye (10) not subjected to the laser beam (21), said chromatic contrast being defined as said graphic pattern (GP). In an 81st aspect according to any of the preceding aspects, said layer in paper material comprises said dye (10).

[0116] In an 82nd aspect according to any of the above aspects, said layer of paper material contains said dye (10).

[0117] In an 83rd aspect according to any of the preceding aspects, said layer of paper material extending in thickness between a first surface and a second surface, said dye (10) being dispersed in said layer of paper material between said first surface and said second surface.

[0118] In an 84th aspect according to the previous aspect, said dye (10) is absorbed by said layer in paper material.

[0119] In an 85th aspect according to any one of the preceding aspects in combination with at least aspect 42, said second layer (4) of paper material contains said dye (10), in particular wherein said dye (10) is absorbed by the paper material of the second layer.

[0120] In an 86th aspect according to any one of the preceding aspects, said laser beam (21), during the printing procedure, chromatically modifies said dye (10) by making said dye (10), in regions which have been subjected to said laser beam (21), lighter than regions comprising said dye (10) which have not been subjected to said laser beam (21).

[0121] In an 87th aspect according to any of the above aspects, said laser beam (21), during the printing process, chromatically modifies said dye (10) by reducing its saturation.

[0122] In an 88th aspect according to any of the above aspects, said laser beam (21), during the printing process, chromatically modifies said dye (10) by increasing a brightness of reflected light.

[0123] In an 89th aspect according to any of the above aspects, said laser beam (21), during the printing process, permanently changes said dye (10) chromatically.

[0124] In any of the above 90th aspects, during the printing process, the container (1) is held in place.

[0125] In a 91st aspect according to any of the preceding aspects, said method involves moving said containers (1) or a semi-finished product made of paper material along a manufacturing line through one or more processing stations, and where, during the printing process, the container (1) is stationary in position.

[0126] In a 92nd aspect according to any of the above aspects, the printing procedure involves moving the laser beam along a print region of the container to define the print pattern.

[0127] In a 93rd aspect according to any of the above aspects, where the laser beam is of the scanning type.

[0128] In a 94th aspect according to any one of the preceding aspects, said container (1) comprises at least one curved surface, the printing procedure comprising commanding said laser emitter (20) to direct the laser beam (21) along said curved surface.

[0129] In a 95th aspect according to the previous aspect, said curved surface defines a set of points having varying distances from the laser emitter (20). In a 96th aspect according to any one of the preceding aspects 94 and 95, the printing procedure comprises moving (104) said laser emitter (20) or at least one active component of the laser emitter (20) according to a curvature of said curved container surface (1).

[0130] In a 97th aspect according to the preceding aspect, said active component comprises at least one of one or more lenses of the laser emitter (20) and a laser source.

[0131] In a 98th aspect according to any one of aspects 96 to 97 above, the phase of moving (104) said laser emitter (20) or said active component of the laser emitter (20) is simultaneous with the phase of emitting the laser beam (21).

[0132] In a 99th aspect according to any one of the preceding aspects 96 to 98, the step of moving said laser emitter (20) or said active component of said laser emitter (20) comprises moving said laser emitter (20) or said active component of said laser emitter (20) closer to and further away from the curved surface of said container (1).

[0133] In a 100th aspect according to any one of the preceding aspects 94 to 99, during the printing procedure, said laser beam (21) is directed at said curved surface to define a printing area on said container (1), the printing procedure comprising moving said laser emitter (20) or said active component of said laser emitter (20) to compensate for a variation in distance between said laser emitter (20) and a region of said printing area.

[0134] In a 101st aspect according to any of the above aspects, said laser emitter (20) comprises a focusing mechanism configured to vary the position of a focus point of the laser beam (21).

[0135] In a 102nd aspect according to the preceding aspect, the printing procedure comprises controlling said focusing mechanism to vary the position of said focus point during an emission of said laser beam (21 ) in order to maintain said focus point substantially at the curved surface of the container (1).

[0136] In a 103rd aspect according to any of aspects 94 to 102 above, said curved surface has a radius of curvature between 2 cm and 20 cm, optionally between 6 cm and 13 cm.

[0137] In a 104th aspect according to any of the preceding aspects 94 to 103, said side wall (2) of the container (1) comprises said curved surface.

[0138] In a 105th aspect according to any one of the preceding aspects 94 to 104, during the printing procedure, said laser beam (21) impinges on said curved surface to define a printing area on said container (1), said printing area extending along said curved surface, said curved surface extending along:

[0139] - a first curved trajectory, and

[0140] - a second trajectory orthogonal to the first trajectory

[0141] In a 106th aspect according to the previous aspect, said second trajectory is a straight line.

[0142] In a 107th aspect according to any of the preceding aspects 105 to 106, the printing procedure involves: - i) perform a first laser pass by moving the laser beam (21) along the first trajectory, keeping the laser beam (21) fixed in position in relation to the second trajectory;

[0143] - (ii) move the laser beam (21) along the second trajectory and then perform (iii) a second laser pass moving the laser beam (21) along a further trajectory essentially parallel to the first trajectory while keeping the laser beam (21) fixed in position relative to the second trajectory.

[0144] In a 108th aspect according to the previous aspect, the printing procedure comprises of:

[0145] - (iv) move the laser beam (21 ) along the second trajectory and then perform (v) a third laser pass by moving the laser beam (21) along a new trajectory essentially parallel to the first trajectory while keeping the laser beam (21) fixed in position in relation to the second trajectory.

[0146] In a 109th aspect according to any one of the preceding aspects, said container (1) comprises at least one bottom wall (3), and at least one side wall (2) connected to and extending transversely from said bottom wall (3).

[0147] In a 110th aspect according to the previous aspect, said at least one bottom wall (3) and said at least one side wall (2) define a containment volume to accommodate the foodstuff.

[0148] In a 111th aspect according to any of the two previous aspects, said container (1) extends in height between the bottom wall (3) and a top edge (6) of the side wall (2).

[0149] In a 112th aspect according to the preceding aspect in combination with aspect 105, said first trajectory is substantially parallel to said top edge (6) of the container (1).

[0150] In a 113th aspect according to any of the four preceding aspects in combination with aspect 105, said first trajectory extends substantially parallel to the bottom wall (3).

[0151] In a 114th aspect according to any one of the preceding aspects 109 to 113, said laser beam (21), during the printing procedure, impinges on at least one of said at least one bottom wall (3) and said at least one side wall (2).

[0152] In a 115th aspect according to any one of the preceding aspects 109 to 114, said side wall (2) is curved, said laser beam (21), during the printing procedure, impinges on said side wall (2).

