Method for manufacturing a coated paperboard

Abstract

The present invention discloses a method of manufacturing a coated paperboard, the method comprising the steps of: - forming a paperboard substrate comprising a first major side and a second major side opposed from said first major side, - providing a first aqueous dispersion composition comprising binder and pigment at a binder:pigment dry weight ratio of from 10:100 to 25:100, wherein the binder in the dispersion composition is a latex having a glass transition temperature (Tg) as measured using ASTM D2765-16 of less than 15 ºC and wherein the polymer particles of the latex have a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017, applying the first aqueous dispersion composition on the first major side forming a dispersion coating layer. The method of the invention has been shown to manufacture a coated paperboard with both a surface excellent for printing and a good adhesion to optionally additional barrier layers. Especially, the coated surface exhibits an improved wet rub resistance.

Description

[0001] METHOD FOR MANUFACTURING A COATED PAPERBOARD

[0002] FIELD OF USE

[0003] The present invention relates to the field of manufacturing a coated paperboard, and a coated paperboard made by the method.

[0004] BACKGROUND

[0005] Fiber-based products, like paperboard with a pigment-coated side, are commonly utilized for packaging food, cosmetics, luxury items, and frozen goods. The pigment coating not only functions as a printing surface but may also form a foundation for applying additional barrier layers, such as extrusion-coated polyolefin or barrier dispersion coating layers. Therefore, it's crucial that the pigment coating not only offers superb printability but also excellent adhesion to potential barrier coating layers. Additionally, the durability of the packaging material needs to withstand various conditions, including converting.

[0006] Wet rub resistance is an important feature for pigment coating of paperboard as it determines the durability of the printed image or text when exposed to moisture or rubbing. It is also significant when in contact with solvent or aqueous-based inks or fountain solutions. Poor wet rub resistance can lead to print defects and poor runnability in printing machines. It is crucial that the printed information or graphics on the paperboard do not detach or rub off easily during transportation, handling, or storage. Wet rub resistance ensures that the packaging remains legible and attractive even when subjected to moist conditions or condensed water, enhancing the visual appeal of the product and protecting its contents. Thus, wet rub resistance is a critical quality parameter for pigment coating of paperboard, ensuring that the packaging meets the necessary standards for durability and aesthetic appeal.

[0007] Pigment-coated paperboards also need to have sustainable properties, such as being easily recyclable and having a lower carbon and water footprint. While the pigment plays a crucial role in coating quality, the binder chemistry and physical properties of the coating composition are equally important for performance and sustainability. In the case of multilayer coatings with different pigments, it's beneficial to optimize the binder based on the pigment type and properties.

[0008] To address the aforementioned challenges, one potential solution is to incorporate a primer into the pigment coating. However, this solution can increase costs and require additional processing steps. Alternatively, increasing the binder level could be an option, but this may negatively impact the recycling of coated broke. The use of insolubilizer may also address the issue. However, the use of insolubilizer requires optimal reaction conditions, such as specific drying temperature and moisture content, as well as the addition of appropriate types of additives for it to work efficiently.

[0009] Therefore, there remains a need for a pigment-coated board that offers excellent coating quality, including increased smoothness, optimized gloss, and excellent dry and wet rub resistance, which pigment-coated board is able to withstand converting and provides a good adhesion to additional barrier coating layers.

[0010] DESCRIPTION OF THE INVENTION

[0011] The object of the invention is to provide a method for manufacturing a coated paperboard that exhibits excellent wet rub resistance and provides good adhesion to potential additional barrier coating layers.

[0012] This object, as well as other objects as will realized by the skilled person in light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0013] According to a first aspect illustrated herein, there is provided a method of manufacturing a coated paperboard, the method comprising the steps of:

[0014] - forming a paperboard substrate comprising a first major side and a second major side opposed from said first major side,

[0015] - providing a first aqueous dispersion composition comprising binder and pigment at a binder: pigment dry weight ratio of from 10:100 to 25:100, wherein the binder in the dispersion composition is a latex having a glass transition temperature (Tg) as measured using ASTM D2765-16 of less than 15 °C and wherein the polymer particles of the latex have a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017,

[0016] - applying the first aqueous dispersion composition on the first major side forming a dispersion coating layer.

