Heat sealable coated paper product

Abstract

The present disclosure relates to a heat sealable coated paper product comprising a cellulosic fiber substrate comprising a first face and a second face, the first face comprising a single coating applied in direct contact with the fiber substrate, the coating includes an ethylene (meth) acrylic acid copolymer (EAA / EMAA) or an ethylene-acrylic acid-methacrylic acid terpolymer (EAAMAA) or a mixture thereof in an amount of at least 51% or more by weight based on the dry weight of the coating, and a pigment that is talc and / or calcium carbonate (CaCO3). The present disclosure also relates to a method of producing the heat sealable coated paper product.

Description

Technical Field

[0001] The present disclosure relates to the field of heat - sealable coated paper products. Background Art

[0002] Traditionally, food or food - service packaging has used plastic wrapping materials for the packaging material, which require heat - sealing and provide a certain barrier property. Recently, paper materials with multi - layer plastic material coatings and metal foil layers have been used as heat - sealable barrier materials, replacing the previously used plastic materials.

[0003] For environmental reasons, there is an increasing need to minimize the use of plastic materials and minimize the amount of plastic materials used for coating fiber substrates, because such materials generate a higher carbon footprint and are more troublesome to recycle. However, reducing the amount of plastic materials may have a negative impact on heat - sealability and make the process of applying the coating more difficult, resulting in a higher number of defective products, a greater amount of production waste, and higher costs.

[0004] In view of these needs, it is necessary to develop heat - sealable paper materials to reduce the carbon footprint, be more easily recyclable, while not affecting the heat - sealability and processability of paper products. Summary of the Invention

[0005] The object of the present disclosure is to provide a paper that at least partially overcomes the above - mentioned defects. This is achieved by the heat - sealable coated paper product according to claim 1 and the method for producing a heat - sealable paper product according to claim 17.

[0006] The heat - sealable coated paper disclosed herein includes a fiber substrate, the substrate including a first side and a second side, the first side including a single coating applied in direct contact with the fiber substrate, the coating including ethylene (meth) acrylic acid copolymer (EAA / EMAA) or ethylene - acrylic acid - methacrylic acid terpolymer (EAAMAA) or a mixture thereof, in an amount of 51% or more by weight based on the dry weight of the coating, and a pigment, the pigment being talc and / or calcium carbonate (CaCO3).

[0007] The heat - sealable paper product according to the present invention includes only a single coating, is an environmentally friendly and easily recyclable paper product, while still providing satisfactory heat - sealability. In addition, the heat - sealable paper product is easy to produce, and the number of defective products remains at a low level, having both environmental advantages and cost advantages.

[0008] The single coating according to the present invention comprises the following combination: at least 51% by weight of EAA / EMAA, preferably an EAA / EMAA / EAAMAA in the range of 51% to 85% by weight, and a pigment, which is talc and / or CaCO3, and the single coating has beneficial density properties. It has been found that the beneficial density properties contribute to evenly coating a relatively thin layer on a fibrous substrate in conventional coating techniques such as knife coating without a primer coating.

[0009] Thus, the EAA / EMAA / EAAMAA can be present in an amount in the range of 51 to 85% by weight based on the dry weight of the coating, preferably in the range of 53 to 85% by weight based on the dry weight of the coating, more preferably in the range of 60 to 80% by weight based on the dry weight of the coating.

[0010] The pigment can be present in an amount in the range of 15% to 45% by weight based on the dry weight of the coating, preferably in the range of 20% to 40% by weight based on the dry weight of the coating, and most preferably in the range of 25% to 35% by weight based on the dry weight of the coating. It has been found that this can impart favorable density properties to the coating mixture, thereby improving the processability of the single coating during coating of the fibrous substrate.

[0011] The pigment can have a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater. It has been found that the fact that the pigment has a relatively high aspect ratio can improve the coating performance of the coating.

[0012] The pigment can be talc. In the context of the present disclosure, talc, due to its flaky nature, has been found to provide beneficial coating properties for the EAA / EMAA / EAAMAA and pigment mixture when used in the single coating. The pigment is preferably talc having a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater.

[0013] The fibrous substrate is a cellulose fibrous substrate.

[0014] The fibrous substrate according to the present disclosure includes only one layer of coating on its first side and thus has no primer coating or protective coating. The fact that talc has a flaky shape and a high aspect ratio helps to cover the pores of the fibrous substrate and balance the amount of coating mixture on the surface and in the pores, thereby facilitating uniform coverage of the fibrous substrate.

[0015] At least 90% by weight of the dry coating weight can consist of EAA / EMAA / EAAMAA and pigments, preferably at least 95% by weight of the dry coating weight consists of EAA / EMAA / EAAMAA and pigments. In the context of the present invention, it has been found that coating mixtures in which at least 90% by weight of the dry coating weight can consist of EAA / EMAA / EAAMAA and pigments provide excellent heat sealability, uniform coverage of a single coating on a fibrous substrate, and improved processability.

[0016] The dry coating weight of the coating can be in the range of 4 g / m 2 to 9 g / m 2 Preferably, the dry coating weight of the coating can be in the range of 5 g / m 2 to 8 g / m 2 The inventors have found that such amounts provide improved coverage of the overcoat on the paper substrate, which is particularly important for single-coated paper products.

[0017] The single coating can include surfactants, such as ionic or non-ionic surfactants. Preferred surfactants are non-ionic and anionic surfactants. The single coating can also contain defoamers, blocking agents, and rheology modifiers.

