ES3015200T3 - Barrier paper or board - Google Patents

Abstract

A process for improving the barrier properties of a barrier layer in a pulp-based substrate layer having a barrier layer, comprising the steps of providing a pulp-based substrate layer having a layer of an aqueous barrier composition applied thereto, and then drying the pulp-based substrate layer having a layer of aqueous barrier composition applied thereto to form a pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is below 2.5% by weight, preferably below 2% by weight, based on the weight of the pulp-based substrate layer having a barrier layer. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Barrier paper or cardboard

Technical field

The present invention relates to pulp-based substrate layers having barrier properties and methods for obtaining such pulp-based substrate layers, in particular pulp-based substrate layers such as paper or cardboard having barrier properties.

Prior art

Paper has been used for packaging applications for many decades. In the past, due to its lack of inherent barrier properties, paper has been used primarily as a print medium in laminated and/or composite packaging solutions, where it is combined with other materials exhibiting barrier functionality, such as plastic films and/or aluminum layers. Plastic films can be made of a single material or can be multilayer films incorporating multiple layers of different polymers, and such plastic films can be applied by extrusion coating or a lamination process. Aluminum layers can be applied as thin aluminum foils or by well-known deposition techniques such as atomic layer deposition. Combinations of plastic films and aluminum layers are also well-known in the packaging field.

In recent years, it has become possible to produce papers with barrier properties that can compete with polymer films, while still being recyclable.

Such barrier properties can be achieved by coating the paper with relatively low amounts of one or more dispersions, specifically one or more solutions, of a barrier compound, thereby reducing or replacing plastic film-based materials or metallic layers in the final product. Furthermore, due to the light and thin nature of the layers formed when these aqueous dispersions or solutions dry, barrier papers can be repulped and recycled as paper.

However, cost pressures in the packaging sector are demanding increasingly high-performance barrier papers, where improved barrier properties must be achieved at the same or even lower cost.

EP 1395705 B1 discloses a process comprising forming a free-flowing multi-layer composite curtain, the curtain having a solids content of at least 45% by weight, and contacting the curtain with a continuous web substrate of base paper or base board. No excessive drying is described.

EP 1666 637 A1 discloses a gas barrier composite plastic film or sheet obtained by coating at least one side of a plastic film or sheet made of at least one plastic selected from the group consisting of polyolefins, polyesters, polyamides and polystyrenes with a coating material composition having a gas barrier property at a coating weight such as to provide a dry coating layer thickness of 0.1 to 100 µm. No overdrying is described.

WO2012/175621 A1 discloses a method for producing coated vacuum metallized substrates with good vapor and oxygen barrier properties in which a liquid coating material is dried, but does not disclose a drying step for the barrier composition in which the barrier composition is dried to a humidity of less than 2.5%.

WO2010/042162 A1 discloses a method for producing multi-layer coatings for paper-based substrates with good barrier properties in which a liquid coating composition is dried, but does not disclose a drying step for the barrier composition in which the barrier composition is dried to a moisture content of less than 2.5%.

WO2009/112255 A1 discloses a method for manufacturing packaging films and packages made therefrom by applying a liquid film coating of a liquid gas barrier composition and subsequently drying it, but does not disclose a step of drying the barrier composition in which the barrier composition is dried to a humidity of less than 2.5%.

Summary of the invention

The present invention provides a process that allows for improved barrier properties, such as WVTR (Water Vapor Transmission Rate) or OTR (Oxygen Transmission Rate), to be achieved on pulp-based substrates without having to increase the amount of barrier compound in the barrier composition applied to the substrate and/or without having to add additional barrier layers to the substrate. This allows for improved barrier properties to be achieved without increasing the material cost.

It is an object of the present invention to provide a process for improving the barrier properties of a barrier layer comprised in a pulp-based substrate layer having a barrier layer, comprising the steps of

a) providing a paste-based substrate layer having applied a layer of an aqueous barrier composition, wherein said barrier composition comprises a barrier compound,

b) drying the pulp-based substrate layer having a layer of an aqueous barrier composition applied thereto to form a pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is less than 2.5% by weight, preferably less than 2% by weight, preferably less than 1.5% by weight, based on the weight of the pulp-based substrate layer having a barrier layer.

It is a further object of the present invention to provide a packaging material comprising at least one pulp-based substrate layer having, in this order,

optionally, a primer layer adjacent to the paste-based substrate layer,

a first barrier layer adjacent to the paste-based substrate layer, wherein the first barrier layer is obtainable according to the process of the first subject of the invention,

optionally, a sealing layer such as a cold or hot seal layer adjacent to the first barrier layer, wherein the combined amount of the first barrier layer ranges from 4 g/m2 to 11 g/m2, preferably from 4 to 6 g/irP, and wherein the packaging material has a WVTR under tropical conditions (38 °C, 90% RH) of 11 to 5 g/(m2.d), and wherein the pulp-based substrate layer does not contain a metallic layer.