[0153] In a 116th aspect according to any of the above aspects, said container (1) has a shape in the group between cylindrical, conical, truncated cone or semi-spherical.

[0154] In a 117th aspect according to any of the above aspects, said laser beam (21), during the printing process, is directed at one container (1) at a time.

[0155] In a 118th aspect according to any of the preceding aspects, the printing procedure (102) involves commanding said laser emitter (20) to emit the laser beam (21) within a power range capable of causing a thermal decomposition or degradation process of the dye (10) of the container (1).

[0156] In an aspect 118A according to the preceding aspect, said decomposition or degradation process results in a chromatic contrast on the container (1) between areas containing the dye (10) that are exposed to the laser beam (21) and areas containing the dye (10) that are not exposed to the laser beam (21), said chromatic contrast defining the graphic pattern (GP).

[0157] In a 118B aspect according to the previous aspect, said decomposition or degradation process determines said colour contrast permanently.

[0158] In a 119th aspect according to any of the preceding aspects 118, 118A and 118B, said process of thermal decomposition or degradation comprises:

[0159] - if said container (1) includes natural dyes: o breaking chemical bonds within the dye molecule (10), optionally breaking carbon-carbon or carbon-oxygen bonds; and / or o formation of decomposition products including compounds such as amines and / or diazones.

[0160] In a 120th aspect according to any of the preceding aspects 118 to 119, said process of thermal decomposition or degradation comprises:

[0161] - if said container (1) includes azo dyes: o breaking of azo bonds, in particular the breaking of the azo functional group (-N=N-) consisting of two nitrogen groups joined by a double bond; and / or o formation of decomposition products including compounds such as aldehydes, ketones, anhydrides in the case of azo dyes.

[0162] In a 121st aspect according to any of the preceding aspects 118 to 120, said process of thermal decomposition or degradation comprises:

[0163] - in case said container (1) includes organic dyes: o breaking chemical bonds within the dye molecule (10), optionally breaking carbon-carbon or carbon-oxygen bonds; and / or o formation of decomposition products including compounds such as aldehydes, ketones, anhydrides.

[0164] In a 122nd aspect according to any of the preceding aspects 118 to 121 , said thermal decomposition or degradation process comprises setting said laser emitter at a laser beam power between 10 Watts and 50 Watts.

[0165] In an aspect 122A according to any one of the preceding aspects 118 to 122, said thermal decomposition or degradation process comprises setting said laser emitter at a laser beam power between 20 Watts and 30 Watts.

[0166] In a 123rd aspect according to any of the above aspects, said laser beam (21) has a power during said printing process of between 10 watts and 50 watts, optionally between 20 watts and 30 watts. In an aspect 123A according to any of the preceding aspects 118 to 123, said thermal decomposition or degradation process comprises setting a laser beam scanning speed between 2000 mm / s and 6000 mm / s, optionally between 3000 mm / s and 4000 mm / s.

[0167] In an aspect 123B according to the previous aspect, said thermal decomposition or degradation process includes setting the scanning speed of the laser beam to 3500 mm / s optionally± 10%.

[0168] In a 124th aspect according to any of the above aspects, during the printing process, said laser beam (21) has a scanning speed of between 2000 mm / s and 6000 mm / s, optionally between 3000 mm / s and 4000 mm / s.

[0169] In a 125th aspect according to the previous aspect, during the printing process, said laser beam (21) has a scanning speed of essentially 3500 mm / s optionally± 10%.

[0170] In an aspect 125A according to any of the preceding aspects 118 to 125, said thermal decomposition or degradation process comprises setting a laser beam pulse frequency between 50 kHz and 200 kHz, optionally between 70 kHz and 150 kHz, plus optionally between 90 kHz and 110 kHz.

[0171] In a 125B aspect according to the previous aspect, said thermal decomposition or degradation process includes setting the pulse frequency of the laser beam to essentially 100 kHz optionally± 10%.

[0172] In a 126th aspect according to any of the above aspects, said laser beam (21) has, during the printing process, a pulse frequency between 50 kHz and 200 kHz, optionally between 70 kHz and 150 kHz, plus optionally between 90 kHz and 110 kHz.

[0173] In a 127th aspect according to the previous aspect, said laser beam has a pulse frequency during the printing process of essentially 100 kHz.

[0174] In a 128th aspect according to any of the above aspects, during the printing procedure, a working distance is interposed between said laser emitter (20) and said container (1), said working distance being between 140 mm and 400 mm, optionally between 170 mm and 350 mm.

[0175] In an aspect 128A according to any of the above aspects, the laser emitter (20) is a CO2 laser emitter.

[0176] In a 128B aspect according to any of the above aspects, said laser beam (21) comprises light in an infrared frequency range.

[0177] In a 128C aspect according to any of the above aspects, said laser beam (21) has a wavelength between 10 microns and 11 microns, optionally 10.6 microns.

[0178] In a 129th aspect according to any of the above aspects, during the printing procedure, a working distance is interposed between said laser emitter (20) and said container (1), said working distance being between 189 mm and 300 mm.

[0179] A aspect 130 is directed to an apparatus (200) for printing on containers (1) for food products, said apparatus (200) comprising:

[0180] • at least one laser emitter (20) configured to emit a laser beam (21 ); • at least one holder (30) for one container (1 ) of foodstuffs;

[0181] • at least one control unit operationally connected to said laser emitter (20); in which said control unit is configured to execute the printing procedure (102) of the printing method (100) according to any of the above aspects.

[0182] In a 131st aspect according to the preceding aspect, said holder (30) is movable by rotation about its own axis of rotation (R), said holder (30) comprising at least one gripping portion (31) configured to receive and bind one container (1), optionally wherein a gripping portion (31) is configured to receive and bind one and only one container (1) at a time.

[0183] In a 132nd aspect according to the preceding aspect, said apparatus (200) comprises at least one motor operatively connected to said holder (30) and configured to rotate said holder (30) about said axis of rotation, said control unit is configured to:

[0184] • command a rotation of said motor to position said grip portion (31) at a printing station facing said laser emitter (20);

[0185] • stop a rotation of said motor to lock said grip portion (31) in said print station;

[0186] • carry out the printing procedure (102).

[0187] In a 133rd aspect according to any one of the preceding aspects 130 to 132, said apparatus (200) comprises a forming station configured to define a shape of the container (1), optionally to define the bottom wall (3) and side wall (2) of the container (1).

[0188] In a 134th aspect according to the preceding aspect, said apparatus (200) comprises a conveyor belt configured to move said containers (1) or a semi-finished product made of paper material from the forming station to at least the printing station.

