WO2024206171A1

WO2024206171A1 - Sodium bentonite containing water-based barrier coating and method of making the same

Info

Publication number: WO2024206171A1
Application number: PCT/US2024/021198
Authority: WO
Inventors: Pradnya Dilip RAO; Sherman David COX
Original assignee: Specialty Minerals Michigan Inc
Current assignee: Specialty Minerals Michigan Inc
Priority date: 2023-03-24
Filing date: 2024-03-22
Publication date: 2024-10-03
Anticipated expiration: 2025-09-24
Also published as: CN120936550A

Abstract

An aqueous barrier coating for paper products can include a chemically unmodified sodium bentonite dispersed in a binder, wherein the sodium bentonite is dispersed under high shear conditions such that the sodium bentonite is present in the form of tactoids.

Description

SODIUM BENTONITE CONTAINING WATER-BASED BARRIER COATING AND METHOD OF MAKING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The benefit of priority to U.S. Provisional Patent Application No. 63/454,536 filed March 24, 2023, is hereby claimed and the disclosure is incorporated herein by reference in its entirety.

FIELD

[0002] The disclosure relates to water-based barrier coatings and method for making waterbased barrier coatings that contain sodium bentonite.

BACKGROUND

[0003] Paper-based packaging materials are utilized around the world. Currently, the barrier coatings of paper and packaging applications primarily depend on petroleum-based materials and synthetic polymers such as waxes, polyvinyl alcohol, polyolefins (Gironi & Piemonte, 201 1). These materials are cost-effective, easily available, and provide a significant barrier against water vapor, oil/grease, and oxygen for packaging applications. However, these materials have major disadvantages such as poor recyclability of coated paper and non-biodegradability which can adversely impact the environment. Ideal packaging material in the context of food packaging must have a good barrier to oxygen, water vapor, and oil/grease while being derived from biobased, recyclable, compostable, and/or otherwise ecofriendly sources. Barrier property needs can vary depending on the coating application and ultimate use of the paper product.

[0004] Nanoclays have been used in a variety of applications and are generally found advantageous for their ability to swell in water. Sun et al reported a nanoclay/latex composite for improving barrier properties in coatings. See Sun et al., Comps Science Tech 67 (2007) 1823-1829. Consistent with conventional expectations and uses of nanoclays, Sun et al. teaches that the nanoclay must be fully exfoliated in the coating and that cationic surface modifications of the clay and/or use of dispersants was required. Specifically, Sun concludes that the barrier properties of the polymer/clay nano-composites strongly depended on the exfoliation degree of the nanoclay layers and that full exfoliation was necessary to get good barrier performance.

SUMMARY

[0005] In accordance with the disclosure, a process for preparing an aqueous barrier coating for a paper substrate can include admixing a dry powder of chemically unmodified sodium bentonite with a binder; and subjecting the admixture to high shear mixing under conditions such that the sodium bentonite disperses in the binder and at least a portion of the sodium bentonite maintains a tactoid form to thereby form the barrier coating. The binder can be water-based or water soluble.

[0006] In accordance with the disclosure, a process for preparing an aqueous barrier coating for a paper substrate can include admixing a dry powder of chemically unmodified sodium bentonite with a polymer latex binder; and subjecting the admixture to high shear mixing under conditions such that the sodium bentonite disperses in the polymer latex and at least a portion of the sodium bentonite maintains a tactoid form to thereby form the barrier coating.

[0007] The process in accordance with the disclosure can further include coating a paper substrate with the barrier coating.

[0008] In accordance with the disclosure, an aqueous barrier coating can include unmodified sodium bentonite dispersed in a binder, wherein the sodium bentonite is dispersed under high shear conditions such that the sodium bentonite is present in the form of tactoids.

[0009] The coating can be free of dispersant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a graph showing liquid water resistance of barrier coated papers by Water Cobb.

[0011] Figure 2 is a graph showing water vapor transmission rates of barrier coatings at tropical conditions 90% RH and 38 °C.

[0012] Figure 3 is a photograph of oil barrier property testing on a coating in accordance with the disclosure.

[0013] Figures 4A to 4D are particle size distribution graphs of sodium bentonite for use in coatings in accordance with the disclosure.

[0014] Figure 5 is a scanning electron microscopy image of a coating in accordance with the disclosure, showing tactoids of sodium bentonite being present in the coating.

[0015] Figure 6 is a graph showing water vapor transmission rate performance for coatings in accordance with the disclosure and conventional coatings formed as single layer coatings and tested under tropical conditions. [0016] Figure 7 is a graph showing water vapor transmission rate performance for coatings in accordance with the disclosure and conventional coatings formed as double layer coatings and tested under tropical conditions.

DETAILED DESCRIPTION

[0017] Water-based coatings in accordance with the disclosure include chemically unmodified sodium bentonite dispersed in a binder to advantageously provide a barrier coating that is aqueous based. It has been advantageously found that barrier coating properties can be achieved through the incorporation of dry sodium bentonite, with the sodium bentonite used as the raw material in the coating being its natural hydrophilic state and without exfoliation. Exfoliation of the sodium bentonite can occur under the high shear mixing conditions used in dispersing the sodium bentonite in the binder when preparing the coatings of the disclosure. Advantageously, no pre-processing of the sodium bentonite is needed before dispersing within the binder.

