Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/10—Packing paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/02—Metal coatings
  • D21H19/08—Metal coatings applied as vapour, e.g. in vacuum
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/10—Coatings without pigments
  • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
  • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/10—Coatings without pigments
  • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
  • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/22—Polyalkenes, e.g. polystyrene
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/54—Starch
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/16—Sizing or water-repelling agents

Definitions

• the present disclosure relates to the field of paper-based packaging materials and in particular to aluminium coated paper-based packaging materials.
• Metallization is a technique that has been used for a long time in graphical applications, on for example plastic substrates.
• Metallization is a vacuum coating technology used for deposition of a layer of a metal onto a substrate.
• a typical metal deposited is aluminium.
• An objective of the present disclosure is to provide a method for vacuum coating a paper with aluminium in a process that combines production speed with appearance and adhesion of the aluminium to the paper at a reasonable production cost.
• the present disclosure provides a method of vacuum coating a paper with aluminium comprising the steps:
• the present disclosure also provides use of a paper with a first side and a second side in vacuum coating with aluminium, wherein the paper is having a moisture content of ⁇ 6.0% as determined according to ISO 638-1:2022, wherein the first side is coated with a coating comprising a polysaccharide or a polyolefin as a top surface, and the second side is uncoated.
• the present disclosure further provides an aluminium vacuum coated paper comprising a paper having a first side and a second side, wherein the first side is coated with a coating comprising a polysaccharide or a polyolefin and an aluminium vacuum coating in that order and the second side is uncoated, as well as a packaging comprising the aluminium vacuum coated paper.
• a method of vacuum coating a paper with aluminium comprising the steps:
• the vacuum coating with aluminium is a metallization of the paper.
• Aluminium vacuum deposition is a process used to coat the paper with a layer of aluminium. This technique involves placing the substrate and aluminium source material inside a vacuum chamber. The chamber is then evacuated to create a high vacuum environment, significantly reducing the presence of air and other gases. Once the vacuum is achieved, the aluminium is heated until it evaporates or sublimates. The aluminium vapor then condenses onto the surface of the substrate, forming a coating.
• the vacuum coating with aluminium comprises aluminium, Al 2 O 3 and/or AlOx.
• the inventors have realized that by provision of a coating comprising a polysaccharide or a polyolefin as a top surface on the first side while leaving the second side uncoated, the paper is dense on one side and moisture is allowed to be extracted from the paper in the direction of the second side.
• the coating comprising a polysaccharide or a polyolefin comprises a polysaccharide or a polyolefin in a content of at least 8owt% by dry weight, such as at least 90% by dry weight, such as at least 95% by dry weight of the total weight of the coating.
• the second side is opposite of the first side of the paper.
• a coating comprising a polysaccharide or a polyolefin has been found to provide such properties at a single coating step. Accordingly, the coating comprising a polysaccharide or a polyolefin is preferably coated directly onto the paper without any intermediate coatings.
• the paper may have been surface sized with starch on the first side prior to coating with the coating comprising a polysaccharide or a polyolefin.
• the moisture content of the provided paper is ⁇ 6.0% as determined according to ISO 638-1:2022. Such moisture content has been realized to provide good appearance and properties of the aluminium coating as well as high production speed. To provide such moisture content the paper is typically dried to the desired moisture content at the production site of the paper.
• the coating comprising a polysaccharide or a polyolefin is the top surface meaning that it is the coating at the top which is visible to the user.
• the first side is coated with a coating comprising a polysaccharide
• the first side is typically coated with a coating comprising starch, such as oxidized starch.
• the first side is coated with a coating comprising oxidized starch and dextrin.
• dextrin is a polysaccharide. The inventors have realized that the first side is dense and smooth enough for the aluminium coating and provides a good adhesion of the aluminium coating.
• a preferred type of dextrin is maltodextrin.
• the coating comprises oxidized starch in an amount of 5-95 %, such as 10-50 %, such as 10-30 %, based on the dry weight of the coating and dextrin in an amount of 95-5 %, such as 90-50 %, such as 90-70 %, based on the dry weight of the coating.
• 10-50 % by dry weight of the coating is oxidized starch and 90-50 % by dry weight of the coating is dextrin.
• 10-30% by dry weight of the coating is oxidized starch and 90-70 % by dry weight of the film is dextrin.
• the first side is coated with a coating comprising starch, wherein the starch is a starch having a molecular weight of 0.03-10 ⁇ 10 8 Da, i.e. 0.03 ⁇ 10 8 - 10 ⁇ 10 8 Da.
• starch provides good film formation.
• the first side is coated with a coating comprising a polyolefin.
