FOIL-FREE, LOW MOISTURE VAPOR TRANSMISSION RATE PACKAGING MATERIAL

TECHNICAL FIELD

[0001]The present disclosure relates to a food packaging material and a method of manufacturing a food packaging material. In particular, this disclosure relates to a low moisture vapor transmission rate packaging material that is devoid of a metal foil.

BACKGROUND

[0002]In the quick service (also known as “fast-food”) restaurant industry, food wrappers serve multiple functions including containment of food products during preparation, protection during transport from service counter to customer, maintenance of food temperature, prevention of contamination, and facilitation of convenient handling and consumption. Currently available commercial food wrappers comprise sheets of foil-lined paper that are folded around food items such as hamburgers, sandwiches, burritos, and similar handheld food products. Despite widespread use, existing food wrapper designs suffer from several drawbacks. For example, the currently available commercial wrappers that do not comprise foil-lined paper often fail to maintain structural integrity when exposed to moisture, grease, or heat from hot food items, resulting in wrapper failure, food spillage, and unsatisfactory customer experience. Other wrappers that do not comprise foil-lined paper do not provide adequate insulation properties, allowing excessive escape of moisture and transfer of heat that can cause customer discomfort when handling hot food items or, conversely, allowing rapid cooling that degrades food quality. Moreover, a significant environmental concern with currently commercially available food wrappers relates to their recyclability and end-of-life disposal. The majority of existing food wrappers employed in fast-food establishments are not recyclable due to their composite material construction. As environmental regulations become increasingly stringent and consumer demand for sustainable packaging solutions intensifies, the quick service restaurant industry faces mounting pressure to develop wrapper alternatives that maintain requisite functional performance while offering improved recyclability, compostability, or biodegradability characteristics.

[0003]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.

[0004]The packaging material should also be fabricated from materials that are safe for food contact and ideally be recyclable.

[0005]Fluorofree paper-based packaging material 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 on the paper machine.

[0006]In addition, packaging materials not comprising plastic films and/or papers containing fluorochemicals are generally insufficient in controlling the moisture content of packed products such as food. However, in food packaging, moisture control is desirable in order to maintain food quality. Accordingly, in addition to addressing the problems mentioned above there is a need for a packaging material maintaining the quality of moisture sensitive food products.

[0007]There is a demand for a packaging material that is suitable for food and that is able to control moisture of moisture sensitive products. An indication of the permeability of water vapor through a substance is the moisture vapor transmission rate (MVTR). A low MVTR indicates an improved vapor barrier. To be specific, there is a demand for a food packaging material that has a low MVTR, such as a MVTR of less than 75 g/m²/24 h determined at 85% RH and 23° C.

[0008]Ideally, the packaging material is at the same time substantially free from fluorochemicals such as per- and polyfluoroalkyl substances (PFAS), has good grease-proof properties and maintains optimal mechanical strength such that it can withhold heavy weight.

[0009]Furthermore, there is a demand for this packaging material to be manufacturable with food safe and recyclable materials. That is, conventional packaging materials comprising plastic films, a high amount of coating and/or fluorochemicals may give low MVTR but recyclability would be affected. Accordingly, there is demand for a packaging material providing satisfactory moisture barrier properties while being recyclable.

SUMMARY

[0010]The present invention is aimed at solving the aforementioned problem of the prior art by providing a food packaging material comprising 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 coated on at least the first or the second side with a coating comprising wax and a copolymer selected from styrene butadiene copolymer and/or styrene acrylic copolymer.

[0011]Further, the present invention relates to a method of manufacturing the food packaging material, wherein the coating is applied to the paper substrate by direct gravure or using a single rod or by curtain coating or by spray coating or size press coating or air knife coating or flexography coating.

[0012]It has been found that coating of a paper substrate with a coating comprising both wax and a copolymer selected from at least one of the group consisting of a styrene butadiene copolymer and a styrene acrylic copolymer allows to obtain a food packaging material having low MVTR thereby extending the shelf life of moisture sensitive food products.

[0013]Furthermore, the inventors of the present invention have found that the combination of wax and styrene copolymer according to the invention allows to provide a packaging material having satisfactory moisture barrier properties even when the coating is present only at relatively low amounts. This allows to provide a packaging material having satisfactory moisture barrier properties and being recyclable.

[0014]Without wishing to be bound by any theory, the combination of a wax with a styrene copolymer according to the invention appears to result in a particular suitable interaction within the coating that improves moisture barrier properties. The long aliphatic hydrocarbon chains in the wax likely interact well with the hydrophobic parts in the copolymers. Moreover, the hydrocarbon chains of the wax are more flexible in their configurations and can fold more easily than, for example, styrene copolymers, which have more bulky phenyl groups on their backbones. The hydrocarbon chains of the wax may thus fill gaps in the pore structures of the paper substrate that have been left unblocked by the copolymer due to its rather ridged structure. As the hydrocarbon chains of the wax are water-repellent, moisture barrier properties may be improved.