[0017] The method of the invention has been shown to manufacture a coated paperboard with both a surface excellent for printing and a good adhesion to optionally additional barrier layers. Especially, the coated surface exhibits an improved wet rub resistance.

[0018] The binder pigment ratio as used herein refers to the dry weight ratio. If not specifically denoted otherwise, given % as used herein are weight%, and are calculated on the basis of a dry weight of 100 weight% of the respective object, such as a layer, a ply, a furnish or a composition.

[0019] Preferably, the latex has a glass transition temperature (Tg) of less than 13 °C, even more preferably of less than 10 °C or less than 5 °C, such as in the range of from -5 °C to 15 °C, or from -5 to 13 °C or from 0 to 15 °C, or from 0 to 10 °C. The polymer particles of the latex have preferably a mean particle size of less than 120 nm, even more preferably of less than 118 nm, such as in the range of 100 - 125 nm or 100 - 120 nm or 100 - 118 nm.

[0020] Latex refers to an emulsion of polymer particles in an aqueous medium. In the dispersion coating composition, the binder is in the form of latex. Preferably, the latex is selected from the group of styrene-acrylate (SA) latex and styrene-butadiene (SB) latex or a mixture thereof. SA-latex is the preferred choice, as it has been proven to cause less odor problems and requires less cleaning. The monomers used to make styrene acrylate can be chosen from the group of styrene, butyl acrylate, ethyl acrylate and methyl methacrylate or mixtures thereof. In some embodiments, the latex is a mixture of SA- and SB-latex. In these embodiments, the mixture preferably comprises at least 70 wt% of SA-latex and at most 30 wt% of SB-latex (dry weight).

[0021] The latex emulsion can be stabilized with additives such as surfactants and / or surface active polymers. Preferably the styrene / acrylate contains 0.5-7.5% of acid such as acrylic acid, methacrylic acid or mixture of both which is added to the latex during emulsion polymerization. It is also possible to add such as 0.5-10 wt% of such monomeric or polymeric acid after polymerization in order to stabilize emulsion and adjust e.g. rheological performance. Post addition of acids will also affect runnability and strength of the coating layer.

[0022] Preferably, the aqueous dispersion composition comprises the latex and the pigments to 95 - 100 wt%, more preferably to 98 - 100 wt% (dry weight). The remaining 0 - 5 wt% (dry weight) of the aqueous dispersion composition may be performance or functional additives. Such additives may include rheology modifiers, dispersants, pH regulators, biocides, lubricants, and / or insolubilizers.

[0023] In embodiments, the aqueous dispersion composition comprises less than 1 wt% and most preferably to less than 0.5 wt% such as 0-0.5 wt% of insolubilizers, as calculated on the total dry content of the aqueous dispersion composition. The insolubilizer may be chosen from the group of glyoxal, glyoxated resins, urea formaldehyde, melamine formaldehyde, amino resins, or metal salts such as ammonium zirconium carbonate, potassium zirconium carbonate, zirconium chelates, or reactive polysaccharides such as dialdehyde starch or dialdehyde cellulose. The method of the invention enables the use of a low amount of insolubilizer and still achieve an excellent wet rub resistance.

[0024] The pigments in the aqueous dispersion composition may e.g. be selected from the group comprising clay, calcium carbonate and / or talc. The aqueous dispersion composition is preferably applied to form a dispersion coating layer with a grammage in the range of from 6 to 12 gsm, preferably in the range of 6 - 11 gsm.

[0025] The aqueous dispersion composition can be applied on the first major side by use of any conventional coating techniques such as roll coating, blade coating, spray coating, or curtain coating and / or various configurations and metering concepts thereof such as short dwell time coating, jet coater such as OptiCoat Jet coater (Valmet). Additionally, the coating can be applied using a single- or multi-layer coating process, depending on the desired properties of the final product. The coated paperboard can then be further processed using conventional techniques, such as drying, calendering, and winding, to create a finished product with the desired properties.

[0026] In the optional drying process, the coated paperboard is preferably dried to a moisture content in the range of from 4 to 12 wt%, more preferably in the range of from 5 to 10 wt% and to a surface temperature of above 75 °C, preferably in the range of 90 - 100 °C. These conditions facilitate excellent film formation and adhesion and cohesion of the coating layer.

