Sodium bentonite-containing aqueous barrier coating, and method for producing the same.

Abstract

Aqueous barrier coatings for paper products may contain chemically unmodified sodium bentonite dispersed in a binder, which is dispersed under high shear conditions such that the sodium bentonite exists in a tactoid form.

Description

[Technical Field]

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

[0002] This disclosure relates to aqueous barrier coatings and methods for producing aqueous barrier coatings containing sodium bentonite. [Background technology]

[0003] Paper-based packaging materials are used worldwide. Currently, barrier coatings for paper and packaging applications rely primarily on petroleum-based materials and synthetic polymers such as waxes, polyvinyl alcohol, and polyolefins (Gironi & Piemonte, 2011). These materials are cost-effective, readily available, and provide significant barriers against water vapor, oil / grease, and oxygen for packaging applications. However, these materials have major drawbacks, such as the poor recyclability and non-biodegradability of coated paper, which can have adverse environmental impacts. Ideal packaging materials in the context of food packaging need to have good barriers against oxygen, water vapor, and oil / grease while being bio-based, recyclable, compostable, and / or derived from otherwise environmentally friendly sources. The need for barrier properties can vary depending on the coating application and the end-use of the paper product.

[0004] Nanoclay is used in a variety of applications and is generally found to be advantageous due to its ability to swell in water. Sun et al. reported on nanoclay / latex composites for improving barrier properties in coatings. See Sun et al., Comps Science Tech 67(2007)1823-1829. Consistent with conventional expectations and intended uses of nanoclay, Sun et al. teach that the nanoclay must be completely exfoliated in the coating and that cationic surface modification of the clay and / or the use of dispersants are necessary. Specifically, Sun concludes that the barrier properties of polymer / clay nanocomposites are strongly dependent on the degree of exfoliation of the nanoclay layer, and that complete exfoliation is necessary to obtain good barrier performance. [Overview of the project]

[0005] According to this disclosure, a process for preparing an aqueous barrier coating for a paper substrate may include mixing a dry powder of chemically unmodified sodium bentonite with a binder, and subjecting the mixture to high-shear mixing under conditions such that the sodium bentonite is dispersed in the binder and at least a portion of the sodium bentonite maintains a tactoid shape, thereby forming a barrier coating. The binder may be aqueous or water-soluble.

[0006] According to this disclosure, a process for preparing an aqueous barrier coating for a paper substrate may include mixing a dry powder of chemically unmodified sodium bentonite with a polymer latex binder, and subjecting the mixture to high-shear mixing under conditions such that the sodium bentonite is dispersed in the polymer latex and at least a portion of the sodium bentonite maintains a tactoid shape, thereby forming a barrier coating.

[0007] The process described herein may further include coating a paper substrate with a barrier coating.

[0008] According to this disclosure, the aqueous barrier coating may contain unmodified sodium bentonite dispersed in a binder, the sodium bentonite being dispersed under high shear conditions such that the sodium bentonite exists in a tactoid form.

[0009] The coating may not contain a dispersant. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the liquid water resistance of barrier-coated paper using WaterCobb. [Figure 2] This graph shows the water vapor transmission rate of a barrier coating under tropical conditions of 90% RH and 38°C. [Figure 3] This is a photograph of the oil barrier properties test on the coating according to this disclosure. [Figure 4A-4D] This is a particle size distribution graph of sodium bentonite for use in coatings according to this disclosure. [Figure 5] This is a scanning electron microscope image of the coating according to this disclosure, showing the sodium bentonite tactoid present in the coating. [Figure 6] This graph shows the water vapor transmission performance of the coating described herein and a conventional coating formed as a single layer, tested under tropical conditions. [Figure 7] This graph shows the water vapor transmission performance of the coating described herein and a conventional coating formed as a two-layer coating, tested under tropical conditions. [Modes for carrying out the invention]

[0011] The aqueous coating according to the present disclosure includes chemically unmodified sodium bentonite dispersed in a binder in order to advantageously provide a barrier coating that is water-based. The barrier coating properties can be achieved through incorporating dry sodium bentonite, which is used as a raw material in the coating and has been found to be advantageously in its natural hydrophilic state and without exfoliation. Exfoliation of sodium bentonite can occur under the high shear mixing conditions used to disperse the sodium bentonite in the binder when preparing the coatings of the present disclosure. Advantageously, no pretreatment of the sodium bentonite is necessary prior to dispersion within the binder.

[0012] The coating of the present disclosure includes 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 a tactoid shape. FIG. 5 is a SEM image of a coating according to the present disclosure, showing the presence of tactoids in the coating. The coating of the present disclosure can be a water-based barrier coating.

