EP4528026A1

EP4528026A1 - Grease barrier packaging material

Info

Publication number: EP4528026A1
Application number: EP23198510.2A
Authority: EP
Inventors: Eric Rousset; Florence VIDAL; Gilles VETTER; Robin ABDERRAHMEN; Pascal Gallaire
Original assignee: Ahlstrom Corp
Current assignee: Ahlstrom Corp
Priority date: 2023-09-20
Filing date: 2023-09-20
Publication date: 2025-03-26
Also published as: WO2025061873A1; EP4528027A1

Abstract

The present invention relates to a food packaging material, a method for producing a food packaging material and uses thereof. The food packaging material of the present invention comprises (i) a paper substrate having a first side and a second side, the second side being opposite to the first side, wherein the paper substrate is impregnated with a composition comprising a grease barrier precursor, and (ii) a barrier layer coated onto at least the first side of the impregnated paper substrate, the barrier layer comprising a polymer, wherein the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material.

Description

Technical field

The present invention relates to a food packaging material, a pet food container comprising said food packaging material, a method for producing a food packaging material and uses thereof.

Background art

Conventional food containers such as pet food containers are often made with plastic films and/or with papers containing fluorochemicals. Thanks to this structure, conventional pet food containers have a good grease barrier and suitable mechanical properties for the purpose of storing pet food.
However, there are food safety and environmental concerns regarding fluorochemicals, which are being banned in most countries. Plastic content in packaging is also linked to increasing environmental concerns, as they are not fully recyclable.
Packaging material that is envisioned for the use in pet food containers must satisfy specific requirements. Pet food typically includes high amounts of oil and fats, therefore the packaging material for pet food typically needs to be greaseproof. If the packaging material does not show satisfactory greaseproof properties, grease will penetrate through the packaging material, and grease stains will appear on the outer surface of the container. Furthermore, through grease leaking the packaging material may lose its structural integrity and the risk of breakage of the container will increase.
Furthermore, the packaging material used in pet food containers should have suitable mechanical properties for converting, i.e. for producing pet food containers. Moreover, it is important that the packaging material is able to withstand handling and holding heavy loads. A standard weight of pet food units may be as high as up to 12 Kg or even more. Thus, a packaging material for pet food should be able to resist a high load. An optimal tensile, stiffness and tear resistance is therefore required, along with the optimal grease resistance properties.
The packaging material should also be fabricated from materials that are safe for food contact and ideally be recyclable.
Fluorofree paper-based packaging material for the pet food market are often not satisfactory from the viewpoints mentioned above, because their grease barrier level in the absence of fluorochemicals is too low both at the surface and at the core of the packaging material. Generally, such fluorofree packaging materials use a laminate film, which often contains plastic, to increase the surface grease barrier. However, the use of laminated film reduces the recycling yield of the packaging, the biopolymer content, and does not improve the grease resistance of the core of the material. Furthermore, lamination needs to be performed offline and the production costs thereof are higher than those of a method that can be fully performed online on the paper machine.

Technical problem

Accordingly, there is a demand for a packaging material that is suitable for pet food containers and which is substantially free from fluorochemicals such as per- and polyfluoroalkyl substances (PFAS), which has good greaseproof properties and at the same time optimal mechanical strength such that it can withhold heavy weight, and that can be manufactured with food safe and recyclable materials.

Summary of the invention

The present invention is aimed at solving the problems of the prior art by providing a food packaging material comprising:

(i) a paper substrate having a first side and a second side, the second side being opposite to the first side,
wherein the paper substrate is impregnated with a composition comprising a grease barrier precursor; and
(ii) a barrier layer coated onto at least the first side of the impregnated paper substrate, the barrier layer comprising a polymer;
wherein the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material.

Further, the present invention relates to a method for producing a food packaging material, the method comprising the steps of:

(i) providing a paper substrate having a first side and a second side, the second side being opposite to the first side;
(ii) impregnating the paper substrate with a composition comprising a grease barrier precursor;
(iii) applying a barrier layer comprising a polymer onto at least the first side of the impregnated paper substrate;

Moreover, the present invention relates to the use of the food packaging material according to the present invention as a pet food container.
It has been found that the impregnation of a paper substrate with a composition comprising a grease barrier precursor, in combination with a coating of the paper substrate with barrier layer comprising a polymer, allows to obtain optimal grease barrier and mechanical properties without introducing fluorochemicals, thus resulting in a product that is safe for food contact and has a lower environmental impact (that is, a higher recyclability).
The inventors have found that balancing production parameters such as the refining of the paper substrate and the application of a barrier layer in a multi-step process, that is, the application of e.g. two barrier layers, further improves these properties. The food packaging material of the present invention may be furthermore fully produced online on a paper machine, which allows to reduce the costs of production.

Brief description of the drawings

Figure 1 is a schematic illustration of an embodiment of the present invention.
Figure 2 is a schematic illustration of a preferred embodiment of the present invention in which the barrier layer further comprises a filler.
Figure 3 is a schematic illustration of a preferred embodiment of the present invention in which the food packaging material further comprises an additional barrier layer coated on the barrier layer.
Figure 4 is a schematic illustration of a preferred embodiment of the present invention in which the food packaging material further comprises a printing layer.
Figure 5 is a schematic illustration of a preferred embodiment of the present invention in which the food packaging material further comprises an additional barrier layer coated on the barrier layer and a printing layer.

Detailed description of the invention

Definitions

In the present invention, the term "average" denotes mean average, unless stated otherwise.
In the present invention, references to amounts "by weight" are intended to be synonymous with "by mass". Further, as used herein, the term weight percent (wt%) refers to a percentage amount by weight.
In the present invention, the term "polymer" denotes a compound comprising at least ten repeating units such as, for example, a homopolymer, a copolymer, a graft copolymer, a branch copolymer or a block copolymer.
In the context of the present invention, the term "biodegradable" is generally defined in line with EN13432. The term "biodegradable" when applied to a material or a product means that the material or the entire product will biodegrade. By "biodegrade" it is meant that the chemical structure or the material breaks down under the action of microorganisms. More specifically, a material or a product is considered "biodegradable" if at least 90 wt% of the material is converted into CO₂ under the action of microorganisms in less than 6 months as measured by the laboratory test method EN 14046, thereby meeting the requirement for biodegradability according to EN 13432.
The term "compostable" is generally defined in line with EN13432. In the context of the present invention, a material is "compostable" when it comprises a maximum of 10 wt% and preferably of 5 wt% of non-biodegradable components, thereby meeting EN13432. The term "compostable" when applied to a material or a product means that the material, or the entire product, will both biodegrade and disintegrate. By the term "disintegrates" it is meant that the material, or the product made from it, will physically fall apart into fine visually indistinguishable fragments, at the end of a typical composting cycle.
An "industrial compostable" material may be compostable as described above in an industrial setting: The material may disintegrate and biodegrade at temperatures between 55 °C to 60 °C in less than 6 months. In detail, disintegration in an industrial setup may take less than 3 months, while biodegradation may take less than 6 months. If a material is described as "home compostable," it is compostable as described above under conditions present in a domestic composter setting: The material may disintegrate and biodegrade at temperatures below 55 °C, preferably at temperatures between 10 to 45 °C and most preferably between 25 to 30 °C in less than 12 months. In detail, disintegration may take less than 6 months, while biodegradation may take less than 12 months in a domestic composter setting.
Where the present description refers to "preferred" embodiments/features, combinations of these preferred embodiments/features shall also be deemed as disclosed as long as this combination is technically meaningful.
Hereinafter, the use of the term "comprising" should be understood as disclosing in a non-limited way, that is to say that additional components or steps can be present or implemented, as long as this is technically meaningful. For a more restricted embodiment, the terms "consisting of" will be used and have to be understood as disclosing in a limited way, that is to say without any additional component or step.

Packaging material

The present invention relates to a food packaging material (hereinafter also referred to as "packaging material") comprising: (i) a paper substrate having a first side and a second side, the second side being opposite to the first side, wherein the paper substrate is impregnated with a composition comprising a grease barrier precursor; and (ii) a barrier layer coated onto at least the first side of the impregnated paper substrate, the barrier layer comprising a polymer; wherein the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material.
With reference to Figure 1, the packaging material (1) of the present invention comprises a paper substrate (10) which has a first and a second side, and which is impregnated with a composition comprising a grease barrier precursor (12). Further, the packaging material (1) comprises a barrier layer (11) which is coated onto at least the first side of the paper substrate (10) and which comprises a polymer (13).