[0018] Coatings of the disclosure include a chemically unmodified sodium bentonite dispersed in a binder using high shear mixing conditions such that at least a portion of the sodium bentonite is present in the coating in the form of tactoids. Figure 5 is an SEM image of a coating in accordance with the disclosure, showing the presence of tactoids in the coating. The coatings of the disclosure can be aqueous-based barrier coatings.

[0019] Methods of making aqueous based barrier coatings in accordance with the disclosure can include admixing a dry powder of chemically unmodified sodium bentonite with a binder and subjecting the admixture to high-shear mixing under conditions such that the sodium bentonite disperses in the binder and at least a portion of the sodium bentonite maintains a tactoid form.

[0020] As used herein, “sodium bentonite” refers to bentonite having at least 50% sodium cation. The sodium bentonite used in the methods and coatings of the disclosure is chemically unmodified sodium bentonite and optionally can be mechanically unmodified. As used herein, “mechanically unmodified sodium bentonite” refers to sodium bentonite that may or may not have sodium ion exchange, but that has not been subject to mechanical shearing prior to incorporation into a coating, and that retains its natural hydrophilic state. As used herein, “chemically unmodified sodium bentonite” refers to a sodium bentonite that may or may not have sodium ion exchange, but not been subject to chemical modification, such as with organic modifiers. In some coatings of the disclosure, the sodium bentonite admixed with the binder is chemically and mechanically unmodified and optionally exfoliated during dispersion of the sodium bentonite in the binder thereby modifying the sodium bentonite present in the final coating by mechanical shearing. In some coatings of the disclosure, the sodium bentonite admixed with the binder is chemically unmodified. In some coatings of the disclosure, the sodium bentonite is chemically unmodified. Figures 4A to 4D show particle size distributions for unmodified sodium bentonites which can be used in the coatings and methods of the disclosure.

[0021] The sodium bentonite used in the coatings and methods of the disclosure can have less than about 12% moisture. The sodium bentonite is incorporated into the binder of the coatings in a dry particulate or powder state, without pre-swelling or exfoliation, and dispersed in the binder using high-shear mixing. High shear mixing conditions can be selected and tailored to provide for exfoliation of the sodium bentonite while dispersing the sodium bentonite in the binder. It has been found that use of sodium bentonite that has been exfoliated during dispersion results in high shape factor sodium bentonite being present in the final coating. High shaper factor as used herein refers to a shape factor above 4 as measure by the ratio of the Horiba dso measured with static light scattering to the Zave particles size measured with dynamic light scattering. It has advantageously been found that exfoliation during dispersion within the binder increases the shape factor of the sodium bentonite, while allowing a portion of the sodium bentonite to be maintained in tactoid form.

[0022] The sodium bentonite can have at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80% montmorillonite.

[0023] It has been observed that in the coatings of the disclosure, at least a portion of the sodium bentonite is maintained in a tactoid form. It was surprisingly found that improved barrier coating properties were achieved without full exfoliation of the sodium bentonite and, instead, with maintenance of at least a portion of the sodium bentonite in tactoid form. Figure 5 illustrates that tactoids of sodium bentonite remained in the coating. It has been observed that the use of the dry powder form of the sodium bentonite combined with the high-shear mixing used to disperse the sodium bentonite in the binder allows the sodium bentonite to be incorporated into the coatings such that tactoids are present and dispersed in the binder.

[0024] The coatings of the disclosure have been observed to achieve improved barrier properties, as compared to conventional talc and kaolin containing coatings. The coatings of the disclosure can achieve comparable, if not improved, barrier coating properties, as compared to talc or kaolin containing coatings with significantly reduced loading levels of the sodium bentonite. Additionally, the coatings of the disclosure can be formed without the need for added dispersant.

[0025] The sodium bentonite is dispersed in the binder using high shear mixing conditions that achieve a coating in which at least a portion of the sodium bentonite is present in tactoid form. Such high shear mixing can be achieved, for example, by mixing with a tip speed of about 655 ft/min to about 3300 ft/min (200 m/min to 1010 m/min). High shear mixing can be performed using any known methods or combinations of methods, including, but not limited to, using a Cowles mixer, sonication, and rotor-stator mixing. High shear mixing can include, for example, sonication for at least 1 min. Sonication times can be about 1 min to about 40 min, about 10 min to about 30 min, or about 5 min to about 25 min. Other suitable times include about 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13,14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, 35, 36, 37, 38, 39, and 40 mins and values therebetween and ranges defined by those values. High shear can be performed for example under conditions to reduce or protect against overheating. For example, sonication can be performed using a jacketed vessel with water circulation and a pulsing method to prevent overheating.