• the coating is typically a polyolefin dispersion coating.
• polyolefin dispersion refers to an aqueous suspension of polymer particles of polyolefins. As opposed to water-soluble polymers that are those polymers that forms solutions instead of dispersions in an aqueous solvent. After application, the particles form a solid coating after drying. There are polyolefin dispersion available including Rhobarr TM and Hypod TM provided by Dow. Polyolefin dispersion coatings, as opposed to polyolefin extrusion coatings are beneficial in terms of repulpability.
• the coating may be applied by the use of roller coating, spray coating, curtain, blade coating, slot coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, film press and/or combinations thereof.
• the grammage of the paper is 30-65 g/m 2 , such as 35-55 g/m 2 , such as 35-50 g/m 2 according to ISO 536-2019.
• a too high grammage makes it difficult to extract sufficient moisture at a high enough speed in the drying zone of the vacuum coating equipment.
• the inventors have realized that in case the grammage is above 65 g/m 2 , it is severely challenging to extract the residual moisture in the paper in the vacuum coater.
• the coating on the paper has been applied in a single coating station as multiple coating stations are more complicated and adds cost, in particular for a full-scale production.
• the production speed during drying and vacuum coating is at least 400 m/min, such as at least 450 m/min, such as at least 500 m/min.
• Such production speed provides for an efficient production and is made possible by the one-sided coated paper and facilitated by a not too high grammage.
• the grammage of the paper is the grammage of the paper not including the coating.
• the grammage of the coating is typically 0.4-0.4-3 g/m 2 , such as 0.4-1.6 g/m 2 in addition to the grammage of the paper.
• the coating comprises a polysaccharide.
• the grammage of the coating may be higher, typically 1-10 g/m 2 , such as 2-8 g/m 2 in addition to the grammage of the paper.
• Vacuum coating typically results in very thin coatings.
• the vacuum coating has a thickness of 10-200 nm, such as 10-100 nm, such as 10-60 nm, such as 10-45 nm. This can be compared to conventional aluminium foils used in packaging lamination, which typically has a thickness of about 7 ⁇ m.
• Such thickness of the vacuum coating allows for the coated paper to be recycled with standard paper recycling processes, while providing the desired appearance of the aluminium vacuum coated paper.
• the vacuum coated paper has a reject rate according to PTS RH 021/97 of less than 30%, such as less than 20%, such as less than 10%.
• reject rate is the same as a recyclability measured according to PTS Method PTS-RH 021/97 of at least 70%, such as at least 80%, such as at least 90%.
• the coating may further comprise a crosslinker.
• a crosslinker typically, in case the coating comprises a polysaccharide.
• An example of such a crosslinker is a PAE resin.
• the amount of the crosslinker in the coating may for example be 1-9 %, such as 3-7 %, based on the dry weight of oxidized starch and dextrin.
• the crosslinker is capable of crosslinking the polysaccharide.
• the paper is typically a kraft paper.
• Kraft paper is a strong, durable, and versatile type of paper made from wood pulp produced in the kraft process. Kraft pulp is also known as sulphate pulp.
• the paper is typically bleached for facilitated provision of desirable appearance of the aluminium vacuum coating. Alternatively, the paper is unbleached for provision of a paper with a natural brown colour. Typically, at least 80%, such as at least 90%, by dry weight of the fibres used to produce the paper are virgin fibres.
• the kraft paper can be made from softwood kraft pulp, hardwood kraft pulp or a mixture thereof.
• the coating can be provided on any side of the paper. Accordingly, the first side of the paper is the side coated with the coating comprising starch.
• the paper is typically a machine-glazed (MG) paper or a machine-finished (MF) paper.
• the MG paper is having a smooth side and a rough side.
• the MG paper or MF paper may be calendered.
• the MG paper or MF paper is typically a kraft paper.
• the smooth side of the MG paper is the side that faced the Yankee cylinder (a polished metal cylinder sometimes referred to as a MG cylinder) used for drying the paper web in the MG papermaking machine. The contact with the polished metal surface during drying makes the smooth side smoother than the rough side.
• MF paper is instead dried by a large number of smaller, steam-heated cylinders to dry the paper which is alternately wrapped one way and then the other way so that both sides of the paper receive the same finish.
• the finish on both sides of an MF paper is typically similar to the rough side of an MG paper.
• the coating can be provided on any side of the paper.
• MG paper is particularly advantageous for its high strength and durability, making it suitable for packaging applications that require a robust material. It can withstand handling, shipping, and storage without easily tearing or deteriorating.
• the paper provided in step a) has a water vapor transmission rate (WVTR) measured according to ISO 15106-1 at 23°C and 50% relative humidity (RH) of below 600 g/(m 2 day), such as below 500 g/(m 2 day).
• WVTR water vapor transmission rate
• RH relative humidity
