Paperboard for packaging liquid and / or frozen food products

Abstract

The present invention relates to paperboard for packaging liquid and / or frozen food products. Disclosed is paperboard for packaging liquid and frozen food products comprising a dispersion coating as the only barrier layer on its outer / printing side. It has been surprisingly found that a dispersion coating comprising latex and pigment applied on the outer / printing side of paperboard for liquid and / or frozen food products can act as the only barrier against the moisture produced by condensation.

Description

[0001] This application is application number 201880081285.2, filed on December 20, 2018, and the invention title is " For Cardboard for packaging liquids and / or frozen foods A divisional application of the patent application for "". Technical Field

[0002] This invention relates to paperboard for packaging liquids and / or frozen foods, methods for producing such paperboard, and packaging of liquids and / or frozen foods containing such paperboard. Background Technology

[0003] Fiber-based materials used in packaging or cups for liquids or frozen foods typically have barrier coatings on both the inner (facing the packaged item) and outer (printed) sides. The barrier coating applied to the inner side makes the material resistant to substances such as liquids, greases, and / or odors, and allows it to withstand the effects of the packaged item on the packaging material. The barrier coating should also be heat-sealable. The barrier applied to the outer side protects the packaged item from the surrounding environment, particularly from water vapor and condensation that can form on the surface due to temperature fluctuations or the temperature difference between the outer and inner sides of the cup (during filling).

[0004] Barriers are typically created by coating a fiber-based substrate with a composition that provides barrier properties. The most commonly used materials for forming barriers on fiber-based products are polyolefins, such as polyethylene (PE) or polypropylene (PP). Bio-based versions, including other bio-based polymers such as PLA, are also currently used. Liquid packaging boards generally have a polymer coating on both sides and often an additional aluminum coating on the inside. Cardboard intended for use in cups typically has a polyolefin coating to provide barrier properties on both the inside and outside / printed sides facing the liquid contents (to provide barrier properties against condensation).

[0005] Polymers can be laminated or extruded onto fiber-based products, for example. Currently, most barrier coatings are manufactured using extrusion coating technology and are therefore prepared offline in separate coating units. This increases the flexibility of paper or board making machines because different operating schedules can be used on the paper or board making machine and the extrusion coating unit. However, a drawback is that this is not cost-effective because it requires additional roll handling and additional changeover steps. Furthermore, such coatings may not be biodegradable or recyclable. Extrusion-coated polymers are difficult to decompose and reuse as part of waste paper treatment in paper and paperboard manufacturing. Polyolefin coatings also limit the printability of the surface and are not compatible with all kinds of inks.

[0006] Environmental concerns and rising oil prices have further fueled interest in the restoration of barrier materials based on non-fossil materials. This has increased interest in dispersion barrier coating technology.

[0007] In the prior art, dispersion barrier coatings have been proposed. Generally, these coatings contain a relatively small amount of filler or pigment, primarily to ensure good convertibility, i.e., to prevent breakage and to ensure good moisture barrier properties. EP2358942 discloses paperboard coated with first and second barrier coatings consisting of an aqueous polymer dispersion comprising about 70–90 wt% polymer emulsion and 10–30 wt% pigment. However, such coated surfaces are not optimized for printing. WO2015155413 discloses coated food cardboard in which a dispersion barrier coating is applied between the board layer and a pigment coating. WO9854410 discloses a coated board containing talc, which contains a polymer dispersion barrier layer. However, talc does not produce the desired optical properties to provide a high-quality, printable outer surface.

[0008] There is still a need for dispersion-coated cardboard for liquid and / or frozen foods, which provides a barrier against moisture generated by condensation and still retains good optical properties. Summary of the Invention

[0009] Surprisingly, a dispersion coating containing latex and pigments applied to the outer / printed side of cardboard for liquid and / or frozen foods has been found to act as a sufficiently effective barrier against moisture generated during condensation.

[0010] In a first aspect, the present invention discloses a cardboard for packaging liquids and / or frozen foods, comprising...