[0015]The food packaging material according to the present invention further facilitates obtaining optimal mechanical properties. These objects of the present invention are achieved without introducing plastic films and/or papers containing fluorochemicals, thus the invention results in a product that is safe for food contact and has a lower environmental impact (that is, a higher recyclability).

[0016]The food packaging material of the present invention thus may form a food packaging for the food items served in a food service establishment, particularly suitable for serving the food items for consumption during a short period of time having optimal mechanical properties without introducing aluminum foil, plastic films and/or papers containing fluorochemicals.

[0017]While the packaging material of the present invention is particularly suitable for the food items served in quick service restaurants and similar food establishments, it is equally suitable for any hot or cold, cooked or uncooked food items, as it is obviously also suitable for other products, including not only food in general but also non-food products.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic illustration of an embodiment of the present invention.

[0019]FIG. 2 is a schematic illustration of another embodiment of the present invention in which the coating layer further comprises a filler.

[0020]FIG. 3 is a schematic illustration of another embodiment of the present invention in which the food packaging material further comprises a printing layer.

DETAILED DESCRIPTION

Definitions

[0021]In the present invention, the term “average” denotes mean average, unless stated otherwise.

[0022]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.

[0023]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.

[0024]In the context of the present invention, the term “biodegradable” is generally defined in line with EN13432:2000. 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 13432:2000.

[0025]The term “compostable” is generally defined in line with EN13432:2000. 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 EN 13432:2000. 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.

[0026]An “industrial compostable” material may be compostable as described above in an industrial setting: The material may disintegrate and biodegrade at temperatures of 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 of 10 to 45° C. and most preferably of 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.

[0027]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.

[0028]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

[0029]The present invention relates to a food packaging material comprising 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 coated on at least the first or the second side with a coating comprising wax and a copolymer. In an embodiment, the copolymer may be selected from styrene butadiene copolymer and/or styrene acrylic copolymer.

[0030]The paper substrate is advantageous because the discovery of superior steam retention properties represents a distinct and unexpected finding. A material that functions as an effective barrier to moisture vapor transmission does not automatically function as an effective barrier to steam penetration. Steam involves water vapor at or near its saturation point, often accompanied by condensation, elevated temperatures, and raised humidity that create different transport mechanisms and material interactions compared to moisture vapor diffusion at ambient conditions. The MVTR test method measures steady-state diffusion of water vapor under controlled temperature and humidity gradients, and does not replicate the conditions materials encounter during steam exposure where condensation, elevated temperature, and raised humidity occur simultaneously. The inventors unexpectedly discovered that the packaging materials described herein exhibit steam penetration resistance that would not be predicted based on their MVTR values, indicating that the materials possess features that specifically address the distinct challenges posed by steam exposure.

[0031]With reference to FIG. 1, the packaging material (1) of the present invention comprises a paper substrate (10) having a first side and a second side, the second side being opposite to the first side, which optionally is pre-coated on at least the first or the second side with a pre-coating composition (12), the paper substrate (10) being coated on a first side with a coating (11) comprising wax and a copolymer (13).

Paper Substrate

[0032]The term “paper substrate” as used herein refers to planar element such as a sheet of paper having a first side and a second side, the second side being opposite to the first side.

[0033]The paper substrate of the present invention refers to a base paper before coating and the optional pre-coating described below.

[0034]In the present invention, the paper substrate is preferably a cellulose fiber base sheet.

[0035]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 μm, 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.

[0036]The terms “cellulose fiber base sheet”, “paper substrate” or “base paper” refer 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).

[0037]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).

[0038]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. The cellulose fibers can be unbleached or bleached cellulose fibers. 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.

[0039]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 15 wt. % or more, preferably 20 wt. % or more, more preferably 30 wt. % or more, and even more preferably 40 wt. % or more, and preferably 55 wt. % or less, more preferably 40 wt. % or less, further preferably 30 wt. % or less relative to the total amount of fibers in the cellulose fiber base sheet. Adjusting the amount of hardwood fibers contributes to the tightness and foldability of the paper.

[0040]Further, the paper substrate used in the present invention preferably comprises natural softwood fibers contributing to mechanical strength of the paper. Preferably the paper substrate comprises softwood fibers in an amount of 45 wt. % or more, preferably 55 wt. % or more, and preferably 85 wt. % or less, more preferably 80 wt % or less, more preferably 70 wt. % or less, further preferably 50 wt. % or less relative to the total amount of fibers in the cellulose fiber base sheet.

[0041]In a preferred embodiment of the present invention, the paper substrate is made of natural cellulosic fibers, from the viewpoint of biodegradability. It is particularly preferable that the paper substrate is biodegradable. The paper substrate therefore preferably contains no more than 25 wt. % of non-biodegradable material or material of undetermined compostability in order to meet the requirements of the EN 13432:2000 standard. It is even more preferable that the paper substrate is more than 90% biodegradable, for example more than 95%, more than 98%, more than 99%, or 100% biodegradable, that is, that the paper substrate contains less than 10 wt %, less than 5 wt %, less than 2 wt. %, less than 1 wt. %, or 0 wt % of non-biodegradable material or material of undetermined compostability. Most preferably, any additives added to the paper substrate are compostable. The paper substrate preferably comprises at least 50 wt. % of cellulosic fibers, preferably at least 60 wt. % of cellulosic fibers, more preferably at least 85 wt. % of cellulosic fibers, and even more preferably at least 90 wt. % of cellulosic fibers. In a more preferable embodiment, at least 95 wt. % and most preferably 100 wt. % of the fibers in the paper substrate are natural cellulosic fibers.