[0189] An aspect 135 is directed to a container (1) for food products comprising a graphic pattern (GP) executed by means of a printing method (100) in accordance with any one of aspects 1 to 129 and / or by means of a printing apparatus (200) for printing in accordance with any one of aspects 130 to 134.

[0190] BRIEF DESCRIPTION OF THE DRAWINGS

[0191] Certain embodiments and aspects of the invention will be described herein with reference to the accompanying drawings, which are provided for illustrative purposes only and are therefore not limitative:

[0192] - Figure 1 is a perspective view of a container presenting a graphic pattern printed by the printing method of the present invention;

[0193] - Figure 2 is a further perspective view of a container presenting a graphic pattern printed by the printing method of the present invention; - Figure 3 is a cross-sectional view of the sheet material printable by the printing method of the present invention;

[0194] - Figure 4 is a cross-sectional view of sheet material printable by the printing method of the present invention and including a dye layer;

[0195] - Figure 5 is a sectional view of the paper sheet material printable by the printing method of the present invention and including dye dispersed within the paper material layer;

[0196] - Figure 6 is a schematic representation in side view of the laser emitter and container during the printing process;

[0197] - Figure 7 is a schematic representation, rotated 90° from the representation in figure 6, of the laser emitter and container during the printing process;

[0198] - Figure 8 shows a printing apparatus according to the present invention;

[0199] - Figure 9 shows a flow chart representing the main steps of the printing method;

[0200] - Figure 10 shows: (a) 'Novacarf laser printing on smooth black paper material and (b) 'Mota Milano' laser printing on corrugated brown paper material;

[0201] - Figure 11 shows the FTIR analysis of (a, b) smooth black paper material and (c, d) corrugated brown paper material;

[0202] - Figure 12 shows the SEM analysis of the surface of the smooth black paper material (a-d), the laser print area of the smooth black paper material (e-h), the surface of the wavy brown paper material (i-l) and the laser print area of the wavy brown paper material (m-p) at different magnifications;

[0203] - Figure 13 shows the SEM analysis of the laser print area of the smooth black paper material (a) and the laser print area of the corrugated brown paper material (b);

[0204] - Figure 14 shows the surface roughness properties of black and brown corrugated paper material; and

[0205] - Figure 15 shows the properties of water contact angle (a) and water absorption (b) of black and brown corrugated paper material.

[0206] DEFINITIONS AND CONVENTIONS

[0207] Note that in the present detailed description corresponding parts illustrated in the various figures are indicated by the same numerical references. The figures may illustrate the subject-matter of the invention by means of non-scaled representations; therefore, parts and components illustrated in the figures relating to the subject-matter of the invention may relate only to schematic representations.

[0208] Control units

[0209] The printing apparatus described and claimed herein may comprise at least one control unit for controlling the operating conditions of the apparatus itself and for controlling the steps of the relevant printing method. The control unit can be a single unit or consist of several separate control units depending on design choices and operational requirements.

[0210] The term control unit is understood to mean an electronic type component which may comprise at least one of: a digital processor (CPU), an analogue type circuit, or a combination of one or more digital processors with one or more analogue type circuits. The control unit can be "configured" or "programmed" to perform certain steps: this can be achieved in practice by any means that allows the control unit to be configured or programmed. For example, in the case of a control unit comprising one or more CPUs and one or more memories, one or more programs may be stored in appropriate memory banks attached to the CPU(s); the program(s) contain instructions which, when executed by the CPU(s), program or configure the control unit to perform the operations described in relation to the control unit. Alternatively, if the control unit is or includes analogue type circuitry, then the circuitry of the control unit may be designed to include circuitry configured, in use, to process electrical signals to perform the steps related to the control unit.

[0211] DETAILED DESCRIPTION

[0212] Printing method

[0213] A printing method 100 has been collectively referred to as a printing method using a laser emitter 20 capable of emitting a laser beam 21 to a paper substrate to be printed. The present printing method 100 can be used to provide graphic patterns GP, such as logos, lettering, and alpha numeric codes to a surface of the paper substrate to be printed.

[0214] The method 100 thus comprises a first step 101 of providing the paper product, and then performing a printing procedure 102 on the paper product to define the graphic pattern GP. The printing procedure 102 involves emitting a laser beam 21 onto the paper product using a laser emitter 20 to imprint the graphic pattern GP onto the paper product.

[0215] The paper product may be a container 1 for food products as shown in figures 1 and 2. In an embodiment not shown in the accompanying figures, the container 1 may have a flat shape, thus defining an essentially two-dimensional flat tray.

[0216] The container 1 may alternatively have a three-dimensional shape, i.e. have at least one bottom wall 3, and at least one side wall 2 connected to the bottom wall 3 and extending transversally from the bottom wall 3. The bottom wall 3 and the side wall 2 in combination define a containment volume capable of accommodating the foodstuff. The containment volume may have a capacity of between 0.1 litre and 4 litres, optionally between 1 litre and 3 litres. The food product may include a baked food product, e.g. a panettone, pandora, muffin or similar. In accordance with the design shape of figures 1 and 2, container 1 may have a truncated cone shape. Alternatively, the container may have a shape in the group between cylindrical, conical, or semi-spherical. Note that the printing procedure 102 allows the graphic pattern to be printed even if the container has a three-dimensional shape.

[0217] The container may include at least one curved surface: for example, according to Figures 1 and 2, side wall 2 defines the curved surface. The curved surface may have a radius of curvature between 2 cm and 20 cm, or between 2 cm and 13 cm. Bakery cake containers, e.g. for panettone and pandora, can have a radius of curvature between 6 cm and 13 cm.

[0218] Container 1 is made, at least in part, of paper material: in particular, at least 85% by weight, and optionally at least 88% by weight, of container 1 is made of paper material. The paper material of the container is food-grade paper, i.e. paper suitable for contact with food. The paper material can be in baking paper, i.e. paper resistant up to temperatures of 300°, optionally up to 250°. In particular, the paper material may be suitable for contact with foodstuffs during their cooking, e.g. during baking.

[0219] Below are the main characteristics of the paper material subject to the printing procedural 02, i.e. the paper material on which the laser beam is directed at to define the GP graphic pattern.

[0220] The paper material comprises water in a concentration of between 4% and 8% by weight, optionally between 5% and 7%. In an embodiment, the paper material comprises water in a concentration of essentially 6%.

[0221] The paper material may comprise cellulose fibres in a concentration of between 75% and 95% by weight, optionally between 85% and 90%. In one embodiment, the paper material may contain approximately 88% cellulose fibres.