[0027] The coated paperboard may further be subjected to calendering, preferably by use of a soft nip calender at a nip pressure of less than 100 kN / m, preferably less than 75 kN / m at a surface temperature of less than 200 °C, preferably less than 150 °C. In embodiments, the coated paperboard is subjected to moisturizing prior to calendering. Preferably, the amount of water applied is within the range of 0.5- 7 g / m2, to at least one side, and should be applied at a temperature 5 - 70 °C such as 10-40 °C. By doing so, the coated paperboard is cooled down before calendaring. This cooling process ensures that the coated paperboard maintains its targeted bulk and smoothness. Moisturizing can also be combined with air blow or air chill to remove any excess water. The coated paperboard produced by the method of the invention offers excellent durability, even when subjected to moisturizing and water cooling before calendering. The high wet rub resistance of the paperboard produced by the method counteracts the tendency of particles and coating fragments to be detached during subsequent mechanical treatment, such as calendering.

[0028] In embodiments, the method further comprises the step of applying a pre-coating composition on the first side of the paperboard substrate to form a pre-coating layer, which step is performed before the step of applying the first aqueous dispersion composition on the first side whereby the aqueous dispersion composition is applied on the pre-coating layer. Preferably, the pre-coating composition comprises binder and pigments at a binder to pigments ratio (dry weight) of 10:100 to 40:100. The binder in the pre-coating composition is preferably a latex selected from the group of styrene-acrylate latex and styrene-butadiene latex. The binder of the pre-coating composition can be the same or have the same properties as the binder of the first aqueous dispersion composition. The binder / latex of the pre-coating composition has preferably also a glass transition temperature (Tg) as measured using ASTM D2765- 16 of less than 15 C and °C, preferably of less than 13 °C, even more preferably of less than 10 °C or less than 5 °C, such as in the range of from -5 °C to 15 °C, or from -5 to 13 °C or from 0 to 15 °C, or from 0 to 10 °C, and the polymer particles of the latex in the pre-coating composition have preferably a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017, preferably of less than 120 nm, even more preferably of less than 118 nm, such as in the range of 100 - 125 nm or 100 - 120 nm or 100 - 118 nm.

[0029] In embodiments, the pigment in the pre-coating composition comprises at least 70 wt% calcium carbonate, preferably 70 - 100 wt% calcium carbonate and 30 - 0 wt% clay, based on the total weight of the pigment. The calcium carbonate used in the pre-coating is preferably a fine carbonate having median diameter of less than 1.1 pm, preferably less than 1.2 pm. Most preferably at least 60 wt% of the calcium carbonate pigment particles have a diameter of less than 2 pm.

[0030] The paperboard substrate is preferably a multiply paperboard comprising cellulosic fibers having two or more plies. The paperboard may for example comprise a top ply, a back ply and one or several middle layers, which middle layers provide bulk to the paperboard substrate. The grammage of the paperboard substrate is preferably in the range of 150 - 450 gsm.

[0031] The middle ply or plies preferably comprises bleached or unbleached CTMP or high- temperature CTMP (HT-CTMP) from softwood and / or from hardwood. Preferably the middle ply / plies comprises 20 - 80 wt%, preferably 20 - 80 wt% of CTMP or HT- CTMP, or 20 - 40 wt% CTMP or HT-CTMP. In embodiments the at least one middle ply comprises at least 40 wt% CTMP or HT-CTMP, such as between 40 - 80 wt% CTMP. The middle ply / plies may further comprise softwood or hardwood kraft pulp and up to 30wt% recycled fibers and / or broke.

[0032] The top ply and back ply preferably comprise bleached or unbleached kraft pulp from hardwood and / or softwood, preferably in an amount of at least 75 wt%, such as in the range of 75 - 100 wt%. In preferred embodiments, the back ply comprises or consists of unbleached kraft pulp.

[0033] The invention is especially beneficial when using a paperboard substrate that contains a significant quantity of bulky fibers, such as CTMP, and a top ply of a low grammage, as the coating composition applied counters any adverse impact that such a substrate may have on the printing quality.

[0034] In embodiments, the paperboard substrate exhibits a bulk of above 1.3 m3 / kg, preferably above 1.4 m3 / kg, such as above 1.5 m3 / kg as measured using ISO 534 and a density between 800 - 450 kg / m3, preferably between 800 - 500 kg / m3 as measured using ISO 534.