[0026] The high shear mixing process can result in exfoliation of the sodium bentonite during dispersion within the binder, while also allowing tactoid form of the sodium bentonite to remain present in the coating. The sodium bentonite within the coating can, as a result, have increased shape factor as compared to the starting material before dispersion. The sodium bentonite after dispersion can have a shape factor, for example, of at above 4. Shape factor as referenced herein is a ratio of the Horiba dso measurement using static light scattering to the Zave size as measured by dynamic light scattering. It has been observed that sodium bentonite having a shape factor above 4 can be obtained by high shear mixing with the binder, such as by sonication for 5 min or more or using a roto-stator type shearing device.

[0027] The coating can include any suitable aqueous binder . For example, the binder can be an aqueous polymer latex. For example, non-latex binders can also be used. For example, binders can be one or more of an anionic polymer latex, such as Styrene butadiene, polyolefin, styrene acrylates, ethylene acrylic acid copolymers, ethylene vinyl alcohol copolymers, polyurethanes, epoxy resins, polyesters, polyolefins, carboxylated styrene-butadiene latexes, carboxylated styrene acrylate latexes; polyvinylidene chlorides; polyvinyl chlorides; starches; styrene-acrylic copolymers; styrene-maleic anhydrides; polyvinyl alcohols; polyvinyl acetates; carboxymethyl celluloses; silicones; waxes; neoprene; polyhydroxy ethers; lacquers; polylactic acids; copolymers of polylactic acid; polymers containing fluorine atoms; copolymers of acrylonitrile; and carboxylated styrene-butadiene acrylonitrile copolymers.

[0028] The sodium bentonite can be added to the binder in amounts of about 1wt% to about 20wt%, about 1 wt% to about 5 wt%, about 3 wt% to about 15 wt%, or about 10 wt% to about 20 wt%, based on a total weight of the coating on a dry weight basis. Other suitable amounts include, based on a total weight of the coating on a dry weight basis, of about 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, and 20 wt%, and any values therebetween, and any ranges defined by such values. Unless specified otherwise, reference to a percent (%) of sodium bentonite in the coatings of the disclosure refers to a weight percent based on a total weight of the coating on a dry weight basis. Loading levels of sodium bentonite can be significantly lower than required with talc or kaolin in conventional coatings, while maintaining or even exhibiting improved barrier properties. For example, the sodium bentonite loading in the coatings of the disclosure can be 2 to 60 times lower than required for other platy minerals- based barrier coatings, such as talc or kaolin coatings.

[0029] The coatings of the disclosure are for use in coating porous substrate, such as paper and paperboard. For suitability in such applications, the coatings of the disclosure can have a solids content of about 5% to about 55%, about 15% to about 55%, about 20% to about 40%, about 30% to about 50%, or about 10% to about 25%. Other suitable solids content includes about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55% and any values therebetween and ranges defined by such values.

[0030] Coatings prepared by the dry addition of the sodium bentonite can advantageously have solids contents that are equal to or greater than the solids content of the binder. In contrast, coatings prepare with wet addition of the sodium bentonite have lower solids content than the binder as a result of the liquid present in the slurry of the sodium bentonite.

[0031] The coatings of the disclosure can be coated by conventional paper coating methods, such as drawdown coating, blade coating, curtain coating, rotogravure coating (gravure coating), machine roll-to-roll coating, size press, reverse roll coating, hot melt coating flexbar coating/Flexo coating, film transfer coating, die-slot coating, wet film applicator coating, coating film casting using filtration and evaporation, dip coater, extrusion coating. The substrate can be coated, for example, with any desired coating weight and/or number of coating layers. For example, the coatings can be coated with a coating weight of about 1 g/m² to about 35 g/m², about 1 g/m² to about 25 g/m², about 5 g/m² toa bout 15 g/m². For example, the coating weight can be about 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, or 35 g/m² and any values therebetween or ranges defined by such values.

[0032] The coatings of the disclosure can be a single layer coating and have a coat weight of less than 10 g/m², for example, about 2 g/m² to less than 10 g/m², or about 4 g/m² to about 8 g/m². Other suitable single-layer coat weights can include about 1 , 2, 3, 4, 5, 6, 7, 8, and 9 g/m² and any values therebetween and ranges defined by such values. It has been advantageously observed that the beneficial effects of the coatings of the disclosure, including sodium bentonite as opposed to kaolin or talc, can allow for single layer coatings to be used while achieving desired barrier properties. This is advantageous as double or multilayer coatings may not be practical in many applications, particularly when using multifunctional layers/coatings. At singlelayer coat weights, the coatings of the disclosure demonstrated a 31 % improvement in barrier properties with a 3% dry addition of sodium bentonite in the coating as compared to pure latex. Coatings of the disclosure having 3% dry addition of the sodium bentonite also demonstrated a 39% improvement over a comparative coating formulation containing 40% loading of competitive product Barrisurf™ LX kaolin clay. Dry addition of the sodium bentonite in the coating demonstrated a more than 30% improvement in barrier properties as compared to wet addition.

