COATED BARRIER PAPER

Abstract

 The present disclosure provides a coated paper product comprising:
- a paper substrate comprising a first and a second side;
- a first coating layer on the first side of the paper substrate comprising a binder; and
- a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);
- a third coating layer on the second coating layer, wherein the third coating layer comprises talc and ethylene-acrylic acid (EAA) or talc and a polyolefin, and wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:5 and 100:70.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of paper-based materials.

BACKGROUND

[0002] The current legislative trends regarding packaging are driving consumers and brands to change their packaging from plastic to paper. There are many large market segments where barrier papers are required to effectively replace traditional plastic packaging and demand for paper-based solutions is growing strongly. Examples include flow wrapped products, bags and other wrappings.

[0003] Flow wrapping is a horizontal-motion process in which products of any shape are wrapped in a wrapping material. It is used to pack single solid items, such as confectionery bars or multiple products already collated in trays. Traditionally, the wrapping material has been a clear plastic film or a printed opaque plastic film. The package resulting from the flow wrapping process has a longitudinal fin seal and end fin seals. The longitudinal fin seal is typically folded over so that the fin lies flat on the backside wall of the package rather than projecting from it.

[0004] The vertical form fill sealing (VFFS) machine is a type of automated assembly-line product packaging system. It is commonly used in the packaging industry for food and a wide variety of other products. The machine often constructs plastic bags out of a flat roll of plastic film, while simultaneously filling the bags with product and sealing the filled bags. Both solids and liquids can be bagged using this packaging system.

[0005] Overwrapping is the process of wrapping an item inside a protective material. The item is overwrapped by the packaging material and sealed, thereby making a sealed package.

SUMMARY

[0006] The present disclosure aims to provide a paper-based material that can replace plastic films in packaging in for example flow wrapping processes, sealed paper bags, e-commerce bags, tissue wrapping and bedding wrappings.

[0007] The inventors have realized that such a paper-based material, to be commercially successful, should meet the majority, preferably all, of the following criteria:

• ductility of the coating, i.e. cracking resistance during processing or usage;
• minor or even non-existing blocking during processing;
• providing a grease barrier (preventing fat from the packed/wrapped product from staining and/or weakening the paper-based material);
• repulpable according to applicable standards;
• protecting the packed/wrapped product from ambient moisture as well as oxygen;
• heat-sealable so that a sealed package can be produced without further sealant layers;
• satisfactory printability when using existing printing technology; and
• acceptable cost of production, preferably on existing machinery or requiring only minor investments in new equipment.
• sealant layer adhesion (i.e. capable of binding a sealant composition applied in a high-speed process).

[0008] Accordingly, the present disclosure provides the following listing of itemized embodiments:

1. A coated paper product comprising:

• a paper substrate comprising a first and a second side;
• a first coating layer on the first side of the paper substrate comprising a binder; and
• a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);
• a third coating layer on the second coating layer, wherein the third coating layer comprises talc and ethylene-acrylic acid (EAA) or talc and a polyolefin, and wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:5 and 100:70.

2. The coated paper product of item 1, wherein the binder of the first coating layer is EAA or vinyl acetate acrylate copolymer (VAcA) or styrene-acrylate (SA) or styrene-butadiene (SB), acrylic latex or polyolefin latex.

3. The coated paper product of item 1 or 2, wherein the first coating layer comprises pigment.

4. The coated paper product of item 3, wherein the pigment in the first coating layer is talc and/or calcium carbonate (CaCO₃) and/or clay and/or mica.

5. The coated paper product of item 4, wherein the first coating layer comprises talc in a binder to talc ratio between 100:5 and 100:110, such as between 100:30 and 100:110, such as between 100:30 and 100:75, or CaCO₃ in a binder to CaCO₃ ratio between 100:20 and 100:70, such as between 100:30 and 100:65 or kaolin clay in a binder to kaolin clay ratio between 100:5 and 100:110, such as between 100:30 and 100:110, such as between 100:30 and 100:75 or mica in a binder to mica ratio between 100:5 and 100:110, such as between 100:30 and 100:110, such as between 100:30 and 100:75 or bentonite clay in a binder to bentonite clay ratio between 100:30 and 100:110, such as between 100:30 and 100:75.

6. The coated paper product of any one of the items 3-5, wherein the total pigment content is 5-70 % by dry weight of the first coating layer, such as 10-50 % by dry weight of the first coating layer.

7. The coated paper product of any one of the preceding items, wherein the coat weight of the first coating layer is at least 3 g/m², such as 3-10 g/m².

8. The coated paper product of any one of the preceding items, wherein the coat weight of the second coating layer is 0.5-8 g/m², such as 1-6 g/m².

9. The coated paper product of any one of the preceding items, wherein the coat weight of the third coating layer is at least 3 g/m², such as 3-10 g/m².

10. The coated paper product of any one of the preceding items, wherein the paper substrate comprises a pre-coating layer between the paper substrate and the first coating layer.

11. The coated paper product of item 10, wherein the pre-coating layer comprises PVOH or starch.

12. The coated paper product of item 10 or 11, wherein the coat weight of the pre-coating layer is 0.1-2 g/m², such as 0.3-1.5 g/m².

13. The coated paper product of any one of the preceding items, wherein the grammage measured according to ISO 536:2020 of the paper substrate is 40-135 g/m², such as 40-100 g/m², such as 40-90 g/m², such as 40-60 g/m², such as 42-55 g/m².

14. The coated paper product of any one of the preceding items, wherein the grammage measured according to ISO 536:2020 of the coated paper product is 50-150 g/m², such as 52-110 g/m², such as 52-95 g/m², such as 52-71 g/m², such as 56-68 g/m².

15. The coated paper product of any one of the preceding items, wherein the paper substrate is a machine-glazed (MG) kraft paper or a machine finished (MF) kraft paper.

16. The coated paper product of item 15, wherein paper substrate is a MG paper and the first side of the paper substrate is the non-glazed side of the MG paper and wherein the glazed side is optionally printed.

17. The coated paper product of any one of the preceding items, wherein at least 80 dry wt.% of the fibres used to form the paper substrate are never-dried.

18. The coated paper product of any one of the preceding items, wherein the second coating layer comprises pigment.

19. The coated paper product of item 18, wherein the pigment in the second coating layer is clay, such as bentonite clay.

20. The coated paper product of any one of items 18-19, wherein the dry weight ratio of PVOH and/or EVOH to pigment in the second coating is between 100:1 and 100:30, such as between 100:5 and 100:25.

21. The coated paper product of any one of the preceding items, wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:10 and 100:70, such as between 100:10 and 100:60, such as between 100:15 and 100:60, such as between 100:15 and 100:40.

22. The coated paper product of any one of items 3-21, wherein the first and/or third coating layer comprises clay, such as kaolin clay and/or bentonite clay, wherein the clay preferably is a platy clay, preferably having a form factor of at least 20, such as at least 30, such as at least 40.