Impregnated paper substrate

The packaging material of the present invention comprises a paper substrate which is impregnated with a composition comprising a grease barrier precursor.
The term "paper substrate" as used herein refers to a base paper before impregnation with the composition comprising a grease barrier precursor. The term "impregnated paper substrate" refers to a base paper which is impregnated with said composition.
The terms "substrate" and "support" are used herein as synonyms, unless otherwise indicated.

Paper substrate

In the present invention, the paper substrate is preferably a cellulose fiber base sheet.
The term "fiber" as used herein refers to a material form characterized by an extremely high ratio of length to diameter. Generally, cellulose fibers have a very broad range of diameters and length based on fiber type and source of fiber.
The average length of a wood pulp fiber as preferably used in the present invention is typically in the range of between from 0.3 mm to 3.5 mm, preferably from 0.3 mm to 3.0 mm, more preferably from 0.8 mm to 2.5 mm and even more preferably from 1.0 mm to 2.0 mm. The diameter of a wood pulp fiber is typically in the range of from 10 µm to 40 pm, preferably from 15 µm to 35 µm and more preferably from 20 µm to 30 µm. The aspect ratio (ratio of fiber length to fiber diameter) of a wood pulp fiber is therefore typically in the range of from 7.5 to 350, preferably from 7.5 to 300, more preferably from 10 to 200 and even more preferably from 20 to 150. The terms "fiber" and "filament" can be used interchangeably for the purposes of the present invention unless otherwise specifically indicated.
The term "cellulose fiber base sheet" refers to a non-woven fiber base sheet having a structure of individual fibers which are interlaid, but not in an identifiable manner as in a woven or knitted fabric, wherein the non-woven fiber base sheet is derived or prepared from cellulose fibers. A cellulose fiber is a fiber comprised substantially of cellulose. Non-woven materials can be formed from many processes such as, for example, spin laying, carding, air laying and water laying processes. The basis weight of non-woven materials such as a cellulose fiber base sheet is usually expressed in weight per unit area, for example in grams per square meter (gsm = g/m²) or ounces per square foot (osf).
The cellulose fiber base sheet used in the present invention is preferably a wet-laid paper sheet. Cellulose fiber base sheets be used in embodiments of the present invention are preferably cellulose fibers from natural sources (for example, native cellulose fibers).
The term "native cellulose fibers" refers to cellulose fibers from natural sources such as woody plants including deciduous and coniferous trees or non-woody plants including cotton, flax, esparto grass, kenaf, sisal, abaca, milkweed, straw, jute, hemp and bagasse. Preferably, the native cellulosic fibers used in the present invention are derived from woody plants. Suitable fibers are, for example, Eucalyptus fibers, Birch fibers or other annual plant fibers. The native cellulosic fibers form a crystalline material comprising a crystallized fraction with the crystalline form of Cellulose I comprising all-parallel-oriented cellulose chains.
Preferably, the cellulose fiber base sheet is a wood pulp paper sheet. The paper substrate used in the present invention preferably comprises natural hardwood fibers, more preferably eucalyptus fibers. Preferably, the paper substrate comprises hardwood fibers in an amount of 20 wt% or more, preferably 30 wt% or more, more preferably 40 wt% or more, and further more preferably 50 wt% or more relative to the total amount of fibers in the cellulose fiber base sheet.
Further, the paper substrate used in the present invention preferably comprises natural softwood fibers, preferably in an amount of 10 wt% or more, preferably 20 wt% or more, more preferably 30 wt% or more, and preferably 70 wt% or less, more preferably 60 wt% or less, further preferably 50 wt% or less relative to the total amount of fibers in the cellulose fiber base sheet.
In a preferred embodiment of the present invention, at least 50 wt%, preferably at least 60 wt%, even more preferably at least 80 wt% of the fibers in the paper substrate are natural cellulose fibers. In a more preferable embodiment, at least 90 wt%, preferably at least 95 wt% and most preferably 100 wt% of the fibers in the paper substrate are natural cellulose fibers.
The fibers of the paper substrate are preferably natural cellulose fibers from the viewpoint of biodegradability. It is most preferable that the paper substrate is 100% biodegradable. The paper substrate therefore preferably contains no more than 5 wt% of non-biodegradable material or material of undetermined compostability in order to meet the requirements of the EN 13432 standard. Most preferably, any additives added to the paper substrate are compostable.
The diameter of the cellulose fibers is preferably 10 µm to 40 pm, more preferably from 15 µm to 35 µm and even more preferably from 20 µm to 30 µm. The length of the cellulose fibers is preferably 0.3 mm to 3.5 mm, more preferably from 0.3 mm to 3.0 mm, even more preferably from 0.8 mm to 2.5 mm and most preferably from 1.0 mm to 2.0 mm. Therefore, the average aspect ratio (ratio between the length and the diameter of the cellulose fibers) is preferably 7.5 to 350, more preferably from 7.5 to 300, even more preferably from 10 to 200 and most preferably from 20 to 150.
The paper substrate typically has an average thickness of from 30 µm to 150 pm, preferably from 40 µm to 120 pm, even more preferably from 45 µm to 80 µm and most preferably about 65 µm from the viewpoint of achieving excellent mechanical reinforcement properties.
Typically, the paper substrate will not have fillers. In particular, a total amount of titanium dioxide, calcium carbonate, and clay in the paper substrate is preferably not more than 5 wt%, more preferably not more than 2 wt%, even more preferably not more than 1 wt%. More preferably, a total amount of fillers in the paper substrate is not more than 2 wt%, more preferably not more than 1 wt%, even more preferably not more than 0.5 wt%.

Composition comprising a grease barrier precursor

The paper substrate is impregnated with a composition comprising a grease barrier precursor. The term "impregnated with a composition" as used herein denotes that the composition penetrates the cavities within the paper substrate along at least a portion of the thickness of the paper substrate. Preferably, the composition penetrates the cavities within the paper substrate along the whole thickness thereof. Preferably, the composition impregnates the paper substrate across its whole surface. The composition comprising a grease barrier precursor may also additionally cover a surface of the paper substrate.
In the context of the present invention, the term "grease barrier precursor" refers to compounds which are able to increase the grease resistance of a material containing them as compared to the same material that does not contain them.
For example, grease barrier precursors as described herein may increase the grease resistance of the paper substrate impregnated with a composition containing them as compared to the base paper substrate before impregnation.
For example, the grease barrier precursor may be a compound that, when used in a composition that impregnates the paper substrate, decreases the edge wicking of the impregnated paper substrate by at least 10%, preferably at least 20%, even more preferably at least 30% as compared to the non-impregnated paper substrate, wherein the edge wicking is determined as described below in Experimental Example 3.
Preferably, the grease barrier precursor is selected from starch, a starch derivative, carboxymethyl cellulose, polylactic acid, ethylene vinyl alcohol copolymer, polyvinyl alcohol and a mixture thereof. More preferably, the grease barrier precursor is starch, a starch derivative such as cationic, anionic and non-ionic starch, carboxymethyl cellulose, or a mixture thereof. Most preferably, the grease barrier precursor is cationic starch, anionic starch, carboxymethyl cellulose or a mixture thereof. In the present invention, the term "cationic starch" denotes starch which contains groups that are positively charged at pH 7, wherein said groups may be one or more selected from amine groups, ammonium groups, imino groups, or phosphonium groups. In the present invention, "anionic starch" denotes starch which contains groups that are negatively charged at pH 7, wherein said groups may be for example carboxylic groups. In the context of the present invention, cationic starch and anionic starch are particularly preferable as grease barrier precursor from the viewpoint of improving both the mechanical properties to fit pet-food converting requirements, as well as to improve the grease barrier at the core of the material.
Advantageously, impregnating the base paper with the composition comprising the grease barrier precursor is useful in reducing the penetration of the barrier layer which is coated thereon into the paper core. This may help minimizing the surface defects of the barrier layer and thus reducing the formation of weak points through which grease may pass.
Preferably, the grease barrier precursor is present in an amount of 1 to 15 wt%, preferably 2 to 12 wt%, more preferably 3 to 10 wt% of the total weight of the impregnated paper substrate.
Preferably, the grease barrier precursor is present in an amount of 1 to 10 wt%, preferably 3 to 8 wt% of the total weight of the packaging material.
In a preferred embodiment, the impregnated paper substrate represents 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more of the total weight of the packaging material. Further, the impregnated paper substrate preferably represents 99 wt% or less, preferably 95 wt% or less, more preferably 90 wt% or less of the total weight of the packaging material.