[0042]The diameter of the cellulose fibers is preferably 10 μm to 40 μm, 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.

[0043]The paper substrate typically has an average thickness of from 30 μm to 150 μm, preferably from 40 μm to 120 μm, even more preferably from 45 μm to 80 μm and most preferably about 65 μm from the viewpoint of achieving excellent mechanical reinforcement properties.

[0044]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. %.

[0045]The cellulosic fibers described above are obtained by refining a pulp to have a desired refining degree as quantified herein using Schopper Riegler number, ° SR. The lower Schopper Riegler number values signify less refined cellulosic fibers, providing a reliable measurement for lower energy consumption during the overall processes of paper substrate manufacturing. In some specific embodiments, the cellulosic fibers described above are not refined or refined to the value of a Schopper Riegler number of about 0. In alternative embodiments, the cellulosic fibers are refined to 10° SR or more, preferably to 15° SR or more, further preferably to 20° SR or more, furtherer more preferably to 25° SR or more, even more preferably to 30° SR or more, and most preferably to 35° SR or more, and to 50° SR or less, even more preferably to 40° SR or less as measured according to ISO 5267.

[0046]The paper substrate preferably has an air transmittance of 10 ml/min or more, preferably 20 ml/min or more, more preferably 25 ml/min or more, even 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.

[0047]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 90° 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 barrier performance may be achieved when controlling the refining such that the refining degree/air transmittance is within the ranges described above.

[0048]The paper substrate preferably has a Gurley porosity greater than 3,000 sec/100 cm³, preferably greater than 10,000 sec/100 cm³, preferably greater than 20,000 sec/100 cm³. The paper substrate preferably has a Gurley porosity of 30,000 sec/100 cm³ or less, preferably 25,000 sec/100 cm³ or less, more preferably 18,000 sec/100 cm³ or less. The Gurley porosity is determined according to ISO 5636-5 test method. The Gurley porosity is determined using PROFILE/Plus® Roughness & Porosity Automated Test System by Technidyne.

[0049]Preferably, the paper substrate has a basis weight of 30 g/m² or more, preferably 35 g/m² or more, and even more preferably 40 g/m² or more. Moreover, the paper substrate preferably has a basis weight of 200 g/m² or less, preferably 180 g/m² or less, more preferably 160 g/m² or less, and even more preferably 150 g/m² or less. Preferably, the paper substrate has a basis weight of 30 to 200 g/m², more preferably of 40 to 200 g/m²; or preferably, the paper substrate has a basis weight of 30 to 150 g/m², more preferably of 40 to 150 g/m². When the grammage of the paper substrate is within the above limits, the mechanical properties of the final packaging material are improved.

[0050]In an embodiment, the paper substrate is not calendered. In another embodiment, the paper substrate is calendered and/or supercalendered. To be specific, the paper substrate may not be calendered, or alternatively, may be calendered, supercalendered, or both, calendered and supercalendered. More preferably, the paper substrate is either not calendered or is calendered prior to coating the base paper with the composition according to the invention.

[0051]A preferred step of calendering the base paper in a method of manufacturing the packaging material according to the present invention is described below. A calendered and/or supercalendered paper substrate may be advantageous in terms of improving the edge wicking (described below) 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.

[0052]Preferably, before coating or optional pre-coating of the base paper, the paper substrate has a Sheffield surface smoothness/roughness of less than 300 Sheffield Units (SU), preferably less than 200 SU, more preferably less than 160 SU. Moreover, the paper substrate preferably has a Sheffield surface smoothness/roughness of greater than 100 SU. The Sheffield surface smoothness/roughness is determined according to Tappi T538 standard.

[0053]In a preferred embodiment, the packaging material of the present invention may comprise a paper substrate which is pre-coated with a pre-coating composition. The term “pre-coated paper substrate” as used herein refers to a base paper which is pre-coated with said composition. The term “pre-coated 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. However, in some aspects, a pre-coating does not penetrate the entire paper substrate but provides a film at the surface, which allows for the use of less material, a pre-coating on the surface of the paper substrate is beneficial in terms recyclability of the packaging material. Preferably, the composition pre-coats the paper substrate across its whole surface. In some embodiments, the pre-coating composition may serve as a grease barrier precursor. In some specific embodiments, the optional pre-coating is preferably performed prior to calendering and/or supercalendering the paper substrate as described above.