[0013] A method of making a water-based barrier coating according to the present 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 is dispersed in the binder and at least a portion of the sodium bentonite maintains a tactoid shape.

[0014] As used herein, “sodium bentonite” refers to bentonite having at least 50% sodium cations. The sodium bentonite used in the methods and coatings of this disclosure is chemically unmodified sodium bentonite and may optionally be mechanically unmodified. As used herein, “mechanically unmodified sodium bentonite” refers to sodium bentonite that may or may not have sodium ion exchange but has not been subjected to mechanical shearing before being incorporated into the coating and retains its natural hydrophilic state. As used herein, “chemically unmodified sodium bentonite” refers to sodium bentonite that may or may not have sodium ion exchange but has not been subjected to chemical modification, such as the use of organic modifiers. In some coatings of this disclosure, the sodium bentonite mixed with the binder is chemically and mechanically unmodified and optionally exfoliated during the dispersion of sodium bentonite in the binder, thereby modifying the sodium bentonite present in the final coating by mechanical shearing. In some coatings of this disclosure, the sodium bentonite mixed with the binder is chemically unmodified. In some of the coatings of this disclosure, the sodium bentonite is chemically unmodified. Figures 4A to 4D show the particle size distribution of unmodified sodium bentonite that can be used in the coatings and methods of this disclosure.

[0015] The sodium bentonite used in the coatings and methods of the present disclosure can have less than about 12% moisture. The sodium bentonite is incorporated into the coating binder in dry particle or powder form without prior swelling or delamination and dispersed in the binder using high-shear mixing. High-shear mixing conditions can be selected and adjusted to provide delamination of the sodium bentonite while dispersing the sodium bentonite in the binder. By using delaminated sodium bentonite during dispersion, it is brought about that high aspect ratio sodium bentonite is present in the final coating. As used herein, the high aspect ratio refers to an aspect ratio greater than 4, measured by the ratio of Horiba d

[0018] , measured by static light scattering to the Zave particle size measured by dynamic light scattering. Delamination during dispersion in the binder has been found to be advantageous in increasing the aspect ratio of the sodium bentonite while allowing a portion of the sodium bentonite to remain in tactoid form.

[0016] 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.

[0017] In the coatings of the present disclosure, it has been observed that at least a portion of the sodium bentonite remains in tactoid form. Surprisingly, it has been found that improved barrier coating properties are achieved not by complete delamination of the sodium bentonite, but instead by maintaining at least a portion of the tactoid form of the sodium bentonite. Figure 5 illustrates that a tactoid of sodium bentonite remains in the coating. It has been observed that by using the dry powder form of sodium bentonite in combination with high-shear mixing used to disperse the sodium bentonite in the binder, it is possible to incorporate the sodium bentonite into the coating such that tactoids are present and disperse in the binder.

[0018] The coatings of this disclosure have been observed to achieve improved barrier properties compared to conventional talc and kaolin-containing coatings. The coatings of this disclosure can achieve comparable barrier coating properties even when the sodium bentonite packing level is significantly reduced compared to talc or kaolin-containing coatings, without improvement. In addition, the coatings of this disclosure can be formed without the need for additional dispersants.

[0019] Sodium bentonite is dispersed in a binder using high-shear mixing conditions to achieve a coating in which at least a portion of the sodium bentonite exists in a tactoid shape. Such high-shear mixing can be achieved, for example, by mixing at a tip speed of about 655 feet / min to about 3300 feet / min (200 m / min to 1010 m / min). High-shear mixing can be carried out using any known method or combination of methods, including but not limited to the use of a Cowles mixer, sonication, and rotor-stator mixing. High-shear mixing can include, for example, sonication for at least 1 minute. The sonication time can be about 1 minute to about 40 minutes, about 10 minutes to about 30 minutes, or about 5 minutes to about 25 minutes. Other suitable times include approximately 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 minutes, as well as values ​​between them, and the ranges defined by those values. High shear can be carried out, for example, under conditions that reduce or prevent overheating. For example, ultrasonic treatment can be carried out using a jacketed vessel with water circulation and a pulse method to prevent overheating.

[0020] The high-shear mixing process can lead to the exfoliation of sodium bentonite during dispersion in the binder, while simultaneously allowing the tactoid shape of the sodium bentonite to remain present in the coating. As a result, the sodium bentonite in the coating can have an increased shape factor compared to the starting material before dispersion. The dispersed sodium bentonite can have a shape factor greater than, for example, 4. The shape factor referred to herein is measured using static light scattering versus dynamic light scattering (Horiba d) 50 This is the ratio. It has been observed that sodium bentonite with a shape factor greater than 4 can be obtained by high-shear mixing with a binder, such as by ultrasonic treatment for 5 minutes or more, or by using a roto-stator type shear device.