[0222] In a preferred embodiment, the paper material does not include filler material, in order to make it suitable for contact with foodstuffs. The term filler material means at least one of the following compounds:

[0223] - calcium carbonate, having in particular the chemical composition CaCOs;

[0224] - starch comprising amylose and amylopectin, where the chemical composition of starch is CeHioOsn where 'n' represents the number of glucose units repeated in the polymer chain;

[0225] - talc having the chemical composition MgsSiziOioOFb;

[0226] - kaolinite or Kaolin having the chemical composition Al2Si2OsOH .

[0227] Optionally, the paper material comprises filler material in a concentration of less than 3% by weight, optionally less than 1 % by weight.

[0228] The paper material may comprise an additive concentration of less than 10% by weight, optionally less than 8% by weight. In more detail, the additive concentration of the paper material may be between 5% and 7% by weight. Optionally, the additive concentration of the paper material is substantially 6%.

[0229] Such additives may include retention agents, dyes, and surface treatment materials. Retention agents may include polyacrylamides, polyacrylates, starch and alum. Surface treatment materials for the paper material are designed to make the paper material waterproof and / or non-stick and may include paraffin, natural wax, a polyethylene layer, a polylactic acid PLA layer, silicone, and water-based resins.

[0230] The paper material further comprises at least one dye 10 defining a colour characteristic of the container on which the GP graphic pattern is printed. The dye 10 of the paper material may comprise a natural dye 10, an organic dye 10, a direct dye 10 comprising azo dyes, vegetable charcoal, or a mineral pigment comprising iron oxide. In an embodiment, the paper material may comprise any one of a natural dye 10, an organic dye 10, and a direct dye 10 comprising azo dyes. In a further specific but not limiting embodiment, the dye 10 comprises an azo dye.

[0231] The paper material can have a concentration of dye 10 between 1 % and 3% by weight.

[0232] Dye 10 in container 1 may be brown.

[0233] In the embodiment shown in Figure 4, the dye 10 may be affixed to a surface of the paper material, thereby defining a layer of dye material 10 distinct from the paper layer: the dye layer 10 is then adhered to the paper layer. In such a case, the paper material is interposed between the container containment volume and the dye layer 10.

[0234] In a further embodiment shown in Figure 5, the paper material may comprise the dye 10. In such a case, the dye 10 is absorbed by the paper material. In other words, specified that the paper material extends in thickness between a first surface and a second surface, the dye 10 is dispersed within the paper material between the first surface and the second surface. In this embodiment, a process for making the paper material involves mixing cellulose and dye 10 together to define a pasty material, which is subsequently laminated to make sheets of paper material.

[0235] Note that the laser beam 21 , during the printing procedure, impinges on the dye 10 described above to define the graphic pattern. In particular, the printing procedure 102 involves commanding the laser emitter 20 to emit the laser beam 21 towards the paper material comprising at least one of the above-mentioned dyes in order to define the graphic pattern.

[0236] The paper material can be a super calendered paper, i.e. a paper made by a respective mechanical calendering process. The calendering process comprises a step in which the paper passes through calendered cylinders or rollers that apply pressure and heat to the surface of the paper material. The calendering process improves the strength of the paper material. The calendering process can also make the paper material more resistant to the thermal stress of the laser beam 21 during the printing process 102.

[0237] The paper material may be between 60 g / m2and 95 g / m2.

[0238] It should also be noted that paper material can be produced without using post-consumer recycled material. In an embodiment not shown in the accompanying figures, the container 1 is defined by a single layer of paper material. This single layer may present a substantially smooth surface, or it may present a wavy shape to define a corrugated paper material. The laser procedure can be particularly advantageous when there is a need to print a graphic pattern on corrugated paper material.

[0239] Alternatively, as shown in the sectional view in Figure 3, the container 1 may comprise a first layer 5 intended for contact with the foodstuff and thus facing the containment volume, and a second layer 4 attached and facing the first layer 5, defining at least in part an outer surface of the container. The first layer 5 and the second layer 4 are both made of paper material. In detail, as expressed above with respect to the paper material, the first layer and the second layer comprise at least 85% by weight of paper material.

[0240] The second layer 4 may have an undulating surface comprising valleys and ridges, with each valley contacting the first layer 5 and each ridge rising away from the first layer 5. In fact, the second layer 4 defines a corrugated paper layer

[0241] The second layer 4 comprises paper material having the characteristics described above. Similarly, the second layer comprises dye 10 having the technical characteristics described above. In greater detail, figure 4 shows an embodiment in which the dye 10 is affixed on top of the second layer 4, defining a layer of dye 10, such that the second layer is interposed between the first layer 5 and the layer of dye 10. Figure 5 shows instead a further embodiment in which the dye 10 is dispersed within the second layer 4. In this case, therefore, the second layer 4 comprises the dye 10 itself: in fact, the dye 10 has been absorbed by the second layer 4 in paper material.

[0242] The printing procedure may then involve emitting the laser beam 21 on the corrugated surface of the second layer 4, defining the graphic pattern on it. In such a case, the printing procedure is then capable of defining the graphic pattern on the outer surface of the container 1 .

[0243] Instead, the first layer 5 may have a substantially smooth surface, as shown in Figure 3, suitable for contacting the foodstuff intended to be contained in the containment volume of the container 1 . The first layer 5 is made of paper material, wherein the latter may have substantially the same characteristics as those of the second layer. Alternatively, the first layer 5 may comprise a paper material having slightly different compositional characteristics than the characteristics of the second layer 4: in greater detail, the first layer 5 may differ from the second layer 4 in the concentration, or absence, of dye 10. In particular, the concentration of dye 10 in the first layer 5 may be lower than the concentration of dye 10 present in the second layer. In an embodiment, the dye 10 in the first layer 5 may be absent.

[0244] The main characteristics of the paper material of the first layer 5 are given below.

[0245] The first layer 5 may comprise cellulose fibres in a concentration of between 80% and 97% by weight, optionally between 89% and 95%, plus optionally substantially 91 %. The container 1 may comprise a waterproof and / or non-stick coating applied to the first layer 5 and facing the container containment volume: in such a case, the first layer 5 is interposed between the waterproof and / or non-stick coating and the second layer 4. The waterproof and / or non-stick coating may comprise paraffin, natural wax, a polyethylene layer, a polylactic acid PLA layer, silicone, or water-based resins. In a preferred embodiment, the first layer 5 of the paper material does not comprise filler material. The term filler material means at least one of the following compounds:

[0246] - calcium carbonate, having in particular the chemical composition CaCOs;

[0247] - starch comprising amylose and amylopectin, where the chemical composition of starch is CeHioOsn where 'n' represents the number of glucose units repeated in the polymer chain;

[0248] - talc having the chemical composition MgsSiziOioOH?;

[0249] - kaolinite or Kaolin having the chemical composition Al2Si2OsOH .