In the context of the present invention, all MVTR values are determined and measured under tropical conditions (38°C, 90% RH) according to ASTM F1249 and all OTR values are determined and measured under normal conditions (23°C, 50% RH) according to ASTM D3985, unless otherwise indicated.

Other embodiments of the invention are set forth in the dependent claims and in the specification.

Brief description of the drawings

Preferred embodiments of the invention are described below with reference to the drawings, which are intended to illustrate the present preferred embodiments of the invention and not to limit them. In the drawings,

Figure 1 shows a cross-section of a packaging material according to an embodiment of the present invention, where a first barrier layer (2) and a second barrier layer (3) are arranged on a pulp-based substrate (1) and are adjacent to each other.

Figure 2 shows a cross-section of a packaging material according to an embodiment of the present invention, where a first barrier layer (2) and a second barrier (3) are arranged on a pulp-based substrate (1), where an inorganic barrier layer (4) is between the first barrier layer (2) and a second barrier (3) and adjacent to said barrier layers (2,3).

Figure 3 shows a cross-section of a packaging material according to an embodiment of the present invention, where a first barrier layer (2) and a second barrier (3) are arranged on a pulp-based substrate (1), where a primer layer (5) is between the pulp-based substrate (1) and a first barrier (2) and adjacent to each of them.

Figure 4 shows a cross-section of a packaging material according to an embodiment of the present invention, wherein a first barrier layer (2) and a second barrier layer (3) are arranged on a pulp-based substrate (1), wherein an inorganic barrier layer (4) is between the first barrier layer (2) and a second barrier layer (3) and adjacent to said barrier layers (2,3) and wherein a primer layer (5) is between the pulp-based substrate (1) and a first barrier layer (2) and adjacent to each of them.

Description of preferred embodiments

It is an object of the present invention to provide a process for improving the barrier properties of a barrier layer comprised in a pulp-based substrate layer having a barrier layer, or of a barrier layer in a packaging material comprising a pulp-based substrate layer having a barrier layer, comprising the steps of

a) providing a paste-based substrate layer having applied a layer of an aqueous barrier composition, wherein said barrier composition comprises a barrier compound,

b) drying the pulp-based substrate layer having a layer of an aqueous barrier composition applied thereto to form a pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is less than 2.5% by weight, preferably less than 2% by weight, based on the weight of the pulp-based substrate layer having a barrier layer.

In the context of the present invention, the term "improving a barrier property" means that a barrier property of a layer with respect to at least one substance, such as, for example, water vapor or oxygen, is modified in such a way as to allow less diffusion of said substance through the layer. Specifically, in the case of water vapor and oxygen, such an improvement is expressed by lower numerical values in the water vapor transmission rate and the oxygen transmission rate, respectively.

It has been discovered that when a paste-based substrate layer having applied thereto a layer of an aqueous barrier composition is dried to a moisture content lower than that normally required for mere drying and formation of a barrier film, the barrier properties of the resulting paste-based substrate layer having a barrier layer are significantly improved.

The pulp-based substrate layer used in the process according to the present invention may be based on any type of pulp originating from a plant, such as, for example, softwood or hardwood. Examples of pulp types that may be comprised in the pulp-based substrate layer include chemical pulps, such as kraft or sulfite pulps, or chemithermomechanical pulps.

In a preferred embodiment, the pulp-based substrate layer comprises both hardwood and softwood chemical pulp.

The process of the invention includes a step of providing a paste-based substrate layer having a layer of an aqueous barrier composition applied thereto. The layer of an aqueous barrier composition may be applied by known techniques that can be used to apply a liquid coating, such as, for example, knife coating, rod coating, curtain coating, reverse gravure coating, gravure coating, spray coating, dip coating, or air knife coating.

The aqueous barrier composition may be applied to the pulp-based substrate layer in-line during production of the pulp-based substrate layer on a paper machine, or off-line after the pulp-based substrate layer, which may or may not already have a primer layer, has been produced, in a separate coating apparatus. In the case where the pulp-based substrate layer includes more than one barrier layer, the barrier layers may be formed by subsequently passing the pulp-based substrate layer through multiple coating apparatuses or by repeatedly passing the pulp-based substrate layer through a single coating apparatus.

The coating apparatus is equipped with a coating unit that applies the water-based barrier composition to the paste-based substrate layer and a drying unit that dries the paste-based substrate layer and the applied water-based barrier composition. The coating unit may be a knife coating unit, rod coating unit, curtain coating unit, reverse gravure coating unit, gravure coating unit, spray coating unit, dip coating unit, or air knife coating unit.