[0021] The coating may contain any suitable aqueous binder. For example, the binder may be an aqueous polymer latex. For example, non-latex binders may also be used. For example, the binder may be one or more anionic polymer latexes such as styrene-butadiene, polyolefin, styrene acrylate, ethylene acrylic acid copolymer, ethylene vinyl alcohol copolymer, polyurethane, epoxy resin, polyester, polyolefin, carboxylated styrene-butadiene latex, carboxylated styrene-acrylate latex, polyvinylidene chloride, polyvinyl chloride, starch, styrene-acrylic copolymer, styrene-maleic anhydride, polyvinyl alcohol, polyvinyl acetate, carboxymethylcellulose, silicone, wax, neoprene, polyhydroxyether, lacquer, polylactic acid, polylactic acid copolymer, polymer containing fluorine atoms, acrylonitrile copolymer, and carboxylated styrene-butadiene acrylonitrile copolymer.

[0022] Sodium bentonite can be added to the binder in amounts of about 1% to about 20% by weight, about 1% to about 5% by weight, about 3% to about 15% by weight, or about 10% to about 20% by weight, based on the total weight of the coating on a dry weight basis. Other preferred amounts include about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20% by weight, based on the total weight of the coating on a dry weight basis, as well as any value between them, and any range defined by such values. Unless otherwise specified, references to percentages (%) of sodium bentonite in coatings in this disclosure refer to weight percentages based on the total weight of the coating on a dry weight basis. The level of sodium bentonite filling can be significantly lower than the levels required for talc or kaolin in conventional coatings, while maintaining or even exhibiting improved barrier properties. For example, the sodium bentonite filling in the coatings of this disclosure can be 2 to 60 times lower than that required for other plate-like mineral-based barrier coatings, such as talc or kaolin coatings.

[0023] The coatings of this disclosure are intended for use in coating porous substrates such as paper and cardboard. For suitability in such applications, the coatings of this disclosure may have 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 value in between, as well as the ranges defined by such values.

[0024] The coating prepared by the addition of dry sodium bentonite can advantageously have a solids content that is above the solids content of the binder. In contrast, the coating prepared by the addition of wet sodium bentonite has a lower solids content than the binder as a result of the liquid present in the slurry of sodium bentonite.

[0025] The coatings of the present disclosure can be coated by conventional paper coating methods such as drawdown coating, blade coating, curtain coating, rotary gravure coating (gravure coating), machine roll-to-roll coating, size press, reverse roll coating, hot melt coating, flex bar coating / flexo coating, film transfer coating, die slot coating, wet film applicator coating, coating film casting using filtration and evaporation, dip coater, extrusion coating, etc. The substrate can be coated, for example, with any desired coating weight and / or number of coating layers. For example, the coating can be coated at a coating weight of about 1 g / m 2 ~ about 35 g / m 2 、about 1 g / m 2 ~ about 25 g / m 2 、about 5 g / m 2 ~ about 15 g / m 2 . For example, the coating weight can be 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, or 35 g / m 2 、and any value between them, or a range defined by such values.

[0026] The coatings of the present disclosure can be single-layer coatings, less than 10 g / m 2 、for example, about 2 g / m 2 ~ 10 g / m 2 less than, or about 4 g / m 2~about 8g / m 2 The coating weight can be as follows. Other suitable single-layer coating weights include approximately 1, 2, 3, 4, 5, 6, 7, 8, and 9 g / m². 2 , as well as any values ​​between them, and the range defined by such values ​​can be cited. The beneficial effect of the coatings of the present disclosure, as opposed to kaolin or talc, has been observed to be advantageous in that they can enable the use of single-layer coatings while achieving desired barrier properties. This is advantageous because two-layer or multi-layer coatings may not be practical in many applications, especially when using multi-functional layers / coatings. In single-layer coat weight, the coatings of the present disclosure demonstrated a 31% improvement in barrier properties with a 3% dry addition of sodium bentonite in the coating compared to pure latex. The coatings of the present disclosure with a 3% dry addition of sodium bentonite also demonstrated a 39% improvement over a comparative coating formulation containing 40% filler of the competing product Barrisurf® LX kaolin clay. Dry addition of sodium bentonite in the coating demonstrated an improvement of more than 30% in barrier properties compared to wet addition.

[0027] Porous substrates used with the coatings of this disclosure generally include any paper or cardboard product to which a barrier coating is desired. Paper substrates that can be coated with the coatings of this disclosure include, but are not limited to, solid bleached sulfuric acid (SBS) paper, folded cardboard (FBB), white topliner (WTL), low basis weight paper such as fast food packaging paper, copy paper, coated and uncoated paper, coated and uncoated cardboard, coated unbleached kraft (CUK) paper, and coated recycled cardboard.