[0018] The single coating can include additives in an amount of 0.01% to 10%. For example, including surfactants in the single coating can improve the running properties of the coater and improve the interaction with the underlying fibrous substrate. The fact that the interaction with the underlying fibrous substrate is improved enhances the film formation of the coating mixture on the fibrous substrate, resulting in a more homogeneous coating even at lower coating amounts.

[0019] The heat seal strength that the coating can have at 120° is preferably 2.5 N / 15 mm or higher. The maximum heat seal strength is measured on a 15 mm test strip sealed for 0.5 s at 120 °C and 3 bar at a non-supported 90-degree angle at 200 mm / min according to ASTM F88 Technique A. This means that 2.5 N is required to separate the sealed paper strips.

[0020] The second side of the fibrous substrate may have been treated with water to reduce the curling of the finished product.

[0021] The recyclability score of the heat-sealable coated paper, measured according to the recyclability test method PTS-RH 021:2012-CatII, can be in the range of 80% to 100%.

[0022] The heat-sealable coated paper has a kinetic friction in the range of 0.15 to 0.25, which is measured on the coated surface and according to the standard method ISO 15359:2011 for measuring the coefficient of kinetic friction. This is beneficial for forming the coated paper into a package suitable for the present disclosure. Higher kinetic friction may pose a risk of abrasion to the coating when formed into a package, which is particularly undesirable for single-coated paper. Lower kinetic friction may indicate that the coated paper is too slippery for the type of package targeted by the heat-sealable coated paper product.

[0023] The second side may not have a heat-sealable coating.

[0024] Measured according to the standard method ISO 536:2020, the grammage of the fiber substrate can be in the range of 30 to 150 g / m 2 of the range.

[0025] The fiber substrate can be a machine-glazed (MG) paper substrate or a machine-finished (MF) paper substrate. Typical applications of these papers include tissue wrapping, dry food packaging, confectionery and baked goods, cosmetics and toiletries, toy packaging, and home textiles, etc. These packages require heat sealing, but the requirements for barrier properties are not as high as those for, for example, vacuum-packed food.

[0026] The fiber substrate can be, for example, an MG fiber substrate and has a grammage in the range of 30 to 120 g / m 2 of the range.

[0027] The fiber substrate can be a machine-glazed (MG) paper and has a tensile energy absorption index (TEA index) in the range of 1 J / g to 6 J / g, preferably in the range of 1.2 J / g to 3.0 J / g, which is measured according to the standard method ISO 1924-3.

[0028] The fiber substrate can be an MG paper substrate, and the first side of the fiber substrate has a Bendtsen roughness value of 1400 ml / min or lower, preferably 1300 ml / min or lower, such as in the range of 170 ml / min to 1200 ml / min, which is measured according to the standard method ISO 8791-2:2013.

[0029] It has been found that when measuring the first side of a fibrous substrate, MG paper substrates having a Bentts roughness value in the range of 170 ml / min to 1400 ml / min, particularly in the range of 190 ml / min to 1350 ml / min, such as in the range of 200 ml / min to 1200 ml / min, provide a surface that is smooth enough to prevent the coating mixture from penetrating down into the paper substrate, while still allowing a high enough coating as disclosed herein, thus providing favorable heat-sealing properties for the paper product.

[0030] The Gurley porosity of the MG paper substrate according to the present disclosure can be 25 s or greater, preferably 30 or greater, such as in the range of 25 to 2000 s.

[0031] The Gurley porosity is measured according to ISO 5636-5. The air resistance according to Gurley, i.e., the Gurley porosity, is the time (s) required for 100 ml of air to pass through a specified area of the paper. A short time means a high porosity of the paper, while a high Gurley porosity value indicates a low porosity of the paper substrate. In the context of the present disclosure, a relatively low porosity may be preferred because it means a lower tendency for the coating to penetrate through the low-porosity paper. Thus, by reducing the Gurley porosity of the paper substrate and combining a large amount of EAA / EMAA / EAAMAA as disclosed herein, an environmentally friendly coated paper product with good heat-sealing properties can be obtained.

[0032] The fibrous substrate can alternatively be an MF paper substrate and has a grammage in the range of 50 g / m 2 to 150 g / m 2 optionally in the range of 55 g / m 2 to 130 g / m 2 of the range.

[0033] The fibrous substrate can be an MF paper substrate and has a Bentts roughness value on the first side of the fibrous substrate in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min, which is measured according to the standard method ISO 8791-2:2013.

[0034] It has been found that a MF paper substrate having a Bentts roughness value on the first side of the fibrous substrate in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min, provides a surface smooth enough to prevent the coating mixture from penetrating down into the paper substrate while still allowing a high enough coating as disclosed herein, thereby providing favorable heat seal properties for the paper product.

[0035] The Gurley air permeability of the MF paper substrate according to the present disclosure can be 30 s or greater, such as 32 s or greater, such as in the range of 30 to 2000 s. The Gurley air permeability is measured according to ISO 5636-5.

[0036] The fibrous substrate can be a MF paper substrate and has a tensile energy absorption index (TEA index) in the range of 1 J / g to 6 J / g, which is measured according to the standard method ISO 1924-3.

[0037] The MF paper substrate for filling heavier packages can suitably have a TEA index in the range of 2 to 3 J / g, while the MF paper substrate for filling lighter high-end packages can suitably have a TEA index in the range of 1 to 2 J / g.