The aqueous barrier composition may be applied to the paste-based substrate layer in the form of a liquid dispersion, specifically as a liquid solution, which may preferably have a solids content of up to 55% by weight, wherein the solids content may more preferably be between 5% by weight and 55% by weight, based on the weight of the aqueous barrier composition.

The paste-based substrate layer can have any shape or form.

In one embodiment, the pulp-based substrate layer is in the form of a flat web, for example, of paper or board. This is largely, but not necessarily, the case where the waterborne barrier composition is applied to the pulp-based substrate layer on a paper machine, which paper machine forms the pulp-based substrate layer as paper or board and applies the waterborne barrier composition in-line. Alternatively, the waterborne barrier composition is applied to the pulp-based substrate layer in the form of a flat web in a coating apparatus comprising at least one coating unit, configured to apply the waterborne barrier composition, and a drying unit, configured to dry the pulp-based substrate layer having the waterborne barrier composition applied thereto to the required moisture content. In order to coat paste-based substrate layers in the form of a flat web, the coating unit is preferably a knife coating unit, rod coating unit, curtain coating unit, reverse gravure coating unit, gravure coating unit, spray coating unit or air knife coating unit.

In another embodiment, the pulp-based substrate layer, such as paper or cardboard, is not shaped into a flat web, but is instead given a desired three-dimensional shape, such as, for example, a cup, a tray, or a bottle. In this case, the water-based barrier composition is applied to the pulp-based substrate layer in a coating apparatus comprising at least one coating unit configured to apply the water-based barrier composition and a drying unit configured to dry the pulp-based substrate layer having the water-based barrier composition applied thereto to the required moisture content. In order to coat three-dimensional pulp-based substrate layers, the coating unit is preferably a spray coating unit, a dip coating unit, or a curtain coating unit.

In a preferred embodiment, the aqueous barrier composition may be applied to the pulp-based substrate layer on one side or both sides of the pulp-based substrate layer.

The pulp-based substrate layer may be freely selected in terms of basis weight, provided that the pulp-based substrate layer can be provided without pinholes to avoid holes in the barrier layer. In this case, the pulp-based substrate layer is a paper, the basis weight may preferably be greater than 15 g/m2 and less than 225 g/m2, more preferably 40 to 120 g/m2, while, in case the pulp-based substrate layer is a board, the basis weight may preferably be greater than 225 g/m2.

It is understood that the pulp-based substrate layer may be pre-coated or pre-treated before being provided in the process according to the invention in ways known in particular in the art of paper and/or board production. For example, the pulp-based substrate layer may be calendered, pressed, smoothed or otherwise mechanically pre-treated before step a) and/or the pulp-based substrate layer may be provided with an internal or external size or a print coating or otherwise pre-treated before step a). As such, the term "pulp-based substrate layer" includes what are known as "base papers" in the field of packaging paper.

In a preferred embodiment, the aqueous barrier composition may be applied to the pulp-based substrate layer such as to result in a barrier layer having a basis weight of 0.5 g/mf to 15 g/mf, preferably 2 to 12 g/m2, more preferably 4 to 11 g/m2 or 4 to 10 g/m2. Alternatively, the barrier layer may also have a basis weight of 9 g/mf to 11 g/m2.

In the process according to the present invention, the drying of the pulp-based substrate layer having an aqueous barrier composition layer applied thereto to form a pulp-based substrate layer having a barrier layer is carried out such that the moisture content of the pulp-based substrate layer having a barrier layer is less than 2.5% by weight or 0.5 to 2.5% by weight, preferably less than 2% by weight or 0.5 to 2% by weight, more preferably less than 1.5% by weight or 0.5 to 1.5% by weight, based on the weight of the pulp-based substrate layer having a barrier layer.

It is understood that, before drying, the moisture content of the pulp-based substrate layer to which the water-based barrier composition is applied is greater than 2.5% by weight or greater than 5% by weight depending on the weight of the pulp-based substrate layer and the water-based barrier composition applied thereto. It has been determined that the pulp-based substrate layer to which the water-based barrier composition is applied typically has, due to the amount of water added by the water-based barrier composition, a moisture content of approximately 9% by weight when the pulp-based substrate layer is a paper, through appropriate measurements or calculations. In the case of a paperboard, due to the higher grammage, the moisture content will be lower, but in any case greater than 2.5% by weight.

The moisture content may be measured in-line at the paper machine by a calibrated moisture content measuring apparatus configured to correlate the measured moisture content with the moisture content measured in accordance with Tappi Standard T412; or it may be measured off-line by taking samples and measuring the moisture content in accordance with Tappi Standard T412. It is understood that one of ordinary skill in the art will be able to correlate the measured in-line moisture content with the moisture content in accordance with Tappi Standard 412 to calibrate the in-line moisture content measuring apparatus.