Barrier layer

The packaging material of the present invention comprises a barrier layer. The barrier layer is coated onto at least the first side of the impregnated paper substrate and comprises a polymer.
Preferably, the barrier layer is coated on the entire surface of at least the first side.
Further, in a preferred embodiment, the barrier layer is coated onto the first side but not onto the second side of the paper substrate.
The barrier layer in the packaging material of the present invention allows to minimize defects of the surface of the paper substrate and ensure a high grease barrier resistance.
Preferably, the barrier layer represents 5 wt% or more, preferably 6 wt% or more, more preferably 7 wt% or more, even more preferably 10 wt% or more of the total weight of the packaging material. Preferably, the barrier layer represents 20 wt% or less, preferably 18 wt% or less, more preferably 15 wt% or less of the total weight of the packaging material.
The basis weight of the barrier layer is preferably 0.5 g/m² or more, preferably 1 g/m² or more, more preferably 2 g/m² or more, more preferably 4 g/m² or more, and 25 g/m² or less, preferably 20 g/m² or less, more preferably 15 g/m² or less. A weight per unit area within the above ranges is advantageous in that it improves the barrier properties of the packaging material, while still ensuring a good recyclability and without incurring in a blocking effect.

Polymer

Preferably, the polymer comprised in the barrier layer is selected from styrene-butadiene rubber latex, polyvinyl alcohol, starch, polyurethane, ethylene vinyl-acetate copolymer, styrene (meth)acrylic acid copolymer, poly (meth)acrylic acid or a mixture thereof. More preferably, the polymer comprised in the barrier layer is styrene-butadiene rubber latex, polyvinyl alcohol or a mixture thereof. That is, the barrier layer may comprise one or more polymers. When the barrier layer comprises more than one polymer, it may be described herein as comprising a "polymer blend".
The total amount of polymer (or polymer blend) in the barrier layer may be 30 wt% or more, preferably 35 wt% or more, more preferably 40 wt% or more, further preferably 50 wt% or more, even more preferably 55 wt% or more relative to the total amount of barrier layer components. Further, the amount of polymer in the barrier layer may be 80 wt% or less, preferably 75 wt% or less, more preferably 70 wt% or less, even more preferably 65 wt% or less relative to the total amount of barrier layer components.

Filler

In a preferred embodiment, the barrier layer further comprises a filler.
Figure 2 is a schematic illustration of a preferred embodiment in which a filler is comprised in the barrier layer. As shown in Figure 2, in such an embodiment the packaging material (2) comprises a paper substrate (20) which is impregnated with a composition comprising a grease barrier precursor (22), and a barrier layer (22) coated onto the impregnated paper substrate (29), wherein the barrier layer (22) comprises a polymer (23) and a filler (24). The properties and components of the impregnated paper substrate and of the barrier layer are as described above for the present invention.
The filler that may be included in the barrier layer is preferably selected from calcium carbonate, clay, talc and a mixture thereof. More preferably, the filler that may be included in the barrier layer is calcium carbonate.
When a filler is present, the amount of filler may be 1 wt% or more, preferably 5 wt% or more, more preferably 10 wt% or more, even more preferably 20 wt% or more relative to the total amount of barrier layer components. Further, when present, the amount of filler may be 60 wt% or less, preferably 55 wt% or less, more preferably 50 wt% or less, even more preferably 45 wt% or less relative to the total amount of barrier layer components.
The inclusion of a filler in the barrier layer may be advantageous in that it improves drying and reduces the foaming of the barrier layer, without negatively affecting the barrier properties.

Additional components of the barrier layer

The barrier layer of the packaging material of the present invention may comprise additional components, such as defoamers, thickeners such as carboxymethyl cellulose, and/or crosslinking agents such as glyoxal-based compounds.

Additional barrier layer

In a preferred embodiment of the present invention, the packaging material further comprises (iii) an additional barrier layer which is coated onto the barrier layer and comprises a polymer.
In the context of the present invention, when an additional barrier layer is present, the barrier layer that is coated on the impregnated paper substrate may be referred to as the "first barrier layer" and the additional barrier layer may be referred to as the "second barrier layer".
Figure 3 is a schematic illustration of a preferred embodiment in which a second barrier layer is present onto the first barrier layer. As shown in Figure 3, the packaging material (3) of such an embodiment comprises a paper substrate (30) which is impregnated with a composition comprising a grease barrier precursor (32), a first barrier layer (31) coated onto the impregnated paper substrate (30) and comprising a polymer (33), and a second barrier layer (34) coated onto the first barrier layer (31) and comprising a polymer (35).
The properties and components of the impregnated paper substrate and of the first barrier layer are as described above for the present invention. Further, the first barrier layer and/or the second barrier layer may further comprise a filler as described above. The type and amount of filler may be as described above.
When a second barrier layer is present, the polymer(s) comprised in said second barrier layer may be the same or different as the polymer(s) comprised in the first barrier layer. That is, the composition of the second barrier layer and that of the first barrier layer may be the same or different from each other. The polymer comprised in the second barrier layer may be selected from styrene-butadiene rubber latex, polyvinyl alcohol, starch, polyurethane, ethylene vinyl-acetate copolymer, styrene (meth)acrylic acid copolymer, poly (meth) acrylic acid or a mixture thereof. Preferably, the second barrier layer comprises a polymer selected from styrene-butadiene rubber latex, polyvinyl alcohol and a mixture thereof.
In a preferred embodiment, the first barrier layer of the packaging material of the present invention comprises styrene-butadiene rubber latex, and the second barrier layer comprises polyvinyl alcohol. In a more preferred embodiment, the first barrier layer of the packaging material of the present invention comprises styrene-butadiene rubber latex and calcium carbonate, and the second barrier layer comprises polyvinyl alcohol and talc.
Preferably, the second barrier layer represents 3 wt% or more, preferably 5 wt% or more, more preferably 6 wt% or more of the total weight of the packaging material. Preferably, the second barrier layer represents 18 wt% or less, preferably 15 wt% or less, more preferably 10 wt% or less of the total weight of the packaging material.
Preferably, the total amount of all barrier layers in the packaging material is 5 wt% or more, preferably 6 wt% or more, more preferably 8 wt% or more, even more preferably 10 wt% or more, and 30 wt% or less, preferably 25 wt% or less, more preferably 20 wt% or less, even more preferably 15 wt% or less of the total weight of the packaging material.
The basis weight of the second barrier layer is preferably 0.5 g/m² or more, preferably 1 g/m² or more, more preferably 2 g/m² or more, more preferably 4 g/m² or more, and 25 g/m² or less, preferably 20 g/m² or less, more preferably 15 g/m² or less. A weight per unit area within the above ranges is preferable from the viewpoint of the barrier properties of the packaging material, while still ensuring a good recyclability and without incurring in a blocking effect.
Preferably, the total weight per unit area of all barrier layers in the packaging material is 1 g/m² or more, more preferably 2 g/m² or more, more preferably 4 g/m² or more, and 25 g/m² or less, preferably 20 g/m² or less, more preferably 15 g/m² or less.
The presence of a second barrier layer may be advantageous in terms of further improving the grease barrier properties of the final packaging material. In particular, using a first barrier layer and a second barrier layer may further improve grease barrier properties as compared to using one single barrier layer with the same basis weight. Without wishing to be bound to any theory, it is believed that the reason for this may be that using two lighter barrier layers instead of one single heavier barrier layer may allow to coat surface effects that may appear on the first single barrier layer and compensate for the weak points therein, through which grease may pass. With two layers, the probability of such defects may be decreased.
These effects may be observed even when the first and second layer have the same composition, but have been deposited in two consecutive coating steps.