[0028] The coatings of this disclosure can be adjusted to provide water vapor permeability or other barrier properties based on the intended use of the paper substrate. For example, the barrier coating may be 40 g / m² under tropical conditions (38°C and 90% RH). 2Water vapor transmission rate (WVTR) less than / d, and / or 1 g / m 2 It can provide less than 60 minutes of water COBB. For ultra-high barrier applications in tropical conditions, the WVTR is 10 g / m². 2 The value is less than / d, and for high barrier applications, 100g / m 2 The value is less than / d, and for medium barrier applications, it is 100-400 g / m². 2 The low barrier is 400 g / m². 2 It is generally understood in the art that the value is greater than / d. The barrier coatings according to this disclosure can be adapted for any of the aforementioned applications. [Examples]

[0029] Example 1: Dry addition vs. Wet slurry addition Three different methods were used to prepare the coating formulations. In the first method according to this disclosure, sodium bentonite is added to the latex as a dry powder, which is hereinafter referred to as "dry addition." In the comparative second method, a slurry of sodium bentonite in water is prepared and then added to the latex, which is referred to as "No Acumer." In the comparative third example, a dispersant chemical is first added to water, then the dry sodium bentonite powder is added, and finally this pre-dispersed sodium bentonite slurry is added to the latex, which is referred to as "0.08% Acumer."

[0030] Drying addition: 5% dry addition of sodium bentonite The aqueous barrier coating according to this disclosure was prepared as follows: 370 g of Tykote® 1004 styrene-butadiene latex with a solid content of 52% was weighed into a 1000 ml steel container. To this, 10.7 g of sodium bentonite with 10% moisture and 27.7 g of water were added. The resulting slurry was thoroughly mixed for 30 minutes at a tip speed of 2945 ft / min using a Premier Model 2500HV Cowles mixer with a 2.5-inch (6.35 cm) diameter blade. The final solid content of the formulation was determined to be 45% using the oven drying method.

[0031] No Acumer: 5% wet addition of sodium bentonite without dispersant. A sodium bentonite aqueous slurry was prepared by adding 11.1 g of dry sodium bentonite with 10% moisture to 200 g of water. The suspension was then stirred for 15 minutes at a tip speed of 2945 ft / min using a Premier Model 2500HV Cowles mixer with a 2.5-inch (6.35 cm) diameter blade. The solids content of this aqueous sodium bentonite slurry was determined to be 5% using the oven drying method. A barrier coating formulation was produced in a 1000 ml steel container by mixing 370 g of Tykote® 1004 styrene-butadiene latex with a 52% solids content and 178.1 g of the prepared sodium bentonite slurry with a 5% solids content. The mixture was then stirred for 15 minutes at a tip speed of 2945 ft / min using the same Cowles mixer. The final solids content of the mixture was determined to be 45% using the oven drying method.

[0032] 0.08% Acumer: 5% wet addition of sodium bentonite with dispersant. A 300 g / m³ aqueous slurry of sodium bentonite was prepared by adding 0.0608 g of ACUMER 9300 with 45% solids, followed by 38 g of powder with 10% moisture. The mixture was stirred for 15 minutes using a Premier Model 2500HV Cowles mixer with 2.5-inch (6.35 cm) diameter blades at a tip speed of 2945 ft / min. The final solids content of the slurry was determined to be 11% using the oven drying method. To prepare the barrier formulation, 70.4 g of the slurry with 11% solids was added to 304 g of Tykote® 1004 styrene-butadiene latex with 52% solids. The resulting barrier formulation was stirred for 15 minutes at a tip speed of 2945 ft / min using the same Cowles mixer.

[0033] coating Using the drawdown coating method, 350 g / m 2 A barrier coating was prepared on SBS (solid bleached sulfuric acid) cardboard. Each cardboard had a two-layer coating of the same formulation, and different coating weights were produced using lot numbers 4 to 13. The two coat weights were 13 to 15 g / m². 2 and 23-25 ​​g / m 2 The average coat weight was used for production. The paper coated with the barrier formulation was then tested for liquid water resistance (water cobb) using TAPPI 441, water vapor transmission rate (WVTR) using TAPPI T 464, and oil and grease barrier (OGR) using oil cobb. The oil cobb method is a modified TAPPI 441 method for testing OGR. In this procedure, the surface of the barrier-coated paper was covered with oil-saturated blotter paper for 30 minutes, and the number of oil cobbs was determined by measuring the weight change caused by oil absorption. The results for the barrier coating are shown in Figures 1, 2, and 3.