[0011] - A fiber-based substrate comprising first and second sides, and

[0012] - At least one first dispersion barrier layer is applied to the first side, the dispersion barrier layer forming a printing surface, wherein the dispersion barrier layer comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay calcium carbonate, all percentages being calculated based on the dry weight of the dispersion coating.

[0013] Such dispersion barrier layers have been shown to provide high barrier properties against both moisture and water vapor generated by condensation. Furthermore, the barrier layer provides the paperboard with good optical properties, creating a surface suitable for printing. This invention enables the dispersion coating to be applied as the sole coating on the outer / printed side of liquid / frozen food packaging materials, resulting in cost savings and a reduced carbon footprint. The dispersion barrier coating can further provide barrier properties against greases, oxygen, or other gases. In this document, "printed surface" refers to a surface suitable for printing. Therefore, at least one barrier layer forming the printed surface forms the outermost layer of the paperboard.

[0014] The resulting dispersion-coated paperboard exhibits both excellent barrier properties against liquids, particularly moisture generated by condensation, and superior optical properties (making the surface suitable for printing). In one embodiment, the dispersion-coated paperboard exhibits a brightness of at least 70%, preferably at least 80%, and a water vapor migration rate (WVTR) of less than 10 g / m² / 24 h, preferably less than 5 g / m² / 24 h. The dispersion-coated paperboard may further exhibit a water absorption rate of 1-10 g / m², preferably 1-5, measured using a COBB 3600.

[0015] In a second aspect, the present invention defines a method for producing paperboard, comprising the following steps:

[0016] - Provide a fiber-based substrate comprising at least two layers and having first and second sides,

[0017] - At least one dispersion barrier layer is applied to the first side to form a dispersion-coated substrate.

[0018] -Dry the substrate coated with the dispersion, and

[0019] The at least one dispersion barrier layer comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay and calcium carbonate, all percentages being calculated based on the dry weight of the dispersion barrier layer.

[0020] In a third aspect, the invention defines packaging for liquids and / or frozen foods comprising the aforementioned cardboard. This packaging is suitable for both cold and hot liquids. Detailed Implementation

[0021] As used herein, "fiber-based substrate" refers to an untreated paper or paperboard substrate containing cellulose fibers. Typical paperboard substrates for packaging materials comprise at least one layer, preferably several layers. The paperboard substrate is preferably a multi-layer packaging paperboard comprising at least two layers, a back layer and a top layer. The paperboard substrate may include, for example, a top layer and a back layer, and at least one intermediate layer. The basis weight of the paperboard substrate may be at least 150 gsm, preferably at least 200 gsm. Such multi-layer paperboard is particularly suitable for liquid and / or food packaging.

[0022] As used in this article, the term "latex" refers to an aqueous suspension of polymer particles (which may be natural polymers, synthetic polymers, biomass-derived synthetic polymers, or combinations thereof).

[0023] The term "dispersion coating" used in this article to form a barrier involves a coating technique in which an aqueous dispersion (such as latex) containing fine polymer particles is applied to the surface of a fiber-based substrate to form a substantially non-porous film that is solid upon drying. The dispersion barrier layer is formed by dispersion coating.

[0024] The brightness values ​​expressed in this article are based on measurements according to ISO 2470.

[0025] The water vapor migration rates expressed in this article were measured using a Mocon instrument at 23ºC and 50%RH according to ASTM F1249.

[0026] The water absorption rates expressed in this article were measured using a COBB 3600 according to SCAN-P 12:64.

[0027] This invention relates to paperboard having first and second sides (forming first and second surfaces) for packaging liquids and / or frozen foods. The paperboard is provided with a first dispersion barrier layer forming a printable surface on its first side. The at least one dispersion barrier layer comprises 30–50% by weight, preferably 30–40% by weight, of latex and 50–70% by weight, preferably 60–70% by weight, of pigment selected from clay (preferably kaolin clay) and calcium carbonate, all percentages calculated based on the dry weight of the dispersion barrier layer.