[0035] The first side is preferably formed by the outermost surface of the top side. In embodiments, the surface roughness of the first side, as measure on the uncoated, optionally surface sized surface, is in the range of 200 ml / min - 600 ml / min, preferably in the range of 250 - 500 ml / min as measured using ISO 8791-4. A too low surface roughness would have an adverse effect on the coating, whereas a too high surface roughness would diminish the coating smoothness. The quite high roughness is obtained by the use of more bulky fibers in the middle ply in combination with a quite low grammage of the top ply.

[0036] The smoothness of the first side, as measured on the uncoated, optionally surface sized surface, is preferably in the range of 2.5 - 8 pm, more preferably in the range of 3 - 7 pm as measured using PPS 1.0 MPa according to ISO 8791-4. The paperboard substrate (uncoated, potentially surface sized) may further exhibit a COBB Unger (30s) of less than 10 g / m2as measured using SCAN-P 37:77 and / or COBB60 value as measured using SCAN-P 12:64 of between 15 - 50 g / m2, preferably 18 - 40 g / m2. These properties of the paperboard substrate further enhance the wet and dry rub resistance. For example, a too high COBB60 or excessive roughness, can cause the binder to migrate and negatively impact the wet and dry rub resistance of the substrate. To achieve the desired properties, the paperboard substrate, before being coated, may be subjected to a calendering step, preferably at a nip pressure of between 10 - 120 kN / m and at a roll surface temperature of below 250 °C, preferably 50 - 200 °C. In this way, the bulk is also retained. Preferably, the calendering step includes a pre-moisturizing step, in which moisture or water is applied to the web prior to the nip. The water is preferably applied in an amount of around 1 - 7 gsm, with a water temperature of between 10 - 60 °C.

[0037] In embodiments, the paperboard substrate is surface sized on the first side with a surface sizing composition before the application of the dispersion coating composition and the optional pre-coating composition, wherein the surface sizing composition comprises a cationic polymer, preferably selected from the group of cationic starch, cationic polyacrylamide, polyvinyl amine (PVAm), polyethylene imine, and glyoxalated polyacrylamide (GPAM) or combinations thereof. The surface sizing composition is preferably applied in an amount to form a coat weight of 0.5 - 5 gsm. The starch may be cationic starch from potato, corn, tapioca, barley or wheat. In embodiments, the surface sizing composition comprises 50 - 100 wt% of cationic starch and 0 - 50 wt% of a second cationic polymer. The surface sizing composition may further comprise hydrophobic agents. Cationic starch is preferred as sizing agent due to its ability to enhance surface strength and adhesion, as well as improve the efficiency of fiber recycling.

[0038] In embodiments, the dispersion coating layer forms an outermost layer suitable for printing. The inventive dispersion coating forms a quite matte finish, which is desirable in certain applications. The method may further comprise the step of applying a print on the dispersion coating layer, and, optionally, the step of applying a varnish on the printed dispersion coating layer. The printing can be water or solvent based flexography or inkjet, rotogravure. Printing can also be offset or digital printing with liquid or dry toner technology. The method of the invention generates a surface that is durable for the application of water-based varnish. It is further suitable for the application of UV based varnishes.

[0039] In embodiments, the method comprises the step of forming a barrier layer on the dispersion coating layer.

[0040] The barrier layer may be formed by applying a dispersion barrier composition on the dispersion coating layer. The dispersion barrier composition may comprise binder and optionally pigments. The binder in the dispersion barrier composition may be a latex, such as styrene-acrylate latex or styrene-butadiene latex, or a polyolefin dispersion.

[0041] In alternative embodiments, the barrier layer may be formed by extrusion coating of a polyolefin, preferably polyethylene, on the dispersion coating layer. The invention enables the application of thinner barrier layer. In embodiments, the extrusion coating of a polyolefin is applied in an amount to form a polyolefin layer with a grammage of less than 20 gsm, preferably less than 15 gsm, e.g. in a range of 10 - 20 gsm or 10 - 15 gsm. The barrier layer may also be film laminated onto the dispersion coating layer. The invention significantly enhances the adhesion of the barrier layer. io

[0042] In some embodiments, the barrier layer may be formed by first applying a dispersion barrier composition on the dispersion coating layer forming a dispersion barrier coating layer and thereafter applying an extrusion coating layer of a polyolefin on the dispersion barrier coating layer. In this embodiment, the barrier layer thus includes two sub-layers; one dispersion barrier coating layer and one extrusion coating layer.