In the process according to the present invention, the moisture content of the pulp-based substrate layer and the barrier layer is less than 2.5% by weight, preferably less than 2% by weight, more preferably less than 1.5% by weight, based on the weight of the pulp-based substrate layer. The moisture content may be determined in accordance with Tappi standard T412. It is understood that, due to the differential water retention properties between the pulp-based substrate layer and the water-based barrier composition, the measured moisture content is the sum of the individual moisture content fractions contained in the pulp-based substrate layer and the barrier layer, respectively, at the time of measurement and it is not easy to accurately attribute the fraction of the overall moisture content originating from the pulp-based substrate layer or the water-based barrier composition. However, it has been discovered that when the overall measured moisture content of the pulp-based substrate layer and the barrier layer is less than the thresholds given above, the barrier properties of the pulp-based substrate layer having a barrier layer are improved compared to the barrier properties of a pulp-based substrate layer having a barrier layer that has been dried to a more conventional moisture content greater than the thresholds given above.

In the pulp-based substrate layer having a barrier layer, obtained by the process according to the invention, a WVTR under tropical conditions (38 °C, 90% RH) of less than 10 g/(m2.day), and preferably less than 5 g/(m2.day) and more preferably between 1 and 5 g/(m2.day) when measured in accordance with ASTM F1249 can be achieved with a barrier layer having a thickness of about 5 microns or less, or between 1 and 5 microns, which is an unexpectedly low WVTR for a thickness of about 5 microns or less. An OTR (23°C, 50% RH) of less than 0.2 cc/(m2.day), more specifically between 0.05 and 0.1 cc/(m2.day) can be achieved with a barrier layer that is approximately 1 micron thick or less when measured according to ASTM D3985, which is an unexpectedly low OTR for a thickness of approximately 5 microns or less.

The aforementioned barrier properties are achieved without including a metallic or inorganic layer in the pulp-based substrate layer having a barrier layer. However, it may be desirable to further improve the overall barrier properties of the pulp-based substrate layer having a barrier layer, obtained by the process according to the invention, by adding a metallic layer, a non-metallic inorganic layer, or both.

The aqueous barrier composition comprises a barrier compound, preferably in the form of an aqueous dispersion, specifically in the form of an aqueous solution, of a barrier compound. The barrier compound may be any compound, in particular an organic compound, which is capable of improving barrier properties such as, for example, the OTR or WVTR of the pulp-based substrate layer when formed in a layer on the pulp-based substrate layer. Suitable barrier compounds may be chosen from polymer barrier compounds which may be artificial or natural, such as, for example, polyesters, polyolefins or polyamides. In particular, the artificial polymer barrier compounds may be chosen from PVDC, PE, PP, PET, PA, PVOH, EVOH, PVC, PLA, PHA, styrene acrylate and styrene butadiene, nanocellulose, cellulose nanocrystals or cellulose nanofibrils. In another embodiment, the aqueous barrier composition further comprises, in addition to the aforementioned polymer compounds, one or more inorganic barrier compounds. The inorganic barrier compounds may be selected from mineral barrier compounds, such as nanopigments, which are preferably platelet-shaped, such as, for example, nanoclays. In the case where inorganic barrier compounds are included in the aqueous barrier composition, the aqueous barrier composition is preferably an aqueous solution of a barrier compound, such as a water-soluble polymer compound, in which the inorganic barrier compound is dispersed.

The aqueous barrier composition may, in preferred embodiments, further include a wax. In a preferred embodiment, when the aqueous barrier composition comprises a wax, the aqueous barrier composition may preferably be in the form of an aqueous latex, such as, for example, a styrene-butadiene latex or a styrene-acrylic latex. Waxes are not soluble in an aqueous medium, such as aqueous solutions or water. It is understood that the wax suitable for the aqueous barrier composition may be an artificial or natural wax, for example, an artificial wax, such as polyethylene wax or alkane wax, or, for example, a natural wax, such as a wax ester.

The aqueous barrier composition may be in the form of an aqueous dispersion of a barrier compound. "A barrier compound" is understood to mean one or more barrier compounds, i.e., a single barrier compound or a combination of two or more different barrier compounds. In a preferred embodiment, the aqueous dispersion of a barrier compound may comprise one or more barrier compounds, such as, for example, two different artificial and/or natural polymer compounds. An exemplary aqueous dispersion of a barrier compound is an aqueous dispersion of PVDC. Other examples are aqueous dispersions of styrene butadiene, styrene acrylic, polyethylene copolymer, or polyvinyl acetate. The term "aqueous dispersion of a barrier compound" is understood to also encompass, without limitation, an aqueous latex of a barrier compound. Some examples of an aqueous latex of a barrier compound are styrene butadiene latex or styrene acrylic latex.