[0033] The porous substrates for use with coatings of the disclosure can generally include any paper or paperboard products for which a barrier coating is desired. Paper substrates onto which the coatings of the disclosure can be coated can include, but are not limited to, solid bleached sulfate (SBS) paper, folding box board (FBB), white top liner (WTL), low basis weight papers such as fast-food wrappers, copy paper, coated and uncoated paper and paperboard, coated unbleached kraft (CUK) paper, and coated recycled paperboard.

[0034] Coatings of the disclosure can be tailored to provide water vapor transmission rates or other barrier properties based on intended application of the paper substrate. For example, the barrier coating can provide a <40 g/m²/d water vapor transmission rate (WVTR) at tropical conditions (38°C and 90% RH), and/or water COBB 60 mins <1 g/m². It is generally understood in the art that WVTR at tropical conditions for ultra-high barrier applications is <10 g/m²/d, high barrier applications is <100 g/m²/d, medium barrier applications is 100-400 g/m²/d, and low barrier >400 g/m²/d. Barrier coatings in accordance with the disclosure can be tailored for any of the foregoing applications.

EXAMPLES Example 1 : Dry Addition vs Wet Slurry Addition

[0035] Three different methods were used to create the coating formulations. In the first method, which is in accordance with the disclosure, sodium bentonite was added to the latex as a dry powder, which is referred to as “dry addition” below. A comparative second method was used in which sodium bentonite was made into a slurry in water before being added to the latex, which is referred to as “No Acumer”. In a comparative third example, a dispersant chemical was added to water first, then the dry sodium bentonite powder, and finally this pre-dispersed sodium bentonite slurry was added to the latex, which is referred to as “0.08% Acumer”.

Dry addition: 5% dry addition of Sodium Bentonite

[0036] The aqueous barrier coating in accordance with the disclosure was prepared as follows: In a 1000 ml steel container, 370 g of Tykote® 1004 Styrene-butadiene latex at 52% solids was weighed. To that, 10.7 g of sodium bentonite at 10% moisture and 27.7 g of water were added. The resulting slurry was mixed thoroughly using a Premier model 2500HV Cowles- type mixer with a 2.5-inch (6.35 cm) diameter blade at a tip speed of 2945 ft/min for 30 mins. Using the oven drying method, the final solid content of the formulation was determined to be 45%.

No Acumer: 5% wet addition of Sodium Bentonite without dispersant

[0037] A slurry of sodium bentonite was created in water by adding 11.1 g of dry sodium bentonite at 10% moisture to 200 g of water. Then using a Premier model 2500HV Cowles-type mixer with a 2.5-inch (6.35 cm) diameter blade, the suspension was stirred at a tip speed of 2945 ft/min for 15 minutes. Using the oven drying method the solid content of this water-based sodium bentonite slurry was determined to be 5%. The barrier coating formulation was generated in a 1000 ml steel container by mixing 370 g of Tykote® 1004 Styrene-butadiene latex at 52% solids content and 178.1 g of the prepared sodium bentonite slurry at 5% solid content. Then the mixture was stirred at a tip speed of 2945 ft/min for 15 mins using the same Cowles-type mixer. Using the oven drying method, the final solid content of the formulation was determined to be 45%.

0.08% Acumer: 5% wet addition of Sodium Bentonite with dispersant

[0038] A slurry of sodium bentonite was created in 300 gm of water by adding 0.0608 g of ACUMER 9300 at 45% solids followed by 38 g of powder at 10% moisture. Stirred the mixture for 15 mins using a Premier model 2500HV Cowles-type mixer with a 2.5-inch (6.35 cm) diameter blade at a tip speed of 2945 ft/min. Using the oven drying method, the final solid content of the slurry was determined to be 11%. To make barrier formulation, 70.4 g of slurry at 1 1% solids was added to 304 g of Tykote® 1004 Styrene-butadiene latex at 52% solids. Stirred the resulting barrier formulation for 15 mins at a tip speed of 2945 ft/min using the same Cowles-type mixer.

Coating

[0039] A drawdown coating method was used to make barrier coatings on 350 g/m² SBS (solid bleached sulfate) board. Each paper board has double-layer coatings of the same formulation and Rod numbers from 4-13 were used to make different coat weights. Two coat weights were produced with average coat weights of 13-15 g/m² and 23-25 g/m². Paper coated with barrier formulation was then tested for liquid water resistance (water Cobb) by TAPPI 441 , water vapor transmission rate (WVTR) by TAPPI T 464, and Oil and grease barrier (OGR) by Oil cobb. The oil cobb method is modified TAPPI 441 method to test OGR. In this procedure, the surface of the barrier-coated papers was covered with oil-saturated blotter paper for 30 minutes, after which the weight change caused by oil absorption was measured to determine the oil Cobb number. The results of the barrier coatings are shown in Figures 1 , 2 and 3

Example 2: Determining Shape Factor and Mixing Conditions Effect on Shape Factor

[0040] Raw, chemically unmodified sodium bentonite having a moisture content of 8% and a dry particle size of a minimum 99.00% finer than 200 mesh (74 microns) and wet particle size of a minimum of 99.75% finer than 200 mesh (74 microns). The particle size of dispersed sodium bentonite was determined using the Horiba LA950 static light scattering instrument. A 1 .0% bentonite suspension was created by adding 0.5 g of bentonite powder to 50 ml of a D.L water solution with a 0.005% DAXAD® 30 dispersant concentration. The resulting suspension was sonicated using 0.5-inch horn at setting 1 .5, for 8 minutes to disperse it. The dispersed suspension was added dropwise to the Horiba LA950 cell to achieve a red laser % transmittance of 89-91%, and the particle size was determined using standard settings and refractive indices for calcium carbonate. This method measures a particle size related to the larger, basal plane dimension of the bentonite.