23. The coated paper product of any one of the preceding items, wherein the total pigment content of the third coating layer is 4-70 % by dry weight, such as 5-50 % by dry weight of the third coating layer.

24. The coated paper product of any one of the preceding items, wherein the paper product is heat-sealable.

25. The coated paper product of item 24, wherein the maximum heat seal strength measured according to ASTM F88 & EN 868-5 of the coated paper product is at least 2.2 N measured on a 15 mm test strip sealed for 0.5 s at 160 °C and 3 bar.

26. The coated paper product of any one of the preceding items, wherein the density measured according to ISO 534:2011 of the paper substrate is 750-950 kg/m³.

27. The coated paper product of any one of the preceding items, wherein the paper substrate is bleached, e.g. has an ISO Brightness according to ISO 2470 of at least 77 or unbleached, e.g. has an ISO brightness according to ISO 2470 of below 60.

28. The coated paper product of any one of the preceding items, wherein the repulpability measured according to PTS Method PTS-RH 021/97 of the coated paper product is at least 80%.

29. The coated paper product of any one of the preceding items, wherein a heat-seal layer is provided on at least part of the second side of the paper substrate.

30. The coated paper product of item 28, wherein the heat-seal layer comprises binder and, optionally, pigment.

31. The coated paper product of any one of the preceding items, wherein the second side is a print side.

32. The coated paper product of any one of the preceding items, wherein the polarity of the binder in the first coating layer is lower than the polarity of PVOH and/or EVOH in the second coating layer.

33. A flow-wrapped product obtained by flow-wrapping a product in a coated paper product according to any one of the preceding items, wherein the flow-wrapped product has a longitudinal fin seal and end fin seals.

34. A sealed bag produced from a coated paper product according to any one of the items 1-32, such as a gusseted bag or a pillow bag, having a longitudinal seal and each end portion is sealed by a fin seal.

35. Use of a coated paper product according to any one of the items 1-32 for wrapping a product, such as flow-wrapping a product, in sealable paper bags, such as a gusseted bag or a pillow bag, in e-commerce packaging, in bedding packaging, such as pillow packaging, or in tissue wrapping.

36. A method of producing a coated paper comprising the steps of:

• providing a paper substrate comprising a first and second side; and
• coating the first side of the paper substrate with a first coating layer, wherein the first coating layer comprises a binder; and
• coating a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);
• coating a third coating layer on the second coating layer, wherein the third coating layer comprises ethylene-acrylic acid (EAA) latex and talc, and wherein the dry weight ratio of EAA latex to talc in the third coating layer is between 100:5 and 100:70.

37. The method of producing a coated paper product according to item 36, wherein all the coating layers are applied in-line.

38. The method for producing a coated paper product according to any one of the items 36-37, wherein the second coating layer is produced in one single coating step or in a plurality of coating steps.

39. The method for producing a coated paper product according to any one of the items 36-38, wherein the first coating layer and a first sub-layer of the second coating layer forming a part of the second coating layer are applied in the same coating step and the third coating layer in a separate coating step.

40. The method for producing a coated paper product according to the item 38, wherein a second sub-layer of the second coating layer is applied in a separate coating step prior to application of the third coating layer.

41. The method for producing a coated paper product according to item 39, wherein the second coating layer consists of the first and second sub-layers.

42. The method for producing a coated paper product according to any one of the items 36-38, wherein the first coating layer and a first sub-layer of the second coating layer forming a part of the second coating layer are applied in the same coating step and a second sub-layer of the second coating layer forming a part of the second coating layer and the third coating layer are applied in the same coating step.

43. The method for producing a coated paper product according to item 42, wherein the second coating layer consists of the first and second sub-layers.

44. The method for producing a coated paper product according to any one of the items 38, wherein the first coating layer, second coating layer and third coating layer are all applied in separate coating steps.

45. The method for producing a coated paper product according to any one of the items 36-43, wherein the coating layers are applied using a blade coater, rod coater, air-knife coater, rotogravure coater or curtain coater.

46. The method for producing a coated paper product according to any one of the items 36-45, wherein a pre-coating layer is applied to the paper substrate prior to the first coating layer.

47. The method for producing a coated paper product according to item 46, wherein the pre-coating layer comprises PVOH or starch.

48. The method for producing a coated paper product according to item 46 or 47, wherein the pre-coating layer is applied using a size press or a film press.

49. The method for producing a coated paper product according to any one of the items 36-48 comprising drying between coating the second layer and third coating layer.

50. The method for producing a coated paper product according to any one of the items 36-49, wherein the PVOH and/or EVOH is dispersed or dissolved in water when coating the second coating layer on the first coating layer.

51. The method for producing a coated paper product according to any one of the items 36-50, wherein a heat-seal layer is coated on at least part of the second side of the paper substrate.

52. A method of flow-wrapping a product comprising a step of flow-wrapping the product in a coated paper product according to any one of the items 1-32, wherein said flow-wrapping step comprises formation of a fin seal by sealing the coated paper product.

53. The method of flow wrapping a product of item 52, wherein the sealing is conducted by heat-sealing the third coating layer.

54. The method of flow wrapping a product of item 53, wherein the method further comprises the step of applying a sealant layer, preferably a cold-seal layer, onto part of the third coating layer prior to formation of a fin seal and sealing is conducted by sealing said sealant layer.

55. The method of flow wrapping a product of any one of the items 52-54, wherein the base paper is an MG paper.

56. The method of flow wrapping a product of item 55 further comprising printing the second side of the paper substrate.

57. The method of flow wrapping a product of item 56, wherein the printing of the second side of the paper substrate and the application of the sealant layer are carried out in the same machine.

58. The method of flow wrapping a product of any one of the items 52-57, wherein the coated paper product is formed into a bag, filled and sealed in a machine, such as a form fill sealing (FFS) machine, such as a vertical form fill sealing (VFFS) machine or horizontal form fill sealing (HFFS) machine.

59. Method of forming a filled bag, in which a coated paper product according to any one of items 1-32 is formed into a bag, filled and sealed in a machine, such as a form fill sealing (FFS) machine, such as a vertical form fill sealing (VFFS) machine or horizontal form fill sealing (HFFS) machine.

60. Method of forming a wrapped item comprising the steps of:

a) providing a paper product of any one of items 1-32;

b) wrapping an item with the paper product; and

c)heat-sealing at least part of the paper product so that a sealed wrapping is formed.

61. The method of item 60, wherein the paper product is sealed to itself in step c).

62. The method of item 60, wherein the paper product is sealed to a second paper product in step c).

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] 

Fig 1 is a schematic illustration of an embodiment of a coated paper product 1 of the present disclosure. The paper product consists of a paper substrate 101, a first coating layer 102, a second coating layer 103 and a third coating layer 104.

Fig 2 is a schematic illustration of another embodiment of a coated paper product 2 of the present disclosure. The paper product consists of a paper substrate 101, a first coating layer 102, a second coating layer 103, a third coating layer 104 and a pre-coating layer 105.