• the paper provided in step a) has an air permeance measured according to ISO 5636-5:2013 of 200-1000 s, such as 250-1000, such as 300-1000 s. It is beneficial with a dense surface of the coated paper to be vacuum coated, and provision of such air permeance of the paper from the coating is beneficial for provision of an aluminium coating with desirable appearance and properties, such as that ink stays on the surface when written onto the aluminium coated side of the paper. Air permeance is also known as Gurley value or Gurley seconds. Moreover, it is advantageous if the air permeance is not too high, as an even higher air permeance is typically obtained by extensive refining on the fibres used in the production of the paper, and such extensively refined fibres are difficult to dewater. Hence, it is also challenging to dry the paper to the desired moisture content.
• the paper is provided with a moisture content as determined according to ISO 638-1:2022 of ⁇ 5.5%, such as ⁇ 5.0% in step b).
• a moisture content as determined according to ISO 638-1:2022 of ⁇ 5.5%, such as ⁇ 5.0% in step b).
• Such moisture content is beneficial for provision of an aluminium coating with desirable appearance and properties, such as that ink stays on the surface when written onto the aluminium coated side of the paper.
• a paper in vacuum coating with aluminium wherein the paper is having a moisture content of ⁇ 6.0% as determined according to ISO 638-1:2022, wherein the first side is coated with a coating comprising a polysaccharide or a polyolefin as a top surface, and the second side is uncoated.
• an aluminium vacuum coated paper comprising a paper having a first side and a second side, wherein the first side is coated with a coating comprising a polysaccharide or a polyolefin and an aluminium vacuum coating in that order and the second side is uncoated.
• a packaging comprising the aluminium vacuum coated paper of the third aspect of the present disclosure.
• An example of a packaging comprising the aluminium vacuum coated paper is a paper bag formed from the paper by folding and sealing. Another example is a wrapped product. Yet another example is the aluminium vacuum coated paper laminated to a paperboard and a package produced from the laminate.
• a machine glazed (MG) kraft paper was formed on a full-scale paper machine equipped with a Yankee cylinder to provide a paper (40 g/m 2 ) having a rough side and a smooth side.
• the rough side has a similar character to that of any type of paper as it has not been in contact with the Yankee cylinder.
• the uncoated MG kraft paper was coated by the use of a film press on the rough side, i.e. the side of similar character of any type of paper, while leaving the smooth side uncoated.
• the coating on the rough side consisted of 100 pph of a starch mixture of oxidized starch (20 wt%) and maltodextrin (80 wt%) (Perfectafilm B4085 from Avebe), 5 pph (based on the amount of starch mixture) of PAE resin (Kymene GHP20 from Solenis, a crosslinker), and 3 pph of AKD (Solenis Aquapel F220).
• the applied dry amount of the coating on the rough side was 0.96 g/m 2 .
• the uncoated MG kraft paper was coated by the use of a film press on both the rough side, i.e. the side of similar character of any type of paper, and the smooth side.
• the coating on the rough side was the same as for the paper coated on one side only.
• the smooth side was coated with a coating consisting of 100 pph of a starch mixture of oxidized starch (20 wt%) and maltodextrin (80 wt%) (Perfectafilm B4085 from Avebe) and 5 pph (based on the amount of starch mixture) of PAE resin (Kymene GHP20 from Solenis, a crosslinker).
• the applied dry amount of the coating on the rough side was 0.86 g/m 2 .
• Each of the papers were vacuum coated with aluminium in an offline coater running with a machine speed of up to 600 m/min (i.e. full speed) and coating aluminium coatings on the papers with a thickness of 40 nm.
• the papers were provided dried from the paper and starch coating machines and had a moisture content of 5, 6 or 6.5 % prior to coating in the vacuum coater.
• Inside the vacuum coater there is a drying zone and a vacuum coating zone.
• the drying zone allows for vaporizing of residual moisture to be able to vacuum coat the papers.
• the distance in the drying zone prior to the vacuum coating zone is about 10 cm, i.e. there is a limitation on how much moisture that can be vaporized in the drying zone running at full speed. In particular if the paper is somewhat thick.
• WVTR water vapor transmission rate measured according to ISO 15106-1 at 23°C and 50% relative humidity (RH) was evaluated.
• the aluminium adheres well to the paper, that it is not easily scraped off during normal handling by a customer.
• the latter was evaluated by scraping hard with fingernails on the coating and if it stays on it was classified as "Excellent”. If the aluminium stays on after coating but can be scraped off with minor effort, this was classified as “Good” and if the aluminium is scraped off with hardly any effort this was classified as "Bad”.
• the paper coated on both sides could not be vacuum coated at all due to that the pressure could not be sufficiently decreased inside the vacuum coater.
• the non-coated paper could not be coated at high machine speed, but had to be set to half machine speed. Moreover, the aluminium coating obtained had a dark colour of the aluminium coating.
• the paper coated on one side only having a moisture content of 6.5% provided good results on the aluminium coating. But the paper could not be coated at high machine speed, but had to be set to half machine speed.
• the paper coated on one side only having a moisture content of 5% provided good results on the aluminium coating and could be coated at 90% of full machine speed ensuring sufficient production efficiency.

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Citations (6)

• 2024
  • 2024-06-10 EP EP24181022.5A patent/EP4663848A1/fr active Pending
• 2025
  • 2025-06-09 WO PCT/EP2025/065970 patent/WO2025257101A1/fr active Pending

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