Printing layer

In a further preferred embodiment, in the packaging material of the present invention the barrier layer is applied onto the first side of the impregnated paper substrate, and the packaging material further comprises (iv) a printing layer applied onto the second side of the impregnated paper substrate. Specifically, the barrier layer is preferably applied onto the first side of the impregnated paper substrate but not on the second side, and a printing layer is applied onto the second side of the impregnated paper substrate.
Preferably, the printing layer is applied on the entire surface of the second side of the impregnated paper substrate.
Figure 4 illustrates a preferred embodiment of the present invention in which such a printing layer is present. As shown in Figure 4, the packaging material (4) comprises a paper substrate (40), which is impregnated with a composition comprising a grease barrier precursor (42), and a barrier layer (41) which is coated on a first side of the impregnated paper substrate (40) and comprises a polymer (43). Further, the packaging material (4) of this embodiment comprises a printing layer (44) which is coated on a second side of the paper substrate (40).
The properties and components of the impregnated paper substrate and of the barrier layer are as described above for the present invention. Further, the barrier layer may further comprise a filler as described above. The type and amount of filler may be as described above.
Further, as shown in Figure 5, in a preferred embodiment, the packaging material (5) may comprise, in addition to the printing layer (56) coated onto the second side of the paper substrate (50), also an additional barrier layer (54) comprising a polymer (55) coated onto the barrier layer (51), which is in turn coated onto the first side of the paper substrate (50). That is, the preferred embodiment described above in which an additional barrier layer is present may further comprise a printing layer. The properties and components of the additional barrier layer are as described above for the embodiment comprising an additional barrier layer. Further, the additional barrier layer may also comprise a filler as described above.
The printing layer preferably comprises a binder selected from styrene-butadiene-based binders (such as Styronal D 517 F produced by BASF, or L7066 from EOC), styrene-acrylic-based binders (such as Acronal S360D from BASF), or starch, or starch derivative, or carboxymethyl cellulose, or a mixture thereof.
The amount of binder in the printing layer is preferably 10 wt% or more, more preferably 15 wt% or more, further preferably 20 wt% or more and 60 wt% or less, preferably 50 wt% or less, more preferably 40 wt% or less with respect to the total amount of components in the printing layer.
The printing layer preferably comprises a filler selected from calcium carbonate, clay and a mixture thereof.
The amount of filler in the printing layer is preferably 40 wt% or more, more preferably 50 wt% or more, further preferably 60 wt% or more and 90 wt% or less, preferably 85 wt% or less, more preferably 80 wt% or less with respect to the total amount of components in the printing layer.
The printing layer may comprise further additives such as defoaming agents, dispersant, lubricant, crosslinker, thickener, pH modifier and gloss-imparting agents.
When present, the printing layer may represent 1 wt% or more, preferably 2 wt% or more, more preferably 4 wt% or more, and 12 wt% or less, preferably 10 wt% or less, further preferably 8 wt% or less of the total weight of the packaging material.
When a printing layer is present, its basis weight may be 1 g/m² or more, preferably 2 g/m² or more, more preferably 3 g/m² or more, and 10 g/m² or less, preferably 8 g/m² or less, more preferably 6 g/m² or less.

Content of sizing agents, wet strength agents and fluorochemicals

One objective of the present invention is providing a packaging material having an optimal balance between mechanical properties and grease barrier properties while reducing the amount of per- and polyfluoroalkyl substances in the packaging material, which are conventionally used to improve the grease barrier properties.
In particular, in the packaging material of the present invention, the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material. Preferably, the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 15 ppm, preferably 10 ppm, more preferably 5 ppm based on the total weight of the packaging material.
In a further preferred embodiment, the total amount of fluorine-containing substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material. Preferably, the total amount of fluorine-containing substances does not exceed 15 ppm, preferably 10 ppm, more preferably 5 ppm based on the total weight of the packaging material.
In the present invention, preferably the amount of standard sizing agents is limited. Examples of sizing agents are alkyl ketene dimers, soap rosin, anionic rosin and cationic rosin.
It has been found that keeping the amount of such sizing agents below a certain limit helps the penetration of the grease barrier precursor into the paper substrate. This results in an improvement of the grease barrier properties of the paper substrate, which can be achieved without using per- and polyfluoroalkyl substances. When these sizing agents are present in a high amount in the paper substrate, they may interfere with the penetration of the grease barrier precursor into the paper and affect the grease barrier performance.
More specifically, in the present invention the total amount of alkyl ketene dimers, soap rosin, anionic rosin and cationic rosin in the paper substrate is preferably less than 0.5 wt%, more preferably less than 0.35 wt%, even more preferably less than 0.2 wt% based on the total weight of the paper substrate. More preferably, the total amount of sizing agents in the paper substrate is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate.
Further, in the present invention it is preferable that the amount of wet strength agents is also limited. Examples of wet strength agents are polyamidoamine-epichlorohydrin resin, polyethylene imine, urea formaldehyde, and melamine formaldehyde resins.
Preferably, in the present invention the total amount of polyamidoamine-epichlorohydrin resin, polyethylene imine, urea formaldehyde, and melamine formaldehyde resins in the paper substrate is less than 0.5 wt%, more preferably less than 0.35 wt%, even more preferably less than 0.2 wt% based on the total weight of the paper substrate. More preferably, the total amount of wet strength agents in the paper substrate is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate.
In a more preferred embodiment, the total amount of alkyl ketene dimers, soap rosin, anionic rosin, cationic rosin, polyamidoamine-epichlorohydrin resin, polyethylene imine, urea formaldehyde, and melamine formaldehyde resins is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate.
In a more preferred embodiment, the total amount of sizing agents and wet strength agents is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate.
In a preferred embodiment, the amount of polyethylene and polypropylene is less than 0.5 wt%, preferably less than 0.3 wt%, more preferably less than 0.2 wt% based on the total weight of the packaging material.
Preferably, the amount of plastic film in the packaging material is less than 0.5 wt%, preferably less than 0.3 wt%, more preferably less than 0.2 wt% based on the total weight of the packaging material.

Physical and mechanical properties

The basis weight of the packaging material according to the present invention is preferably 40 g/m² or more, more preferably 50 g/m² or more, further preferably 60 g/m² or more, even more preferably 70 g/m² or more, and preferably 130 g/m² or less, more preferably 120 g/m² or less, further preferably 110 g/m² or less, even more preferably 100 g/m² or less.
The thickness of the packaging material according to the present invention is preferably 50 µm or more, preferably 55 µm or more, more preferably 60 µm or more, even more preferably 70 µm or more, and 120 µm or less, preferably 110 µm or less, more preferably 100 µm or less, even more preferably 95 µm or less.
A tensile strength in the machine direction (MD) of the packaging material of the present invention as determined by ISO 1924 is preferably 4 kN/m or more, more preferably 5 kN/m or more, further preferably 6 kN/m or more, and 12 kN/m or less, preferably 10 kN/m or less, further preferably 8 kN/m or less.
A tensile strength in the cross direction (CD) of the packaging material of the present invention as determined by ISO 1924 is preferably 2 kN/m or more, more preferably 3 kN/m or more, even more preferably 3.5 kN/m or more, and 8 kN/m or less, more preferably 7 kN/m or less, even more preferably 6 kN/m or less.

Recyclability

Preferably, the packaging material of the present invention is recyclable by repulping with at least 50 wt% being recoverable according to EN13430. The term "repulping" describes a process whereby a material that has previously undergone or has been formed by at least one pulping step is subjected to a further pulping step. The term "recyclable by repulping" describes a material which can be at least partially recovered and converted into a new material or object during a repulping step. Said material may be waste product. The term "recyclable" is generally described in line with EN13430. The expression "recyclable by repulping with at least 50 wt% being recoverable according to EN13430" therefore describes a material, which has been formed by or otherwise undergone at least one pulping step, and from which, upon subjecting it to a further pulping step, at least 50 wt% of the material can be recovered.
In one embodiment, the packaging material is recyclable by repulping with at least 55 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 60 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 65 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 70 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 75 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 80 wt% of the packaging material being recoverable according to EN13430, more preferably with at least 85 wt% of the packaging material being recoverable according to EN13430, and even more preferably with at least 90 wt% of the packaging material being recoverable according to EN13430.

Compliance with standards for food contact

The packaging material of the present invention is a food packaging material, which means that it is suitable as packaging material for food. Preferably, the packaging material of the present invention is a pet food packaging material.
In one embodiment, the packaging material is food contact approved according to any of EU 1935/2004, BfR 36, FDA 21 CFA §176-170 & 176-180.