[0054]In some embodiments relating to a pre-coated paper substrate, the pre-coating composition is selected from at least one of the groups consisting of polysaccharides such as starch, a starch derivative, carboxymethyl cellulose, carboxyethyl cellulose, chitosan, alginate, dextrin, ethylene vinyl alcohol copolymer, polyvinyl alcohol and a mixture thereof. More preferably, the pre-coating composition is starch, a starch derivative such as cationic, anionic and non-ionic starch, carboxymethyl cellulose, carboxyethyl cellulose, chitosan, alginate, dextrin, or a mixture thereof. Most preferably, the pre-coating composition is cationic starch, anionic starch, carboxymethyl cellulose or a mixture thereof.

[0055]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, as well as to improve the grease barrier at the core of the material.

Coating

[0056]The packaging material of the present invention comprises a paper substrate that is coated on at least the first or the second side with a coating (hereinafter also referred to as coating layer). The coating is coated on at least the first or the second side of the paper substrate described above and comprises a wax and a copolymer as described below.

[0057]Preferably, the coating is coated on the entire surface of at least the first or the second side. Further, in a preferred embodiment, the coating is coated onto the first side but not onto the second side of the paper substrate.

[0058]The coating layer in the packaging material of the present invention allows to minimize defects of the surface of the paper substrate and to ensure an effective heat and steam retention properties, low MVTR as described below in further detail.

[0059]The MVTR test measures water vapor transmission at 85% relative humidity (RH) and 23° C., conditions that do not replicate the elevated temperatures and condensation events encountered during steam exposure. Steam retention involves resistance to water in both liquid and vapor forms, whereas MVTR measures only vapor transmission and Cobb testing measures only liquid water absorption under ambient conditions. The elevated temperatures present during steam exposure increase the rate at which water molecules pass through the material and can alter material properties such as polymer mobility and fiber structure. Consequently, MVTR values and/or Cobb measurements obtained under standard test conditions do not predict steam penetration resistance under the distinct thermal and physical conditions of steam exposure.

[0060]Preferably, the coating comprises the wax and the copolymer is present in an amount of at most 25 wt. %, more preferably at most 20 wt. %, and even more preferably of at most 15 wt. %, based on the paper substrate and the coating. Preferably, the coating comprises the wax and the copolymer is present in an amount of at least 1 wt. %, more preferably at least 5 wt. %, based on the paper substrate and the coating. The amount of the coating within the above ranges is advantageous in that it improves recyclability of the packaging material, while still ensuring good barrier properties and low MVTR.

[0061]The basis weight of the coating layer is 3.25 g/m² or more, preferably 3.25 g/m² or more, preferably 4.5 g/m² or more, more preferably 5.0 g/m² or more, more preferably 5.5 g/m² or more, and 10 g/m² or less, preferably 8.1 g/m² or less, more preferably 5.7 g/m² or less. A weight per unit area within the above ranges is advantageous in that it improves barrier properties and low MVTR of the packaging material, while still ensuring a good recyclability and without incurring in a blocking effect.

[0062]In the present invention, the coating comprises a wax. The term “wax” as used herein has its ordinary meaning to those skilled in the art. That is, the term “wax” refers to organic compounds characterized in that they comprise acid esters having long aliphatic hydrocarbon chains. The total amount of wax in the coating layer may preferably be 40 wt. % or less, more preferably 35 wt. % or less, and even more preferably 30 wt. % or less. Moreover, the total amount of wax in the coating layer may preferably be 1 wt. % or more, more preferably 5 wt. % or more, even more preferably 10 wt. % or more and most preferably 15 wt. % or more relative to the total amount of the coating.

[0063]The wax may be a natural wax, a synthetic wax or a mixture thereof. Natural waxes may comprise unsaturated bonds and various functional groups such as fatty acids, primary and secondary alcohols, ketones, aldehydes and fatty acid esters. Natural waxes include waxes derived from beeswax, epicuticular waxes of plants such as carnauba wax, jojoba oil, candelilla wax, rice bran oil and ouricury wax. Synthetic waxes may comprise long-chain aliphatic hydrocarbons (alkanes or paraffins), preferably synthetic waxes do not comprise functional groups. Synthetic waxes include paraffin wax.

[0064]The wax according to the present invention is preferably at least one selected from at least one of the group consisting of beeswax, carnauba wax or paraffin wax. More preferably, the wax is paraffin wax.

[0065]In the present invention, the coating further comprises a copolymer selected from at least one of the group consisting of a styrene butadiene copolymer and a styrene acrylic copolymer. Preferably, the copolymer may be a styrene acrylic copolymer. The total amount of a copolymer selected from styrene butadiene copolymer and styrene acrylic copolymer in the coating layer may preferably be 60 to 90 wt. %, and more preferably 65 to 85 wt. % relative to the total amount of the coating.

[0066]The styrene butadiene copolymer is a polymer derived from polymerization of a styrene monomer and a butadiene monomer. Preferably, the styrene butadiene copolymer is at least one selected from a styrene butadiene rubber latex and a styrene butadiene rubber obtained from emulsion polymerization or solution polymerization.

[0067]The styrene acrylic copolymer is a polymer derived from polymerization of a styrene monomer with an acrylic ester monomer and/or an acrylic acid monomer. Preferably, the styrene acrylic copolymer is a water-based styrene acrylic emulsion polymer obtained from emulsion polymerization.