[0034] Example 2: Determination of shape factor and its effect on the mixing conditions Chemically unmodified, untreated sodium bentonite with a moisture content of 8%, containing at least 99.00% dry particles finer than 200 mesh (74 microns) and at least 99.75% wet particles finer than 200 mesh (74 microns). The particle size of the dispersed sodium bentonite was determined using a Horiba LA950 static light scattering instrument. A 1.0% bentonite suspension was prepared by adding 0.5 g of bentonite powder to 50 ml of a deionized aqueous solution with a dispersant concentration of 0.005% DAXAD® 30. The resulting suspension was dispersed by sonication for 8 minutes using a 0.5-inch horn set to 1.5. The dispersed suspension was dropped into a Horiba LA950 cell to achieve a red laser % transmittance of 89-91%, and the particle size was determined using the standard setting and refractive index of calcium carbonate. This method measures the particle size related to the larger basal surface dimensions of the bentonite.

[0035] Undispersed sodium bentonite samples were also tested. Aqueous suspensions of sodium bentonite with any solid content of approximately 1-10% can be prepared, and varying degrees of shearing can be applied using any type of mixing or sonicating equipment. This suspension is added to a Horiba LA950 cell, and the particle size is measured as described above. [Table 1]

[0036] The particle size of sodium bentonite was also determined by dynamic light scattering (DLS) technique using a Malven Zetasizer 1000 instrument. Either a dispersed or non-dispersed suspension could be used. The suspension was diluted to 0.1% solids using deionized water. The diluted suspension was transferred to an instrument cuvette (1 cm × 1 cm plastic with all sides transparent), and the cuvette was placed in the instrument measurement chamber. Using standard software settings, the size was measured using water as the solvent and the refractive index of sodium bentonite (1.503). The obtained Zave value (hydrodynamic diameter) is reported. This instrument is designed to measure nanoparticles, and therefore, the inventors used this technique to provide values ​​related to the dimensions of thinner sodium bentonite plates, although the values ​​were much thicker than those of thinner plates. The measured Zave values ​​of sodium bentonite varied from 500 to 1500 nm.

[0037] The shape factor (SF) of bentonite was determined to be calculated as a ratio of two particle size methods, using the ratio of the diameter from static light scattering (Horiba LA-950) to the diameter from dynamic light scattering (DLS). It was observed that the sedimentation method could not be used for bentonite due to its extremely long sedimentation time. The shape factor (SF) was calculated by taking the ratio of the median particle size (d50) determined by Horiba light scattering to the Zave particle size (microns) determined using Malvern Zetasizer 1000DLS. The resulting SF values ​​for sodium bentonite can vary from 3.5 to 7, with higher values ​​indicating higher delamination and higher particle aspect ratios.

[0038] Two samples, one with high SF and the other with low SF, were prepared as follows. Low SF: A sodium bentonite slurry with 5% solids in deionized water was prepared in the same manner as in the "No Acumer" example above, except that the volume was 500 mL and high-speed mixing using Cowles was performed for only 5 minutes at 2000 rpm. High SF: Another 500 mL of 5% solids starting slurry was sonicated in a water-cooled beaker for a total of 20 minutes while being constantly mixed with a propeller stirrer. To avoid overheating, the sonication was switched on and off in 10-second on / 20-second off cycles for a total of 20 minutes on schedule. [Table 2]

[0039] This demonstrates that the mixing method used to disperse sodium bentonite within the binder can be selected to produce a final composition having sodium bentonite with high or low shape moduli present therein. High shear mixing methods, such as sonication, have been observed to result in materials with high shape moduli.

[0040] Example 3: Effect of shape factor and drying additive on barrier performance Coatings according to the Disclosure were prepared using sodium bentonite with high and low shape coefficients, as well as with dry and wet additions of sodium bentonite. Chemically unmodified sodium bentonite as described in Example 2 was used as the starting material in the coatings of the Disclosure. Each coating according to the Disclosure contained 3% sodium bentonite on a dry weight basis. The barrier performance of these coatings was compared not only with each other, but also with coatings containing Tykote® 1004 (pure latex) and coatings containing Barrisurf® LX (kaolin).

[0041] A coating according to this disclosure having a low shape factor and a 3% dry sodium bentonite additive was prepared by combining 150 g of Tykote® 1004 with 2.6 g of dry sodium bentonite powder. To create a low shape factor formulation, this mixture was stirred for 5 minutes at 2000 RPM using a 2.5-inch diameter Cowles blade. The formulation was diluted to 47% by adding deionized water. After holding the formulation overnight, viscosity, pH, and solids content were measured.