DETAILED DESCRIPTION

[0010] As a first aspect of the present disclosure, there is provided a coated paper product comprising:

• a paper substrate comprising a first and a second side;
• a first coating layer on the first side of the paper substrate comprising a binder; and
• a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);
• a third coating layer on the second coating layer, wherein the third coating layer comprises talc and ethylene-acrylic acid (EAA) or talc and a polyolefin, and wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:5 and 100:70.

[0011] The second coating layer is preferably provided on the first coating layer, i.e. directly on top of the first coating layer, and the third coating layer is preferably provided directly on top of the second coating layer, forming a triple superposed coating arrangement.

[0012] The paper substrate is typically a machine-glazed (MG) paper or a machine finished (MF) paper. The paper substrate may be calendered. The MG 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 or MF paper are never-dried fibres (i.e. virgin fibres).

[0013] An MG paper has glazed side and a non-glazed side. The glazed side 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 glazed side smoother than the non-glazed side. Typically, the first coating layer is applied to the less smooth, non-glazed, side of the paper substrate, i.e. the first side of the paper substrate. Onto the first coating layer, the second coating layer is applied. The opposite side, i.e. the second side being the smooth, glazed side, in such case is typically printed. It is beneficial to apply the coating on the non-glazed side to provide the glazed side for printing.

[0014] An MF paper is produced by a drying technique using 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 similar to the non-glazed side of an MG paper.

[0015] A heat-seal layer may be provided on at least part of the second side of the paper substrate. Such heat-seal layer typically comprises binder and, optionally, pigment. The heat-seal layer may be provided in one or may strips to cover at least part of the second side. Alternatively, the heat seal-layer covers the second side completely. A heat-seal layer on the second side is for example advantageous if the coated paper product is to be sealed with a second paper, wherein that second paper is not heat-sealable by itself. An example of such seal is a lap seal.

[0016] The second side is typically a print side. A lacquer may be provided on the optional print, e.g. to modify gloss, friction and/or release properties.

[0017] The grammage measured according to ISO 536:2020 of the paper substrate is typically 40-135 g/m², 40-100 g/m², such as 40-90 g/m², such as 40-60 g/m², such as 42-55 g/m². A suitable density (measured according to ISO 534:2011) for the paper substrate is 750-950 kg/m³. A too low density is disadvantageous since such paper is too porous for application of a thin barrier.

[0018] Typically, if the paper is used for flow wrapping, a suitable thickness (measured according to ISO 534:2011) of the paper substrate is 40-80 µm, such as 50-64 µm, such as 52-61 µm. A too high grammage or thickness makes the paper not suitable for a flow wrapping process as the paper should be flexible.

[0019] The paper substrate may be bleached, e.g. has an ISO Brightness according to ISO 2470 of at least 77 or unbleached, e.g. has an ISO Brightness according to ISO 2470 of below 60.

[0020] Typically, the coat weight of the first coating layer is at least 3 g/m², such as 3-10 g/m². The first coating layer is typically arranged directly on top of the paper substrate. Alternatively, the paper substrate comprises a pre-coating layer between the paper substrate and the first coating layer. The purpose of the pre-coating layer is to act as a pore-filling layer that provides a smoother surface for the first coating layer to be provided on, and thereby avoid too great penetration of the first coating layer into the paper substrate. In case the paper product comprises a pre-coating layer between the paper substrate and the first coating layer, the grammage of the first coating layer can be lower than if the paper product does not comprise any pre-coating layer. The pre-coating layer typically comprises PVOH or starch. In such case, it is preferred that the pre-coating layer contains at least 50% by dry weight of PVOH or starch based on the dry weight of the pre-coating layer. The coat weight of the pre-coating layer is typically 0.1-3 g/m², such as 0.3-2.5 g/m². Since the grammage of the first coating layer can be lower, it is an advantage of a pre-coating layer that if a fossil-based binder is used in the first coating layer, the amount of such binder can be lower, thereby reducing the carbon footprint. The pre-coating layer is typically applied using a size press or a film press. If a pre-coating layer is provided, it is applied to the paper substrate prior to the first coating layer is applied. After application of the pre-coating layer, calendering of the paper may be conducted to smoothen the surface prior to coating the first coating layer.

[0021] The binder of the first coating layer is typically EAA or vinyl acetate acrylate copolymer (VAcA) or styrene-acrylate (SA) or styrene-butadiene (SB) or acrylic latex. The first coating may comprise a rheology modifier to facilitate the coating operation. The first coating layer may comprise pigments, in such case the pigments is typically talc and/or calcium carbonate (CaCO₃) and/or clay and/or mica. The clay is typically kaolin clay and/or bentonite clay. Typically, bentonite clay contains parts of montmorillonite (MMT). In case of the pigment being talc or CaCO₃, it is preferred that the first coating layer comprises talc in a binder to talc ratio between 100:5 and 100:110, such as between 100:30 and 100:110, such as between 100:30 and 100:75, or CaCO₃ in a binder to CaCO₃ ratio between 100:20 and 100:70, such as between 100:30 and 100:65. Typically, the total pigment content is 5-70 % by dry weight of the first coating layer, such as 10-50 % by dry weight of the first coating layer. The third coating layer may comprise additional pigments, in addition to talc. Typically, the total pigment content of the third coating layer is 4-70 % by dry weight, such as 5-50 % by dry weight of the third coating layer. The first and/or third coating layer may comprise clay, such as kaolin clay. In such case, the clay is preferably a platy clay, preferably having a form factor of at least 20, such as at least 30, such as at least 40.

[0022] The polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH) in the second coating layer contributes with oxygen barrier properties to the coated barrier product. Since both PVOH and EVOH are hygroscopic, the oxygen barrier properties of the coated barrier product are improved by inclusion of the third coating layer protecting the second coating layer from ambient moisture. Preferably, there is no other binder in the second coating layer than PVOH and/or EVOH. Typically, the polarity of the binder in the first coating layer is lower than the polarity of the PVOH and/or EVOH of the second coating layer. By having a lower polarity in the first coating layer, the second coating layer is protected from moisture also from the paper side. Particularly advantageous binders in the first coating layer having a lower polarity than PVOH and/or EVOH and protecting the second coating layer from moisture from the paper side are EAA or VAcA or SA or SB or acrylic latex. By PVOH it is also meant derivatives of PVOH including ethylated PVOH. An example of PVOH is the product with the trade name "Poval" from Kuraray. An example of an ethylated PVOH is the product with the trade name "Exceval" from Kuraray. An ethylated PVOH typically has an ethylene content of about 5-10 % by weight, whereas a non-ethylated PVOH is typically free of ethylene groups. EVOH typically has an ethylene content of above 10 % by weight. The coat weight of the second coating layer is typically 0.5-8 g/m², such as 1-6 g/m².