[0068]In an embodiment of the invention, the coating may comprise one or more additional polymers selected from polyvinyl alcohol, starch, polyurethane, ethylene vinyl-acetate copolymer, styrene (meth)acrylic acid copolymer, and poly (meth)acrylic acid. That is, the coating layer may comprise one or more polymers. When the coating layer comprises more than one polymer, it may be described herein as comprising a “polymer blend”. The total amount of the polymer blend in the coating layer may be 1 to 15 wt. % or more, and more preferably 2 to 10 wt. % or more relative to the total amount of the coating. Further, the amount of the polymer blend in the coating layer may be 2 to 30 wt. % or less, and more preferably 4 to 20 wt. % or less relative to the total amount of the coating.

[0069]In an alternative embodiment, the coating layer may further comprise a filler selected from calcium carbonate, clay, talc and a mixture thereof. More preferably, the filler 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 coating 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 coating layer components. The inclusion of a filler in the coating layer may be advantageous in that it improves drying and reduces the foaming of the coating layer, without negatively affecting the barrier properties.

[0070]FIG. 2 is a schematic illustration of a preferred embodiment in which a filler is comprised in the coating layer. As shown in FIG. 2, in such an embodiment the packaging material (2) comprises a paper substrate (20) which optionally is pre-coated with a pre-coating composition (22), the paper substrate (20) being coated on a first side with a coating (21) comprising a filler (24) in addition to a wax and a copolymer (23) selected from styrene butadiene copolymer and/or styrene acrylic copolymer.

[0071]The coating 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.

[0072]In a preferred embodiment of the present invention, the packaging material may further comprise an additional coating layer coated onto the coating layer that comprises a wax and a copolymer as described below. In the context of the present invention, when an additional coating layer is present, the coating layer that is coated on the paper substrate may be referred to as the “first coating layer” and the additional coating layer may be referred to as the “second coating layer”.

[0073]In a further preferred embodiment, in the packaging material of the present invention the coating is applied on a first side of the paper substrate, and the packaging material further comprises a printing layer applied on the second side of the paper substrate. Specifically, the coating is preferably applied on the first side of the paper substrate but not on the second side, and a printing layer is applied on the second side of the paper substrate. Preferably, the printing layer is applied on the entire surface of the second side of the paper substrate.

[0074]FIG. 3 illustrates a preferred embodiment of the present invention in which a printing layer is present. As shown in FIG. 3, the packaging material (4) comprises a paper substrate (40), which optionally is pre-coated with a pre coating substrate (42), the paper substrate (40) being coated on a first side with a first coating (41) comprising wax and a copolymer (43) selected from styrene butadiene copolymer and/or styrene acrylic copolymer, and the paper substrate (40) being coated on a second side with a printing layer (44).

[0075]In the further preferred embodiment, 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.

[0076]In the further preferred embodiment, the printing layer preferably comprises a filler selected from calcium carbonate, clay, talc 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.

[0077]In the further preferred embodiment, the printing layer may comprise further additives such as defoaming agents, dispersant, lubricant, crosslinker, thickener, pH modifier and gloss-imparting agents.

[0078]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.

[0079]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.

[0080]In an embodiment, the packaging material is substantially free of per- and polyfluoroalkyl substances. In particular, the total amount of fluorine-containing organic substances (including per- and polyfluoroalkyl substances) in the packaging material of the present invention does not exceed 20 ppm, preferably 15 ppm, more preferably 10 ppm, and most preferably 5 ppm, based on the total weight of the packaging material.

[0081]In a further preferred embodiment, the total amount of elemental fluorine in the packaging material, namely the fluor content, does therefore not exceed 100 ppm, preferably does not exceed 90 ppm, and more preferably does not exceed 80 ppm, based on the total weight of the packaging material. To be specific, the packaging material according to this preferred embodiment has a fluor content of less than 100 ppm, preferably of less than 90 ppm, and more preferably of less than 80 ppm.

[0082]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 2.0 wt. %, more preferably less than 1.5 wt. %, more preferably less than 1.0 wt. %, and even more preferably less than 0.5 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 2.0 wt. %, preferably less than 1.5 wt. %, more preferably less than 1.0 wt. %, and even more preferably less than 0.5 wt. % based on the total weight of the paper substrate.

[0083]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.

[0084]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.

[0085]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.

[0086]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.

[0087]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

[0088]The basis weight of the packaging material according to the present invention is preferably 50 g/m² or more, further preferably 60 g/m² or more, even more preferably 70 g/m² or more. Furthermore, the basis weight of the packaging material according to the present invention is preferably 220 g/m² or less, more preferably 130 g/m² or less, further preferably 120 g/m² or less, even more preferably 110 g/m² or less, and most preferably 100 g/m² or less.