[0250] In an optional design, the first layer 5 of paper material comprises filler material in a concentration of less than 3 wt%, optionally less than 1 wt%.

[0251] The first layer 5 may comprise an additive concentration lower than an additive concentration of the second layer 4. The first layer 5 may comprise an additive concentration of less than 6% by weight, optionally less than 4% by weight. In greater detail, the additive concentration of the first layer 5 may be between 1 % and 4% by weight. Optionally, the concentration of additives in the first layer is substantially 3%.

[0252] Such additives may include retention agents, dyes, surface treatment materials for the first layer 5 of paper material. Retention agents may include polyacrylamides, polyacrylates, starch and alum. Materials for surface treatment of the paper material may include paraffin, natural wax, a layer of polyethylene, a layer of PLA polylactic acid, silicone, and water-based resins. In fact, the waterproof and / or non-stick coating described above includes such materials for the surface treatment of paper material.

[0253] The first layer 5 of the paper material does not include any dye to avoid contamination of the food contact. Alternatively, the first layer 5 may comprise dye 10 in a concentration less than a concentration of dye 10 in the second layer 4. In particular, the concentration of dye 10 in the first layer 5 may be less than half the concentration of dye 10 in the second layer 4. In detail, the concentration of dye 10 in the first layer may be less than 1 % by weight. The dye 10 of the first layer 5 may comprise a natural dye 10, an organic dye 10, a direct dye 10 comprising azo dyes, vegetable charcoal, or mineral pigments optionally comprising iron oxide. In detail, the dye 10 of the first layer 5 may comprise a natural dye 10, an organic dye 10, or a direct dye 10 comprising azo dyes. The paper material of the first layer 5 may be a super calendered paper made by a respective mechanical calendering process comprising a step in which the paper passes through calendered cylinders or calendered rollers that apply pressure and heat to the surface of the paper material. The paper material of the first layer 5 may have a grammage included between 60 g / m2and 95 g / m2. It should also be noted that the paper material of the first layer 5 may be produced without using post-consumer recycled paper material.

[0254] Printing procedure 102

[0255] As mentioned above, the printing procedure 102 involves emitting a laser beam 21 directed at container 1 , so as to define the GP graphic pattern.

[0256] The laser beam, when striking the dye 10 of the paper material, changes the surface appearance of the paper material, thereby defining the graphic pattern GP. In particular, in the case where the paper material comprises the dye 10, the laser beam 21 causes a process of thermal decomposition or degradation of the dye 10 of the container 1 when the latter is struck by the laser beam. In other words, the laser beam during the printing procedure 102 at least partially decomposes the dye 10 of the paper material, thereby changing its colour characteristic. Specifically, the laser beam can result in a reduction in the colour saturation of the dye 10: the contrast between the regions that have been hit by the laser beam compared to the regions that have not been hit by the laser beam generates the graphic pattern GP shown in Figures 1 and 2. In fact, the laser beam 21 , during the printing procedure, chromatically modifies the dye 10 by making the dye 10, in the regions that have been hit by the laser beam 21, lighter than the regions of the dye 10 that have not been hit at the laser beam 21. In detail, the laser beam 21 , during the printing procedure 102, can chromatically modify the dye 10 by reducing its saturation and increasing a brightness of reflected light, thereby making the colour expressed by the dye 10 lighter than the colour of the dye 10 not affected by the laser beam. For example, in the case of a brown azo dye, the laser beam 21 makes the shade of brown lighter in the regions affected by the laser beam, while maintaining the colour appearance of brown in those regions. In fact, therefore, the printing procedure 102 of the present invention can only change the colour saturation and / or reflected brightness.

[0257] In greater detail, in the case of natural dyes, the process of thermal decomposition or degradation comprises the breaking of chemical bonds within the dye molecule 10, for example the breaking of carboncarbon or carbon-oxygen bonds. The process of thermal decomposition or degradation may further or alternatively comprise the formation of decomposition products comprising compounds such as amines and / or diazones.

[0258] In the case of azo dyes, the process of thermal decomposition or degradation comprises the breaking of azo bonds, in particular the breaking of the azo -N=N- functional group consisting of two nitrogen groups joined by a double bond. The process of thermal decomposition or degradation may further or alternatively comprise the formation of decomposition products comprising compounds such as aldehydes, ketones, anhydrides in the case of azo dyes. In the case of organic dyes, the process of thermal decomposition or degradation comprises the breaking of chemical bonds within the dye molecule 10, for example the breaking of carbon-carbon or carbon-oxygen bonds. The process of thermal decomposition or degradation may additionally or alternatively include the formation of decomposition products comprising compounds such as aldehydes, ketones, anhydrides.

[0259] In order to determine the thermal decomposition or degradation process, the laser beam 21 can be between 10 Watt and 50 Watt, optionally between 20 Watt and 30 Watt.

[0260] The pulse frequency of the laser beam 21 can be between 50 kHz and 200 kHz, optionally between 70 kHz and 150 kHz, more optionally between 90 kHz and 110 kHz, even more optionally substantially 100 kHz.

[0261] During the printing process, a working distance between laser emitter 20 and container 1 can be between 140 mm and 400 mm, optionally between 170 mm and 350 mm, even more optionally between 189 mm and 300 mm.

[0262] During the printing process, the laser beam 21 can have a scanning speed of between 2000 mm / s and 6000 mm / s, optionally between 3000 mm / s and 4000 mm / s, specifically 3500 mm / s optionally ± 10%. The scanning speed defines the speed at which the laser beam moves relative to the surface to be printed, i.e. in this case relative to the surface of container 1 .

[0263] A specific embodiment comprises setting the power of the laser beam between 20 Watt and 30 Watt, setting a scanning speed of the laser beam at 3500 mm / s, setting a pulse frequency of the laser beam at 100 kHz and setting a distance between the surface to be printed and said laser emitter between 180 mm and 310 mm. However, this specific embodiment is not to be considered as limiting, but on the contrary, the printing procedure 102 of the present invention can be performed using different numerical values and preferably within the numerical ranges stated above.

[0264] In an embodiment, the printing procedure 102 involves directing the laser beam 21 towards a flat surface of the container 1 , so as to define the graphic pattern on said flat surface.