[0023] The second coating layer may comprise pigment. In such case, the pigment is typically clay, such as bentonite clay. The D50 value, i.e. the median particle size, is typically below 50 µm for the clay. In the case wherein the second coating layer comprises pigments, the dry weight ratio of PVOH and/or EVOH to pigment in the second coating is preferably between 100:1 and 100:30, such as between 100:5 and 100:25.

[0024] It is beneficial for combining coating ductility, barrier properties, non-blocking, repulpability, heat sealability and possibility to coat with a sealant layer that the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:5 and 100:70. Typically, the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:10 and 100:70, such as between 100:10 and 100:60, such as between 100:15 and 100:60, such as between 100:15 and 100:40. The coat weight of the third coating layer is typically at least 3 g/m², such as 3-10 g/m².

[0025] The coated paper product is typically heat-sealable. EAA is inherently heat-sealable and by addition of a dry weight ratio of EAA to talc in the third coating layer of between 100:5 and 100:70, this heat-sealability is typically maintained. A higher talc content impairs the sealability as well as the barrier crack resistance. Typically, the maximum heat seal strength measured according to ASTM F88 & EN 868-5 of the coated paper product is at least 2.2 N measured on a 15 mm test strip sealed for 0.5 s at 160 °C and 3 bar. This means that 2.2 N is required to separate the sealed strip. It is advantageous for the coated paper product to be heat-sealable in order to allow the formation of a packaging by sealing the paper to itself.

[0026] The third coating layer typically forms a surface to which a sealant layer can be applied, typically a cold-sealant layer. To facilitate the application of the sealant layer, the contact angle between water and the third coating layer surface is preferably less than 95°, such as less than 90°, such as less than 80°. The contact angle may be measured according to TAPPI T 558. This standard stipulates measuring the contact angle at different checkpoints. Suitably, the contact angle at the 1.0 s checkpoint is selected. Moreover, the contact angle between di-iodomethane (DIM) and the second coating layer surface is preferably less than 60° and the surface energy is at least 30 mJ/m² at the 1.0 s checkpoint measured according to TAPPI T 558. The surface energy is derived from the contact angle measurements by plotting (1+cosθ)/2^∗(σ_L/σ_L^d)^½) vs (σ_L^p/σ_L^d)^½, wherein θ is the contact angle formed between the liquid drop and solid surface, σ_L is the liquid surface tension, and superscripts d and p stand respectively for dispersive and polar components of the liquid surface tension. After plotting, the points are fitted to a straight line to calculate σ_s^p and σ_s^d from the slope and intersection with the vertical axis, respectively. σ_s is the solid surface free energy and the surface energy is the sum of σ_s^p + σs^d.

[0027] It is advantageous that the third coating layer typically can either be heat-sealed without the need for an additional sealant layer or coated by and sealed by an additional sealant layer, typically a cold seal layer.

[0028] The grammage measured according to ISO 536:2020 of the coated paper product is typically 50-150 g/m², such as 52-110 g/m², such as 52-95 g/m², such as 52-71 g/m², such as 56-68 g/m². A suitable density (measured according to ISO 534:2011) of the coated paper product is 900-1100 kg/m³. Typically, if the paper is used for flow wrapping, a suitable thickness (measured according to ISO 534:2011) of the coated paper product is 52-68 µm, such as 54-66 µm.

[0029] The repulpability measured according to PTS Method PTS-RH 021/97 of the coated paper product is typically at least 80%. It is preferred that the coated paper product is repulpable from an environmental perspective.

[0030] In a particularly preferred embodiment of the coated paper product the first coating layer comprises EAA to talc in a ratio of between 100:30 and 100:75, the second coating layer comprises EVOH and/or PVOH and clay in a EVOH and/or PVOH to clay ratio of between 100:1 and 100:30, and the third coating layer comprises EAA to talc in a ratio of 100:15 to 100:60. Such embodiment is advantageous as it combines barrier properties, barrier crack resistance, blocking resistance, grease resistance, heat sealability and possible application of a sealant layer.

[0031] In another particularly preferred embodiment of the coated paper product the first coating layer comprises EAA to talc in a ratio of between 100:30 and 100:75, the second coating layer comprises EVOH and/or PVOH, and the third coating layer comprises EAA to talc in a ratio of 100:15 to 100:60. Such embodiment is advantageous as it combines water vapour and oxygen barrier properties, barrier crack resistance, blocking resistance, grease resistance, heat sealability and possible application of a sealant layer.

[0032] As a second aspect of the present disclosure, there is provided a flow-wrapped product obtained by flow-wrapping a product in a coated paper product according to the first aspect, wherein the flow-wrapped product has a longitudinal fin seal and end fin seals. A flow-wrapped product is obtainable from a HFFS machine.

[0033] The examples and embodiments discussed above in connection to the first aspect apply to the second aspect mutatis mutandis.

[0034] As a third aspect of the present disclosure, there is provided a sealed bag, such as a gusseted bag or a pillow bag, having a longitudinal seal and each end portion is sealed by a fin seal produced from a coated paper product according to the first aspect.

[0035] A filled gusseted bag is obtainable from a VFFS machine. Such bag has a longitudinal seal adhering two overlapping ends of the paper material to each other to form a lap seal. In an alternative embodiment of the filled bag, the longitudinal seal is a fin seal. Further, the bag has a top end sealed by a fin seal and a bottom end sealed by a fin seal.

[0036] A filled pillow bag is obtainable from a VFFS machine. Such bag has a longitudinal seal adhering two overlapping ends of the paper material to each other to form a lap seal. In an alternative embodiment of the filled bag, the longitudinal seal is a fin seal. Further, the bag has a top end sealed by a fin seal and a bottom end sealed by a fin seal.

[0037] The examples and embodiments discussed above in connection to the first and second aspect apply to the third aspect mutatis mutandis.

[0038] As a fourth aspect of the present disclosure, there is provided use of a coated paper product according to the first aspect for wrapping a product, such as flow-wrapping a product, in sealable paper bags, such as a gusseted bag or a pillow bag, in e-commerce packaging, in bedding packaging, such as pillow packaging, or in tissue wrapping.

[0039] The examples and embodiments discussed above in connection to the first, second and third aspect apply to the fourth aspect mutatis mutandis.

[0040] As a fifth aspect of the present disclosure there is provided a method of producing a coated paper comprising the steps of:

• providing a paper substrate comprising a first and second side; and
• coating the first side of the paper substrate with a first coating layer, wherein the first coating layer comprises a binder; and
• coating a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);
• coating a third coating layer on the second coating layer, wherein the third coating layer comprises ethylene-acrylic acid (EAA) latex and talc, and wherein the dry weight ratio of EAA latex to talc in the third coating layer is between 100:5 and 100:70.

[0041] All the coating layers may be applied in-line (also referred to as on-line). In such case, the productivity is increased by eliminating the handling operations linked to off-line treatment and by eliminating, or at least reducing, the amount of waste. When an in-line process is conducted, the coating weight is typically below 10 g/m² in the first, second and third coating layers to allow for sufficient drying between coating steps as well as prior to reeling. A non-blocking coating is in such case also advantageous.