[0041] Undispersed sodium bentonite samples were also tested. A water suspension of sodium bentonite at any solids content from about 1 to 10% can be prepared and varying degrees of shear may be applied using any type of mixing or sonication equipment. This suspension is added to the Horiba LA950 cell and particle size measured as described above. Table 1

[0042] The particle size of sodium bentonite was also determined by the dynamic light scattering (DLS) technique using a Malven Zetasizer 1000 instrument. Either a dispersed or undispersed suspension can be used. The suspension was diluted to 0.1% solids using DI water. The diluted suspension was transferred to an instrument cuvette (1 cm x 1 cm plastic with all faces transparent), and the cuvette placed in the instrument measurement chamber. Standard software settings were used to measure size using water as a solvent and refractive index of sodium bentonite (1 .503). The resulting Zave value (the hydrodynamic diameter) is reported. This instrument is designed to measure nanoparticles and hence we used this technique to provide a value related to, though much larger than the smaller thickness dimension of the sodium bentonite plates. Measured Zave values of sodium bentonite varied from 500 to 1500 nm.

[0043] It was determined that shape factor (SF) of bentonite could be calculated as a ratio of two particle size methods - using the ratio of diameters from static light scattering (Horiba LA- 950) to diameters from dynamic light scattering (DLS). With bentonite it was observed that sedimentation could not be used due to it extremely long settling time. The shape factor (SF) was calculated by taking the ratio of median particle size (d50) determined by Horiba light scattering to the Zave particle size determined using Malvern Zetasizer 1000 DLS in microns. The resulting SF values for sodium bentonite may vary from 3.5 to 7, with higher values indicating a higher degree of delamination and higher particle aspect ratio.

[0044] Two samples with high and low SF were made as follows:

[0045] Low SF: A 5% solids sodium bentonite slurry in DI water was made as in the above "No Acumer" example, except the volume was 500 mL and high-speed mixing with the Cowles was only at 2000 rpm for 5 minutes.

[0046] High SF: Another 500 mL of 5% solids starting slurry was sonicated for a total of 20 minutes in a water-cooled beaker with constant mixing with a propeller stirrer. To avoid heating, sonication was turned on and off in 10 seconds on/20 seconds off cycles for a total of 20 minutes on time.

Table 2

[0047] This demonstrates that the mixing method used to disperse the sodium bentonite within the binder can be selected to produce a final composition with high or low shape factor sodium bentonite present therein. High shear mixing methods, such as sonication, was observed to result in high shape factor materials.

Example 3: Effect of Shape Factor and Dry Addition on Barrier Performance

[0048] Coatings in accordance with the disclosure were prepared having high and low shaped factor sodium bentonite, as well as with dry and wet addition of the sodium bentonite. The chemically unmodified sodium bentonite as described in Example 2 was used as the starting material in the coatings of the disclosure. The coatings in accordance with the disclosure each included 3% sodium bentonite on a dry weight basis. Barrier performance of these coatings were compared to each other, as well as to a coating of Tykote® 1004 (pure latex) and a Barrisurf™ LX (kaolin) containing coating.

[0049] A coating in accordance with the disclosure having dry addition of 3% sodium bentonite with a low shape factor was prepared by combining 150 g of Tykote® 1004 with 2.6 g of dry sodium bentonite powder. To create the low shape factor formulation, this mixture was stirred at 2000 RPM for 5 minutes using a 2.5-inch diameter Cowles blade. The formulation was diluted to 47% by adding DI water. This formulation was kept overnight then viscosity, pH, and solids were measured.

[0050] A coating in accordance with the disclosure having dry addition of 3% sodium bentonite with a high shape factor was prepared by combining 150 g of Tykote® 1004 with 2.6 g of dry sodium bentonite powder. For the high shape factor formulation, this mixture was stirred at 2000 RPM for 5 minutes, followed by sonication for 20 minutes with a pulsing function, alternating between 30 seconds on and 30 seconds off. The pulsing function was used to prevent overheating. The formulation was diluted to 47% by adding DI water. This formulation was kept overnight then viscosity, pH, and solids were measured.