[0038] In one embodiment, the fibrous substrate is a stretchable paper substrate; that is, according to ISO 1924-3:2005, the paper substrate has a stretch ratio of at least 7% in the machine direction (MD) of the paper machine and at least 7% in the cross direction (CD). Preferably, according to ISO 1924-3:2005, the stretch ratio in the machine direction (MD) is at least 8% and the stretch ratio in the cross direction (CD) is at least 8%.

[0039] In an embodiment, according to ISO 1924-3:2005, the stretchable paper substrate can have a stretch ratio of at least 9% in at least one of the machine direction (MD) and the cross direction (CD) of the paper machine. The stretchable paper has a stretch ratio of at least 10% in the MD or CD.

[0040] The stretchable paper substrate can have a stretch ratio in the CD direction in the range of 7 to 15%, optionally in the range of 8% to 15%, which is measured according to the standard method ISO 1924-3; optionally the fibrous substrate is a MF paper substrate. In addition, the fibrous substrate can have a stretch ratio in the MD direction in the range of 7 to 25%, optionally in the range of 8% to 20%, which is measured according to the standard method ISO 1924-3.

[0041] This stretchable paper substrate is particularly suitable for preparing molded articles from a paper substrate, such as for replacing plastic articles and reducing the amount of coating while still providing heat-sealability, which is of great significance.

[0042] This stretchable paper substrate may comprise at least 50% softwood pulp, preferably at least 75% softwood pulp, and more preferably at least 90% softwood pulp, and wherein the fiber substrate has a stretch ratio of at least 7% in the machine direction (MD) and at least 7% in the cross direction (CD), optionally, the fiber substrate has a stretch ratio of at least 9% in the machine direction (MD) and at least 9% in the cross direction (CD), as measured according to the standard method ISO 1924-3:2005.

[0043] The stretchable paper substrate according to the present disclosure may have a grammage in the range of 80 to 300 g / m 2 .

[0044] The first side of the fiber substrate of the stretchable paper substrate according to the present disclosure may have a Bendtsen roughness value in the range of 1200 to 2000 ml / min.

[0045] As measured according to the standard method ISO 1924-3:2005, the stretch energy absorption (TEA) index of the stretchable paper substrate may be at least 3.5 J / g in the machine direction (MD) and / or at least 2.9 J / g in the cross direction (CD).

[0046] The Gurley air permeability of the stretchable paper substrate according to the present disclosure may be higher than 15 s, preferably higher than 20 s.

[0047] According to a second aspect, the present disclosure relates to a method of producing a heat-sealable coated paper product, comprising the steps of:

[0048] - providing a fiber substrate comprising a first side and a second side; and

[0049] - coating the first side of the fiber substrate with a coating applied in direct contact with the fiber substrate, the coating comprising ethylene (meth)acrylic acid (EAA / EMAA) or ethylene-acrylic acid-methacrylic acid terpolymer (EAAMAA) or a mixture thereof, in an amount of 51% or more by weight based on the dry weight of the coating, and a pigment, the pigment being talc and / or calcium carbonate (CaCO3), the coating being a single coating on the first side of the fiber substrate.

[0050] The coating provided on the first surface of the fibrous substrate comprises the following combination: at least 51% by weight of EAA / EMAA, EAAMAA, preferably in the range of 51% to 85% by weight of EAA / EMAA / EAAMAA, and a pigment, said pigment being talc and / or CaCO3, and the coating has beneficial density properties. It has been found that the beneficial density properties contribute to the uniform coating of a relatively thin layer on the fibrous substrate in conventional coating techniques such as knife coating without a primer coating.

[0051] Thus, EAA / EMAA / EAAMAA can be present in an amount in the range of 51 to 85% by weight based on the dry weight of the coating, preferably in the range of 53 to 85% by weight based on the dry weight of the coating, more preferably in the range of 60 to 80% by weight based on the dry weight of the coating.

[0052] The pigment can be present in an amount in the range of 15% to 45% by weight based on the dry weight of the coating, preferably in the range of 20% to 40% by weight based on the dry weight of the coating, most preferably in the range of 25% to 35% by weight based on the dry weight of the coating. It has been found that this enables the coating mixture to have favorable density properties, thereby improving the processability of the single coating during coating of the fibrous substrate.

[0053] The pigment can have a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater. It has been found that the fact that the pigment has a relatively high aspect ratio can improve the coating performance of the coating.

[0054] The pigment can be talc. In the context of the present disclosure, talc, due to its flaky nature, has been found to provide beneficial coating properties for the EAA / EMAA / EAAMAA and pigment mixture when used in a single coating. The pigment is preferably talc having a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater.

[0055] The fibrous substrate is a cellulose fibrous substrate.

[0056] At least 90% by weight of the dry coating weight of the coating can consist of EAA / EMAA / EAAMAA and the pigment, preferably at least 95% by weight of the dry coating weight consists of EAA / EMAA / EAAMAA and the pigment. In the context of the present invention, it has been found that a coating mixture in which at least 90% by weight of the dry coating weight consists of EAA / EMAA / EAAMAA and the pigment provides excellent heat sealability, uniform coverage of the single coating on the fibrous substrate, and promotes processability.