[0042] The coating layers are typically applied using a blade coater, rod coater, air-knife coater, rotogravure coater or curtain coater. The first, second and third coating layers may be applied with the same coating technique or different coating techniques.

[0043] The second coating layer may be produced in one single coating step or in a plurality of coating steps. In the latter case, the second coating layer is built up by a plurality of sub-layers applied in various runs. In such case, each of the sub-layers preferably have identical composition so that the formed second coating layer is homogenous. The first coating layer and at least part of the second coating layer, i.e. a first sub-layer of the second coating layer, may be applied in the same coating step. The rest of the second coating layer, i.e. a second sub-layer, in a separate coating step and the third coating layer in yet another separate coating step. Alternatively, the second sub-layer of the second coating layer and the third coating layer are coated in the same coating step. In such case, the first coating layer and the first sub-layer of the second coating layer are coated in one step and the second sub-layer of the second coating layer and the third coating layer coated in one step so that the three coating layers are coated in a total of two coating steps. Preferably, in case the second coating layer is built up by a plurality of sub-layers, the second coating layer consists of the first and second sub-layers. A curtain coater is preferably used to allow for application of different superposed coating compositions at the same time. Consequently, in the case of two coating steps two curtain coaters are used.

[0044] In case the polarity of the binder in the first coating layer is lower than the polarity of the PVOH and/or EVOH in the second coating layer, it is beneficial to coat the first coating layer at the same time as a first sub-layer of the second coating layer from a perspective of wetting. The inventors have realized that coating of a less polar binder on the paper substrate as well as the more polar PVOH and/or EVOH in the second coating layer is facilitated if done "wet-on-wet", i.e. application of at least part of the second layer prior to drying of the first coating layer.

[0045] The first coating layer, second coating layer and third coating layer may, alternatively, be applied in separate coating steps.

[0046] In one embodiment, the method comprises drying between the application of the second coating layer and the application of the third coating layer. Drying is typically performed with non-contact drying, such as IR and/or hot air, or contact drying, such as a drying cylinder, or a combination of non-contact and contact drying.

[0047] The PVOH and/or EVOH is typically dispersed in water when coating the second coating layer on the first coating layer. PVOH is inherently soluble, or at least dispersible, in water. Ethylated PVOH is also dispersible in water. EVOH, having a higher ethylene content than PVOH, is typically not inherently soluble or dispersible in water. It is, thus, preferred that the EVOH is a water-dispersible copolymer of EVOH and a polar monomeric unit such as a carboxylic acid. An example of such water-dispersible copolymer of EVOH is described in EP1762585 A1 by SUMITOMO SEIKA CHEMICALS CO., LTD.

[0048] The examples and embodiments discussed above in connection to the first, second, third and fourth aspects apply to the fifth aspect mutatis mutandis.

[0049] As a sixth aspect of the present disclosure there is provided a method of flow-wrapping a product comprising a step of flow-wrapping the product in a coated paper product according to the first aspect of the present disclosure, wherein said flow-wrapping step comprises formation of a fin seal by sealing the coated paper product.

[0050] Typically, the sealing is conducted by heat-sealing. Alternatively, the method further comprises the step of applying a sealant layer, preferably a cold-seal layer, onto part of the third coating layer prior to formation of a fin seal and sealing is conducted by sealing said sealant layer.

[0051] The base paper is typically an MG paper. In such case, the method may further comprise the step of printing the glazed side of the coated paper product. The printing of the glazed side of the coated paper product and the printing and the application of the sealant layer may be carried out in the same machine. Typically, the coated paper product is formed into a bag, filled and sealed in a machine, such as a form fill sealing (FFS) machine, such as a vertical form fill sealing (VFFS) machine or horizontal form fill sealing (HFFS) machine.

[0052] A typical product to be flow-wrapped in the paper-based material of the present disclosure is a protein bar, a snack bar or a chocolate bar.

[0053] The examples and embodiments discussed above in connection to the first, second, third, fourth and fifth aspects apply to the sixth aspect mutatis mutandis.

[0054] As a seventh aspect of the present disclosure there is provided a method of forming a filled bag, in which a coated paper product according to the first aspect of the present disclosure is formed into a bag, filled and sealed in a machine, such as a form fill sealing (FFS) machine, such as a vertical form fill sealing (VFFS) machine or horizontal form fill sealing (HFFS) machine.

[0055] A typical product to be packed in a sealed barrier bag made from the paper-based material of the present disclosure are dry foods, such as confectionary or baked goods. Alternatively, the product is cosmetics and toiletries.

[0056] The examples and embodiments discussed above in connection to the first, second, third, fourth, fifth and sixth aspects apply to the seventh aspect mutatis mutandis.

[0057] As an eight aspect of the present disclosure there is provided a method of forming a wrapped item comprising the steps of:

a) providing a coated paper product according to the first disclosure;

b) wrapping an item with the paper product; and

c)heat-sealing at least part of the paper product so that a sealed wrapping is formed.

[0058] The paper product may be sealed to itself in step c). In such case, the wrapped item can be produced from a single paper product by folding the paper product followed by heat-sealing. Alternatively, the paper product is sealed to a second paper product in step c). In such case, the overwrapped item can be produced without the need for folding any of the paper products.

[0059] A typical item, i.e. product, that is wrapped is tissue wrapping, such as wrapping of rolls of kitchen paper towels and/or toilet paper, or bedding wrappings, such as pillows and duvets.

[0060] The examples and embodiments discussed above in connection to the first, second, third, fourth, fifth, sixth and seventh aspects apply to the eight aspect mutatis mutandis.

EXAMPLES

Coating of paper

Paper substrate

[0061] The following paper substrates were used:

• A machine-glazed (MG) base paper (release 85, Billerud) having a grammage of 48 g/m² produced from never-dried bleached SW pulp that was coated on the glazed side or on the non-glazed side.
• A machine-finished (MF) base paper (Axello tough white, Billerud) having a grammage of 80 g/m² produced from never-dried bleached SW pulp that was coated on the calendered or on the non-calendered (rough) side.

First coating layer

Binder

[0062] Ethylene acrylic acid (EAA) latex (Michem Flex HS 1130 or Paramelt EAA) having a solids content of about 45% or acetate acrylate copolymer (VAcA) latex (CHP 125) having a solids content of about 50% or acrylic latex (Rhobarr 214, DOW) having a solids content of about 45% or polyolefin latex (Rhobarr 325, DOW) having a solids content of about 45%.

Pigment

[0063] The first coating layer was either produced with or without pigments. Talc (Finntalc C15B2), kaolin clay (Barrisurf LX, form factor 60) or CaCO₃ (Setacarb HG-ME 75%)) was added to and dispersed in one of the binders.