[0028] The inventors have discovered that dispersion coatings can be used as the sole barrier against moisture generated by condensation on the outer / printed side of the packaging board. This provides an environmentally friendly (recyclable) and repulpingable coating on the printed side. Recycling of fiber-based products coated with dispersions is facilitated both during the papermaking process and after recycling at the end of their life cycle. Dispersion coatings added to paper or board are more easily recycled compared to laminated or extruded barriers.

[0029] The latex used in the first and / or second dispersion barrier layer may be selected from: styrene-butadiene latex, styrene-acrylate latex, acrylate latex, vinyl-acetic acid latex, acrylate latex, vinyl acetate latex, vinyl acetate-acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene-acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, or mixtures of these latexes. The latex is preferably: styrene-butadiene (SB) latex or styrene-acrylate (SA) latex, acrylate latex, vinyl acetate latex, or vinyl acetate-acrylate latex, or mixtures of these latexes. The latex may be bio-based, i.e., derived from biomass, such as bio-based styrene-acrylate or styrene-butadiene latex. Bio-based latexes provide similar properties and offer an improved carbon footprint.

[0030] In addition to latex and pigments, one or more dispersion barrier layers may also contain small amounts of additives, such as 0.1–5% by weight, or 0.1–1%, or 1–5% by weight, based on the dry weight of the dispersion barrier layer. Additives may include: thickeners, defoamers or antifoaming agents, dispersants, additional pigments, crosslinking agents, slip additives, fillers, release agents, preservatives, and anti-sticking agents.

[0031] According to one embodiment of the invention, the at least one dispersion coating comprises a crosslinking agent. As used herein, a crosslinking agent refers to an agent that specifically reacts with carboxyl and / or hydroxyl groups. The crosslinking agent is preferably selected from: ammonium zirconium carbonate (AZC), potassium zirconium carbonate, potassium zirconium acetate (methylated) melamine-formaldehyde resin or (methylated) urea-formaldehyde resin, glyoxal, imidazoline derivatives, dialdehyde-polysaccharides, and combinations thereof. The crosslinking agent is preferably added in an amount of 0.1–5% by weight or 1–2% by weight, based on the dry weight of the dispersion barrier layer. The crosslinking agent further improves the barrier properties, for example, by providing a denser coating with lower porosity. Furthermore, surface smoothness is also improved. In a preferred embodiment, the crosslinking agent is selected from dialdehyde-polysaccharides such as dialdehyde cellulose (DAC) and dialdehyde starch.

[0032] Before applying one or more dispersion barrier layers, a fiber-based substrate surface may be sizinged onto the first side. The surface sizing agent may comprise or consist of modified starch, or may contain surface sizing agents such as acrylic copolymers. This further enhances the barrier properties of the dispersion coating.

[0033] In a preferred embodiment of the invention, the paperboard further comprises one or more polymer layers on a second opposing side of the fiber-based substrate relative to the dispersion barrier layer. In addition to providing liquid barrier properties to the inside of the formed cup or package, such a structure also provides high stiffness to the paperboard. Applying such a polymer layer can, for example, increase the stiffness of the paperboard by 5–10%. The structure of the present invention gives papermakers the possibility of reducing the amount of fiber in the paperboard while still achieving high stiffness – thus enabling source reduction. This polymer layer can be extruded and coated or laminated to the second side of the substrate. Preferably, the polymer is a polyolefin such as polyethylene (PE) or polypropylene (PP), or alternatively polyethylene terephthalate (PET), ethylene vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), and / or polylactic acid (PLA). The polymer is preferably derived from biomass.

[0034] In one embodiment, the polymer layer is formed of a foamed polymer, such as foamed polyethylene. Therefore, in this embodiment, the polymer (e.g., polyethylene) is applied to the second, and also the inner, side of the cardboard via a foam coating. The use of a foamed polymer coating further improves the stiffness of the board.