[0089]The Sheffield surface smoothness/roughness of the packaging material according to the present invention is preferably less than 200 SU, more preferably less than 180 SU, and even more preferably less than 150 SU, when determined according to the Tappi T538 standard as described above. The foldability in bounceback in the machine direction (MD) of the packaging material according to the present inventive concept is less than 15 mm, preferably less than 10 mm, more preferably less than 5 mm, and most preferably about 0 mm. Furthermore, the foldability in bounceback in the cross direction (CD) of the packaging material is less than 10 mm, preferably less than 5 mm, most preferably about 0 mm. Noticeably, the foldability in bounceback extends further to the paper substrate. The foldability in bounceback in the machine direction (MD) of the paper substrate is less than 15 mm, preferably less than 10 mm, more preferably less than 5 mm, and most preferably about 0 mm. Furthermore, the foldability in bounceback in the cross direction (CD) of the packaging material is less than 10 mm, preferably less than 5 mm, most preferably about 0 mm.

[0090]The thickness of the paper substrate 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.

[0091]A tensile strength in the machine direction (MD) of the paper substrate of the present invention as determined by ISO 1924 is 1 kN/m or more, preferably 2 kN/m or more, more preferably 3 kN/m or more, further preferably 3.5 kN/m or more, and 12 kN/m or less, preferably 10 KN/m or less, further preferably 8 kN/m or less.

[0092]A tensile strength in the cross direction (CD) of the paper substrate of the present invention as determined by ISO 1924 is preferably 0.5 kN/m or more, more preferably 1 kN/m or more, even more preferably 1.5 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.

[0093]Adjusting the tensile strength in MD and/or CD within the above ranges further improves mechanical strength resulting in improved handling resistance, particularly when the packaging material is intended to contain heavy contents.

Recyclability

[0094]Preferably, the packaging material of the present invention is recyclable by repulping and recoverable according to EN13430:2000 at least 85 wt. %. The amount of material that is recoverable by repulping is determined using version 3 of the Cepi Recyclability Test Method. 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 EN13430:2000. The expression “recyclable by repulping and recoverable according to EN13430:2000 at at least 85%” 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 85 wt. % of the material can be recovered. In a more preferred embodiment, the packaging material is recyclable by repulping and recoverable according to EN13430:2000 at at least 90 wt. %, and even more preferably at least 95 wt. %.

Compliance with Standards for Food Contact

[0095]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 quick service retail food packaging material.

[0096]In one embodiment, the packaging material is food contact approved according to any of Regulation EC 1935/2004, BfR 36, FDA 21 CFA § 176-170 & 176-180.

Barrier Properties

[0097]In the present invention, the packaging material comprises a paper substrate that is coated on at least the first or the second side with a coating. The coating layer in the packaging material comprises a wax and a copolymer as described above and allows to minimize defects of the surface of the paper substrate and to ensure a low MVTR thereby achieving very good steam retention properties and to ensure a high heat retention. In some embodiments, in addition to the steam and heat retention properties, the coating layer of the packaging material may provide grease barrier properties. These properties, individually or in combination, represent distinctive advantages of the present packaging material, making it particularly suitable for quick service restaurant (QSR) applications.

[0098]In a preferred embodiment, the packaging material has a moisture vapor transmission rate (MVTR) of less than 50 g/m²/24 h, preferably of less than 40 g/m²/24 h, more preferably of less than 35 g/m²/24 h or less, even more preferably of less than 30 g/m²/24 h or less, and most preferably of less than 25 g/m²/24 h or less, determined at 85% RH and 23° C. MVTR is determined according to ISO 2528.

[0099]The MVTR is an indication of the permeability of water vapor through a substance. A low MVTR indicates an improved vapor barrier. In QSR food packaging, moisture control is critical to maintain food quality and presentation. MVTR generally decreases with increasing thickness of a barrier coating layer, and increases with increasing temperature. The packaging material of the present invention therefore is able to reduce the loss of moisture of packed food products.

[0100]In another embodiment, the packaging material has a Cobb at 30 minutes measured according to TAPPI 441 of less than 10 g/m², preferably less than 8 g/m². Yet in another embodiment, the packaging material has a Cobb at 2 minutes measured according to TAPPI 441 of less than 2 g/m², preferably less than 1 g/m², preferably less than 0.5 g/m². 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.

[0101]Contrary to expectations based on the MVTR values, the ability of the packaging material to resist penetration of steam was a surprising discovery by the inventors. Moisture Vapor Transmission Rate (MVTR) values provide information about the rate at which water vapor passes through a material under controlled conditions of temperature and humidity. MVTR has been used in the industry to evaluate moisture barrier properties of materials. As to the packaging material of the inventive concept, the ability to resist penetration of steam is unexpected compared to what would have been predicted from measurements of MVTR values alone, and would not have been pursued based solely on MVTR measurements. These unexpected results are evidenced in the inventive and comparative examples below.

Food Packaging

[0102]The food packaging material of the present invention may form a food packaging, e.g., a wrapper, bag, or pouch. As the food packaging is formed by the packaging material described above, a food packaging is provided that provides heat retention and resistance to steam penetration keeping the food items served in the QSR applications fresh and visually appealing for the customers while maintaining optimal mechanical properties without introducing aluminum foil and/or papers containing fluorochemicals. The food packaging of the invention is thus safe for food contact and has a lower environmental impact (that is, a higher recyclability).