Second coating layer

Binder

[0064] Polyvinyl alcohol (PVOH, Poval) or ethylated PVOH (Exceval HR3010) dispersed in water were used as binders.

Pigment

[0065] Bentonite clay (Cloisite Na+) having a typical dry particle size <25 µm (D₅₀).

Third coating layer

Binder

[0066] Ethylene acrylic acid (EAA) latex (Michem Flex HS 1130 or Paramelt EAA) having a solids content of about 45%.

Pigment

[0067] Talc (Finntalc C15B2), kaolin clay (Barrisurf LX, form factor 60) or CaCO₃ (Setacarb HG-ME 75%)) was added to and dispersed in one of the binders.

[0068] The coatings of all layers were either coated with a pilot-scale blade coater, or lab-scale rod coater or pilot-scale curtain coater.

[0069] The composition of each coating is presented in Table 1. The coatings coated with a lab-scale rod coater are marked with "a". The rest of the coatings were applied using a pilot-scale blade coater.

[0070] Samples 1-22 are dual-coated samples with only the first and third coating layer applied without the second coating layer.

[0071] Samples 23 & 29 are also a dual-coated samples, but instead with only the first and second coating applied.

[0072] Samples 24-28 & 30 are triple-coated samples with the first, second and third coating applied.

[0073] Sample 31 is a single-coated sample.

[0074] In samples 1-25 a pilot-scale blade coater or lab-scale rod coater. In samples 26-31 a pilot-scale curtain coater was used.

[0075] In samples 24-25 all three coating layers were applied in separate coating runs.

[0076] In samples 26-30 the first coating layer and a second coating layer was coated together in one single coating run. In samples 26-8 & 30 an additional run of coating with the second coating layer was applied prior to drying. The second coating layer applied in the first run and the second coating layer applied in the second run merged into one single second coating layer after drying. Thereafter, the third coating layer was coated in yet another separate coating run for samples 26-28 & 30.

Barrier properties

WVTR

[0077] To evaluate the barrier properties against water vapour, the water vapour transmission rate (WVTR) was measured according to ISO 15106-1 at 23 °C and 50% relative humidity (RH) as well as at 30°C and 80% RH.

HVTR

[0078] To evaluate mineral oil migration barrier properties, the hexane/heptane vapour transmission rate (HVTR) was measured. The determination of the hexane vapour transmission rate (HVTR) was performed in a permeability cup (evaporation chamber) with a sealable closure fixable with screws. The closure has an open surface area which is sealed with the barrier material. A volume of hexane or heptane (9-10 ml) is filled into the evaporation chamber onto a sponge (to reach a liquid/gas equilibrium as quickly as possible) and the weight of hexane/heptane vapour that goes through the exposed surface of a functional barrier, is expressed in gram per square meter of the surface area per day. The samples were prepared by using a punch and visually inspected to see that there were no surface defects or damages (e.g. creases or pin holes). Under controlled experimental conditions (23° ± 1°C and 50 ± 2% relative humidity), the paper sample was fixed into the closure head, the barrier coatings facing the inner side. The chamber was closed as quickly as possible. The filled evaporation chamber is then weighed after 1, 2, 4 hrs and 1 day. The HVTR was then calculated according to:

OTR

[0079] To evaluate the barrier properties against oxygen gas, the oxygen transmission rate (OTR) was measured according to ASTM D3985 at 23 °C and 50% relative humidity (RH) as well as at 23°C and 80% RH.

[0080] The results of WVTR, HVTR and OTR measurements are presented in Table 2 and the sample numbering is the same as in Table 1.

Table 2. Results of WVTR, HVTR and OTR measurements.

Sample	WVTR (g/m2*d) (23°C/50%RH)	WVTR (g/m2*d) (30°C/80%RH)	HVTR (g/m2*d)	OTR (g/m2*d) (23°C/50%RH)	OTR (g/m2*d) (23°C/80%RH)
1	7.86	71.43
2	6.67	40.89
3	4.10	31.90
4	6.19	40.10
5	4.91	41.51
6	7.15	53.89
7	9.58	58.73
8	8.78	46.06
9	9.02	66.77
10	9.00	52.73
11	10.42	63.57	179.3
12	6.80	30.08	191.1
13	20.45	101.74	57.9
14	18.64	75.33	91.3
15	18.92	80.93	43.6
16	24.40	95.31	98.6
17	6.6	22.5
18	5	67
19	4.5	38.8
20	5.6	41.8
21	15.9	90
22	8	39.9	23
23	1.1			130
24	0.6	35.2		6.5	38.5
25	2.7			Fail
26	4	50.8		Fail
27	2	31.2		224
28	2	40.9		63.2
29	2.8			Fail
30	2.7			7.7
31		108

[0081] Good barrier properties against water vapour were obtained for both a pigmented first coating layer (samples 1-16, 18-31) as well as a first coating layer free of pigments (sample 17). The same applies to the lower grammage MG paper (samples 1-17 & 23-25) as well as the higher grammage MF paper (samples 18 & 25-30). Moreover, it is concluded based on the data that irrespective of binder in the first coating layer, the barrier properties against water vapour were satisfactory. In addition, it has shown that it does not matter on which side, i.e. smooth or rough, of the paper substrate the coating is applied to obtain good barrier properties.

[0082] Barrier properties against mineral oil, i.e. HVTR barrier, was provided independently of binder in the pre-coating. A particularly good barrier was provided using VAcA latex (samples 13-16) or acrylic latex (sample 22) in the pre-coating, especially acrylic latex.

[0083] In samples 23-30 barrier properties against oxygen were evaluated. In case only the first and second coating layers were applied (sample 23, 27 & 29), the oxygen barrier properties were not satisfactory at 23°C and 50%RH. On the other hand, when also the third coating layer was applied both the water vapour barrier properties and oxygen barrier properties were good (samples 24, 28 & 30). As shown in sample 24, the oxygen barrier properties were good also at 23°C and 80%RH. Moreover, independently if the second coating layer was applied in one single step (sample 24) or in two steps (samples 28 & 30) the oxygen barrier properties were good. In addition, the second coating layer provides oxygen barrier properties independently on if clay was added (samples 28 & 30) or not added (sample 24). Moreover, both PVOH (sample 24) and ethylated PVOH (sample 30) showed good oxygen barrier properties.

[0084] Based on the barrier properties, it is concluded that a paper substrate coated with a first coating with a binder, a second coating comprising an oxygen barrier polymer, and a third coating comprising EAA provides good water vapour and oxygen barrier properties.

Runnability & handling

Folded paper oil resistance - crack-resistance measurement

[0085] By measuring the folded oil resistance from the barrier side, the ductility is measured, i.e. how well the formed barrier resists cracking. The methods is described in detail herein.

[0086] Rape seed oil was mixed with 1 % colorant (Sudan blue II) and stirred on a magnetic stirrer until fully mixed.