In one embodiment of the process according to the invention, after drying step b), the process further comprises step c) of moistening the pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is 3.5% by weight or higher, or between 3.5% and 6% by weight, depending on the weight of the pulp-based substrate layer and the barrier layer. This might be necessary in certain circumstances if the pulp-based substrate layer having a barrier layer is subsequently converted or printed immediately downstream of the paper machine or at a subsequent stage, since a moisture content of less than 3% by weight causes an increase in brittleness and a loss of flexibility of the pulp-based substrate layer. An increase in moisture content above 3% by weight improves the flexibility of the pulp-based substrate layer. Likewise, wetting reduces curling and eliminates static charges from the pulp-based substrate layer. Wetting can be achieved by applying steam, water spray, water, or an aqueous coating, preferably to the reverse side of the pulp-based substrate layer, i.e., the side of the pulp-based substrate layer opposite the side having the barrier layer. It has been observed that although the wetting step increases the moisture content after drying in step b), this does not adversely affect the barrier properties of the pulp-based substrate layer having a barrier layer. Occasionally, after drying step b), the moisture content of the pulp-based substrate layer having a barrier layer can be further increased to 4.5% by weight or higher, or between 4.5% and 6% by weight, depending on the weight of the pulp-based substrate layer and the barrier layer.

Optionally, the wetting step may be followed by a further drying step to adjust the moisture content to a predetermined content greater than 3% by weight, preferably from 3% by weight to 5% by weight. Particularly, but not exclusively, when rewetting is achieved by applying another coating layer or water (pure or not) to the reverse side of the pulp-based substrate layer, drying is preferred to prevent blocking, wrinkling, or curling.

In a preferred embodiment of the process according to the present invention, drying the pulp-based substrate layer having an applied layer of aqueous barrier composition to form a pulp-based substrate layer having a barrier layer is achieved by exposing the pulp-based substrate layer having a layer of aqueous barrier composition to heat, radiation, or negative pressure, or a combination of two or more thereof. The heat may be applied, for example, by hot air or steam, the radiation may be in the form of infrared radiation or microwaves. It is understood that the same options may be employed in the further drying step after the wetting step.

In a preferred embodiment of the process according to the present invention, drying the pulp-based substrate layer having an applied layer of aqueous barrier composition to form a pulp-based substrate layer having a barrier layer is achieved by heating the pulp-based substrate layer having an aqueous barrier composition layer to a temperature of at least 100°C, preferably at least 115°C, more preferably at least 130°C. This may be done at ambient pressure, i.e. without pressure control, or at a negative pressure, i.e. pressure control such that the pressure is lower than ambient pressure. In the case where negative pressure is used, the drying time at the same drying temperature may be further reduced compared to the case where the drying is carried out at ambient pressure and/or the drying temperature at the same drying time may be further reduced compared to the case where the drying is carried out at ambient pressure. Since the paste-based substrate layer can be heated to over 100°C, this means that the substrate does not experience thermal shrinkage like most polymer films such as, for example, PET, PE or PP, commonly used in barrier film packaging.

In a preferred embodiment of the process according to the present invention, the paste-based substrate layer having a layer of an aqueous barrier composition further comprises an intermediate layer positioned between the layer of a barrier composition and the paste-based substrate layer. In a preferred embodiment, the intermediate layer positioned between the layer of a barrier composition and the paste-based substrate layer is a primer layer, which primer layer is preferably chosen such that it smooths and closes the surface of the side of the paste-based substrate layer to which the aqueous barrier composition is to be applied. In the case where an aqueous barrier composition is also to be applied on the opposite side, a primer layer may or may not be present on that side and, if so, positioned between the respective layer of a barrier composition and the paste-based substrate layer.

In a preferred embodiment of the process according to the present invention, in step a), the pulp-based substrate layer having a layer of an aqueous barrier composition applied thereto has an intermediate layer, such as a primer layer, positioned between the pulp-based substrate layer and the layer of aqueous barrier composition. The intermediate layer, such as a primer layer, can smooth the underlying pulp-based substrate layer, close any pores or pinholes, and provide flexibility that allows for easier processing. As such, the intermediate or primer layer may have any composition, provided that it can provide at least one of the above functions, and may, for example, comprise starch in modified or unmodified form, artificial polymer dispersions, or even barrier compounds.

In a preferred embodiment of the process according to the present invention, the paste-based substrate layer having a barrier layer further comprises an inorganic barrier layer or a metallic barrier layer, wherein the inorganic barrier layer or a metallic barrier layer may be adjacent to the barrier layer. The inorganic barrier layer or a metallic barrier layer is preferably deposited by techniques known as thin-film deposition techniques. In a preferred embodiment of the process according to the present invention, the inorganic barrier layer or a metallic barrier layer is deposited by chemical deposition, such as atomic layer deposition, or physical deposition. It is understood that the inorganic barrier layer or the metallic barrier layer can only be applied once the paste-based substrate layer having a barrier layer has been formed or before applying the aqueous barrier composition to the paste-based substrate layer. It is not possible to apply the inorganic barrier layer by thin-film deposition to the undried aqueous barrier composition.