[0035] According to one embodiment, the pigment in the first and optional second dispersion coating is clay, preferably kaolin clay. The first and optional second dispersion barrier layers may thus contain 30–50% or 35–45% by weight of latex and 50–70% or 55–65% by weight of clay. The dispersion barrier coating containing latex and clay in these proportions produces excellent surface coverage, which further enhances the barrier properties of the coating.

[0036] In another embodiment, the pigment in the first and optionally second dispersion coatings is calcium carbonate. The dispersion coating may therefore contain 30–50% by weight of latex and 50–70% by weight of calcium carbonate. Dispersion barrier coatings containing latex and calcium carbonate in these proportions produce good optical properties, such as high brightness.

[0037] The paperboard may comprise first and second dispersion barrier layers. In this embodiment, the first dispersion barrier layer may be applied directly to a first side of an untreated or surface-sized paperboard substrate, and the second dispersion barrier layer may be applied over the first dispersion barrier layer, thereby forming a printable surface. The double coating provides better surface coverage and thus enhanced barrier properties. The second dispersion barrier layer may comprise 30–50 wt% or 30–40 wt% of latex and 50–70 wt% or 60–70 wt% of pigment, while the first dispersion layer may comprise 70–100 wt% of latex and 30–0 wt% of pigment and optionally 1–5 wt% of additives, based on the dry weight of the layers. In other embodiments, the first dispersion barrier layer may, like the second dispersion barrier layer, comprise 30–50 wt% or 35–45 wt% of latex and 50–70 wt% or 55–65 wt% of pigment.

[0038] According to a preferred embodiment, the first dispersion layer comprises latex and clay, and the second dispersion barrier layer comprises latex and calcium carbonate. In this way, the dispersion coating optimally combines the good covering properties of clay with the high gloss of calcium carbonate. This effect is further enhanced when different pigments are used in different layers. The first dispersion layer comprising latex and clay can be formed directly on and in contact with the board substrate (or a surface-sizing board substrate), and the second dispersion layer comprising latex and calcium carbonate can be formed as a second layer on top of the first layer, which forms the printing surface.

[0039] According to one embodiment of the invention, a dispersion layer is applied to a first side of the paperboard, which is the only barrier layer applied to the first side (printing side) of the paperboard and forms a printing surface. Therefore, in this embodiment, an untreated or surface-sized paperboard has one or two barrier layers applied directly to the first side / surface of the untreated or surface-sized paperboard, which form a printing surface.

[0040] The dispersion-coated paperboard of this invention exhibits a brightness of at least 70%, preferably at least 80%, and a water vapor migration rate (WVTR) of less than 10 g / m² / day (ASTM F1249). The dispersion-coated paperboard also exhibits a water absorption rate of 1-6 g / m², preferably 1-5, measured using a COBB 3600. The paperboard also exhibits a contact angle of at least 80, preferably at least 90, 100, or 110 degrees [SCAN-P 18:66] and a gloss of at least 8% [TAPPI T 480]. All parameters are measured on the dispersion-coated printed side of the paperboard.

[0041] The basis weight of one or more dispersion barrier layers is preferably 10–30 g / m², more preferably 10–20 g / m². In embodiments where the first and second dispersion barrier layers are applied to the substrate, the basis weight of the first layer is preferably 5–15 g / m², more preferably 5–10 g / m², and the basis weight of the second layer is about 5–15 g / m², more preferably 5–10 g / m². In embodiments where only one dispersion barrier layer is applied to a first side of the substrate, the basis weight of the dispersion barrier layer may be 5–15 g / m².

[0042] A method for producing the paperboard of the present invention includes: applying at least one dispersion barrier layer to a paperboard substrate to form a dispersion-coated substrate and drying the dispersion-coated substrate. In one embodiment, the fiber-based substrate has a first moisture content before the application of the at least one dispersion barrier layer and a second moisture content after drying the dispersion-coated substrate, wherein the difference between the first and second moisture contents is less than 2% by weight, preferably less than 1% by weight. In this way, the tendency to break is reduced.