Method for Producing a Packaging Material

[0103]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.

[0104]A method of manufacturing the food packaging material of the present invention includes a step of applying the coating layer as described above. At industrial scale, the coating is applied by direct gravure or using a single rod or by curtain coating or by spray coating or size press coating or air knife coating or flexography coating to the paper substrate described above.

[0105]To be specific, the coating layer comprising wax and a copolymer selected from styrene butadiene copolymer and/or styrene acrylic copolymer according to the present invention is applied to the paper substrate by at least one selected from direct gravure, using a single rod, curtain coating, spray coating, size press coating, air knife coating and flexography coating.

[0106]The coating 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.

[0107]Preferably, the coating is applied on the entire surface of at least the first or the second side. Further, in a preferred embodiment, the coating is applied only on the first side but not on the second side of the paper substrate.

[0108]In the method according to the invention, the components of the coating layer may be dispersed or dissolved in a liquid medium. The liquid medium used to disperse or dissolve the components of the coating layer is preferably water.

[0109]The step of applying the coating layer may be performed by applying a composition comprising the components of the coating layer as described above. To be specific, the components of the coating comprise the wax and the copolymer selected from styrene butadiene copolymer and/or styrene acrylic copolymer as described above. In addition, the coating may comprise one or more additional polymers, fillers, defoamers, thickeners and any component as described above for the coating layer of the packaging material of the present invention.

[0114]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 an optional pre-coating of the packaging material of the present invention.

[0115]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. Adjusting the Cobb value within these ranges further improves efficient pre-coating with the grease barrier precursor in optional step (ii).

[0116]The method of the present invention includes an optional step (ii) of pre-coating the paper substrate with a composition comprising a pre-coating composition.

[0117]In the method of the present invention, the composition used for the pre-coating step is preferably a composition 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.

[0118]The pre-coating may be performed by any means known in the art and is preferably carried out by size press, or metering size-press or flooded nip size press. For example, the pre-coating may be performed by a two-step method including a step of adding in wet-end a composition comprising a pre-coating composition or a grease barrier precursor, and a step of further pre-coating 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, pre-coating composition or 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 pre-coating with the composition comprising the grease barrier precursor may be performed online on the paper machine without a converting step.

[0119]The method according to the present invention may include a step (ii′) of calendering the optionally pre-coated paper substrate after step (ii) and/or a step (iii′) of calendering the optionally pre-coated paper substrate coated with the coating layer after step (iii).

[0120]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.

[0121]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.

[0122]The method according to the present invention may include a step (iv) of applying an additional coating layer on the coating layer obtained in step (iii) and optionally calendered in step (iii′). The additional coating layer may be as described above for the additional coating layer of the packaging material of the present invention. As described above, the additional coating layer may be referred to as the “second coating layer” and the coating layer on which the additional coating layer is applied may be referred to as the “first coating layer”.

[0123]The step (iv) of applying said second coating layer may be carried out in the same way as described above for the step (iii) of applying the coating layer onto the optionally pre-coated paper substrate.

[0124]Preferably, before the application of the second coating layer in step (iv), a step (iii″) of drying the first coating layer obtained in step (iii) is performed. A step (iv′) of drying the second coating layer after step (iv) may also be carried out.

[0125]The advantages of applying a second coating layer are as described above for the second coating layer of the packaging material of the present invention. Such advantages may be observed even when the second coating layer optionally added with step (iv) has the same composition as the first coating layer applied with step (iii).

[0126]The method according to the present invention may further include a step (v) of applying a printing layer onto the second side of the optionally pre-coated paper substrate. The printing layer may be as described above. The step (v) 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

[0127]The examples for this application were obtained by machine trials using a direct gravure coating method.

[0128]A paper substrate, which is a 40 #(#=1b/3000 ft²) paper substrate called “Paper Substrate 1,” was made as follows. The fibers of the paper substrate were 62% softwood fibers, particularly northern softwood fibers, and 38% hardwood fibers, particularly northern hardwood fibers. The percentages of softwood fibers and hardwood fibers are based on the total composition of the fiber blend. Fillers were added (0.3 wt. % talc and 1.2 wt. % TiO₂) and the paper was sized (0.2 wt. % AKD). Paper Substrate 1 was pre-coated with pre-coating composition comprising starch (3.2 wt. %). The pre-coated paper substrate was machine calendered and had a density of 875 g/m³, a smoothness of 130 Sheffield Units (SU) on the wire side, which is the side on which the coating was applied.

[0129]A paper substrate, which is a 41 #paper substrate called “Paper Substrate 3,” was made as follows. The fibers of the paper substrate were 85% softwood fibers, particularly northern softwood fibers, and 15% hardwood fibers, particularly northern hardwood fibers. The percentages of softwood fibers and hardwood fibers are based on the total composition of the fiber blend. Fillers were added (0.8 wt. % TiO₂), and the paper was sized (1.2 wt. % AKD). Paper Substrate 3 was pre-coated with pre-coating composition comprising starch (3 wt. %). The pre-coated paper substrate was machine calendered and had a density of 875 g/m³, a smoothness of 230 Sheffield Units (SU) on the wire side, which is the side on which the coating was applied.