[0051] A coating in accordance with the disclosure having wet addition of 3% sodium bentonite with a low shape factor was prepared by first forming a sodium bentonite slurry. The slurry was prepared as described in Example 3 for preparing a low shape factor sodium bentonite slurry. In particular, 25 g of sodium bentonite dry powder was mixed with 475 g of water, sheared at 2000 RPM for 5 minutes using 2.5-inch Cowles blade to achieve a final bentonite slurry solids concentration of 5%. Subsequently, 150 g of Tykote® 1004 were combined with 48.2 g of the wet 5% sodium bentonite slurry. The Tykote® 1004 latex and sodium bentonite slurry were then mixed at 800 RPM for 15 minutes using a propeller-type overhead mixer. This formulation was kept overnight then viscosity, pH, and solids were measured.

[0052] A coating in accordance with the disclosure having wet addition of 3% sodium bentonite with a high shape factor was prepared by first forming a sodium bentonite slurry. The slurry was prepared as described in Example 3 for preparing a high shape factor sodium bentonite slurry. In particular, 25 g of sodium bentonite dry powder was mixed with 475 g of water, sheared at 2000 RPM for 5 minutes using 2.5-inch Cowles blade. Further to achieve a high shape factor, the same formulation was sonicated for 20 minutes with a pulsing function, alternating between 10 seconds on and 20 seconds off. The pulsing function was used to prevent overheating. The final solids of sodium bentonite slurry was 5%. 150 g of Tykote® 1004 were combined with 48.2 g of the wet 5% sodium bentonite slurry. The Tykote® 1004 latex and sodium bentonite slurry were then mixed at 800 RPM for 15 minutes using a propeller-type overhead mixer. This formulation was kept overnight then viscosity, pH, and solids were measured

[0053] The Barrisurf™ LX (kaolin) comparative example coating was prepared as a 40% Barrisurf™ LX - Tykote® 1004 formulation. 150 g of Tykote® 1004 were combined with 84.4 g of Barrisurf™ LX slurry. Barrisurf™ LX slurry had a solid content of 61 .6%. This mixture was then blended at 800 RPM for 15 minutes using a propeller-type overhead mixer. This formulation was kept overnight then viscosity, pH, and solids were measured. [0054] For each of the coating formulations, the coatings were applied to 175 g/m² white top liner using an automated draw-down coater at a speed of 40 m/min. The coatings underwent drying in the oven at 103°C for 10 minutes, followed by conditioning in the CTH room for 24 hours. Both single and double layers of coating were applied. For the single-layer coating, the targeted coat weight was 5.8 ± 0.4 g/m², while for the double-layer coating, the targeted coat weight was 10.8 ± 0.3 g/m². Subsequently, circles with a diameter of 7.62 cm were cut and utilized for WVTR testing under tropical conditions (38 °C ,90% RH).

[0055] Table 3 provides the viscosity, pH, and solids content of the coating formulations prepared.

Table 3

*3% sodium bentonite refers to 3 wt% sodium bentonite based on the total weight of the coating on a dry weight basis.

[0056] Water vapor transmission rate was tested by (WVTR) by TAPPI T 464 under tropical conditions (38 °C ,90% RH). Referring to Figure 6, single layer coatings of the disclosure demonstrated a significant improvement in water vapor transmission rate properties as compared to the Tykote® 1004 only coating and the Barrisurf™ LX (kaolin) containing coating. Additionally, an improvement in water vapor transmission rate performance was also observed for the dry addition of the sodium bentonite in the coatings of the disclosure as compared to the wet addition. Finally, improvement in water vapor transmission rate performance was also observed when using process of formulating the coating that results in a high shape factor sodium bentonite being present in the coating. In particular, the following quantitative improvements in performance were observed:

[0057] A 31% reduction in WVTR for 3% dry addition high aspect ratio sodium bentonite containing formulation compared to pure latex.

[0058] A 36% reduction in WVTR for high aspect ratio dry addition sodium bentonite containing formulation compared to high aspect ratio wet addition sodium bentonite containing formulation.

[0059] A 32% reduction in WVTR for low aspect ratio dry addition sodium bentonite containing formulation compared to low aspect ratio wet addition sodium bentonite containing formulation.

[0060] A 39% reduction in WVTR for 3% dry addition high aspect ratio sodium bentonite containing formulation compared to Barrisurf™ LX

[0061] Referring to Figure 7 the significance of the reduction in WVTR between the coatings of the disclosure and the Tykote® 1004 and Barrisurf™ (kaolin) comparative coatings is less pronounced when using a double layer coating. A reduction of the water vapor transmission rates is still observed, particularly with respect to the dry addition of the sodium bentonite. Further, it was surprisingly and beneficially observed that coatings in accordance with the disclosure with dry addition of the sodium bentonite with a high shape factor could provide similar or even improved water vapor transmission rate performance when formed as a singlelayer coating as compared to the double layer coatings of the Tykote® 1004 and Barrisurf™ coatings. The coatings of the disclosure can, therefore, avoid the need for double layer coatings, which can be complicated and impractical in some applications, while maintaining at least the same level of barrier performance as a double layer coating of conventional kaolin coatings.

[0062] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the disclosure may be apparent to those having ordinary skill in the art. [0063] All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In the case of conflict, the present description, including definitions, will control.