[0057] The dry coating weight of the coating can be in the range of 4 g / m 2 to 9 g / m 2 range. Preferably, the dry coating weight of the coating can be in the range of 5 g / m2 in the range of from 1 g / m to 8 g / m 2 The inventors have found that such amounts provide improved coverage of the coating on the paper substrate, which is particularly important for single-coated paper products.

[0058] The single coating may include surfactants such as ionic or non-ionic surfactants. Preferred surfactants are non-ionic and anionic surfactants. The single coating may also contain defoamers, blocking agents, and rheology modifiers.

[0059] The single coating may include additives in an amount of from 0.01% to 10%. For example, including surfactants in the single coating can improve the runnability of the coater and improve the interaction with the underlying fiber substrate. The fact that the interaction with the underlying fiber substrate is improved enhances the film formation of the coating mixture on the fiber substrate, resulting in a more homogeneous coating even at lower coating amounts.

[0060] The method may include the step of treating the second side of the fiber substrate with water to reduce curling of the finished product.

[0061] The second side may be free of a heat-sealable coating.

[0062] The grammage of the fiber substrate, measured according to the standard method ISO 536:2020, may be in the range of 30 to 150 g / m 2 .

[0063] The fiber substrate may be a machine-glazed (MG) paper substrate or a machine-finished (MF) paper substrate.

[0064] The fiber substrate may be, for example, an MG fiber substrate and have a grammage in the range of 30 to 120 g / m 2 .

[0065] The fiber substrate may be a machine-glazed (MG) paper and have a tensile energy absorption index (TEA index) in the range of 1 J / g to 6 J / g, preferably in the range of 1.2 J / g to 3.0 J / g, as measured according to the standard method ISO 1924-3.

[0066] The fiber substrate may be an MG paper substrate and the first side of the fiber substrate may have a Bendtsen roughness value of 1400 ml / min or lower, preferably 1300 ml / min or lower, such as in the range of 170 ml / min to 1200 ml / min, as measured according to the standard method ISO 8791-2:2013.

[0067] It has been found that when measuring the first side of a fibrous substrate, an MG paper substrate having a Bendtsen roughness value in the range of 170 ml / min to 1400 ml / min, particularly in the range of 190 ml / min to 1350 ml / min, such as in the range of 200 ml / min to 1200 ml / min, provides a sufficiently smooth surface to prevent the coating mixture from penetrating downward into the paper substrate while still allowing a sufficiently high coating as disclosed herein, thereby providing favorable heat-sealing properties for the paper product.

[0068] The Gurley porosity of the MG paper substrate according to the present disclosure can be 25 s or greater, preferably 30 or greater, such as in the range of 25 to 2000 s.

[0069] The Gurley porosity is measured according to ISO 5636-5. The air resistance according to Gurley, i.e., the Gurley porosity, is the time (s) required for 100 ml of air to pass through a specified area of the paper. A short time means a high porosity of the paper, while a high Gurley porosity value indicates a low porosity of the paper substrate. In the context of the present disclosure, a relatively low porosity may be preferred because it means a lower tendency for the coating to penetrate through the low-porosity paper. Thus, by reducing the Gurley porosity of the paper substrate and combining a large amount of EAA / EMAA / EAAMAA as disclosed herein, an environmentally friendly coated paper product with good heat-sealing properties can be obtained.

[0070] The fibrous substrate can alternatively be an MF paper substrate and has a grammage in the range of 50 g / m 2 to 150 g / m 2 optionally in the range of 55 g / m 2 to 130 g / m 2 of the range.

[0071] The fibrous substrate can be an MF paper substrate and has a Bendtsen roughness value on the first side of the fibrous substrate in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min, which is measured according to the standard method ISO 8791-2:2013.

[0072] It has been found that a MF paper substrate having a Bent surface roughness value on the first side of the fibrous substrate in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min, provides a sufficiently smooth surface to prevent the coating mixture from penetrating down into the paper substrate while still allowing a sufficiently high coating as disclosed herein, thereby providing favorable heat seal properties for the paper product.

[0073] The Gurley air permeability of the MF paper substrate according to the present disclosure can be 30 s or greater, such as 32 s or greater, such as in the range of 30 to 2000 s. The Gurley air permeability is measured according to ISO 5636-5.

[0074] The fibrous substrate can be a MF paper substrate and has a Tensile Energy Absorption Index (TEA Index) in the range of 1 J / g to 6 J / g, which is measured according to the standard method ISO 1924-3.

[0075] The MF paper substrate for filling heavier packages can have a TEA Index preferably in the range of 2 to 3 J / g, while the MF paper substrate for filling lighter high-end packages can have a TEA Index preferably in the range of 1 to 2 J / g.

[0076] In one embodiment, the fibrous substrate is a stretchable paper substrate; that is, according to ISO 1924-3:2005, the paper substrate has a stretch rate of at least 7% in the machine direction (MD) of the paper machine and at least 7% in the cross direction (CD). Preferably, according to ISO 1924-3:2005, the stretch rate in the machine direction (MD) is at least 8% and the stretch rate in the cross direction (CD) is at least 8%.

[0077] In an embodiment, according to ISO 1924-3:2005, the stretchable paper substrate can have a stretch rate of at least 9% in at least one of the machine direction (MD) and the cross direction (CD) of the paper machine. The stretchable paper has a stretch rate of at least 10% in the MD or CD.

