Patent Application
20250025350
The present disclosure relates to the field of heat-sealable papers and in particular to recyclable heat-sealable papers.
Heat-sealable materials are used in various packaging applications. Traditionally, the packaging material has been a free-standing plastic material, such as a film. Alternatively, a plastic material has been coated onto a non-sealable material, such as paper or board, and sealed together with a free-standing plastic material, such as a film. The sealed package is protecting its content from the outside environment.
The present disclosure aims to provide a recyclable plastic-free heat-sealable paper-based material that can replace plastic materials in packaging applications.
Accordingly, the present disclosure provides the following listing of itemized embodiments:
Oxidized starch and dextrin are combined in one coating. Such combination provides a synergistic effect. Oxidized starch as well as dextrin have long been known to be used individually as adhesives for paper. However, the inventors have now realized that when combined into one single coating, a heat-sealable coating is provided that forms a superficial film being absorbed just enough by the paper substrate upon coating to provide for heat-sealability by wetting the film without the need for a plastic heat-sealable film.
Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:
As a first aspect of the present disclosure, there is provided a method of forming a package or container or paper stick comprising the steps of:
The oxidized starch and dextrin in the film is sufficient for providing the heat-sealability without the use of any additional polymer layers. Moreover, if the paper substrate is not coated with any plastic film, the package or container or paper stick produced is, thus, bio-based as well as the need for plastics is reduced or even avoided. A package or container of such type is typically a grease-proof package such as an open bag that can be used for example for french fries or pastry goods or a sealed bag that can be used for example for cereals or porridge or a sealed paperboard package or container.
The inventors have realized that by using a combination of oxidized starch and dextrin in the coating, it is possible to coat a paper substrate with a film that is absorbed enough to stick to the paper substrate but not too much to be absorbed into, and impregnate, the paper substrate. Thereby a superficial film can be formed. Wetting of the film is then sufficient to provide heat-sealability. Preferably, 10-50% by dry weight of the film is oxidized starch and 90-50% by dry weight of the film is dextrin. More preferably, 10-30% by dry weight of the film is oxidized starch and 90-70% by dry weight of the film is dextrin. Besides synergistically providing a heat-sealing capability, the dextrin is believed to provide barrier properties while the oxidized starch is believed to provide a film forming capability.
The paper product may be sealed to itself in step c). In such case, a package or bag or paper stick can be produced from a single paper substrate by folding or rolling the paper product followed by heat-sealing. Alternatively, the paper product is sealed to a second paper product in step c). In such case, a package or bag can be produced without the need for folding any of the paper products. Moreover, production of a pouch being of different shapes on top and bottom side is facilitated. The second paper product is in such case typically comprising a paper substrate being coated with a film, wherein the film comprises oxidized starch and dextrin, such as maltodextrin.
The paper substrate is typically a paper or a paperboard.
Typically, two wetted films comprising oxidized starch and dextrin, such as maltodextrin, are contacted with each other in step c).
In one embodiment, the film further comprises a wet-strength agent. In such embodiment, the wet-strength agent is typically present in an amount of 3-7%, such as 4-6%, based on the dry weight of the film. Addition of a wet strength agent is beneficial for the strength of the portion of the film being wetted.
The grammage of the film is typically 0.5-10 g/m2, such as 0.5-5 g/m2, such as 0.5-3 g/m2, such as 1-3 g/m2. A too low grammage can impair the heat-seal and a too high grammage increases the cost.
The film typically comprises at least 50%, such as at least 70%, such as at least 90% oxidized starch and dextrin based on the dry weight of the film.
The moisture content of the film in step a) is typically less than 30%, such as less than 20%, such as less than 10%, based on the dry weight of the film. The film-coated paper substrate is typically, at least partially, dried prior to heat-sealing. The coated paper substrate may therefore be produced at one site, followed by drying and transportation to another site where it is heat-sealed into a bag or package or paper stick. Alternatively, it is dried and heat-sealed into a bag or package or paper stick at the same facility.
In embodiments the paper product may be a package or container and the paper substrate a paper. The grammage measured according to ISO 536:2020 of the paper substrate is typically 30-60 g/m2, such as 35-55 g/m2. A suitable density (measured according to ISO 534:2011) for the paper substrate is 700-900 kg/m3, such as 750-900 kg/m3, such as 800-900 kg/m3. Typically for a package or container where the paper substrate is a paper, a too low density is not suitable since such paper is too porous for coating with the film comprising oxidized starch and dextrin. When forming forming a package or container, the grammage measured according to ISO 536:2020 of the paper product is typically 32-62 g/m2, such as 37-57 g/m2.
The paper substrate may be 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, and typically at least 80%, preferably at least 90%, by dry weight of the fibres used to produce the MG paper are virgin fibres. 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.