In a preferred embodiment of the process according to the present invention, after step c), the process further comprises step d) of applying an inorganic barrier layer or a metallic barrier layer to the barrier layer by thin film deposition.

If a metallic barrier layer is deposited, the metal is preferably aluminum. In a preferred embodiment of the process according to the present invention, the metallic barrier layer is aluminum.

In the case where an inorganic barrier layer is deposited, the inorganic barrier is preferably chosen from metal oxides such as aluminium oxide or silica, for example, AlxOy or SiOx.

When depositing an inorganic barrier layer or a metallic barrier layer, the surface on which it is deposited may or may not have been pretreated prior to deposition of the inorganic barrier layer or metallic barrier layer. Examples of surface treatments include plasma treatment or corona treatment.

In a preferred embodiment of the process according to the present invention, the inorganic barrier layer or the metallic barrier layer is adjacent to, and deposited directly onto, the barrier layer.

In a preferred embodiment of the process according to the present invention, after step d), the process further comprises step e) of applying a further layer of aqueous barrier composition to the inorganic barrier layer or a metallic barrier layer and drying the resulting layer stack having the applied further layer of aqueous barrier composition to form a further barrier layer such that the moisture content of the resulting layer stack having a further barrier layer is less than 2.5% by weight, preferably less than 2% by weight, based on the weight of the resulting layer stack having a barrier layer. The aqueous barrier composition and the further aqueous barrier composition may have the same composition or may have different compositions.

It is understood that the paste-based substrate layer having a barrier layer may further be coated with a functional layer such as, for example, a sealing layer, which may or may not furthermore be a printable layer.

It is a further object of the present invention to provide a packaging material comprising at least one pulp-based substrate layer having a barrier layer obtained by the process as described above, for example a wrapping paper for perishable products such as snacks, candies, nuts, cereals, chocolate, frozen sweets, toffee, chips, dried fruit, biscuits, tea leaves, coffee beans or ground coffee, pepper, spices, cured meats, dairy products, fresh foods such as vegetables, fruit and meat, dry pet food, tobacco, dehydrated foods, non-food products, such as vitamins or minerals, household or personal care products, for example, wherein the pulp-based substrate layer does not contain a metal layer.

It is a further object of the present invention to provide a packaging material comprising at least one pulp-based substrate layer having, in this order,

optionally, a primer layer adjacent to the paste-based substrate layer,

a first barrier layer adjacent to the pulp-based substrate layer or the primer layer, wherein the first barrier layer is obtainable according to the process of claim 1, optionally a sealing layer such as a cold or hot sealing layer adjacent to the first barrier layer, wherein the amount of the first barrier layer ranges from 4 g/m2 to 11 g/m2, preferably from 4 to 6 g/irP, and wherein the packaging material has a WVTR under tropical conditions (38 ° C, 90% RH) of 1 to 5 g/(m2.d), and wherein the pulp-based substrate layer does not contain a metallic layer.

In a preferred embodiment of the packaging material according to the present invention, the packaging material comprises at least one pulp-based substrate layer having, in this order, a primer layer adjacent to the pulp-based substrate layer,

a first barrier layer adjacent to the primer layer,

an inorganic barrier layer adjacent to the first barrier layer, where the inorganic barrier layer is deposited by thin film deposition,

a second barrier layer adjacent to the inorganic barrier layer,

optionally, a sealing layer such as a cold or hot seal layer adjacent to the second barrier layer, wherein the combined amount of the first barrier layer and the second barrier layer ranges from 4 g/irP to 11 g/irP, preferably from 4 to 6 g/irP, and wherein the packaging material has a WVTR under tropical conditions (38 °C, 90% RH) of 1 to 5 g/(m2.d), and wherein the pulp-based substrate layer does not contain a metallic layer. In a preferred embodiment, the first and second barrier layers have the same composition and preferably comprise PVDC or a nanopigment. PVDC is expected to be phased out and replaced in the coming years by other barrier compounds that have the same or better barrier properties and are more environmentally friendly.

In preferred embodiments of the packaging material, the packaging material comprises at least one pulp-based substrate layer having, in this order,

a barrier layer adjacent to the pulp-based substrate layer, wherein the first barrier layer is obtainable according to the process of claim 1,

optionally, a sealing layer such as a cold or hot seal layer adjacent to the second barrier layer, wherein the combined amount of the first barrier layer and the second barrier layer ranges from 4 g/m2 to 11 g/m2, preferably from 4 to 6 g/m2, and wherein the packaging material has a WVTR under tropical conditions (38 °C, 90% RH) of 1 to 5 g/(m2.d) and wherein the pulp-based substrate layer does not contain a metallic layer.