[0042] A coating according to this disclosure, having a 3% dry sodium bentonite additive 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, the mixture was stirred at 2000 RPM for 5 minutes, followed by 20 minutes of sonication with a pulse function, alternating between 30 seconds on and 30 seconds off. The pulse function was used to prevent overheating. The formulation was diluted to 47% by adding deionized water. After holding the formulation overnight, viscosity, pH, and solids content were measured.

[0043] Coatings according to this disclosure, having a 3% sodium bentonite wetting addition with a low shape factor, were prepared by first forming a sodium bentonite slurry. To prepare the sodium bentonite slurry with a low shape factor, the slurry described in Example 3 was prepared. Specifically, 25 g of dry sodium bentonite powder was mixed with 475 g of water and sheared for 5 minutes at 2000 RPM using a 2.5-inch Cowles blade to obtain a final bentonite slurry with a solid content of 5%. Subsequently, 150 g of Tykote® 1004 was combined with 48.2 g of the wet 5% sodium bentonite slurry. Then, the Tykote® 1004 latex and sodium bentonite slurry were mixed for 15 minutes at 800 RPM using a propeller-type overhead mixer. After holding the mixture overnight, the viscosity, pH, and solid content were measured.

[0044] Coatings according to this disclosure, having a high shape factor and a 3% sodium bentonite wetting addition, were prepared by first forming a sodium bentonite slurry. To prepare a sodium bentonite slurry with a high shape factor, the slurry described in Example 3 was prepared. Specifically, 25 g of dry sodium bentonite powder was mixed with 475 g of water and sheared for 5 minutes at 2000 RPM using a 2.5-inch Cowles blade. Furthermore, to obtain a high shape factor, the same formulation was sonicated for 20 minutes using a pulse function, alternating between 10 seconds on and 20 seconds off. The pulse function was used to prevent overheating. The final solids content of the sodium bentonite slurry was 5%. 150 g of Tykote® 1004 was combined with 48.2 g of a 5% wetting sodium bentonite slurry. The Tykote® 1004 latex and sodium bentonite slurry were then mixed for 15 minutes at 800 RPM using a propeller-type overhead mixer. After holding this mixture overnight, its viscosity, pH, and solids content were measured.

[0045] A comparative coating of Barrisurf® LX (kaolin) was prepared as a 40% Barrisurf® LX-Tykote® 1004 formulation. 150 g of Tykote® 1004 was combined with 84.4 g of Barrisurf® LX slurry. The Barrisurf® LX slurry had a solids content of 61.6%. The mixture was then blended at 800 RPM for 15 minutes using a propeller-type overhead mixer. After holding the formulation overnight, the viscosity, pH, and solids content were measured.

[0046] For each coating compound, the coating was applied at a rate of 40 m / min using an automatic drawdown coater at a rate of 175 g / m². 2The coating was applied to a white top liner. The coating was dried in an oven at 103°C for 10 minutes, followed by conditioning in a CTH chamber for 24 hours. Both single and double-layer coatings were applied. For single-layer coatings, the target coat weight was 5.8 ± 0.4 g / m². 2 However, in the case of a two-layer coating, the target coating weight is 10.8 ± 0.3 g / m². 2 Next, a circular section with a diameter of 7.62 cm was cut out and used for a WVTR test under tropical conditions (38°C, 90%RH).

[0047] Table 3 provides the viscosity, pH, and solids content of the prepared coating formulations. [Table 3]

[0048] Water vapor transmission rate (WVTR) was tested using TAPPI T 464 under tropical conditions (38°C, 90%RH). Referring to Figure 6, the single-layer coatings of this disclosure demonstrated significant improvement in water vapor transmission characteristics compared to Tykote® 1004 alone and Barrisurf® LX (kaolin)-containing coatings. In addition, improvement in water vapor transmission performance was observed with dry addition of sodium bentonite in the coatings of this disclosure compared to wet addition. Finally, improvement in water vapor transmission performance was also observed when using a coating formulation process that resulted in high shape factor sodium bentonite present in the coating. In particular, quantitative improvements were observed in the following performance aspects: Compared to pure latex, the WVTR of the high-aspect-ratio sodium bentonite-containing formulation with 3% dry addition is reduced by 31%. Compared to formulations containing sodium bentonite added with a high aspect ratio and wet addition, the WVTR of formulations containing sodium bentonite added with a high aspect ratio and dry addition was reduced by 36%. Compared to formulations containing low aspect ratio wet-added sodium bentonite, formulations containing low aspect ratio dry-added sodium bentonite showed a 32% reduction in WVTR. Compared to Barrisurf® LX, the WVTR of the high-aspect-ratio sodium bentonite-containing formulation with 3% dry addition is reduced by 39%.