[0043] The dispersion coating is preferably applied using methods such as roll coating, spraying, curtain coating, doctor blade coating, slot coating, dip coating, gravure roll coating, reverse gravure coating, rod coating, soft-tip doctor blade coating, and / or combinations thereof. Preferred coating methods involve the use of a rod coating machine or a soft-tip doctor blade coating machine. These techniques provide improved coverage, which further enhances barrier properties. The dispersion coating is preferably applied online in a paper machine or a board making machine. The coating is preferably applied online on a hot web. In one embodiment, the temperature of the web at the point of application of the dispersion coating is at least 60ºC, preferably above 70ºC. In this way, film formation is improved, resulting in improved barrier properties. Additionally, the coating adheres to the surface of the web more quickly in this manner.

[0044] The solid content of the dispersion coating can be 25-70% by weight. The viscosity of the dispersion used for dispersion coating is preferably 500-1000 mPas. However, the dispersion can be diluted with water or any other solvent to achieve the desired viscosity.

[0045] The present invention also relates to packaging comprising cardboard according to the invention for liquid and / or frozen foods. This packaging is preferably made by using heat sealing.

[0046] In embodiments where an extruded polymer layer is provided on the second side, the polymer-coated second side can form the inner surface of the formed package and the dispersion-coated first side can form the outer / printed surface.

[0047] In embodiments where at least one barrier dispersion layer is provided on the second side, the dispersion-coated second side can form the inner surface of the formed package and the dispersion-coated first side can form the outer / printed surface.

[0048] Further features of the invention will become apparent from the embodiments and accompanying drawings, wherein:

[0049] Figure 1 This is a schematic diagram of packaging materials according to one embodiment of the present invention.

[0050] Figure 1 The paperboard shown comprises a fiber-based substrate 1, which includes three layers: a top layer 1a, a middle layer 1b, and a back layer 1c. The top layer 1a of the paperboard is coated with a first dispersion barrier layer 2, wherein the first dispersion barrier layer 2 comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay and calcium carbonate. A second dispersion barrier layer 3 is disposed on the first barrier layer 2, wherein the second dispersion barrier layer also comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay and calcium carbonate. The dispersion barrier layer is applied to the paperboard substrate via dispersion barrier coating. Figure 1 The cardboard shown also includes a polymer coating (4) applied to the backing layer. The polymer coating is preferably extruded and applied to the cardboard substrate. For example... Figure 1 The cardboard shown is particularly suitable for heat-sealing packaging of liquids and / or frozen foods. The cardboard can be printed directly on the outermost barrier layer (3). In the resulting package, a polymer layer (4) forms the inner side that comes into contact with the contents, preferably liquids and / or frozen foods.

[0051] Example

[0052] Experiments were conducted to evaluate the barrier properties of the paperboard of the present invention.

[0053] An uncoated paperboard substrate (Cupforma Natura™, 214 g / m²) comprising a top layer of sulfate pulp, an intermediate layer of sulfate pulp and CTMP, and a back layer of sulfate pulp was coated on its first side with two dispersion barrier layers (1+2) using a roller and rod coater. A second layer was applied over the first layer. The first layer (layer 1) had a basis weight of 10 g / m² and the second layer (layer 2) had a basis weight of 5 g / m². The dispersion coating composition was prepared according to Table 1. These sheets were then dried to achieve a moisture content of approximately 7%.

[0054] Table 1

[0055]

[0056] The sheet is further extruded and coated with polyethylene (PE) (15 g / m²) on the inner side, which is also the second side, of the cardboard substrate.

[0057] result:

[0058] The properties of the paperboard coated with dispersion 1 (forming the first layer) and dispersion 2 (forming the second layer) are summarized in Table 2. All properties were measured on the outer / printing side, i.e., on the first side coated with dispersion barrier according to the present invention.