Typically, when the paper substrate is a MG paper, the film is coated on the smooth side of the paper substrate. Coating on the smooth side is especially beneficial if a package is produced in a Multivac sealing machine. In such case the grammage of the film is advantageously 0.5-2.5 g/m2, such as 0.5-1.5 g/m2. A Multivac sealing machine is a widely used sealing equipment for packaging of foodstuffs in sealed packages. A common use of the Multivac sealing equipment is to arrange a sheet or a tray, typically made of plastic or plastic-coated paper, with foodstuff on top and an additional sheet arranged on top of the food followed by heat-sealing to enclose the foodstuff inside a sealed package. Thereby, a package or container can be formed consisting of a paper tray and a substantially flat paper on top. Alternatively, a pouch having similar shape on both papers can be produced.
Alternatively, the film is coated on the rough side of the MG paper substrate and in such case the grammage of the film is typically 1-3 g/m2, such as 1-2 g/m2.
The heat-sealing in step c) is typically performed at a temperature in the interval of 110° C.-200° C., such as 110° C.-190° C., such as such as 150° C.-188° C. The heat-sealing in step c) is typically performed at a pressure of 3-10 bar. The heat-sealing in step c) is typically performed at a press time of 1-10 seconds.
The film has typically been formed from a coating mixture applied by means of a film press or a size press. Alternatively, the coating mixture has been applied by spraying. In yet another alternative, a curtain coater, direct rod coater or blade coater has been used to apply the coating mixture forming the film.
In the embodiment where the method is a method of forming a paper stick, the method further comprising the step:
Typically step b) and step b1) are conducted in a paper stick production machine, and preferably step b) is conducted during step b1) in the paper stick production machine. By conducting step b) during step b1) the efficiency is increased since the same machine can be used for wetting and rolling.
Typically, the portion of the film being wetted is forming at least part of an outer layer in the paper stick, such as forming part of the two outermost layers in the paper stick. It is preferred that at least a portion of the outer layer has been wetted as it otherwise will be a loose edge. Heat-sealing in step c) is typically conducted by drying the paper stick with the outer layer being wetted to seal the rolled paper stick. Drying is typically a non-contact drying, such as IR-drying and/or hot air drying. The paper substrate is typically a machine-finished (MF) or machine-glazed (MG) paper and the grammage of the paper substrate is as measured according to ISO 536:2020 is typically 50-90 g/m2, such as 55-85 g/m2, and the grammage measured according to ISO 536:2020 of the paper product is typically 52-92 g/m2, such as 57-87 g/m2.
In embodiments where the paper product may be a package or container and the paper substrate a paperboard. The density measured according to ISO 534:2011 of the paper substrate is typically 550-900 kg/m3, such as 550-750 kg/m3. The grammage measured according to ISO 536:2020 of the paper substrate is typically 150-400 g/m2, such as 200-350 g/m2. The grammage measured according to ISO 536:2020 of the paper product is typically 152-402 g/m2, such as 202-352 g/m2.
As a second aspect of the present disclosure, there is a paper stick produced according to the first aspect of the present disclosure. There is also disclosed a cotton bud comprising the paper stick produced according to the first aspect of the present disclosure. Cotton buds consist of one or two small wads of cotton wrapped around one or both ends of a short rod made of paper stick. They may typically be used for ear cleaning, first aid, cosmetics application, cleaning, and crafts.
As a third aspect of the present disclosure, there is provided a sealed package or container comprising a paper substrate and a film coated on the paper substrate, wherein the film comprises oxidized starch and dextrin, such as maltodextrin.
The paper product may have been sealed to itself to produce the package or container. Alternatively, the paper product may have been sealed to a second paper product to produce the package or container. Typically, the second paper product comprises a film, wherein the film comprises oxidized starch and dextrin, such as maltodextrin.
In one embodiment, the package or container comprises a sealing line and a product within the package or container, wherein the sealing line is arranged so that a product is sealed within the package or container. In such embodiment, the product is enclosed inside the sealed package independently on which direction the package is arranged in. Example of such package is a closed sealed pouch sealed all around the product. Such product may be produced using a Multivac-equipment or similar. Alternatively, the package is folded around the product and the open edges being sealed.
In an alternative embodiment, the package or container comprises a sealing arranged so that the package or container is partly open so that a product can be inserted and removed without breaking the sealing line or the package or container. Example of such package is a bag sealed on all sides but one leaving an opening, or a folded paper sealed on one edge leaving an opening.
The examples and embodiments discussed above in connection to the first aspect apply to the second and third aspects mutatis mutandis.
The present disclosure will now be described hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.
These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.