[0049] Referring to Figure 7, the significance of the reduction in WVTR between the coating of this disclosure and comparative coatings of Tykote® 1004 and Barrisurf® (kaolin) is not so pronounced when using a two-layer coating. A reduction in water vapor transmission rate is still observed, particularly with respect to the dry addition of sodium bentonite. Furthermore, it was surprisingly and beneficially observed that, when formed as a single-layer coating, the coating of this disclosure with the dry addition of sodium bentonite having a high shape factor can provide similar or even improved water vapor transmission rate performance compared to two-layer coatings of Tykote® 1004 and Barrisurf® coatings. Therefore, the coating of this disclosure can avoid the need for a two-layer coating, which can be complex and impractical in some applications, while maintaining at least the same level of barrier performance as a two-layer coating of conventional kaolin coatings.

[0050] The foregoing explanation is provided solely for the purpose of clarifying understanding, and no unnecessary limitations should be inferred therefrom, as modifications within the scope of this disclosure may be obvious to those skilled in the art.

[0051] All patents, patent applications, government publications, government regulations, and references cited herein are incorporated herein by reference in their entirety. In the event of any conflict, this description, including definitions, shall prevail.

[0052] Throughout this specification, where a compound, composition, method, and / or process is described as including components, steps, or materials, unless otherwise specified, the compound, composition, method, and / or process is intended to also essentially consist of, or may consist of, any combination of the listed components or materials. Component concentrations may be expressed in units of weight concentration unless otherwise specifically indicated. Combinations of components are intended to include homogeneous and / or heterogeneous mixtures, as will be understood by those skilled in the art in light of the foregoing disclosures.

Claims

1. A process for preparing an aqueous barrier coating for paper substrates, The process involves mixing chemically unmodified sodium bentonite dry powder with a binder, A process comprising subjecting a mixture to high-shear mixing under conditions such that the sodium bentonite is dispersed in the binder, at least a portion of the sodium bentonite maintains a tactoid shape, thereby forming the barrier coating, wherein the binder is aqueous or water-soluble.

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

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

4. The process according to claim 3, wherein the anionic polymer latex comprises one or more of styrene-butadiene, polyolefin, styrene acrylate, ethylene acrylic acid copolymer, ethylene vinyl alcohol copolymer, polyurethane, epoxy resin, polyester, polyolefin, and carboxylated styrene-butadiene.

5. The process according to any one of the prior claims, wherein the binder comprises one or more of the following: carboxylated styrene acrylic latex, polyvinylidene chloride, polyvinyl chloride, starch, styrene-acrylic copolymer, styrene-maleic anhydride, polyvinyl alcohol, polyvinyl acetate, carboxymethylcellulose, silicone, wax, neoprene, polyhydroxyether, lacquer, polylactic acid, copolymer of polylactic acid, polymer containing a fluorine atom, copolymer of acrylonitrile, and carboxylated styrene-butadiene acrylonitrile copolymer.

6. A process for preparing an aqueous barrier coating for paper substrates, The process involves mixing a chemically unmodified sodium bentonite dry powder with an aqueous polymer latex binder, A process comprising subjecting the admixture to high-shear mixing under conditions such that the sodium bentonite is dispersed in the polymer latex and at least a portion of the sodium bentonite maintains a tactoid shape, thereby forming the barrier coating.

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

8. The process according to claim 7, wherein the anionic polymer latex comprises one or more of styrene-butadiene, polyolefin, styrene acrylate, ethylene acrylic acid copolymer, ethylene vinyl alcohol copolymer, polyurethane, epoxy resin, polyester, polyolefin, and carboxylated styrene-butadiene.

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

10. The process according to any one of the prior claims, wherein high-shear mixing is carried out at a tip speed of approximately 655 feet / min to approximately 3300 feet / min (200 m / min to 1010 m / min).

11. The process according to any one of the prior claims, wherein the dry powder of chemically unmodified sodium bentonite contains less than 12% moisture.

12. The process according to any one of the prior claims, wherein high-shear mixing is performed using a Cowles mixer, an ultrasonic device, or a roto-stator mixer.

13. The process according to claim 12, wherein high-shear mixing is carried out using an ultrasonic device.

14. The process according to claim 13, comprising ultrasonic treatment for approximately 1 minute to approximately 40 minutes.

15. The high-shear mixing is carried out under conditions that disperse the sodium bentonite while dispersing it in the binder, and as a result the sodium bentonite present in the coating is measured by static light scattering relative to the Zave particle size measured by dynamic light scattering. ５０ The process according to any one of the prior claims, having a shape factor greater than 4, as measured by the ratio of .