[0059] Table 2

[0060]

[0061] As can be seen from the brightness and gloss values ​​in Table 2, the substrate coated with the dispersion according to the present invention provides paperboard with good optical properties. The WVTR, COBB, and contact angle values ​​further demonstrate that the paperboard provides good moisture barrier properties, sufficient to withstand moisture generated by condensation.

Claims

1. Cardboard for packaging liquids and / or frozen foods, comprising - A fiber-based substrate comprising first and second sides, and - At least one dispersion barrier layer applied to the first side, the at least one dispersion barrier layer forming a printing surface, characterized in that the dispersion barrier layer comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay and calcium carbonate, all percentages being calculated based on the dry weight of the dispersion barrier layer.

2. The paperboard according to claim 1, wherein the fiber-based substrate surface is sizing on the first side and wherein at least one dispersion barrier layer is applied to the surface-sizing fiber-based substrate.

3. The paperboard according to any one of claims 1 and 2, wherein the paperboard further comprises a polymer layer applied to the second side.

4. The paperboard according to any one of claims 1-3, wherein the polymer layer is formed of a foamed polymer such as foamed polyethylene.

5. The paperboard according to any one of claims 1-4, wherein the at least one dispersion coating further comprises 0.1-5% by weight of a crosslinking agent, calculated based on the dry weight of the dispersion barrier layer.

6. The paperboard according to any one of claims 1-5, wherein the pigment is clay.

7. The paperboard according to any one of claims 1-5, wherein the pigment is calcium carbonate.

8. The paperboard according to any one of claims 1-7, wherein first and second dispersion barrier layers are applied on the first side.

9. The paperboard of claim 8, wherein the first dispersion layer comprises latex and clay and the second dispersion barrier layer comprises latex and calcium carbonate.

10. The paperboard according to any one of claims 1-7, wherein a dispersion barrier layer is applied on a first side of the fiber-based substrate, the dispersion layer being the only barrier layer applied on the first side and the dispersion layer forming a printable surface.

11. The paperboard according to any one of claims 1-10, wherein the paperboard coated with the dispersion exhibits a brightness of at least 70%, preferably at least 80%, and a water vapor migration rate (WVTR) of less than 10 g / m² / day.

12. The paperboard according to any one of claims 1-11, wherein the dispersion-coated paperboard exhibits a water absorption rate of 1-6 g / m², preferably 1-5, as measured using a COBB 3600.

13. A method for producing the paperboard according to claims 1-12, comprising the following steps: - Provide a fiber-based substrate comprising at least two layers and having first and second sides, - At least one dispersion barrier layer is applied to the first side to form a dispersion-coated substrate. -Dry the substrate coated with the dispersion, and The at least one dispersion barrier layer comprises 30–50% by weight of latex and 50–70% by weight of pigment selected from clay and calcium carbonate, all percentages being calculated based on the dry weight of the dispersion barrier layer.

14. The method of claim 13, wherein the fiber-based substrate has a first moisture content before the application of the at least one dispersion barrier layer and a second moisture content after drying the dispersion-coated substrate, wherein the difference between the first and second moisture contents is less than 2% by weight, preferably less than 1% by weight.

15. The method according to any one of claims 13 or 14, comprising the step of applying first and second dispersion barrier layers on a first side of the substrate.

16. The method according to any one of claims 13-15, wherein the method further comprises the step of applying a polymer layer on the second side.

17. The method of claim 16, wherein the polymer layer is applied by foam coating.

18. Packaging for liquid and / or frozen foods, comprising cardboard according to any one of claims 1-12.

19. Packaging for liquid and / or frozen foods, comprising cardboard according to any one of claims 3-12.

20. The packaging of claim 19, wherein the second side coated with polymer forms the inner surface of the packaging and the first side coated with dispersion forms the outer / printed surface.

21. The packaging according to any one of claims 18-20, wherein the outer surface / printed surface is further provided with printing ink on the dispersion barrier layer.

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