[0064] Throughout the specification, where the compounds, compositions, methods, and/or processes are described as including components, steps, or materials, it is contemplated that the compounds, compositions, methods, and/or processes can also comprise, consist essentially of, or consist of any combination of the recited components or materials, unless described otherwise. Component concentrations can be expressed in terms of weight concentrations, unless specifically indicated otherwise. Combinations of components are contemplated to include homogeneous and/or heterogeneous mixtures, as would be understood by a person of ordinary skill in the art in view of the foregoing disclosure.

Claims

What is claimed is:

1 . A process for preparing an aqueous barrier coating for a paper substrate, comprising: admixing a dry powder of chemically unmodified sodium bentonite with a binder; and subjecting the admixture to high shear mixing under conditions such that the sodium bentonite disperses in the binder and at least a portion of the sodium bentonite maintains a tactoid form to thereby form the barrier coating, wherein the binder is water-based or water soluble.

2. The process of claim 1 , wherein the binder comprises a polymer latex.

3. The process of claim 2, wherein the polymer latex is an anionic polymer latex.

4. The process of claim 3, wherein the anionic polymer latex comprises one or more of styrene butadiene, polyolefin, styrene acrylates, ethylene acrylic acid copolymers, ethylene vinyl alcohol copolymers, polyurethanes, epoxy resins, polyesters, polyolefins, and carboxylated styrene-butadiene.

5. The process of any one of the preceding claims, wherein the binder comprises one or more of carboxylated styrene acrylate latexes, polyvinylidene chlorides, polyvinyl chlorides, starches, styrene-acrylic copolymers, styrene-maleic anhydrides, polyvinyl alcohols, polyvinyl acetates, carboxymethyl celluloses, silicones, waxes, neoprene, polyhydroxy ethers, lacquers, polylactic acids, copolymers of polylactic acid, polymers containing fluorine atoms, copolymers of acrylonitrile, and carboxylated styrene-butadiene acrylonitrile copolymers.

6. A process for preparing an aqueous barrier coating for a paper substrate, comprising: admixing a dry powder of chemically unmodified sodium bentonite with an aqueous polymer latex binder; and subjecting the admixture to high shear mixing under conditions such that the sodium bentonite disperses in the polymer latex and at least a portion of the sodium bentonite maintains a tactoid form to thereby form the barrier coating.

7. The process of claim 6, wherein the polymer latex is an anionic polymer latex.

8. The process of claim 7, wherein the anionic polymer latex comprises one or more of styrene butadiene, polyolefin, styrene acrylates, ethylene acrylic acid copolymers, ethylene vinyl alcohol copolymers, polyurethanes, epoxy resins, polyesters, polyolefins, and carboxylated styrene-butadiene.

9. The process of any one of the preceding claims, wherein the aqueous barrier coating has a solids content of about 5% to about 55%.

10. The process of any one of the preceding claims, wherein high shear mixing is performed at a tip speed of about 655 ft/min to about 3300 ft/min (200 m/min to 1010 m/min).

1 1 . The process of any one of the preceding claims, wherein the dry powder of chemically unmodified sodium bentonite comprises less than 12% moisture.

12. The process of any one of the preceding claims, wherein high shear mixing is performed using a Cowles mixer, a sonicator, or a roto-stator mixer.

13. The process of claim 12, wherein high shear mixing is performed using a sonicator.

14. The process of claim 13, comprising sonicating for about 1 min to about 40 min.

15. The process of any one of the preceding claims, wherein the high shear mixing is performed under conditions to exfoliate the sodium bentonite while dispersing the sodium bentonite in the binder such that the sodium bentonite present in the coating has a shape factor of above 4 as measured by a ratio of the Horiba dso measured with static light scattering to the Zave particle size measured with dynamic light scattering.

16. The process of any one of the preceding claims, wherein the dry powder of chemically unmodified sodium bentonite is added to the binder in an amount of about 1wt% to about 20wt% based on the total weight of the admixture on a dry weight basis.

17. The process of any one of the preceding claims, wherein the admixture is free of dispersants.

18. The process of any one of the preceding claims, wherein the chemically unmodified sodium bentonite is chemically and mechanically unmodified sodium bentonite

19. A process for preparing a barrier coating for a paper substrate, comprising: admixing a dry powder of chemically unmodified sodium bentonite with a binder; subjecting the admixture to high shear mixing under conditions such that the sodium bentonite disperses in the binder and at least a portion of the sodium bentonite maintains a tactoid form to thereby form the barrier coating; and coating the paper substrate with the barrier coating with a coating weight of about 1 .5 g/m² to about 25 g/m², wherein the binder is water-based or water soluble.

20. The process of claim 19, wherein the coating weight is less than 10 g/m².

21 . The process of claim 19 or 20, wherein the paper substrate is solid bleached sulfate (SBS) paper, folding box board (FBB), White top liner (WTL), low basis weight paper wrappers, copy paper, coated or uncoated paper and paper board, Coated Unbleached Kraft (CUK), Coated Recycled Paperboard.