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

17. The process according to any one of the prior claims, wherein the admixture does not contain a dispersant.

18. The process according to any one of the prior 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, The process involves mixing chemically unmodified sodium bentonite dry powder with a binder, The mixture is subjected to high-shear mixing under conditions such that the sodium bentonite is dispersed in the binder, at least a portion of the sodium bentonite maintains a tactoid shape, thereby forming the barrier coating. Approximately 1.5 g / m² of the aforementioned paper substrate ２ ~Approx. 25g / m ２ The process includes coating with the barrier coating having a coating weight of, A process wherein the binder is aqueous or water-soluble.

20. The aforementioned coating weight is 10 g / m ２ The process according to claim 19, wherein the process is less than [amount missing].

21. The process according to claim 19 or 20, wherein the paper substrate is solid bleached sulfuric acid (SBS) paper, folded cardboard (FBB), white top liner (WTL), low basis weight paper packaging paper, copy paper, coated paper or uncoated paper and coated or uncoated cardboard, coated unbleached kraft paper (CUK), or coated recycled cardboard.

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

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

24. The process according to claim 23, wherein the anionic polymer latex comprises one or more of styrene-butadiene, polyolefin, styrene acrylate, ethylene acrylic acid copolymer, ethylene vinyl alcohol copolymer, polyurethane, epoxy resin, polyester, polyolefin, and carboxylated styrene-butadiene.

25. The process according to any one of claims 19 to 24, wherein the binder comprises one or more of the following: carboxylated styrene acrylic latex, polyvinylidene chloride, polyvinyl chloride, starch, styrene-acrylic copolymer, styrene-maleic anhydride, polyvinyl alcohol, polyvinyl acetate, carboxymethylcellulose, silicone, wax, neoprene, polyhydroxyether, lacquer, polylactic acid, polylactic acid copolymer, polymer containing a fluorine atom, acrylonitrile copolymer, and carboxylated styrene-butadiene acrylonitrile copolymer.

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

27. The process according to any one of claims 19 to 26, wherein high-shear mixing is carried out at a tip speed of approximately 655 feet / min to approximately 3300 feet / min (200 m / min to 1010 m / min).

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

29. The process according to any one of claims 19 to 28, wherein high-shear mixing is performed using a Coules mixer, an ultrasonic device, or a Roto-stator mixer.

30. The process according to claim 29, wherein high-shear mixing is carried out using an ultrasonic device.

31. The process according to claim 30, comprising ultrasonic treatment for approximately 1 minute to approximately 40 minutes.

32. The high-shear mixing is carried out under conditions that disperse the sodium bentonite while dispersing it in the binder, and as a result the sodium bentonite present in the coating is measured by static light scattering relative to the Zave particle size measured by dynamic light scattering. ５０ The process according to any one of claims 19 to 31, having a shape factor greater than 4, as measured by the ratio of .

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

34. The process according to any one of claims 19 to 33, wherein the admixture does not contain a dispersant.

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

36. A water-based barrier coating, 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 exists in a tactoid form, and the binder is aqueous or water-soluble.

37. The sodium bentonite is measured by static light scattering relative to the Zave particle size measured by dynamic light scattering. ５０ The coating according to claim 36, having a shape factor greater than 4, as measured by the ratio of .

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

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

40. The coating according to claim 39, wherein the anionic polymer latex comprises one or more of styrene-butadiene, polyolefin, styrene acrylate, ethylene acrylic acid copolymer, ethylene vinyl alcohol copolymer, polyurethane, epoxy resin, polyester, polyolefin, and carboxylated styrene-butadiene.

41. The coating according to any one of claims 36 to 40, wherein the binder comprises one or more of the following: carboxylated styrene acrylic latex, polyvinylidene chloride, polyvinyl chloride, starch, styrene-acrylic copolymer, styrene-maleic anhydride, polyvinyl alcohol, polyvinyl acetate, carboxymethylcellulose, silicone, wax, neoprene, polyhydroxyether, lacquer, polylactic acid, polylactic acid copolymer, polymer containing a fluorine atom, acrylonitrile copolymer, and carboxylated styrene-butadiene acrylonitrile copolymer.

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

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

44. The coating according to any one of claims 36 to 43, wherein the coating does not contain a dispersant.

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

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

47. The barrier-coated paper substrate according to claim 46, wherein the paper substrate is solid bleached sulfuric acid (SBS) paper, folded cardboard (FBB), white top liner (WTL), low basis weight paper packaging paper, copy paper, coated paper or uncoated paper and coated or uncoated cardboard, coated unbleached kraft paper (CUK), or coated recycled cardboard.

48. The coating is 10 g / m ２ Coating weight less than 400 g / m² ２ A barrier-coated paper substrate according to claim 46 or 47, having a water permeability of less than / d.

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