[0078] The stretch rate of the stretchable paper substrate in the CD direction can be in the range of 7 to 15%, optionally in the range of 8% to 15%, which is measured according to the standard method ISO 1924-3; optionally the fibrous substrate is a MF paper substrate. In addition, the stretch rate of the fibrous substrate in the MD direction can be in the range of 7 to 25%, optionally in the range of 8% to 20%, which is measured according to the standard method ISO 1924-3.

[0079] This stretchable paper substrate is particularly suitable for preparing molded articles using a paper substrate, such as for replacing plastic articles and reducing the amount of coating while still providing heat-sealability, which is crucial.

[0080] This stretchable paper substrate may comprise at least 50% softwood pulp, preferably at least 75% softwood pulp, and more preferably at least 90% softwood pulp, and wherein the fibrous substrate has a stretch ratio of at least 7% in the machine direction (MD) of the paper machine and at least 7% in the cross direction (CD), optionally, the fibrous substrate has a stretch ratio of at least 9% in the machine direction (MD) of the paper machine and at least 9% in the cross direction (CD), which is measured according to the standard method ISO 1924-3:2005.

[0081] The stretchable paper substrate according to the present disclosure may have a grammage in the range of 80 to 300 g / m 2 of.

[0082] The Bendtsen roughness value of the first side of the fibrous substrate of the stretchable paper substrate according to the present disclosure may be in the range of 1200 to 2000 ml / min.

[0083] Measured according to the standard method ISO 1924-3:2005, the tensile energy absorption (TEA) index of the stretchable paper substrate may be at least 3.5 J / g in the machine direction (MD) of the paper machine and / or at least 2.9 J / g in the cross direction (CD).

[0084] The Gurley air permeability of the stretchable paper substrate according to the present disclosure may be higher than 15 s, preferably higher than 20 s.

[0085] The method optionally includes a step of treating the second side with water or a diluted starch solution of about 1-3% to control curling. The treatment can be carried out by steam, spraying or coating. Detailed Description

[0086] Therefore, the present invention relates to a single-coated heat-sealable fibrous substrate, wherein the single coating comprises an ethylene (meth)acrylic acid copolymer (EAA / EMAA) or an ethylene-acrylic acid-methylacrylic acid terpolymer (EAAMAA) or a mixture thereof, and a pigment, the pigment being talc and / or calcium carbonate (CaCO3), and the single coating comprises at least 51% by weight of EAA / EMAA / EAAMAA based on the dry weight of the coating.

[0087] Since the coating comprises 51% or more by weight of EAA / EMAA / EAAMAA based on the total dry coating weight, the coated paper product can be heat-sealable. Accordingly, the amount of pigment is at most 49% by weight. It has been found that a higher talc content weakens the heat-sealability. Preferably, the maximum heat-seal strength of the coated paper product measured according to ASTM F88 Technique A at a non-supported 90-degree angle at 200 mm / min is 2.5 N or greater, which is measured on a 15 mm test strip sealed at 120 °C and 3 bar for 0.5 s. This means that 2.5 N is required to separate the sealed paper strip.

[0088] Accordingly, the coating may comprise ethylene acrylic copolymer (EAA) and / or ethylene methacrylic copolymer (EMAA) and / or ethylene-acrylic-methacrylic terpolymer (EAAMAA). The coating may comprise only one of these polymers, or a mixture of two polymers, or a mixture of all three polymers. The EAA / EMAA / EAAMAA may be bio-based and / or recyclable.

[0089] The amount of EAA / EMAA / EAAMAA present in the coating may range from 51 to 90% by weight based on the dry weight of the coating, preferably from 53 to 85% by weight based on the dry weight of the coating, more preferably from 60 to 70% by weight based on the dry weight of the coating.

[0090] The pigment may be present in an amount ranging from 15% to 45% by weight based on the dry weight of the coating, preferably from 20% to 40% by weight based on the dry weight of the coating, and most preferably from 25% to 35% by weight based on the dry weight of the coating.

[0091] The pigment may have a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater. Optionally, the pigment has a shape factor in the range of 75 to 100. It has been found that the fact that the pigment has a relatively high aspect ratio can improve the coating performance of the coating.

[0092] The pigment may be talc and / or CaCO3. However, in the context of the present disclosure, it has been found that due to the flaky nature of talc, when used in a single coating, talc can provide beneficial coating performance for the EAA / EMAA / EAAMAA and pigment mixture. The pigment is preferably talc having a shape factor of 40 or greater, preferably 50 or more preferably 75 or greater.

[0093] The dry coating weight of the coating may range from 4 to 9 g / m 2 The ratio of the dry weight of the fibrous substrate to the dry weight of the coating may preferably range from 5 to 8 g / m 2 within the range.

[0094] The single coating may include an additive in an amount of 0.01% to 10%. For example, including a surfactant in the single coating can improve the operability of the coater and improve the interaction with the underlying fibrous substrate. The fact that the interaction with the underlying fibrous substrate is improved enhances the film formation of the coating mixture on the fibrous substrate, resulting in a more homogeneous coating even at lower coating amounts. The surfactant can be a nonionic surfactant or an ionic surfactant, preferably a nonionic surfactant or an anionic surfactant.

[0095] The heat-sealable paper product is a paper-based product that can be used, for example, to replace plastic wrapping materials for packaging that require heat sealing. The heat-sealable paper product can be suitable for preparing packaging containers for powders and granules, where the packaging containers are prepared by a vertical form-fill-seal process. In addition, the packaging material can also be suitable for preparing packages for articles, tablets, and strips, which are prepared by a horizontal form-fill-seal process.