Barrier properties

In the present invention, the barrier layer is coated on the first side of the impregnated paper substrate. The barrier layer may be further coated with an additional barrier layer. The second side may be uncoated or coated with a printing layer. A Cobb value as measured on the second side (herein also referred to as "Cobb value UCS") is preferably larger than a Cobb value as measured on the first side which is coated with the barrier layer(s) (herein also referred to as "Cobb value CS"), wherein the Cobb values CS and UCS are determined according to ISO 535.
In a preferred embodiment, the Cobb value CS is 0.5 g/m² or more, preferably 1 g/m² or more, more preferably 2 g/m² or more, further preferably 3 g/m² or more. Further, the Cobb value CS may be 15 g/m² or less, preferably 12 g/m² or less, more preferably 10 g/m² or less, further preferably 8 g/m² or less.
In a preferred embodiment, the Cobb value UCS is 10 g/m² or more, preferably 12 g/m² or more, more preferably 18 g/m² or more. Further a Cobb value UCS may be 60 g/m² or less, preferably 50 g/m² or less, more preferably 40 g/m² or less, further preferably 30 g/m² or less.
A ratio between the Cobb value UCS and the Cobb value CS of the packaging material of the present invention may be 1 or more, preferably 1.5 or more, more preferably 2 or more, further preferably 3 or more, and 60 or less, preferably 50 or less, more preferably 30 or less, even more preferably 20 or less.
The Cobb value is an indication of the amount of water that is taken up by a defined area of paper sample through one-sided contact with water, within a certain amount of time (60 seconds according to ISO 535). A higher Cobb value indicates a higher water pick-up and therefore a lower barrier activity.
In the present invention, the side of the packaging material wherein a barrier layer is coated onto the impregnated paper substrate can achieve a particularly low Cobb value, which is an indication of good barrier properties.
In one embodiment, the packaging material is grease-proof according to TAPPI T454.
In one embodiment, the packaging material is greaseproof as determined according to TAPPI T454 with 30 seconds without grease leakage, preferably with 60 seconds without leakage, more preferably with 180 seconds without leakage, more preferably with 300 seconds without leakage, more preferably with 600 seconds without leakage, and even more preferably with 1800 seconds without leakage.

Pet food container

The present invention also relates to a pet food container comprising the packaging material of the present invention. The type of pet food container is not particularly limited, but it is preferably in the form of a bag or a box. Preferably, the side which is coated with the barrier layer(s) is the side which faces the inside of the pet food container. When the pet food container is in use, the side which is coated with the barrier layer(s) is the side which is in direct contact with the pet food.
The food to be contained in the pet food container is not particularly limited and may be preferably fatty food containing at least 5 wt% of fat. For example, the food to be contained in the pet food container may be any one of pellets, kibbles, flakes, biscuits, powders, croquets, and mixtures thereof.

Method for producing a packaging material

The present invention also relates to a method for producing a food packaging material, the method comprising the steps of:

(i) providing a paper substrate having a first side and a second side, the second side being opposite to the first side;
(ii) impregnating the paper substrate with a composition comprising a grease barrier precursor; and
(iii) applying a barrier layer comprising a polymer onto at least the first side of the impregnated paper substrate;

Preferably, the packaging material of the present invention described above is obtainable by the method for producing a packaging material according to the present invention and described herein.

Paper substrate

The method according to the present invention includes a step (i) of providing a paper substrate having a first side and a second side.
The paper substrate may be as described above for the paper substrate before impregnation of the packaging material of the present invention.
Specifically, the paper substrate may be obtained with the methods described above for the paper substrate of the packaging of the present invention.
Preferably, the paper substrate is obtained by refining a paper pulp to have a desired refining degree (defined herein as Schopper-Riegler number, °SR) and air transmittance (defined herein in ml/min).
More preferably, the paper substrate has a refining degree of 30° SR or more, preferably 35° SR or more, more preferably 40° SR or more, and 100° SR or less, preferably 95° SR or less, more preferably 90° SR or less as measured according to ISO 5267.
The paper substrate preferably has an air transmittance of 20 ml/min or more, preferably 25 ml/min or more, more preferably 30 ml/min or more, and 80 ml/min or less, preferably 75 ml/min or less, more preferably 70 ml/min or less as determined according to ISO 5636-3.
When the refining degree and air transmittance of the paper substrate is within the above ranges, good barrier and mechanical properties can be achieved in the final packaging material. In particular, this refining degree and air transmittance may be achieved by adjusting the refining of the pulp when producing the paper substrate. A too low air transmittance, such as below 20 ml/min, or a too high refining degree, such as above 100 °SR, indicates a high refining of the paper and may reduce the mechanical properties. The inventors of the present invention have found that a good balance in terms of mechanical properties and greaseproof performance may be achieved when controlling the refining such that the refining degree/air transmittance is within the ranges described above.
Preferably, the paper substrate has a basis weight of 10 g/m² or more, preferably 15 g/m² or more, more preferably 20 g/m² or more, further more preferably 35 g/m² or more, and even more preferably 50 g/m² or more. Moreover, the paper substrate in the packaging material of the present invention has a basis weight of 120 g/m² or less, preferably 110 g/m² or less, more preferably 100 g/m² or less, further more preferably 90 g/m² or less, and even more preferably 80 g/m² or less. When the grammage of the paper substrate is within these limits, the mechanical properties of the final packaging material are improved.
The paper substrate preferably has a Cobb value as measured according to ISO 535 as measured on the first and/or on the second side thereof of 30 g/m² or more, preferably 35 g/m² or more, more preferably 40 g/m² or more, and 130 g/m² or less, preferably 120 g/m² or less, more preferably 100 g/m² or less, even more preferably 90 g/m² or less.

Impregnation step

The method of the present invention includes a step of (ii) impregnating the paper substrate with a composition comprising a grease barrier precursor.
The grease barrier precursor comprised in the composition used in step (ii) may be as described above for the grease barrier precursor in the packaging material of the present invention.
In the method of the present invention, the composition used for the impregnation step is preferably a composition in which the grease barrier precursor as described above is dispersed or dissolved in a liquid medium. The liquid medium used to disperse or dissolve the grease barrier precursor may be an aqueous medium and is preferably water.
The concentration of the grease barrier precursor in the composition used in the impregnation step may be adjusted according to the desired final amount of grease barrier precursor in the packaging material. For example, the grease barrier precursor may be present in the composition used in the impregnation step in an amount of 2 wt% or more, preferably 5 wt% or more, more preferably 10 wt% or more, and 40 wt% or less, preferably 30 wt% or less, more preferably 25 wt% or less, and even more preferably 20 wt% or less relative to the total amount of composition used in the impregnation step.
The impregnation may be performed by any means known in the art and is preferably carried out by size press. For example, the impregnation may be performed by a two-step method including a step of adding in wet-end a composition comprising a grease barrier precursor, and a step of further impregnating the paper substrate by size press with a composition comprising a grease barrier precursor which may be the same or different as the one used in wet end. For example, the grease barrier precursor added in wet-end may be cationic starch and/or carboxymethyl cellulose, and the grease barrier precursor added by size press may be anionic starch. Advantageously, the impregnation with the composition comprising the grease barrier precursor may be performed online on the paper machine without a converting step.
In a preferred embodiment, a Cobb value of the impregnated paper substrate measured on the first and/or on the second side thereof is 5 g/m² or more and 70 g/m² or less, preferably 15 g/m² or more and 50 g/m² or less as determined by ISO 535.
In a preferred embodiment, the impregnated paper substrate has a basis weight of 20 g/m² or more, preferably 25 g/m² or more, more preferably 30 g/m² or more, further more preferably 50 g/m² or more, and even more preferably 70 g/m² or more. Moreover, the paper substrate in the packaging material of the present invention has a basis weight of 130 g/m² or less, preferably 120 g/m² or less, more preferably 110 g/m² or less, further more preferably 100 g/m² or less, and even more preferably 90 g/m² or less. When the grammage of the impregnated paper substrate is within these limits, the mechanical properties thereof are improved.
The composition comprising a grease barrier precursor used in the impregnation step may be added to the paper substrate with a basis weight of 1 g/m² or more, preferably 2 g/m² or more, more preferably 4 g/m² or more, and 15 g/m² or less, preferably 12 g/m² or less, more preferably 10 g/m² or less.