[0043] According to a second aspect illustrated herein, there is provided a coated paperboard made by the method according to the first aspect.

[0044] According to a third aspect illustrated herein, there is provided a coated paperboard comprising:

[0045] - a paperboard substrate comprising a first major side and a second major side opposed from said first major side,

[0046] - a dispersion coating layer applied on the first major side, wherein the dispersion coating layer comprises binder and pigment at a binderpigment dry weight ratio from 10:100 to 25:100, wherein the binder in the dispersion layer is a latex having a glass transition temperature (Tg) as measured using ASTM D2765-16 of less than 15 °C and wherein the polymer particles of the latex have a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017.

[0047] The coated paper according to the second and third aspects may be further defined by the same features as the coated paperboard manufactured by the method according to the first aspect.

[0048] Preferably, the surface smoothness of the dispersion coating layer is preferably less than 2 pm, preferably less than 1.8 pm, as measured using PPS 1.0 MPa according to ISO 8794-4.

[0049] In embodiments, the brightness of the paperboard coated with the dispersion coating layer is higher than 90% as measured using ISO 2470-2 (D65 / 1O0). The brightness is measured on the dispersion coating layer. The coated paperboard may further exhibit a taint value of less than 0.5 according to the Robinson chocolate test as measured using standard EN 1230-2-2009, the multicomparison test.

[0050] The coated paperboard may further have a density of below 780 kg / m3, preferably of below 730 kg / m3, most preferably of below 700 kg / m3, as measured using ISO 534:2011. Surprisingly, the paperboard may be double coated and still exhibit such low density.

[0051] The coated paperboard of the invention is suitable to be used in packaging material for packaging of e.g. food, liquids, cosmetics and luxury items.

[0052] Example 1

[0053] In order to evaluate the coated paperboard of the invention, a test series was performed in which the wet rub resistance and the polyolefin adhesion of a coated paperboard manufactured in accordance with the invention was evaluated in a laboratory trials.

[0054] A multiply paperboard with a grammage of 240 gsm, comprising a top ply consisting of bleached kraft pulp, a back ply consisting of bleached kraft pulp and a middle ply comprising CTMP, kraft pulp and broke was used as a paperboard substrate. The paperboard substrate was coated with a pre-coating composition and a dispersion coating composition. Pre-coating comprised 100 pph (parts per hundred parts) of ground calcium carbonate, 16 pph latex, 0.4 pph of Ammonium Zirconium Carbonate insolubilizer and 1.3 pph of Sodium carboxymethyl cellulose as rheology modifier and water retention agent. The binder and additives are calculated based on dry weight of the pigment.

[0055] In the top coating, 68 pph of kaolin was used and 32 pph of fine ground calcium carbonate, 17 pph latex and 0.4 pph of Ammonium Zirconium Carbonate insolubilizer and 1.2 pph of Sodium carboxymethyl cellulose and synthetic thickener as rheology modifier and water retention agent. In both cases, NaOH was added to adjust pH of the slurries to a target of 8.

[0056] Thus, the recipes confirms also that the said latex and inventive recipe is suitable for both high (100%) and low (<35%) calcium carbonate based coating dispersions. A latex emulsion with poor colloidal stability and Calcium ions sensitivity would likely agglomerate and reduce the performance of the coated paperboard.

[0057] The same SA-latex was used in the both coating compositions for each trial point. The coat weights of each coating layer were 9 - 10 gsm and the moisture content was 5.5 wt%. Table 1 shows the properties of the latex used and the wet rub resistance of the double coated paperboard of the references (Ref 1 , Ref 2, and Ref 3), and of the paperboard made according to the invention (Sample 1 and Sample 2). All samples, including the references and the Samples, were extrusion coated with polyethylene (around 15 gsm), and their PE adhesion is also included in table 1.

[0058] Table 1 :

[0059] Wet rub was determined by rubbing the surface using Taber Abrasion tester based on TAPPI T 476. The coated paperboard was rubber under wet conditions, whereafter the turbidity of the water was determined. Higher value means more particles released from surface whereas a low means a good and water durable surface. As can be seen in Table 1 , the coated paperboard manufactured according to the invention (Sample 1 and Sample 2) exhibit both good wet rub resistance and excellent PE adhesion.