[0096] The second side of the fibrous substrate has been treated with water to reduce the curling of the finished product.

[0097] The cellulose fibrous substrate can be machine-glazed (MG) paper or machine-finished (MF) paper.

[0098] The grammage of the fibrous substrate measured according to ISO 536:2020 is typically 35 to 150 g / m 2 , such as 40 - 120 g / m 2 , such as 42 - 100 g / m 2 . The suitable thickness of the fibrous substrate (measured according to ISO 534:2011) is 40 - 200 μm, such as 48 - 115 μm.

[0099] In one embodiment, the fibrous substrate is an MG paper substrate. Kraft paper is preferred, and at least 80%, preferably at least 90%, by dry weight of the fibers typically used to produce the MG paper substrate are fibers that have never been dried (i.e., virgin fibers). The MG paper has a glazed side and an unglazed side. The glazed side is the side facing the Yankee cylinder (a polished metal cylinder, sometimes called the MG cylinder) used to dry the paper web in the MG paper machine. Contact with the polished metal surface during drying makes the glazed side smoother than the unglazed side.

[0100] Typically, the coating is applied to the less smooth side of the fibrous substrate, the unglazed side. In this case, the opposite side, the glazed side, is usually printed. It is advantageous to apply the coating on the unglazed side to provide the glazed side for printing. A thin layer of water or starch solution (≤1 g / m 2 ) can be applied to the glazed side to control curling. A lacquer can be provided on the optional printed matter, for example, to change the gloss, friction, and / or peel properties.

[0101] The fibrous substrate can be a machine glazed (MG) paper substrate and has a tensile energy absorption index (TEA index) in the range of 1 J / g to 6 J / g, preferably in the range of 1.2 J / g to 3.0 J / g, which is measured according to the standard method ISO 1924-3.

[0102] Tensile strength is the maximum force that the paper can withstand before breaking. In the standard test ISO 1924-3, a strip with a width of 15 mm and a length of 100 mm is used and a constant elongation rate is maintained. Tensile energy absorption (TEA) is sometimes considered the paper property that best reflects the relevant strength of the paper. Tensile strength is a parameter in the TEA measurement, and another parameter is the elongation rate. Tensile strength, elongation rate, and TEA values can be obtained in the same test. The TEA index is the TEA value divided by the grammage. In the same way, the tensile index is obtained by dividing the tensile strength by the grammage.

[0103] The fibrous substrate can be an MG paper substrate, and the first side of the fibrous substrate has a Bendtsen roughness value of 1400 ml / min or lower, preferably 1300 ml / min or lower, such as in the range of 170 ml / min to 1200 ml / min, which is measured according to the standard method ISO 8791-2:2013.

[0104] It has been found that an MG paper substrate having a Bendtsen roughness value on the first side of the fibrous substrate in the range of 170 ml / min to 1400 ml / min, particularly in the range of 190 ml / min to 1350 ml / min, such as in the range of 200 ml / min to 1200 ml / min, provides a sufficiently smooth surface to prevent the coating mixture from penetrating down into the paper substrate while still allowing a sufficiently high coating as disclosed herein, thereby providing favorable heat-sealing properties for the paper product.

[0105] The Gurley air permeability of the MG paper substrate according to the present disclosure can be 25 s or greater, preferably 30 or greater, such as in the range of 25 to 2000 s. The Gurley air permeability is determined according to ISO 5636-5. In the context of the present disclosure, a relatively low porosity may be preferred because this means a lower tendency for the coating to penetrate through the low-porosity paper. Therefore, by reducing the Gurley air permeability of the paper substrate and combining a large amount of EAA / EMAA / EAAMAA as disclosed herein, an environmentally friendly coated paper product with good heat-sealing properties can be obtained.

[0106] According to Gurley air resistance, i.e., Gurley permeability, it is the time (s) required for 100 ml of air to pass through a specified area of the paper. A short time means a high porosity of the paper, while a high Gurley permeability value indicates a low porosity of the paper substrate.

[0107] In an alternative embodiment, the fibrous substrate is an MF paper substrate. For an MF paper substrate, kraft paper is preferred, and at least 80%, preferably at least 90%, by dry weight of the fibers typically used to produce the MF paper are fibers that have never been dried (i.e., virgin fibers). One side of the MF paper substrate is optionally calendered, or neither side is calendered. Drying is accomplished via a plurality of drying cylinders. Optionally, the paper can be compacted by using a Clupac or expanda unit to increase the tensile properties in the machine direction.

[0108] Typically, the coating is applied to the less smooth, uncalendered side of the fibrous substrate. If the opposite side is calendered, i.e., the smooth side, this side is typically printed. The smooth side can be coated with a thin layer of water or starch solution (≤1 g / m 2 ) to control curling. A lacquer can be provided on the optional printed matter, for example, to change the gloss, friction, and / or peel properties.

[0109] The basis weight of the MF paper substrate according to the present disclosure can be in the range of 50 g / m 2 to 150 g / m 2 , optionally in the range of 55 g / m 2 to 130 g / m 2 .

[0110] The Gurley permeability of the MF paper substrate according to the present disclosure can be 30 s or greater, such as 32 s or greater, such as in the range of 30 to 2000 s. The Gurley permeability is determined according to ISO 5636-5.