Application of a barrier layer

The method according to the present invention includes a step of (iii) applying a barrier layer comprising a polymer onto at least the first side of the impregnated paper substrate. Preferably, the barrier layer is applied only on the first side and not on the second side of the impregnated paper substrate, and preferably the barrier layer is applied on the whole surface of the first side of the impregnated paper substrate.
The barrier layer applied onto the impregnated paper substrate may be as described above for the barrier layer of the packaging material of the present invention.
Preferably, in the method according to the invention, the components of the barrier layer are dispersed or dissolved in a liquid medium. The liquid medium used to disperse or dissolve the components of the barrier layer is preferably water.
That is, step (iii) may be performed by applying a composition comprising the components of the barrier layer onto at least the first side of the impregnated paper substrate, wherein the composition comprises the polymer included in the barrier layer and any other optional component of the barrier layer. For example, said composition may comprise fillers, defoamers, thickeners and any component as described above for the barrier layer of the packaging material of the present invention.
The concentration of the polymer contained in the barrier layer in the composition used in step (iii) of the method of the invention may be adjusted according to the desired final amount of polymer in the barrier layer. For example, the polymer may be present in the composition used in the step of applying the barrier layer in an amount of 20 wt% or more, preferably 30 wt% or more, more preferably 40 wt% or more, even more preferably 50 wt% or more, and 100 wt% or less, preferably 90 wt% or less, more preferably 80 wt% or less, and even more preferably 70 wt% or less relative to the total amount of composition used for the application of the barrier layer.
The application of the barrier layer may be performed by any means known in the art, and is preferably carried out by rod coating, blade coating, curtain coating, air knife, gravure roll, reverse roll or a combination thereof. More preferably, the application of the barrier layer is carried out by rod coating. Advantageously, the application of the barrier layer may be performed online on the paper machine without a converting step.
The barrier layer may be applied at a speed of 50 m/min or more, preferably 60 m/min or more, more preferably 80 m/min or more, even more preferably 100 m/min or more, and 1000 m/min or less, preferably 900 m/min or less, more preferably 800 m/min or less.

Calendering

The method according to the present invention may include a step (ii') of calendering the impregnated paper substrate after step (ii) and/or a step (iii') of calendering the impregnated paper substrate coated with the barrier layer after step (iii) .
Including a calendering step (ii') and/or (iii') may be advantageous in terms of improving the edge wicking of the packaging material and thus improving its grease resistance properties. For example, a calendering step may help to achieve a denser packaging material, which may increase the grease barrier of the core material without negatively affecting the mechanical properties for converting. Further, a calendering step may improve the printability of the material.
The optional calendering step (ii') and/or (iii') may be carried out by a soft calender, hard calender, shoe calender or supercalender. The number of calendering nip could be from 1 to 16. This step is preferably carried out by a soft calender with 4 nip, online on the paper machine.

Application of an additional barrier layer

The method according to the present invention may include a step (iv) of applying an additional barrier layer comprising a polymer onto the barrier layer obtained in step (iii) and optionally calendered in step (iii').
The additional barrier layer may be as described above for the additional barrier layer of the packaging material of the present invention. As described above, the additional barrier layer may be referred to as the "second barrier layer" and the barrier layer onto which the additional barrier layer is applied may be referred to as the "first barrier layer".
The step (iv) of applying said second barrier layer may be carried out in the same way as described above for the step (iii) of applying the barrier layer onto the impregnated paper substrate.
Preferably, before the application of the second barrier layer in step (iv), a step (iii") of drying the first barrier layer obtained in step (iii) is performed. A step (iv') of drying the second barrier layer after step (iv) may also be carried out.
The advantages of applying a second barrier layer are as described above for the second barrier layer of the packaging material of the present invention. Such advantages may be observed even when the second barrier layer optionally added with step (iv) has the same composition as the first barrier layer applied with step (iii).

Application of a printing layer

The method according to the present invention may include a step (v) of applying a printing layer onto the second side of the impregnated paper substrate.
The printing layer may be as described above for the printing layer of the packaging material of the present invention. The step (v) of applying said printing layer may be carried out by any method known in the art for the application of printing layer on paper-based packaging materials and may be preferably applied by blade coating, liquid application system or gravure coating.

Examples

Example 1

A wet-laid paper substrate was produced with a fiber composition of 60 wt% hardwood and 40 wt% softwood, without adding any fillers, alkyl ketene dimers, polyamidoamine-epichlorohydrin resin, soap rosin, anionic rosin, cationic rosin, polyethylene imine, urea formaldehyde, and melamine formaldehyde resins.
The cellulosic fibers were refined to a value comprised between 40° SR and 70° SR as measured according to ISO 5267 and an air transmittance of 40 ml/min as determined according to ISO 5636-3. The basis weight of the paper substrate was 55 g/m².
A composition comprising 15 wt% of starch (Perfectafilm X85 from Avebe) was used as the composition for the impregnation step. The paper substrate was impregnated with such composition by size press.
A first barrier layer was applied on the first side of the impregnated paper substrate by rod coating. The composition used for the application of the barrier layer is as shown below in Table 1.
The first barrier layer formed onto the impregnated paper substrate included about 60 wt% of a styrene-butadiene rubber latex (Epotal 550D from BASF), mixed with about 40 wt% of calcium carbonate (Econocarb T200 from OMYA) .
A second barrier layer was applied onto the first barrier layer by blade coating. The composition used to apply the second barrier layer is as shown below in Table 1.
The second barrier layer applied onto the first barrier layer included about 50 wt% of polyvinyl alcohol (Exceval HR3010 from Kuraray) and 50 wt% of talc (Finntalc C15 from Elementis) .
A printing layer was applied online on the back side of the paper substrate, i.e. on the second side which was not coated with the barrier layers. The printing layer was applied by liquid application system and the composition used for the application of said layer was as shown below in Table 1.
Table 2 below reports the final compositions of the barrier layers and printing layer applied on the impregnated paper substrate.

Table 3 reports the physical and barrier properties of the obtained packaging material.

Table 1

Function	Commercial name	Chemical composition	Grease-barrier precursor composition	First barrier layer	Second barrier layer	Printing layer
			wt%	wt%	wt%	wt%
Grease-barrier precursor	Perfectafilm X85	Starch	15	-	-	-
Solvent	water	water	85	43	43	42
Barrier polymer	Epotal 550	SBR latex	-	34.1	34.1	-
Filler	Econocarb T200	Calcium carbonate	-	22.7	22.7	12.1
Filler	Hydragloss 90	Clay	-	-	-	28.3
Thickener	Blanose	CMC	-	0.1	0.1	0.1
Anti-foam agent	Advantage LC5008		-	0.1	0.1	0.1
Binder	Styronal D517	SBR latex	-	-	-	16.1
Crosslinker	Marebond SZ20	Ammonium Zirconium Carbonate	-	-	-	0.04
Dispersant	Topserse GXN	Polycarboxylate	-	-	-	0.04

Table 2

Function	Commercial name	Chemical composition	First barrier layer	Second barrier layer	Printing layer
			wt%	wt%	wt%
Grease-barrier precursor	Perfectafilm X 85	Starch
Solvent	water	water	-	-	-
Barrier polymer	Epotal 550	SBR latex	59.8	59.8	-
Filler	Econocarb T200	Calcium carbonate	39.8	39.8	20.9
Filler	Hydragloss 90	Clay	-	-	48.7
Thickener	Blanose	CMC	0.2	0.2	0.2
Anti-foam agent	LC5008		0.2	0.2	0.2
Binder	Styronal D517	SBR latex			27.8
Crosslinker	Marebond SZ20	Ammonium Zirconium Carbonate			0.1
Dispersant	Topserse GXN	Polycarboxylate			0.1

Experimental Example 1 - Evaluation of grease resistance (i)

The grease resistance of the packaging material was tested with the KIT test Tappi T559 and with the turpentine test Tappi T454. The results are reported in Table 3.

Experimental Example 2 - Evaluation of grease resistance (ii)

The grease resistance was also tested with the European pet food test, which determined the behavior of an oleophobic paper in direct contact with animal food.
The materials and apparatus for the test are as follows:

(i) FIRLABO SP 260 climatic chamber set at 70°C and 65% RH
(ii) Stainless steel ring with an inner diameter of 100 mm and a height of 50 mm
(iii) Stainless steel plate with a diameter of 96 mm and a thickness of 3 mm weighing approximately 0.2 kg
(iv) Stainless steel weight with a diameter of 90 mm and a weight of 3.5 kg
(v) Dog food "PURINA Puppy ProPlan Medium Optistart 10-25 kg", fat content 19.9% in 3 kg bags
(vi) Report paper (untreated coated paper, GERSTAR HC 120 g/m2 of Stenay)
(vii) Blotter for Cobb test

The test was performed as follows. The stainless steel parts were placed in the climatic chamber and the chamber was preheated to 70°C.
A 12 x 12 cm square of the sample, report paper and blotter were cut. The three cut pieces were stapled in the following order, from bottom to the top: blotting paper, paper transfer (wherein the side comprising fluorinated substances faced upwards), sample paper.
The assembly was placed in the climatic chamber. The stainless steel was placed on the assembly and filled with the equivalent of 100 ml of kibble (1 single-use cup).
The surface of the croquettes was flattened, then the stainless steel plate was placed on top of the ring. The stainless steel weight was placed on the top of the plate. The pressure thus exerted on the kibbles was 47 g/cm².
The climatic chamber was turned on at 65% RH and 70°C and the samples were left in the chamber for 16 hours. After 16 hours, the kibbles were discarded and the transparency and report were determined as follows.
For the transparency, the sample was placed on a black background. The intensity of black coloration of the coated surface was compared with a transparentization reference plate. The transparentization was expressed as a number from 0 to 7, wherein a lower number indicates a lower transparentization and hence a higher grease proof performance. For the purpose of the present invention, a transparentization of less than 5 was considered as an acceptable value for the purpose of a packaging material for use in a pet food container.
For the report, the transfer paper was placed on an illuminated table. The coated side of the transfer paper was compared with a reference scale to estimate the extent of the stains thereon. The evaluation scale was as follows:

0: no stains
1: a single point of small diameter
2: several small diameter points
3: at least one larger surface spot corresponding to the grouping of two level 2 points
4: at least one even larger surface spot, corresponding to the grouping of two level 3 spots
5: stains of significant size
6: a single large stain, corresponding to almost the entire sample.