[0060] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS1. A method of manufacturing a coated paperboard, the method comprising the steps of:- forming a paperboard substrate comprising a first major side and a second major side opposed from said first major side,- providing a first aqueous dispersion composition comprising binder and pigments at a binderpigment weight ratio of from 10:100 to 25:100, wherein the binder in the dispersion composition is a latex having a glass transition temperature (Tg) as measured using ASTM D2765-16 of less than 15 °C and wherein the polymer particles of the latex have a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017,- applying the first aqueous dispersion composition on the first major side forming a dispersion coating layer.

2. A method according to claim 1 , wherein the latex has a glass transition temperature of less than 13 °C, preferably in the range of from -5 to 13 °C.

3. A method according to anyone of the preceding claims, wherein the polymer particles of the latex have a mean particle size of less than 120 nm, preferably in the range of 100 - 120 nm.

4. A method according to anyone of the preceding claims, wherein the latex is selected from the group of styrene-acrylate latex and styrene-butadiene latex or a mixture thereof.

5. A method according to anyone of the preceding claims, wherein the aqueous dispersion composition comprises the latex and the pigments to 95 - 100wt% as calculated on the total dry weight of the first aqueous dispersion composition.

6. A method according to anyone of the preceding claims, wherein the aqueous dispersion composition comprises less than 0.5 wt% of insolubilizers based on the total dry weight of the aqueous dispersion composition.

7. A method according to anyone of the preceding claims, wherein the first aqueous dispersion composition is applied in an amount to form a dispersion coating layer with a grammage in the range of from 6 to 12 gsm, as measured using ISO536.

8. A method according to anyone of the preceding claims, further comprising the step of applying a pre-coating composition on the first side of the paperboard substrate to form a pre-coating layer, which step is performed before the step of applying the first aqueous dispersion composition on the first side whereby the aqueous dispersion composition is applied on the pre-coating layer and wherein the pre-coating composition comprises binder and pigments at a binder to pigments ratio of 10: 100 to 40: 100.

9. A method according to anyone of the preceding claims, wherein the paperboard substrate is a multi-ply paperboard substrate comprising a top ply, a back ply and at least one middle ply, wherein the middle ply comprises 20 - 80 wt% CTMP or HT-CTMP, preferably 40 - 80 wt% CTMP or HT-CTMP.

10. A method according to anyone of the preceding claims, wherein the paperboard substrate exhibits a surface roughness as measured on the first side in the range of 200 ml / min - 600 ml / min, preferably 250 - 500 ml / min as measured using ISO 8791-2.

11. A method according to anyone of the preceding claims, wherein the paperboard substrate is surface sized with a surface sizing composition before the application of the dispersion coating composition and the optional pre-coating composition, wherein the surface sizing composition comprises a cationic polymer, preferably selected from the group of cationic starch,cationic polyacrylamide, polyvinyl amine (PVAm), polyethylene imine, and glyoxalated polyacrylamide (GPAM) or combinations thereof.

12. A method according to anyone of the preceding claims, wherein the dispersion coating layer forms an outermost layer suitable for printing.

13. A method according to anyone of the claims 1 - 11, wherein the method further comprises a forming a barrier layer on the dispersion coating layer.

14. A coated paperboard made by the method according to anyone of the claims 1 - 13.

15. A coated paperboard comprising:- a paperboard substrate comprising a first major side and a second major side opposed from said first major side,- a dispersion coating layer applied on the first major side, wherein the dispersion coating layer comprises binder and pigment at a binderpigment dry weight ratio from 10:100 to 25:100, wherein the binder in the dispersion layer is a latex having a glass transition temperature (Tg) as measured using ASTM D2765-16 of less than 15 °C and wherein the polymer particles of the latex have a mean particle size of less than 125 nm as measured with light scattering according to ISO 22412:2017.

16. A coated paperboard according to anyone of the claims 14 or 15, wherein the surface smoothness of the dispersion coating layer is less than 2 pm, preferably less than 1.8 pm, as measured using PPS 1.0 MPa according to ISO 8794-4.

17. A coated paperboard according to anyone of the claims 20 - 21, wherein the brightness of the paperboard coated with the dispersion coating layer is higher than 90% as measured using ISO 2470-2 (D65 / 1O0).

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