In preferred embodiments of the packaging material, the packaging material comprises at least one pulp-based substrate layer having, in this order,

a primer layer adjacent to the paste-based substrate layer,

a barrier layer adjacent to the primer layer, wherein the first barrier layer is obtainable according to the process of claim 1,

optionally, a sealing layer such as a cold or hot seal layer adjacent to the second barrier layer, wherein the combined amount of the first barrier layer and the second barrier layer ranges from 4 g/irP to 11 g/irP, preferably from 4 to 6 g/irP, and wherein the packaging material has a WVTR under tropical conditions (38 °C, 90% RH) of 1 to 5 g/(m2.d) and wherein the pulp-based substrate layer does not contain a metallic layer.

It is understood that, in the above packaging materials, the respective barrier layers are preferably obtained by applying an aqueous barrier composition to the pulp-based substrate layer, the primer layer, or the inorganic barrier layer, as the case may be, and then drying the resulting layer stack having the applied aqueous barrier composition, so that a layer stack having a barrier layer is formed and so that the moisture content of the resulting layer stack having a barrier layer is less than 2.5% by weight, preferably less than 2% by weight, based on the weight of the layer stack having a barrier layer. For the avoidance of doubt, the layer stack includes the pulp-based substrate layer.

EXPERIMENTAL DATA

Comparative example 1

A 70 g/irP base paper was coated with an aqueous PVDC dispersion to give a coating weight of 10/-1 g/irP and dried to a moisture content of 3%. In general, one of ordinary skill in the art will know how to achieve a given coating weight when provided with an aqueous barrier composition having a given barrier compound solids content by applying an appropriate amount of barrier composition to the base paper.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 3 to 5 g/(m2.d), when measured according to ASTM F1249, and OTR under normal conditions (23°C, 50% RH) greater than 5 cc/(m2.d.).

Example 1

A 70 g/irP base paper was coated with an aqueous PVDC dispersion to give a coating weight of 10/-1 g/irP and dried to a moisture content of 1.7 %.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 1.5-2.5 g/(m2.d), when measured according to ASTM F1249, and an OTR under normal conditions (23°C, 50% RH) of between 0.5-2.5 cc/(m2.d.).

Comparative example 2

An 80 g/m2 base paper was coated with an aqueous dispersion of SBR (styrene-butadiene rubber) and a wax latex mixture in such a way as to obtain a coating weight of 6 /-1 g/m2 and dried to a moisture content of 2.8 %.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 28 to 40 g/(m2.d), when measured according to ASTM F1249.

Example 2

An 80 g/m2 base paper was coated with an aqueous dispersion of SBR and a wax latex mixture in such a way as to obtain a coating weight of 6 /- 1 g/irP and dried to a moisture content of 1.8 %.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 3 g/(m2.d), when measured according to ASTM F1249.

Comparative example 3

An 80 g/m2 base paper was coated with an aqueous solution of polyvinyl alcohol to give a coating weight of 3/-1 g/m² and dried to a moisture content of 3.2%.

The resulting barrier paper exhibited a WVTR under ambient conditions (23°C, 50% RH) of approximately 2.5 g/(m2.d), when measured according to ASTM F1249.

Example 3

An 80 g/irP base paper was coated with an aqueous solution of polyvinyl alcohol to give a coating weight of 3/-1 g/irP and dried to a moisture content of 3.2 %.

The resulting barrier paper exhibited a WVTR under ambient conditions (23°C, 50% RH) of approximately 1 g/(m2.d), when measured according to ASTM F1249.

Comparative example 4

An 80 g/m³ base paper was first coated with an aqueous solution predominantly of polyvinyl alcohol to give a coating weight of 2/-1 g/m³ and dried to a moisture content of 3.4%. This was followed by a second coating with an aqueous dispersion of SBR and a wax latex mixture to give a coating weight of 7/-1 g/m³ and dried to a moisture content of 3.5%.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 18 to 23 g/(m2.d), when measured according to ASTM F1249.

The resulting barrier paper showed an OTR (23 °C, 50% RH) greater than 3 cc/(m2.d).

Example 4

An 80 g/m³ base paper was first coated with an aqueous solution predominantly of polyvinyl alcohol to give a coating weight of 2.0 g/m³ and dried to a moisture content of 2.0%. This was followed by a second coating with an aqueous dispersion of SBR and a wax latex mixture to give a coating weight of 7.0 g/m³ and dried to a moisture content of 1.4%.