A report value of less than 3 was considered as an acceptable value for the purpose of a packaging material for use in a pet food container. The results of the pet food test are reported in Table 3.

Experimental Example 3 - Evaluation of grease resistance (iii)

The edge wicking test was performed to evaluate the grease diffusion from the edges of the packaging material. A lower edge wicking value indicates a better grease resistance of the material.
The test was performed as follows.

(i) Two 10 x 10 cm samples per test paper were cut. CD (cross direction) and MD (machine direction) were marked.
(ii) The papers were rolled to form a tube, held in place with a paper clip or staple. The tube should be formed with the crosswise direction of the paper as shown in Figure 6. The paper at the bottom of the tube must not be overlapped to avoid capillary rise of the RP2 sauce between two layers of paper.
(iii) 10 ml of colored RP2 solution (red dyed synthetic oil provided by Ralston-Purina) were added to a Petri dish under fume hood.
(iv) The paper tube was positioned standing vertically on the Petri dish in such a way that the bottom edge touched the bottom of the Petri dish. The start of the contact time with the RP2 liquid was noted.
(v) The tube on the Petri dish was left in a fume hood at room temperature for 24 hours.
(vi) After 24 hours, the paper sample was removed and pressed between two waterleaves (1 back-forth, standard roll 3 or 10 kg) .
(vii) The maximum total height reached by the RP2 simulant was measured on two samples, starting from the bottom of the paper.

The results of the edge wicking test are reported in Table 3.

Experimental Example 4 - Evaluation of grease resistance (iv)

The greaseproof properties of the materials prepared in the examples were also assessed with the crease testing or RP2 fat test. Test requirements: Ottawa sand, grain size 20 to 30 Mesh (595 to 840 pm); colored RP2 solution (red dyed synthetic oil provided by Ralston-Purina); oven at 60°C; metal hand roll, in accordance with Pressure Sensitive Tape Council (P.S.T.C.) standard, Appendix B, Section 2.8; transfer paper (grid sheet supplied by Ralston-Purina, 100 cm2, grid every cm, paper coated on both sides); support sheet (coated paper two sides, not squared, supplied by Ralston-Purina); stainless steel ring with inner diameter 83 mm and height 10 mm; funnel-shaped rubber tube; disposable pipette.
The procedure is as follows. Samples were cut in 115 x 115 mm pieces. The sample was laid on a glass plate and folded in half, then the crease was lightly hand pressed and then rolled with a roller (2.5 kg) over the crease. The sample was unfolded and a roll pass was performed on the unfolded sample, then a new crease was folded perpendicular to the first one but with the reverse side inward, hand pressed and rolled with the roller. The sample was unfolded again and a roll pass was performed on the unfolded sample.
The grid printed sheet was placed on the top of a support sheet, then the creased sample was placed on the grid. A metal ring was placed on each sample. 5 grams of sand were placed onto each sample, and 1.3 ml of 60°C RP2 liquid was added to each sand pile. Samples were placed in the oven at 60°C for 24 hours, then removed and examined.
The amount of stain on the grid printed sheet were graded, where each grid square was equal to 1%. The grading standard was as follows: each grid square that was 7 % or more stained counted as 1% of the total; each grid square that was from 1 to 7% stained counted as 0.5% of the total; each grid square that was 0.25% to 1% stained counted as 0.25% of the total; each grid square that had only a few specks to 0.25% stained counted as 0.1% of the total. A total percentage for each sample sheet was calculated. 0% was taken as representing no oil leaking through, whereas 100% was taken as representing the entire grid being covered. An amount of oil leaking through below 2% was considered acceptable for the purposes of the present invention.
The results of the RP2 crease test are reported in Table 3.

Experimental Example 5 - Recycling yield

The recyclability of the packaging material was determined according to the standard EN13430 and was expressed as recycling yield (rate of recovered material). The recycling yield of the packaging material of Example 1 is reported in Table 3.

Table 3

Test	Unit	Standard	Example 1
KIT test	3M Kit #	Tappi T 559	>8
Turpentine test	Time	Tappi T 454	> 1800 s
RP2 crease test	Percentage	Internal standard	<10%
Edge wicking	mm	Internal standard	< 15 mm
Pet food test - transparentisation	Grade	Internal standard	< 5
Pet food test - report	Grade	Internal standard	< 2
Recyclability	Yield	EN 13430	> 80%

Example 2

A wet-laid paper substrate was produced in a similar way to Example 1, but with a fiber composition of 45 wt% of softwood and 55 wt% of hardwood. The pulp was refined at 70° SR. The paper substrate was impregnated with a solution comprising starch as described above in Example 1, but not coated with a barrier layer.

Example 3

A paper substrate was prepared as in Example 2, and then further coated with a barrier layer containing 54 wt% of Epotal 550D and 46 wt% delaminated talc (Steaplus prime from Imerys) on its first side.

Comparative Example 1

A paper substrate was prepared as in Example 2, except that it was not impregnated with the solution comprising starch.

Comparative Example 2

A paper substrate was prepared as in Example 2, except that the paper substrate was impregnated with a solution comprising 1 wt% of alkyl ketene dimer instead of starch.

Experimental Example 6 - Effect of impregnation on barrier properties

The Cobb value of the samples prepared in Examples 2 and 3 and in Comparative Examples 1 and 2 was determined according to ISO 535 on the first side of the paper sample. The results are shown in Table 4. In Table 4, a higher Cobb value indicates a higher barrier activity. As shown in Table 4, the impregnation with starch is able to reduce the Cobb value of the paper substrate without sizing, thus making it suitable for the use as a packaging material upon coating with the barrier layer.

Table 4

	Comparative Example 1	Comparative Example 2	Example 2	Example 3
	No impregnation	Sizing agent	Impregnation with starch	Impregnation with starch + barrier layer
Sizing	-	1% AKD	-	-
Starch impregnation	-	-	6 g/m²	6 g/m²
Water Cobb 1 min CS (g/m²)	80	21	43	5
Water Cobb 1 min UCS (g/m²)	82	20	44	39

Experimental Example 7 - Impact of wet strength agents on recyclability

A paper substrate was prepared as described in Example 2, except that the paper substrates were not impregnated with starch and that a wet strength agent (polyamidoamine-epichlorohydrin resin, Kymene) was added to the pulp in the amounts indicated in Table 5.
The recycling yield was determined according to EN 13430 by measuring the amount recovered by repulping, and the results are shown in Table 5. As shown in Table 5, the papers wherein the amount of wet strength agent was very low or even absent, such as Samples D and F, had a recycling yield above 50%. Table 5

Samples Content of wet strength agent (Kimene) (wt% on dry basis) Recycling yield %

A 1.28% 0%

B 0.46% 25%

C 0.30% 40%

D 0.16% 72%

E 0.00% 100%

Examples 4-6 and Comparative Examples 3-5

Paper substrates were prepared as described in Example 2, except for the following. In Examples 4 and 5, the fiber composition was 35 wt% softwood and 65 wt% hardwood, and the paper pulps were refined to an air permeability of 20 ml/min as determined by ISO 5636-3 and a Cobb value of 47 g/m² as determined according to Experimental Example 6 (ISO 535). In Example 6 and Comparative Examples 3 to 5, the fiber composition was 40 wt% softwood and 60 wt% hardwood, and the paper pulps were refined to 130 ml/min as determined by ISO 5636-3 and a Cobb value of 70 g/m² as determined according to Experimental Example 6 (ISO 535). The paper substrates were impregnated with the compositions reported in Table 6 below.
The edge wicking was determined as explained in Experimental Example 3 and the results are reported in Table 6 below.
As shown in Table 6 below, the impregnation with starch allows for a lower edge wicking, which is indicative of better grease barrier properties, as compared to paper substrates which are not impregnated at all (Comparative Example 3) or impregnated with standard sizing agents (Comparative Examples 4 and 5). In particular, this is shown for paper substrates having the same level of refining (Example 6 compared with Comparative Examples 3 to 5).