[0087] 3 samples (14×14 cm) of each coated paper were prepared. The samples were one by one arranged in a folding punch with the barrier side downwards. The folding punch has a V-shaped punch and a V-shaped weight is arranged on top so that when the sample is pushed down by the weight, a 90° fold-line along the entire paper is formed. The weight was applied on the opposite side of the paper from the barrier coating pushing the barrier side downwards. Two additional fold-lines were formed on the paper. All three fold-lines were evenly distributed with a distance of about 4 cm. After the third fold-line had been formed, the paper was turned 90° and three additional fold-lines were made in the same way, thereby obtaining a grid pattern.

[0088] In a cobb ring a blotting paper was arranged with one paper sample on top of the blotting paper. The paper sample had the barrier coated side upwards. The coloured rape seed oil (10 ml) was dosed into the ring and evenly distributed over the paper sample immediately. After 2 minutes the paper sample was taken out from the ring and excess oil was removed with additional blotting papers and lint-free drying paper.

[0089] Within 10 minutes from the removal, the paper sample was scanned in a computer scanner and the number of visible blue dots counted manually. The blue dots appear where the barrier has cracked and oil could enter into the paper. The criteria for evaluation are shown in Table 3 below. The analysis was performed in triplicate and the presented result in Table 5 is the average result.

Table 3. Criteria for evaluation of barrier ductility measurements.

Number of dots	Category
<5	Excellent
<15	Good
15-30	Moderate
>30	Poor

Blocking

[0090] After coating of the paper with the first and second coatings layers the paper was reeled up. After about 24 h, the paper was reeled out and blocking was evaluated according to the following criteria presented in Table 4.

Table 4. Criteria for evaluation of blocking resistance.

	Blocking
Possible to reel out the paper without any sticking of the coating	No
Possible to reel out the paper but the coating was sticking to some extent	Yes, some
Not possible to reel out the paper due to major sticking of the coating	Yes

Heat-sealing

[0091] The maximum heat seal strength was measured according to ASTM F88 & EN 868-5 and settings were 0.5 s, 160 °C and 3 bar on 15 mm wide samples. The results are presented in Table 5.

Table 5. Results from evaluation of runnability & handling properties.

Sample	Barrier crack resistance	Blocking	Heat seal Fmax (N)
1	Poor	No	2.86±0.15
2	Poor	No	2.85±0.21
3	Poor	No	2.90±0.19
4	Moderate	No	2.86±0.12
5	Poor	No
6	Good	No
7	Moderate	No
8	Good	No
9	Poor	No
10	Moderate	No
11	Good	No	2.95±0.21
12	Excellent	No	3.02±0.27
13	Good	No
14	Excellent	No
15	Excellent	No
16	Excellent	No
17	Excellent	No
18	Excellent	No	3.9
19	Poor
20	Poor
21	Poor	Yes, some
22	Good	No
23	Excellent	No
24	Excellent	No
25	Excellent	No
26	Excellent	No
27	Excellent	No
28	Excellent	Tacky	6.8
29	Excellent	No
30	Excellent	No	2.3
31	Excellent	No

[0092] A high barrier crack resistance in combination with blocking resistance was obtained for both a pigmented first coating (samples 11-16,18-19, 23-27 & 29-31) as well as a pre-coating free of pigments (sample 17). The same applies to the lower grammage MG paper (samples 11-17 & 23-25) as well as the higher grammage MF paper (samples 18-19, 26-27 & 29-31), and heat-sealibilty was obtained independently of MG paper (samples 11-12) or MF paper (samples 18, 28 & 30).

[0093] It is fair to assume that it is the outer coating layer that is most important with respect to heat-sealability and blocking resistance. As shown, the heat-sealability of a sample containing a triple coating (sample 28) was in fact even higher than that of the dual-coatings. However, this barrier paper had a tacky outer coating leading to problems with blocking, which is believed to be due to the absence of talc in the EAA of the third coating layer.

[0094] As shown in samples 8, 11-18, 22 & 30, an outer coating layer comprising EAA and talc, wherein the ratio between EAA and talc is from 100:12 (sample 8) to 100:68 (sample 22) provides heat-sealability and blocking resistance. Using calcium carbonate instead of talc (samples 7 & 9) or kaolin clay instead of talc (samples 1, 3 & 4) in the outer coating layer yields unsatisfactory crack resistance. Likewise, an outer coating free of talc (samples 19-20) as well as an outer coating containing EAA and talc in a weight ratio of 100:80 (sample 21) or above (samples 2 & 5) yields unsatisfactory crack resistance.

[0095] In combination with the findings of the barrier properties it can thereby be concluded that a paper substrate coated with a first coating with a binder, a second coating comprising an oxygen barrier polymer represented by PVOH or ethylated PVOH, and a third coating comprising EAA and talc in a weight ratio of about 100:5 to 100:70 provides good water vapour and oxygen barrier properties as well as heat-sealability and blocking resistance.

Contact angle and surface energy

[0096] Water and di-iodomethane (DIM) contact angle was measured according to TAPPI T 558 on the surface of the second coating layer to evaluate the wetting of the surface. The surface energy is derived from the contact angle measurements by plotting (1+cosθ)/2^∗(σ_L/σ_L^d)^½) vs (σ_L^p/σ_L^d)^½, wherein θ is the contact angle formed between the liquid drop and solid surface, σ_L is the liquid surface tension, and superscripts d and p stand respectively for dispersive and polar components of the liquid surface tension. After plotting, the points were fitted to a straight line to calculate σ_s^p and σ_s^d from the slope and intersection with the vertical axis, respectively. σ_s is the solid surface free energy and the surface energy is the sum of σ_s^p + σ_s^d.

[0097] The contact angle as well as surface energy reflects the ability of the surface to be coated, i.e. wetted, with a sealant layer. The measurement was conducted at the 1.0 s checkpoint. The results are presented in Table 6.

Cold-seal wetting

[0098] To further evaluate the possibility to coat the surface with an additional sealant, a cold-seal (Loctite Liofol CS 22-422, Henkel) was applied onto the third coating layer by using a lab rod coater. If a uniform coating was formed, i.e. did coating did not form pearls, the surface could be wet by the cold-seal.

[0099] The total surface energy is the key factor to wetting. Moreover, it is believed by the inventors that it is the top-coating that contributes the most to the total surface energy. A similar top-coat to that in samples 9-11 is therefore fair to assume that such top-coat is also wettable with a cold-seal. Both samples 10 & 11 have an outer coating consisting of EAA and talc and the weight ratio is 100:12 (sample 10) and 100:50 (sample 11).

[0100] Thereby, in combination with the findings it is concluded that a paper substrate coated with a first coating with a binder, a second coating comprising an oxygen barrier polymer, and a third coating comprising EAA and talc in a weight ratio of about 100:5 to 100:70 provides good water vapour and oxygen barrier properties as well as heat-sealability and blocking resistance, and is also wettable with a cold-seal.

Table 6. Water contact angle, Di-iodomethane (DIM) contact angle and surface energy.