22. The process of any one of claims 19 to 21 , wherein the binder comprises a polymer latex.

23. The process of claim 22, wherein the polymer latex is an anionic polymer latex.

24. The process of claim 23, wherein the anionic polymer latex comprises one or more of styrene butadiene, polyolefin, styrene acrylates, ethylene acrylic acid copolymers, ethylene vinyl alcohol copolymers, polyurethanes, epoxy resins, polyesters, polyolefins, and carboxylated styrene-butadiene.

25. The process of any one claims 19 to 24, wherein the binder comprises one or more of carboxylated styrene acrylate latexes, polyvinylidene chlorides, polyvinyl chlorides, starches, styrene-acrylic copolymers, styrene-maleic anhydrides, polyvinyl alcohols, polyvinyl acetates, carboxymethyl celluloses, silicones, waxes, neoprene, polyhydroxy ethers, lacquers, polylactic acids, copolymers of polylactic acid, polymers containing fluorine atoms, copolymers of acrylonitrile, and carboxylated styrene-butadiene acrylonitrile copolymers.

26. The process of any one of claims 19 to 25, wherein the aqueous barrier coating has a solids content of about 5% to about 55%.

27. The process of any one of claims 19 to 26, wherein high shear mixing is performed at a tip speed of about 655 ft/min to about 3300 ft/min (200 m/min to 1010 m/min).

28. The method of any one of claims 19 to 27, wherein the dry powder of chemically unmodified sodium bentonite comprises less than 12% moisture.

29. The process of any one of claims 19 to 28, wherein high shear mixing is performed using a Cowles mixer, a sonicator, or a roto-stator mixer.

30. The process of claim 29, wherein high shear mixing is performed using a sonicator.

31 . The process of claim 30, comprising sonicating for about 1 min to about 40 min.

32. The process of any one of claims 19 to 31 , wherein the high shear mixing is performed under conditions to exfoliate the sodium bentonite while dispersing the sodium bentonite in the binder such that the sodium bentonite present in the coating has a shape factor of above 4 as measured by a ratio of the Horiba dso measured with static light scattering to the Zave particle size measured with dynamic light scattering.

33. The process of any one of claims 19 to 32, wherein the dry powder of unmodified sodium bentonite is added to the binder an amount of about 1wt% to about 20wt% based on the total weight of the admixture on a dry weight basis.

34. The process of any one of claims 19 to 33, wherein the admixture is free of dispersants.

35. The process of any one of claims 19 to 34, wherein the chemically unmodified sodium bentonite is chemically and mechanically unmodified sodium bentonite.

36. An aqueous barrier coating, comprising: chemically unmodified sodium bentonite dispersed in a binder, wherein the sodium bentonite is dispersed under high shear conditions such that at least a portion of the sodium bentonite is present in the form of tactoids, wherein the binder is water-based or water-soluble.

37. The coating of claim 36, wherein the sodium bentonite has a shape factor of above 4 as measured by a ratio of the Horiba dso measured with static light scattering to the Zave particle size measured with dynamic light scattering.

38. The coating of claim 36 or 37 , wherein the binder comprises a polymer latex.

39. The coating of claim 38, wherein the polymer latex is an anionic polymer latex.

40. The coating of claim 39, wherein the anionic polymer latex comprises one or more of styrene butadiene, polyolefin, styrene acrylates, ethylene acrylic acid copolymers, ethylene vinyl alcohol copolymers, polyurethanes, epoxy resins, polyesters, polyolefins, and carboxylated styrene-butadiene.

41 . The coating of any one claims 36 to 40, wherein the binder comprises one or more of carboxylated styrene acrylate latexes, polyvinylidene chlorides, polyvinyl chlorides, starches, styrene-acrylic copolymers, styrene-maleic anhydrides, polyvinyl alcohols, polyvinyl acetates, carboxymethyl celluloses, silicones, waxes, neoprene, polyhydroxy ethers, lacquers, polylactic acids, copolymers of polylactic acid, polymers containing fluorine atoms, copolymers of acrylonitrile, and carboxylated styrene-butadiene acrylonitrile copolymers.

42. The coating of any one of claims 36 to 41 , wherein the aqueous barrier coating has a solids content of about 5% to about 55%.

43. The coating of any one of claims 36 to 42, wherein the sodium bentonite present in the coating in an amount of about 1wt% to about 20wt% based on the total weight of the coating on a dry weight basis.

44. The coating of any one of claims 36 to 43, wherein the coating is free of dispersants.

45. The coating of any one of claims 36 to 44, wherein the coating has a solids content that is equal to or greater than the solids content of the binder.

46. A barrier coated paper substrate comprising a paper substrate coated with the coating of any one of claims 36 to 45.

47. The barrier coated paper substrate of claim 46, wherein the paper substrate is solid bleached sulfate (SBS) paper, folding box board (FBB), White top liner (WTL), low basis weight paper wrapper, copy paper, coated or uncoated paper and paper board, Coated Unbleached Kraft (CUK), Coated Recycled Paperboard.

48. The barrier coated paper substrate of claim 46 or 47, wherein the coating has a coat weight of less than 10 g/m² and a water transmission rate of less than 400 g/m²/d.