[0265] Alternatively, the printing procedure 102 involves directing the laser beam 21 towards the curved surface of the container 1 , so as to define the graphic pattern on said curved surface. As shown schematically in Figure 7, the curved surface defines a locus of points having a variable distance from the laser emitter 20. The printing procedure 102 may thus comprise moving 104 the laser emitter 20 or at least one active component of the laser emitter 20 according to a curvature of the curved surface of the container 1 , so as to compensate for the variable distance between the curved surface and the laser emitter. The active component may comprise one or more lenses of the laser emitter 20 and / or a laser source of the laser emitter 20. While the laser beam is being emitted, the printing procedure 102 may therefore comprise the step of moving 104 the laser emitter 20 or the active component of the laser emitter 20 to compensate for the varying distance, for example by moving the laser emitter or its active component closer to and further away from the container surface. Note that the laser beam has a focus point where the laser light converges after being emitted by the laser source. This phenomenon is due to the focusing of the beam through an appropriate combination of lenses or mirrors. The exact distance between the laser source and the focus point depends on the optical configuration of the system. When the laser beam is focused, its light intensity is highest at the point of focus: this is where the beam energy is optimally concentrated. Printing procedure 102 is to keep the focus point of the laser beam at the surface of the container. In the case of a curved surface, wherein the distance varies with respect to the laser emitter, the printing procedure 102 includes varying the point of focus to maintain the point of focus substantially at the surface of the container 1. In this regard, the laser emitter 20 has a focusing mechanism configured to vary in position the point of focus of the laser beam 21 : the printing procedure 102, and in particular the step of moving 104, therefore includes the step of commanding the focusing mechanism to maintain the point of focus substantially at the surface of the container.

[0266] The curved surface of the container extends along a first curved trajectory and a second trajectory orthogonal to the first trajectory. The first trajectory may be substantially parallel to a top edge 6 of the container 1. In detail, the first trajectory may be substantially parallel to the bottom wall 3 of the container. In fact, the first trajectory follows the curvature of the curved surface of the container, i.e. the curvature of the side wall 2 of the container.

[0267] The second trajectory is transverse to the top edge 6 of the container and / or the bottom wall 3. The second trajectory may be curved or straight: in particular, the truncated conical shape of the container 1 shown in Figures 1 and 2 defines a substantially straight second trajectory.

[0268] The printing procedure 102 may comprise performing i) a first laser pass by moving the laser beam 21 along the first trajectory, while keeping the laser beam 21 fixed in position with respect to the second trajectory. At the end of step (i), the printing procedure 102 may then comprise (ii) moving the laser beam 21 along the second trajectory and subsequently performing (iii) a second laser pass by moving the laser beam 21 along a further trajectory substantially parallel to the first trajectory while keeping the laser beam 21 fixed in position with respect to the second trajectory. In other words, the printing procedure 102 involves making multiple passes with the laser beam parallel to the first trajectory at the previously stated scanning speed.

[0269] Note that the printing procedure 102 may comprise a plurality of laser passes, each along a different trajectory parallel to the first trajectory, until the graphic pattern GP is completed. For example, the printing procedure 102 may comprise moving (iv) again, atthe end of step (iii), the laser beam 21 along the second trajectory and subsequently performing (v) a third laser pass by moving the laser beam 21 along a new trajectory substantially parallel to the first trajectory while keeping the laser beam 21 fixed in position relative to the second trajectory. Printing Apparatus 200

[0270] The present description is also directed to an apparatus 200, schematically shown in Figure 8, and configured to perform the printing procedure 102 described above and to manufacture said containers. The method 100 comprises moving containers 1 along a manufacturing line through one or more processing stations of the apparatus 200. In detail, the apparatus 200 may comprise a forming station configured to define the bottom wall 3 and side wall 2 of the container 1 . The forming station may comprise a press configured to act on a semi-finished product made of paper material, for example a flat sheet of paper material, so as to define the bottom wall 3 and side wall 2 of the container 1 . A conveyor belt may be pre-positioned to move the container, or a semi-finished product made of paper material, along the fabrication line. The apparatus 200 may comprise the laser emitter 20 configured to emit the laser beam 21 , at least one holder 30 for a food container 1 , and at least one control unit operatively connected to the laser emitter 20. The control unit is then configured to command the execution of the previously described printing procedure 102 to define a printing pattern GP on the container 1 . In accordance with a non-limiting embodiment shown in Figure 8, the holder 30 comprises at least one socket portion 31 configured to receive and bind one container 1 : optionally, the socket portion 31 is configured to receive and bind one and only one container 1 at a time. The socket portion 31 may comprise a suction mechanism designed to bind the container(s) 1. In an embodiment, the holder 30 may comprise three or more receptacle portions 31 , each of which is adapted to receive and bind a respective container 1. The holder 30 may be movable by rotation about its own axis of rotation R, and configured to move the container(s) about the axis of rotation R. The apparatus 200 may comprise at least one motor operatively connected to the holder 30 and configured to rotate the holder 30 about the axis of rotation. The control unit may be configured to:

[0271] • command a rotation of said motor to position said socket portion 31 at a printing station facing the laser emitter 20;

[0272] • stop a rotation of the motor to block the socket portion 31 at the printing station;

[0273] • execute print procedure 102.

[0274] Note that, during the printing procedure 102, the container is stationary in position. The laser emitter 20 may be a CO2 laser emitter. A CO2 laser emitter is a type of laser that uses carbon dioxide (CO2) as an active medium. The operation of a CO2 laser involves the process of excitation of CO2 molecules, which switch to an excited state and then release energy in the form of coherent photons. The light emitted is generally in the infrared, optionally at a wavelength of about 10.6 microns. Laboratory analysis of three-dimensional food-grade paper containers printed with laser beam

[0275] Two different three-dimensional containers (made of food-grade paper material) were printed by applying the laser beam to the curved surface of the side wall using the technology described above. A first container is made of black paper material with a smooth surface, a second container is made of brownish paper material with a wavy layer on which the printing was obtained. The paper materials were marked with a CO2 laser, wavelength: 10.6 pm, power: 30 W (Class 4) (Keyence ML-Z Series, model ML-Z9620). The inkless laser printed cardboards were printed by the Applicant. The description of the paper materials and their names are presented in Table 1 .

[0276] SI Description of printed material Name no.