Sample	Water contact angle (°)	DIM contact angle (°)	Total surface energy (mJ/m2)	Cold-seal wetting
1
2
3
4
5
6
7
8
9	76.9	52.7	36.2	Yes
10	96.1	59.0	29.2	Yes
11	90.9	54.6	32.0	Yes
12	89.6	55.2	31.8
13	92.2	55.8	31.2
14	91.4	56.8	30.8
15	92.5	55.6	31.3
16	93.1	56.9	30.5
17
18	97		25.9
19
20
21
22
23
24
25
26
27
28
29
30
31

Grease resistance

Show through time

[0101] The show through times of palm kernel oil is a measure of grease resistance and was measured according to Standard ISO 16532-1. Minimum time as well as average time are presented in Table 7.

Table 7. Show through time of palm kernel oil.

Sample	Average show through (min)	Minimum show through (min)
1	313	190
2	130	80
3	243	120
4	213	120
5	165	113
6	189	109
7	103	103
8	70	53
9	193	115
10	160	148
11	90	54
12	537	43
13	48	36
14	576	335
15	60	10
16	182	34
17
18	603
19
20
21	49	37
22	379	93
23
24
25
26
27
28
29
30	1500	1500
31

[0102] Application of two coating layers on either MG paper (samples 12 & 14) or on MF paper (sample 18) was shown to provide a good grease barrier. By application of the three coating layers a barrier paper having an excellent grease resistance (sample 30) was provided.

Repulpability & ash content

Repulpability

[0103] The repulpability was measured according to PTS Method PTS-RH 021/97 and the results are presented in Table 8.

Ash content

[0104] To fulfil food-grade packaging legislation in Italy it is required that the ash content is below 10 %.

[0105] The ash content was calculated according: (3% ash in 48 g/m² base paper + X1 % pigment in Y1 g/m² in first coating layer + X2 % pigment in Y2 g/m² second coating layer) / Z g/m²; wherein

• X1 and X2 are the pigment contents in the first and second coating layer, respectively;
• Y1 and Y2 are the coating grammages of the first and second coating layer, respectively; and
• Z is the total grammage of the coated paper.

[0106] The calculated ash contents are presented in Table 8.

Table 8. Repulpability according to PTS Method PTS-RH 021/97 and ash content.

Sample	Repulpability	Ash content (total)
1		14%
2		13%
3		15%
4		9%
5		17%
6		11%
7		10%
8	80.1%	7%
9		16%
10	77.6%	10%
11	79.7%	8%
12	81.0%	7%
13	86.9%	8%
14	84.6%	7%
15	84.9%	9%
16	85.1%	8%
17
18	80.0%
19
20
21
22	86.4%
23
24
25
26
27
28	83.0%
29
30
31

[0107] There are four sublevels of repulpability (level A+, A, B, C). The result of the assessment according to the PTS Method PTS-RH 021/97 was that the coated paper product samples having a repulpability of at least 80 % were classified as level A repulpable.

[0108] Both for the lower grammage MG paper and the higher grammage MF paper a level A repulpable classification was measured and obtained for samples 8, 12-16, 23 (MG paper) and 18 (MF paper). Inclusion of the second coating barrier layer (sample 28) did not affect the level A repulpable classification as shown in Table 8.

[0109] Thereby, based on all findings, it is concluded that a paper substrate coated with a first coating with a binder, a second coating comprising an oxygen barrier polymer, and a third coating comprising EAA and talc in a weight ratio of about 100:5 to 100:70 provides good water vapour and oxygen barrier properties as well as heat-sealability and blocking resistance, is also wettable with a cold-seal, is grease-resistant and repulpable.

Claims

1. A coated paper product comprising:

- a paper substrate comprising a first and a second side;

- a first coating layer on the first side of the paper substrate comprising a binder; and

- a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);

- a third coating layer on the second coating layer, wherein the third coating layer comprises talc and ethylene-acrylic acid (EAA) or talc and a polyolefin, and wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:5 and 100:70.

2. The coated paper product of claim 1, wherein the binder of the first coating layer is EAA or vinyl acetate acrylate copolymer (VAcA) or styrene-acrylate (SA) or styrene-butadiene (SB), acrylic latex or polyolefin latex.

3. The coated paper product of claim 1 or 2, wherein the coat weight of the first coating layer is at least 3 g/m², such as 3-10 g/m².

4. The coated paper product of any one of the preceding claims, wherein the coat weight of the second coating layer is 0.5-8 g/m², such as 1-6 g/m².

5. The coated paper product of any one of the preceding claims, wherein the coat weight of the third coating layer is at least 3 g/m², such as 3-10 g/m².

6. The coated paper product of any one of the preceding claims, wherein the paper substrate comprises a pre-coating layer between the paper substrate and the first coating layer.

7. The coated paper product of any one of the preceding claims, wherein the grammage measured according to ISO 536:2020 of the paper substrate is 40-135 g/m², such as 40-100 g/m², such as 40-90 g/m², such as 40-60 g/m², such as 42-55 g/m².

8. The coated paper product of any one of the preceding claims, wherein the second coating layer comprises pigment.

9. The coated paper product of claim 8, wherein the pigment is clay, such as bentonite clay.

10. The coated paper product of any one of the preceding claims, wherein the dry weight ratio of EAA or polyolefin to talc in the third coating layer is between 100:10 and 100:70, such as between 100:10 and 100:60, such as between 100:15 and 100:60, such as between 100:15 and 100:40.

11. A flow-wrapped product obtained by flow-wrapping a product in a coated paper product according to any one of the preceding claims, wherein the flow-wrapped product has a longitudinal fin seal and end fin seals.

12. A sealed bag produced from a coated paper product according to any one of the claims 1-10, such as a gusseted bag or a pillow bag, having a longitudinal seal and each end portion is sealed by a fin seal.

13. Use of a coated paper product according to any one of the claims 1-10 for wrapping a product, such as flow-wrapping a product, in sealable paper bags, such as a gusseted bag or a pillow bag, in e-commerce packaging, in bedding packaging, such as pillow packaging, or in tissue wrapping.

14. A method of producing a coated paper comprising the steps of:

- providing a paper substrate comprising a first and second side; and

- coating the first side of the paper substrate with a first coating layer, wherein the first coating layer comprises a binder; and

- coating a second coating layer on the first coating layer, wherein the second coating layer comprises polyvinyl alcohol (PVOH) and/or ethylene vinyl alcohol (EVOH);

- coating a third coating layer on the second coating layer, wherein the third coating layer comprises ethylene-acrylic acid (EAA) latex and talc, and wherein the dry weight ratio of EAA latex to talc in the third coating layer is between 100:5 and 100:70.

15. The method for producing a coated paper product according to claim 14, wherein the first coating layer and a first sub-layer of the second coating layer forming a part of the second coating layer are applied in the same coating step and a second sub-layer of the second coating layer forming a part of the second coating layer and the third coating layer are applied in the same coating step.

Drawing