[0111] The Bendtsen roughness value of the first side of the fibrous substrate of the MF paper substrate can be in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min, which is measured according to the standard method ISO 8791-2:2013. It has been found that an MF paper substrate having a Bendtsen roughness value of the first side of the fibrous substrate in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min provides a sufficiently smooth surface to prevent the coating mixture from penetrating downward into the paper substrate, while still allowing a sufficiently high coating as disclosed herein, thus providing favorable heat-sealing properties for the paper product.

[0112] The MF paper substrate has a Tensile Energy Absorption (TEA) index that can range from 1 J / g to 6 J / g, as measured according to the standard method ISO 1924-3.

[0113] The MF paper substrate for filling heavier packages can preferably have a TEA index in the range of 2 to 3 J / g, while the MF paper substrate for filling lighter, high-end packages can preferably have a TEA index in the range of 1 to 2 J / g.

[0114] In yet another embodiment, the fibrous substrate is stretchable paper; that is, according to ISO 1924-3:2005, the paper has a stretch rate of at least 7% in the machine direction (MD) and at least 7% in the cross direction (CD). Preferably, according to ISO 1924-3:2005, the stretch rate in the machine direction (MD) is at least 8% and the stretch rate in the cross direction (CD) is at least 8%.

[0115] In an embodiment, according to ISO 1924-3:2005, the stretchable paper can have a stretch rate of at least 9% in at least one of the machine direction (MD) and the cross direction (CD). The stretch rate of the stretchable paper in the MD or CD is at least 10%.

[0116] Preferably, the paper is stretchable in both the MD and CD. The upper limit of the stretch rate in the MD can be, for example, 20% or 25%. The upper limit of the stretch rate in the CD can be, for example, 15%.

[0117] The stretch rate (in the MD and CD) is determined according to the standard ISO 1924-3:2005.

[0118] This stretchable fibrous substrate is particularly suitable for molding to prepare paper articles that can replace plastic articles. For such paper articles that replace plastic articles, of particular interest is reducing the coating amount to a minimum while still providing heat-sealing properties to the coated paper product used for molding the paper article.

[0119] Preferably, the stretchable paper has a high tensile strength and Tensile Energy Absorption (TEA) index. In an embodiment, according to ISO 1924-3:2005, the stretchable paper has a Tensile Energy Absorption (TEA) index of at least 3.5 J / g in the machine direction (MD) and / or at least 2.9 J / g in the cross direction (CD). For example, the TEA index can be from 3.5 to 7.5 J / g in the machine direction (MD) and from 2.9 to 3.9 in the cross direction (CD).

[0120] The stretchable paper substrate may have Gurley air permeability higher than 15 s, preferably higher than 20 s, which is measured according to the standard method ISO 5636-5. Compared with many highly stretchable sack papers, the stretchable paper substrate disclosed herein is not particularly porous. Instead, a relatively low porosity may be preferred. In the context of the present disclosure, when the fibrous substrate includes a single coating, the tendency to coat through the low-porosity paper is lower.

[0121] In an embodiment, the Gurley air permeability of the stretchable paper substrate is at least 25 s, such as at least 35 s. The upper limit can be, for example, 300 s or 250 s. The Gurley air permeability is determined according to ISO 5636-5.

[0122] The pulp used to form the stretchable paper substrate of the present disclosure can be virgin pulp, such as kraft pulp (sometimes referred to as "kraft paper pulp"), which provides high tensile strength. Therefore, the paper of the present disclosure is preferably kraft paper.

[0123] For the same reason, the starting material used to prepare the pulp preferably includes softwood (which has longer fibers and forms stronger paper). Therefore, the pulp used to form the paper of the present disclosure can include at least 50% softwood pulp, preferably at least 75% softwood pulp, and more preferably at least 90% softwood pulp. These percentages are based on the dry weight of the pulp. Preferably, the paper of the present disclosure is a softwood kraft paper formed from 100% virgin fibers.

[0124] The stretchable paper substrate suitable for the present disclosure can be produced according to the processes disclosed in WO2018 / 185213, WO2018 / 185215 or WO2018 / 185216, the entire contents of which are incorporated herein by reference.

[0125] The stretchable paper substrate can be a paper commercialized by Billerud under the trademark for commercialization.

[0126] The second side of the fibrous substrate can be an uncoated side, or can be coated with only a thin layer of starch (≤1 g / m 2 ) to control curling. If the second side is intended to have printed matter, a varnish can be provided on the optional printed matter, for example, to change the gloss, friction, and / or peel properties, that is, the second side can be an uncoated side, or at least a non-thermally sealable side.

[0127] Examples

[0128] Samples were prepared by coating two different types of fibrous substrates. Fibrous substrate 1 (FS1) is a calendered fibrous substrate produced from pure bleached pulp with a grammage of 80 gsm, and fibrous substrate 2 (FS2) is a calendered unbleached kraft paper with 80 gsm.

[0129] Each sample was coated with a coating mixture comprising ~70 wt.% of EEA and ~30 wt.% of talc. In addition, small amounts of a thickening agent, an antifoaming agent, and a surfactant were added.

[0130] Table 1

[0131]

[0132] The results are shown in Table 2 below.