[0130]The two inventive packaging materials, both using Paper Substrate 1, were then coated with coating. The coating contained styrene acrylic emulsion and wax (Joncryl HPB 1631-A). 3.5 #of the coating was applied to example 1-3.5, 2.5 #of the coating was applied to example 1-2.5, and 1.6 #of the coating was applied to comparative example 1-1.6. No coating was applied to example 1-0, which is Paper Substrate 1 alone. Additionally, as a comparative example, foil-lined paper 2-F was used

[0131]One factor used to assess the quality of the packaging material is the resistance to the penetration of steam. To rate this performance, the following experiment is performed. The packaging material is folded into a pouch, and a hot chicken sandwich is placed inside. The pouch is folded closed about one inch from the open edge of the pouch. The experiment begins when the internal temperature of the pouch reaches 125-150° F. The pouch is placed on a top of an absorbent backing paper. After 30 minutes, the pouch is removed, and the absorbent paper is evaluated for evidence of water breakthrough. Visual inspection was used to determine the extent of water breakthrough. The second factor used to rate the resistance to the penetration of steam is sandwich quality after 30 minutes, which can be “Moist” or “Dry”. Sandwich quality results are displayed in Table 1. The packaging material receives a “Pass” in resistance to the penetration of steam if sandwich quality is assessed to be “Moist” and there are no observable water breakthrough stains on the absorbent backing paper wherein a straight line 0.5 inch in length can be drawn across the stain from any point on the perimeter to any other point without reaching dry paper.

[0132]Another factor used to assess the quality of the packaging material is the heat retention. The heat retention test is performed concurrently with the steam retention performance test. A starting temperature (° F.) is recorded when the internal temperature of the pouch reaches 125-150° F. A final temperature is recorded 30 minutes after the starting temperature is recorded. The heat retention is calculated as

$\frac{\mathrm{starting}\mathrm{temperature},\mathrm{°F}-\mathrm{final}\mathrm{temperature},\mathrm{°F}}{\mathrm{starting}\mathrm{temperature},\mathrm{°F}}*100\%$

[0133]All examples displayed in Table 1 exhibited similar heat retention properties within 5% of the foil-lined control, 2-F, including example 1-0, the uncoated Paper Substrate 1. From these heat retention results, it can be concluded that Paper Substrate 1 without coating provides heat retention properties suitable for QSR applications. Additionally, from example 1-0 to example 1-3.5, the coat weight of the coating increases from 0 to 3.5 #. In this range the heat retention decreases from 22.1% to 19.9%. This inverse trend indicates that applying the coating only increases the heat retention properties of the paper. Thus, in terms of heat retention, there is no maximum or minimum suitable amount of coating when applied to Paper Substrate 1.

[0134]In addition to heat retention, experimental examples 1-2.5 and 1-3.5 also passed the steam retention test. There was no observable difference between the foil-lined paper 2-F comparative example and example 1-3.5, neither of which demonstrated any observable water breakthrough after holding a sandwich for 30 minutes. Example 1-2.5 exhibited minimal water breakthrough but still passed the test. Examples 1-1.6 and 1-0 did not pass the steam breakthrough test. Experimental examples that passed the steam retention test had a coat weight of at least 2.0 #.

[0135]Additionally, the 2 minute water Cobb value of examples 1-0, 1-1.6, 1-2.5, 1-3.5 and 2-F is provided. Table 2 shows that papers with higher 2 minute Cobb value perform worse on the steam retention test. Experimental examples that passed the steam retention test had a 2 minute Cobb value below 1.0 g/m².

[0136]Additional tests were performed to analyze the foldability of the packaging material example 1-3.5. The foldability of this packaging material was compared to the foldability of another paper with a higher Gurley porosity and an equivalent coating, example 3-3.5. Foldability is determined by bounceback, measured in mm, where a higher bounceback represents a lower foldability. Bounceback in the machine direction and cross direction is shown in Table 2.

[0137]Table 2 shows the foldability as represented by bounceback of examples 1-3.5 and 3-3.5, as well as physical characteristics of the paper substrate for each example. 1-3.5 has a significantly lower Gurley porosity than 3-3.5, which indicates that paper 1-3.5 has lower tightness. The lower Gurley porosity is also an effect of a decreased amount of refining used in the process of producing example 1-3.5. As a result, it would take less energy to produce example 1-3.5 than example 3-3.5. Despite the more efficient processing conditions employed in the production of 1-3.5, the bounceback is 5 and 3 mm in the cross-direction (CD) and machine-direction (MD), respectively, which is not worse than the bounceback of example 3-3.5 and achieves a high level of foldability. This effect may be attributed to the increased smoothness of 1-3.5 and higher percentage of hardwood fibers in the fiber blend.