[0277] 1 Original black paper material N1

[0278] 2 Plain black paper material with laser-printed text N2

[0279] 3 Original in brown corrugated paper material M1

[0280] 4 Corrugated brown paper material with laser-printed text M2

[0281] MiliQ water was used for the analysis. The morphology of the material was characterised by scanning electron microscopy (SEM) of the surface of the paper materials using a JEOL JSM-6490LA variable pressure microscope equipped with a tungsten thermionic electron source operating in high vacuum with an accelerating voltage of 15 kV. To analyse the molecular structure and types of organic functional groups present in the paper material, attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) was performed using the Brucker V70 FTIR instrument (Bruker Analytik GmbH, Germany) equipped with an ATR (diamond crystal) unit. Scanning was performed in the wavenumber range of 400 to 3600 cm-1with 64 repetitive averaged scans per spectrum and a scan resolution of 4 cm-1. The surface roughness of the original and ink-free printed surfaces of the paper material was quantitatively determined by profilometer analysis (Ambios XP-2, USA). The surfaces of the samples were photographed in the reflection mode of a laser scanning confocal microscope. Multiple images were recorded through the z- plane (step size = 0.5 mm). The average surface roughness (Ra) was calculated as the average of 10 images per side of each sample. Static water contact angle (WCA) measurements were performed using a contact angle goniometer, DataPhysics OCAH 200 (Kruss, Germany). Water droplets (3 pL volume of deionised water) were placed on the surfaces of the paper material and static WCA measurements were performed within 30 seconds. For each sample, at least five measurements were taken in different areas and the results were averaged to obtain a mean value and standard deviation. To determine the adsorption capacity of the water, a defined amount of each paper sample was first weighed at room temperature on an electronic balance with an accuracy of 0.0001 g, and then immersed in 30 mL of MiliQ water for 6 hours. Then, after removal from the water, the samples were weighed again and the water absorption capacity was calculated from the weight differences of the paper material before and after immersion in water.

[0282] Figure 10 shows laser printing without ink on two different paper materials (a) smooth pigmented black paper material and (b) corrugated pigmented brown paper material. From figure 10, it can be seen that the laser can effectively print on both smooth and corrugated surfaces, as the words 'Novacart' and 'Motta Milano 1919' can be successfully printed. In this case, the laser irradiates the coloured surface of the paper material; the surface is carbonised due to the photothermal radiation effect of the laser, leaving graphitised carbon on the surface of the paper material, whereby the required text or graphics are formed on the paper material due to thermal energy.

[0283] The chemical composition of the paper material before and after laser printing was analysed using Fourier transform infrared spectroscopy (FTIR). Figure 11 shows the FTIR spectra of the black and brown corrugated paper material before and after laser printing. The characteristic absorption peak corresponds to the stretching of the -OH groups, shifted from 3282 cm-1to 3334 cm-1for the black paper materials and from 3334 cm-1to 3346 cm-1for the brown corrugated paper materials Figure 11 (a, c). The COOH peak also shifted from 1730 to 1710 cm-1for smooth black and remained unchanged at 1747 cm-1for wavy brown paper materials. The absorption peaks at around 1160 and 1024 cm-1correspond to the C-O-C skeleton of the cellulose in the paper material, Figure 11 (b, d). At the same time, the absorption peak of the C-H bending vibrations at about 2916 and 2848 cm-1(Figure 11 a, c) overlaps with the absorption peak of the bending vibrations of the laser-printed paper material, showing that both paper materials (black and corrugated brown) are composed of cellulose.

[0284] The surface morphology of the paper material was characterised by scanning electron microscopy (SEM), as shown in Figure 12 (a-p). From Figure 12, it can be seen that the laser printing has charred the surfaces of the paper material and some gaps and holes are observed for both the smooth black, Figure 12 (g, h), and the wavy brown, Figure 12 (o, p), respectively.

[0285] To further examine the charred microstructure (including holes), SEM images of the laser-printed areas are presented in Figures 13 (a, b), further confirming that the laser printing charred the surface and created voids and holes on the surfaces of the paper material.

[0286] The surface roughness of the paper material affects the uniformity of the print and thus the quality of inkless printing. In this case, two different smooth and corrugated paper materials with different surface roughness were performed for inkless laser printing (Figure 14). The surface roughness of the original black and brown corrugated paper material was 13.3 ±2.4 m and 21.5 ±2.5 pm, respectively, while the surface roughness after laser printing was 12.6 ±0.8 pm and 12.2 ±2.0 pm, respectively. It can be seen that there is no significant change in surface roughness for the smooth black paper material. In the case of the brown corrugated paper material, the surface roughness decreased slightly. This shows that laser ablation can perform inkless printing on both surfaces (smooth and corrugated) without being significantly influenced by the surface roughness of the paper material. To verify the water stability of the laser-printed text and paper material, the water contact angle and water absorption analysis were performed. The water contact angle of the smooth black paper material before and after laser printing remains almost the same (124.2 ±2.6° and 129.3 ±3.8°), indicating that laser printing does not affect the hydrophobic / hydrophilic properties of the surface of the paper material. In the case of the brown corrugated paper material, the contact angle with water could not be measured, as the water droplet (3 pm) was deposited on the lower corrugated area and filled the corrugated area with water, Figure 15(a). In addition, to test the water absorption capacity of the original and laser-printed paper materials, the paper materials were immersed in water for 6 hours and the water absorption capacity was analysed. From Figure 15(b), it can be seen that the water absorption capacity of the original paper material and the laser-printed material is almost the same, indicating that the laser print has the same water stability as the original paper material.

Claims

CLAIMS1. Method (100) of printing on containers (1) for food products, said method (100) comprising at least the following steps:• provide (101) a container (1) for foodstuffs, said container (1) comprising at least one layer of paper material,• perform a printing procedure (102) on said container (1) to define a graphic pattern (GP), said printing procedure (102) comprising emitting (103) a laser beam (21) on said container (1) by means of a laser emitter (20), in which said laser beam (21), during the printing process (102), is directed at said layer of paper material to define said graphic pattern (GP) on said layer of paper material.

2. Printing method according to the preceding claim, wherein at least 85% by weight, and optionally at least 88% by weight, of the container (1) is paper material, said paper material being suitable for contact with food products, wherein the paper material has a grammage between 60 g / m2and 95 g / m2, and wherein the paper material is a super calendered paper, said super calendered paper being made by a respective mechanical calendering process including a step wherein the paper passes through calendered cylinders or rollers configured to apply pressure and heat to the surface of the paper material.

3. Printing method according to any one of the preceding claims, wherein said container (1) comprises at least one colourant (10) defining a respective colour of the container (1), wherein said colourant (10) includes at least one between a natural colourant (10), an organic colourant (10), a direct colourant (10) including azo colourants, vegetable charcoal, mineral pigments including optionally iron oxide, said laser beam (21), during the printing procedure (102), impinging on said colourant (10) of the container (1).