[0133] Table 2

[0134]

[0135] The heat seal strength, dynamic friction, Bendtsen roughness, and Gurley air permeability of four product samples were measured. The WVTR of Samples 1 and 2 was measured. The Bendtsen roughness of the first and second sides of the paper substrate was measured according to the standard method ISO 8791-4, and the Gurley air permeability of the first side was measured according to the standard method ISO 5636-5. As can be seen from Table 2, a relatively high Gurley air permeability in combination with a coating weight of at least 5.4 g / m 2 provides a favorable heat seal above 2.5 N / 15 mm. It was also found that a relatively low Bendtsen roughness on the first side improved the heat seal strength of the coated paper product according to the present disclosure. The dynamic friction was measured on the coated surface of the paper, and the dynamic friction of each sample was in the range of 0.16 to 0.19, which is favorable when forming packages of the heat-sealable coated paper product.

Claims

1. A heat-sealable coated paper product comprising a cellulose fiber substrate having a first side and a second side, the first side comprising a single coating applied in direct contact with the fiber substrate, the coating comprising ethylene (meth) acrylic acid copolymer (EAA / EMAA) or ethylene-acrylic acid-methylacrylic acid terpolymer (EAAMAA) or a mixture thereof, in an amount of at least 51% by weight based on the dry weight of the coating, and a pigment, the pigment being talc and / or calcium carbonate (CaCO3).

2. The heat-sealable coated paper product according to claim 1, wherein, The pigment is present in an amount in the range of 15% to 45% by weight based on the dry weight of the coating, preferably in the range of 20% to 40% by weight based on the dry weight of the coating, and most preferably in the range of 25% to 35% by weight based on the dry weight of the coating.

3. The heat-sealable coated paper product according to claim 1 or 2, wherein, At least 90% by weight of the dry weight of the coating consists of EAA / EMAA / EAAMAA and the pigment, preferably at least 95% by weight of the dry weight of the coating consists of EAA / EMAA / EAAMAA and the pigment.

4. The heat-sealable coated paper product according to any one of the preceding claims, wherein, The dry coating weight of the coating is in the range of 4 g / m 2 to 9 g / m 2 and preferably in the range of 5 g / m 2 to 9 g / m 2 .

5. The heat-sealable coated paper product according to any one of the preceding claims, wherein, Measured according to ISO 536:2020, the grammage of the fiber substrate is in the range of 30 to 150 g / m 2 .

6. The heat-sealable coated paper product according to claim 5, wherein, The fiber substrate is machine-glazed (MG) paper, or machine-finished (MF) paper.

7. The heat-sealable coated paper product according to any one of claims 1 to 5, wherein, The fiber substrate is MG paper, and measured on the first side of the fiber substrate according to the standard method ISO 8791-2:2013, the Gurley roughness value of the fiber substrate is 1400 ml / min or less, preferably 1300 ml / min or less, such as in the range of 170 ml / min to 1200 ml / min.

8. A heat-sealable coated paper product according to any one of claims 1 to 5 or claim 7, wherein, The fiber substrate is an MG fiber substrate, and measured according to the standard method ISO 5636-5, the Gurley air permeability of the fiber substrate is 25 s or greater, preferably 30 s or greater.

9. The heat-sealable coated paper product according to any one of claims 1 to 5, wherein, The fiber substrate is an MF paper substrate, and measured on the first side of the fiber substrate according to the standard method ISO 8791-2:2013, the Gurley roughness value of the fiber substrate is in the range of 200 ml / min to 550 ml / min, preferably in the range of 220 ml / min to 500 ml / min, such as in the range of 200 ml / min to 460 ml / min.

10. The heat-sealable coated paper product according to any one of claims 1 to 5 or claim 9, wherein, The fiber substrate is an MF paper substrate, and measured according to the standard method ISO 5636-5, the Gurley air permeability of the fiber substrate is 30 s or greater, preferably 32 s or greater.

11. The heat-sealable paper according to any one of claims 1 to 5, wherein, Measured according to the standard method ISO 1924-3:2005, the fiber substrate has an elongation rate of at least 7%, preferably at least 9% in the CD direction.

12. The heat-sealable paper according to any one of claims 1 to 5 or claim 11, wherein, Measured according to the standard method ISO 1924-3:2005, the fiber substrate has an elongation rate of at least 7%, preferably at least 9% in the MD direction.

13. The heat-sealable paper according to any one of claims 11 or 12, wherein, The Gurley air permeability of the fiber substrate is higher than 15 s, preferably higher than 20 s.

14. The heat-sealable paper according to any one of claims 11 to 13, wherein, Measured according to ISO 536:2020, the grammage of the fiber substrate is in the range of 80 to 300 g / m 2 Preferably in the range of 90 to 290 g / m 2 of the range.

15. The heat-sealable coated paper product according to any one of the preceding claims, wherein, The second side of the fiber substrate is not coated or alternatively is only coated with a single layer comprising or consisting of starch.

16. Use of the heat-sealable coated paper product according to any one of the preceding claims as a packaging material.

17. A method for producing a heat-sealable coated paper product, comprising the following steps: - providing a fibrous substrate comprising a first side and a second side; and - coating the first side of the fibrous substrate with a coating applied in direct contact with the fibrous substrate, the coating comprising ethylene (meth)acrylic acid (EAA / EMAA) or ethylene-acrylic acid-methacrylic acid terpolymer (EAAMAA) or a mixture thereof, in an amount of at least 51% of the dry weight of the coating, and a pigment, the pigment being talc and / or calcium carbonate (CaCO3), the coating being a single coating on the first side of the fibrous substrate; and - optionally treating the second side of the fibrous substrate with water or starch.

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