The resulting barrier paper exhibited a WVTR under tropical conditions (38°C, 90% RH) of approximately 2.5 g/(m2.d), when measured according to ASTM F1249.

The resulting barrier paper exhibited an OTR (23 °C, 50% RH) of approximately 0.1 cc/(m2.d).

Example 5

A 100 g/irP base paper with a moisture content of about 4% by weight was coated with an aqueous barrier composition comprising about 50% by weight of a barrier compound and about 50% by weight of water. The aqueous barrier composition was applied to the base paper with a wet coating weight of about 20 g/irP to give a barrier layer with a dry coating weight of about 10 g/irP, and the base paper to which the aqueous barrier composition had been applied was then dried to a moisture content of about 2% by weight to form a base paper with a barrier layer. After drying, the base paper having the barrier layer was rewetted to a moisture content of about 4.5% by weight. The quantities used are detailed in Table 1.

Table 1

List of reference symbols

1 paste-based substrate

2 first layer of barrier

3 second layer of barrier

4 layer inorganic barrier

5 coat of primer

Claims (13)

1. A process for improving the barrier properties of a barrier layer comprised in a pulp-based substrate layer having a barrier layer, comprising the steps of a) providing a paste-based substrate layer having applied a layer of an aqueous barrier composition, wherein said barrier composition comprises a barrier compound, b) drying the pulp-based substrate layer having a layer of an aqueous barrier composition applied thereto to form a pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is less than 2.5% by weight, preferably less than 2% by weight, based on the weight of the pulp-based substrate layer having a barrier layer. 2. The process according to claim 1, wherein the pulp-based substrate layer is a paper or cardboard layer. 3. The process according to claim 1 or 2, wherein the aqueous barrier composition comprises a barrier compound in the form of an aqueous dispersion of a barrier compound or specifically an aqueous solution of a barrier compound. 4. The process according to any one of claims 1 to 3, wherein the aqueous barrier composition comprises a moisture vapor barrier compound, an oxygen barrier compound, or both. 5. The process according to any one of claims 1 to 4, wherein, after step b), the process further comprises step c) of moistening the pulp-based substrate layer having a barrier layer, such that the moisture content of the pulp-based substrate layer having a barrier layer is 3.5% by weight or higher, based on the weight of the pulp-based substrate layer having a barrier layer. 6. The process according to any one of claims 1 or 2, wherein the aqueous barrier composition comprises a polymer barrier compound and an inorganic barrier compound. 7. The process according to any one of claims 1 to 6, wherein drying the pulp-based substrate layer having an aqueous barrier composition layer applied thereto to form a pulp-based substrate layer having a barrier layer is achieved by exposing the pulp-based substrate layer having an aqueous barrier composition layer to heat, radiation, or negative pressure, or a combination of two or more thereof. 8. The process according to claim 7, wherein drying the pulp-based substrate layer having an aqueous barrier composition layer applied thereto to form a pulp-based substrate layer having a barrier layer is achieved by heating the pulp-based substrate layer having an aqueous barrier composition layer to a temperature of at least 100°C, preferably at least 115°C, more preferably at least 130°C. 9. The process according to any one of claims 1 to 8, wherein, in step a), the paste-based substrate layer having a layer of an aqueous barrier composition applied thereto has a primer layer positioned between the paste-based substrate layer and the layer of the aqueous barrier composition. 10. The process according to any one of claims 6 to 9, wherein, after step c), or with any one of claims 1 to 5, wherein, after step b), the process further comprises step d) of applying an inorganic barrier layer or a metallic barrier layer to the barrier layer by thin film deposition. 11. The process according to claim 10, wherein, after step d), the process further comprises step e) of applying an additional layer of aqueous barrier composition to the inorganic barrier layer or a metallic barrier layer and drying the resulting layer stack having the additional layer of aqueous barrier composition applied to form an additional barrier layer such that the moisture content of the resulting layer stack having an additional barrier layer is less than 2.5% by weight, preferably less than 2% by weight, based on the weight of the resulting layer stack having an additional barrier layer. 12. A packaging material comprising at least one pulp-based substrate layer having, in this order, optionally, a primer layer adjacent to the paste-based substrate layer, a first barrier layer adjacent to the paste-based substrate layer or the primer layer, wherein the first barrier layer is obtainable according to the process of claim 1, optionally a sealing layer such as a cold or hot sealing layer adjacent to the first barrier layer, wherein the amount of the first barrier layer ranges from 4 g/m2 to 11 g/m2, preferably from 4 to 6 g/m2, and wherein the packaging material has a WVTR under tropical conditions (38 °C, 90% RH) of 1 to 5 g/(m2d), and where the paste-based substrate layer does not contain a metallic layer. 13. The packaging material according to any one of claims 12, wherein the packaging material is a wrapping paper or a food tray.