4. Printing method according to the preceding claim, wherein said paper material comprises a concentration of said at least one colorant (10) between 1 % and 3% by weight of the paper material layer, optionally said colorant concentration being substantially 2% by weight.

5. Printing method according to any one of the preceding claims 3 and 4, wherein said layer in paper material contains said colourant (10),wherein said layer in paper material extends in thickness between a first surface and a second surface, said colourant (10) being dispersed in said layer in paper material between said first surface and said second surface, wherein said at least one colourant (10) optionally has a brown colour.

6. Printing method according to any one of the preceding claims, wherein said container (1) comprises at least one curved surface, the printing procedure comprising commanding said laser emitter (20) to direct the laser beam (21) along said curved surface, wherein said curved surface defines a locus of points having a different distance from each other with respect to the laser emitter (20).

7. Printing method according to the preceding claim, wherein the printing procedure (102) comprises moving (104) said laser emitter (20) or at least one active component of the laser emitter (20) based on a curvature of said curved container surface (1), said active component comprising at least one between one or more laser emitter lenses (20) and a laser source of the laser emitter (20), wherein the step of moving (104) said laser emitter (20) or said active component of the laser emitter (20) is simultaneous with the step of emitting (103) the laser beam (21).

8. Printing method according to any one of the preceding claims, wherein said laser emitter (20) includes a focusing mechanism configured to vary in position a focus point of the laser beam (21 ), the printing procedure (102) including to command said focusing mechanism to vary the position of said focus point during an emission (103) of said laser beam (21) to keep said focus point substantially at the curved surface of the container (1).

9. Printing method according to any one of the preceding claims, wherein said container (1) includes:• at least one bottom wall (3), and• at least one side wall (2) connected to and extending transversely from said bottom wall (3), said at least one bottom wall (3) and said at least one side wall (2) defining a containment volume configured for accommodating the food product, and wherein said laser beam (21), during the printing procedure (102), is directed at at least one between said at least one bottom wall (3) and said at least one side wall (2).

10. Printing method according to the previous claim, wherein said side wall (2) is curved,said laser beam (21), during the printing procedure (102), being directed at said side wall (2), and wherein said container (1) has a shape in the group between cylindrical, conical, truncated-cone or semi-spherical.

11. Printing method according to any one of the preceding claims, wherein the container (1) is a baking mould made of paper material for food products, in particular an oven baking mould.

12. Printing method according to any one of the preceding claims, wherein the printing procedure (102) is an inkless printing procedure.

13. Printing method according to any one of the preceding claims, wherein a laser beam energy (21) is absorbed by the paper material layer in the form of excitation of atomic electron vibrations and at least in part the laser beam energy is converted into thermal energy, in particular the absorption of energy, increases a local temperature of the paper material layer and causes a carbonisation reaction to fade the surface, thereby resulting in an inkless print.

14. Printing method according to any of the preceding claims, in which the layer of paper material comprises cellulose, said laser beam (21), during the printing procedure, modifying the cellulose to partially carbonise the cellulose by means of localised temperature increase, the partial carbonisation altering a colour of portions of the paper material where the laser beam operated.

15. Printing method according to any one of the preceding claims, in which the layer of paper material in which the graphic pattern (GP) is made shows gaps and holes when analysed by scanning electron microscopy (SEM).

16. Printing method according to any one of the preceding claims in combination with claim 4, wherein said laser emitter (20), during the printing procedure (102), emits (103) the laser beam (21) within a power range configured to cause a process of thermal decomposition or degradation of the colourant (10) of the paper material layer, wherein decomposition or degradation process modifies or is configured to chromatically modify said colorant (10) to define said graphic pattern (GP), and wherein said decomposition or degradation process causes a chromatic contrast on said container (1) between regions comprising said colorant (10) subjected to the laser beam (21) and regions comprising said colorant (10) not subjected to the laser beam (21), said chromatic contrast defining said graphic pattern (GP).

17. Printing method according to the preceding claim, wherein said thermal decomposition or degradation process includes at least one between:- in case said container (1) includes natural colorants: o breaking of chemical bonds within the colorant molecule (10), optionally breaking of carbon-carbon or carbon-oxygen bonds; and / or o formation of decomposition products including compounds such as amines and / or diazones;- in case said container (1) includes azo colorants: o breakage of azo bonds, particularly the breakage of the azo functional group (-N=N-) consisting of two nitrogen groups joined by a double bond; and / or o formation of decomposition products including compounds such as aldehydes, ketones, anhydrides in the case of azo colorants;- in case said container (1) includes organic colorants: o breaking of chemical bonds within the colorant molecule (10), optionally breaking of carbon-carbon or carbon-oxygen bonds; and / or o formation of decomposition products including compounds such as aldehydes, ketones, anhydrides.

18. Printing method according to any one of the preceding claims, wherein the printing procedure (102) includes:- setting the laser emitter to emit (103) said laser beam (21 ) at a power between 10 watts and 50 watts, optionally between 20 watts and 30 watts,- setting a scanning speed of said laser beam (21 ) between 2000 mm / s and 6000 mm / s, optionally between 3000 mm / s and 4000 mm / s, even more optionally at 3500 mm / s optionally ± 10%;- setting a pulse frequency of said laser beam (21) between 50 kHz and 200 kHz, optionally between 70 kHz and 150 kHz, more optionally between 90 kHz and 110 kHz, even more optionally substantially equal to 100 kHz;- setting a working distance between said laser emitter (20) and said container (1) between 140 mm and 400 mm, optionally between 170 mm and 350 mm, even more optionally between 189 mm and 300 mm.

19. Printing method according to any one of the preceding claims, wherein the paper material of said container (1) includes:• a first layer (5) intended for food contact, and• a second layer (4) adhered to and facing the first layer (5), said second layer (4) defining at least part of an outer surface of the container (1), said second layer (4) comprising said colorant (10), wherein the first layer (5) has a substantially smooth surface, and wherein the second layer (4) has an undulating surface comprising valleys and ridges, wherein each valley contacts with said first layer (5) and each ridge rises away from said first layer (5), said second layer (4) defining a corrugated paper layer, wherein said laser beam (21), during the printing procedure (102), is directed at said undulating surface of the second layer (4).

20. Printing method according to any one of the preceding claims, wherein said method (100) involves moving said containers (1) along a manufacturing line through one or more processing stations, and wherein, during the printing procedure (102), the container (1) is stationary in place.

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