Machine glazed (MG) paper (40 g/m2) was coated by the use of a film press with a coating consisting of Perfectafilm B4085 from Avebe (100 pph) and Kymene GHP20 from Solenis (5 pph). Perfectafilm B4085 is a mixture of oxidized starch (20 wt %) and maltodextrin (80 wt %). The MG paper was coated either on the smooth side (MG-OX/MD) with a grammage of 1 g/m2 or on the rough side (RS-OX/MD) with a grammage of about 1.5 g/m2.
Moreover, in addition to the mixture in the product Perfectafilm B4085, different mixtures of oxidized starch and maltodextrin were prepared. In addition, two reference coatings being either free of oxidized starch or free of maltodextrin were prepared. These were all coated on an MG paper with a grammage of about 2 g/m2. The coatings were coated on the smooth side of the MG paper apart from the reference free of maltodextrin (RS-100/0) that was coated on the rough side. These mixtures and references are presented in Table 1.
Three additional references were prepared: MG paper coated on the MG side with a polyethylene coating (MG-PE), MG paper coated on the MG side with a maltodextrin coating (MG-MD), free of oxidized starch, with a grammage of 1 g/m2, and MG paper without any coating (non-coated) (MG).
The coated sides of two MG-OX/MD papers were wetted with water, put together and sealed under heat (180° C., 195° C. or 200° C.) and pressure (7 bar) for 5 seconds (at 180° C.), 9 seconds (at 195° C.) or 3 seconds (at 200° C.) to form sealed strips. The coating in these papers were made with Perfectafilm B4085 and accordingly contained 20 wt % oxidized starch and 80 wt % maltodextrin.
The manually prepared mixtures of oxidized starch and maltodextrin were wetted with water, put together and sealed under heat (180° C.) and pressure (7 bar) for 5 seconds.
The coated sides of two MG-MD papers were wetted with water, put together and sealed under heat (180° C.) and pressure (7 bar) for 5 seconds. Two MG papers (non-coated) were also sealed under heat (180° C.) and pressure (7 bar) for 5 seconds.
The coated sides of two MG-PE papers were put together and sealed under heat (170° C.) and pressure (4 bar) for 4 seconds.
Maximum heat seal strength (N) was thereafter evaluated according to ASTM F88 & EN 868-5 on a 15 mm test strip and the results are presented in Table 2.
As shown below in the Multivac test, heat-sealability can be achieved on both sides (MG and RS) of the paper. Hence it is concluded that the unfavourable seal strength value obtained for RS-100/0 in table 2 above is not primarily an effect of the side of the paper that was coated, but of the composition of the coating. Accordingly, it is concluded that dextrin must be included in the coating to achieve sufficient seal strength.
The reason why the manually prepared mixture of MG-20/80 obtained a higher seal strength than coating with Perfectafilm B4085 containing 20 wt % oxidized starch and 80 wt % maltodextrin is that the coating grammage was higher for the manually prepared mixture, 2 g/m2 instead of 1 g/m2. For the reference, MG-MD (180° C.) and MG-0/100, on the other hand, they were also coated at different grammages, but there the seal strength did not improve with increased coating grammage.
In a Multivac machine regularly used for sealing a plastic film onto a tray, a sealing test was performed. The coated sides of two MG-OX/MD papers were put together and sealed under heat (110° C.) and pressure (7 bar) for 1.5 seconds to form a sealed pouch. In the same way 2 more pouches were prepared from the following: one RS-OX/MD paper and one MG-OX/MD paper as well as two RS-OX/MD papers.
Seal strength was evaluated for the pouch prepared from two MG-OX/MD papers. Moreover, two sets of all 3 pouches were prepared and the first set was tested for fiber tear when intending to separate the two papers in each pouch and the second set was kept for long-term testing by visual inspection of the seal after 3 months.
For the first set of pouches, all of them displayed fiber tear when pulling apart the papers. The appearance of fiber tear shows that the seal is stronger than the papers themselves so that a coherent failure occurs, i.e. a strong seal had been formed independently on which side of the paper that had been coated.
For the second set of pouches, still 3 months after sealing, the seal between the papers in all 3 pouches was intact. This further shows that coating on both MG and RS side provides a strong seal.
The experimental data shows that a coating based on oxidized starch and dextrin provides for a seal strength both as free-standing strips and when produced as pouches in the Multivac that is well-comparable to that of a sealed PE-coating.
Moreover, the data also shows that it is the combination of oxidized starch and dextrin that provides this effect as paper coated with only maltodextrin or only oxidized starch as well as paper without coating does not yield the same seal strengths. All tested mixtures of oxidized starch and dextrin (ranging from 80/20 to 10/90) resulted in a seal strength comparable to that obtained with a PE-coated paper.
| Number | Date | Country | Kind |
|---|---|---|---|
| EPO 21212318.6 | Dec 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/083955 | 11/30/2022 | WO |