Further, a comparison between Example 4 and Example 6 shows that the refining of the base paper may also influence the grease barrier properties, with a higher refining leading to a lower edge wicking. Moreover, the impregnation of the paper substrate with a composition comprising a grease barrier precursor allows for optimal and even improved grease barrier properties even in the absence of fillers in the composition (Example 4 compared to Example 5).

Table 6

Samples	Components of composition used for impregnation	Composition of impregnation formulation	Refining (ml/min)	Edge wicking - max height (mm)
Example 4	Perfectafilm B3085	100% starch	20	10.5
Example 5	Perfectafilm B3085 and Steaplus Prime	50% starch and 50% talc	20	13.3
Example 6	Perfectafilm X85	100% starch	130	29
Comparative Example 3	-	-	130	51.25
Comparative Example 4	Aquapel J215	1 % AKD	130	39
Comparative Example 5	HiPhase 35J	1 % Colophane	130	49

Examples 7 to 9

Paper substrates were prepared as described in Example 1 and one or two barrier layers were coated onto the impregnated paper substrates, the barrier layers having the compositions and basis weight reported in Table 7 below.
The obtained packaging materials were subject to the pet food test as described in Experimental Example 2 above. The results of the test are reported in Table 7 below.
As shown in Table 7 below, all Examples showed a good performance in terms of grease resistance, as the transparentisation was below 5 for all samples. The pet food test report was also satisfactory for all samples, but the use of calcium carbonate as filler in the barrier layer allowed for a better result (report below 2) as compared to talc.

The presence of an additional barrier layer in Example 9 allowed for a further improvement both in terms of transparentisation and report.

Table 7

				Test conditions : 3,5 kg ; 70° C; 65 % RH; 16 hours
Samples	Number of barrier layer (basis weight)	Components of the barrier layers	Chemical composition of the barrier layers	Pet food test /2 measures
Samples	Number of barrier layer (basis weight)	Components of the barrier layers	Chemical composition of the barrier layers	transparentisation	report
Example 7	1 (5gsm)	70 % Epotal 550D + 30% deliminated talc	70% Latex SBR + 30 % talc	4.5	4
Example 8	1 (7 gsm)	60 % Epotal 550D + 40% Calcium carbonate	60% latex SBR + 40% clacium carbonate	1.8	1.3
Example 9	2 (7gsm + 3 gsm)	60 % Epotal 550D + 40% Calcium carbonate, ,	60% latex SBR + 40% clacium carbonate	0.3	0

Examples 10 and 11 and Comparative Example 6

Paper substrates were prepared in a similar way as in Example 1, except that the fiber composition of the paper substrate was 43 wt% softwood and 57 wt% hardwood, and the fiber pulp was refined to 60° SR. The paper substrates were impregnated with a composition containing 15 wt% starch in the same amounts as described in Example 1, then coated with a first barrier layer (Example 10) or a first and a second barrier layers (Example 11) having the composition reported in Table 8 below, or not coated (Comparative Example 6). The obtained packaging materials were tested according to Experimental Example 4 (RP2 crease test) and the results are reported in Table 8 below.

Table 8

Samples	First barrier layer	Second barrier layer	RP2 crease test (%)
Samples	First barrier layer	Second barrier layer	2 measures/sample
Example 10	4,5 gsm of Esacote BIO BC 50	--	4.5
Example 11	2,5 gsm of Esacote BIO BC 50	2,5 gsm of Esacote BIO BC 50	2.4
Comparative Example 6	--	--	54.0

As shown in Table 8, both Examples 10 and 11 showed good greaseproof performances (RP2 crease test below 10%), which were remarkably improved as compared to the paper substrate which was only impregnated but not coated with any barrier layer (Comparative Example 6). When two barrier layers are present, even if the total weight of the layers and the composition are the same as in the sample with only one barrier layer, a further improvement in grease resistance was observed.

Claims

A food packaging material (1, 2, 3, 4, 5) comprising:
(i) a paper substrate (10, 20, 30, 40, 50) having a first side and a second side, the second side being opposite to the first side,
wherein the paper substrate is impregnated with a composition comprising a grease barrier precursor (12, 22, 32, 42, 52); and

(ii) a barrier layer (11, 21, 31, 41, 51) coated onto at least the first side of the impregnated paper substrate, the barrier layer comprising a polymer (13, 23, 33, 43, 53);
wherein the total amount of per- and polyfluoroalkyl substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material.
The food packaging material according to claim 1,
wherein the total amount of alkyl ketene dimers, soap rosin, anionic rosin and cationic rosin in the paper substrate is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate; and/or

wherein the total amount of polyamidoamine-epichlorohydrin resin, polyethylene imine, urea formaldehyde, and melamine formaldehyde resins in the paper substrate is less than 0.5 wt%, preferably less than 0.35 wt%, more preferably less than 0.2 wt% based on the total weight of the paper substrate; and/or

wherein the total amount of fluorine-containing substances in the packaging material does not exceed 20 ppm based on the total weight of the packaging material.
The food packaging material according to claim 1 or 2, wherein the grease barrier precursor is selected from starch, a starch derivative, carboxymethyl cellulose, polylactic acid, ethylene vinyl alcohol copolymer, polyvinyl alcohol and a mixture thereof.
The food packaging material according to any one of claims 1 to 3, wherein the polymer comprised in the barrier layer is selected from styrene-butadiene rubber latex, polyvinyl alcohol, starch, polyurethane, ethylene vinyl-acetate copolymer, styrene (meth)acrylic acid copolymer, poly (meth)acrylic acid or a mixture thereof.
The food packaging material according to any one of claims 1 to 4, wherein the barrier layer further comprises a filler (24) selected from calcium carbonate, clay, talc and a mixture thereof.
The food packaging material according to any one of claims 1 to 5, further comprising (iii) an additional barrier layer (34) which is coated onto the barrier layer (31) and comprises a polymer (35) selected from styrene-butadiene rubber latex, polyvinyl alcohol, starch, polyurethane, ethylene vinyl-acetate copolymer, styrene (meth)acrylic acid copolymer, poly (meth)acrylic acid or a mixture thereof.
The food packaging material according to any one of claims 1 to 6, wherein the grease barrier precursor is present in an amount of 1 to 10 wt% of the total weight of the packaging material.
The food packaging material according to any one of claims 1 to 7, wherein the total weight per unit area of all the barrier layers is 1 to 15 g/m², and/or wherein the weight per unit area of the impregnated paper substrate is 30 to 120 g/m².
The food packaging material according to any one of claims 1 to 8, wherein the barrier layer (41) is applied onto the first side of the impregnated paper substrate (40), and the packaging material further comprises (iv) a printing layer (44) applied onto the second side of the impregnated paper substrate.
The food packaging material according to any one of claims 1 to 9, and a Cobb value as measured on the second side is larger than a Cobb value as measured on the first side which is coated with the barrier layer (s), the Cobb values being determined according to ISO 535.
The food packaging material according to any one of claims 1 to 10, wherein the packaging material is recyclable by repulping with at least 50 wt% being recoverable according to EN13430.
A pet food container comprising the food packaging material according to any one of claims 1 to 11.
A method for producing a food packaging material, the method comprising the steps of:
(i) providing a paper substrate having a first side and a second side, the second side being opposite to the first side;

(ii) impregnating the paper substrate with a composition comprising a grease barrier precursor;

(iii) applying a barrier layer comprising a polymer onto at least the first side of the impregnated paper substrate;
wherein the total amount of per- and polyfluoroalkyl substances in the obtained packaging material is less than 20 ppm based on the total weight of the packaging material.
The method according to claim 13, further comprising a step (iv) of applying an additional barrier layer comprising a polymer onto the barrier layer obtained in step (iii).
Use of the food packaging material according to any one of claims 1 to 11 as a pet food container.